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As filed with the Securities and Exchange Commission on July 21, 2017

Registration No. 333-218249

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

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Amendment No. 2
to

FORM S-4
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

PACWEST BANCORP
(Exact name of registrant as specified in its charter)

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9701 Wilshire Boulevard, Suite 700
Beverly Hills, California 90212
(310) 887-8500
(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant's Principal Executive Offices)

Kori L. Ogrosky
Executive Vice President, General Counsel and Corporate Secretary
9701 Wilshire Boulevard, Suite 700
Beverly Hills, California 90212
(310) 887-8500
(Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

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Approximate date of commencement of proposed sale of the securities to the public:
As soon as practicable after this registration statement becomes effective and upon completion of the merger.

         If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box:    o

         If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

         If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

         Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company" and "emerging growth company" in Rule 12b-2 of the Exchange Act. (Check one):

         If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.    o

         If applicable, place an ý in the box to designate the appropriate rule provision relied upon in conducting this transaction:

         Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer)    o

         Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer)    o

         The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

   

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Information contained herein is subject to completion or amendment. A registration statement relating to the shares of PacWest Bancorp common stock to be issued in the merger has been filed with the Securities and Exchange Commission. These securities may not be sold, nor may offers to buy be accepted, prior to the time the registration statement becomes effective. This proxy statement/prospectus shall not constitute an offer to sell or the solicitation of an offer to buy nor shall there be any sale of these securities in any jurisdiction in which such offer, solicitation or sale is not permitted or would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

PRELIMINARY PROXY STATEMENT/PROSPECTUS
DATED JULY 21, 2017, SUBJECT TO COMPLETION

Dear Shareholder:

        You are cordially invited to attend a special meeting of the shareholders of CU Bancorp, a California corporation, which we refer to as CUB, which we will hold at City Club Los Angeles—Santa Monica Room, 555 South Flower Street, 51st Floor, Los Angeles, California 90071, on August 24, 2017, at 8:30 a.m., local time. At the special meeting, holders of CUB common shares will be asked to approve the principal terms of the Agreement and Plan of Merger, which we refer to as the merger agreement, dated as of April 5, 2017, by and between PacWest Bancorp, which we refer to as PacWest, and CUB, pursuant to which CUB will merge with and into PacWest, with PacWest as the surviving corporation, which we refer to as the merger, and which proposal we refer to as the merger proposal. Immediately following the merger, California United Bank, a wholly owned subsidiary of CUB, will merge with and into Pacific Western Bank, a wholly owned subsidiary of PacWest, with Pacific Western Bank as the surviving bank.

        At the effective time of the merger, each CUB common share, other than excluded shares and dissenting shares, will be converted into the right to receive (i) $12.00 in cash and (ii) 0.5308 of a share of PacWest common stock, referred to as the exchange ratio, with cash paid in lieu of a fractional share of PacWest common stock. The merger agreement provides that CUB may terminate the merger agreement if (i) the volume weighted average price of PacWest common stock for the 20 consecutive trading days ending on the date that is five business days prior to the closing date, which we refer to as the determination period, falls below $44.84 per share and (ii) the volume-weighted average price of PacWest common stock over the determination period underperforms the average KBW Regional Banking Index, referred to as the KBW Index, for the determination period by more than 15%. If CUB elects to exercise such termination right, then PacWest may reinstate the agreement after increasing the exchange ratio or cash consideration according to formulas set forth in the merger agreement such that the value of the merger consideration is intended to fix at $35.80 per share, as adjusted for any decline in the KBW Index. For a more complete discussion of the termination rights, please refer to the section of this proxy statement/prospectus entitled "The Merger Agreement—Termination of the Merger Agreement."

        The market value of the stock portion of the merger consideration will fluctuate with the price of PacWest common stock. Based on the closing price of PacWest common stock on April 5, 2017, the last trading day before the public announcement of the signing of the merger agreement, the value of the per share merger consideration payable to holders of CUB common shares was $39.45. Based on the closing price of PacWest common stock on July 20, 2017, the last practicable date before the date of this proxy statement/prospectus, the value of the per share merger consideration payable to holders of CUB common shares was $37.87. You should obtain current price quotations for CUB common shares and PacWest common stock. CUB common shares are traded on NASDAQ under the symbol "CUNB" and PacWest common stock is traded on NASDAQ under the symbol "PACW."

        The merger is intended to qualify, and the obligation of PacWest and CUB to complete the merger is conditioned upon the receipt of legal opinions from their respective counsel to the effect that the merger will qualify, as a reorganization within the meaning of Section 368(a) of the Internal Revenue Code. You generally will recognize gain (but not loss) upon receipt of the merger consideration in exchange for CUB common shares in the merger in an amount equal to the lesser of (1) the amount of gain realized (i.e., the excess of the sum of the amount of cash and the fair market value of the PacWest common stock received pursuant to the merger over your adjusted tax basis in the CUB common shares surrendered in the exchange) and (2) the amount of cash received pursuant to the merger (excluding any cash received in lieu of a fractional share of PacWest common stock).

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        The board of directors of CUB has unanimously approved the merger agreement and the transactions contemplated thereby, and determined that the merger agreement and the transactions contemplated thereby are fair to and in the best interests of CUB and its shareholders. The board of directors recommends that the CUB common shareholders vote "FOR" the merger proposal.

        At the special meeting, CUB common shareholders will also be asked to vote on a proposal to approve one or more adjournments of the special meeting, if necessary or appropriate, to solicit additional proxies if there are insufficient votes at the time of the special meeting to approve the merger proposal, which we refer to as the adjournment proposal. The board of directors recommends that the CUB common shareholders vote "FOR" the adjournment proposal.

        Your vote is very important. To ensure your representation at the special meeting, please complete and return the enclosed proxy card or submit your proxy by telephone or through the Internet. Whether or not you expect to attend the special meeting, please vote promptly. Submitting a proxy now will not prevent you from being able to vote in person at the special meeting.

        If you hold your shares in "street name" through a broker, bank or other nominee you should follow the directions provided by your broker, bank or other nominee regarding how to instruct your broker, bank or other nominee to vote your shares. Without those instructions, your shares will not be voted, which will have the same effect as voting against the merger proposal and against the adjournment proposal.

        This proxy statement/prospectus provides you with detailed information about the proposed merger. You are encouraged to read the entire proxy statement/prospectus, including the appendices and the documents incorporated by reference, carefully. In particular, you should read the "Risk Factors" section beginning on page 28 for a discussion of the risks you should consider in evaluating the proposed merger and how it will affect you.

        We thank you for your continued support and look forward to seeing you at the special meeting.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the merger, the issuance of the PacWest Bancorp common stock in connection with the merger or the other transactions described in this document, or passed upon the adequacy or accuracy of the disclosures in this document. Any representation to the contrary is a criminal offense.

        The securities to be issued in connection with the merger are not savings accounts, deposits or other obligations of any bank or savings association and are not insured by the Federal Deposit Insurance Corporation or any other governmental agency.

        If you have any questions or need assistance in voting your shares, please call CU Bancorp Investor Relations at (818) 257-7700.

This document is dated July 24, 2017 and is first being mailed to CU Bancorp shareholders on or about July 26, 2017.

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WHERE YOU CAN FIND MORE INFORMATION

        Both PacWest Bancorp and CU Bancorp, referred to as PacWest and CUB, respectively, file annual, quarterly and special reports, proxy statements and other business and financial information with the Securities and Exchange Commission, referred to as the SEC. You may read and copy any materials that either PacWest or CUB files with the SEC at the SEC's Public Reference Room at 100 F Street, N.E., Room 1580, Washington, D.C. 20549, at prescribed rates. Please call the SEC at (800) SEC-0330 or (800) 732-0330 for more information on the public reference room. In addition, PacWest and CUB file reports and other business and financial information with the SEC electronically, and the SEC maintains a website located at http://www.sec.gov containing this information. You may also obtain these documents, free of charge, from PacWest at www.pacwestbancorp.com under the "Public Filings" link or from CUB at www.cubancorp.com under the "Filings" tab and then under the heading "Documents."

        PacWest has filed a registration statement on Form S-4 of which this document forms a part. As permitted by SEC rules, this document does not contain all of the information included in the registration statement or in the exhibits or schedules to the registration statement. You may read and copy the registration statement, including any amendments, schedules and exhibits, at the addresses set forth below. Statements contained in this document as to the contents of any contract or other documents referred to in this document are not necessarily complete. In each case, you should refer to the copy of the applicable contract or other document filed as an exhibit to the registration statement. This document incorporates by reference documents that PacWest and CUB have previously filed with the SEC. They contain important information about the companies and their financial condition. For more information, please see the section entitled "Incorporation of Certain Documents by Reference." These documents are available without charge to you upon written or oral request to the applicable company's principal executive offices. The respective addresses and telephone numbers of such principal executive offices are listed below.

        To obtain timely delivery of these documents, you must request the information no later than August 17, 2017 in order to receive them before CUB's special meeting of shareholders.

        PacWest common stock is traded on the NASDAQ Global Select Market under the symbol "PACW," and CUB common shares are traded on the NASDAQ Capital Market under the symbol "CUNB." Both the NASDAQ Global Select Market and the NASDAQ Capital Market are referred to herein as the NASDAQ as the context requires.

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CU BANCORP
818 WEST 7TH STREET, SUITE 220
LOS ANGELES, CALIFORNIA 90017
NOTICE OF THE SPECIAL MEETING OF SHAREHOLDERS
TO BE HELD ON AUGUST 24, 2017

        NOTICE IS HEREBY GIVEN that a special meeting of the shareholders of CU Bancorp, referred to as CUB, will be held at City Club Los Angeles—Santa Monica Room, 555 South Flower Street, 51st Floor, Los Angeles, California 90071, on August 24, 2017, at 8:30 a.m., local time for the purpose of considering and voting upon the following proposals:

1.

Merger Proposal.    To approve the principal terms of the Agreement and Plan of Merger, dated as of April 5, 2017, by and between PacWest Bancorp and CUB, as such agreement may be amended from time to time, a copy of which is attached as Appendix A to this proxy statement/prospectus; and



2.

Adjournment Proposal.    To approve one or more adjournments of the special meeting, if necessary or appropriate, including adjournments to permit further solicitation of proxies if there are insufficient votes at the time of the special meeting to approve the merger proposal.

        CUB will transact no other business at the special meeting other than as listed above.

        The CUB board of directors has set June 30, 2017 as the record date for the special meeting. Only holders of record of CUB common shares at the close of business on June 30, 2017 will be entitled to notice of and to vote at the special meeting and any adjournments or postponements thereof.

        Shareholder approval of the merger proposal by the affirmative vote of a majority of the outstanding shares entitled to vote is required to complete the merger.

        The CUB board of directors has unanimously approved the merger agreement and the transactions contemplated thereby and recommends that you vote "FOR" the merger proposal and "FOR" the adjournment proposal.

        Your vote is very important.    To ensure your representation at the special meeting, please (1) complete, sign, date and return the enclosed proxy card in the envelope provided or (2) follow the instructions provided on the proxy card to submit your proxy by telephone or through the Internet. If you hold your shares through a bank, broker or other nominee, you should direct the vote of your shares in accordance with the voting instructions received from your bank, broker or other nominee. Please vote promptly whether or not you expect to attend the special meeting.

        If you plan to attend the special meeting, you will be required to bring certain documents with you to be admitted to the meeting. Please read carefully the sections in the proxy statement/prospectus regarding attending and voting at the special meeting to ensure that you comply with these requirements. You are encouraged to read the entire proxy statement/prospectus, including the appendices and the documents incorporated by reference, carefully. If you have any questions about the proposals or need assistance in voting your shares, please call CUB Investor Relations at (818) 257-7700.

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        In connection with the merger, CUB common shareholders will have the opportunity to exercise dissenters' rights in accordance with the procedures set forth in Section 13 of the California General Corporation Law, or CGCL. A copy of Chapter 13 of the CGCL is attached to this proxy statement/prospectus as Appendix C. A dissenting shareholder who votes "AGAINST" the merger and who follows the required procedures may receive cash in an amount equal to the fair market value of his or her CUB common shares in lieu of the merger consideration provided for under the merger agreement. For additional details and information on how to exercise your dissenters' rights, please refer to "The Merger—Dissenters' Rights" on page 76 and Appendix C of this proxy statement/prospectus. Failure to follow all of the steps required under the CGCL will result in the loss of your dissenters' rights.

BY ORDER OF THE BOARD OF DIRECTORS

Anita Y. Wolman
Executive Vice President, Chief Administrative Officer,
General Counsel and Corporate Secretary

Los Angeles, California
July 24, 2017

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QUESTIONS AND ANSWERS ABOUT THE SPECIAL MEETING

        The following are answers to certain questions that you may have regarding the special meeting of shareholders of CU Bancorp, which we refer to as the special meeting. You should carefully read the remainder of this document because the information in this section may not provide all the information that might be important to you in determining how to vote. Additional important information is also contained in the appendices to, and the documents incorporated by reference in, this document.

Q:

WHAT IS THE MERGER?

A.

PacWest Bancorp, a Delaware corporation, referred to as PacWest, and CU Bancorp, a California corporation, referred to as CUB, have entered into an agreement and plan of merger, which we refer to as the merger agreement, pursuant to which and subject to the terms and conditions of the merger agreement, CUB will merge with and into PacWest, with PacWest continuing as the surviving corporation, which transaction is referred to as the merger. A copy of the merger agreement is attached as Appendix A to this document. Immediately following the merger, California United Bank, a wholly owned subsidiary of CUB, referred to as CU Bank, will merge with and into Pacific Western Bank, a wholly owned subsidiary of PacWest, with Pacific Western Bank continuing as the surviving bank, which transaction is referred to as the bank merger. In order to complete these transactions, the CUB shareholders must approve the principal terms of the merger agreement, and the applicable banking regulators must approve both the merger and the bank merger.

Q:

WHY AM I RECEIVING THIS PROXY STATEMENT/PROSPECTUS?

A.

CUB is sending these materials to its shareholders to help them decide how to vote their CUB common shares with respect to the merger agreement and other matters to be considered at the special meeting.

The merger cannot be completed unless CUB common shareholders approve the principal terms of the merger agreement. CUB is holding a special meeting of its shareholders to vote on the proposal to approve the principal terms of the merger agreement as well as other related matters. Information about this special meeting, the merger and the other business to be considered by shareholders at the special meeting is contained in this document.

This document constitutes both a proxy statement of CUB and a prospectus of PacWest. It is a proxy statement because the CUB board of directors is soliciting proxies from CUB common shareholders using this document with respect to the matters to be considered at the special meeting. It is a prospectus because PacWest, in connection with the merger, is offering shares of its common stock in exchange for outstanding CUB common shares in the merger.

Q:

WHAT WILL CUB SHAREHOLDERS RECEIVE IN THE MERGER?

A:

In the merger, each CUB common share owned by a CUB shareholder, other than excluded shares and dissenting shares, will be converted into the right to receive (i) $12.00 in cash, referred to as the cash consideration, and (ii) 0.5308 of a share of PacWest common stock, par value $0.01 per share, referred to as PacWest common stock, which ratio is referred to as the exchange ratio, subject to adjustment as set forth in the merger agreement and as further described in the following question and answer and in the section entitled "The Merger Agreement—Termination of the Merger Agreement." The cash consideration and PacWest common stock to be exchanged for each CUB common share is referred to collectively as the merger consideration. For each fractional share that would otherwise be issued, PacWest will pay cash in an amount equal to the fraction of a share of PacWest common stock which the holder would otherwise be entitled to receive multiplied by the volume-weighted average price of PacWest common stock as quoted on

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the NASDAQ over the 20 consecutive trading days ending on the fifth business day immediately prior to the closing date. No interest will be paid or accrue on cash payable to holders in lieu of fractional shares.

This 20 consecutive trading day average price is referred to as the PacWest average closing price; the fifth business day immediately prior to the closing date is referred to as the determination date; and the 20 consecutive trading day period ending on the determination date is referred to as the determination period.

Based on the closing price of PacWest common stock on April 5, 2017, the value of the per share merger consideration payable to holders of CUB common shares was $39.45. Based on the closing price of PacWest common stock on July 20, 2017, the last practicable date before the date of this document, the value of the per share merger consideration payable to holders of CUB common shares was $37.87.

Q:

WILL THE VALUE OF THE MERGER CONSIDERATION CHANGE BETWEEN THE DATE OF THIS DOCUMENT AND THE TIME THE MERGER IS COMPLETED?

A:

Yes. Although the number of shares of PacWest common stock that CUB shareholders will receive in the merger is fixed, other than in certain circumstances described below, the value of the merger consideration will fluctuate between the date of this document and the completion of the merger based upon the market value of PacWest common stock. Any fluctuation in the market price of PacWest common stock after the date of this document will change the value of the shares of PacWest common stock that CUB shareholders will receive.

In addition, the merger agreement provides that CUB may terminate the merger agreement if:

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the PacWest average closing price is less than $44.84 per share (with a proportionate adjustment for any stock dividend, reclassification, recapitalization, split-up, combination, exchange of shares or similar transaction between the date of the merger agreement and the determination date); and



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the quotient of the PacWest average closing price divided by $52.75 is less than (i) the quotient of the average price of the KBW Regional Banking Index, referred to as the KBW Index, during the determination period (as defined below) divided by 105.39, which quotient is referred to as the index ratio, minus (ii) 0.15.

If CUB elects to terminate the merger agreement and provides written notice thereof to PacWest, then within two business days following PacWest's receipt of such notice, PacWest may elect to reinstate the merger and related transactions, and adjust the exchange ratio to equal the lesser of (i) the quotient of $23.80 divided by the PacWest average closing price and (ii) (a) the quotient of $23.80 divided by the PacWest average closing price (b) multiplied by the index ratio. Alternatively, PacWest may elect not to adjust the exchange ratio, and, in lieu thereof, may increase the cash consideration per CUB common share such that the value of the total consideration received for each share is the same as if the exchange ratio had been adjusted as described above.

For more information, please see the section entitled "The Merger Agreement—Termination of the Merger Agreement."

Q:

WHAT HAPPENS TO CUB EQUITY AWARDS IN THE MERGER?

A:

CUB Stock Options.    At the effective time of the merger, referred to as the effective time, each outstanding option to acquire CUB common shares under CUB's equity incentive plans, referred to as a CUB stock option, whether vested or unvested, will be cancelled and will entitle the holder of such option to receive an amount in cash equal to the product of (i) the total number of CUB

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common shares subject to such option and (ii) the excess, if any, of (A) an amount equal to (1) $12.00 in cash plus (2) the product of the PacWest average closing price and 0.5308, minus (B) the exercise price per CUB common share underlying such option, less any applicable taxes required to be withheld with respect to such payment.

CUB Restricted Shares and RSUs.    At the effective time, any vesting conditions applicable to outstanding restricted share awards and restricted stock units under CUB's equity incentive plans, referred to, respectively, as the CUB restricted shares and the CUB RSUs, will automatically accelerate in full and such CUB restricted shares and CUB RSUs will be converted into, and become exchanged for, the merger consideration, less any applicable taxes required to be withheld with respect to such vesting.

Q:

WHEN WILL THE MERGER BE COMPLETED?

A:

PacWest and CUB are working to complete the merger as soon as practicable. The parties are seeking regulatory approval by the fourth quarter of 2017, with the consummation of the merger to occur as soon as practicable thereafter. Neither PacWest nor CUB know, however, the actual date on which the merger will be completed because it is subject to factors beyond each company's control, including whether or when the required regulatory approvals and the CUB shareholder approval will be received. For more information, please see the section entitled "The Merger Agreement—Conditions to Consummation of the Merger."

Q:

WHO IS ENTITLED TO VOTE?

A:

Holders of record of CUB common shares at the close of business on June 30, 2017, which is the date that the CUB board of directors has fixed as the record date for the special meeting, are entitled to vote at the special meeting.

Q:

WHAT CONSTITUTES A QUORUM?

A:

A majority of the shares entitled to vote, represented in person or by proxy, constitutes a quorum for transacting business at the special meeting. Proxies marked as abstaining on any matter to be acted upon by shareholders will be counted as represented at the meeting for purposes of determining the presence or absence of a quorum.

Q:

WHAT AM I BEING ASKED TO VOTE ON AND WHY IS THIS APPROVAL NECESSARY?

A:

CUB common shareholders are being asked to vote on the following proposals:

1.

to approve the principal terms of the Agreement and Plan of Merger, dated as of April 5, 2017, by and between CUB and PacWest, as such agreement may be amended from time to time, a copy of which is attached as Appendix A, referred to as the merger proposal; and

2.

to approve one or more adjournments of the special meeting, if necessary or appropriate, including adjournments to permit further solicitation of proxies if there are insufficient votes at the time of the special meeting to approve the merger proposal, referred to as the adjournment proposal.

Shareholder approval of the merger proposal, referred to as the CUB shareholder approval, is required to complete the merger. CUB will transact no business at the special meeting other than as listed above.

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Q:

WHAT VOTE IS REQUIRED TO APPROVE EACH PROPOSAL AT THE SPECIAL MEETING?

A:

The Merger Proposal:    The affirmative vote of a majority of outstanding CUB common shares entitled to vote on the proposal is required to approve the merger proposal.

The Adjournment Proposal:    The adjournment proposal requires a vote that satisfies two criteria: (i) the affirmative vote of a majority of the shares represented and voting at a duly held meeting at which a quorum is present, and (ii) the shares voting affirmatively must also constitute at least a majority of the required quorum.

Q:

ARE THERE ANY VOTING AGREEMENTS WITH EXISTING SHAREHOLDERS?

A:

Yes. Each of the directors of CUB, in his or her capacity as a shareholder of CUB, has entered into a voting agreement with PacWest, the form of which is attached as Appendix B, in which such director has agreed to vote all CUB common shares that he or she owns and has the power to vote in favor of the merger proposal and any other matter that is required to be approved by the shareholders of CUB to facilitate the transactions contemplated by the merger agreement. The directors also agreed to vote against any proposal made in opposition to the approval of the principal terms of the merger agreement or in competition with the merger agreement and against any acquisition proposal. As of the close of business on the record date, CUB's directors beneficially owned, in the aggregate, 1,095,309 CUB common shares, allowing them to exercise approximately 6.14% of the voting power of CUB common shares (which does not include shares issuable upon the exercise of stock options or upon the vesting of CUB RSUs that were not outstanding as of the close of business on the record date).

Q:

WHAT DOES THE CUB BOARD OF DIRECTORS RECOMMEND?

A:

The CUB board of directors recommends that CUB shareholders vote "FOR" the merger proposal and "FOR" the adjournment proposal.

Q:

WHAT DO I NEED TO DO NOW?

A:

After carefully reading and considering the information contained in this document, please vote your CUB common shares as soon as possible so that such shares will be represented at the special meeting. Please follow the instructions set forth on the proxy card or on the voting instruction form provided by the record holder if your CUB common shares are held in the name of your broker, bank or other nominee.

Q:

HOW DO I VOTE?

A:

If you are a CUB common shareholder of record as of the close of business on the record date, you may submit your proxy before the special meeting in one of the following ways:

•

use the telephone number shown on your proxy card;

•

visit the website shown on your proxy card to vote via the Internet; or

•

complete, sign, date and return the enclosed proxy card in the enclosed postage-paid envelope.

You may also cast your vote in person at the special meeting.

If your CUB common shares are held in "street name," through a broker, bank or other nominee, that institution will send you separate instructions describing the procedure for voting such shares. "Street name" shareholders who wish to vote at the meeting will need to obtain a proxy form from their broker, bank or other nominee.

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Q:

HOW MANY VOTES DO I HAVE?

A:

You are entitled to one vote for each CUB common share that you owned as of the close of business on the record date. As of the close of business on the record date, there were approximately 17,831,131 outstanding CUB common shares entitled to vote. As of that date, approximately 8.27% of such outstanding CUB common shares were beneficially owned by the directors and executive officers of CUB and their affiliates.

Q:

WHEN AND WHERE IS THE SPECIAL MEETING?

