Mapping of a Molecular Determinant for Protein Kinase C βIIIsozyme Function

Abstract

In human erythroleukemia (K562) cells, the highly related protein kinase C (PKC) alpha and PKC betaII isozymes serve distinct functions in cellular differentiation and proliferation, respectively. Previous studies using two domain switch PKC chimera revealed that the catalytic domains of PKC alpha and betaII contain molecular determinants important for isozyme-specific function (Walker, S. D., Murray, N. R., Burns, D. J., and Fields, A. P. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 9156-9160). We have now analyzed a panel of PKC chimeras to determine the specific region within the catalytic domain important for PKC betaII function. A cellular assay for PKC betaII function was devised based on the finding that PKC betaII selectively translocates to the nucleus and phosphorylates nuclear lamin B in response to the PKC activator bryostatin. This response is strictly dependent upon expression of PKC betaII or a PKC chimera that functions like PKC betaII. We demonstrate that a PKC alpha/betaII chimera containing only the carboxyl-terminal 13 amino acids from PKC betaII (betaII V5) is capable of nuclear translocation and lamin B phosphorylation. These results are consistent with our recent observation that the PKC betaII V5 region binds to phosphatidylglycerol (PG), a potent and selective PKC betaII activator present in the nuclear membrane (Murray, N. R., and Fields, A. P. (1998) J. Biol. Chem. 273, 11514-11520). Soluble betaII V5 peptide selectively inhibits PG-stimulated PKC betaII activity in a dose-dependent fashion, indicating that PG-mediated activation of PKC betaII involves interactions with the betaII V5 region of the enzyme. We conclude that betaII V5 is a major determinant for PKC betaII nuclear function and suggest a model in which binding of PG to the betaII V5 region stimulates nuclear PKC betaII activity during G2 phase of the cell cycle.