Exhibit 99.1

April 5, 2017

PacWest Bancorp

9701 Wilshire Boulevard, Suite 700

Beverly Hills, CA 90212

Ladies and Gentlemen:

As a holder of Company Common Shares (as defined below), the undersigned on behalf of [•] (the “Shareholder”) understands that CU Bancorp, a California corporation (the “Company”), and PacWest Bancorp, a Delaware corporation (“Parent”), are concurrently entering into an Agreement and Plan of Merger, dated as of April 5, 2017 (as it may be from time to time amended, the “Merger Agreement”), which was previously approved by the boards of directors of the Company and Parent, providing for, among other things, a merger of the Company with and into Parent (the “Merger”), in which each of the issued and outstanding common shares, no par value per share, of the Company (the “Company Common Shares”) (other than Excluded Shares and Dissenting Shares) will be converted into the right to receive the Merger Consideration. Terms used without definition in this letter agreement shall have the meanings ascribed thereto in the Merger Agreement.

The Shareholder acknowledges that, as an inducement for Parent to enter into the Merger Agreement, Parent has required that the Shareholder enter into this letter agreement and the Shareholder is willing to enter into this letter agreement.

The Shareholder confirms his or her agreement with Parent, and Parent confirms its agreement with the Shareholder, as follows:

1. As used in this letter agreement, “Shares” means the shares of the Company Common Shares which the Shareholder owns of record or beneficially and has the power to vote (for the avoidance of doubt, excluding any shares underlying options or restricted stock units exercisable for Company Common Shares whether or not such shares are included as beneficially owned by the Shareholder in the Company’s most recent annual proxy statement) as of the date of this letter agreement which are listed on Schedule I hereto. The Shares are owned by the Shareholder free and clear of all encumbrances, voting arrangements and commitments of every kind, except as would not restrict the performance of the Shareholder’s obligations under this Agreement. The Shareholder represents and warrants that the Shareholder has the sole or shared power to vote or direct the vote of all Shares.

2. Subject to paragraph 17 of this letter agreement, at every meeting of the shareholders of the Company called, and at every postponement, recess or adjournment thereof, and on every action or approval by written consent of the shareholders of the Company, the Shareholder agrees to vote, or cause to be voted, the Shares (a) in favor of (i) approval of the principal terms of the Merger Agreement and (ii) any other matter that is required to be approved by the shareholders of the Company to facilitate the transactions

contemplated by the Merger Agreement, (b) against (i) any proposal made in opposition to approval of the principal terms of the Merger Agreement or in competition with the Merger, (ii) any Acquisition Proposal and (iii) to the extent that any of the following actions requires a shareholder vote pursuant to applicable Law or any applicable stock exchange rules, any proposal, transaction, agreement, amendment of the Company’s articles of incorporation or by-laws or other action that is intended to or could reasonably be expected to prevent, impede, interfere with, delay, postpone or discourage consummation of the Merger and (c) as directed by Parent with respect to any postponement, recess, adjournment or other procedural matter at any meeting of the shareholders of the Company relating to any of the matters set forth in the foregoing clauses (a) or (b). Any such vote shall be cast (or consent shall be given) by the Shareholder in accordance with such procedures relating thereto so as to ensure that it is duly counted, including for purposes of determining that a quorum is present and for purposes of recording the results of such vote (or consent). The Shareholder hereby irrevocably and unconditionally waives, and agrees not to exercise, any rights of appraisal, any dissenters’ rights and any similar rights relating to the Merger that the Shareholder may directly or indirectly have by virtue of the ownership of any Shares if the Effective Time occurs.

