A collagen-like peptide stimulates tyrosine phosphorylation of syk and phospholipase

Activation of platelets by collagen is mediated through a PLCg2. Protein tyrosine phosphorylation induced by CRP is tyrosine kinase-dependent pathway that is associated with not altered in the absence of Mg2 " or the presence of mono-phosphorylation of the Fc receptor g chain, the tyrosine ki- clonal antibodies (MoAbs) to the integrin a2b1 (MoAb 6F1 nase syk, and phospholipase Cg2 (PLCg2). We recently de- and MoAb 13), conditions that prevent the interaction of scribed a collagen-related triple-helical peptide (CRP) with collagen with the integrin. In contrast, phosphorylation of the sequence GCP*(GPP*)GCP*G (single letter amino acid syk and PLCg2 by collagen is partially reduced by MoAb 6F1 code: P * ! hydroxyproline; Morton et al, Biochem J 306:337, and MoAb 13 or by removal of Mg2". This may reflect a 1995). The cross-linked peptide is a potent stimulus of plate- direct role of a2b1 in collagen-induced signaling events or let activation but, unlike collagen, does not support a2b1- an indirect role in which the integrin facilitates the binding mediated, Mg2"-dependent adhesion, suggesting that its of collagen to its signaling receptor. The results show an action is independent of the integrin a2b1. This finding sug- a2b1-independent pathway of platelet activation by CRP that gests the existence of a platelet receptor other than a2b1 involves phosphorylation of syk and PLCg2. This pathway that underlies activation. In the present study, we show that appears to contribute to platelet activation by collagen. CRP stimulates tyrosine phosphorylation of the same pat-q 1997 by The American Society of Hematology