Stimulus-selective induction of the orphan nuclear receptor NGFIB underlies different influences of angiotensin II and potassium on the human adrenal gland zona glomerulosa-specific 3β-HSD isoform gene expression in adrenocortical H295R cells

抄録

In the adrenal, the type I 3β-hydroxysteroid dehydrogenase (HSD3B1) is expressed exclusively in the zona glomerulosa (ZG), where aldosterone is produced. Angiotensin II (AngII) and potassium (K⁺) are the major physiological regulators of aldosterone synthesis. However, their respective roles in regulation of aldosterone synthesis are not fully defined, particularly in terms of transcriptional regulation of steroidogenic enzyme genes. We previously showed that AngII can stimulate expression of HSD3B1. But, K⁺ responsiveness of this gene has remained unexplored. Here, we report that K⁺ stimulation lacks the ability to induce HSD3B1 expression in human adrenocortical H295R cells. Both AngII and K⁺ were able to enhance transcription of the aldosterone synthase gene (CYP11B2). Promoter analysis revealed that although both AngII and K⁺ activate transcription from the Ca²⁺/cAMP-responsive element (CRE) located in the CYP11B2 promoter, the orphan nuclear receptor NGFIB-responsive element (NBRE) located in the HSD3B1 promoter fails to respond to K⁺, being only able to enhance transcription after AngII treatment. We found that induction of de novo protein synthesis of NGFIB occurs only after AngII treatment. This sharply contrasts with the phosphorylation that occurs in response to both AngII and K⁺ on the CREB/ATF family transcription factor ATF2. Chromatin immunoprecipitation assay confirmed that the NGFIB protein occupies the HSD3B1 promoter only after AngII, while ATF2 binds to the CYP11B2 promoter in response to both AngII and K⁺. These data provide evidence that downstream signals from AngII and K⁺ can be uncoupled in the regulation of HSD3B1 in the human adrenocortical H295R cells.