ANTI-CD9 MONOCLONAL-ANTIBODY ELICITS STAUROSPORINE INHIBITABLE PHOSPHATIDYLINOSITOL 4,5-BISPHOSPHATE HYDROLYSIS, PHOSPHATIDYLINOSITOL 3,4-BISPHOSPHATE SYNTHESIS, AND PROTEIN-TYROSINE PHOSPHORYLATION IN HUMAN PLATELETS

Phosphoinositide metabolism elicited by anti-CD9 monoclonal antibody, a well-characterized platelet activator, was studied using acetylsalic ylic acid-treated human platelets. TP82, which is an anti-CD9 monoclon al antibody, induced classical phosphatidylinositol 4,5-bisphosphate h ydrolysis, as monitored by intracellular Ca2+ mobilization and phospha tidic acid production, and synthesis of phosphatidylinositol 3,4-bisph osphate, which is a major component of newly-described 3-phosphorylate d inositol phospholipids produced during platelet activation. These ch anges were severely inhibited by 1 muM staurosporine, a potent, though non-selective, protein kinase inhibitor, which also abolished TP82 in duction of tyrosine phosphorylation of multiple platelet proteins. Pro tein-tyrosine phosphorylation appears necessary to initiate both the c lassical phosphoinositide turnover and synthesis of the newly-describe d 3-phosphorylated inositol phospholipids in anti-CD9 monoclonal antib ody-induced platelet activation.