3. The Shareholder hereby revokes any and all previous proxies granted with respect to the Shares. By entering into this letter agreement, subject to the last sentence of this paragraph 3, the Shareholder hereby grants, or agrees to cause the applicable record holder to grant, a revocable proxy appointing Parent, Matthew P. Wagner, Patrick Rusnak and Kori Ogrosky, and each of them, but each with full power of substitution, as the Shareholder’s attorney-in-fact and proxy, for and in the Shareholder’s name, to be counted as present, vote, express consent or dissent with respect to the Shares in the manner contemplated by paragraph 2 as such proxies or their proxies or substitutes shall, in their sole discretion, deem proper with respect to the Shares. The proxy granted by the Shareholder pursuant to this paragraph 3 is granted in consideration of Parent entering into this letter agreement and the Merger Agreement and incurring the obligations therein. If the Shareholder fails for any reason to be counted as present, consent or vote the Shares in accordance with the requirements of paragraph 2 (or anticipatorily breaches such paragraph), then Parent shall have the right to cause to be present, consent or vote the Shares in accordance with the provisions of paragraph 2. The proxy granted by the Shareholder shall be automatically revoked upon termination of this letter agreement in accordance with its terms.

4. The Shareholder represents and warrants (a) that the Shareholder has duly executed and delivered this letter agreement and has all authority and full legal capacity to enter into this letter agreement; (b) that, assuming the due authorization, execution and delivery of this letter agreement by Parent, this letter agreement is the Shareholder’s legal, valid and binding agreement and is enforceable against the Shareholder in accordance with its terms, except to the extent that enforceability may be limited by applicable bankruptcy, insolvency, moratorium or other similar laws affecting the enforcement of creditors’ rights generally and subject to the general principles of equity; and (c) that if the Shareholder is married and the Shares set forth next to such Shareholder’s name on Schedule I constitute community property under applicable Law, this letter agreement has been duly authorized, executed and delivered by, and constitutes the valid and binding agreement of, such Shareholder’s spouse, except to the extent that enforceability may be limited by applicable bankruptcy, insolvency, moratorium or other similar laws affecting the enforcement of creditors’ rights generally and subject to the general principles of equity.

-2-

5. The Shareholder further represents and warrants that the execution and delivery of this letter agreement by the Shareholder does not, and the performance of his or her obligations under this letter agreement and the consummation of the transactions to be consummated by him or her as contemplated hereby will not, (a) conflict with or violate any Law applicable to the Shareholder or by which the Shares are bound or affected, (b) result in any breach of or violation of, or constitute a default (or an event that with notice or lapse of time or both would become a default) under, or give to others any rights of termination, amendment, acceleration or cancellation of, or result in the creation of an encumbrance on any of the Shares pursuant to, any note, bond, mortgage, indenture, contract, agreement, lease, license, permit, franchise or other instrument or obligation to which the Shareholder is a party or by which the Shareholder or the Shares are bound or affected, or (c) require any consent, approval, authorization or permit of, or filing with or notification to, any court or arbitrator or any governmental entity, agency or official except for (i) applicable requirements, if any, of the Securities Exchange Act of 1934, as amended, and (ii) where the failure to obtain such consents, approvals, authorizations or permits, or to make such filings or notifications, would not prevent, impair, delay or adversely affect the performance by the Shareholder of his or her obligations under this letter agreement.

6. The Shareholder agrees that all representations, terms and conditions of this letter agreement will apply to Company Common Shares of which the Shareholder acquires record or beneficial ownership (and the power to vote) after the date hereof and prior to the termination of this letter agreement, whether upon the exercise of options, warrants or rights, the conversion or exchange of convertible or exchangeable securities, or by means of purchase, dividend, distribution, split-up, recapitalization, combination, exchange of shares or the like, gift, bequest, inheritance, or as a successor in interest in any capacity or otherwise.

7. This letter agreement and all obligations of the parties hereunder shall automatically terminate upon the earlier of (a) the Effective Time and (b) the termination of the Merger Agreement in accordance with its terms; provided, however, that (i) this paragraph 7 and paragraphs 11, 12, 13, 14, 15, 18, 20 and 21 hereof shall survive any such termination and (ii) such termination shall not relieve any party of any liability or damages resulting from any willful and intentional breach of this letter agreement occurring prior to such termination.

