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Vol. 16, Issue 7, 3223-3235, July 2005
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1



* Department of Immunology, Centro de Investigaciones Biológicas, CSIC, 28006 Madrid, Spain;
Department of Immunology and Oncology, Centro Nacional de Biotecnología, CSICPfizer, 28049 Madrid, Spain; and
Centro de Investigación del Cáncer, CSIC, 37007 Salamanca, Spain
Submitted December 3, 2004;
Accepted April 27, 2005
Monitoring Editor: Mark Ginsberg
The chemokine CXCL12 promotes T lymphocyte adhesion mediated by the integrin
4
1. CXCL12 activates the GTPase Rac, as well as Vav1, a guanine-nucleotide exchange factor for Rac, concomitant with up-regulation of
4
1-dependent adhesion. Inhibition of CXCL12-promoted Rac and Vav1 activation by transfection of dominant negative Rac or Vav1 forms, or by transfection of their siRNA, remarkably impaired the increase in T lymphocyte attachment to
4
1 ligands in response to this chemokine. Importantly, inhibition of Vav1 expression by RNA interference resulted in a blockade of Rac activation in response to CXCL12. Adhesions in flow chambers and soluble binding assays using these transfectants indicated that initial ligand binding and adhesion strengthening mediated by
4
1 were dependent on Vav1 and Rac activation by CXCL12. Finally, CXCL12-promoted T-cell transendothelial migration involving
4
1-mediated adhesion was notably inhibited by expression of dominant negative Vav1 and Rac. These results indicate that activation of Vav1-Rac signaling pathway by CXCL12 represents an important inside-out event controlling efficient up-regulation of
4
1-dependent T lymphocyte adhesion.
Abbreviations used: VCAM-1, vascular cell adhesion molecule-1; GTPase, guanosine triphosphate-binding proteins; GEF, guanine nucleotide exchange factor.
The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).
Present address: Theodor Kocher Institute, University of Bern, Freiestrasse 1, 3012 Bern, Switzerland.
Address correspondence to: Joaquin Teixidó (joaquint{at}cib.csic.es).
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