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Numerous genes required for adrenocortical steroidogenesis are activated by the nuclear hormone receptor steroidogenic factor 1 (SF-1) (NR5A1). Dax-1 (NR0B1), another nuclear hormone receptor, represses SF-1-dependent activation. Glucocorticoid products of the adrenal cortex provide negative feedback to the production of hypothalamic CRH and pituitary ACTH. We hypothesized that glucocorticoids stimulate an intraadrenal negative feedback loop via activation of Dax-1 expression. Reporter constructs show glucocorticoid-dependent synergy between SF-1 and glucocorticoid receptor (GR) in the activation of Dax-1, which is antagonized by ACTH signaling. We map the functional glucocorticoid response element between -718 and -704 bp, required for activation by GR and synergy with SF-1. Of three SF-1 response elements, only the -128-bp SF-1 response element is required for synergy with GR. Chromatin immunoprecipitation (ChIP) assays demonstrate that dexamethasone treatment increases GR and SF-1 binding to the endogenous murine Dax-1 promoter 10- and 3.5-fold over baseline. Serial ChIP assays reveal that that GR and SF-1 are part of the same complex on the Dax-1 promoter, whereas coimmunoprecipitation assay confirms the presence of a protein complex that contains both GR and SF-1. ACTH stimulation disrupts the formation of this complex by abrogating SF-1 binding to the Dax-1 promoter, while promoting SF-1 binding to the melanocortin-2 receptor (Mc2r) and steroidogenic acute regulatory protein (StAR) promoters. Finally, dexamethasone treatment increases endogenous Dax-1 expression and concordantly decreases StAR expression. ACTH signaling antagonizes the increase in Dax-1 yet strongly activates StAR transcription. These data indicate that GR provides feedback regulation of adrenocortical steroid production through synergistic activation of Dax-1 with SF-1, which is antagonized by ACTH activation of the adrenal cortex.
Gummow et al. (Fri,) studied this question.