The family of protein kinase C in transmembrane signalling for cellular regulation.

Signal-induced hydrolysis of inositol phospholipid produces two second messengers, diacylglycerol and inositol trisphosphate. Diacylglycerol activates protein kinase C, whereas inositol trisphosphate mobilizes Ca2+ from its internal store. Analogously, signal-induced hydrolysis of choline phospholipid generates two second messengers, unsaturated free fatty acid and lysophosphatidylcholine. The free fatty acid synergizes with diacylglycerol to activate protein kinase C and causes full activation of the enzyme even at the basal level of Ca2+. On the other hand, lysophosphatidylcholine dramatically enhances cellular responses such as cell proliferation and differentiation under the conditions where diacylglycerol and Ca2+ are available. It is likely that all of the immediate products of signal-induced degradation of inositol and choline phospholipids are involved directly in concert in the transmembrane control of cellular functions.