Perspectives on the Role of Protein Kinase C in Stimulus-Response Coupling4

Protein kinase C has now attracted great attention for the studies on the activation of cellular functions and proliferation, and our knowledge of the possible role of this enzyme in cell surface signal transduction is expanding rapidly. It is also becoming clear that many of the pleiotropic actions, if not all, of tumor promoters are probably mediated through the action of this enzyme. Under physiologic conditions protein kinase C is activated by association with membrane phospholipids in the presence of diacylglycerol. The diacylglycerol active in this role may arise in the membrane only transiently from the receptor-mediated hydrolysis of inositol phospholipids. The signals that are related to protein kinase C normally differ from those for the group of hormones, neurotransmitters, and many other biologically active substances that produce cAMP. Thus protein kinase C and protein kinase A may transduce distinctly different pieces of information into the cell via their own specific protein phosphorylation. Several aspects of this protein kinase C pathway have been reviewed (1, 2), and this article will describe some overall perspectives on the role of this protein kinase.