Signal transduction by protein kinase mammalian cells

1. The past two decades have witnessed great advances in our understanding of the role of protein kinase C (PKC) in signal transduction, The Ca2+-acti vated, phospholipid-dependent protein kinase discovered by Nishizuka's grou p in 1977 is now a family of at least 11 isoforms. Protein kinase C isoform s exist in different proportions in a host of mammalian cells and each isof orm has a characteristic subcellular distribution in each cell type. 2. Stimulation of a specific PKC isoform often causes redistribution of the isoform from one subcellular compartment to another compartment where it c omplexes with and phosphorylates a specific protein substrate. 3. The interaction of a specific PKC isoform with its protein substrate may directly activate a specific function of the cell or may trigger a cascade of protein kinases that ultimately stimulates a specific response in diffe rentiated cells or regulates growth and proliferation in undifferentiated c ells.