The physiological importance of protein kinase C (PKC) activation is widely appreciated and well documented. It is now clear that there is more than one species of PKC molecule, and several discrete subspecies have been defined. These proteins are derived from both multiple genes and from alternative splicing of a single mRNA transcript, yet possess a primary structure containing conserved structural motifs with a high degree of sequence homology. In mammalian tissues at least seven subspecies can be distinguished, one of which is expressed only in the central nervous tissues. Biochemical and immunocytochemical studies have revealed that these PKC subspecies are differently located in particular cell types, and at limited intracellular locations. The enzyme subspecies purified from tissue show subtle differences in their mode of activation, sensitivity to Ca2+ and catalytic activity. It is worth noting that unsaturated free fatty acids including arachidonic, oleic, and linoleic acids dramatically activate several members of the PKC family in the presence of diacylglycerol at the basal level of Ca2+. It is possible that activation of the enzyme is an integral part of the signal-induced degradation cascade of various membrane phospholipids catalyzed by phospholipases C, A2 and perhaps D as well. Evidence now accumulates that PKC plays pivotal roles in control of a number of membrane functions, such as exocytosis, release reactions, and ion channel conductivity, as well as in cross-talks of various cell-signaling systems. It is also clear that PKC plays roles of crucial importance for regulation of gene expression and cell growth.
Biomedical Reviews 1992; 1: 1-6.
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