EPINEPHRINE INDUCES ASSOCIATION OF PP60SRC WITH GI-ALPHA IN HUMAN PLATELETS

Using specific antibodies against the α subunit of the inhibitory GTP-binding protein Gi, we analyzed the association of Giα with other cellular components in human platelets. Three tyrosine phosphorylated proteins with molecular mass of 63, 58, and 55 kDa were specifically associated with Giα in resting platelets. Stimulation of platelets with epinephrine, but not with thrombin, induced an increase of the reactivity of the 63- and 55-kDa proteins to antiphosphotyrosine antibodies on western blotting. By in vitro kinase assay we found that epinephrine induced the association of kinase activity with Giα and that the 63-kDa protein was phosphorylated by this activity The association of kinase activity with Giα in epinephrine-stimulated platelets paralleled the association of pp60src with Giα as detected by western blotting analysis using specific anti-pp60src monoclonal antibodies. The interaction of pp60src with Giα may play a role in the mechanism of platelet activation by epinephrine or in the epinephrine-induced potentiation of the action of other platelet agonists. © 1992 Academic Press, Inc.