Retinoic X receptors

Norata GD, Ongari M, Uboldi P, Pellegatta F, Catapano AL (2005) Liver X receptor and retinoic X receptor agonists modulate the expression of genes involved in lipid metabolism in human endothelial cells. Int J Mol Med 16 717-722... 

Fig. 2. Summary of the mode of action of peroxisome proliferators (PP) through the nuclear peroxisome proliferator-activated receptor (PPAR). The activation of PPAR requires the retinoic X receptor (RXR). The receptors are found in the cytoplasm and once the ligands bind (1) they undergo a conformational change (2) that allows the complex to enter the nucleus (3). The complex then binds to the peroxisome proliferator response element (PPRE) in the promoter region of target genes to alter transcription (4). Modified from Gervois et alP...

Retinoic X receptors (RXR, a, (3 and " (), also termed rexinoid receptors, are usually classified among orphan receptors, but belong to the thyroid/retinoid family. RXR is an obligatory partner dimerizing with other thyroid/retinoid receptors. RXR selectively bind the 9-cis isomer of retinoic acid, whereas RAR bind aU-tran retinoic acid as well as its 9-cis isomer. RXR selective agonists are termed rexi-noids, like bexarotene used as an antineoplastic in the treatment of cutaneous T-cell lymphoma and the cutaneous lesions of T-cell lymphomas and Kaposi s sarcoma. 

Ligand-Dependent Conformational Changes in Thyroid Hormone and Retinoic Acid Receptors Are Potentially Enhanced by Heterodimerization with Retinoic X Receptor. 

Vitamin A (retinol) is a fat-soluble vitamin important for the maintenance of skin, bone, and blood vessels, as well as for the promotion of vision (Theodosiou et al. 2010). It is obtained from the diet either as all-trans-retinol, retinyl esters, or P-carotene (Blomhoff and Blomhoff 2006) and is stored in the liver (Moise et al. 2007). Vitamin A is converted to retinoic acid (RA), which is formed mainly through intracellular oxidative metabolism by retinal dehydrogenases (RALDHs) (Lampen et al. 2000). RA plays important roles in embryonic development, organogenesis, tissue homeostasis, cell proliferation, differentiation, and apoptosis (Theodosiou et al. 2010). In adult mammals, RALDH is found in intestinal epithelial cells (lECs) and gut associated-dendritic cells (DCs) from Peyer s patches and mesenteric lymph nodes (Iwata 2004, Coombes et al. 2007). Gut-associated DCs and lECs can metabolize vitamin A to RA in vitro (Lampen 2000), which indicates they may be a source of RA in gut mucosa. RA binds to two families of nuclear receptors, RA receptor (RAR) isotypes (a, p, and y) and retinoic X receptor (RXR) isotypes (a, p, and y). RAR and RXR form heterodimers and interact with retinoic acid response elements (RAREs) within the promoters of retinoic acid responsive genes (Blomhoff and Blomhoff 2006). RAR is ubiquitously expressed and up-regulated by RA. RXR also... 

Chambon P et al (1993) Retinoic acid receptors and retinoic X receptors Interactions with endogenous retinoic acids. Proc Natl Acad Sci USA 90 30-34... 

Joseph B, Lefebvre O, Mereau-Richard C, Danze PM, Belin-Plancot MT, Formstecher P (1998) Evidence for the involvement of both retinoic acid receptor- and retinoic X receptor-dependent signalling pathways in the induction of tissue transglutaminase and apoptosis in the human myeloma cell line RMPI 8226. Blood 91 2423-2432... 

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