Effects of prostaglandin E1 on protein kinase activity and endogenous phosphorylation of intact human platelets

Abstract When intact human platelets were treated with prostaglandin E 1 , protein kinase activity of the platelet sonicate was elevated when assayed without cyclic AMP. Total protein kinase activity (assayed with cyclic AMP) remained unchanged. Prostaglandin A 1 mimicked this effect, but other prostaglandins and antiplatelet agents had no effect on protein kinase activity. Phosphoprotein phosphatase activity was not influenced by prostaglandin E 1 . Basal phosphorylation of several endogenous substrates for protein kinase was also elevated when platelets were treated with prostaglandin E 1 . The results demonstrate that prostaglandin E 1 stimulates protein kinase activity and endogenous phosphorylation in intact platelets and suggest that this effect is mediated by the action of prostaglandin E 1 on cyclic AMP levels. An important role of phosphoprotein in mediating the effect of prostaglandin E 1 on platelet function is suggested.