Vitamin Receptors

The retinoid X receptor (RXR) is a nuclear receptor that binds and is activated by certain endogenous retinoids, such as 9-cis-retinoic acid. RXR is the obligatory heterodimerization partner for a large number of nonclassic steroid nuclear receptors, such as thyroid hoimone receptor, vitamin D3 receptor, peroxisome proliferator-activated receptor and pregnane X receptor. 

Figure 29-6. Gene transcription is regulated by retinoic acid.Ah-Zrwm-retinoic acid and 9-cA-retinoic acid are ligands for retinoic acid receptors (RARs) and retinoid X receptors (RXRs), respectively. The RXRs can form heterodimers with RARs and with the thyroid hormone receptors (TRs), the vitamin D receptor (VDR), and the peroxisome proliferator-activated receptors (PPARs) and a number of other hormone- and nutrient-responsive transcription factors to moderate gene transcription. Because of the ability of RXR to form heterodimers with other nuclear receptors, vitamin A has abroad effect on many hormonally and nutrient-responsive genes.

GiguereV (1994) Retinoic acid receptors. In Vitamin Receptors Vitamins and Ligands in Cell Communication, K Daksbinamurti (ed.), Cambridge, UK Cambridge University Press. 

Seetharam B and Li N (2000) Transcobalamin II and its cell surface receptor. Vitamins and Hormones 59, 337-66. 

Much attention hasbeen paid to the natural products becausethey have not only various biological activities but also are possible ligands for nuclear receptors, which are ligand-responsible transcription factors. Naturally occurring vitamin D analogues (vitamin D2, D3, D4, D5, D6 and D ) exhibit biological activities after converting to active metabolites, which act on a nuclear receptor, vitamin D receptor (VDR). 

Insulin or epidermal growth factor receptors Steroid receptors Vitamin D receptors... 

Available data on receptor/vitamin D interaction support the general conclusion that affinity for the receptor is determined primarily by the spatial arrangement of the hydroxy functions of the ligand, and that among the three hydroxy groups of la,25-(OH)2D3, those at C-1 and C-25 exert the most profound effect. The data shown in Fig. 11 offer dramatic confirmation of this general statement 1o,25-(OH)2D3 (13g), the active metabolite in intestine, exhibits highest... 

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