8. The Shareholder is entering into this letter agreement solely in his or her capacity as a record or beneficial owner of the Shares and nothing herein is intended to or shall limit or affect any actions taken by the Shareholder, solely in his or her capacity as a director or officer of the Company (or a Subsidiary of the Company), including any actions Shareholder deems necessary to discharge his or her fiduciary duties with respect to his or her role on the Company Board of Directors.

9. The Shareholder hereby authorizes Parent and the Company to publish and disclose in any announcement or disclosure in connection with the Merger the Shareholder’s identity and ownership of the Shares and the nature of the Shareholder’s obligations under this letter agreement.

-3-

10. The Shareholder agrees that, prior to the termination of this letter agreement, the Shareholder shall not take any action that would make any representation or warranty of the Shareholder contained herein untrue or incorrect or have the effect of preventing, impairing, delaying or adversely affecting the performance by the Shareholder of his or her obligations under this letter agreement other than to a de minimis extent. The Shareholder agrees, without further consideration, to execute and deliver such additional documents and to take such further actions as are reasonably necessary or reasonably requested by Parent to confirm and assure the rights and obligations set forth in this letter agreement.

11. THIS LETTER AGREEMENT SHALL BE DEEMED TO BE MADE IN AND IN ALL RESPECTS SHALL BE INTERPRETED, CONSTRUED AND GOVERNED BY AND IN ACCORDANCE WITH THE LAW OF THE STATE OF CALIFORNIA WITHOUT REGARD TO THE CONFLICT OF LAW PRINCIPLES THEREOF. The parties hereby irrevocably submit to the jurisdiction of the courts of the State of California and the federal courts of the United States of America located in the State of California solely in respect of the interpretation and enforcement of the provisions of this letter agreement and of the documents referred to in this letter agreement, and in respect of the transactions contemplated hereby, and hereby waive, and agree not to assert, as a defense in any action, suit or proceeding for the interpretation or enforcement hereof or of any such documents, that he or she is not subject thereto or that such action, suit or proceeding may not be brought or is not maintainable in said courts or that the venue thereof may not be appropriate or that this letter agreement or any such document may not be enforced in or by such courts, and the parties hereto irrevocably agree that all claims with respect to such action or proceeding shall be heard and determined in such a California State or federal court. The parties hereby consent to and grant any such court jurisdiction over the person of such parties and over the subject matter of such dispute and agree that mailing of process or other papers in connection with any such action or proceeding in the manner provided in paragraph 13 or in such other manner as may be permitted by Law shall be valid and sufficient service thereof.

12. The parties to this letter agreement acknowledge and agree that any controversy which may arise under this letter agreement and the other documents referred to in this letter agreement and in respect of the transactions contemplated hereby and thereby, is likely to involve complicated and difficult issues and, therefore, each such party irrevocably and unconditionally waives any right it may have to a trial by jury in respect of any legal action arising out of or relating to this letter agreement and the other documents referred to in this letter agreement, and in respect of the transactions contemplated hereby and thereby. The parties to this letter agreement certify and acknowledge that (a) such party has not represented, expressly or otherwise, that such party would not seek to enforce the foregoing waiver in the event of a legal action, (b) such party has considered the implications of this waiver, (c) such party makes this waiver voluntarily and (d) such party has been induced to enter into this letter agreement by, among other things, the mutual waivers and certifications in this paragraph 12.

-4-

13. Any notice, request, instruction or other document to be given hereunder by either party to the other shall be in writing and delivered personally or sent by registered or certified mail, postage prepaid, by facsimile or by overnight courier addressed, if to the Shareholder, to the address or facsimile number, as applicable, set forth in Schedule I hereto, and, if to Parent, in accordance with Section 8.07 of the Merger Agreement, or to such other persons or addresses as may be designated in writing by the party to receive such notice as provided above.

