Regulation of vitamin D action.

The control of gene transcription by vitamin D compounds is initiated by binding to the VDR, which enhances the receptor's ability to heterodimerize to RXR, interact with response elements in target genes and attract components of the transcriptional initiation complex. A number of factors are capable of influencing this process, including (i) the rate of uptake and catabolism of the ligand, (ii) the nature of the conformational change induced by a specific ligand, (iii) the cellular content of the VDR, (iv) post-translational modifications of the VDR and (v) the availability of other transcriptional components. Vitamin D analogues may affect these factors differently to 1,25(OH)2D3 to produce unique biological profiles that can be exploited for therapeutic use.