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Transcription Activation by Nuclear Receptors.
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Retinoid X receptor (RXR) and Retinoic Acid receptor (RAR) are nuclear receptors that bind either all trans-retinoic (tRA) or 9-cis-retinoic acid (9-cis-RA). In the absence of ligand, corepressors, such as Nuclear Receptor Corepressor (NCoR), Silencing Mediator of Retinoid and Thyroid Hormone Receptor (SMRT), and Histone Deacetylase-1 (HDAC-1) associate with the RAR:RXR heterodimer complex and repress transcription. The histone deacetylase activity of the complex helps maintain tight association between the deacetylated histones and chromatin that results in this repression. Transcription Activation by Nuclear Receptors
When tRA or 9-cis-RA binds to the RAR:RXR complex, a conformational change in the receptors causes the dissociation of the corepressors and subsequent recruitment and binding of coactivators such as Steroid Receptor Coactivator-1 (SRC-1), Glucocorticoid Receptor Interacting Protein-1 (GRIP-1), CREB Binding Protein (CBP) and CBP-Associated Factor (PCAF). This receptor:coactivator complex activates histone acetyltransferase (HAT). Acetylated histones dissociate from the chromatin and allow for the basal transcription machinery complex to bind to DNA and activate transcription of target genes. Transcription Activation by Nuclear Receptors