| Co-Investigator(Kenkyū-buntansha) |
OHNO Shigeo The Tokyo Metropolitan Inst. of Med. Sci., Molecular Biology, Research Scientist, 遺伝情報研究部門, 研究員 (10142027)
YAJIMA Yukiko The Tokyo Metropolitan Inst. of Med. Sci., Tumor Cell Biology, Research Scientis, 腫瘍細胞研究部門, 主任研究員 (60090114)
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| Research Abstract |
Protein kinase C (PKC) comprises at least four different molecules (designated PKC alpha, betaI, betaII, and gamma ) with closely related structures. Recently, we have isolated cDNA clones encoding a novel protein kinase, nPKCepsilon, which share only part of the sequences with four "conventional" PKCs (cystein-rich repeat and protein kinase sequence), and demonstrated that its expression is tissue specific as well as conventional PKCs. These findings suggest that each PKC and nPKCepsilon plays a crucial role in the different signaling pathway.
In this study, we extensively characterized the biological properties of nPKCepsilon compared with conventional PKCs using a cDNA expression system in COS cells. nPKCepsilon is a serine/threonine- specific protein kinase which is activated by phospholipid, diacylglycerol (DAG), and phorbol esters like conventional PKCs However, nPKCepsilon shows several specific enzymatic properties; Ca^<2+> independence, specificity to a phospholipid CL, and substrate specificity. Moreover, nPKCepsilon also served as phorbol ester receptors, but it is clearly discriminated from four conventional PKCs in Ca^<2+> independence for receptor activity and in its affinity for phorbol ester. Translocation of conventional PKC_<alpha> to the membranes is induced with phorbol ester in a Ca^<2+> dependent manner, whereas the phorbol ester-stimulated translocation of nPKCeplison did not require Ca^<2+>. A matter of great importance to evaluate the crucial role of nPKCepsilon in the cellular responses against DAG and phorbol ester signals is the fact that the activation of nPKCeplison is totally independent of Ca^<2+>.
We believe that the present findings would facilitate the understanding of the physiological function of each conventional PKC type and the novel PKC-related protein, nPKCepsilon, in transmembrane signaling pathway.
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