Transcriptional complexes at the CYP17 CRS

Area of Science:

• Endocrinology
• Molecular Biology
• Cellular Signaling

Background:

• Adrenocorticotropin (ACTH) regulates adrenal steroid hormone biosynthesis through intracellular cAMP signaling.
• cAMP activates protein kinase A (PKA), enhancing steroidogenic gene transcription.

Purpose of the Study:

• To investigate the role of protein interactions and post-translational modifications in ACTH-stimulated CYP17 gene transcription.
• To identify key regulatory factors involved in the cAMP-responsive element (CRS) of the human CYP17 gene.

Main Methods:

• Identified proteins interacting with the human CYP17 CRS: steroidogenic factor 1 (SF-1), p54nrb, and polypyrimidine tract-binding protein-associated splicing factor (PSF).
• Utilized nuclear extracts from cAMP-stimulated H295R cells to assess cAMP-inducible protein binding to the hCYP17 CRS.
• Investigated the role of dual-specificity phosphatase (DSP) activity and mitogen-activated protein kinase phosphatase 1 (MKP-1) in regulating SF-1 activity and hCYP17 transcription.

Main Results:

• Demonstrated cAMP-inducible binding to the hCYP17 CRS, dependent on DSP activity.
• Showed that DSP activity is essential for ACTH/cAMP-stimulated transcription of steroidogenic genes.
• Confirmed that SF-1 transactivation potential is phosphatase-dependent, indicating dephosphorylation of SF-1 upon ACTH/cAMP stimulation.
• Established a role for MKP-1, a nuclear DSP, in mediating SF-1-dependent hCYP17 promoter transcription.

Conclusions:

• A DSP, potentially MKP-1, is essential for enhancing hCYP17 transcription in the adrenal cortex.
• Dephosphorylation of SF-1 by DSP increases its binding affinity for the hCYP17 promoter, along with p54nrb and PSF.
• This mechanism is critical for conveying ACTH/cAMP-stimulated steroidogenic gene expression.