Required role of focal adhesion kinase (FAK) for integrin-stimulated cell migration

FAK localizes to sites of transmembrane integrin receptor clustering and fa cilitates intracellular signaling events. FAK-null (FAK(-)) fibroblasts exh ibit a rounded morphology, defects in cell migration, and an elevated numbe r of cell-substratum contact sites. Here we show that stable re-expression of epitope-tagged FAK reversed the morphological defects of the FAK- cells through the dynamic regulation of actin structures and focal contact sites in fibronectin (FN) stimulated cells. FAK re-expressing fibroblasts (clones DA2 and DP3) exhibit a characteristic fibrillar shape and display indistin guishable FN receptor-stimulated migration properties compared to normal fi broblasts. Expression of various FAK mutants in the FAK(-) cells showed tha t FAK kinase activity, the Tyr-397/SH2 domain binding site, and the first p roline-rich SH3 binding region in the FAK C-terminal domain were individual ly needed to promote full FAK-mediated FAK cell migration to FN whereas dir ect paxillin binding to FAK was not required. Expression of the FAK Phe-397 mutant did not promote FAK- cell migration and overexpression of p50(csk) in DA2 cells inhibited migration to FN suggesting that Src-family PTKs play important roles in FAK-mediated motility events, Expression of the FAK C-t erminal domain, FRNK, promoted FAK dephosphorylation at Tyr-397 and potentl y blocked FAK-mediated cell migration. This dominant-negative effect of FRN K was reversed by a point mutation (Leu-1034 to Ser) which prevented FRNK l ocalization to focal contact sites. Our results show that FAK functions as a key regulator of fibronectin receptor stimulated cell migration events th rough the recruitment of both SH2 and SH3 domain-containing signaling prote ins to sites of integrin receptor clustering.