Evidence for the involvement of p59(fyn) and p53/56(lyn) in collagen receptor signalling in human platelets

The binding of collagen to platelet glycoprotein VI (GPVI) leads to the sub sequent activation of phospholipase C gamma 2 through a pathway that is dep endent on the Fc receptor gamma (FcR gamma) chain and the tyrosine kinase p 72(svk). We have investigated the role of platelet Src-family kinases in th is signalling pathway. The selective Src-family kinase inhibitor PP1 preven ted collagen-stimulated increases in whole-cell tyrosine phosphorylation an d tyrosine phosphorylation of the FcR gamma chain and p72(syk). A similar s et of observations was made for a collagen-related peptide (CRP), which bin ds to GPVI but not to the integrin alpha(2)beta(1) (GPIa/IIa). These effect s were seen at a concentration of PP1 that inhibited platelet aggregation, dense granule release and Ca2+ mobilization induced by CRP, but not aggrega tion and Ca2+ mobilization mediated by the G-protein-coupled receptor agoni st thrombin. After stimulation by CRP or collagen, the Src-family kinases p 59(fyn) and p53/56(lyn) became associated with several tyrosine-phosphoryla ted proteins including the FcR gamma chain. This was not true of the other platelet Src-family kinases, The association between the FcR gamma chain an d p59(fyn) was also seen under basal conditions, and was stable only in the weak detergent Brij96 but not in Nonidet P40, suggesting a non-SH2-depende nt interaction. These results provide strong evidence for the involvement o f p59(fyn) and p53/56(lyn) in signalling via GPVI, with p59(fyn) possibly a cting upstream of FcR gamma chain phosphorylation.