Dexamethasone Stimulates Ribosomal Protein L32 Gene Transcription in Rat Myoblasts

Incubation of rat L6 myoblasts for 24 h with 10(-7) M dexamethasone, a glucocorticoid analogue, resulted in a 2.5-fold increase in the rate of ribosomal protein L32 (rpL32) gene transcription with a corresponding increase in the level of rpL32 mRNA. The increased rate of transcription was accompanied by a dramatic enhancement in binding of the delta, but not beta and gamma, factors to the rpL32 gene promoter as measured by gel mobility shift assays. This increased binding reflects a change in the activity of the delta factor since its level is unchanged by dexamethasone treatment. The presence of the glucocorticoid analogue RU38486 reversed the stimulating effect of dexamethasone on rpL32 gene transcription and binding of the delta factor to the delta element. These results suggest that the mechanism which enhances rpL32 gene transcription in dexamethasone-treated rat L6 myoblasts involves glucocorticoid-receptor mediated changes in the activity of the delta factor.