Effects of various chemical agents on the transformation of rat fibroblasts by an activated c-Ha-ras oncogene.

We have previously reported that the potent tumor-promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA) and a factor from fetal calf serum (FCS) markedly enhance the transformation of mouse C3H 10T1/2 and Rat 6 fibroblasts, when added to cultures following transfection with plasmid pT24 DNA that contains an activated c-Ha-ras oncogene. In the present study, we examined possible enhancing or inhibiting effects of various chemicals on the transformation of Rat 6 fibroblasts by T24 DNA when tested in the presence of calf serum, calf serum plus TPA or FCS. We found that, like TPA, the chemicals mezerein, 1-oleoyl-2-acetylglycerol, and phospholipase C increased the yield of T24-induced foci, thus further implicating protein kinase C as a critical constituent in this process. Low concentrations (10(-6)-10(-7)M) of retinoic acid (both trans and 13-cis) also stimulated cell transformation. Several compounds inhibited T24-induced transformation. These included nontoxic concentrations of the calcium ionophore A23187, indomethacin, and epsilon-amino-n-caproic acid. Compounds that failed to exert a significant reproducible effect included vasopressin, vitamin D3, selenium, antipain, Bowman-Birk inhibitor, vitamin B12, epidermal growth factor, platelet-derived growth factor, insulin, and transferrin. These findings suggest that this simple in vitro system might be useful for detecting enhancers and inhibitors of ras oncogene-induced cell transformation and also elucidating their mechanisms of action.