Inducible overexpression of human protein kinase C alpha in NIH 3T3 fibroblasts results in growth abnormalities.

We have stably overexpressed the human protein kinase C alpha (hPKC alpha) in NIH 3T3 fibroblasts under the control of the interferon (IFN) type I inducible murine Mx promoter. These cells showed a 10-fold increase in the transcription of hPKC alpha mRNA after induction with interferon alpha. The increase in the amount and activity of protein kinase C (PKC)-protein in these cells was only about 3-fold after induction with interferon alpha. Compared to control cells which were transfected with the vector only, the NIH 3T3 fibroblasts transfected with the hPKC alpha cDNA showed already a slightly increased PKC-activity and amount of PKC-protein in the absence of interferon alpha. The hPKC alpha overexpressing cells had an altered, "transformed-like" morphology, which was reversed by staurosporine, an increased growth rate and a higher saturation density. The growth rate was further increased by treating the cells with interferon alpha. The hPKC alpha overexpressing cells were able to grow in soft agarose after treatment with phorbol ester such as TPA (12-O-tetradecanoylphorbol 13-acetate). After phorbol ester and interferon treatment a stronger expression of the protooncogene c-jun was detectable in the hPKC alpha overexpressing cells, whereas expression of c-fos and c-myc was not affected. Since these cells show a specific response pattern due to induced PKC alpha expression they might be useful as an assay system for the development of PKC isozyme-specific inhibitors and activators.