Regulation of gene expression of class I alcohol dehydrogenase by glucocorticoids

The effect of glucocorticoids on gene expression of rat class I alcohol dehydrogenase (ADH; alcohol:NAD⁺ oxidoreductase, EC 1.1.1.1) was investigated. A cDNA clone for the β-subunit of human ADH (ADH2) was used to analyze class I ADH mRNA levels in rat hepatoma cells, which are known to contain a functional glucocorticoid receptor. RNA gel blot analysis of total cellular RNA isolated from these cells showed hybridization of the human ADH2 cDNA probe to a single ≃1500-base RNA species. Treatment of the cells with dexamethasone (0.1 nM to 1 μM) caused a dose-dependent increase in total cellular class I ADN mRNA levels by a factor of 2-4. Maximal levels were reached within 18-24 hr of treatment. This effect was reversible following withdrawal of dexamethasone. The glucocorticoid induction of class I ADH mRNA does not seem to require ongoing protein synthesis since treatment of the cells with cycloheximide did not affect the increase in class I ADH mRNA levels by dexamethasone. The human ADH2 gene contains both upstream and within the coding region sequence motifs that display homology with response elements of genes positively regulated by glucocorticoids. These data suggest a receptor-mediated transcriptional enhancement of the ADH2 gene as the mechanism of regulation. However, analysis of RNA decay in cells treated with actinomycin D indicates that the dexamethasone-induced increase in class I ADH mRNA might, at least in part, be due to enhanced ADH mRNA stability.