A:

The special meeting will be held at City Club Los Angeles—Santa Monica Room, 555 South Flower Street, 51st Floor, Los Angeles, California 90071 at 8:30 a.m., local time, on August 24, 2017. Subject to space availability, all CUB common shareholders as of the close of business on the record date, or their duly appointed proxies, may attend the special meeting. Since seating may be limited, admission to the special meeting will be on a first-come, first-served basis. Registration and seating will begin at 8:00 a.m., local time.

Q:

IF MY SHARES ARE HELD IN "STREET NAME" BY A BROKER, BANK OR OTHER NOMINEE, WILL MY BROKER, BANK OR OTHER NOMINEE VOTE MY SHARES FOR ME?

A:

If your CUB common shares are held in "street name" by a broker, bank or other nominee, you must provide the record holder of your shares with instructions on how to vote your shares. Please follow the voting instructions provided by your broker, bank or other nominee. Please note that you may not vote shares held in "street name" by returning a proxy card directly to CUB or by voting in person at the special meeting unless you provide a "legal proxy," which you must obtain from your broker, bank or other nominee.

Brokers who hold shares in "street name" for the beneficial owner of those shares typically have the authority to vote in their discretion on "routine" proposals when they have not received instructions from the beneficial owner. However, brokers are not allowed to exercise their voting discretion with respect to the approval of matters that are "non-routine" without specific instructions from the beneficial owner. Both proposals to be voted on at the special meeting are considered "non-routine" matters and, therefore, brokers, banks and other nominees do not have discretionary voting power on these matters.

If you are a CUB common shareholder and you do not instruct your broker, bank or other nominee on how to vote your shares, then your broker, bank or other nominee may not vote your shares on either the merger proposal or the adjournment proposal.

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For the merger proposal, shares not represented at the special meeting are still considered outstanding and, therefore, will have the same effect as a vote "AGAINST" the proposal. The merger proposal requires the affirmative vote of a majority of the outstanding shares entitled to vote. Therefore, the failure of a holder of CUB common shares to provide its bank, broker or other nominee with voting instructions will have the same effect as a vote "AGAINST" the merger proposal.



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The adjournment proposal requires a vote that satisfies two criteria: (i) the affirmative vote of a majority of the shares represented and voting at a duly held meeting at which a quorum is present, and (ii) the shares voting affirmatively must also constitute at least a majority of the required quorum. Your bank, broker or other nominee does not have discretionary authority to vote your shares on the special meeting proposals without your instructions. Consequently, failure to provide instructions to your bank, broker or other nominee on how to vote will result in your shares not being represented at the special meeting. Accordingly, for purposes of the adjournment proposal, your shares will not affect the outcome under clause (i), which recognizes

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only actual votes cast. However, your shares will affect the outcome under clause (ii) if the number of shares voting affirmatively, though a majority of the shares represented and voted, does not constitute a majority of the required quorum.

Q:

WHAT IF I ABSTAIN OR DO NOT VOTE?

A:

For purposes of the special meeting, an abstention occurs when a shareholder attends the special meeting, either in person or represented by proxy, but abstains from voting.

Abstentions will be counted as represented at the special meeting for purposes of determining the presence or absence of a quorum for all matters to be voted on at the special meeting.

For the merger proposal, if a CUB common shareholder present in person at the special meeting abstains from voting, or responds by proxy with an "abstain" vote, it will have the same effect as a vote cast "AGAINST" the proposal. If a CUB common shareholder is not present in person at the special meeting and does not respond by proxy, it will also have the same effect as a vote cast "AGAINST" the proposal.

The adjournment proposal requires a vote that satisfies two criteria: (i) the affirmative vote of a majority of the shares represented and voting at a duly held meeting at which a quorum is present, and (ii) the shares voting affirmatively must also constitute at least a majority of the required quorum. Accordingly, for purposes of the adjournment proposal, abstentions will not affect the outcome under clause (i), which recognizes only actual votes cast. However, abstentions will affect the outcome under clause (ii) if the number of shares voting affirmatively, though a majority of the shares represented and voting, does not constitute a majority of the required quorum.

Q:

WHAT WILL HAPPEN IF I RETURN MY PROXY OR VOTING INSTRUCTION CARD WITHOUT INDICATING HOW TO VOTE?

A:

If you hold your CUB common shares in your name as a shareholder of record, and you sign and return your proxy card without indicating how to vote on any particular proposal, the CUB common shares represented by your proxy will be voted "FOR" the merger proposal and "FOR" the adjournment proposal.

If you hold your CUB common shares in "street name" through a broker, bank or other nominee and you do not give your broker, bank or other nominee instructions on how to vote, your broker, bank or other nominee will not be able to vote your CUB common shares on either of the proposals at the special meeting and your CUB common shares will not be represented at the special meeting.

Q:

MAY I CHANGE MY VOTE AFTER I HAVE DELIVERED MY PROXY OR VOTING INSTRUCTION CARD?

A:

Yes. If you hold your CUB common shares in your name as a shareholder of record, you may change your vote at any time before your proxy is voted at the special meeting. You may do so in one of four ways:

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first, by sending a notice of revocation stating that you would like to revoke your proxy;

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second, by sending a completed proxy card bearing a later date than your original proxy card;

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third, by logging onto the Internet website specified on your proxy card in the same manner you would submit your proxy electronically or by calling the telephone number specified on your proxy card, in each case if you were eligible to do so and following the instructions on the proxy card; or

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fourth, by attending the special meeting and voting in person. Attendance at the CUB special meeting will not in itself constitute the revocation of a proxy.

If you are a CUB shareholder of record and you choose to send a written notice of revocation or to mail a new proxy card, you must submit your notice of revocation or your new proxy to CUB's corporate secretary at 15821 Ventura Boulevard, Suite 100, Encino, California 91436. Any proxy that you submitted may also be revoked by submitting a new proxy via the Internet or by telephone no later than Wednesday, August 23, 2017 at 11:59 p.m. Eastern Time, or by voting in person at the special meeting.

If your shares are held in "street name" through a broker, bank or other nominee and you have instructed your nominee how to vote your CUB common shares, you must submit new voting instructions to your nominee. You should follow the instructions you receive from your broker, bank or other nominee in order to change or revoke your vote.

Q:

DO I NEED IDENTIFICATION TO ATTEND THE SPECIAL MEETING IN PERSON?

A:

Yes. If you hold your CUB common shares in your name as a shareholder of record and you wish to attend the special meeting and vote in person, please bring valid picture identification.

If your shares are held in "street name" through a broker, bank or other nominee, you may only vote in person at the special meeting if you have proof of ownership of your CUB common shares as of the record date and obtain a valid legal proxy from your broker, bank or other nominee that is the shareholder of record of such shares and present such items at the special meeting. You must also bring valid picture identification.

Q:

ARE CUB SHAREHOLDERS ENTITLED TO DISSENTERS' RIGHTS?

A:

Under the California General Corporation Law, referred to as the CGCL, CUB common shareholders may be entitled to dissenters' rights in connection with the merger. If you do not wish to accept the merger consideration and you vote "AGAINST" the merger in person or by proxy at the special meeting, you have the right to seek from CUB the "fair market value" of your shares in lieu of the mix of cash and PacWest common stock you would receive if the merger is completed. CUB refers you to the section entitled "The Merger—Dissenters' Rights" and to the applicable provisions of the CGCL attached as Appendix C for information on how to exercise your dissenters' rights. Failure to follow all of the steps required under the CGCL will result in the loss of your dissenters' rights.

Q:

WHAT ARE THE MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGER TO U.S. HOLDERS OF CUB COMMON SHARES?

A:

The merger is intended to qualify, and the obligation of PacWest and CUB to complete the merger is conditioned upon the receipt of legal opinions from their respective counsel to the effect that the merger will qualify as a reorganization within the meaning of Section 368(a) of the Internal Revenue Code. You generally will recognize gain (but not loss) upon receipt of the merger consideration in exchange for CUB common shares pursuant to the merger in an amount equal to the lesser of (1) the amount of gain realized (i.e., the excess of the sum of the amount of cash and the fair market value of the PacWest common stock received pursuant to the merger over your adjusted tax basis in the CUB common shares surrendered in the exchange) and (2) the amount of cash received pursuant to the merger (excluding any cash received in lieu of a fractional share of PacWest common stock).

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For a more detailed discussion of the material U.S. federal income tax consequences of the transaction, please see the section entitled "Material U.S. Federal Income Tax Consequences of the Merger."

The tax consequences of the merger to any particular shareholder will depend on that shareholder's particular facts and circumstances. Accordingly, you are urged to consult your tax advisor to determine your tax consequences from the merger.

Q:

WHAT HAPPENS IF THE MERGER IS NOT COMPLETED?

A:

If the merger is not completed, CUB common shareholders will not receive any consideration for their CUB common shares that otherwise would have been received in connection with the merger. Instead, CUB will remain an independent public company and its common stock will continue to be listed and traded on NASDAQ.

Q:

WHAT HAPPENS IF I SELL MY CUB COMMON SHARES AFTER THE RECORD DATE BUT BEFORE THE SPECIAL MEETING?

A:

The record date of the special meeting is earlier than the date of the special meeting and the date that the merger is expected to be completed. If you sell or otherwise transfer your CUB common shares after the record date but before the date of the special meeting, you will retain your right to vote at the special meeting (provided that such shares remain outstanding on the date of the special meeting), but you will not have the right to receive the merger consideration to be received by CUB shareholders in the merger. In order to receive the merger consideration, you must hold your CUB common shares through completion of the merger.

Q:

WILL I BE ABLE TO SELL THE SHARES OF PACWEST COMMON STOCK THAT I RECEIVE IN THE MERGER?

A:

Yes. You may freely trade the shares of PacWest common stock issued in the merger.

Q:

ARE THERE RISKS INVOLVED IN UNDERTAKING THE MERGER?

A:

Yes. In evaluating the merger, CUB shareholders should carefully consider the factors discussed in "Risk Factors" beginning on page 28 and other information about CUB and PacWest included in the documents incorporated by reference into this proxy statement/prospectus.

Q:

SHOULD CUB SHAREHOLDERS SEND IN THEIR STOCK CERTIFICATES NOW?

A:

No. CUB shareholders SHOULD NOT send in any stock certificates now. If the merger is approved, transmittal materials with instructions for their completion will be provided to CUB shareholders under separate cover and the stock certificates should be sent at that time.

Q:

WHAT SHOULD I DO IF I RECEIVE MORE THAN ONE SET OF VOTING MATERIALS?

A:

CUB common shareholders may receive more than one set of voting materials, including multiple copies of this document and multiple proxy cards or voting instruction cards. If you are a shareholder of record and your shares are registered in more than one name, you will receive more than one proxy card. If you hold CUB common shares in more than one brokerage account, you may receive a separate voting instruction card for each brokerage account in which you hold such shares. In each case, please complete, sign, date and return each proxy card and voting instruction card that you receive or otherwise follow the voting instructions set forth in this document to ensure that you vote every CUB common share that you own.

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Q:

WHOM SHOULD I CONTACT IF I HAVE ANY QUESTIONS ABOUT THE PROXY MATERIALS OR VOTING?

A:

If you are a CUB common shareholder and have any questions about the proxy materials or if you need assistance submitting your proxy or voting your shares or need additional copies of this document or the enclosed proxy card, you should contact CUB Investor Relations at (818) 257-7700.

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RISK FACTORS

        In addition to the other information contained in or incorporated by reference into this document, including the matters addressed under the caption entitled "Cautionary Statement Regarding Forward-Looking Statements," CUB shareholders should carefully consider the following factors in deciding whether to vote for CUB's proposals. Please see the sections entitled "Where You Can Find More Information" and "Incorporation of Certain Documents by Reference."

Because the market price of PacWest common stock will fluctuate, the value of the merger consideration to be received by CUB shareholders may change.

        Upon completion of the merger, other than in certain circumstances described below, each CUB common share (other than excluded shares and dissenting shares) will be converted into the right to receive the merger consideration consisting of $12.00 in cash plus 0.5308 of a share of PacWest common stock. Accordingly, the value of the merger consideration to be received by CUB shareholders will be based on the value of PacWest common stock at closing. The value of the PacWest common stock to be received by CUB shareholders in the merger may vary from the value as of the date the merger was announced, the date that this document was mailed to CUB shareholders, the date of the special meeting and the determination period. Any change in the market price of PacWest common stock prior to completion of the merger will affect the value of the merger consideration that CUB shareholders will receive upon completion of the merger. Accordingly, at the time of the special meeting, CUB shareholders will not know or be able to calculate the value of the per share consideration they would receive upon completion of the merger. Share price changes may result from a variety of factors, including general market and economic conditions, changes in PacWest's or CUB's businesses, operations and prospects, and regulatory considerations, among other things. Many of these factors are beyond the control of PacWest and CUB. CUB shareholders should obtain current market quotations for CUB common shares and PacWest common stock before voting their shares at the special meeting.

        In addition, the merger agreement provides that CUB may terminate the merger agreement if (i) the PacWest average closing price falls below $44.84 per share and (ii) the PacWest average closing price underperforms the average KBW Index for the determination period by more than 15%. If CUB elects to terminate the merger agreement, then PacWest may reinstate the agreement after increasing the exchange ratio or cash consideration according to formulas set forth in the merger agreement such that the value of the merger consideration is intended to fix at $35.80 per share, as adjusted for any decline in the KBW Index. Accordingly, at the time of the CUB special meeting, CUB shareholders may not know or be able to calculate the applicable metrics over the determination period to determine the cash consideration or the exchange ratio used to determine the number of shares of PacWest common stock they would receive with respect to each CUB common share upon completion of the merger, and the number of shares of PacWest common stock or cash consideration to be received by CUB shareholders may be materially less than anticipated by CUB shareholders.

        For a more detailed discussion of potential adjustments to the merger consideration, see the section entitled "The Merger Agreement—Termination of the Merger Agreement."

CUB shareholders will have a reduced ownership and voting interest in PacWest after the merger and will exercise less influence over PacWest's management.

        CUB shareholders currently have the right to vote in the election of the CUB board of directors and on other matters affecting CUB. Upon the completion of the merger, except for shareholders who own common shares in both PacWest and CUB, each CUB shareholder will be a shareholder of PacWest with a percentage ownership of PacWest that is smaller than such shareholder's current percentage ownership of CUB. It is currently expected that former shareholders of CUB as a group will

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receive shares in the merger constituting approximately 7.3% of the outstanding shares of PacWest's common stock immediately after the merger. Because of this, CUB shareholders will have less influence on the management and policies of PacWest than they now have on the management and policies of CUB.

Sales of substantial amounts of PacWest's common stock in the open market by former CUB shareholders could depress PacWest's stock price.

        Shares of PacWest common stock that are issued to CUB shareholders in the merger will be freely tradable without restrictions or further registration under the Securities Act. As of the close of business on June 30, 2017, PacWest had approximately 121,448,321 shares of common stock outstanding. Based on the CUB common shares currently outstanding, PacWest currently expects to issue approximately 9,487,221 shares of its common stock in connection with the merger.

        Because of the significantly enhanced liquidity of PacWest common stock as compared to CUB common shares on account of the greater public float and trading volume of PacWest common stock relative to CUB common shares, if the merger is completed, CUB's former shareholders may sell substantial amounts of PacWest common stock in the public market following completion of the merger. Any such sales may cause the market price of PacWest common stock to decrease. These sales might also make it more difficult for PacWest to sell equity or equity-related securities at a time and price that it otherwise would deem appropriate.

PacWest may fail to realize the anticipated benefits of the merger.

        The success of the merger will depend on, among other things, PacWest's ability to combine and integrate the business of CUB into PacWest's business. If PacWest is not able to successfully achieve this objective, the anticipated benefits of the merger may not be realized fully, or at all, or may take longer to realize than expected.

        PacWest and CUB have operated and, until the consummation of the merger, will continue to operate independently. It is possible that the integration process or other factors could result in the loss or departure of key employees, the disruption of the ongoing business of PacWest or CUB or inconsistencies in standards, controls, procedures and policies. It is also possible that clients, customers, depositors and counterparties of CUB could choose to discontinue their relationships with PacWest post-merger because they prefer doing business with a different financial institution, which would adversely affect the future anticipated performance of PacWest. These transition matters could have an adverse effect on CUB during the pre-merger period and the combined company for an undetermined amount of time after the consummation of the merger.

Regulatory approvals may not be received, may take longer than expected or may impose conditions that are not presently anticipated or cannot be met.

        Before the transactions contemplated by the merger agreement, including the merger and the bank merger, may be completed, various approvals must be obtained from bank regulatory authorities. These governmental entities may impose conditions on the granting of such approvals. Such conditions or changes and the process of obtaining regulatory approvals could have the effect of delaying completion of the merger or of imposing additional costs or limitations on PacWest following the merger. The regulatory approvals may not be received at all, may not be received in a timely fashion, and may contain conditions on the completion of the merger that are not anticipated or cannot be met. If the consummation of the merger is delayed, including by a delay in receipt of necessary governmental approvals, the business, financial condition and results of operations of each company may also be materially adversely affected.

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Failure of the merger to be completed, the termination of the merger agreement or a significant delay in the consummation of the merger could negatively impact PacWest and CUB.

        The merger agreement is subject to a number of conditions which must be fulfilled in order to complete the merger. Those conditions include: (i) approval of the principal terms of the merger agreement by CUB shareholders, (ii) absence of any governmental order or law prohibiting completion of the merger, and (iii) effectiveness of the registration statement of which this document is a part.

        The obligation of each party to consummate the merger is also conditioned upon (i) subject to certain exceptions, the accuracy of the representations and warranties of the other party, (ii) performance in all material respects by the other party of its obligations under the merger agreement, (iii) receipt by such party of a tax opinion to the effect that the merger will qualify as a reorganization within the meaning of Section 368(a) of the Internal Revenue Code, and (iv) the absence of a material adverse effect with respect to the other party since the date of the merger agreement. The obligation of PacWest to consummate the merger is also conditioned upon (i) the adjusted shareholders' equity and allowance for loan losses of CUB being outside of specified levels, (ii) the receipt of certain required regulatory approvals and such approvals not containing materially burdensome regulatory conditions, (iii) the repurchase by CUB of all outstanding shares of CUB's Series A preferred stock held by the U.S. Treasury Department and (iv) holders of not more than 10% of outstanding CUB common shares having duly exercised their dissenters' rights under Chapter 13 of the CGCL. The obligation of CUB to consummate the merger is also conditioned upon the receipt of certain required regulatory approvals.

        These conditions to the consummation of the merger may not be fulfilled and, accordingly, the merger may not be completed. In addition, if the merger is not completed by the end date, either PacWest or CUB may choose not to proceed with the merger, and the parties can mutually decide to terminate the merger agreement at any time, before or after the CUB shareholder approval.

        Furthermore, prior to the CUB shareholder approval, PacWest may terminate the merger agreement and require payment of a $26.5 million termination fee if CUB materially breaches the restriction against soliciting alternative acquisition proposals, if CUB's board of directors recommends against the merger, if CUB's board of directors fails to reaffirm its recommendation in response to an alternative acquisition proposal after receiving a written request to do so from PacWest, or if CUB's board of directors recommends that CUB shareholders tender (or fails to recommend against tendering) their shares in a competing tender offer. CUB must also pay the $26.5 million termination fee if an alternative acquisition proposal has been made or announced, the merger agreement is terminated because the merger was not consummated by the end date and/or the CUB shareholder approval has not been obtained, and within 12 months after the termination of the merger agreement, CUB enters into a definitive agreement with respect to or consummates a proposal by a third party to acquire 50% or more of the assets or voting power of CUB.

        If the merger is not consummated, the ongoing business, financial condition and results of operations of each party may be materially adversely affected and the market price of each party's common stock may decline significantly, particularly to the extent that the current market price reflects a market assumption that the merger will be consummated. If the consummation of the merger is delayed, including by the receipt of a competing acquisition proposal, the business, financial condition and results of operations of each company may be materially adversely affected.

        In addition, each party has incurred and will incur substantial expenses in connection with the negotiation and completion of the transactions contemplated by the merger agreement. If the merger is not completed, the parties would have to recognize these expenses, including, in the case of CUB under certain circumstances, a termination fee, without realizing the expected benefits of the transaction. Any of the foregoing, or other risks arising in connection with the failure of or delay in consummating the merger, including the diversion of management attention from pursuing other

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opportunities and the constraints in the merger agreement on each party's ongoing business during the pendency of the merger, could have a material adverse effect on each party's business, financial condition and results of operations.

        Additionally, PacWest's or CUB's business may be adversely impacted by the failure to pursue other beneficial opportunities due to the focus of management on the merger, without realizing any of the anticipated benefits of completing the merger, and the market price of PacWest common stock or CUB common shares might change to the extent that the current market price reflects a market assumption that the merger will be completed. If the merger agreement is terminated and a party's board of directors seeks another merger or business combination, such party's shareholders cannot be certain that such party will be able to find a party willing to engage in a transaction on more attractive terms than the merger.

CUB will be subject to business uncertainties and contractual restrictions while the merger is pending.

        Uncertainty about the effect of the merger on employees, customers, suppliers and vendors may have an adverse effect on the business, financial condition and results of operations of CUB and, consequently, PacWest. It is currently contemplated that certain CU Bank branches are to be closed or consolidated into nearby Pacific Western Bank branches and certain Pacific Western Bank branches are planned to be closed or consolidated into nearby CU Bank branches. These uncertainties and contemplated changes may impair CUB's ability to attract, retain and motivate key personnel and customers pending the consummation of the merger, as such personnel and customers may experience uncertainty about their future roles following the consummation of the merger. Additionally, these uncertainties and contemplated changes could cause customers, suppliers, vendors and others who deal with CUB to seek to change existing business relationships with CUB or fail to extend an existing relationship with CUB. In addition, competitors may target CUB's existing customers by highlighting potential uncertainties and integration difficulties that may result from the merger.

        CUB has a small number of key personnel. The pursuit of the merger and the preparation for the integration may place a burden on CUB's management and internal resources. Any significant diversion of management attention away from ongoing business concerns and any difficulties encountered in the transition and integration process could have a material adverse effect on CUB's business, financial condition and results of operations.

        In addition, the merger agreement restricts CUB from taking certain actions without PacWest's consent while the merger is pending. These restrictions may, among other matters, and subject to certain exceptions, prevent CUB from pursuing otherwise attractive business opportunities, selling assets, incurring indebtedness, engaging in significant capital expenditures, entering into other transactions or making other changes to CUB's business prior to consummation of the merger or termination of the merger agreement. These restrictions could have a material adverse effect on CUB's business, financial condition and results of operations. Please see the section entitled "The Merger Agreement—Conduct of Business Prior to the Completion of the Merger" for a description of the restrictive covenants applicable to CUB.

CUB directors and officers have interests in the merger different from the interests of other CUB shareholders.

        CUB's executive officers and directors have interests in the merger that are different from, or in addition to, the interests of CUB shareholders generally. Such interests include the following: (1) CUB executive officers have unvested equity awards that will be accelerated and vest in full on the completion of the merger; (2) CUB executive officers are participants in plans and party to agreements that provide for severance payments and other benefits in the event of, or upon a termination of employment within 24 months following, a change in control of CUB; (3) CUB directors and executive officers are entitled to continued indemnification and insurance coverage following the closing of the

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merger; (4) David I. Rainer, CUB's Chief Executive Officer and Chairman, K. Brian Horton, director and President of CUB and Karen Schoenbaum, Executive Vice President and Chief Financial Officer of CUB, have entered into consulting agreements with PacWest that become effective as of, and are conditioned upon, the closing of the merger; and (5) CUB non-employee directors have CUB restricted shares that, depending on the closing date of the merger, may accelerate and become vested upon completion of the merger. These interests are described in more detail under the section entitled "The Merger—Interests of CUB Directors and Executive Officers in the Merger."

Shares of PacWest common stock to be received by CUB shareholders as a result of the merger will have rights different from CUB common shares.

