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Figure 3: Regulation of vitamin D target genes. Circulating 1,25(OH)2D passes into a target cell and binds to the cytoplasmic vitamin D receptor (VDR), which is present in most cells and tissues in the body. This translocates to the nucleus and in turn, interacts with nuclear hormone receptors, most principally, the nuclear retinoic acid X receptor (RXR). The 1,25(OH)2D•VDR•RXR complex then binds to vitamin D response elements (VDREs) on DNA. This binding is accompanied by the formation of large complexes that are able to either facilitate the expression of a target gene (coactivators) or alternatively, inhibit its expression (cosuppressors). Cosupressors act predominantly by deacetylating histones. Coactivators, in contrast, function either to expose the gene for transcription, or to bridge the gap between the VDREs and initiation complex, which stimulates transcription by activating RNA polymerase. The horizontal black line in the figure represents DNA.
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