Positive And Negative Regulation By Slp-76/Adap And Pyk2 Of Chemokine-Stimulated T-Lymphocyte Adhesion Mediated By Integrin Alpha 4 Beta 1

Stimulation by chemokines of integrin alpha 4 beta 1-dependent T-lymphocyte adhesion is a crucial step for lymphocyte trafficking. The adaptor Vav1 is required for chemokine-activated T-cell adhesion mediated by alpha 4 beta 1. Conceivably, proteins associating with Vav1 could potentially modulate this adhesion. Correlating with activation by the chemokine CXCL12 of T-lymphocyte attachment to alpha 4 beta 1 ligands, a transient stimulation in the association of Vav1 with SLP-76, Pyk2, and ADAP was observed. Using T-cells depleted for SLP-76, ADAP, or Pyk2, or expressing Pyk2 kinase-inactive forms, we show that SLP-76 and ADAP stimulate chemokine-activated, alpha 4 beta 1-mediated adhesion, whereas Pyk2 opposes T-cell attachment. While CXCL12-promoted generation of high-affinity alpha 4 beta 1 is independent of SLP-76, ADAP, and Pyk2, the strength of alpha 4 beta 1-VCAM-1 interaction and cell spreading on VCAM-1 are targets of regulation by these three proteins. GTPase assays, expression of activated or dominant-negative Rac1, or combined ADAP and Pyk2 silencing indicated that Rac1 activation by CXCL12 is a common mediator response in SLP-76-, ADAP-, and Pyk2-regulated cell adhesion involving alpha 4 beta 1. Our data strongly suggest that chemokine-stimulated associations between Vav1, SLP-76, and ADAP facilitate Rac1 activation and alpha 4 beta 1-mediated adhesion, whereas Pyk2 opposes this adhesion by limiting Rac1 activation.