T-CELL RECEPTOR-MEDIATED AND BETA-1 INTEGRIN-MEDIATED SIGNALS SYNERGIZE TO INDUCE TYROSINE PHOSPHORYLATION OF FOCAL ADHESION KINASE (PP125(FAK)) IN HUMAN T-CELLS

The beta(1) subfamily of integrins is thought to play an important role in both the adhesion/migration and proliferation/differentiation of T cells. beta(1) integrins can provide T cell costimulation through interaction of very late antigen (VLA) 4 (VLA-4) (alpha(4) beta(1)) and VLA-5 (alpha(5) beta(1)) 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 beta(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 pp125(FAK) by beta(1) integrin engagement and, most recently, indicate a role for pp125(FAK) 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 pp125(FAK) 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 oi pp125(FAK) by the T cell receptor (TCR)-CD3 antigen complex and beta(1) integrins, and provide the first account, in any cell type, of integrin alpha(4) beta(1)-mediated pp125(FAK) tyrosine phosphorylation. We demonstrate a rapid and sustained synergistic increase in tyrosine phosphorylation of human pp125(FAK) in Jurkat T cells after simultaneous (a) triggering of the TCR-CD3 complex, and (b) alpha(4) beta(1) and alpha(5) beta(1) integrin-mediated binding of these cells to immobilized FN or alpha(4) beta(1) integrin-mediated binding to immobilized VCAM-1. Studies with normal peripheral blood-derived CD4(+) human T blasts confirm the synergistic action of a TCR-CD3 complex-mediated costimulus with a FN- or VCAM-1-dependent signal in the induction of T cell pp125(FAK) tyrosine phosphorylation. In vitro kinase assays performed on pp125(FAK) immunoprecipitates isolated from Jurkat cells and normal CD4(+) T cells identified a coprecipitating 57-kD tyrosine-phosphorylated protein (pp57), distinct from pp59(fyn) or pp56(lde). These results indicate, for the first time, the involvement of a specific kinase, pp125(FAK), alpha(4) beta(1)- and alpha(5) beta(1)-mediated T cell-costimulatory signaling pathways. In addition, the data demonstrate novel regulation of pp125(FAK) tyrosine phosphorylation by the TCR-CD3 complex.