The role of protein kinase C isoforms in cell proliferation and apoptosis

Protein kinase C (PKC) was first described as a calcium-activated, phospholipid-dependent serine/threonine protein kinase 22 years ago, and it has since been studied extensively as a second messenger transducing diverse signals regarding cell proliferation, activation of cellular function, differentiation, and even apoptosis. Because PKC consists of at least 11 isoforms, with possibly different biological properties, it is necessary to reevaluate its known functions as functions of each isoform. Recent studies have revealed that several other lipid metabolites generated by signal-induced hydrolysis of membrane phospholipids, such as ceramide and phosphatidylinositol-3,4,5-triphosphate, may also have the potential to mediate external signals. Here we describe the roles of PKC isoforms in cell proliferation and apoptosis, particularly in relation to other lipid metabolites.