Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2002
Publication Date: 11/15/2002
Citation: HE, L., RONIS, M., BADGER, T.M. ETHANOL INDUCTION OF CLASS I ALCOHOL DEHYDROGENASE EXPRESSION IN THE RAT OCCURS THROUGH INDUCTION OF CCAAT/ENHANCER BINDING PROTEINS BETA AND DELTA . JOURNAL OF BIOLOGICAL CHEMISTRY. 2002. v. 46. p. 43572-43577. Interpretive Summary: Ethanol has been shown to have both adverse and beneficial health effects. Since alcohol is a part of the American diet, it is a dietary factor that can affect the health of the developing fetus, nursing infants, children and adults. In addition, the major enzyme that metabolizes ethanol, alcohol dehydrogenase (ADH), has many biological effects in non-alcohol consuming people not related to alcohol metabolism at all. Regulation of this important enzyme has not been well studied, and thus the mechanisms by which dietary factors can turn-on or turn-off this enzyme are not known. In this study, we have determined that ADH is turned on and turned off by inter-conversion of a class of cellular factors called CCAAT/ enhancer binding proteins (C/EBPs). We are currently determining the health implications of these actions, because the same mechanisms involved in ADH regulation are also involved in insulin regulation of metabolism. Thus, understanding how dietary factors regulate ADH could be very important in diabetes, as well as carbohydrate and protein metabolism.
Technical Abstract: Alcohol dehydrogenase (ADH) is the principal ethanol-metabolizing enzyme. Ethanol induces rat Class I ADH mRNA and activity by an as yet unknown mechanism. In the current study, adult male rats were fed an ethanol-containing diet by continuous intragastric infusion for 42 days. Hepatic Class I ADH mRNA, protein and activity levels in the ethanol-infused rats increased 3.9-, 3.3- and 1.7-fold, respectively (p<0.05). Cis-acting elements within the proximal promoter region of the ADH gene were studied by electrophoretic mobility shift assay (EMSA). Hepatic nuclear extract (HNE) binding to either the consensus or ADH-specific CCAAT/ enhancer binding protein (C/EBP) sites was >2.4-fold greater in ethanol-fed rats (p<0.05) than controls. Antibody specific EMSA assays demonstrated binding of the transcription factor C/EBP to the C/EBP site. Western blot immunoblot analysis of HNEs demonstrated 3.5- and 2.3-fold increases in C/EBP (LAP) and C/EBP (p<0.05), respectively, in ethanol-fed rats compared with controls, while levels of the truncated C/EBP (LIP) and C/EBP were lower in ethanol-fed rats (p<0.05). HNE from ethanol-fed rats increased (3-fold) the in vitro transcription of rat Class I ADH (p<0.05) and mutation of the C/EBP element in the proximal promoter region blocked this effect. Anti-sera against LIP or C/EBP enhanced transcription efficiency (p<0.05). These data provide the first evidence for the mechanism by which ethanol regulates rat hepatic Class I ADH gene expression in vivo. This mechanism involves the C/EBP site and the enhancer binding proteins beta and delta.