Involvement of histone acetyltransferase (HAT) in ethanol-induced acetylation of histone H3 in hepatocytes: potential mechanism for gene expression

Ethanol treatment increases gene expression in the liver through mechanisms that are not clearly understood. Histone acetylation has been shown to induce transcriptional activation. We have investigated the characteristics and mechanisms of ethanol-induced histone H3 acetylation in rat hepatocytes. Immunocytochemical and immunoblot analysis revealed that ethanol treatment significantly increased H3 acetylation at Lys9 with negligible effects at Lys14, -18, and -23. Acute in vivo administration of alcohol in rats produced the same results as in vitro observations. Nuclear extracts from ethanol-treated hepatocytes increased acetylation in H3 peptide to a greater extent than extracts from untreated cells, suggesting that ethanol either increased the expression level or the specific activity of histone acetyltransferases (HAT). Use of different H3 peptides indicated that ethanol selectively modulated HAT(s) targeting H3-Lys9. Treatment with acetate, an ethanol metabolite, also increased acetylation of H3-Lys9 and modulated HAT(s) in the same manner as ethanol, suggesting that acetate mediates the ethanol-induced effect on HAT. Inhibitors of MEK (U0126) and JNK (SP600125), but not p38 MAPK inhibitor (SB203580), suppressed ethanol-induced H3 acetylation. However, U0126 and SP600125 did not significantly affect ethanol-induced effect on HAT, suggesting that ERK and JNK regulate histone acetylation through a separate pathway(s) that does not involve modulation of HAT. Chromatin immunoprecipitation assay demonstrated that ethanol treatment increased the association of the class I alcohol dehydrogenase (ADH I) gene with acetylated H3-Lys9. These data provide first evidence that ethanol increases acetylation of H3-Lys9 through modulation of HAT(s) and that histone acetylation may underlie the mechanism for ethanol-induced ADH I gene expression.