NUCLEAR-PROTEIN KINASE-C AND SIGNAL-TRANSDUCTION

Protein kinase C (pKC) is a family of enzymes, consisting of ten isoen zymes. Some of the members of the pKC family are not dependent on calc ium for their activity and also do not bind diacylglycerol. Protein ki nase C is either translocated to the nucleus or present endogenously. Both calcium-dependent as well as calcium-independent isoenzymes are l ocated in the nucleus. Protein kinase C has specific functions in the events activated within the nucleus during signal transduction. Three lines of approach have been taken to discern the nuclear function of p KC: pathways of activation of cytosolic pKC regulating nuclear events; translocation of pKC to the nucleus from the cytosol, and activation of native pKC in isolated nuclei. Protein kinase C contains a nuclear targeting bipartite motif and has a role in the nuclear calcium signal ing process. Targeting and binding of pKC to the sites of replicationa l and posttranscriptional activity may be one of the mechanisms of the pKC signaling process. Protein kinase C-mediated activation of nuclea r phosphatases and dephosphorylation of target nuclear proteins are th e areas where much less attention has been paid. Exploring these avenu es may lead to new insights into the molecular mechanism of nuclear si gnal transduction.