Role of protein kinase C in transmembrane signaling

Many extracellular signals elicit Ca²⁺ mobilization and diacylglycerol formation in their target cells. Diacylglycerol is derived from the receptor‐linked phosphoinositide turnover and serves as a second messenger for the activation of protein kinase C in the presence of Ca²⁺ and phosphatidylserine. Unique diacylglycerols such as 1‐oleoyl‐2‐acetyl‐glycerol, which activate intracellular protein kinase C when added to intact cells, have been synthesized. Tumor‐promoting phorbol esters substitute for such diacylglycerols and directly activate protein kinase C in both intact cell and cell‐free systems. Under appropriate conditions, the synthetic diacylglycerols and phorbol esters induce protein kinase C activation without Ca²⁺ mobilization, whereas Ca²⁺ ionophore A23187 induces Ca²⁺ mobilization without protein kinase C activation. Using these substances, we have obtained evidence that both protein kinase C and Ca²⁺ are involved in and play a synergistic role in exocytosis, cell division, and other cellular functions. In this article, the role of protein kinase C in transmembrane signaling is discussed.