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Molecular and Cellular Biology, November 1999, p. 7870-7885, Vol. 19, No. 11
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Biological and Regulatory Properties of Vav-3, a New Member of the Vav Family of Oncoproteins

Nieves Movilla and Xosé R. Bustelo*

Department of Pathology, State University of New York at Stony Brook, University Hospital, Stony Brook, New York 11794-7025

Received 23 February 1999/Returned for modification 19 April 1999/Accepted 6 July 1999

We report here the identification and characterization of a novel Vav family member, Vav-3. Signaling experiments demonstrate that Vav-3 participates in pathways activated by protein tyrosine kinases. Vav-3 promotes the exchange of nucleotides on RhoA, on RhoG and, to a lesser extent, on Rac-1. During this reaction, Vav-3 binds physically to the nucleotide-free states of those GTPases. These functions are stimulated by tyrosine phosphorylation in wild-type Vav-3 and become constitutively activated upon deletion of the entire calponin-homology region. Expression of truncated versions of Vav-3 leads to drastic actin relocalization and to the induction of stress fibers, lamellipodia, and membrane ruffles. Moreover, expression of Vav-3 alters cytokinesis, resulting in the formation of binucleated cells. All of these responses need only the expression of the central region of Vav-3 encompassing the Dbl homology (DH), pleckstrin homology (PH), and zinc finger (ZF) domains but do not require the presence of the C-terminal SH3-SH2-SH3 regions. Studies conducted with Vav-3 proteins containing loss-of-function mutations in the DH, PH, and ZF regions indicate that only the DH and ZF regions are essential for Vav-3 biological activity. Finally, we show that one of the functions of the Vav-3 ZF region is to work coordinately with the catalytic DH region to promote both the binding to GTP-hydrolases and their GDP-GTP nucleotide exchange. These results highlight the role of Vav-3 in signaling and cytoskeletal pathways and identify a novel functional cross-talk between the DH and ZF domains of Vav proteins that is imperative for the binding to, and activation of, Rho GTP-binding proteins.

* Corresponding author. Mailing address: Department of Pathology, State University of New York, University Hospital, Level 2, Rm. 718-B, Stony Brook, NY 11794-7025. Phone: (516) 444-3478. Fax: (516) 444-3419. E-mail: xbustelo{at}path.som.sunysb.edu.

Molecular and Cellular Biology, November 1999, p. 7870-7885, Vol. 19, No. 11
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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