Inhibitory effects of antipromoters and radical scavengers on the promotion process in two-stage cell transformation.

To find the mechanism of promotion process, we have investigated the antipromoting effects of radical scavengers and specific inhibitors for phospholipid metabolism and for protein kinase C using a two-stage transformation assay system in BALB/3T3 cells. All radical scavengers and inhibitors tested showed the antipromoting effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted transformation. Diacylglycerols, activators of protein kinase C, showed promoting effects in vitro and the promoted-transformation by them was suppressed by radical scavengers employed. By an electron spin resonance (ESR) spin-trapping method, inhibitors, which suppressed promoted-transformation by TPA markedly, had .OH scavenging action. It was found using a ESR spin-trapping method that treatment of TPA on BALB/3T3 cells generates .OH in a dose-dependent manner. These results suggest that generation of oxygen radicals, especially .OH, which occurs in the processes of phospholipid metabolism as well as activation of protein kinase C, is essential to the promotion process.