T Cell Receptor - and Ri Integrin - mediated Signals Synergize to Induce Tyrosine Phosphorylation of Focal Adhesion Kinase ( pp 125 FAK ) in Human T Cells

The R1 subfamily of integrins is thought to play an important role in both the adhesion/migration and proliferation/differentiation of T cells . Rl integrins can provide T cell costimulation through interaction of very late antigen (VLA) 4 (VLA-4) (a4R1) and VLA-5 («.Rl) with the extracellular matrix protein fibronectin (FN), or by VLA-4 binding to its cell surface ligand, vascular cell adhesion molecule (VCAM) 1 . The mechanism by which R 1 integrin members transduce T cell-costimulatory signals is poorly understood . Studies in non-T cells have demonstrated regulation of the tyrosine focal adhesion kinase pp125FAK by R1 integrin engagement and, most recently, indicate a role for pp125FAK in linking integrin-mediated signal transduction to the Ras pathway (Schaller, M. D ., and J . T . Parsons . 1994 . Curr . Opin . Cell . Biol . 6 : 705-710 ; Schlaepfer, D . D., S . K. Hanks, T. Hunter, and P . Van der Geer . 1994 . Nature (Lond.) . 372:786-790) . Although pp125FAK kinase occurs in T cells, there are no reports on its regulation in this cell type . The studies described in this article characterize novel regulation of pp125FAK by the T cell receptor (TCR)-CD3 antigen complex and R1 integrins, and provide the first account, in any cell type, of integrin ct4 (3 1-mediated pp125FAK tyrosine phosphorylation . We demonstrate a rapid and sustained synergistic increase in tyrosine phosphorylation of human pp125FAK in Jurkat T cells after simultaneous (a) triggering of the TCR-CD3 complex, and (b) x 4 (3 1 and 041 integrin-mediated binding of these cells to immobilized FN or et 4R ] integrin-mediated binding to immobilized VCAM-1. Studies with normal peripheral blood-derived CD4+ human T blasts confirm the synergistic action ofa TCR-CD3 complex-mediated costimulus with a FNor VCAM-1-dependent signal in the induction of T cell pp125FAK tyrosine phosphorylation . In vitro kinase assays performed on pp125FAK immunoprecipitates isolated from Jurkat cells and normal CD4+ T cells identified a coprecipitating 57-kD tyrosinephosphorylated protein (pp57), distinct from pp59fy" or pp56'1k . These results indicate, for the first time, the involvement of a specific kinase, pp125FAK in a4R1 and a5Rt-mediated T cellcostimulatory signaling pathways . In addition, the data demonstrate novel regulation of pp125FAK tyrosine phosphorylation by the TCR-CD3 complex .