Composite glucocorticoid regulation at a functionally defined negative glucocorticoid response element of the human...

Glucocorticoid-dependent negative feedback of the hypothalamic-pituitary-adrenal axis is mediated in part through direct inhibition of hypothalamic CRH gene transcription. In the present study, we sought to further localize and characterize glucocorticoid receptor (GR) and AP-1 interactions at a functionally defined negative glucocorticoid response element (nGRE) of the CRH promoter. Transient transfection studies in mouse corticotroph AtT-20 cells demonstrated that internal deletion of the nGRE (-278 to -249 nucleotides) within the context of 1 kb of the intact CRH promoter resulted in decreased 8-BrcAMP stimulation and glucocorticoid-dependent repression of CRH promoter activity. The nGRE conferred transcriptional activation by both cAMP and overexpressed c-jun or c-fos AP-1 nucleoproteins as well as specific glucocorticoid-dependent repression to a heterologous promoter. A similar profile of regulation was observed for the composite GRE derived from mouse proliferin promoter. The CRH nGRE was clearly distinct from the consensus cAMP response element (CRE) at -224 nucleotides, which increased basal activity and cAMP responsiveness of a heterologous promoter but did not confer glucocorticoid-dependent repression. High-affinity binding sites for both GR and AP-1 nucleoproteins were identified at adjacent elements within the nGRE. Mutations that disrupted either GR or AP-1 binding activity were associated with loss of glucocorticoid-dependent repression. These results are consistent with a composite mechanism of glucocorticoid-dependent repression involving direct DNA binding of GR and AP-1 nucleoproteins at discrete adjacent sites within the CRH promoter.