Structural and Functional Studies of Protein Kinase C
It has now become clear that protein kinase C (PKC) plays a fundamental role in cellular growth control in higher eukaryotes. In addition, since PKC has also been shown to be the high-affinity intracellular receptor for several classes of tumor promoters, the study of PKC has also become a central focus of current work in cancer research. We have isolated cDNA clones encoding several forms of this enzyme, and we have used these clones to begin to study in detail the role of PKC in growth control and tumor promotion. The complete primary structure of one of these forms, designated PKC β 1, exhibits structural and functional characteristics which are shared among all of the currently identified forms of PKC. These include an amino terminal cysteine-rich domain which mediates Ca2+ and phospholipid binding, tumor promoter binding, and membrane association, and a carboxy terminal catalytic domain which possesses serine/threonine protein kinase activity. To further characterize the function of PKC, we have generated a series of rat fibroblast cell lines which stably overexpress a full-length cDNA encoding the β1 form of this enzyme. These cell lines contain a 20- to 53-fold increase in PKC activity, and also have an increase in high affinity phorbol ester receptors, relative to control cells. They also exhibit dramatically enhanced morphologic changes in response to treatment with the tumor promoter 12-0-tetradecanoyl phorbol-13-acetate (TPA). These cell lines grow to a higher saturation density in monolayer culture and, when maintained at post-confluence, develop small, dense foci. In contrast to the control cells, which display complete anchorage dependence, the cell lines that overproduce PKC form small colonies in soft agar in the absence of TPA, and larger colonies in the presence of TPA. Thus, the mere overproduction of a single form of PKC is sufficient to confer anchorage independent growth and other growth abnormalities in rat fibroblasts. Taken together, these results provide direct evidence that PKC plays a critical role in normal cellular growth control and that it mediates several, and perhaps all of the cellular effects of the phorbol ester tumor promoters.
KeywordsPhorbol Ester eDNA Clone Phorbol Ester Tumor Promoter Dense Focus Complete Primary Structure
Unable to display preview. Download preview PDF.
- Ashendel, C. The Phorbol Ester Receptor: a phospholipid-regulated protein kinase. (1984) Biochim. Biophys. Acta 822, 219–242.Google Scholar
- Freeman, A. E., Price, P. J., Igel, H. J., Young, J. C., Maryak, J. M. Huebner, R. J. (1970) Morphological transformation of rat embryo cells induced by diethylnitrosamine and murine leukemia viruses. J. Natl. Cancer Inst. 44, pp 65–78.Google Scholar
- Housey. G. M., O’Brian, C. A., Johnson, M. D., Kirschmeier, P., and Weinstein, I. B. (1987) Isolation of cDNA clones encoding protein kinase C: Evidence for a protein kinase C-related gene family. Proc. Natl. Acad. Sci. USA 84, pp 1065–1069Google Scholar
- Housey. G. M., O’Brian, C. A., Johnson, M. D., Kirschmeier, P., and Weinstein, I. B. (1988) Overproduction of Protein Kinase C Causes Disordered Growth Control in Rat Fibroblasts. Cell, in pressGoogle Scholar
- Kirschmeier, P. T., Housey, G. M., Johnson, M. D., Perkins, A. S., & Weinstein, I. B. (1988) Construction and characterization of a retroviral vector demonstrating efficient expression of cloned cDNA sequences. DNA, in press.Google Scholar
- Makowske, M., Birnbaum, M. J., Ballester, R., Rosen, 0. M. (1986) A cDNA encoding PKC identifies two species of mRNA in brain and GH3 cells. J. Biol. Chem. 261, pp 13389–13392Google Scholar
- O’Brian, C. A., Lawrence, D. S., Kaiser, E. T., & Weinstein, I. B. (1984) Protein kinase C phosphorylates the synthetic peptide Arg-Arg-Lys-Ala-Ser-Gly-Pro-Pro-Val in the presence of phospholipid plus either Ca2+ or a phorbol ester tumor promoter. Biochem. Biophys. Res. Commun. 124, 296–302.PubMedCrossRefGoogle Scholar
- Pontremoli, S., Melloni, E., Michetti, M., Sparatore, B., Salamino, F., Sacco, O., and Horecker, B. L. (1987) Phosphorylation and proteolytic modification of specific cytoskeletal proteins in human neutrophils stimulated by phorbol-12-myristate 13-acetate. Proc. Natl. Acad. Sci. 84, 3604–3608.PubMedCrossRefGoogle Scholar
- Ullrich, A., Coussens, L., Hayflick, J. S., Dull, T.J., Gray, A., Tam, A. W., Lee, J., Yarden, Y., Libermann, T. A., Schlessinger, J., Downward, J., Mayes, E. L. V., Whittle, N., Waterfield, M. D., and Seeburg, P. H. Human epidermal growth factor receptor cDNA sequence and abberrant expression of amplified gene in A431 epidermoid carcinoma cells. Nature 309, 418–425.Google Scholar