Synthetic retinoids dissociate coactivator binding from corepressor release

Area of Science:

• Molecular Biology
• Endocrinology
• Genetics

Background:

• Ligand-activated retinoid receptors, Retinoid X Receptor (RXR) and Retinoic Acid Receptor (RAR), are crucial regulators of gene transcription involved in development, homeostasis, and disease.
• Current models propose that ligand binding induces a conformational change in RARs, facilitating the exchange of corepressor and coactivator complexes to modulate gene expression.
• The need for precise control over retinoic acid signaling pathways has driven the development of isoform-selective retinoids.

Purpose of the Study:

• To investigate the potential of RARalpha isotype-specific synthetic agonists and antagonists to selectively modulate coactivator recruitment and corepressor release.
• To characterize the distinct mechanisms of action of novel synthetic retinoids on RARalpha transcriptional regulation.

Main Methods:

• Synthesis and characterization of RARalpha isotype-specific synthetic retinoids, including pure agonists, pure antagonists, partial agonists, and partial antagonists.
• Investigation of the interaction of these synthetic retinoids with RARalpha ligand-binding domain (LBD) to assess coactivator recruitment and corepressor release.
• Assessment of the differential effects of partial antagonists on nuclear corepressors SMRT and NCoR.

Main Results:

• Four categories of synthetic retinoids were identified, exhibiting distinct modes of action on RARalpha.
• Pure agonists and antagonists function according to the established model, while partial agonists induce a conformation allowing for both coactivator and corepressor interaction, leading to cell context-specific activity.
• Partial antagonists inhibit both coactivator and corepressor interaction, with one compound specifically dissociating SMRT but not NCoR from the RARalpha LBD.

Conclusions:

• Synthetic retinoids can be designed to selectively target specific aspects of RARalpha-mediated transcription, such as coactivator recruitment or corepressor release.
• Partial agonists and antagonists represent novel tools for dissecting the complex mechanisms of retinoid signaling and offer potential for fine-tuning gene expression.
• The observed differential interaction with SMRT and NCoR by partial antagonists highlights the potential for developing highly specific modulators of retinoid receptor function.