Retinoids exert pleiotropic effects in various biological processes by binding to their nuclear receptors, the retinoic acid receptors (RARs) and retinoid X receptors (RXRs), to regulate gene transcription. Apo-RARs and RXRs repress target gene expression by recruiting corepressors to the target DNA, triggering chromatin condensation by the action of histone deacetylases present in the corepressor complexes. In contrast, holo-RARs and RXRs recruit coactivators, some known to encode histone acetyl transferases, which trigger histone hyperacetylation, chromatin decondensation, and ultimately gene activation. Receptor interacting protein 140 (RIP140) represents a novel RAR / RXR coregulator that suppresses vitamin A-regulated gene expression in a retinoid- dependent manner. This review addresses the action of different retinoid ligands on gene expression, the molecular mechanisms underlying RAR/RXR-mediated gene regulation, and the unique properties of RIP140 as a novel retinoid hormone-dependent negative coregulator for RAR- and RXR-mediated gene regulation.
Keywords: hormones, retinoids, retinoid receptors, receptor complexes, coactivators, corepressors, gene transcription, histone acetylation, chromatin
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