Bombesin promotes synergistic stimulation of DNA synthesis by ethanol and insulin in fibroblasts

In NIH 3T3 fibroblasts and several other cellular systems, ethanol (50-80 m M) was previously shown to greatly enhance the mitogenic effects of insulin particularly in the presence of zinc. Here we report that in NIH 3T3 fibro blasts the combined stimulatory effects of ethanol and insulin on DNA synth esis can be further increased by bombesin both in the absence and presence of zinc. Bombesin also enhanced insulin-plus-ethanol-induced DNA synthesis in mouse Swiss ST3 and Balb/c 3T3 fibroblasts, but in these cells bombesin was effective only in the presence of zinc. In NIH 3T3 fibroblasts, the pot entiating effects of ethanol on insulin-induced DNA synthesis by the zinc-d ependent and bombesin-dependent mechanisms were additive. Wortmannin, an in hibitor of phosphatidylinositol 3'-kinase (PI3K), prevented the comitogenic effect of ethanol in the presence of bombesin but not in the presence of z inc. Furthermore, bombesin, but not ethanol, was found to enhance the stimu latory effect of insulin on PI3K activity. Rapamycin, an indirect inhibitor of p70 S6 kinase actions, inhibited the comitogenic effects of ethanol in the presence of both zinc and bombesin. However, only ethanol, but not bomb esin, enhanced the stimulatory effect of insulin on p70 S6 kinase activity; this effect of ethanol was zinc-dependent. Neither ethanol nor bombesin en hanced the stimulatory effects of insulin on the phosphorylation (activatio n) of p38/p42/p44 mitogen-activated protein kinases. The results suggest th at in mouse fibroblasts maximal stimulation of DNA synthesis by physiologic ally relevant concentrations of ethanol occurs if both PI3K and p70 se kina se are activated. These data suggest a mechanism by which ethanol may affec t growth in affected human tissues during its tumor promoting actions. (C) 1999 Academic Press.