Ethanol inhibition of insulin signaling in hepatocellular carcinoma cells

Chronic ethanol toxicity impairs liver regeneration, inhibits DNA synthesis , and mutes cellular responses to growth factor stimulation, Previous studi es demonstrated that the adverse effects of ethanol are mediated by inhibit ion of tyrosyl phosphorylation of the insulin receptor and the insulin rece ptor substrate-type 1 (IRS-1), However, overexpression of IRS-1 leads to in creased DNA synthesis and cellular transformation due to constitutive activ ation of mitogen-activated protein (MAP) kinase, The present study examines the effects of ethanol on insulin signaling through IRS-1 in FOCUS hepatoc ellular carcinoma cells, which overexpress IRS-l,to determine whether such cells were resistant to the inhibitory effects of ethanol, The results demo nstrated that ethanol treatment (100 mM) caused 30 to 50% reductions in the levels of insulin-stimulated tyrosyl phosphorylation of the insulin recept or beta-subunit, tyrosyl phosphorylation of IRS-1, phosphorylation of Erk2, association of phosphatidylinositol-3 kinase with tyrosyl-phosphorylated I RS-1, and MAP kinase and phosphatidylinositol-3 kinase activities. In contr ast, ethanol treatment had no effect on epidermal growth factor-stimulated tyrosyl phosphorylation of Shc. Corresponding with the pronounced inhibitio n of MAP kinase, ethanol treatment resulted in 30 to 50% reductions in the expression levels of two important insulin-responsive genes: glyceraldehyde -3-phosphate dehydrogenase (GAPDH) and proliferating cell nuclear antigen ( PCNA). The findings suggest that, in FOCUS hepatocellular carcinoma cells, which overexpress IRS-1, ethanol treatment substantially inhibits IRS-1 and MAP kinase signaling and growth-associated gene expression, but has no eff ect on Shc phosphorylation, which activates p21(ras) through an IRS-1 indep endent pathway.