Human platelets activation by convulxin is accompanied by tyrosyl-phosphorylation of PLCγ2 and occurs independently of integrin α(IIb)β₃

In the present report we show that convulxin (Cvx), a C-type lectin from Crotalus durissus terrificus venom, induces platelet agregation and phospholipase C (PLC) activation by a protein tyrosine kinase (PTK)-dependent pathway. In addition, Cvx stimulates a rapid increase in tyrosine phosphorylation of human platelet proteins with molecular masses of 40, 72/74, 78/80 and 120 kDa, followed by dephosphorylation of some proteins. However, platelet aggregation was accompanied by the phosphorylation of a 105-kDa molecular mass protein. Furthermore, Cvx stimulates a rapid-tyrosyl phosphorylation of a 145-kDa protein that was identified as PLCγ2. Protein tyrose phosphatase (PTP) induced by Cvx was not blocked when platelets were stimulated in the presence of indomethacin, apyrase, EDTA or RGDS peptide, but inhibited by staurosporine and genistein. These results indicate that PTP is chronologically proximal to Cvx binding to platelets, and it is independent of platelet aggregation or fibrinogen binding to integrin α(IIb)β₃. On the other hand, the dephosphorylation step, and the phosphorylation of the 105-kDa protein, were both inhibited by RGDS and EDTA, which suggests that the integrin α(IIb)β₃ is involved in these steps. Our results, taken together, show that Cvx induces platelet aggregation in a similar manner as collagen and collagen-related peptides that also trigger platelet aggregation by a PTK-dependent pathway, and stimulate tyrosyl-phosphorylation of PLCγ2. However, Cvx is unique among platelet receptor agonists, because under test-tube stirring conditions it induces a PTP profile independently of integrin α(IIb)β₃.