Molecular Pharmacology of Protein Kinase C

Abstract

When Castagna et al.¹ demonstrated that the potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) could stimulate protein kinase C activity, protein kinase C caught the attention of many scientists and has resulted in a vast and ever-growing literature on the role of protein kinase C in numerous biologic processes induced by TPA.² Indeed, the hypothesis that protein kinase C is the one of the binding protein of the phorbol esters was attractive for cancer researchers and helped rationalize the broad range of biological activities that has been observed previously for the phorbol esters. However, could we attribute all the biological effects induced by phorbol esters to the activation of the function of protein kinase C. The gel overlay experiment using [³H]12-0-tetradecanoylphorbol-13-acetate, for example, did not give a single band of protein kinase C, suggesting that we must have more pharmacological tools for elucidating the function of protein kinase C. Therfore we have started to synthesize a specific inhibitor of protein kinase C. Since synthesizing H-7 in 1986,⁴ we have succeeded in utilizing the inhibitor as an affinity ligand and could purified protein kinase C reproducibly. By using this enzyme preparation, we have determined that structure of isozyme of protein kinase C and obtained monoclonal antibodies against three isozymes. We established enzyme immunoassay method and determined tissue distribution of these three isozymes.