Role of glucocorticoids and cAMP-mediated repression in limiting corticotropin-releasing hormone transcription during stress.
Résumé
The role of glucocorticoids and the repressor isoform of cAMP response element (CRE) modulator (CREM), inducible cAMP early repressor (ICER), in limiting corticotropin-releasing hormone (CRH) transcription during restraint stress were examined in both intact and adrenalectomized rats receiving glucocorticoid replacement. CRH primary transcript, measured by intronic in situ hybridization, increased after 30 min of restraint and returned to basal levels by 90 min, despite the persistent stressor. The decline was independent of circulating glucocorticoids, because adrenalectomized rats displayed an identical pattern. ICER mRNA in the hypothalamic paraventricular nucleus (PVN) increased after 30 min and remained elevated for up to 4 h in a glucocorticoid-independent manner. Western blot and electrophoretic mobility shift assay analyses showed increases in endogenous ICER in the PVN of rats subjected to restraint stress for 3 h. Chromatin immunoprecipitation assays showed the recruitment of CREM by the CRH CRE in conjunction with decreases in RNA polymerase II (Pol II) binding in the PVN region of rats restrained for 3 h. These data show that stress-induced glucocorticoids do not mediate the limitation of CRH transcription. Furthermore, the ability of CREM to bind the CRH CRE and the time relationship between elevated CREM and reduced Pol II recruitment by the CRH promoter suggest that inhibitory isoforms of CREM induced during stress contribute to the decline in CRH gene transcription during persistent stimulation.