Selective association of the tyrosine kinases Src, Fyn, and Lyn with integrin-rich actin cytoskeletons of activated, nonaggregated platelets

Integrin-mediated interactions between cytoskeletal proteins and extracellular fibrinogen are required for platelet adhesion. We have previously demonstrated that the major platelet integrin, α(IIb),β₃, becomes incorporated into the actin cytoskeleton of platelets in an activation-dependent, aggregation-independent manner. To determine if regulatory molecules are also associated with these integrin-rich cytoskeletal complexes, we examined actin cytoskeletons for the presence of kinases and phosphoproteins. Western immunoblot analysis revealed that the tyrosine kinases Src, Fyn, and Lyn are specifically associated with actin cytoskeletons of activated, nonaggregated platelets. However, as noted by others, the cytoskeletal association of focal adhesion kinase depends on platelet aggregation. Actin cytoskeletons isolated from ³²P-labeled platelets also contain a number of phosphorylated proteins. Interestingly, an ~18-kDa phosphoprotein was uniquely present in activated platelet cytoskeletons. Collectively, our results demonstrate that actin cytoskeletons of activated, nonaggregated platelets contain not only integrins, but also kinases and phosphoproteins that could regulate platelet adhesion and transmembrane communication.