Interaction of vitamin D and retinoid receptors on regulation of gene expression

Vitamin D and retinoic acid (RA) receptors (VDRs and RARs, respectively), b ind as heterodimers with the retinoid X receptor (RXR) to hormone response elements (HREs) in target genes. In some cases RA and vitamin D can coopera te to stimulate transcription through the same HRE. However, VDR/RXR hetero dimers bind in a transcriptionally unproductive manner and without a define d polarity on certain RA response elements, and under these circumstances v itamin D inhibits the response to RA. Although competition for binding to D NA may contribute to this inhibitory response, titration of common coactiva tors; by VDR also appears to be involved in transrepression. Therefore, the transcriptional response to RA and vitamin D depends on a complex combinat ory pattern of interaction among different receptors wih DNA and coactivato rs. Copyright (C) 2001 S. Karger AG, Basel.