Glucocorticoid repression of 3',5'-cyclic-adenosine monophosphate-dependent human corticotropin-releasing-hormone gene promoter activity in a transfected mouse anterior pituitary cell line.

The regulation of the expression of the human corticotropin-releasing-hormone gene (hCRH) was studied in a mouse anterior pituitary cell line (AtT20) after transiently transfection with a chimeric gene containing the hCRH gene promoter fused to the bacterial chloramphenicol acetyltransferase (CAT) gene. Expression of the chimeric hCRH-CAT gene in AtT20 cells was enhanced by the cAMP analog (8-bromo-cAMP) about 5-fold but not by phorbol 12-myristate-13-acetate. The cAMP phosphodiesterase inhibitor isobutylmethylxanthine also strongly stimulated 15-fold the expression of the chimeric hCRH-CAT gene. Coincubation of cAMP analog and isobutylmethylxanthine resulted in a moderate 2-fold synergistic enhancement of CAT activity. Sequence comparison of the hCRH gene revealed a core sequence for a cAMP responsive element 5'-TGACGTCA-3' at -221 relative to the cap site. This regulatory element also confers cAMP inducibility on a heterologous promoter when placed upstream of the thymidine kinase promoter from herpes simplex virus. Finally, treatment with 0.5 microM dexamethasone reduced CAT activity about 2.0-fold in cAMP-stimulated cells. This result suggests that cAMP and glucocorticoids coordinately control hCRH gene expression.