PLATELET-ADHESION TO COLLAGEN VIA THE ALPHA(2)BETA(1) INTEGRIN UNDER ARTERIAL FLOW CONDITIONS CAUSES RAPID TYROSINE PHOSPHORYLATION OF PP125(FAK)

Adhesion of human platelets to collagen under arterial flow conditions mediated by the alpha2beta1 integrin increased tyrosine phosphorylati on of several proteins, one of which was the focal adhesion tyrosine k inase, pp125FAK. Tyrosine phosphorylation of pp125FAK did not occur in non-adherent flowing platelets or in platelets attached to poly(L-lys ine). Neither adhesion nor tyrosine phosphorylation was affected by pr etreatment of platelets with GRGDSP peptide or by anti-alpha(IIb)beta3 monoclonal antibody P2. Adherent platelets retained their discoid sha pe, suggesting that induction of pp125FAD precedes platelet spreading. The tyrosine kinase inhibitor erbstatin decreased tyrosine phosphoryl ation in non-stimulated platelets and blocked platelet adhesion. These results suggest that pp125FAK plays an important role in platelet adh esion to collagen via the alpha2beta1 integrin.