Retinoic Acid Receptor Coregulators in Epigenetic Regulation of Target Genes

This chapter focuses on coregulatory proteins of retinoid acid (RA) receptors (RARs)-retinoid X receptors (RXRs) that can modulate the transcriptional activity of the receptors and contribute to epigenetic regulation of RAR/RXR targeted gene expression. The coregulatory proteins were first functionally classified as either coactivators or corepressors, depending upon their effects on RA-regulated gene expression. Post-translational modification's (PTM) functional role in epigenetic regulation and chromatin remodeling is best elucidated for certain hormonal target genes, such as genes regulated by RA and thyroid hormones in the stem cell-adipocyte differentiation model. While the hormone is the major signal input to activate transcription of hormone target genes, other factors that can modulate the actions of chromatin remodelers, modifiers or Mediator all can contribute to epigenetic regulation of these hormone-target genes. Finally, the most desirable experiment is to rigorously examine the action of endogenous coregulators on the endogenous gene targets in the form of chromatin.