Evidence for the involvement of p59fyn and p53/56lyn in collagen receptor signalling in human platelets

The binding of collagen to platelet glycoprotein VI (GPVI) leads to the subsequent activation of phospholipase C gamma 2 through a pathway that is dependent on the Fc receptor gamma (FcR gamma) chain and the tyrosine kinase p72(svk). We have investigated the role of platelet Src-family kinases in this signalling pathway. The selective Src-family kinase inhibitor PP1 prevented collagen-stimulated increases in whole-cell tyrosine phosphorylation and tyrosine phosphorylation of the FcR gamma chain and p72(syk). A similar set of observations was made for a collagen-related peptide (CRP), which binds to GPVI but not to the integrin alpha(2)beta(1) (GPIa/IIa). These effects were seen at a concentration of PP1 that inhibited platelet aggregation, dense granule release and Ca2+ mobilization induced by CRP, but not aggregation and Ca2+ mobilization mediated by the G-protein-coupled receptor agonist thrombin. After stimulation by CRP or collagen, the Src-family kinases p59(fyn) and p53/56(lyn) became associated with several tyrosine-phosphorylated proteins including the FcR gamma chain. This was not true of the other platelet Src-family kinases, The association between the FcR gamma chain and 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-dependent interaction. These results provide strong evidence for the involvement of p59(fyn) and p53/56(lyn) in signalling via GPVI, with p59(fyn) possibly acting upstream of FcR gamma chain phosphorylation.