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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 Cgamma2, 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 Cgamma2 by collagen stimulation is absent in mice lacking the Fc receptor gamma-chain. Tyrosine phosphorylation of phospholipase Cgamma2 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 Fc receptor gamma-chain or Syk is accompanied by a loss of secretion and 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.

Original publication




Journal article



Publication Date





2333 - 2341


Animals, Arachidonic Acid, Bleeding Time, Collagen, Enzyme Precursors, Intracellular Signaling Peptides and Proteins, Isoenzymes, Mice, Mice, Inbred C57BL, Phenotype, Phospholipase C gamma, Phosphorylation, Platelet Activation, Platelet Aggregation, Platelet Count, Protein-Tyrosine Kinases, Receptors, IgG, Serotonin, Signal Transduction, Syk Kinase, Thrombin, Type C Phospholipases, Tyrosine