Focal adhesion kinase regulates β₁ integrin-dependent T cell migration through an HEF1 effector pathway

Although β₁ integrin-dependent T cell migration is required for immune function, little is known of the signaling pathways regulating this migration. We now show that the cytoplasmic tyrosine kinase, focal adhesion kinase (FAK) plays an essential role in the β₁ integrin-stimulated migration of T cells through regulation of the unique Crk-associated substrate (Cas) family docking protein, human enhancer of filamentation 1 (HEF1) and effects on "outside-in" β₁ integrin signaling. Overexpression of wild-type FAK promoted β₁ integrin-dependent Jurkat T cell migration, whereas FAK mutated in either its autophosphorylation site or proline rich region 1 (PR1)/HEF1 SH3 domain-binding site had a dominant negative effect on migration. In contrast, neither wild-type nor mutant FAK affected Jurkat cell adhesion to fibronectin, a β₁ integrin ligand. The migration of FAK-overexpressing cells directly correlated with the β₁ integrin-inducible tyrosine phosphorylation of endogenous plus wild-type exogenous FAK, and not with phosphorylation of the FAK-related kinase, Pyk2. FAK was also found to regulate both HEFl -promoted migration, and HEF1 tyrosine phosphorylation in β₁ integrin-stimulated cells, in a manner dependent upon the FAK autophosphorylation and PR1 sites, and HEF1 SH3 domain. Together, our results indicate that β₁ integrin-stimulated T cell migration requires a linear β₁ integrin-FAK-HEF1 affector pathway.