ETHANOL POTENTIATES THE STIMULATORY EFFECTS OF INSULIN AND PHOSPHOCHOLINE ON MITOGENESIS BY A ZINC-DEPENDENT AND RAPAMYCIN-SENSITIVE MECHANISM IN FIBROBLASTS AND JB6 CELLS

In most cellular systems ethanol inhibits growth factor-induced cell g rowth. Here we examined the effects of ethanol on DNA synthesis and ce ll proliferation induced by insulin and phosphocholine (PCho) in NIH 3 T3 fibroblasts, Swiss 3T3 fibroblasts and mouse epidermal JB6 cells. I n serum-starved low (12-18) passage NIH 3T3 fibroblasts, 60 mM ethanol enhanced the mitogenic effect of insulin in the absence or presence o f 25 mu M zinc about 2- or 12-fold, respectively. In contrast, in seru m-starved high (30-47) passage NIH 3T3 cells 60 mM ethanol had large ( 20-40-fold) potentiating effects on insulin-induced DNA synthesis even in the absence of zinc. Furthermore, ethanol also enhanced the effect s of PCho on DNA synthesis in both the absence and presence of insulin . The potentiating effects of ethanol on insulin- and PCho-induced DNA synthesis were associated with 1.2-1.3-fold stimulation of cell proli feration. Rapamycin, an inhibitor of p70 S6 kinase action, strongly in hibited the potentiating effects of ethanol on insulin- and PCho-induc ed mitogenesis. Unexpectedly, ethanol inhibited synergistic activation of p42/p44 mitogen-activated protein kinases by insulin and PCho. In both Swiss 3T3 and JB6 cells, ethanol potentiated insulin-induced DNA synthesis only in the presence of zinc. In these cells, ethanol also i ncreased the effects of PCho on both DNA synthesis and cell proliferat ion in the co-presence of either insulin or ATP. The results indicate that in various cell lines physiologically relevant concentrations of ethanol can increase the ability of insulin and PCho to induce DNA syn thesis and, to smaller extents, cell proliferation. In low passage NIH 3T3 cells as well as in Swiss 3T3 and JB6 cells potentiation of insul in-induced DNA synthesis by ethanol requires the presence of zinc.