CAMP DOES NOT INHIBIT CONVULXIN-INDUCED TYROSYL-PHOSPHORYLATION OF HUMAN PLATELET PROTEINS, INCLUDING PLC-GAMMA-2, BUT COMPLETELY BLOCKS THE INTEGRIN ALPHA(IIB)BETA(3)-DEPENDENT DEPHOSPHORYLATION STEP - COMPARISONS WITH RGDS PEPTIDE, CYTOCHALASIN-D, AND PHENYLARSINE OXIDE

Convulxin (Cvx) isolated from Crotalus durissus terrificus venom, indu ces platelet aggregation, phospholipase C (PLC) activation, and tyrosy l-phosphorylation (PTP) of multiple proteins, including PLC gamma 2 by a mechanism independent of integrin alpha(IIb)beta(3). However, PTP i nduced by Cvx is followed by a dephosphorylation step in a platelet ag gregation-dependent manner. Here we show that increasing intraplatelet content of cAMP with forskolin is associated with the inhibition of C vx-induced platelet aggregation, ATP secretion, and inositol-phosphate s production. However, the early onset of Cvx-induced PTP is not sensi tive to cAMP (including PLC gamma 2), and it also occurs in the presen ce of integrin alpha(IIb)beta(3)-antagonist (RGDS peptide, RGDS) or in hibitors of actin polymerization (cytochalasin D, CD) and tyrosine-pho sphatases (phenylarsine oxide, PAO). However, forskolin, RGDS, and CD prevented the dephosphorylation step together with inhibition of plate let aggregation, whereas in the presence of phenylarsine oxide (PAO) t he dephosphorylation step was replaced by an increase in the number an d intensity of tyrosyl-phosphorylated proteins. Our data provide evide nce to conclude that (i) cAMP inhibits platelet aggregation at a downs tream site to PLC gamma 2 tyrosyl-phosphorylation; (ii) Cvx-induced PT P is independent on integrin alpha(IIb)beta(3) engagement, actin polym erization, and tyrosine-phosphatases activation; (iii) integrin alpha( IIb)beta(3) mediates the dephosphorylation step in a platelet aggregat ion-dependent manner; and (iv) Cvx and collagen stimulate platelets by a similar signal transduction pathway. (C) 1998 Academic Press.