        Upon completion of the merger, the rights of former CUB shareholders will be governed by the certificate of incorporation and bylaws of PacWest. The rights associated with CUB common shares are different from the rights associated with PacWest common stock. In addition, the rights of stockholders under Delaware law, where PacWest is incorporated, may differ from the rights of shareholders under California law, where CUB is incorporated. Please see the section entitled "Comparison of Shareholders' Rights" for a discussion of the different rights associated with PacWest common stock.

The merger agreement contains provisions that may discourage other companies from trying to acquire CUB.

        The merger agreement contains provisions that may discourage a third party from submitting a business combination proposal to CUB that might result in greater value to CUB shareholders than the merger. These provisions include a general prohibition on CUB from soliciting, or, subject to certain exceptions, entering into discussions with any third party regarding any acquisition proposal or offers for competing transactions. In addition, in some circumstances upon termination of the merger agreement, CUB may be required to pay PacWest a $26.5 million termination fee. However, the failure of CUB shareholders to approve the merger agreement will not in and of itself trigger CUB's obligation to pay a termination fee, unless other factors also exist, including a third-party proposal to acquire CUB and entry into a definitive agreement with respect to an acquisition of CUB, or consummation of an acquisition of CUB, in each case within 12 months following termination.

        Each of the directors of CUB, in his or her capacity as a shareholder of CUB, has entered into a voting agreement with PacWest in which such director has agreed to vote all CUB common shares that he or she owns and has the power to vote in favor of the merger proposal and any other matter that is required to be approved by the shareholders of CUB to facilitate the transactions contemplated by the merger agreement. The directors also agreed to vote against any proposal made in opposition to the approval of the principal terms of the merger agreement or in competition with the merger agreement and against any acquisition proposal. As of the close of business on the record date, CUB's directors beneficially owned, in the aggregate, 1,095,309 CUB common shares, allowing them to exercise approximately 6.14% of the voting power of CUB common shares (which does not include shares issuable upon the exercise of stock options or upon the vesting of CUB RSUs that were not outstanding as of the close of business on the record date). For more information, please see the section entitled "The Merger Agreement—Voting Agreements." CUB also has an unqualified obligation to submit the merger proposal to a vote of CUB shareholders, even if CUB receives a proposal that its board of directors believes is superior to the merger.

In connection with the announcement of the merger agreement, two shareholder class action lawsuits are pending, seeking, among other things, to enjoin the merger, and an adverse judgment in one or both of these lawsuits may prevent the merger from becoming effective in the fourth quarter of 2017, if at all.

        Two putative shareholder class action lawsuits have been filed in connection with the merger agreement. The Parshall complaint was filed on June 9, 2017 in the United States District Court for the Central District of California. The Parshall complaint alleges that the members of the CUB board of

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directors violated Sections 14(a) and 20(a) of the Exchange Act, based upon alleged omissions and misrepresentations in the initial registration statement, by approving the proposed merger for inadequate consideration and by entering into the merger agreement containing preclusive deal protection devices. The plaintiff in this action seeks injunctive relief prohibiting consummation of the merger, rescission and damages in the event the merger is consummated, an accounting of damages suffered by the plaintiff and the putative class, attorneys' fees and costs and other and further relief.

        The Klein complaint was filed on June 12, 2017 in the United States District Court for the Central District of California. The Klein complaint alleges that the members of the CUB board of directors violated Sections 14(a) and 20(a) of the Exchange Act, based upon alleged omissions and misrepresentations in the initial registration statement, by approving the proposed merger for inadequate consideration and by entering into the merger agreement containing preclusive deal protection devices. The plaintiff in this action seeks injunctive relief prohibiting consummation of the merger, rescission and damages in the event the merger is consummated, an accounting of damages suffered by the plaintiff and the putative class, attorneys' fees and costs and other and further relief.

        At this stage, it is not possible to predict the outcome of the proceedings in the merger litigation or their impact on CUB, PacWest or the merger. If the plaintiffs are successful in enjoining the consummation of the merger, the lawsuits may prevent the merger from becoming effective in the fourth quarter of 2017, if at all.

PacWest expects to incur substantial expenses related to the merger.

        PacWest expects to incur substantial expenses in connection with consummation of the merger and integrating the business, operations, networks, systems, technologies, policies and procedures of CUB into that of PacWest. Although PacWest and CUB have assumed that a certain level of transaction and combination expenses would be incurred, there are a number of factors beyond their control that could affect the total amount or the timing of their combination expenses. Many of the expenses that will be incurred, by their nature, are difficult to estimate accurately at the present time. As a result of these expenses, both PacWest and CUB expect to take charges against their earnings before and after the completion of the merger. The charges taken in connection with the merger are expected to be significant, although the aggregate amount and timing of such charges are uncertain at present.

The opinion of CUB's financial advisor will not reflect changes in circumstances between the date of the opinion and the completion of the merger.

        On April 5, 2017, the CUB board of directors received an opinion from KBW, its financial advisor, to the effect that, as of such date and subject to the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by KBW as set forth in its opinion, the merger consideration in the proposed merger was fair, from a financial point of view, to the holders of CUB common shares. Subsequent changes in the operations and prospects of CUB or PacWest, general market and economic conditions and other factors that may be beyond the control of CUB or PacWest, and on which KBW's opinion was based, may significantly alter the value of CUB or PacWest or the prices of PacWest common stock or CUB common shares by the time the merger is completed. Because CUB does not anticipate asking KBW to update its opinion, the opinion will not address the fairness of the merger consideration from a financial point of view at the time the merger is completed or as of any other date other than the date of such opinion. For a description of the opinion that CUB received from its financial advisor, please refer to the section entitled "The Merger—Opinion of CUB's Financial Advisor."

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

        This proxy statement/prospectus contains certain forward-looking information about PacWest, CUB, and the combined company after the close of the merger and the bank merger that is intended to be covered by the safe harbor for "forward-looking statements" provided by the Private Securities Litigation Reform Act of 1995. All statements other than statements of historical fact are forward-looking statements. Such statements involve inherent risks, uncertainties and contingencies, many of which are difficult to predict and are generally beyond the control of PacWest, CUB and the combined company. Readers are cautioned that a number of important factors could cause actual results to differ materially from those expressed in, or implied or projected by, such forward-looking statements. In addition to factors previously disclosed in reports filed by PacWest and CUB with the SEC, risks and uncertainties for each institution and the combined institution include, but are not limited to:

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lower than expected revenues;



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credit quality deterioration or a reduction in real estate values, which could cause an increase in the provision for credit losses and allowance for credit losses and a reduction in net earnings;



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increased competitive pressure among depository institutions;



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the ability to complete the merger and the bank merger, including by obtaining regulatory approvals and approval by the shareholders of CUB, or any future transaction, or to integrate such acquired entities successfully, or to achieve expected beneficial synergies and/or operating efficiencies, in each case within expected time-frames or at all;



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the reaction by CUB's or PacWest's customers, employees and counterparties to the merger;



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changes in the stock price of either PacWest or CUB prior to the completion of the merger as a result of the financial performance of PacWest or CUB prior to closing;



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the possibility that regulatory approvals will not be received on expected timeframes or at all;



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the possibility that personnel changes/retention will not proceed as planned;



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the possibility that a change in the interest rate environment may reduce net interest margins;



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higher than anticipated operating expenses;



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the effectiveness of PacWest's risk management framework;



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asset/liability re-pricing risks and liquidity risks;



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the costs and effects of legal, compliance, and regulatory actions, changes and developments, including the impact of adverse judgments or settlements in litigation;



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the initiation and resolution of regulatory or other governmental inquiries or investigations, and/or the results of regulatory examinations or reviews;



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general economic conditions, either nationally or in the market areas in which the entities operate or anticipate doing business, which may be less favorable than expected; and



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other risk factors described in documents filed by PacWest and CUB with the SEC.

        All forward-looking statements included in this proxy statement/prospectus are based on information available at the time of the proxy statement/prospectus. Pro forma, projected and estimated numbers are used for illustrative purposes only and are not forecasts, and actual results may differ materially.

        PacWest and CUB are under no obligation to (and expressly disclaim any such obligation to) update or alter these forward-looking statements, whether as a result of new information, future events or otherwise except as required by law.

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CUB SPECIAL MEETING OF SHAREHOLDERS

Date, Time and Place

        The special meeting will be held at City Club Los Angeles—Santa Monica Room, 555 South Flower Street, 51st Floor, Los Angeles, California 90071, on August 24, 2017, at 8:30 a.m., local time. On or about July 26, 2017, CUB commenced mailing of this proxy statement/prospectus and the enclosed form of proxy to its shareholders entitled to vote at the special meeting.

Purpose of the Special Meeting

        At the special meeting, CUB common shareholders will be asked to consider and vote upon the following proposals:

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Merger Proposal.  To approve the principal terms of the merger agreement, dated as of April 5, 2017, by and between PacWest and CUB, as such agreement may be amended from time to time, a copy of which is attached as Appendix A to this proxy statement/prospectus; and



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Adjournment Proposal.  To approve one or more adjournments of the special meeting, if necessary or appropriate, including adjournments to permit further solicitation of proxies if there are insufficient votes at the time of the special meeting to approve the merger proposal.

        CUB will transact no other business at the special meeting other than as listed above.

Recommendation of the CUB Board of Directors

        After careful consideration, the CUB board of directors has unanimously approved the merger agreement and the transactions contemplated thereby, and determined that the merger agreement and the transactions contemplated thereby are fair to and in the best interests of CUB and its shareholders.

        The CUB board of directors recommends that you vote "FOR" the merger proposal and "FOR" the adjournment proposal. Please see the section entitled "The Merger—Recommendation of the CUB Board of Directors and Reasons for the Merger."

Record Date and Quorum

        The CUB board of directors has fixed the close of business on June 30, 2017 as the record date for determining the holders of CUB common shares entitled to receive notice of and to vote at the special meeting.

        As of the close of business on the record date, there were 17,831,131 CUB common shares outstanding and entitled to vote at the special meeting held by 594 shareholders of record. Each CUB common share entitles the holder to one vote on each proposal to be considered at the special meeting.

        A majority of shares entitled to vote, represented in person or by proxy, constitutes a quorum for transacting business at the special meeting. Abstentions will be counted as represented at the special meeting for purposes of determining the presence or absence of a quorum for all matters voted on at the special meeting.

        Since none of the proposals to be voted on at the CUB special meeting are routine matters for which brokers may have discretionary authority to vote, there can be no broker non-votes at the special meeting. Consequently, failure to provide instructions to your bank, broker or other nominee on how to vote will result in your shares not being counted as represented for purposes of establishing a quorum at the CUB special meeting. Please see "—Shares Held in 'Street Name"' below for further information.

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        As of the close of business on the record date, directors and executive officers of CUB and their affiliates owned and were entitled to vote 1,473,883 CUB common shares, representing approximately 8.27% of the CUB common shares outstanding on that date. As of the close of business on the record date, PacWest beneficially held no CUB common shares.

        In connection with the merger agreement, each of the directors of CUB, in his or her capacity as a shareholder of CUB, has entered into a voting agreement with PacWest in which such director has agreed to vote all CUB common shares that he or she owns and has the power to vote in favor of the merger proposal and any other matter that is required to be approved by the shareholders of CUB to facilitate the transactions contemplated by the merger agreement. The directors also agreed to vote against any proposal made in opposition to the approval of the principal terms of the merger agreement or in competition with the merger agreement and against any acquisition proposal. As of the close of business on the record date, CUB's directors beneficially owned, in the aggregate, 1,095,309 CUB common shares, allowing them to exercise approximately 6.14% of the voting power of CUB common shares (which does not include shares issuable upon the exercise of stock options or upon the vesting of CUB RSUs that were not outstanding as of the close of business on the record date).

Required Vote

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Merger Proposal:  The affirmative vote of a majority of the outstanding shares entitled to vote on the proposal is required to approve the merger proposal.



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Adjournment Proposal:  The adjournment proposal requires a vote that satisfies two criteria: (i) the affirmative vote of a majority of the shares represented and voting at a duly held meeting at which a quorum is present, and (ii) the shares voting affirmatively must also constitute at least a majority of the required quorum.

Treatment of Abstentions; Failure to Vote

        For purposes of the special meeting, an abstention occurs when a CUB common shareholder attends the special meeting, either in person or represented by proxy, but abstains from voting.

        Abstentions will be counted as represented at the special meeting for purposes of determining the presence or absence of a quorum for all matters voted on at the special meeting.

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For the merger proposal, if a CUB common shareholder present in person at the special meeting abstains from voting, or responds by proxy with an "abstain" vote, it will have the same effect as a vote "AGAINST" the proposal. If a CUB common shareholder is not present in person at the special meeting and does not respond by proxy, it will also have the same effect as a vote "AGAINST" the proposal.



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The adjournment proposal requires a vote that satisfies two criteria: (i) the affirmative vote of a majority of the shares represented and voting at a duly held meeting at which a quorum is present, and (ii) the shares voting affirmatively must also constitute at least a majority of the required quorum. Accordingly, for purposes of the adjournment proposal, abstentions will not affect the outcome under clause (i), which recognizes only actual votes cast. However, abstentions will affect the outcome under clause (ii) if the number of shares voting affirmatively, though a majority of the shares represented and voting, does not constitute a majority of the required quorum.

Voting on Proxies; Incomplete Proxies

        Giving a proxy means that a shareholder authorizes the persons named in the proxy to vote such holder's shares at the special meeting in the manner such holder directs. A CUB common shareholder may vote by proxy or in person at the special meeting.

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        The method of voting by proxy differs for shares held by shareholders of record and shares held in "street name."

Shareholders of Record:

        If your CUB common shares are registered directly in your name, you are considered the shareholder of record with respect to these shares. If you hold your shares in your name as a shareholder of record, you may submit your proxy before the special meeting in one of the following ways:

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By telephone: Use the telephone number shown on your proxy card. Use any touch-tone telephone to vote your proxy 24 hours a day, 7 days a week. Have your proxy card handy when you call. You will be prompted to enter your control number(s), which is located on your proxy card, and then follow the directions given.



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Through the Internet: Visit the website shown on your proxy card to vote via the Internet. Use the Internet to vote your proxy 24 hours a day, 7 days a week. Have your proxy card handy when you access the website. You will be prompted to enter your control number(s), which is located on your proxy card, to create and submit an electronic ballot.



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By mail: Complete, sign, date and return the proxy card in the enclosed envelope. The envelope requires no additional postage if mailed in the United States.

        You may also cast your vote in person at the special meeting. Please see "—Attending the Special Meeting and Voting in Person" below for further information.

        CUB requests that CUB common shareholders vote by telephone, over the Internet or by completing, dating and signing the accompanying proxy and returning it to CUB as soon as possible in the enclosed postage-paid envelope. When the accompanying proxy is returned properly executed, the CUB common shares represented by it will be voted at the special meeting in accordance with the instructions contained on the proxy card. Electronic proxies submitted via the Internet or by telephone must be received no later than Wednesday, August 23, 2017 at 11:59 p.m. Eastern Time.

        If you hold your CUB common shares in your name as a shareholder of record, and you sign and return your proxy card without indicating how to vote on any particular proposal, the CUB common shares represented by the proxy will be voted "FOR" the merger proposal and "FOR" the adjournment proposal.

Shares Held in "Street Name":

        If your CUB common shares are held in an account with a bank, broke or other nominee, which are referred to as shares held in "street name," the bank, broker or other nominee is considered the shareholder of record with respect to these shares and you are the beneficial owner of these "street name" shares.

        If your shares are held in "street name" through a broker, bank or other nominee, you will receive instructions from your broker, bank or other nominee that you must follow in order to vote your shares. You should refer to the voting form used by that firm to determine whether you may vote by telephone, Internet or mail.

        If your shares are held in "street name," CUB recommends that you mark, date, sign and promptly mail the voting instruction form provided by your bank, broker or other nominee in accordance with the instructions provided by such nominee. If you do not give your bank, broker or other nominees instructions on how to vote your CUB common shares, your bank, broker or other nominees will not be able to vote your shares on either of the proposals at the special meeting and your shares will not be represented at the special meeting.

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        If your shares are held in "street name" through a broker, bank or other nominee you must either direct your nominee on how to vote your shares or obtain a proxy from such nominee to vote in person at the CUB special meeting. If your shares are held in "street name," you may only vote in person at the CUB special meeting if you have proof of ownership of your CUB common shares as of the record date and obtain a valid legal proxy from your bank, broker or other nominee that is the shareholder of record of such shares and present such items at the CUB special meeting. Please see "—Attending the Special Meeting and Voting in Person" below for further information.

        Every shareholder's vote is important. Accordingly, each CUB common shareholder should promptly submit a proxy, whether or not the shareholder plans to attend the special meeting.

        If you are a shareholder of record and your shares are registered in more than one name, you will receive more than one proxy card. If you hold your shares in more than one brokerage account, you may receive a separate voting instruction card for each brokerage account in which you hold shares. In each case, please complete, sign, date and return each proxy card and voting instruction form that you receive.

Shares Held in "Street Name"

        If your CUB common shares are held in "street name" through a bank, broker or other nominee, you must provide the bank, broker or other nominee, as the shareholder of record of your shares, with instructions on how to vote your shares. Please follow the instructions provided by your bank, broker or other nominee. You may not vote shares held in "street name" by returning a proxy card directly to CUB or by voting in person at the special meeting unless you provide a "legal proxy," which you must obtain from your broker, bank or other nominee.

        Brokers, banks or other nominees who hold shares in "street name" for the beneficial owner are not allowed to vote with respect to the approval of matters that are "non-routine" without specific instructions from the beneficial owner. Both proposals to be voted on at the CUB special meeting are considered "non-routine" matters and, therefore, brokers, banks and other nominees do not have discretionary voting power on these matters. A "broker non-vote" occurs on an item when (i) a bank, broker or other nominee has discretionary authority to vote on one or more proposals to be voted on at a meeting of shareholders, but is not permitted to vote on other proposals without instructions from the beneficial owner of the shares and (ii) the beneficial owner fails to provide the bank, broker or other nominee with such instructions. Because none of the proposals to be voted on at the CUB special meeting are routine matters for which brokers may have discretionary authority to vote, there can be no broker non-votes at the CUB special meeting.

        Accordingly, if your CUB common shares are held in "street name," your bank, broker or other nominee will NOT be able to vote your CUB common shares on either the merger proposal or the adjournment proposal, and your shares will not be counted as represented for purposes of establishing a quorum at the special meeting unless you have properly instructed your bank, broker or other nominee on how to vote.

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For the merger proposal, shares not represented at the special meeting are still considered outstanding and, therefore, will have the same effect as a vote "AGAINST" the proposal. The merger proposal requires the affirmative vote of a majority of the outstanding shares entitled to vote. Therefore, the failure of a holder of CUB common shares to provide its bank, broker or other nominee with voting instructions will have the same effect as a vote "AGAINST" the merger proposal.



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The adjournment proposal requires a vote that satisfies two criteria: (i) the affirmative vote of a majority of the shares represented and voting at a duly held meeting at which a quorum is present, and (ii) the shares voting affirmatively must also constitute at least a majority of the

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required quorum. Your bank, broker or other nominee does not have discretionary authority to vote your shares on the special meeting proposals without your instructions. Consequently, failure to provide instructions to your bank, broker or other nominee on how to vote will result in your shares not being represented at the special meeting. Accordingly, for purposes of the adjournment proposal, your shares will not affect the outcome under clause (i), which recognizes only actual votes cast. However, your shares will affect the outcome under clause (ii) if the number of shares voting affirmatively, though a majority of the shares represented and voting, does not constitute a majority of the required quorum.

Revocability of Proxies and Changes to a Shareholder's Vote

        If you hold your CUB common shares in your name as a shareholder of record, you may change your vote at any time before your proxy is voted at the special meeting. You may do this in one of four ways:

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first, by sending a notice of revocation stating that you would like to revoke your proxy;



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second, by sending a completed proxy card bearing a later date than your original proxy card;



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third, by logging onto the Internet website specified on your proxy card in the same manner you would submit your proxy electronically or by calling the telephone number specified on your proxy card, in each case if you were eligible to do so and following the instructions on the proxy card; or



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fourth, by attending the special meeting and voting in person. Attendance at the CUB special meeting will not in itself constitute the revocation of a proxy.

        If you are a CUB shareholder of record and you choose to send a written notice of revocation or to mail a new proxy card, you must submit your notice of revocation or your new proxy to CUB's corporate secretary at 15821 Ventura Boulevard, Suite 100, Encino, California 91436. Any proxy that you submitted may also be revoked by submitting a new proxy via the Internet or by telephone no later than Wednesday, August 23, 2017 at 11:59 p.m. Eastern Time, or by voting in person at the special meeting.

        If your shares are held in "street name" through a broker, bank or other nominee and you have instructed your nominee how to vote your CUB common shares, you must submit new voting instructions to your nominee. You should follow the instructions you receive from your bank, broker or other nominee on how to change or revoke your vote.

Attending the Special Meeting and Voting in Person

        The special meeting will be held at City Club Los Angeles—Santa Monica Room, 555 South Flower Street, 51st Floor, Los Angeles, California 90071, on August 24, 2017, at 8:30 a.m., local time. Subject to space availability, all CUB common shareholders as of the close of business on the record date, or their duly appointed proxies, may attend the special meeting. Since seating may be limited, admission to the special meeting will be on a first-come, first-served basis. Registration and seating will begin at 8:00 a.m., local time.

        If you hold your CUB common shares in your name as a shareholder of record and you wish to attend the special meeting and vote in person, please bring valid picture identification.

        If your shares are held in "street name" through a broker, bank or other nominee, you may only vote in person at the CUB special meeting if you have proof of ownership of your CUB common shares as of the record date and obtain a valid legal proxy from your bank, broker or other nominee that is the shareholder of record of such shares and present such items at the CUB special meeting. You must also bring valid picture identification.

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        Any representative of a shareholder who wishes to attend the CUB special meeting must present acceptable documentation evidencing his or her authority, acceptable evidence of ownership by the holder of CUB common shares and an acceptable form of identification.

Dissenters' Rights

        In connection with the merger, CUB common shareholders will have the opportunity to exercise dissenters' rights in accordance with the procedures set forth in Section 13 of the California General Corporation Law, or CGCL. A copy of Chapter 13 of the CGCL is attached to this proxy statement/prospectus as Appendix C. A dissenting shareholder who votes "AGAINST" the merger in person or by proxy at the special meeting and who follows the required procedures may receive cash in an amount equal to the fair market value of his or her CUB common shares in lieu of the merger consideration provided for under the merger agreement. For additional details and information on how to exercise your dissenters' rights, please refer to "The Merger—Dissenters' Rights" on page 76 and Appendix C of this proxy statement/prospectus. Failure to follow all of the steps required under the CGCL will result in the loss of your dissenters' rights.

Householding

        The SEC's proxy rules permit companies and intermediaries, such as brokers and banks, to satisfy proxy statement delivery requirements for two or more shareholders sharing an address by delivering one proxy statement to those shareholders. This procedure, known as "householding," reduces the amount of duplicate information that shareholders receive and lowers printing and mailing costs.

        If you share an address with another shareholder, you may receive only one set of proxy materials. If you wish to receive a separate copy of proxy materials now or in the future, please request the additional copies: (i) by sending a request to CU Bancorp, 15821 Ventura Boulevard, Suite 100, Encino, California 91436, Attention: Corporate Secretary, (ii) by email to awolman@cunb.com, (iii) by facsimile to (818) 257-7703 or (iv) by calling CUB Investor Relations at (818) 257-7700. The proxy statement/prospectus is also available on the internet at http://www.viewproxy.com/cubancorp2017. Similarly, if you are receiving multiple copies of the proxy materials and would like to receive only one copy for your household, you should contact your bank, broker or other nominee, or you may contact CUB in the same manner as set forth above.

Solicitation of Proxies

        CUB is soliciting proxies for the special meeting from CUB common shareholders on behalf of its board of directors. CUB will bear all of the costs of the proxy solicitation for the special meeting, including the costs of preparing, printing and mailing this proxy statement/prospectus to its shareholders. In addition to solicitations by mail, CUB's directors, officers and employees may solicit proxies in person or by telephone, email, facsimile or other electronic methods without additional compensation. CUB has engaged Alliance Advisors, LLC to assist CUB in the solicitation of proxies and the mailing of the proxy materials for the special meeting, as well as to provide related advice and informational support. Such firm will be paid a fee of approximately $20,000 plus reimbursement of reasonable out-of-pocket expenses.

