Retinoid X receptor alpha (RXR-alpha), also known as NR2B1 (nuclear receptor subfamily 2, group B, member 1) is a nuclear receptor that in humans is encoded by the RXRA gene. [5]
Retinoid X receptors (RXRs) and retinoic acid receptors (RARs), are nuclear receptors that mediate the biological effects of retinoids by their involvement in retinoic acid-mediated gene activation. These receptors exert their action by binding, as homodimers or heterodimers, to specific sequences in the promoters of target genes and regulating their transcription. The protein encoded by this gene is a member of the steroid and thyroid hormone receptor superfamily of transcription factors. [6] In the absence of ligand, the RXR-RAR heterodimers associate with a multiprotein complex containing transcription corepressors that induce histone deacetylation, chromatin condensation and transcriptional suppression. On ligand binding, the corepressors dissociate from the receptors and associate with the coactivators leading to transcriptional activation. The RXRA/PPARA heterodimer is required for PPARA transcriptional activity on fatty acid oxidation genes such as ACOX1 and the cytochrome P450 system genes. [7]
Click on genes, proteins and metabolites below to link to respective articles. [§ 1]
Retinoid X receptor alpha has been shown to interact with:
Histone acetyltransferase p300 also known as p300 HAT or E1A-associated protein p300 also known as EP300 or p300 is an enzyme that, in humans, is encoded by the EP300 gene. It functions as histone acetyltransferase that regulates transcription of genes via chromatin remodeling by allowing histone proteins to wrap DNA less tightly. This enzyme plays an essential role in regulating cell growth and division, prompting cells to mature and assume specialized functions (differentiate), and preventing the growth of cancerous tumors. The p300 protein appears to be critical for normal development before and after birth.
The thyroid hormone receptor (TR) is a type of nuclear receptor that is activated by binding thyroid hormone. TRs act as transcription factors, ultimately affecting the regulation of gene transcription and translation. These receptors also have non-genomic effects that lead to second messenger activation, and corresponding cellular response.
The vitamin D receptor (VDR also known as the calcitriol receptor) is a member of the nuclear receptor family of transcription factors. Calcitriol (the active form of vitamin D, 1,25-(OH)2vitamin D3) binds to VDR, which then forms a heterodimer with the retinoid-X receptor. The VDR heterodimer then enters the nucleus and binds to Vitamin D responsive elements (VDRE) in genomic DNA. VDR binding results in expression or transrepression of many specific gene products. VDR is also involved in microRNA-directed post transcriptional mechanisms. In humans, the vitamin D receptor is encoded by the VDR gene located on chromosome 12q13.11.
The retinoic acid receptor (RAR) is a type of nuclear receptor which can also act as a ligand-activated transcription factor that is activated by both all-trans retinoic acid and 9-cis retinoic acid, retinoid active derivatives of Vitamin A. They are typically found within the nucleus. There are three retinoic acid receptors (RAR), RAR-alpha, RAR-beta, and RAR-gamma, encoded by the RARA, RARB, RARG genes, respectively. Within each RAR subtype there are various isoforms differing in their N-terminal region A. Multiple splice variants have been identified in human RARs: four for RARA, five for RARB, and two for RARG. As with other type II nuclear receptors, RAR heterodimerizes with RXR and in the absence of ligand, the RAR/RXR dimer binds to hormone response elements known as retinoic acid response elements (RAREs) complexed with corepressor protein. Binding of agonist ligands to RAR results in dissociation of corepressor and recruitment of coactivator protein that, in turn, promotes transcription of the downstream target gene into mRNA and eventually protein. In addition, the expression of RAR genes is under epigenetic regulation by promoter methylation. Both the length and magnitude of the retinoid response is dependent of the degradation of RARs and RXRs through the ubiquitin-proteasome. This degradation can lead to elongation of the DNA transcription through disruption of the initiation complex or to end the response to facilitate further transcriptional programs. Due to RAR/RXR heterodimers acting as subtrates to the non steroid hormone ligand retinoid they are extensively involved in cell differentiation, proliferation, and apoptosis.
The retinoid X receptor (RXR) is a type of nuclear receptor that is activated by 9-cis retinoic acid, which is discussed controversially to be of endogenous relevance, and 9-cis-13,14-dihydroretinoic acid, which is likely to be the major endogenous mammalian RXR-selective agonist.
The liver X receptor (LXR) is a member of the nuclear receptor family of transcription factors and is closely related to nuclear receptors such as the PPARs, FXR and RXR. Liver X receptors (LXRs) are important regulators of cholesterol, fatty acid, and glucose homeostasis. LXRs were earlier classified as orphan nuclear receptors, however, upon discovery of endogenous oxysterols as ligands they were subsequently deorphanized.
The nuclear receptor coactivator 2 also known as NCoA-2 is a protein that in humans is encoded by the NCOA2 gene. NCoA-2 is also frequently called glucocorticoid receptor-interacting protein 1 (GRIP1), steroid receptor coactivator-2 (SRC-2), or transcriptional mediators/intermediary factor 2 (TIF2).
The nuclear receptor coactivator 3 also known as NCOA3 is a protein that, in humans, is encoded by the NCOA3 gene. NCOA3 is also frequently called 'amplified in breast 1' (AIB1), steroid receptor coactivator-3 (SRC-3), or thyroid hormone receptor activator molecule 1 (TRAM-1).
The nuclear receptor co-repressor 1 also known as thyroid-hormone- and retinoic-acid-receptor-associated co-repressor 1 (TRAC-1) is a protein that in humans is encoded by the NCOR1 gene.
Retinoic acid receptor alpha (RAR-α), also known as NR1B1 is a nuclear receptor that in humans is encoded by the RARA gene.
Nuclear receptor-interacting protein 1 (NRIP1) also known as receptor-interacting protein 140 (RIP140) is a protein that in humans is encoded by the NRIP1 gene.
Retinoid X receptor gamma (RXR-gamma), also known as NR2B3 is a nuclear receptor that in humans is encoded by the RXRG gene.
Retinoid X receptor beta (RXR-beta), also known as NR2B2 is a nuclear receptor that in humans is encoded by the RXRB gene.
COUP-TFII, also known as NR2F2 is a protein that in humans is encoded by the NR2F2 gene. The COUP acronym stands for chicken ovalbumin upstream promoter.
Thyroid hormone receptor beta (TR-beta) also known as nuclear receptor subfamily 1, group A, member 2 (NR1A2), is a nuclear receptor protein that in humans is encoded by the THRB gene.
Mediator of RNA polymerase II transcription subunit 1 also known as DRIP205 or Trap220 is a subunit of the Mediator complex and is a protein that in humans is encoded by the MED1 gene. MED1 functions as a nuclear receptor coactivator.
Nuclear receptor coactivator 6 is a protein that in humans is encoded by the NCOA6 gene.
Tripartite motif-containing 24 (TRIM24) also known as transcriptional intermediary factor 1α (TIF1α) is a protein that, in humans, is encoded by the TRIM24 gene.
Activating signal cointegrator 1 is a protein that in humans is encoded by the TRIP4 gene.
Vitamin D response element (VDRE) is a type of DNA sequence that is found in the promoter region of vitamin D regulated genes. This sequence binds the vitamin D receptor (VDR), when complexed with calcitriol (1,25(OH)2D), the active form of vitamin D, and so regulates the expression of many genes.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.