14. This letter agreement shall not be assignable by operation of law or otherwise. Any purported assignment in violation of this letter agreement is void.

15. The Shareholder recognizes and acknowledges that a breach of any covenants or agreements contained in this letter agreement will cause Parent to sustain damages for which it would not have an adequate remedy at law for money damages, and therefore the Shareholder agrees that in the event of any such breach, Parent shall be entitled to specific performance of such covenants and agreements and injunctive and other equitable relief in addition to any other remedy to which Parent may be entitled, at law or in equity. It is accordingly agreed that Parent shall be entitled to an injunction or injunctions to prevent breaches of this letter agreement and to enforce specifically the terms and provisions of this letter agreement in any court of the United States or any state having jurisdiction.

16. The effectiveness of this letter agreement shall be conditioned upon the execution and delivery of the Merger Agreement by the parties thereto, which shall occur concurrently herewith.

17. The Shareholder agrees, prior to termination of this letter agreement, not to (i) offer for sale, sell, transfer, tender, pledge, encumber, assign or otherwise dispose of, or enter into any contract, option or other arrangement or understanding with respect to, or consent to the offer for sale, sale, transfer, tender, pledge, encumbrance, assignment or other disposition of any of the Shares or (ii) except as set forth herein, enter into any voting arrangement, whether by proxy, voting agreement, voting trust or otherwise, with respect to any of the Shares, and shall not commit or agree to take any of the foregoing actions; provided that the foregoing shall not prohibit the Shareholder from (a) disposing of or surrendering Shares to the Company in connection with the vesting, settlement or exercise of Company Options, Company Restricted Shares or Company RSUs for the payment of taxes thereon or, in respect of Company Options, the exercise price thereon or (b) disposing of Shares in a broker-assisted cashless exercise of Company Options expiring during the term of this letter agreement up to the amount necessary to pay the exercise price in respect thereof and any related taxes. In furtherance of the foregoing, the Shareholder hereby authorizes and instructs the Company to instruct its transfer agent to enter a stop transfer order with respect to all of the Shares.

18. Parent acknowledges and agrees that nothing in this letter agreement shall be deemed to vest in Parent any direct or indirect ownership or incidence of ownership of or with respect to any Shares. All rights, ownership and economic benefits of and relating to the Shares shall remain vested in and belong to the Shareholder, and Parent shall have no authority to manage, direct, superintend, restrict, regulate, govern or administer any of the policies or operations of the Company or exercise any power or authority to direct the Shareholder in the voting of any of the Shares, except as otherwise expressly provided herein.

-5-

19. Any provision of this letter agreement may be (i) waived in whole or in part in writing by the party benefited by the provision or by both parties or (ii) amended or modified at any time by an agreement in writing between the parties hereto executed in the same manner as this letter agreement.

20. The Merger Agreement and this letter agreement (including the documents and instruments referred to herein) constitute the entire agreement among the parties hereto with respect to the subject matter hereof, and supersede all other prior agreements and understandings, both written and oral, between the parties, with respect to the subject matter hereof.

21. In the event that any provision of this letter agreement, or the application thereof, becomes or is declared by a court of competent jurisdiction to be illegal, void or unenforceable, the remainder of this letter agreement will continue in full force and effect and the application of such provision to other persons or circumstances will be interpreted so as reasonably to effect the intent of the parties hereto. The parties further agree to replace such void or unenforceable provision of this letter agreement with a valid and enforceable provision that will achieve, to the extent possible, the economic, business and other purposes of such void or unenforceable provision.

-6-

Please confirm that the foregoing correctly states the understanding between the undersigned and you by signing and returning to a counterpart hereof.

[Signature Page to Voting Agreement]

Accepted and agreed as of the date set forth above.

[Signature Page to Voting Agreement]

Schedule I: Shareholder Information