RAS DOWN-REGULATION OF PROTEIN-KINASE-C MESSENGER-RNA IN C3H 10T1 2 FIBROBLASTS/

C3H 10T1/2 fibroblasts transformed by oncogenic ras have lower levels of protein kinase C (PKC) activity and protein. It was previously sugg ested that elevated levels of diacylglycerol in ras-transformed fibrob lasts lead to activation-induced proteolysis of cellular PKC. We found that stable expression of T24ras in C3H 10T1/Z fibroblasts resulted i n a significant decrease in levels of PKC alpha and PKC epsilon mRNA. Using C3H 10T1/2 cell lines in which the levels of activated ras can b e exogenously regulated (by addition of zinc to induce the expression of a metallothionein-promoted human Ha-ras oncogene), we examined the temporal dependence of oncogenic ras expression on PKC downregulation. In these cells, downregulation of PKC protein and activity was induce d but was not preceded by activation of PKC. The downregulation of PKC levels correlated with the appearance of a highly transformed morphol ogy and was seen only at high levels of ras expression. In the inducib le cells, the decrease in levels of PKC alpha mRNA had the same depend ence on the levels of ras expression as did protein downregulation. Th ese experiments provide evidence that downregulation of PKC protein le vels by expression of oncogenic Ha-ras in C3H 10T1/2 fibroblasts is pr imarily due to altered transcriptional regulation. Because the downreg ulation of PKC was coupled with the onset of morphological transformat ion, the data suggest that this downregulation is involved in or facil itates the maintenance of a ras-transformed phenotype in C3H 10T1/Z fi broblasts. (C) 1996 Wiley-Liss, Inc.