The retinoid X receptor (RXR) is a type of

nuclear receptor In the field of molecular biology, nuclear receptors are a class of proteins responsible for sensing steroid hormone, steroids, thyroid hormone, thyroid hormones, vitamins, and certain other molecules. These receptors work with other proteins to ...

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. In a novel review publication, this 9-''cis''-13,14-dihydroretinoic acid was shown to be a metabolite not originating from the known

vitamin A Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably ...

(vitamin A1) pathway and its nutritional precursors all-''trans''-

retinol Retinol, also called vitamin A1, is a fat-soluble vitamin in the vitamin A family found in food and used as a dietary supplement. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xeroph ...

( vitamin A (vitamin A1) or all-''trans''- beta-carotene (

provitamin A A provitamin is a substance that may be converted within the body to a vitamin. The term previtamin is a synonym. The term "provitamin" is used when it is desirable to label a substance with little or no vitamin activity, but which can be converted ...

(provitamin A1)). An independent pathway for generating this endogenous RXR-ligand 9-''cis''-13,14-dihydroretinoic acid from 9-''cis''-13,14-dihydroretinol present in food source and named vitamin A5 or alternatively via provitamin A5 has been suggested as the first novel vitamin identified since 1948,

cobalamin Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. ...

vitamin B12 Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. ...

. There are three retinoic X receptors (RXR): RXR-alpha, RXR-beta, and RXR-gamma, encoded by the , , genes, respectively. RXR heterodimerizes with subfamily 1 nuclear receptors including CAR, FXR, LXR,

PPAR In the field of molecular biology, the peroxisome proliferator-activated receptors (PPARs) are a group of nuclear receptor proteins that function as transcription factors regulating the expression of genes. PPARs play essential roles in the reg ...

, PXR,

RAR RAR or Rar may refer to: * Radio acoustic ranging, a non-visual technique for determining a ship's position at sea * "rar", the ISO 639-2 code for the Cook Islands Māori language * RAR (file format), a proprietary compressed archive file format i ...

, TR, and VDR. As with other type II nuclear receptors, the RXR heterodimer in the absence of ligand is bound to hormone response elements complexed with

corepressor In the field of molecular biology, a corepressor is a molecule that represses the expression of genes. In prokaryotes, corepressors are small molecules whereas in eukaryotes, corepressors are proteins. A corepressor does not directly bind to DNA, ...

protein. Binding of agonist

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...

s to RXR results in dissociation of corepressor and recruitment of coactivator protein, which, in turn, promotes transcription of the downstream target

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

into

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...

and eventually

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

References

External links

* Intracellular receptors Transcription factors {{receptor-stub

See also

References

External links