The Vitamin D receptor (VDR), a nuclear hormone receptor for vitamin D3, is a protein that mediates the physiological actions of vitamin D by behaving as both a receptor for the vitamin, as well as a transcription factor for target genes. VDR is a member of the NR1I family, which also includes pregnane X (PXR) and constitutive androstane (CAR) receptors that form heterodimers with members of the retinoid X receptor family.