CYCLOHEXIMIDE INHIBITION OF HORMONAL INDUCTION OF ALPHA-2U-GLOBULIN MESSENGER-RNA

The induction of hepatic α2u-globulin synthesis by glucocorticoids in isolated hepatocytes occurs via an increase in the level of its mRNA as measured by cell-free translation and by hybridization to an α2u-globulin cDNA probe. To explore whether induction of this mRNA is a direct or an indirect consequence of the interaction of the dexamethasone-receptor complex with the α2u-globulin genome, the requirement for ongoing protein synthesis was examined. Concentrations of cycloheximide too low to prevent precursor incorporation into total poly(a)-containing RNA do prevent the hormonal induction of α2u-globulin mRNA. Furthermore, incorporation of 3H-labeled amino acids into total protein was decreased by only 40-50%, and the appearance of the dexamethasone-induced glycosylated forms of α2u-globulin was completely prevented in these cycloheximide-treated hepatocytes. The results suggest that the synthesis of a protein mediator(s) may be required for the induction of α2u-globulin mRNA by glucocorticoids and that the steroid-receptor complex may not interact directly with the α2u-globulin genome.