The Fc receptor gamma-chain and the tyrosine kinase Syk are essential for activation of mouse platelets by collagen

Activation of mouse platelets by collagen is associated with tyrosine phosphorylation of multiple proteins including the Fc receptor gamma-chain, the tyrosine kinase Syk and phospholipase C gamma 2, suggesting that collagen signals in a manner similar to that of immune receptors, This hypothesis has been tested using platelets from mice lacking the Fc receptor gamma-chain or Syk, Tyrosine phosphorylation of Syk and phospholipase C gamma 2 by collagen stimulation is absent in mice lacking the Fe receptor gamma-chain, Tyrosine phosphorylation of phospholipase C gamma 2 by collagen stimulation is also absent in mice platelets which lack Syk, although phosphorylation of the Fc receptor gamma-chain is maintained, In contrast, tyrosine phosphorylation of platelet proteins by the G protein-coupled receptor agonist thrombin is maintained in mouse platelets deficient in Fc receptor gamma-chain or Syk, The absence of Fe receptor gamma-chain or Syk is accompanied by a loss of secretion rind aggregation responses in collagen- but not thrombin-stimulated platelets, These observations provide the first direct evidence of an essential role for the immunoreceptor tyrosine-based activation motif (ITAM) in signalling by a non-immune receptor stimulus.