Retinoid X receptors.

Retinoids are metabolites of retinol (vitamin A), which act as signalling molecules in embryogenesis and as stimulators of cellular differentiation. The potency of retinoids as differentiating agents has led to their successful use in treating skin diseases and some forms of cancer. The retinoid X receptors (RXRs) are receptors for the vitamin A metabolite 9-cis retinoic acid, and they are members of the steroid/thyroid hormone receptor superfamily of DNA binding nuclear hormone receptor. The RXRs are also cofactors required for transcription activated by some other members of the steroid/thyroid hormone receptor superfamily, including the all-trans retinoic acid, thyroid hormone, vitamin D and peroxisome proliferator-activated receptors. The biological importance of the RXRs has been demonstrated in recent genetic studies which have shown that some RXR null mutations in mice have phenotypic effects similar to vitamin A deficiency.