Regulation of Expression of Liver Alcohol Dehydrogenase

Crabb, David

Abstract

The rate of alcohol metabolsim by the liver is determined in part by the total amount of alcohol dehydrogenase (ADH) present. We are interested in the factors, especially endocrine factors, which control the expression of ADH in liver cells. In the first two years of support, we have examined the effects of hormones on ADH activity in intact rats, hypophysectomized rats, and cultured rat liver cells. Growth hormone, androgens, thyroid hormone, glucagon, and insulin have been implicated as possible regulators or ADH expression in the liver in studies we and others have carried out. To gain a more detailed understanding of the control of expression of this enzyme, we have cloned the cDNA and gene for rat liver ADH. We have also demonstrated that the expression of this gene can be influenced by hormones in hepatoma cells. We now propose to: 1. Fully characterized the induction of ADH and ADH mRNA in rat hepatoma cells by dexamethosone to determine whether the effect is transcriptional or due to stabilization of the mRNA. 2. Test the effects of growth hormone, insulin, glucagon, T3 and androgens on ADH activity and mRNA level in hepatoma cells. 3. Test the ADH-promoter for hormone-responsiveness by transfecting promoter-CAT fusion genes into cultured cells known to possess hormone receptors and examining the effect of hormones on the strength of the promoter. 4. Identify sequences in the rat ADH promoter which are responsible for liver-specific and hormone-modified expression of this gene by deletion mapping. 5. Identify sequences in rat ADH mRNA which confer stability on the mRNA. 6. Isolate and characterize DNA-binding proteins which interact with the promoter and which may thereby influence transcription rates. 7. Identify and characterize ADH mRNA-binding proteins which influcence mRNA stability. These studies should extend our previous observations made on whole animals, primary hepatocyte cultures, and hepatoma cells and lead to an understanding of the molecular details of control of the ADH gene in liver.