The vitamin D-3 receptor in the context of the nuclear receptor superfamily - The central role of the retinoid X receptor

The nuclear hormone 1 alpha,25-dihydroxyvitamin D-3 (VD) is an important regulator of calcium homeostasis and is also a modulator of the cell cycle. The genomic actions of the hormone are mediated by a single transcription factor, the vitamin D-3 receptor (VDR), On the majority of the known VD response elements, VDR binds as heterodimeric complex with the retinoid X receptor (RXR), which is a member of the nuclear receptor superfamily like VDR. RXR supports not only the DNA binding affinity and specificity of VDR, but allosterically also its transactivation properties. Moreover, RXR is a partner in other hormone response systems, which supports the idea that the different nuclear hormone signaling pathways are functionally linked.