COUP‐TF and Transcriptional Co‐Regulators in Adrenal Steroidogenesis

Abstract

Chicken ovalbumin upstream promoter‐transcription factors (COUP‐TFs) and steroidogenic factor‐1 (SF‐1) play key roles in the transcriptional regulation of steroidogenic P450 genes. Transfection studies showed that SF‐1 activated bovine CYP17 promoter activity, whereas COUP‐TFs repressed it from the CRS2 element in a mutually exclusive manner in mouse adrenocortical Y‐1 cells. COUP‐TFI and SF‐1 competitively bind to the Ad5 element of the human CYP11B2 gene promoter. Unexpectedly, overexpression of COUP‐TFI increased the CYP11B2 promoter activity, whereas overexpression of SF‐1 repressed it in human adrenocortical H295R cells. In cortisol‐producing adrenal cortical adenomas, down‐regulation of nuclear receptors, including COUP‐TFs was found. We therefore screened for COUP‐TFI‐interacting proteins using a yeast two‐hybrid system and have identified Ubc9 and PIAS1, SUMO‐1 conjugating enzyme and ligase, respectively. Coexpression of Ubc9 and PIAS1 synergistically enhanced COUP‐TFI‐mediated transrepression of CYP17 gene as well as transactivation of CYP11B2 gene. The SUMOylation‐defective mutants of these proteins continued to function as co‐regulators of COUP‐TFI. These findings indicate that Ubc9 and PIAS1 can function as transcriptional co‐regulators of COUP‐TFI to modulate adrenal cortical steroidogenesis in a SUMOylation‐independent manner.