The vitamin D receptor (VDR) typically binds DNA in a heterodimer complex with the retinoid X receptor (RXR) to direct repeat sequences separated by three base pairs, or vitamin D response elements (VDREs). A modified yeast one-hybrid screen was utilized to search for partner proteins capable of associating with the VDR on a repressor VDRE. Screening of a HeLa cell cDNA library revealed that retinoic acid receptor gamma 2 (RARgamma2) could specifically interact with VDREs, either in the presence or absence of the VDR. Importantly, the A-domain of RARgamma2 appeared to be crucial for this interaction as evidenced by the inability of RARgamma1 to affect reporter gene activity. Transfection data in COS-7 cells revealed the combination of both receptor ligands strongly attenuated transcriptional activation from an enhancer VDRE when RARgamma2 was co-transfected into these cells with the VDR. Furthermore, a VDR/RARgamma2 complex was detected in the mobility shift assay from nuclear extracts of transfected cells. Thus, the data highlight the novel ability of RARgamma2 to interact with VDREs and impact vitamin D activity, which would allow for additional fine-tuning of a transcriptional response depending on ligand availability and expression profile of these nuclear receptors in a given cell type.
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