HUMAN PLATELETS ACTIVATION BY CONVULXIN IS ACCOMPANIED BY TYROSYL-PHOSPHORYLATION OF PLC-GAMMA-2 AND OCCURS INDEPENDENTLY OF INTEGRIN ALPHA(IIB)BETA(3)

In the present report we show that convulxin (Cvx), a C-type lectin fr om Crotalus durissus terrificus venom, induces platelet agregation and phospholipase C (PLC) activation by a protein tyrosine kinase (PTK)-d ependent pathway. In addition, Cvx stimulates a rapid increase in tyro sine phosphorylation of human platelet proteins with molecular masses of 40, 72/74, 78/80 and 120kDa, followed by dephosphorylation of some proteins. However, platelet aggregation was accompanied by the phospho rylation of a 105-kDa molecular mass protein. Furthermore, Cvx stimula tes a rapid-tyrosyl phosphorylation of a 145-kDa protein that was iden tified as PLC gamma 2. Protein tyrose phosphatase (PTP) induced by Cvx was not blocked when platelets were stimulated in the presence of ind omethacin, apyrase, EDTA or PODS peptide, but inhibited by staurospori ne and genistein. These results indicate that PTP is chronologically p roximal to Cvx binding to platelets, and it is independent of platelet aggregation or fibrinogen binding to integrin alpha(IIb)beta(3). On t he other hand, the dephosphorylation step, and the phosphorylation of the 105-kDa protein, were both inhibited by PODS and EDTA, which sugge sts that the integrin alpha(IIb)beta(3) is involved in these steps. Ou r results, taken together, show that Cvx induces platelet aggregation in a similar manner as collagen and collagen-related peptides that als o trigger platelet aggregation by a PTK-dependent pathway, and stimula te tyrosyl-phosphorylation of PLC gamma 2. However, Cvx is unique amon g platelet receptor agonists, because under test-tube stirring conditi ons it induces a PTP profile independently of integrin alpha(IIb)beta( 3).