| Abstract: | Using inhibitors and activators of protein kinase C, it was demonstrated that in isolated plasma membranes of target cells estradiol-17 beta selectively stimulates protein phosphorylation by endogenous protein kinase C. In estradiol-dependent tissues, estradiol effectuates the translocation of protein kinase C from the cytosol to the membrane fraction within 10-12 minutes. Estradiol activates protein kinase C in cellular membranes of target tissues via a mechanism which is different from that of phorbol ester (TPA): 3H-estradiol, in contrast with 3H-TPA, it is not bound by protein kinase C and, in contrast with TPA, estradiol-17 beta does not activate purified protein kinase C in vitro. In this case, the specific stimulation of protein kinase C translocation to membranes and the estradiol-induced increase in the phosphorylation of plasma membrane proteins seem to be due to the estradiol-induced activation of the transmembrane system of polyphosphoinositide degradation, eventually resulting in the formation of diacylglycerol, a protein kinase C activator. |
