EFFECTS OF GLUCOCORTICOID ON CORTICOTROPIN-RELEASING HORMONE GENE-REGULATION BY 2ND MESSENGER PATHWAYS IN NPLC AND ATT-20 CELLS

We have examined the regulation of the hypothalamic secretagogue CRH by glucocorticoid and the protein kinase-A and -C second messenger pathways in cultured cells. We show that the human primary liver carcinoma NPLC expresses the endogenous CRH gene. Dexamethasone reduced CRH mRNA levels by more than 90%, with half-maximal suppression at 5 nM. Phorbol ester treatment to activate the protein kinase-C pathway increased CRH mRNA levels up to 30-fold, whereas forskolin treatment to activate the protein kinase-A pathway had no effect. In coincubation experiments, dexamethasone completely suppressed phorbol ester-induced CRH mRNA levels in NPLC cells, maintaining them at the levels seen in untreated cells. We contrasted this regulation with the effects of glucocorticoid on CRH mRNA induction by forskolin in R1, a mouse anterior pituitary cell line (AtT-20) stably transfected with the human CRH gene. Dexamethasone suppressed forskolin-induced CRH mRNA levels by 70% in R1 cells, but only to levels that were still 10-fold greater than those in untreated cells. These results suggest that CRH induction in vivo by ligands that act via protein kinase-A may be less effectively suppressed by glucocorticoid feedback than CRH induction by ligands that act via protein kinase-C. This differential effect of glucocorticoid on CRH mRNA regulation could help explain the abnormal CRH production observed in clinical disorders such as anorexia nervosa and major depression.