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 b y glucocorticoid and the protein kinase-A and -C second messenger path ways in cultured cells. We show that the human primary liver carcinoma NPLC expresses the endogenous CRH gene. Dexamethasone reduced CRH mRN A levels by more than 90%, with half-maximal suppression at 5 nM. Phor bol ester treatment to activate the protein kinase-C pathway increased CRH mRNA levels up to 30-fold, whereas forskolin treatment to activat e the protein kinase-A pathway had no effect. In coincubation experime nts, dexamethasone completely suppressed phorbol ester-induced CRH mRN A levels in NPLC cells, maintaining them at the levels seen in untreat ed cells. We contrasted this regulation with the effects of glucocorti coid on CRH mRNA induction by forskolin in R1, a mouse anterior pituit ary cell line (AtT-20) stably transfected with the human CRH gene. Dex amethasone suppressed forskolin-induced CRH mRNA levels by 70% in R1 c ells, 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 suppress ed by glucocorticoid feedback than CRH induction by ligands that act v ia protein kinase-C. This differential effect of glucocorticoid on CRH mRNA regulation could help explain the abnormal CRH production observ ed in clinical disorders such as anorexia nervosa and major depression .