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Regulation of differential COUP-TF-coregulator interactions in adrenal cortical steroidogenesis
Hirotaka Shibata1, Isao Kurihara, Sakiko Kobayashi
1Health Center, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan. hiro405@cb3.so-net.ne.jp
Abstract:
Hyperfunctioning adrenocortical adenomas produce excessive amounts of various corticosteroids due to dysregulated expression of steroidogenic enzymes. Since no genetic mutations in steroidogenic enzyme genes have been identified as yet, the dysregulated expression at the transcription level may be crucial. 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 and COUP-TFs repressed the transcription of bovine CYP17 gene promoter from the CRS2 element in a mutually exclusive manner in Y-1 cells. The results indicate that COUP-TFs negatively regulate the transcriptional activity of SF-1, a steroidogenic cell-specific activator of various steroidogenic P450 genes. Expression of both COUP-TFI and COUP-TFII was significantly decreased in the cortisol-producing adenomas, in which CYP17 was drastically overexpressed, indicating that decreased expression of COUP-TFs play a key role in overexpression of CYP17 in this type of tumors. We then screened for COUP-TFI-interacting proteins from a cortisol-producing adenoma cDNA library using a yeast two-hybrid system and identified a novel RING finger-containing protein which can function as a coregulator for COUP-TFI. Notably, COUP-TFI activated rather than repressed several target genes including the human CYP11B2 gene promoter, the results of which were opposite to those of the CYP17 promoter. The bifunctional activities of COUP-TFI may be derived from the promoter context and our newly identified COUP-TFI coregulator.
Insights
Decreased expression of Chicken ovalbumin upstream promoter-transcription factors (COUP-TFs) is linked to CYP17 overexpression in cortisol-producing adenomas. A novel coregulator suggests COUP-TFs have bifunctional roles in gene regulation.
Area of Science:
- Endocrinology
- Molecular Biology
- Cancer Genetics
Background:
- Hyperfunctioning adrenocortical adenomas involve excessive corticosteroid production due to dysregulated steroidogenic enzyme expression.
- Transcriptional dysregulation, rather than genetic mutations, is suspected as the cause of altered enzyme activity.
Purpose of the Study:
- To investigate the role of Chicken ovalbumin upstream promoter-transcription factors (COUP-TFs) and steroidogenic factor-1 (SF-1) in the transcriptional regulation of steroidogenic genes in adrenocortical adenomas.
- To identify potential coregulators of COUP-TFs involved in tumor development.
Main Methods:
- Transfection studies using Y-1 cells to analyze the interaction between SF-1 and COUP-TFs on the CYP17 gene promoter.
- Quantitative analysis of COUP-TFI and COUP-TFII expression in cortisol-producing adenomas.
- Yeast two-hybrid screening to identify proteins interacting with COUP-TFI.
Main Results:
- COUP-TFs repress SF-1 transcriptional activity on the CYP17 promoter, indicating a negative regulatory role.
- Expression of COUP-TFI and COUP-TFII is significantly decreased in cortisol-producing adenomas with high CYP17 expression.
- A novel RING finger-containing protein interacting with COUP-TFI was identified, which can act as a coregulator.
Conclusions:
- Reduced expression of COUP-TFs contributes to CYP17 overexpression in cortisol-producing adenomas.
- COUP-TFI exhibits bifunctional transcriptional activity (activation and repression) depending on promoter context and coregulators, as exemplified by its opposing effects on CYP17 and CYP11B2 promoters.