        CUB will reimburse brokerage firms and other custodians, nominees and fiduciaries for their reasonable out-of-pocket expenses incurred by them in forwarding proxy materials to the beneficial owners of CUB common shares held in "street name" by such persons.

Questions and Additional Information

        If you have any questions or need assistance in voting your shares, please call CUB Investor Relations at (818) 257-7700.

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CUB PROPOSALS

Merger Proposal

        As discussed throughout this proxy statement/prospectus, CUB is asking its common shareholders to approve the merger proposal. Holders of CUB common shares should read carefully this document in its entirety, including the appendices, for more detailed information concerning the merger agreement and the merger. In particular, holders of CUB common shares are directed to the merger agreement, a copy of which is attached as Appendix A to this proxy statement/prospectus.

The CUB board of directors recommends a vote "FOR" the merger proposal.

Adjournment Proposal

        The special meeting may be adjourned to another time and place, if necessary or appropriate, to permit, among other things, the further solicitation of proxies if there are insufficient votes at the time of the special meeting to approve the merger proposal.

        If, at the special meeting, we do not have the affirmative vote of a majority of the outstanding shares entitled to vote to approve the merger proposal, CUB intends to move to adjourn the special meeting in order to enable the board of directors to solicit additional proxies for approval of the merger proposal. If the common shareholders approve the adjournment proposal, CUB could adjourn the special meeting and use the additional time to solicit additional proxies, including the solicitation of proxies from common shareholders who have previously voted.

The CUB board of directors recommends a vote "FOR" the adjournment proposal.

No Other Matters

        Under Section 601(a) of the CGCL, CUB may not transact any other business at the special meeting other than as listed above.

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INFORMATION ABOUT THE COMPANIES

PacWest Bancorp
9701 Wilshire Boulevard, Suite 700
Beverly Hills, California 90212
Phone: (310) 887-8500

        PacWest Bancorp, a Delaware corporation, is a bank holding company registered under the BHC Act, with corporate headquarters in Beverly Hills, California. PacWest's principal business is to serve as the holding company for PacWest's wholly owned subsidiary.

        PacWest is focused on relationship-based business banking to small, middle-market and venture-backed businesses nationwide. It offers a broad range of loan and deposit products and services through 74 full-service branches located throughout the state of California, one branch located in Durham, North Carolina, and several loan production offices located in cities across the country. It also provides commercial banking services, including real estate, construction, and commercial loans, and comprehensive deposit and treasury management services to small and middle-market businesses. In addition, PacWest offers products and services through its CapitalSource and Square 1 Bank Divisions. The CapitalSource Division provides cash flow, asset-based, equipment, and real estate loans and treasury management services to established middle-market businesses on a national basis. The Square 1 Bank Division offers a comprehensive suite of financial services focused on entrepreneurial businesses and their venture capital and private equity investors, with offices located in key innovation hubs across the United States. PacWest also provides investment advisory and asset management services to select clients through Square 1 Asset Management, Inc., a wholly owned subsidiary of Pacific Western Bank and a SEC-registered investment adviser.

        PacWest Bancorp was established in October 1999 and has achieved strong market positions by developing and maintaining extensive local relationships in the communities it serves. By leveraging its business model, service-driven focus, and presence in attractive markets, as well as maintaining a highly efficient operating model and robust approach to risk management, PacWest has achieved significant and profitable growth, both organically and through disciplined acquisitions. PacWest has successfully completed 28 acquisitions since 2000 which have contributed to its growth and expanded its market presence throughout the United States.

        As of March 31, 2017, PacWest had total assets of $21.9 billion, loans and leases, net of deferred fees, of $15.6 billion, total deposits of $16.3 billion, and stockholders' equity of $4.5 billion.

        PacWest's stock is traded on NASDAQ under the symbol "PACW."

        Additional information about PacWest and its subsidiaries may be found in the documents incorporated by reference into this document. Please also see the section entitled "Where You Can Find More Information."

CU Bancorp
818 West 7th Street, Suite 220
Los Angeles, California 90017
Phone: (213) 430-7000

        CU Bancorp, a California corporation, headquartered in downtown Los Angeles, California, is a bank holding company registered under the BHC Act and within the meaning of Section 1280 of the California Financial Code. CUB's principal business is to serve as the holding company for its wholly owned subsidiary, CU Bank. The common shares of CUB are listed on the NASDAQ Capital Market under the trading symbol "CUNB."

        CU Bancorp was incorporated as a California corporation on November 16, 2011, and became the holding company for CU Bank on July 31, 2012. CUB is a California state-chartered banking

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corporation and is not a member of the Federal Reserve System. CU Bank was incorporated on September 30, 2004, under the laws of the State of California, and commenced operations on May 23, 2005.

        CU Bank is a full-service commercial business bank offering a broad range of banking products and services including: deposit services, lending and cash management to small- and medium-sized businesses, to non-profit organizations, to business principals and entrepreneurs, to the professional community, including attorneys, certified public accountants, financial advisors, healthcare providers and investors. CU Bank is a Small Business Administration, or SBA, Preferred Lender. CU Bank's deposit products include demand, money market, and certificates of deposit. CU Bank's loan products include commercial, real estate construction, commercial real estate, SBA and personal loans. CU Bank also provides cash management services, online banking, commercial credit cards and other primarily business-oriented products. In addition to the Los Angeles headquarters office of CUB and CU Bank, CU Bank has eight additional full-service branches in the Ventura/Los Angeles/Orange County/San Bernardino metropolitan area located in Encino, West Los Angeles, Valencia, Thousand Oaks, Gardena, Anaheim, Irvine/Newport Beach and Ontario.

        As of March 31, 2017, CUB had consolidated total assets of $3.1 billion, total loans of $2.0 billion, total deposits of $2.8 billion and total shareholders' equity of $346.4 million.

        CUB's stock is traded on NASDAQ under the symbol "CUNB."

        Additional information about CUB and its subsidiaries may be found in the documents incorporated by reference into this document. Please see the section entitled "Where You Can Find More Information."

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THE MERGER

        The following is a discussion of the merger and the material terms of the merger agreement between PacWest and CUB. You are urged to read carefully the merger agreement in its entirety, a copy of which is attached as Appendix A to this document and incorporated by reference herein. This summary does not purport to be complete and may not contain all of the information about the merger agreement that is important to you. This section is not intended to provide you with any factual information about PacWest or CUB. Such information can be found elsewhere in this document and in the public filings PacWest and CUB make with the SEC, as described in the section entitled "Where You Can Find More Information."

Terms of the Merger

Transaction Structure

        PacWest's and CUB's boards of directors have approved the merger agreement. The merger agreement provides for the merger of CUB with and into PacWest, with PacWest continuing as the surviving corporation. Immediately after the merger, CU Bank, a California state-chartered bank and a wholly owned subsidiary of CUB, will merge with and into Pacific Western Bank, a California state-chartered bank and a wholly owned subsidiary of PacWest, with Pacific Western Bank as the surviving bank.

Merger Consideration

        In the merger, each CUB common share owned by a CUB shareholder, other than certain specified excluded shares and dissenting shares described under "The Merger Agreement—Merger Consideration—Cancellation of Excluded Shares and Dissenting Shares," will be converted into the right to receive (i) $12.00 in cash and (ii) 0.5308 of a share of PacWest common stock. For each fractional share that would otherwise be issued, PacWest will pay cash in an amount equal to the fraction of a share of PacWest common stock which the holder would otherwise be entitled to receive multiplied by the PacWest average closing price.

        The market value of the stock portion of the merger consideration will fluctuate with the price of PacWest common stock, and the value of the shares of PacWest common stock that holders of CUB common shares will receive upon consummation of the merger may be different than the value of the shares of PacWest common stock that holders of CUB common shares would receive if calculated on the date PacWest and CUB announced the merger, on the date that this document is being mailed to CUB shareholders, or on the date of the special meeting of CUB shareholders. Based on the closing price of PacWest common stock on April 5, 2017, the value of the per share merger consideration payable to holders of CUB common shares was $39.45. While the transaction value at the signing of the merger agreement represented a $0.05 discount to the closing price of CUB common shares on April 5, 2017, the price of CUB common shares had increased approximately 10% year to date and approximately 68% since the date of the 2016 presidential election, while the KBW Index had decreased approximately 7% and increased approximately 18% since such dates, respectively. For more discussion regarding how the increase in the price of CUB common shares was considered by the CUB board of directors in determining to approve the merger agreement, please see the section entitled "The Merger—Background of the Merger." Based on the closing price of PacWest common stock on July 20, 2017, the last practicable date before the date of this document, the value of the per share merger consideration payable to holders of CUB common shares was $37.87.

Treatment of CUB Stock Options, Restricted Shares and RSUs

        CUB Stock Options.    At the effective time, each outstanding CUB stock option, whether vested or unvested, will be cancelled and will entitle the holder thereof to receive an amount in cash equal to the product of (i) the total number of CUB common shares subject to such option and (ii) the excess, if

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any, of (A) an amount equal to (1) $12.00 in cash plus (2) the product of the PacWest average closing price and 0.5308 over (B) the exercise price per CUB common share underlying such option, less any applicable taxes required to be withheld with respect to such payment.

        CUB Restricted Shares and RSUs.    At the effective time, any vesting conditions applicable to each outstanding CUB restricted share and CUB RSU will automatically accelerate in full and such CUB restricted shares and CUB RSUs will be converted into, and become exchanged for, the merger consideration, less any applicable taxes required to be withheld with respect to such vesting.

Background of the Merger

        The CUB board of directors and executive management team regularly review and assess strategic opportunities that may be available to CUB. In addition, the CUB board of directors and executive management team hold an annual strategic planning retreat which, over the last three years, has had as its primary focus a discussion of strategic options potentially available to CUB, with the goal of enhancing value for CUB shareholders. The most recent strategic planning retreat was held in early November 2016. As part of the strategic planning process at this retreat, the CUB board of directors compared the benefits and challenges of continuing as an independent bank to the benefits and challenges of engaging in a strategic combination with another institution. The CUB board of directors considered a number of factors, including the growth and composition of CU Bank's loan portfolio, CU Bank's deposit franchise, management succession, economic indicators and regulatory developments and requirements. The CUB board of directors also invited KBW to address types of strategic alternatives potentially available to CUB. After considering the presentation by KBW and other discussions, and in an effort to develop better information regarding CUB's strategic options involving combinations with larger banks, the CUB board of directors directed Mr. Rainer, CUB's Chief Executive Officer and Chairman, with the assistance of KBW, to reach out informally to likely potential merger partners to establish a relationship that would allow CUB to gauge their interest in considering a transaction with CUB and obtain a sense of their merger philosophies and estimated valuations for CUB.

        In its presentation at the November retreat, KBW listed a number of financial institutions, including PacWest, that could be potential merger partners based on, among other things, market capitalization, prospects, reputation and business and cultural alignment. Between November 2016 and February 2017, representatives of KBW and/or Mr. Rainer contacted nine financial institutions that had been included on the KBW list from the November retreat. The discussions were preliminary and informal. CUB did not provide nonpublic due diligence information and did not enter into confidentiality agreements with any of those parties other than PacWest. During that same period, stock prices for financial institutions were benefiting from a post-election rise, which saw the KBW Index experience a greater than 20% increase, and which saw CUB's share price experience a steady increase of more than 70%, from $23.15 on November 3, 2016, the first day of the CUB board of directors' 2016 retreat, to $39.55 on February 21, 2017, the day prior to the first discussion with PacWest. As explained to KBW and then communicated to Mr. Rainer, none of the other parties was interested in exploring detailed discussions with CUB at that time, primarily due to CUB's purchase price expectation that the merger consideration would reflect the recent appreciation in CUB's share price.

        Mr. Rainer reported to the CUB board of directors in the executive session at its February 7, 2017 meeting on the feedback given to KBW and Mr. Rainer by potential merger candidates. The CUB board of directors discussed the input and directed Mr. Rainer and KBW to continue the investigation of the market to determine whether there were parties who would be interested in a transaction with CUB at a valuation that would reflect its then-current share price.

        On February 22, 2017, KBW reached out to Matthew P. Wagner, Chief Executive Officer of PacWest, to explore PacWest's interest in a potential merger with CUB at a price that, among other things, would reflect CUB's then-current share price, which as of that date had climbed to $39.55.

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Mr. Wagner expressed an interest in further discussions. Thereafter, KBW arranged a meeting on February 27, 2017 between Mr. Wagner and Mr. Rainer to continue to discuss PacWest's interest in a potential merger with CUB. At that meeting, Mr. Wagner expressed an interest in engaging in a more in-depth discussion regarding a potential merger between PacWest and CUB, and Mr. Rainer informed Mr. Wagner that he believed that the CUB board of directors would be looking for a premium for CUB shareholders over the current market price. The next day, KBW, on behalf of CUB, sent PacWest a form of a mutual non-disclosure agreement, pursuant to which CUB and PacWest each agreed to keep the other's proprietary information and the merger discussions confidential and for a period of one year to refrain from directly or indirectly acquiring more than 5.0% of the other's outstanding shares or assets without the prior approval of the other party's board of directors. The mutual non-disclosure agreement also included restrictions on representatives of CUB and PacWest who were provided access to the other party's customer or employee information from soliciting such customers or the other party's employees for a period of one year. The mutual non-disclosure agreement was executed on March 3, 2017. On that same day, based on previous guidance from the CUB board of directors, KBW informed PacWest's financial advisor, Sandler O'Neill + Partners, L.P., referred to as Sandler, that CUB expected no less than $42.00 per share. Sandler responded that PacWest was adamant that it would not pay more than $40.00 per share.

        On March 7, 2017, PacWest sent CUB a draft non-binding letter of intent, referred to as the LOI, outlining a potential merger. The draft LOI called for a merger of CUB into PacWest in which CUB shareholders would receive 0.7101 of a share of PacWest common stock for each CUB common share, or an implied price of $40.00 per CUB common share, based on the March 6, 2017 closing price for PacWest of $56.33 per share. CUB's closing price on March 6, 2017 was $38.10 per share. The draft LOI contemplated that Mr. Rainer would join PacWest's board of directors and CUB's directors and executive officers would execute non-solicitation and non-competition agreements. Further, the draft LOI provided PacWest 60 days of exclusivity from the date of the draft LOI to draft and negotiate a definitive merger agreement.

        At a special telephonic meeting of the CUB board of directors on March 8, 2017, Mr. Rainer and Anita Wolman, CUB's General Counsel, outlined the principal terms of the draft LOI and summarized the previous discussions between KBW and Mr. Rainer, on behalf of CUB, and PacWest. Ms. Wolman reminded the CUB board of directors that this matter was confidential and that that there could be no trading in CUB common shares or PacWest common stock until further notice by Ms. Wolman. Recognizing that the CUB board of directors and CUB management needed sufficient time to analyze the terms of the draft LOI, engage outside counsel and negotiate the terms of an engagement with KBW, the CUB board of directors agreed to meet later in the week and agreed at the meeting to ratify the execution of the mutual non-disclosure agreement with PacWest. To facilitate the negotiation process, and in furtherance of the exercise of the CUB board of directors' fiduciary duty, the CUB board of directors also formed the Special Transactions Committee, referred to as the Special Committee, and appointed to the Special Committee three independent directors with the requisite background and experience to serve in that capacity, namely Mr. Holman, CUB's Lead Independent Director and former and long-time commercial bank executive, Mr. Kentor, a corporate attorney and former General Counsel and Executive Management Committee member at MiniMed Inc., and Mr. Salter, former global leader of FTI Consulting's Valuation and Financial Advisory Services group. The CUB board of directors appointed Mr. Kentor as Special Committee Chairman, adopted a Special Committee Charter and authorized the Special Committee to review, consider, evaluate and direct and oversee the negotiation of the terms and conditions of the draft LOI and possibly a definitive merger agreement and make recommendations for or against the draft LOI and the proposed merger to the CUB board of directors.

        On March 9, 2017, the Special Committee met at the offices of CUB's outside legal counsel, Manatt, Phelps & Phillips, LLP, referred to as Manatt, to discuss the draft LOI. In addition to the members of the Special Committee, the meeting was attended by Mr. Rainer, Ms. Wolman, Karen

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Schoenbaum, CUB's Chief Financial Officer, a lawyer from Manatt and representatives from KBW. Manatt reviewed its presentation on fiduciary duties given to the full CUB board of directors at two different previous annual retreats, and discussed in detail the CUB directors' legal duties applicable to their consideration of a strategic transaction. Representatives of KBW then discussed a preliminary financial analysis of each of CUB and PacWest on a standalone basis and in the context of the proposed merger. The Special Committee also discussed with Manatt and KBW the impact of a provision in the draft LOI pursuant to which CUB could terminate the merger agreement in the event that PacWest's volume weighted average stock price over a determined period prior to the closing (i) declined by more than 15%, and (ii) underperformed the KBW Index by greater than 15%, subject to PacWest's ability to reinstate the transaction by adjusting the merger consideration to fill the shortfall either by including a cash component, an adjusted exchange ratio or both. KBW discussed the recent increase in bank stock prices in general and the even-greater increase in CUB's share price, and how that impacted the pricing of the proposed merger. KBW advised that, based on its analysis, the receipt of a comparable or better offer was not reasonably likely. Following the report by KBW, the Special Committee discussed potential synergies in a strategic transaction with PacWest; the scope and results of the market outreach efforts conducted by Mr. Rainer and KBW since November 2016; the overlap between PacWest and CUB's operations; the importance to PacWest of CUB's deposit relationships; PacWest's dividend payment history; the significant increase in trading liquidity that would inure to the benefit of CUB shareholders from a merger with PacWest; and the likelihood of consummating a strategic transaction with PacWest on a timely basis, considering PacWest's experience in completing acquisitions of financial institutions the size of CUB, including its recent acquisition of Square 1 Financial, Inc., referred to as Square 1. The Special Committee, KBW, Manatt and CUB executive management then discussed the proposed merger consideration in detail, including whether PacWest would be willing to increase the exchange ratio and the advisability of any price protections, such as a collar. Mr. Rainer and KBW reported that they did not believe there was an opportunity to increase the merger consideration based upon conversations with Mr. Wagner and Sandler. Mr. Rainer and KBW also reported that they believed there was a risk that PacWest would terminate discussions if CUB were to attempt to negotiate further on merger consideration, including both the amount and the inclusion of price protections. KBW also advised that the inclusion of price protections such as a collar may not be in the best interests of CUB shareholders given the relative valuations of CUB and PacWest. The Special Committee questioned KBW about the provision in the draft LOI requiring non-employee directors to execute non-competition agreements and specifically asked whether it was customary. KBW explained that it was more customary to limit non-competition agreements to members of executive management responsible for significant customer relationships and strategic initiatives. The Special Committee then asked KBW whether PacWest would consider entering into consulting agreements with reasonable non-competition clauses for Mr. Rainer and Mr. Horton and perhaps other key members of management. KBW agreed to follow up with Sandler about the consulting agreements.

        KBW was excused from the meeting so the Special Committee could discuss KBW's draft engagement letter that had previously been distributed to the members of the Special Committee. Taking into consideration the services KBW had performed on behalf of CUB since November and its review of investment banking compensation in comparable transactions, the Special Committee resolved to recommend to the CUB board of directors that CUB formally engage KBW on the material terms proposed. The Special Committee also resolved to recommend to the CUB board of directors that CUB execute the draft LOI with PacWest subject to, among other things, clarifying CUB's right to conduct reverse due diligence, limiting the persons required to execute non-competition agreements to certain executive officers and modifying the board representation provision to provide for either Mr. Rainer or another mutually agreed upon CUB director to join the PacWest board of directors upon the closing of the proposed transaction.

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        On March 10, 2017, the full CUB board of directors met telephonically. Representatives of KBW and Manatt and members of CUB executive management participated in the meeting. KBW discussed PacWest's proposed deal terms, including a preliminary financial analysis of the parties and the proposed transaction. Representatives of Manatt reminded the CUB directors of their fiduciary duties in the context of a strategic transaction, as well as restrictions on trading in the stock of both CUB and PacWest and the importance of confidentiality. The CUB board of directors discussed the status of CUB's business options, recent macro-economic and regulatory trends and CUB's organic and strategic growth possibilities, including taking into account expansionary limitations imposed on CUB due to the Consent Order, dated September 23, 2016, among CU Bank, the FDIC and the CDBO, referred to as the Consent Order. Mr. Rainer reiterated portions of the discussions from the November 2016 strategic planning retreat regarding the challenges and opportunities for CUB if it remained independent, as well as the opportunity presented for CUB shareholders by the significant increase in CUB's share price. The Special Committee summarized for the CUB board of directors its findings and recommendations with respect to entering into the engagement agreement with KBW and executing the LOI, copies of each of which had previously been delivered to the CUB board of directors. After careful consideration of PacWest's offer, the current regulatory environment and uncertainties of the market and the economy, as well as discussions with Manatt and KBW, the CUB board of directors instructed management to sign the LOI and instructed the Special Committee to oversee further negotiations with PacWest regarding a definitive agreement. PacWest returned the countersigned LOI that same day.

        Following the execution of the LOI, representatives of management and the outside advisors to PacWest and CUB began more detailed discussions on the potential transaction, and Sandler sent an initial due diligence request list to KBW to allow PacWest and its advisors to commence credit, operational and legal due diligence of CUB through an online dataroom established on March 14, 2017. KBW and Manatt reviewed financial and other information regarding PacWest, including documentation for PacWest's recent acquisition of Square 1.

        On March 14, 2017, the CUB board of directors held a special meeting. Representatives from Manatt and members of CUB's executive management attended the meeting. Mr. Rainer advised the CUB board of directors that PacWest desired to sign a definitive agreement in early April and close a transaction, subject to the receipt of the requisite approvals and satisfaction of closing conditions, in the fourth quarter of 2017. He called upon representatives from Manatt to discuss the approval process for the proposed merger transaction, PacWest's proposed timeline and possible events that could disrupt the process and/or delay the closing, including a review by the SEC of PacWest's Form S-4, Community Reinvestment Act objections, protests or hearings and shareholder litigation related to the merger. A representative from Manatt advised the CUB board of directors on issues related to shareholder litigation that sometimes follow merger announcements by public companies. KBW was formally engaged as of March 15, 2017.

        On March 16, 2017, PacWest and Pacific Western Bank held a joint meeting of their boards of directors at which they and members of PacWest's executive management team discussed the strategic rationale and status of the negotiations with CUB. Mr. Wagner discussed with the joint boards of directors, among other things, the proposed consideration contained in the LOI, CUB's strong deposit base and low cost of deposits, CUB's exceptional credit and asset composition, CUB's business model and its similarities to PacWest's, and the Consent Order and the remediation steps undertaken by CUB to address the matters noted therein.

        On March 21, 2017, PacWest's outside legal counsel, Sullivan & Cromwell LLP, referred to as S&C, sent an initial draft of a definitive merger agreement to Manatt. On March 22, 2017, the Special Committee met telephonically. Representatives from Manatt, as well as Mr. Rainer and Ms. Wolman, participated in the meeting. Manatt explained that based on its initial review, the draft merger agreement was similar in form and content to the merger agreement for the Square 1 transaction that

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had previously been distributed to the Special Committee and that it was continuing to review the draft merger agreement. Mr. Rainer told the Special Committee that KBW had informed him that KBW had followed up with Sandler to request that PacWest consider entering into consulting or non-competition agreements with Mr. Rainer, Mr. Horton and Ms. Schoenbaum and that Sandler recently reported back that PacWest intended to offer consulting agreements to those three executive officers. The Special Committee requested that Manatt communicate with S&C to ensure that drafts of the ancillary agreements, including the voting, non-competition, non-solicitation agreements and consulting agreements were delivered to Manatt at the earliest possible time. Mr. Rainer also explained that representatives from KBW would be attending the meeting of the CUB board of directors scheduled for the following day at which time they would discuss with the CUB board of directors the impact on the transaction of the downward trend in the price of PacWest's stock since the date the LOI was signed, including possible changes to the merger consideration such as adding cash or changing the exchange ratio.

