Protein kinase C, an enzyme that is activated by diacylglycerol resulting from the receptor-mediated hydrolysis of inositol phospholipids, relays information of a variety of extracellular signals across the cell membrane to regulate many intracellular processes. Since this enzyme also serves as a major receptor for phorbol esters, a class of tumor promoters, it has attracted great attention from biologists interested in the mechanism of signal transduction and carcinogenesis. Recent analysis has revealed that protein kinase C is a large family of proteins, with the multiple subspecies that possess subtle individual enzymological characteristics. Biochemical and immunohistochemical studies indicate that the protein kinase C subspecies may be differently distributed in particular cell types and with limited intracellular locations. Presumably, each member of the family plays discrete roles in the processing of various physiological and pathological responses to external signals, such as in the modulation of membrane functions and the activation of gene transcription.
Nishizuka Y. The Family of Protein Kinase C for Signal Transduction. JAMA. 1989;262(13):1826–1833. doi:10.1001/jama.1989.03430130102042