The Association between Vitamin D Receptor Expression and

The vitamin D receptor (VDR) belongs to the nuclear class II receptor family of two known families (Bettoun et al. 2003). The first one includes the estrogen, androgen, pro-gesterone, and mineralocorticoid receptors the second one the thyroid (THR), vitamin D (VDR), retinoic acid (RAR), peroxisome proliferator-activated, and retinoid X receptors (RXR). It is a ligand transcription factor and mediates the actions of 1,25-dihydroxyvitamin D3, the active metabolite of vitamin D, which is involved in cell growth and differen-tiation in normal and malignant breast tissue, where it shows antiproliferative effects (Perez-Fernandez et al. 2007). VDRs are able to form heterodimers, for example, with RXR, THR, or RAR. These heterodimers have been thought to be nonpermissive because they neither bind nor show activation by RXR ligands (Forman et al. 1995)