        At the meeting of the CUB board of directors on March 23, 2017, representatives from KBW discussed the decrease in PacWest's stock price since March 10, 2017. KBW discussed, among other things, the market factors weighing on bank stock prices generally, noting that PacWest's stock had performed in line with the KBW Index over that same time period. The CUB board of directors and KBW readdressed the benefits and risks of a fixed exchange ratio transaction and considered the impact of a "take under" transaction, where the value of the merger consideration at announcement is less than the trading price of the target's stock. With respect to the risks of a take under transaction, KBW explained that KBW's analysis of the fairness of the proposed transaction would be based on the value of CUB using various financial analyses and not on the daily changes in the stock prices of PacWest and CUB. The CUB board of directors then asked KBW to discuss the possibility that PacWest would add cash to the merger consideration. The Special Committee and Mr. Rainer informed the CUB board of directors that they had directed KBW to discuss with Sandler augmenting the proposed merger consideration, and KBW told the CUB board of directors that those discussions between KBW and Sandler had begun. A representative from Manatt then outlined for the CUB board of directors provisions in the draft merger agreement that warranted further discussion with S&C and provisions in the merger agreement that were still under review.

        Between March 23, 2017 and April 3, 2017, representatives of CUB and PacWest and their respective legal counsel and financial advisors, conducted negotiations regarding the terms of the merger transaction, including, among other terms, the process and timing of the repurchase of CUB's Series A preferred stock held by the U.S. Department of the Treasury, the scope of the representations, warranties, covenants and closing conditions, employee retention and severance, board representation, tax opinions and termination provisions and termination fees. In addition, the terms of voting, non-solicitation and consulting agreements between PacWest and the individual directors of CUB and certain executive officers of CUB were negotiated.

        On March 27, 2017, Sandler sent a supplemental due diligence request list to KBW, requesting additional materials to be made available to allow PacWest and its advisors to continue credit, operational and legal due diligence of CUB. Sandler was formally engaged by PacWest as of March 28, 2017.

        On March 28, 2017, members of CUB's executive management team, along with a representative from KBW, interviewed members of PacWest's executive management at PacWest's headquarters, as part of CUB's reverse due diligence investigation of PacWest and in response to a written reverse due diligence request list delivered to PacWest's financial advisor on March 23, 2017. During this meeting, CUB received information from PacWest's executive management team regarding, among other things, history of recent acquisition activity and benefits received, their assessment of PacWest's strengths and weaknesses and information on PacWest's prospects, loan quality, compliance with regulatory requirements, information technology and pending litigation.

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        During the period from March 23, 2017 through April 5, 2017, Mr. Rainer and the Special Committee met or communicated regularly to discuss the changes in the price of PacWest common stock, the status of the due diligence process, plans for communications with CUB's staff, customers, shareholders and regulators and negotiation of the proposed merger terms, including, among other things, employee retention and severance arrangements. Representatives from Manatt and KBW were also in attendance.

        On April 3, 2017, Sandler contacted KBW regarding a proposed alternative pricing structure for the transaction, providing for 70% PacWest common stock and 30% cash consideration through a fixed exchange ratio of 0.5308, plus $12.00 in cash per share. The revised exchange ratio was set based on PacWest's common stock price of $52.75 as of April 3, 2017, which resulted in the value of the merger consideration being equal to $40.00, the value as negotiated pursuant to PacWest's first offer to CUB per the LOI. Each of the Special Committee members supported the change, subject to reviewing KBW's analysis. On April 4, 2017, PacWest delivered to each of Messrs. Rainer and Horton agreements regarding consulting services to be rendered for PacWest following the merger. On April 5, 2017, PacWest delivered to Ms. Schoenbaum an agreement regarding consulting services to be rendered for PacWest following the merger. See "—Interests of CUB Directors and Executive Officers in the Merger."

        On April 5, 2017, a special meeting of the CUB board of directors was held. Representatives of KBW and Manatt participated. KBW and Manatt summarized the negotiations that had taken place and reviewed the change in the merger consideration to be received by the CUB shareholders, including comparing the original merger consideration offered to the current offer. Executive management of CUB reported on the satisfactory results of its reverse due diligence meeting with PacWest's senior management. The CUB board of directors also considered PacWest's stock price performance as compared to that of CUB's common shares and the KBW Index since 2015. At this meeting, KBW reviewed the financial aspects of the proposed transaction and rendered to the CUB board of directors an oral opinion (later confirmed in writing) to the effect that, as of April 4, 2017 and subject to the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by KBW as set forth in its opinion, the merger consideration in the proposed merger was fair, from a financial point of view, to the holders of CUB common shares. Manatt then reviewed with the CUB board of directors the CUB directors' fiduciary duties under applicable law. Following this review, Manatt outlined for the directors the terms of the merger agreement, a marked copy of which had been distributed to the directors prior to the meeting, and the related voting agreements, non-solicitation agreements and consulting agreements to be entered into in connection therewith, copies of which had been made available to the directors in advance of the meeting. The CUB board of directors then engaged in a vigorous discussion of the terms of the agreements, and the representatives of Manatt and KBW answered the CUB directors' various questions. After extensive discussion and taking into account the factors described below under "—Recommendation of the CUB Board of Directors and Reasons for the Merger", the CUB board of directors adopted resolutions approving the merger agreement and transactions contemplated thereby.

        On April 5, 2017, a special meeting of the PacWest board of directors was also held. Representatives of Sandler and S&C participated. Sandler and S&C summarized the negotiations that had taken place and reviewed the merger consideration to be paid by PacWest. S&C outlined for the PacWest directors the terms of the merger agreement, a marked copy of which had been distributed to the PacWest directors prior to the meeting, and the related voting agreements, non-solicitation agreements and consulting agreements to be entered into in connection therewith, copies of which had been made available to the PacWest directors in advance of the meeting. S&C then reviewed with the PacWest board of directors the PacWest directors' fiduciary duties under applicable law. The PacWest board of directors then engaged in a vigorous discussion of the terms of the agreements and the representatives of S&C and Sandler answered the PacWest directors' various questions. After extensive discussion and taking into account the factors described below under "—PacWest's Reasons for the

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Merger", the PacWest board of directors adopted resolutions approving the merger agreement and transactions contemplated thereby.

        Following the CUB and PacWest boards of directors meetings, the terms of the merger agreement and related agreements were finalized, and the agreements were executed and delivered. The transaction was publicly announced on the morning of April 6, 2017, in a press release jointly issued by CUB and PacWest. Based on a $51.72 per share closing price of PacWest common stock on April 5, 2017, the aggregate merger consideration was approximately $705 million, or $39.45 per share.

Recommendation of the CUB Board of Directors and Reasons for the Merger

        The CUB board of directors has determined that the merger is fair to and in the best interests of CUB and its shareholders and, by the unanimous vote of all of the directors of CUB, approved and adopted the merger agreement and the merger. ACCORDINGLY, THE CUB BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT ALL HOLDERS OF CUB COMMON SHARES VOTE "FOR" THE MERGER PROPOSAL.

        In reaching its decision to approve the merger agreement and the transactions contemplated thereby, the CUB board of directors evaluated the merger agreement in consultation with CU Bank's executive management and determined that the merger was the best option reasonably available for its shareholders in the current challenging and uncertain banking market. The CUB board of directors also consulted with its legal counsel regarding its fiduciary duties, the terms of the merger agreement and related issues, and reviewed with its financial advisors and its executive management, the financial aspects of the proposed transaction, considerations of the broader financial market and the fairness of the transaction to the shareholders from a financial point of view, among other matters.

        In reaching its determination to approve the merger agreement, the CUB board of directors considered all factors it deemed material. The CUB board of directors analyzed information with respect to the financial condition, results of operations, business and prospects of CUB. In this regard, the CUB board of directors considered the performance trends of CUB over the past several years. The board also considered the ability of CUB to grow as an independent institution, the impact of the Consent Order (discussed in the section entitled "—Background of the Merger") on CUB's ability to expand its operations through acquisitions, its ability to further enhance shareholder value without engaging in a strategic transaction and the opportunity for CUB's shareholders to derive the benefit of the recent increase in CUB's share price, which was significantly greater than the increase experienced by its peer institutions and the KBW Index. In this regard, the CUB board of directors considered the long-term as well as the short-term interests of CUB and its shareholders, including whether those interests might best be served by continued independence.

        In reaching its decision to approve the merger agreement and the merger, the CUB board of directors also considered a number of factors, including the following:

•

information with respect to CUB's business, earnings, operations, financial condition, asset quality and prospects, and information with respect to PacWest's business, earnings, operations, financial condition, asset quality and prospects, the potential cost savings and synergies unique to a transaction between CUB and PacWest, taking into account the results of CUB's due diligence review of PacWest and information provided by PacWest's management;



•

the recent increase of CUB's share price relative to its peer institutions and the opportunity presented by the PacWest merger for CUB shareholders to capitalize on this price increase, in particular through the significant cash component of the merger consideration;



•

the lack of prospects for a superior offer for a strategic combination;



•

its knowledge of the current environment in the financial services industry, including national, regional and local economic conditions and the interest rate environment, continued

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consolidation, the uncertainties in the regulatory climate for financial institutions, increased operating costs resulting from regulatory initiatives and compliance mandates, including increasing capital requirements, increasing competition, the current environment for community banks, particularly in Southern California, and current financial market conditions;

•

the financial and growth prospects for CUB and its shareholders in a business combination with PacWest as compared to continuing to operate as a stand-alone entity;



•

the greater market capitalization and trading liquidity of PacWest common stock in the event that CUB shareholders desire to sell the shares of PacWest common stock to be received by them following completion of the merger;



•

the merger consideration in the transaction where the stock component will allow CUB's shareholders to continue to participate in the future success of PacWest and derive the benefits from PacWest's dividends and any synergies achieved or any future transactions that might be pursued by PacWest as well as the cash component, which will allow CUB's shareholders to "de-risk";



•

PacWest's successful track record, including, among other things, with respect to the integration of acquisitions;



•

the benefits to CUB and its customers of operating as part of a larger organization, including higher lending limits, potential enhancements to products and services, mitigation of business risks through diversification and greater financial resources;



•

the career opportunities afforded by a larger organization;



•

its belief that combining the two companies would create a larger and more diversified financial institution that is both better equipped to respond to economic and industry developments and better positioned to develop and build on its existing market position in Southern California;



•

its assessment of the likelihood that the merger would be completed in a timely manner, including the likelihood that the merger will receive all necessary regulatory approvals in a timely manner;



•

the results of discussions with third parties that the CUB board of directors believed, in consultation with its financial advisor, were the parties likely to have the strategic interest and financial capability to pursue a potential strategic transaction with CUB;



•

the financial analyses presented by representatives of KBW to the CUB board of directors with respect to PacWest and the merger, and the opinion of KBW that, as of the date of that opinion and subject to the qualifications and assumptions set forth in the opinion, the merger consideration was fair to the holders of CUB common shares from a financial point of view (see "—Opinion of CUB's Financial Advisor");



•

the CUB board of directors' belief that the merger consideration exceeds CUB's likely value in the absence of a merger, including its potential for future growth, which belief was based on a number of factors, including:



•

the risks and uncertainties associated with maintaining CUB's performance as a standalone company; and



•

the CUB board of directors' analysis of other strategic alternatives available to CUB;



•

the expectation that the merger will qualify as a "reorganization" for United States federal income tax purposes; and



•

the terms of the merger agreement, including the fixed exchange ratio, the form of merger consideration and the inclusion of a significant cash component, expected tax treatment, the

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achievability of the closing conditions, deal protection and termination fee provisions, which it reviewed with its outside legal and financial advisors, which terms are described more fully under the section entitled "The Merger Agreement".

        In the course of its deliberations regarding the merger, the CUB board of directors also considered potential risks and potentially negative factors associated with the merger, including the following material factors:

•

the need to obtain approval by shareholders of CUB, as well as regulatory approvals, in order to complete the transaction and the risk that those or other conditions will not be satisfied;



•

the risks associated with the operations of the combined company including the challenges both of integrating CUB's business, operations and employees with those of PacWest and of achieving the anticipated cost savings;



•

the fact that the value of the aggregate and per share merger consideration will fluctuate with the market price of PacWest's common stock and the risk that PacWest's common stock price might decline reducing the aggregate and per share merger consideration from the values at the time the merger agreement was approved;



•

the potential risk of diverting management focus and resources from other strategic opportunities and from operational matters while working to implement the merger;



•

the risk of potential employee attrition or negative effects on CUB's business and customer relationships as a result of the pending merger;



•

the merger-related costs;



•

the fact that executive officers of CUB have interests in the merger and have arrangements that are different from or in addition to those of CUB shareholders generally; and



•

the fact that CUB would be prohibited from affirmatively soliciting acquisition proposals after execution of the merger agreement and will be obligated to pay a termination fee of $26.5 million to PacWest if the merger agreement is terminated under certain circumstances, all of which may discourage other parties potentially interested in a strategic transaction with CUB from pursuing such a transaction.

        This description of the information and factors considered by the CUB board of directors is not intended to be exhaustive, but is believed to include all material factors the CUB board of directors considered. In determining whether to approve and recommend the merger agreement, the CUB board of directors did not assign any relative or specific weights to any of the foregoing factors, and individual directors may have weighed factors differently. After deliberating with respect to the merger and the merger agreement, considering, among other things, the reasons discussed above, the CUB board of directors approved the merger agreement and the merger as being in the best interests of CUB and its shareholders, based on the total mix of information available to the CUB board of directors.

        This explanation of CUB's reasons for the merger and other information presented in this section is forward-looking in nature and should be read in light of the section entitled "Cautionary Statement Regarding Forward-Looking Statements."

Opinion of CUB's Financial Advisor

        CUB engaged KBW to render financial advisory and investment banking services to CUB, including rendering an opinion to the CUB board of directors as to the fairness, from a financial point of view, to the holders of CUB common shares of the merger consideration to be received by such shareholders in the proposed merger of CUB with and into PacWest. CUB selected KBW because KBW is a nationally recognized investment banking firm with substantial experience in transactions

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similar to the merger. As part of its investment banking business, KBW is continually engaged in the valuation of financial services businesses and their securities in connection with mergers and acquisitions.

        As part of its engagement, representatives of KBW attended the meeting of the CUB board of directors held on April 5, 2017, at which the CUB board of directors evaluated the proposed merger. At this meeting, KBW reviewed the financial aspects of the proposed merger and rendered to the CUB board of directors an opinion to the effect that, as of such date and subject to the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by KBW as set forth in its opinion, the merger consideration in the proposed merger was fair, from a financial point of view, to the holders of CUB common shares. The CUB board of directors unanimously approved the merger agreement at this meeting.

        The description of the opinion set forth herein is qualified in its entirety by reference to the full text of the opinion, which is attached as Appendix D to this document and is incorporated herein by reference, and describes the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by KBW in preparing the opinion.

        KBW's opinion speaks only as of the date of the opinion. The opinion was for the information of, and was directed to, the CUB board of directors (in its capacity as such) in connection with its consideration of the financial terms of the merger. The opinion addressed only the fairness, from a financial point of view, as of the date of the opinion, of the merger consideration in the merger to the holders of CUB common shares. It did not address, among other things as set forth in KBW's opinion, the underlying business decision of CUB to engage in the merger or enter into the merger agreement or constitute a recommendation to the CUB board of directors in connection with the merger, and it does not constitute a recommendation to any holder of CUB common shares or any shareholder of any other entity as to how to vote in connection with the merger or any other matter, nor does it constitute a recommendation regarding whether or not any such shareholder should enter into a voting, shareholders' or affiliates' agreement with respect to the merger or exercise any dissenters' or appraisal rights that may be available to such shareholder.

        KBW's opinion was reviewed and approved by KBW's Fairness Opinion Committee in conformity with KBW's policies and procedures established under the requirements of Rule 5150 of the Financial Industry Regulatory Authority.

        In connection with the opinion, KBW reviewed, analyzed and relied upon material bearing upon the financial and operating condition of CUB and PacWest and bearing upon the merger, including, among other things, the following:

•

a draft of the merger agreement dated April 4, 2017 (the most recent draft then made available to KBW);



•

the audited financial statements and the Annual Reports on Form 10-K for the three fiscal years ended December 31, 2016 of CUB;



•

the audited financial statements and the Annual Reports on Form 10-K for the three fiscal years ended December 31, 2016 of PacWest;



•

certain regulatory filings of CUB and PacWest and their respective subsidiaries, including the quarterly reports on Form FR Y-9C and call reports filed with respect to each quarter during the three year period ended December 31, 2016;



•

certain other interim reports and other communications of CUB and PacWest to their respective shareholders; and



•

other financial information concerning the businesses and operations of CUB and PacWest that was furnished to KBW by CUB and PacWest or which KBW was otherwise directed to use for purposes of KBW's analyses.

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        KBW's consideration of financial information and other factors that it deemed appropriate under the circumstances or relevant to its analyses included, among others, the following:

•

the historical and current financial position and results of operations of CUB and PacWest;



•

the assets and liabilities of CUB and PacWest;



•

the nature and terms of certain other merger transactions and business combinations in the banking industry;



•

a comparison of certain financial and stock market information for CUB and PacWest with similar information for certain other companies the securities of which were publicly traded;



•

publicly available consensus "street estimates" of CUB for 2017 and 2018, as well as assumed long-term CUB growth rates provided to KBW by CUB management, all of which information was discussed with KBW by such management and used and relied upon by KBW at the direction of CUB management and with the consent of the CUB board of directors;



•

publicly available consensus "street estimates" of PacWest for 2017 and 2018, as well as assumed long-term PacWest growth rates that were discussed with KBW by PacWest management and used and relied upon by KBW based on such discussions, at the direction of CUB management and with the consent of the CUB board of directors; and



•

estimates regarding certain pro forma financial effects of the merger on PacWest (including, without limitation, the cost savings and related expenses expected to result or be derived from the merger) that were prepared by, and provided to and discussed with KBW by the management of PacWest, and used and relied upon by KBW based on such discussions, at the direction of CUB management and with the consent of the CUB board of directors.

        KBW also performed such other studies and analyses as it considered appropriate and took into account its assessment of general economic, market and financial conditions and its experience in other transactions, as well as its experience in securities valuation and knowledge of the banking industry generally. KBW also participated in discussions with the managements of CUB and PacWest regarding the past and current business operations, regulatory relations, financial condition and future prospects of their respective companies and such other matters as KBW deemed relevant to its inquiry. In addition, KBW considered the results of the efforts undertaken, with KBW's assistance, by or on behalf of and at the direction of CUB, to solicit indications of interest from third parties regarding a potential transaction with CUB.

        In conducting its review and arriving at its opinion, KBW relied upon and assumed the accuracy and completeness of all of the financial and other information that was provided to it or that was publicly available and did not independently verify the accuracy or completeness of any such information or assume any responsibility or liability for such verification, accuracy or completeness. KBW relied upon the management of CUB as to the reasonableness and achievability of the publicly available consensus "street estimates" of CUB and the assumed CUB long-term growth rates referred to above, and KBW assumed that such information was reasonably prepared and represents, or in the case of the publicly available consensus "street estimates" of CUB that such information is consistent with, the best currently available estimates and judgments of CUB management and that such forecasts, projections and estimates would be realized in the amounts and in the time periods estimated. KBW further relied, with the consent of CUB, upon PacWest management as to the reasonableness and achievability of the publicly available consensus "street estimates" of PacWest and the assumed PacWest long-term growth rates referred to above, as well as the estimates regarding certain pro forma financial effects of the merger on PacWest (and the assumptions and bases therefor, including without limitation the cost savings and related expenses expected to result or be derived from the merger) referred to above, and KBW assumed, with the consent of CUB, that such information was reasonably prepared

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and represents, or in the case of the publicly available consensus "street estimates" of PacWest that such information was consistent with, the best currently available estimates and judgments of PacWest management and that such forecasts, projections and estimates would be realized in the amounts and in the time periods estimated.

        It is understood that the forecasts, projections and estimates of CUB and PacWest provided to KBW were not prepared with the expectation of public disclosure and that such information, together with the publicly available consensus "street estimates" of CUB and PacWest referred to above that KBW was directed to use, was based on numerous variables and assumptions that are inherently uncertain, including, without limitation, factors related to general economic and competitive conditions and that, accordingly, actual results could vary significantly from those set forth in such information. KBW assumed, based on discussions with the respective managements of CUB and PacWest and with the consent of the CUB board of directors, that all such information provided a reasonable basis upon which KBW could form its opinion and KBW expressed no view as to any such information or the assumptions or bases therefor. KBW relied on all such information without independent verification or analysis and did not in any respect assume any responsibility or liability for the accuracy or completeness thereof.

        KBW also assumed that there were no material changes in the assets, liabilities, financial condition, results of operations, business or prospects of either CUB or PacWest since the date of the last financial statements of each such entity that were made available to KBW. KBW is not an expert in the independent verification of the adequacy of allowances for loan and lease losses and KBW assumed, without independent verification and with CUB's consent, that the aggregate allowances for loan and lease losses for CUB and PacWest are adequate to cover such losses. In rendering its opinion, KBW did not make or obtain any evaluations or appraisals or physical inspection of the property, assets or liabilities (contingent or otherwise) of CUB or PacWest, the collateral securing any of such assets or liabilities, or the collectability of any such assets, nor did KBW examine any individual loan or credit files, nor did it evaluate the solvency, financial capability or fair value of CUB or PacWest under any state or federal laws, including those relating to bankruptcy, insolvency or other matters. Estimates of values of companies and assets do not purport to be appraisals or necessarily reflect the prices at which companies or assets may actually be sold. Because such estimates are inherently subject to uncertainty, KBW assumed no responsibility or liability for their accuracy.

        KBW assumed, in all respects material to its analyses:

•

that the merger would be completed substantially in accordance with the terms set forth in the merger agreement (the final terms of which KBW assumed would not differ in any respect material to KBW's analyses from the draft reviewed by KBW and referred to above) with no adjustments to the merger consideration and with no additional payments in respect of the CUB common shares;



•

that any related transactions (including the bank merger and the repurchase of the Series A preferred stock) would be completed as contemplated in the merger agreement and as further described to KBW by representatives of CUB;



•

that the representations and warranties of each party in the merger agreement and in all related documents and instruments referred to in the merger agreement were true and correct;



•

that each party to the merger agreement and all related documents would perform all of the covenants and agreements required to be performed by such party under such documents;



•

that there were no factors that would delay or subject to any adverse conditions, any necessary regulatory or governmental approval for the merger or any related transactions (including the bank merger and the repurchase of the Series A preferred stock) and that all conditions to the

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completion of the merger and any related transaction would be satisfied without any waivers or modifications to the merger agreement or any of the related documents; and

•

that in the course of obtaining the necessary regulatory, contractual, or other consents or approvals for the merger and any related transaction (including the bank merger and the repurchase of the Series A preferred stock), no restrictions, including any divestiture requirements, termination or other payments or amendments or modifications, would be imposed that would have a material adverse effect on the future results of operations or financial condition of CUB, PacWest or the pro forma entity, or the contemplated benefits of the merger, including, without limitation the cost savings and related expenses expected to result or be derived from the merger.

        KBW assumed that the merger would be consummated in a manner that complies with the applicable provisions of the Securities Act of 1933, as amended, the Securities Exchange Act of 1934, as amended, and all other applicable federal and state statutes, rules and regulations. KBW was further advised by representatives of CUB that CUB relied upon advice from its advisors (other than KBW) or other appropriate sources as to all legal, financial reporting, tax, accounting and regulatory matters with respect to CUB, PacWest, the merger and any related transaction (including the bank merger and the repurchase of the Series A preferred stock), and the merger agreement. KBW did not provide advice with respect to any such matters.

        KBW's opinion addressed only the fairness, from a financial point of view, as of the date of the opinion, to the holders of CUB common shares of the merger consideration to be received by such holders in the merger. KBW expressed no view or opinion as to any other terms or aspects of the merger or any term or aspect of any related transaction (including the bank merger and the repurchase of the Series A preferred stock), including without limitation, the form or structure of the merger (including the form of the merger consideration or the allocation thereof between cash and stock) or any related transaction, any consequences of the merger or any related transaction to CUB, its shareholders, creditors or otherwise, or any terms, aspects, merits or implications of any employment, consulting, voting, support, shareholder or other agreements, arrangements or understandings contemplated or entered into in connection with the merger or otherwise. KBW's opinion was necessarily based upon conditions as they existed and could be evaluated on the date of such opinion and the information made available to KBW through such date. Developments subsequent to the date of KBW's opinion may have affected, and may affect, the conclusion reached in KBW's opinion and KBW did not and does not have an obligation to update, revise or reaffirm its opinion. KBW's opinion did not address, and KBW expressed no view or opinion with respect to:

•

the underlying business decision of CUB to engage in the merger or enter into the merger agreement;



•

the relative merits of the merger as compared to any strategic alternatives that are, have been or may be available to or contemplated by CUB or the CUB board of directors;



•

the fairness of the amount or nature of any compensation to any of CUB's officers, directors or employees, or any class of such persons, relative to the compensation to the holders of CUB common shares;



•

the effect of the merger or any related transaction on, or the fairness of the consideration to be received by, holders of any class of securities of CUB (other than the holders of CUB common shares, solely with respect to the merger consideration as described in KBW's opinion and not relative to the consideration to be received by holders of any other class of securities) or holders of any class of securities of PacWest or any other party to any transaction contemplated by the merger agreement;

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•

whether PacWest has sufficient cash, available lines of credit or other sources of funds to enable it to pay the aggregate amount of the cash consideration to the holders of CUB common shares at the closing of the merger;



•

whether CUB has sufficient cash, available lines of credit or other sources of funds to enable it to effect the repurchase of the Series A preferred stock concurrently with or prior to the closing of the merger;



•

any adjustment (as provided in the merger agreement) to the merger consideration assumed for purposes of KBW's opinion;



•

the actual value of PacWest common stock to be issued in the merger;



•

the prices, trading range or volume at which CUB common shares or PacWest common stock would trade following the public announcement of the merger or the prices, trading range or volume at which PacWest common stock would trade following the consummation of the merger;



•

any advice or opinions provided by any other advisor to any of the parties to the merger or any other transaction contemplated by the merger agreement; or



•

any legal, regulatory, accounting, tax or similar matters relating to CUB, PacWest, their respective shareholders, or relating to or arising out of or as a consequence of the merger or any related transaction (including the bank merger and the repurchase of the Series A preferred stock), including whether or not the merger would qualify as a tax-free reorganization for United States federal income tax purposes.

        In performing its analyses, KBW made numerous assumptions with respect to industry performance, general business, economic, market and financial conditions and other matters, which are beyond the control of KBW, CUB and PacWest. Any estimates contained in the analyses performed by KBW are not necessarily indicative of actual values or future results, which may be significantly more or less favorable than suggested by these analyses. Additionally, estimates of the value of businesses or securities do not purport to be appraisals or to reflect the prices at which such businesses or securities might actually be sold. Accordingly, these analyses and estimates are inherently subject to substantial uncertainty. In addition, the KBW opinion was among several factors taken into consideration by the CUB board of directors in making its determination to approve the merger agreement and the merger. Consequently, the analyses described below should not be viewed as determinative of the decision of the CUB board of directors with respect to the fairness of the merger consideration. The type and amount of consideration payable in the merger were determined through negotiation between CUB and PacWest and the decision of CUB to enter into the merger agreement was solely that of the CUB board of directors.

        The following is a summary of the material financial analyses performed by KBW and presented by KBW to the CUB board of directors in connection with KBW's opinion. The summary is not a complete description of the financial analyses underlying the opinion or the presentation made by KBW to the CUB board of directors, but summarizes the material analyses performed or presented in connection with such opinion. The financial analyses summarized below include information presented in tabular format. The tables alone do not constitute a complete description of the financial analyses. The preparation of a fairness opinion is a complex analytic process involving various determinations as to appropriate and relevant methods of financial analysis and the application of those methods to the particular circumstances. Therefore, a fairness opinion is not readily susceptible to partial analysis or summary description. In arriving at its opinion, KBW did not attribute any particular weight to any analysis or factor that it considered, but rather made qualitative judgments as to the significance and relevance of each analysis and factor. Accordingly, KBW believes that its analyses and the summary of its analyses must be considered as a whole and that selecting portions of its analyses and factors or focusing on the information presented below in tabular format, without considering all analyses and

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factors or the full narrative description of the financial analyses, including the methodologies and assumptions underlying the analyses, could create a misleading or incomplete view of the process underlying its analyses and opinion.

        For purposes of the financial analyses described below, KBW utilized an implied value of the merger consideration of $40.07 per CUB common share, consisting of the sum of (i) the implied value of the stock consideration based on the closing price of PacWest common stock on April 4, 2017, and (ii) the cash consideration.

        CUB Comparable Companies Analyses.    Using publicly available information, KBW compared the financial performance, financial condition and market performance of CUB to 17 selected U.S. banks which were traded on NASDAQ, the New York Stock Exchange or the New York Stock Exchange Market and headquartered in the Western Region (Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming) and which had total assets between $1 billion and $5 billion. Savings banks and thrifts, ethnic-focused banks and targets of publicly announced merger transactions were excluded from the selected companies.

        The selected companies were as follows:

        To perform this analysis, KBW used profitability and other financial information for, as of, or, in the case of latest 12 months, referred to as LTM, information, through, the most recent completed quarter, referred to as MRQ, available (which in the case of CUB was the fiscal quarter ended December 31, 2016) and market price information as of April 4, 2017. KBW also used 2017 and 2018 EPS estimates taken from consensus "street estimates" for CUB and the selected companies. Where consolidated holding company level financial data for the selected companies was unreported, subsidiary bank level data was utilized to calculate ratios. Certain financial data was prepared by KBW, and as referenced in the tables presented below, may not correspond to the data presented in CUB's historical financial statements as a result of the different periods, assumptions and methods used by KBW to compute the financial data presented.

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        KBW's analysis showed the following concerning the financial performance of CUB and the selected companies:

        KBW's analysis also showed the following concerning the financial condition of CUB and the selected companies:

        In addition, KBW's analysis showed the following concerning the market performance of CUB and the selected companies:

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        None of the selected companies used as a comparison in the above selected companies analyses of CUB is identical to CUB. Accordingly, an analysis of these results is not mathematical. Rather, it involves complex considerations and judgments concerning differences in financial and operating characteristics of the companies involved.

        PacWest Comparable Companies Analysis.    Using publicly available information, KBW compared the financial performance, financial condition and market performance of PacWest to 22 selected U.S. banks which were traded on NASDAQ, the New York Stock Exchange or the New York Stock Exchange Market and which had total assets between $15 billion and $30 billion. Savings banks and thrifts, ethnic-focused banks and targets of publicly announced merger transactions were excluded from the selected companies.

        The selected companies were as follows:

        To perform this analysis, KBW used profitability and other financial information for, as of, or, in the case of LTM information, through, the most recent completed quarter available (which in the case of PacWest was the fiscal quarter ended December 31, 2016) and market price information as of April 4, 2017. KBW also used 2017 and 2018 EPS estimates taken from consensus "street estimates" for PacWest and the selected companies. Where consolidated holding company level financial data for the selected companies was unreported, subsidiary bank level data was utilized to calculate ratios. Certain financial data was prepared by KBW, and as referenced in the tables presented below, may not correspond to the data presented in PacWest's historical financial statements as a result of the different periods, assumptions and methods used by KBW to compute the financial data presented.

        KBW's analysis showed the following concerning the financial performance of PacWest and the selected companies:

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        KBW's analysis showed the following concerning the financial condition of PacWest and the selected companies:

        In addition, KBW's analysis showed the following concerning the market performance of PacWest and the selected companies:

        None of the selected companies used as a comparison in the above selected companies analyses of PacWest is identical to PacWest. Accordingly, an analysis of these results is not mathematical. Rather, it involves complex considerations and judgments concerning differences in financial and operating characteristics of the companies involved.

        Comparable M&A Transactions Analysis.    KBW reviewed publicly available information related to 15 selected whole bank transactions announced since December 31, 2014 with (i) buyers which were traded on NASDAQ, the New York Stock Exchange or the New York Stock Exchange Market, (ii) announced deal values between $250 million and $1 billion and (iii) targets which had nonperforming assets to total assets less than 100 basis points. Terminated transactions, mergers of equals, transactions with no reported deal value (as defined by SNL Financial), transactions with non-bank buyers and transactions where the target was a thrift were excluded from the selected transactions.

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        The selected transactions were as follows:

        For each selected transaction, KBW derived the following implied transaction statistics, in each case based on the transaction consideration value paid for the acquired company and using financial data based on the acquired company's then latest publicly available financial statements prior to the announcement of the transaction:

•

Price per common share to LTM EPS of the acquired company (in the case of selected transactions involving a private acquired company, this transaction statistic was calculated as total transaction consideration divided by LTM earnings);



•

Price per common share to current year EPS consensus "street estimates" of the acquired company (in the case of selected transactions involving a private acquired company, this transaction statistic was excluded);



•

Price per common share to next year EPS consensus "street estimates" of the acquired company (in the case of selected transactions involving a private acquired company, this transaction statistic was excluded);



•

Price per common share to book value per share of the acquired company (in the case of selected transactions involving a private acquired company, this transaction statistic was calculated as total transaction consideration divided by total common equity);



•

Price per common share to tangible book value per share of the acquired company (in the case of selected transactions involving a private acquired company, this transaction statistic was calculated as total transaction consideration divided by total tangible common equity);



•

Total transaction consideration to deposits of the acquired company; and



•

Tangible equity premium to core deposits (total deposits less time deposits greater than $100,000) of the acquired company, referred to as core deposit premium.

        KBW also reviewed the price per common share paid for the acquired company for the selected transactions in which the acquired company was publicly traded as a premium to the closing price of the acquired company one day prior to the announcement of the acquisition (expressed as a percentage and referred to as the one-day market premium) and as a premium to the average closing price of the acquired company for the one-month period ending one day prior to the announcement of the acquisition (expressed as a percentage and referred to as the one-month market premium). The above transaction statistics for the selected transactions were compared with the corresponding transaction

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statistics for the proposed merger based on the implied value of the merger consideration of $40.07 per CUB common share and using historical financial information for CUB as of December 31, 2016 and for the twelve month period ended December 31, 2016 and market price information of CUB as of April 4, 2017.

        The results of the analysis are set forth in the following table:

        None of the companies or transactions used as a comparison in the above selected transaction analysis is identical to CUB or the proposed merger, respectively. Accordingly, an analysis of these results is not mathematical. Rather, it involves complex considerations and judgments concerning differences in financial and operating characteristics of the companies involved.

        Relative Contribution Analysis.    KBW analyzed the relative standalone contribution of PacWest and CUB to various pro forma balance sheet and income statement items of the combined entity post consummation of the merger. This analysis did not include purchase accounting adjustments or cost savings. To perform this analysis, KBW used (i) balance sheet and net income data for PacWest and CUB as of December 31, 2016, and, (ii) publicly available 2017 and 2018 net income consensus "street estimates" of $366.4 million and $400.9 million, respectively, for PacWest, as agreed by PacWest management and approved by CUB management, and 2017 and 2018 EPS consensus "street estimates" of $1.75 and $2.09, respectively, for CUB, as approved by CUB management. The results of KBW's analysis are set forth in the following table, which also compares the results of KBW's analysis with the implied pro forma ownership percentages of PacWest and CUB shareholders in the combined company based on the implied stock consideration of 0.5308 shares of PacWest common stock provided for in the merger agreement (reflecting a 70.1% stock / 29.9% cash implied merger consideration mix) and

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also based on a hypothetical exchange ratio assuming 100% stock consideration in the proposed merger for illustrative purposes:

        Forecasted Pro Forma Financial Impact Analysis.    KBW performed a pro forma financial impact analysis that combined projected income statement and balance sheet information of PacWest and CUB. Using closing balance sheet estimates as of December 31, 2017 for PacWest and CUB based on publicly available consensus "street estimates," publicly available 2017 and 2018 net income consensus "street estimates" of $366.4 million and $400.9 million, respectively, for PacWest, as agreed by PacWest management and approved by CUB management, and publicly available 2017 and 2018 EPS consensus "street estimates" of $1.75 and $2.09, respectively, for CUB, as approved by CUB management, assumed long-term earnings growth rates provided by PacWest management, and pro forma assumptions (including certain purchase accounting adjustments, cost savings and related expenses) provided by PacWest management, KBW analyzed the potential financial impact of the merger on certain projected financial results of PacWest. This analysis indicated the merger could increase assets by 15.9%, increase gross loans by 13.2%, increase deposits by 17.0%, increase Tangible Common Equity by 0.9%, be accretive to PacWest's estimated post-closing 2018 EPS and estimated 2019 EPS and dilutive to PacWest's estimated tangible book value per share as of December 31, 2017. Furthermore, the analysis indicated that each of PacWest's tangible common equity to tangible assets ratio, Common Equity Tier 1 Ratio, leverage ratio and Total Risk-Based Capital Ratio as of December 31, 2017 could be lower on a pro forma basis compared to PacWest on a standalone basis. For all of the above analysis, the actual results achieved by PacWest following the merger may vary from the projected results, and the variations may be material.

        CUB Discounted Cash Flow Analysis.    KBW performed a discounted cash flow analysis of CUB to estimate a range for the implied equity value of CUB. In this analysis, KBW used consensus "street estimates" of CUB for 2017 and 2018 EPS, which were $1.75 and $2.09, respectively, which resulted in a calculation of net income of CUB for 2017 and 2018 of $31.2 million and $37.2 million, respectively, which was used in KBW's analysis. CUB authorized KBW to use street estimates for EPS for 2017 and 2018 (and the resultant calculated net income for such periods as discussed in the previous sentence) rather than CUB's internal estimates for EPS (and net income) because CUB believed that the street estimates for EPS (and corresponding calculated net income) reflected a composite analysis regarding interest rates and other economic assumptions resulting in a more objective view of CUB's projected

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financial performance. Street estimates of EPS were higher than CUB's internal estimates. KBW also used an assumed long-term earnings growth rate of 10.0% and a long-term asset growth rate of 9.0%, each as confirmed by CUB management, and used discount rates ranging from 9.0% to 13.0% based on the capital asset pricing model and KBW's professional judgment. The ranges of values were derived by adding (i) the present value of the estimated excess cash flows that CUB could generate over the five-year period from 2017 to 2021 as a standalone company, and (ii) the present value of implied terminal value at the end of such period. KBW assumed that CUB would maintain a tangible common equity to tangible asset ratio of 8.0% and would retain sufficient earnings to maintain that level. In calculating the terminal value of CUB, KBW applied a range of 14.0x to 18.0x to estimated 2022 earnings based on comparable companies and KBW's professional judgment. This discounted cash flow analysis resulted in a range of implied values per CUB common share of $26.49 to $38.09.

        The discounted cash flow analysis is a widely used valuation methodology, but the results of such methodology are highly dependent on the assumptions that must be made, including asset and earnings growth rates, terminal values, dividend payout rates and discount rates. The foregoing discounted cash flow analyses did not purport to be indicative of the actual values of CUB.

        Miscellaneous.    KBW acted as financial advisor to CUB and did not act as an advisor to or agent of any other person. As part of its investment banking business, KBW is continually engaged in the valuation of bank and bank holding company securities in connection with acquisitions, negotiated underwritings, secondary distributions of listed and unlisted securities, private placements and valuations for various other purposes. As specialists in the securities of banking companies, KBW has experience in, and knowledge of, the valuation of banking enterprises. KBW and its affiliates, in the ordinary course of its and their respective broker-dealer businesses, and further to certain existing sales and trading relationships with each of CUB and PacWest, may from time to time purchase securities from, and sell securities to, CUB and PacWest. In addition, as a market maker in securities, KBW and its affiliates may from time to time have a long or short position in, and buy or sell, debt or equity securities of CUB and PacWest for its and their own accounts and for the accounts of its and their respective customers and clients.

        Pursuant to the KBW engagement agreement, CUB agreed to pay KBW a cash fee equal to 1.2% of the aggregate merger consideration (referred to as the contingent fee), which is contingent upon the closing of the merger, as well as a separate fee of $750,000 (referred to as the opinion fee), which became payable to KBW concurrently with the rendering of its opinion; provided that the opinion fee, to the extent then-previously paid to KBW, will be credited towards the contingent fee. CUB also agreed to reimburse KBW for reasonable out-of-pocket expenses and disbursements incurred in connection with its retention and to indemnify KBW against certain liabilities relating to or arising out of KBW's engagement or KBW's role in connection therewith. Other than this present engagement, during the two years preceding the date of its opinion, KBW has not provided investment banking and financial advisory services to CUB. During the two years preceding the date of its opinion, KBW has not provided investment banking and financial advisory services to PacWest. KBW may in the future provide investment banking and financial advisory services to CUB or PacWest and receive compensation for such services.

PacWest's Reasons for the Merger

        In reaching its decision to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement, the PacWest board of directors consulted with PacWest senior management, as well as its financial and legal advisors, and considered a number of factors, including the following material factors:

•

each of PacWest's, CUB's and the combined company's business, operations, financial condition, asset quality, earnings and prospects;

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•

the potential to grow core deposits and the improvement in PacWest's deposit and liquidity position by adding CUB's strong deposit franchise and liquid balance sheet;



•

the opportunity to grow PacWest's presence in Southern California and complement PacWest's existing franchise by adding CUB's leading commercial and industrial community banking business;



•

the cost savings available in the proposed transaction, as well as the potential for revenue enhancement, which create the opportunity for PacWest to have greater future earnings and prospects compared to PacWest's earnings and prospects on a stand-alone basis;



•

the potential risks associated with successfully integrating CUB's business, operations and workforce with those of PacWest, and PacWest's past record of integrating acquisitions and realizing projected benefits of acquisitions;



•

its review and discussions with PacWest's management and advisors concerning the due diligence examination of CUB;



•

management's expectation that PacWest will continue to have a strong capital position upon completion of the transaction;



•

CUB's asset sensitive balance sheet, which will benefit PacWest in a rising rate environment;



•

its review with its legal advisor, Sullivan & Cromwell LLP, of the merger agreement and other agreements, including the provisions of the merger agreement designed to enhance the probability that the transaction will be completed;



•

the potential risk of diverting management attention and resources from the operation of PacWest's business and towards the completion of the merger and the integration of CUB;



•

the regulatory and other approvals required in connection with the merger and the expected likelihood that such regulatory approvals will be received in a reasonably timely manner and without the imposition of unacceptable conditions; and



•

the possibility of litigation challenging the merger, and PacWest's belief that any such litigation would be without merit.

        The foregoing discussion of the information and factors considered by the PacWest board of directors is not intended to be exhaustive, but includes the material factors considered by the PacWest board of directors. In reaching its decision to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement, the PacWest board of directors did not quantify or assign any relative weights to the factors considered, and individual directors may have given different weights to different factors. The PacWest board of directors considered all these factors as a whole, including discussions with, and questioning of, PacWest's senior management and PacWest's advisors, and overall considered the factors to be favorable to, and to support its determination to approve entering into the merger agreement.

        This explanation of PacWest's reasons for the merger and other information presented in this section is forward-looking in nature and should be read in light of the section entitled "Cautionary Statement Regarding Forward-Looking Statements."

        PacWest's board of directors realized that there can be no assurance about future results, including results expected or considered in the factors listed above, such as assumptions regarding enhanced business prospects, anticipated cost savings and earnings accretion/dilution. The PacWest board of directors concluded, however, that the potential positive factors outweighed the potential risks of completing the transaction.

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Management and Board of Directors of PacWest After the Merger

        The directors and officers of PacWest immediately prior to the effective time will be the directors and officers of the surviving corporation after the consummation of the merger, and will serve until such time as their successors are duly elected and qualified.

Interests of CUB Directors and Executive Officers in the Merger

        In considering the recommendation of the CUB board of directors with respect to the merger, CUB shareholders should be aware that certain of the directors and executive officers of CUB have interests in the merger that may be different from, or in addition to, the interests of CUB shareholders generally. The CUB board of directors was aware of these interests and considered them, among other matters, in approving the merger agreement and the transactions contemplated thereby and in making its recommendation that CUB shareholders vote to approve the CUB merger proposal. These interests are described in further detail below.

Treatment of Outstanding Equity Awards

        CUB Restricted Shares and CUB RSUs.    At the effective time, any vesting conditions applicable to each CUB restricted share and CUB RSU will, automatically and without any action on the part of the holder thereof, accelerate in full and each such CUB restricted share and CUB RSU will be converted into and exchanged for the merger consideration, less any applicable taxes required to be withheld with respect to such vesting. The following table sets forth the dollar value of the CUB restricted shares that may become vested and the CUB RSUs that may become vested or settled at the closing of the merger held by each CUB director and executive officer. For purposes of calculating the value of the equity awards, we have assumed October 1, 2017 as the closing date of the merger and a merger consideration equal to a price per CUB common share of $39.86 calculated by adding (i) the per share cash consideration, or $12.00, and (ii) (x) the average closing price of PacWest common stock over the first

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five business days following the April 5, 2017 signing of the merger agreement multiplied by (y) the exchange ratio of 0.5308.

New Agreements with PacWest

Consulting Agreements

        In connection with the execution of the merger agreement, PacWest entered into consulting agreements with David I. Rainer, Chairman and Chief Executive Officer of CUB (which consulting agreement was subsequently amended), K. Brian Horton, President and a director of CUB, and Karen A. Schoenbaum, Executive Vice President and Chief Financial Officer of CUB, whereby PacWest will retain these CUB executive officers as consultants to PacWest and its subsidiaries to perform certain services, including providing strategic advice and counsel to PacWest and acting as an ambassador for PacWest in dealings with clients and counterparties. The consulting agreements become effective as of, and are conditioned upon, the closing of the merger. If the merger agreement is terminated pursuant to its terms, the consulting agreements will also terminate and be of no force or effect. The term of the consulting agreements will end on the earlier of (A)(1) 65 months from the closing of the merger, in the case of Mr. Rainer, or (2) the two-year anniversary of the closing of the merger, in the case of Mr. Horton and Ms. Schoenbaum, and (B) the termination of the respective consulting agreement pursuant to its terms.

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        Pursuant to the consulting agreements, the executive officers have agreed not to, without the written consent of PacWest, directly or indirectly, represent, become employed by, perform services for, consult to, or advise in any manner or have any material interest in any "competitive enterprise" during the restricted period, which is the period from the effective date of the consulting agreement until its third anniversary, in the case of Mr. Rainer, and its second anniversary, in the case of Mr. Horton and Ms. Schoenbaum. "Competitive enterprise" is defined as any banking organization that competes where CUB or any of its subsidiaries regularly conducted business prior to the closing of the merger, with any of the business activities engaged in by CUB or any of its subsidiaries any time prior to the closing of the merger, or any entity or business attempting to acquire an interest in such banking organization.

        Pursuant to the consulting agreements, during the restricted period, the executive officers are also prohibited from, without the prior written consent of PacWest, in any manner, directly or indirectly: (i) soliciting any client of CUB or any of its subsidiaries to transact business with a competitive enterprise or to reduce or refrain from doing business with PacWest or any of its subsidiaries, (ii) interfering with or damaging any client relationship of PacWest, Pacific Western Bank or CUB, and (iii) soliciting an employee of PacWest or any of its subsidiaries to resign or to apply for or accept employment with a competitive enterprise.

        In addition, each of the executive officers agreed, pursuant to the terms of their respective consulting agreements, not to divulge trade secrets and confidential information, knowledge or data of PacWest and its subsidiaries and their businesses and investments, obtained during the executives' employment with CUB and during their consulting with PacWest.

        The executive officers will receive for their services following consummation of the merger, subject to complying with the non-competition and non-solicitation restrictions and confidentiality provisions of the consulting agreements set forth above, the following annual retainers: (1) $550,000 for Mr. Rainer, payable in substantially equal monthly installments during his 65-month consulting period for a total of $3,000,000; (2) $375,000 for Mr. Horton, payable in equal monthly installments during his two-year consulting period for a total of $750,000; and (3) $100,000 for Ms. Schoenbaum, payable in equal monthly installments during her two-year consulting period for a total of $200,000. The consulting agreements also provide for reimbursement of each of the executive officer's reasonable out-of-pocket expenses, as well as office space at PacWest's Beverly Hills headquarters for Mr. Rainer.

        PacWest may terminate a consulting agreement for cause at any time by written notice to the relevant executive officer. "Cause" is defined as (i) falsification of PacWest's documents or records; (ii) the executive officer's intentional and improper use or disclosure of PacWest's confidential or proprietary information; (iii) any action by the executive officer which was intended to, and has a significant detrimental effect on PacWest's reputation or business; (iv) the executive officer's willful failure to perform any reasonable assigned duties after written notice from PacWest, and a reasonable opportunity to cure, such willful failure; (v) the executive officer's material breach of any written agreement between the executive officer and PacWest or (vi) the executive officer's conviction for theft, dishonesty, or of any criminal act which impairs the executive officer's ability to perform his or her duties with PacWest. Each of the executive officers may terminate his or her consulting agreement for any reason, effective immediately. The consulting agreements provide that the fees payable to the executive officers will not be paid for any period after termination by PacWest for cause, by the executive officer for any reason or due to the executive officer's death or disability. If PacWest terminates a consulting agreement other than for cause prior to the end of the term, PacWest will continue to pay the fees under the consulting agreement through the remainder of the term of the applicable consulting agreement.

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Indemnification and Insurance

        Pursuant to the terms of the merger agreement, following the effective time, PacWest has agreed to indemnify present and former directors and officers of CUB in connection with any claim arising out of actions or omissions occurring at or prior to the effective time to the fullest extent permitted under law and to provide or purchase directors' and officers' liability insurance for a period of six years following the effective time of the merger as described in "The Merger Agreement—Indemnification and Directors' and Officers' Insurance."

Payments Upon Termination or Change in Control

Change in Control Severance Plan

        The CU Bancorp 2012 Change in Control Severance Plan, referred to as the CIC Plan, provides for severance benefits to CUB's executive officers upon termination of employment without cause or resignation for any reason within 24 months following a change in control of CUB. As a condition of receiving the severance benefits under the CIC Plan, the applicable executive officer must execute a release of claims. Specifically, each executive officer is entitled to the following severance benefits under the CIC Plan:

•

A multiple of the executive officer's compensation as follows: three times, in the case of Mr. Rainer, and two times, in the case of each of the other executive officers of CUB, the sum of (x) the base salary in effect on the date of the executive's termination of employment and (y) the average of: (i) the bonus (which includes the value of cash and equity incentive awards awarded to the executive officers under CUB's Management Incentive Plan) paid or payable for the most recently completed full fiscal year performance period prior to the date of the executive's termination of employment, and (ii) the bonus paid for the full fiscal year performance period completed immediately prior to the full fiscal year performance period described in subsection (i) above, and



•

24 months of reimbursement for any COBRA premiums paid for 24 months following termination.

        Any severance benefits under the CIC Plan that would constitute "excess parachute payments" within the meaning of Section 280G of the Internal Revenue Code will be reduced in order to result in no portion of such payments being subject to the excise tax imposed by Section 4999 of the Internal Revenue Code. In addition, pursuant to Section 409A of the Internal Revenue Code, in certain circumstances payments will be delayed for a period of six months following a participant's termination of employment. In such event, the severance benefits will be contributed to a "rabbi trust" for the benefit of the participant and paid at the expiration of the six-month period.

        The following table sets forth the estimated value of the cash severance payments and COBRA premium payments to which CUB's executive officers would be entitled pursuant to the CIC Plan, subject to execution of a release, based on compensation levels as of the date of this proxy statement/prospectus, in the event of and assuming closing of the merger on October 1, 2017 and a termination

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of employment immediately following closing of the merger on such date. The actual amounts, if any, to be received by the executive officers may differ from the amounts set forth below.

Executive Salary Continuation Agreements

        David I. Rainer, K. Brian Horton, Karen A. Schoenbaum, Anne A. Williams and Anita Y. Wolman, collectively, the CUB named executive officers, have previously entered into salary continuation agreements, referred to as the SCAs, with CUB. The SCAs provide the CUB named executive officers with an annual retirement benefit (payable in monthly installments) for 15 years (eight in the case of Ms. Wolman plus two additional years for each year she continues in CUB's employ following attainment of age 65, up to a maximum of 15 years) following their retirement from CUB. All rights to the retirement benefits under the SCAs are currently vested for the CUB named executive officers.

        In the event of a termination of employment within 24 months following a change in control of CUB, the CUB named executive officers become entitled to receive the full retirement benefits that are payable under the SCAs at age 65, the specified normal retirement age. The CUB named executive officers are entitled to a reduced retirement benefit if they leave CUB's employ prior to age 65. The SCAs also provide a death benefit in the event a CUB named executive officer dies while employed by CUB or after becoming entitled to receive benefits under the SCA.

        The following table sets forth the benefits that the CUB named executive officers would be entitled to receive, pursuant to the terms of their salary continuation agreements, in the event of a termination of employment immediately following closing of the merger, assuming closing of the

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merger on October 1, 2017. The actual amounts, if any, to be received by the CUB named executive officers may differ from the amounts set forth below.

2017 Management Incentive Plan

        The CUB executive officers participate in the 2017 Management Incentive Plan, referred to as the MIP, which was approved by CUB's Compensation, Nominating and Corporate Governance Committee and provides a set of goals and metrics for annual incentive compensation to be paid to CUB's executive officers for 2017. Under the MIP, in the event of a change in control of CUB in 2017, incentive performance award payments will be determined and payable based on the target levels for the cash incentive awards and equity incentive awards. In order for an executive participating in the MIP to receive an incentive performance award following a change in control, he or she must be employed by CUB on the day prior to the change in control. Cash incentive award payments will be paid on a prorated basis, based on the number of days in 2017 prior to the change in control divided by 365. Equity incentive awards will be paid in full, based on the target award level. PacWest has the discretion to deliver payment of the equity incentive awards in cash or unrestricted stock.

        The following table sets forth the benefits that CUB's executive officers would be entitled to receive under the MIP in the event of and assuming consummation of the merger on October 1, 2017. The actual amounts, if any, to be received by the executive officers may differ from the amounts set forth below.

Regulatory Approvals Required for the Merger

        Completion of the merger and the bank merger by CUB is subject to the requirement that all consents, registrations, approvals, permits and authorizations required to be obtained prior to the effective time by either party or any of its respective subsidiaries from the FRB, the FDIC and the CDBO which are necessary to consummate the merger and the bank merger, and any other consents, registrations, approvals, permits and authorizations from any governmental authority the failure of which to be obtained is reasonably likely to have, individually or in the aggregate, a material adverse

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effect on PacWest (measured on a scale relative to CUB) or on CUB, have been made or obtained (as the case may be) and remain in full force and effect and all statutory waiting periods in respect thereof have expired.

        Completion of the merger and the bank merger by PacWest is subject to the requirement that all consents, registrations, approvals, permits and authorizations required to be obtained prior to the effective time by either party or any of its respective subsidiaries from the FRB, the FDIC and the CDBO which are necessary to consummate the merger and the bank merger, and any other consents, registrations, approvals, permits and authorizations from or with any governmental authority the failure of which to be obtained is reasonably likely to have, individually or in the aggregate, a material adverse effect on PacWest (measured on a scale relative to CUB) or on CUB, have been made or obtained (as the case may be) and remain in full force and effect and all statutory waiting periods in respect thereof have expired, and none of such consents, registrations, approvals, permits and authorizations contain any "materially burdensome regulatory condition." The merger agreement defines a "materially burdensome regulatory condition" to mean any condition that would reasonably be likely following the effective time to (i) have a material adverse effect with respect to either PacWest (measured on a scale relative to CUB) or CUB, or (ii) require PacWest, Pacific Western Bank, the combined company or the surviving bank in the bank merger to raise additional capital in an amount that would materially reduce the economic benefits of the merger to PacWest or the holders of PacWest common stock (including the CUB shareholders in respect of the shares of PacWest common stock received by them in the merger).

        Notifications and/or applications requesting approval may also be submitted to various other federal and state regulatory authorities and self-regulatory organizations.

        PacWest and CUB have agreed to cooperate and to use their respective reasonable best efforts to prepare and file, or in the case of PacWest cause to be filed, all documentation to effect all necessary notices, reports and other filings and to obtain all permits, consents, approvals and authorizations necessary or advisable to be obtained from any third parties and/or governmental authorities in order to consummate the merger, the bank merger or any of the other transactions contemplated by the merger agreement. PacWest, CUB and/or their respective subsidiaries have filed, or are in the process of filing, applications and notifications to obtain these regulatory approvals.

        Although the parties currently believe they should be able to obtain all required regulatory approvals in a timely manner, they cannot be certain when or if they will obtain them or, if obtained, whether they will contain terms, conditions or restrictions not currently contemplated that will be detrimental to PacWest after the completion of the merger or will contain a materially burdensome regulatory condition.

Federal Reserve Board

        PacWest is a bank holding company as defined in the BHC Act. The primary regulator of PacWest is the FRB. PacWest has filed with the FRB an application under Sections 3(a)(3) and 3(a)(5) of the BHC Act and regulations thereunder for the transactions contemplated by the merger agreement. In considering the approval of the merger, the FRB is required by the BHC Act to review, with respect to PacWest and the companies and insured depository institution to be acquired: (1) the effect of the proposal on competition, (2) the financial condition and future prospects of the combined company and the banks concerned and the managerial resources, including the competence, experience, and integrity of the officers, directors and principal stockholders of PacWest, CUB and their subsidiary banks, (3) the convenience and needs of the communities to be served, including the record of performance under the Community Reinvestment Act of 1977 and the regulations issued thereunder, referred to as the CRA, (4) whether the merger is an interstate merger subject to the Riegle-Neal Interstate Banking and Branching Efficiency Act of 1994, referred to as the Riegle-Neal Act, (5) the banks' record of

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compliance with the CRA, (6) the companies' effectiveness in combating money-laundering activities and (7) the risk to the stability of the United States banking or financial system presented by the merger and the related transactions.

        In connection with its review of the application, the FRB will provide an opportunity for public comment on the application, and is authorized to hold a public meeting or other proceeding if it determines such meeting or other proceeding would be appropriate.

Federal Deposit Insurance Corporation

        The prior approval of the FDIC will be required under Section 18(c) of the Federal Deposit Insurance Act, referred to as the Bank Merger Act, to merge CU Bank with and into Pacific Western Bank. In evaluating an application filed under the Bank Merger Act, the FDIC generally considers: (1) the competitive impact of the transaction, (2) financial and managerial resources of each bank that is a party to the bank merger, (3) the extent to which the bank merger would result in greater or more concentrated risks to the stability of the U.S. banking or financial system, (4) the convenience and needs of the communities in which the banks serve, (5) whether the merger is subject to the Riegle-Neal Act, (6) the performance records of the banks under the CRA, including their CRA rating and (7) each of the banks' effectiveness in combating money-laundering activities and. In connection with its review under the Bank Merger Act, the FDIC will provide an opportunity for public comment on the application for the bank merger, and is authorized to hold a public meeting or other proceeding if it determines that would be appropriate.

        Transactions approved by the FRB or the FDIC generally may not be completed until 30 days after such approval is received, during which time the Department of Justice, referred to as the DOJ, may challenge the transaction on antitrust grounds. With the approval of the FRB or the FDIC, as the case may be, and the concurrence of the DOJ, the waiting period may be reduced to no less than 15 days. The commencement of an antitrust action would stay the effectiveness of such an approval unless a court specifically ordered otherwise. In reviewing the merger and the bank merger, the DOJ could analyze the merger's and the bank merger's effects on competition differently than the FRB or the FDIC, and thus it is possible that the DOJ could reach a different conclusion regarding the merger's and the bank merger's effects on competition. A determination by the DOJ not to object to the merger or the bank merger may not prevent the filing of antitrust actions by private persons or state attorneys general.

California Department of Business Oversight

        The prior approval of the CDBO will be required under the California Financial Code to merge CU Bank with and into Pacific Western Bank. In reviewing the merger of CU Bank with Pacific Western Bank, the CDBO will take competitive considerations into account, as well as capital adequacy, quality of management and earnings prospects, in terms of both quality and quantity. The CDBO will also take into account the record of performance of the banks concerned in meeting the credit needs of the entire community, including low- and moderate-income neighborhoods, served by such companies and depository institutions. The CDBO will also take into account the safety and soundness of the resulting bank following the bank merger. In considering the merger, the California Financial Code also requires the CDBO to consider the fairness of the merger to all parties involved. Approval from the CDBO was received on June 27, 2017.

Additional Regulatory Approvals and Notices

        Notifications and/or applications requesting approval may be submitted to various other federal and state regulatory authorities and self-regulatory organizations.

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        Although PacWest and CUB expect to obtain the required regulatory approvals, there can be no assurances as to if, or when, these regulatory approvals will be obtained, the terms and conditions on which the approvals may be granted, or whether there will be litigation challenging such approvals. There can likewise be no assurances that U.S. or state regulatory authorities will not attempt to challenge the merger on antitrust grounds or for other reasons, or, if such a challenge is made, as to the result of any such challenge.

Accounting Treatment

        In accordance with current accounting guidance, PacWest, as the acquirer, will account for the merger using the acquisition method. The acquisition method requires that (a) the recorded assets and liabilities of PacWest will be carried forward at their recorded amounts, (b) PacWest's historical operating results will be unchanged for the prior periods being reported on, (c) the assets and liabilities of CUB will be adjusted to fair value at the date of the merger and combined with the assets and liabilities of PacWest, and (d) the operating results of CUB will be included in the operating results of PacWest beginning from the date of completion of the merger. In addition, all identifiable intangible assets will be recorded at fair value and included as part of the assets acquired. The amount by which the purchase price, consisting of the value of the cash and shares of PacWest common stock to be issued to former holders of CUB common shares, CUB RSUs and CUB restricted shares and cash to be issued to former holders of CUB stock options, exceeds the fair value of the net assets including identifiable intangible assets of CUB at the merger date will be reported as goodwill. In accordance with current accounting guidance, goodwill is not amortized and will be evaluated for impairment annually. Identified intangible assets will be amortized over their estimated lives.

Public Trading Markets

        PacWest common stock is listed on NASDAQ under the symbol "PACW" and CUB common shares are listed on NASDAQ under the symbol "CUNB." Upon completion of the merger, CUB common shares will be delisted from NASDAQ and thereafter will be deregistered under the Exchange Act. The PacWest common stock issuable in the merger will be listed on NASDAQ.

Exchange of Shares in the Merger

        At or prior to the effective time, PacWest will appoint an exchange agent to handle the exchange of CUB common shares for shares of PacWest common stock. Promptly after the effective time (and in any event within five business days), the exchange agent will send to each holder of record of CUB common shares at the effective time (other than holders of excluded shares or dissenting shares) appropriate transmittal materials and instructions for effecting the exchange of CUB common shares for the merger consideration the holder is entitled to receive under the merger agreement. Upon surrender of certificates or book entry shares for cancellation along with the other documents described in the instructions, a CUB shareholder will receive a certificate (or evidence of shares in book-entry form, as applicable) representing the number of whole shares of PacWest common stock that such holder is entitled to receive based on the exchange ratio of 0.5308 for each CUB common share and a check in the amount (after giving effect to any required tax withholdings as provided in the merger agreement) of the cash consideration for the surrendered shares, and any cash payable in lieu of fractional shares plus any unpaid non-stock dividends and any other dividends or other distributions that such holder has the right to receive pursuant to the merger agreement. After the effective time, CUB will not register any transfers of CUB common shares.

Dissenters' Rights

        CUB shareholders who vote their CUB common shares "AGAINST" the merger proposal and who properly demand the purchase of such shares in accordance with Chapter 13 of the CGCL will not be

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converted into the right to receive the merger consideration otherwise payable for CUB common shares upon consummation of the merger, but will instead be converted into the right to receive such consideration as may be determined to be due pursuant to Chapter 13 of CGCL. A copy of Chapter 13 of the CGCL is attached to this proxy statement/prospectus as Appendix C.

        The following discussion is not a complete statement of the law pertaining to dissenters' rights under the CGCL. The full text of Sections 1300 through 1313 of the CGCL is attached to this proxy statement/prospectus as Appendix C and is incorporated herein by reference. Appendix C should be reviewed carefully by any CUB shareholder who wishes to exercise dissenters' rights or who wishes to preserve the right to do so, since failure to comply with the procedures of the relevant statute in any respect will result in the loss of dissenters' rights.

        All references in Sections 1300 through 1313 of the CGCL and in this summary to a "shareholder" are to the holder of record of CUB common shares as to which dissenters' rights are asserted. A person having a beneficial interest in CUB common shares held of record in the name of another person, such as a broker, bank or nominee, cannot enforce dissenters' rights directly and must act promptly to cause the holder of record to follow the steps summarized below properly and in a timely manner to perfect such person's dissenters' rights.

        ANY HOLDER OF CUB COMMON SHARES WISHING TO EXERCISE DISSENTERS' RIGHTS IS URGED TO CONSULT LEGAL COUNSEL BEFORE ATTEMPTING TO EXERCISE SUCH RIGHTS. FAILURE TO COMPLY STRICTLY WITH ALL OF THE PROCEDURES SET FORTH IN CHAPTER 13 OF THE CGCL, WHICH CONSISTS OF SECTIONS 1300-1313, WILL RESULT IN THE LOSS OF A SHAREHOLDER'S STATUTORY DISSENTERS' RIGHTS.

        Under the CGCL, CUB common shares must satisfy each of the following requirements to qualify as dissenting shares, which are referred to as dissenting shares:

•

such dissenting shares must have been outstanding on the record date;



•

such dissenting shares must have voted "AGAINST" the merger proposal;



•

the holder of such dissenting shares must timely make a written demand that CUB repurchase such dissenting shares at fair market value (as defined below); and



•

the holder of such dissenting shares must submit certificates representing such dissenting shares for endorsement (as described below).

        A vote "AGAINST" the merger proposal does not in and of itself constitute a demand for appraisal under California law.

        Pursuant to Sections 1300 through 1313 of the CGCL, holders of dissenting shares may require CUB to repurchase their dissenting shares at a price equal to the fair market value of such shares determined as of the day before the first announcement of the terms of the merger, excluding any appreciation or depreciation as a consequence of the proposed merger, but adjusted for any stock split, reverse stock split or stock dividend that becomes effective thereafter, referred to as the "fair market value."

        By no later than the date of the special meeting, CUB or its transfer agent must have received from any dissenting shareholder a written demand that CUB repurchase such shareholder's dissenting shares. The written demand must include the number and class of dissenting shares held of record by such dissenting shareholder that the dissenting shareholder demands that CUB purchase. Furthermore, the written demand must include a statement of what such dissenting shareholder claims to be the fair market value of the dissenting shares (which will constitute an offer by the dissenting shareholder to sell the dissenting shares at such price).

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        Within 10 days following approval of the merger proposal by the CUB shareholders, CUB is required to mail a dissenter's notice to each person who is entitled to dissenting shareholder rights. The dissenter's notice must contain the following:

•

a notice of the approval of the merger proposal;



•

a statement of the price determined by CUB to represent the fair market value of dissenting shares (which will constitute an offer by CUB to purchase such dissenting shares at such stated price unless such shares lose their status as "dissenting shares" under Section 1309 of the CGCL);



•

a brief description of the procedure for such holders to exercise their rights as dissenting shareholders; and



•

a copy of Sections 1300 through 1304 of Chapter 13 of the CGCL.

        Within 30 days after the date on which the notice of the approval of the merger proposal by the outstanding shares is mailed to dissenting shareholders, a dissenting shareholder must submit to CUB certificates representing any dissenting shares that the dissenting shareholder demands CUB purchase, so that such dissenting shares may either be stamped or endorsed with the statement that the shares are dissenting shares or exchanged for certificates of appropriate denomination so stamped or endorsed. If the dissenting shares are uncertificated, then such shareholder must provide written notice of the number of shares which the shareholder demands that CUB purchase within 30 days after the date of the mailing of the notice of the approval of the merger proposal. The demand, statement and CUB certificates should be delivered to: CU Bancorp, 15821 Ventura Boulevard, Suite 100, Encino, California 91436, Attention: Corporate Secretary.

        If upon the dissenting shareholder's surrender of the certificates representing the dissenting shares, CUB and a dissenting shareholder agree upon the price to be paid for the dissenting shares and agree that such shares are dissenting shares, then the agreed price is required by law to be paid (with interest thereon at the legal rate on judgments from the date of the agreement) to the dissenting shareholder within the later of (i) 30 days after the date of such agreement or (ii) 30 days after any statutory or contractual conditions to the completion of the merger are satisfied.

        If CUB and a dissenting shareholder disagree as to the price for such dissenting shares or disagree as to whether such shares are entitled to be classified as dissenting shares, such holder has the right to bring an action in California Superior Court of the proper county, within six months after the date on which the notice of the shareholders' approval of the merger proposal is mailed, to resolve such dispute. In such action, the court will determine whether the CUB common shares held by such shareholder are dissenting shares and/or the fair market value of such dissenting shares.

        In determining the fair market value for the dissenting shares, the court may appoint one or more impartial appraisers to make the determination. Within a time fixed by the court, the appraisers, or a majority of them, will make and file a report with the court. If the appraisers cannot determine the fair market value within 10 days of their appointment, or within a longer time determined by the court, or the court does not confirm their report, then the court will determine the fair market value. Upon a motion made by any party, the report will be submitted to the court and considered evidence as the court considers relevant. The costs of the dissenters' rights action, including reasonable compensation to the appraisers appointed by the court, will be allocated between CUB and the dissenting shareholder(s) as the court deems equitable. However, if the appraisal of the fair market value of CUB shares exceeds the price offered by CUB in the notice of approval, then CUB will pay the costs. If the fair market value of the shares awarded by the court exceeds 125% of the price offered by CUB, then the court may in its discretion impose additional costs on CUB, including attorneys' fees, fees of expert witnesses and interest.

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        CUB shareholders considering whether to exercise dissenters' rights should consider that the fair market value of their CUB common shares determined under Chapter 13 of the CGCL could be more than, the same as or less than the value of consideration to be paid in connection with the merger, as set forth in the merger agreement. Also, CUB reserves the right to assert in any appraisal proceeding that, for purposes thereof, the fair market value of dissenting shares is less than the value of the merger consideration to be issued and paid in connection with the merger, as set forth in the merger agreement. CUB shareholders considering whether to exercise dissenters' rights should consult with their tax advisors for the specific tax consequences of the exercise of dissenters' rights.

        Strict compliance with certain technical prerequisites is required to exercise dissenters' rights. CUB shareholders wishing to exercise dissenters' rights should consult with their own legal counsel in connection with compliance with Chapter 13 of the CGCL. Any CUB shareholder who fails to comply with the requirements of Chapter 13 of the CGCL, attached as Appendix C to this proxy statement/prospectus, will forfeit the right to exercise dissenters' rights and will, instead, receive the consideration to be issued and paid in connection with the merger, as set forth in the merger agreement.

        Except as expressly limited by Chapter 13 of the CGCL, dissenting shares continue to have all the rights and privileges incident to their shares until the fair market value of their shares is agreed upon or determined.

        Dissenting shares lose their status as "dissenting shares," and holders of dissenting shares cease to be entitled to require CUB to purchase such shares, upon the happening of any of the following:

•

the merger is abandoned;



•

the dissenting shares are transferred before their submission to CUB for the required endorsement;



•

the dissenting shareholder and CUB do not agree on the status of the shares as dissenting shares or do not agree on the purchase price, but neither CUB nor the shareholder files a complaint or intervenes in a pending action within six months after CUB mails a notice that its shareholders have approved the merger; or



•

with CUB's consent, the dissenting shareholder withdraws the shareholder's demand for purchase of the dissenting shares.

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THE MERGER AGREEMENT

        The following is a summary of selected provisions of the merger agreement. While PacWest and CUB believe this description covers the material terms of the merger agreement, it may not contain all of the information that is important to you and is qualified in its entirety by reference to the merger agreement, which is incorporated by reference in its entirety into, and is attached as Appendix A to, this document. The parties urge you to read the merger agreement in its entirety.

Explanatory Note

        The merger agreement and the summary of its terms in this document have been included only to provide you with information about the terms and conditions of the merger agreement. The representations, warranties and covenants contained in the merger agreement are made by PacWest and CUB only for purposes of the merger agreement and as of specific dates and were qualified and subject to certain limitations and exceptions agreed to by PacWest and CUB in connection with negotiating the terms of the merger agreement. In particular, in your review of the representations and warranties contained in the merger agreement and described in this summary, it is important to bear in mind that the representations and warranties were made solely for the benefit of the parties to the merger agreement and were negotiated for the purpose of allocating contractual risk among the parties to the merger agreement rather than to establish matters as facts. Stockholders are not third-party beneficiaries under the merger agreement. The representations and warranties may also be subject to a contractual standard of materiality or material adverse effect different from those generally applicable to stockholders and reports and documents filed with the SEC, and, in some cases, they may be qualified by disclosures made by one party to the other, which are not necessarily reflected in the merger agreement or other public disclosures made by PacWest or CUB. The representations and warranties contained in the merger agreement do not survive the effective time. Moreover, information concerning the subject matter of the representations, warranties and covenants, which do not purport to be accurate as of the date of this document, may have changed since the date of the merger agreement, and subsequent developments or new information may not be fully reflected in public disclosures of PacWest or CUB.

        For the foregoing reasons, the representations, warranties and covenants or any descriptions of those provisions should not be read alone or relied upon as characterizations of the actual state of facts or condition of PacWest or CUB or any of their respective subsidiaries or affiliates. Instead, such provisions or descriptions should be read only in conjunction with the other information provided elsewhere in this document or incorporated by reference into this document. Please see the section entitled "Where You Can Find More Information." PacWest and CUB will provide additional disclosures in their public reports to the extent they are aware of the existence of any material facts that are required to be disclosed under federal securities laws and that might otherwise contradict the terms and information contained in the merger agreement and will update such disclosure as required by federal securities laws.

The Merger

        Upon the terms and subject to the conditions of the merger agreement, CUB will merge with and into PacWest, with PacWest surviving the merger. The separate corporate existence of CUB will cease, with all its rights, privileges, immunities, power and franchises. The merger agreement also provides that immediately after the merger, CU Bank, a California state-chartered bank and a wholly owned subsidiary of CUB, will merge with and into Pacific Western Bank, a California state-chartered bank and wholly owned subsidiary of PacWest, with Pacific Western Bank as the surviving bank.

Effects of the Merger

        As a result of the merger, there will no longer be any publicly held CUB common shares. CUB shareholders will only participate in the surviving corporation's future earnings and potential growth

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through their ownership of PacWest common stock. All of the other incidents of direct ownership of CUB common shares, such as the right to vote on certain corporate decisions, to elect directors and to receive dividends and distributions from CUB, will be extinguished upon completion of the merger. All of the property, rights, privileges and powers of PacWest and CUB will vest in the surviving corporation, and all obligations, liabilities, debts, restrictions, disabilities and duties of PacWest and CUB will become the obligations, liabilities, debts, restrictions, disabilities and duties of the surviving corporation.

Closing and Effective Time of the Merger

        The merger agreement provides that the merger will be consummated no later than three business days after the satisfaction or waiver of all the closing conditions, except for those conditions that by their nature are to be satisfied at the closing (but subject to the fulfillment or waiver of those conditions), including the receipt of all regulatory and shareholder approvals and after the expiration of all regulatory waiting periods, unless extended by mutual written agreement of PacWest and CUB. The merger will be consummated at the time the certificate of merger has been duly filed with the Secretary of State of the State of Delaware and the agreement of merger has been duly filed with the Secretary of State of the State of California or at such later time as may be agreed by the parties and specified in the Delaware certificate of merger and the California agreement of merger. The parties are seeking regulatory approval by the fourth quarter of 2017, with the consummation of the merger to occur as soon as practicable thereafter. However, there can be no assurance as to when or if the merger will occur.

        If the merger is not completed by the end date, the merger agreement may be terminated by either PacWest or CUB, except to the extent that the failure of the merger to be consummated by that date arises out of or results from the knowing action or inaction of the party seeking to terminate which action or inaction is in violation of its obligations under the merger agreement.

        For a description of the transaction structure, merger consideration and treatment of CUB stock options, CUB restricted shares and CUB RSUs, please see the section entitled "The Merger—Terms of the Merger."

PacWest's Governing Documents, Directors and Officers Following the Closing

Governing Documents

        The certificate of incorporation and bylaws of PacWest will be the certificate of incorporation and bylaws of the surviving corporation as they exist immediately before the effective time, in each case until thereafter changed or amended as provided therein or by applicable law.

Directors and Officers

        The directors and officers of PacWest immediately prior to the effective time will be the directors and officers of the surviving corporation until the earlier of their resignation or removal or until their respective successors are duly appointed and qualified.

Merger Consideration; Exchange Procedures

Conversion of CUB Common Shares

        At the effective time, each CUB common share, other than excluded shares and dissenting shares as described below, issued and outstanding immediately prior to the effective time will be converted into and become exchangeable for (i) $12.00 in cash and (ii) the right to receive 0.5308 of a share of PacWest common stock as described under "The Merger—Merger Consideration," subject to

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adjustment as set forth in the merger agreement and as further described below under "—Termination of the Merger Agreement."

Purchase of Outstanding CUB Series A Preferred Stock

        Prior to closing, PacWest and CUB will reasonably cooperate with respect to the purchase by CUB from the U.S. Treasury Department of all of CUB's Series A preferred stock held by the U.S. Treasury Department, and following CUB's Series A preferred stock purchase (which will occur at or immediately prior to the closing), all of CUB's Series A preferred stock will be cancelled, and no payment or distribution of merger consideration will be made in consideration therefor.

Cancellation of Excluded Shares and Dissenting Shares

        At the effective time, (i) any CUB common shares held by PacWest or any direct or indirect wholly owned subsidiary of PacWest or by CUB or any direct or indirect wholly owned subsidiary of CUB, other than those held in a fiduciary capacity or as a result of debts previously contracted, which are referred to as excluded shares, and (ii) any dissenting shares (subject to the procedures for dissenting shares described herein) will automatically be cancelled and retired and will cease to exist and no consideration will be issued in exchange therefor.

Dissenting Shares

        No later than 10 calendar days after CUB's shareholders approve the merger, CUB will provide each record holder of CUB common shares entitled to vote on the merger with a notice including the information regarding dissenting shareholders' rights set forth in Section 1301(a) of the CGCL.

        To the extent dissenters' rights under Section 1301(a) are applicable to the merger, no dissenting shares will be converted into or represent a right to receive the consideration for such shares set forth in merger agreement. Instead, holders of dissenting shares will be entitled to require CUB to purchase such shares for cash at their fair market value to the extent granted by Chapter 13 of the CGCL. If a holder of dissenting shares thereafter effectively withdraws or loses such dissenters' rights with respect to such shares then, as of the occurrence of such withdrawal or loss, each such share will be deemed as of the effective time to have been converted into and represent only the right to receive the consideration for such shares set forth in the merger agreement.

        For more information regarding dissenters' rights, please see the section entitled "The Merger—Dissenters' Rights."

Rights as Shareholders of CUB

        At the effective time, holders of CUB common shares will cease to be, and will have no rights as, shareholders of CUB other than to receive the merger consideration and any dividends or distributions to which they are entitled under the merger agreement.

Effect of Merger on CUB Stock Options, Restricted Shares and RSUs

        For a description of the treatment of CUB stock options, CUB restricted shares and CUB RSUs in the merger, see the section entitled "The Merger—Treatment of CUB Stock Options, Restricted Shares and RSUs."

Exchange Procedures

        Immediately prior to the effective time, PacWest will deposit (or cause to be deposited) with an exchange agent selected by PacWest with CUB's prior approval (such approval not to be unreasonably withheld or delayed) (i) an amount of cash equal to $12.00 multiplied by the number of CUB shares

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(other than excluded shares and dissenting shares) outstanding immediately prior to the effective time, plus any cash due in lieu of fractional shares, and (ii) certificates, or evidence of shares in book-entry form, representing the shares of PacWest common stock to be exchanged for CUB common shares in the merger. Promptly after the effective time (and in any event within five business days), the exchange agent will provide appropriate transmittal materials to holders of record of CUB common shares, advising such holders of the procedure for surrendering their shares to the exchange agent.

        Upon the surrender of CUB common shares (or affidavits of loss in lieu thereof), the holder will be entitled to receive in exchange therefor:

•

a number of whole shares of PacWest common stock that such holder is entitled to receive pursuant to the merger agreement, as described in "—Conversion of CUB Common Shares" above, evidenced by a stock certificate or in book-entry form; and



•

a check in the amount of the cash consideration for the surrendered shares and any cash payable in lieu of fractional shares plus any unpaid non-stock dividends and any other dividends or other distributions that such holder has the right to receive pursuant to the merger agreement.

Distributions with Respect to Unexchanged Shares

        All shares of PacWest common stock to be issued pursuant to the merger will be deemed issued and outstanding as of the effective time and if a dividend or other distribution is declared by PacWest in respect of the PacWest common stock, the record date for which is at or after the effective time, that declaration will include dividends or other distributions in respect of all shares issuable pursuant to the merger agreement. No dividends or other distributions in respect of PacWest common stock will be paid to any holder of any unsurrendered certificate or book-entry shares representing CUB common shares until such certificate (or affidavit of loss in lieu thereof) or book-entry shares are surrendered for exchange in accordance with the merger agreement. Subject to applicable laws, following surrender of any such certificate (or affidavit of loss in lieu thereof as provided) or book-entry shares, there will be issued and/or paid to the holder of the certificates representing whole shares of PacWest common stock issued in exchange therefor, without interest, (A) at the time of such surrender, the dividends or other distributions with a record date after the effective time theretofore payable with respect to such whole shares of PacWest common stock and not paid and (B) at the appropriate payment date, the dividends or other distributions payable with respect to such whole shares of PacWest common stock with a record date after the effective time but with a payment date subsequent to surrender.

Fractional Shares of PacWest Common Stock

        No fractional shares of PacWest common stock will be issued to any shareholder of CUB upon completion of the merger. For each fractional share that would otherwise be issued, PacWest will pay cash in an amount equal to the fraction of a share of PacWest common stock which the holder would otherwise be entitled to receive multiplied by the PacWest average closing price. No interest will be paid or accrue on cash payable to holders in lieu of fractional shares.

Representations and Warranties

        The merger agreement contains representations and warranties on the part of CUB as to, among other things:

•

organization, standing and authority;



•

capital stock;



•

the organization and existence of any subsidiaries;

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•

corporate power;



•

corporate authority;



•

no conflicts, third party consents and governmental and regulatory approvals required to complete the merger;



•

required filings;



•

availability, accuracy and compliance with GAAP of financial reports and filings with the SEC and regulatory authorities;



•

timely filing of required regulatory reports and absence of regulatory investigations or restrictive agreements with regulators;



•

absence of litigation;



•

compliance with restrictive agreements with regulators;



•

compliance with 12 U.S.C. § 1851 and the regulations promulgated thereunder, known as the Volcker Rule;



•

compliance with laws and permits;



•

material contracts;



•

no broker's or finder's fees, except as contemplated by the merger agreement;



•

employee benefit plans;



•

labor matters;



•

environmental matters;



•

tax matters;



•

interest rate risk management instruments, such as swaps and options;



•

proper and accurate maintenance of books and records;



•

insurance coverage;



•

validity and status of loans;



•

adequacy of its allowance for loan losses under established regulatory and accounting standards;



•

transactions with affiliates;



•

conditions of and title to real and personal property;



•

intellectual property; and



•

exemptions from takeover statutes.

        The merger agreement also contains representations and warranties on the part of PacWest as to, among other things:

•

organization, standing and authority;



•

capital stock;



•

corporate power;



•

corporate authority;

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•

no conflicts, third party consents and governmental and regulatory approvals required to complete the merger;



•

required filings;



•

availability, accuracy and compliance with GAAP and filings with the SEC and regulatory authorities;



•

absence of litigation;



•

absence of restrictive agreements with regulators;



•

compliance with laws and permits;



•

no broker's or finder's fees, except as contemplated by the merger agreement; and



•

tax matters.

        Certain of these representations and warranties are qualified as to "materiality" or "material adverse effect." For purposes of the merger agreement, a "material adverse effect" with respect to PacWest or CUB, as the case may be, means any effect, circumstance, occurrence or change that (i) is material and adverse to the business, assets or deposit liabilities, properties, operations, results of operations, or condition (financial or otherwise) of CUB and its subsidiaries or PacWest and its subsidiaries, as the case may be, or (ii) materially impairs the ability of such party to consummate the merger and the transactions contemplated by the merger agreement on a timely basis. However, none of the following effects, circumstances, occurrences or changes will be considered when determining if a material adverse effect has occurred:

•

any change in law or GAAP or interpretations thereof (except to the extent that such effect, circumstance, occurrence or change disproportionately adversely affects CUB and its subsidiaries or PacWest and its subsidiaries, as the case may be, compared to other companies of similar size and operating in the commercial banking industry in which such party operates, in which case only the disproportionate effect will be taken into account);



•

effects resulting from worsening of geopolitical conditions in the United States or acts of war, sabotage or terrorism (including any escalation or general worsening of any such acts of war, sabotage or terrorism) in the United States or any other country in which either party and any of its respective subsidiaries conduct material operations;



•

any change in market price or trading volume of CUB common shares or PacWest common stock (except that the facts or circumstances giving rise or contributing to such change may be deemed to constitute, or be taken into account in determining whether there has been, a material adverse effect, except to the extent such facts or circumstances are themselves excepted from the definition of material adverse effect pursuant to any other clause of the definition);



•

any action taken by either party with the other party's express written consent or any action taken by either party that such party was expressly required to take pursuant to the terms of the merger agreement, including, in the case of CUB, the repurchase of CUB's Series A preferred stock held by the U.S. Treasury Department pursuant to the merger agreement;



•

any failure, in and of itself, by CUB or PacWest to meet internal or other estimates, predictions, projections or forecasts of revenue, net income or any other measure of financial performance (except that the facts or circumstances giving rise or contributing to the failure to meet estimates or projections may be deemed to constitute, or be taken into account in determining whether there has been, a material adverse effect, except to the extent such facts or circumstances are themselves excepted from the definition of material adverse effect pursuant to any other clause of the definition);

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•

changes in economic conditions affecting commercial banks generally (except to the extent that such change in economic conditions disproportionately adversely affects CUB and its subsidiaries or PacWest and its subsidiaries, as the case may be, compared to other companies of similar size and operating in the commercial banking industry in which such party operates, in which case only the disproportionate effect will be taken into account;



•

for purposes of the conditions set forth in the merger agreement that there not be a material adverse effect on the other party since the date of the merger agreement, those matters disclosed in the PacWest disclosure schedules and CUB disclosure schedules, respectively, in each case, consistent with the standard set forth in the merger agreement and based on the information on those matters made available on or prior to the date of the merger agreement (except to the extent of any adverse developments with respect to such matters arising after the date of the merger agreement); or



•

changes in relationships with customers or employees of the respective parties and their respective subsidiaries that were primarily the result of the announcement or public disclosure of the merger agreement and the transactions contemplated thereby.

        The representations and warranties in the merger agreement do not survive the effective time and, as described below under the section entitled "Termination of the Merger Agreement," if the merger agreement is validly terminated, there will be no liability or damages arising under the representations and warranties of PacWest or CUB, or otherwise under the merger agreement, unless PacWest or CUB willfully and intentionally breached the merger agreement.

Conduct of Business Prior to the Completion of the Merger

        CUB has agreed that, prior to the effective time, except as approved in writing by PacWest, as expressly contemplated by the merger agreement or as required by law, CUB and its subsidiaries' respective businesses will be conducted in the ordinary and usual course and CUB and its subsidiaries will use its reasonable best efforts to preserve its business organizations and assets intact and maintain its rights, franchises, powers and privileges and its existing relations and goodwill with governmental authorities, customers, suppliers, distributors, creditors, lessors, employees and business associates and keep available the services of CUB and its subsidiaries' present employees and agents, and subject to the covenants relating to regulatory applications, as described under "Regulatory Matters" below, CUB and its subsidiaries will take no action that would reasonably be expected to adversely affect or materially delay CUB's ability to obtain any necessary approvals of any regulatory authorities or other governmental authority required for the transactions contemplated by the merger agreement or to perform their covenants and agreements under the merger agreement or to consummate the transactions contemplated by the merger agreement on a timely basis.

        In addition to the general covenants above, CUB has agreed that until the effective time, except as otherwise expressly required by the merger agreement or as required by law, or as PacWest may approve in writing (such approval not to be unreasonably withheld or delayed), subject to certain exceptions (including those set forth in CUB's disclosure schedules), CUB will not and will not permit its subsidiaries to:

Capital Stock

•

issue, sell, pledge, dispose of, encumber, permit to become outstanding or authorize the creation of any shares of capital stock or any rights, other than shares issuable in respect of options, restricted shares or RSUs outstanding on the date of the merger agreement or permitted to be granted thereby; or

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•

permit any shares of capital stock of CUB or any of its subsidiaries to become subject to grants of employee or director stock options, other rights or similar stock-based employee rights;

Dividends and Stock Repurchases

•

make, declare, pay or set aside for payment of dividends payable in cash, stock or property on or in respect of, or declare or make any distribution on, any shares of its capital stock except for dividends paid by any direct or indirect wholly owned subsidiary to CUB or to any other direct or indirect wholly owned subsidiary and except for dividends paid on CUB's Series A preferred stock in accordance with the terms thereof; or



•

directly or indirectly adjust, split, combine, redeem, reclassify, purchase or otherwise acquire any shares of its capital stock (other than the acquisition of CUB common shares from a holder of CUB equity awards in satisfaction of withholding obligations or in payment of the exercise price and other than the repurchase of CUB's Series A preferred stock held by the U.S. Treasury Department);

Compensation

•

enter into, renew, terminate, amend or otherwise modify any employment, retention, change in control, consulting, transition, termination, severance or similar agreement or arrangement with any director, officer, employee or consultant of such party or any of its subsidiaries, enter into any collective bargaining or similar agreement, pay or award, or commit to pay or award, any bonus or incentive compensation, grant any salary or wage increase or increase any employee compensation or benefit (including incentive or bonus payments) or forgive any loans or issue any loans to any employee or consultant of CUB, except (i) for increases in base salary or wage rates for employees who are not executive officers in the ordinary and usual course of business consistent with past practice, provided that no such increase for any employee shall result in an annual adjustment of more than three percent individually or in the aggregate, (ii) to the extent required by the terms of an existing benefit plan as in effect as of the date of the merger agreement or (iii) for other changes that are required by applicable law; or



•

grant or approve the grant of any new stock options or other equity-based awards or, except as provided in the merger agreement, amend or modify the terms of any outstanding stock options or equity-based awards;

Hiring

•

hire any person as an employee of CUB or any of its subsidiaries or engage any independent contractor or promote any employee, other than (i) persons hired or promoted to fill any vacancies arising on or after the date of the merger agreement and (ii) any person hired as an employee or any employee promoted to a position with an annual base salary or wage rate and target cash bonus opportunity of no more than $100,000 in the aggregate or any person engaged as an independent contractor with consulting fees and target cash bonus opportunity of no more than $150,000;

Benefit Plans

•

enter into, terminate, establish, adopt or amend any benefit plans or any other compensation plan, program, policy or arrangement for the benefit or welfare of any current or former director, officer, employee or consultant of CUB or any of its subsidiaries; or fund or in any other way secure the payment of any cash benefits, in each case, except to the extent required by applicable law or the terms of an existing benefit plan as in effect as of the date of the merger agreement;

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Dispositions

•

sell, transfer, lease, license, guarantee, mortgage, pledge, encumber or otherwise create any lien on, dispose of or discontinue any of its assets, deposits, business or properties (other than sales of loans and loan participations) except in the ordinary and usual course of business consistent with past practice and in a transaction that, together with all other such transactions, is not material to CUB and its subsidiaries, taken as a whole;

Acquisitions

•

acquire (other than by way of foreclosures or acquisitions of control in a bona fide fiduciary capacity or in satisfaction of debts previously contracted in good faith, in each case in the ordinary and usual course of business consistent with past practice) all or any portion of the assets, business, equity interests, deposits or properties of any other person (other than purchases of loans and loan participations as permitted by the terms of the merger agreement);

Mergers

•

merge or consolidate CUB or any of its subsidiaries with any other person, except for any such transaction among its wholly owned subsidiaries, or restructure, reorganize or completely or partially liquidate or otherwise enter into any agreements or arrangements imposing material changes or restrictions on its assets, operations or businesses;

Capital Expenditures

•

make any capital expenditures other than in accordance with CUB's budget as provided to PacWest;

Governing Documents

•

amend either the CUB articles of incorporation or bylaws, or the organizational documents of any of its subsidiaries;

Accounting Methods

•

implement or adopt any change in CUB's book or tax accounting principles, practices or methods, other than as may be required by GAAP, and as concurred by CUB's independent public accountants, or as required by the merger agreement; or



•

except as may be required by GAAP, and in the ordinary course of business consistent with past practice, revalue in any material respect any of its assets;

Contracts

•

except with respect to contracts relating to loans or loan participations made in the ordinary and usual course of business consistent with past practice, enter into, renew or allow to renew automatically, modify, amend or terminate, make any payment not then required under or waive, release or assign any material right or claim under, any material contract (as defined in the merger agreement) or any contract which would be a material contract if it were in existence on the date of the merger agreement in each case which is not terminable at will or with 30 calendar days or less notice without payment of any amount other than for products delivered or services performed through the date of termination;

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Claims

•

enter into any settlement, compromise or similar agreement with respect to any action, suit, proceeding, order or investigation to which CUB or any of its subsidiaries is or becomes a party after the date of the merger agreement, involving a payment by CUB or any subsidiary of an amount that exceeds $100,000 individually or $250,000 in the aggregate or would impose any material restriction on the business of the surviving corporation or create adverse precedent for claims that are reasonably likely to be material to CUB and its subsidiaries, taken as a whole;

Adverse Actions

•

take any action or omit to take any action that is intended to or would reasonably be likely to result in: (i) any of CUB's representations or warranties set forth in the merger agreement being or becoming untrue in any material respect at any time at or prior to the effective time; (ii) a condition to the merger not being satisfied; (iii) the merger being prevented or impeded from qualifying as a reorganization within the meaning of Section 368 of the Internal Revenue Code; or (iv) a material violation of any provision of the merger agreement, except as may be required by applicable law;

Risk Management

•

except as required by law or regulation: (i) implement or adopt any material change in its interest rate or other risk management policies, procedures or practices; (ii) fail to follow in all material respects CUB's or its applicable subsidiary's existing policies or practices with respect to managing its exposure to interest rate and other risk; or (iii) fail to use commercially reasonable efforts to avoid any material increase in CUB's aggregate exposure to interest rate risk;

Indebtedness

•

incur or modify any indebtedness for borrowed money or other liability (other than deposits, federal funds borrowings and borrowings from the Federal Home Loan Bank of San Francisco) or assume, guarantee, endorse or otherwise as an accommodation become responsible for the obligations of any other person;

Loans

•

forgive any loans to directors, officers or employees;



•

make any loan or loan commitment to any person which would, when aggregated with all outstanding loans or loan commitm