Vitamin D receptor zinc finger region binds to a direct repeat as a dimer and discriminates the spacing number between each half-site

1 alpha,25-Dihydroxyvitamin D3, the most active metabolite of vitamin D3, is a multifunctional agent. The actions of 1 alpha,25-dihydroxyvitamin D3 are mediated through its receptor that activates the specific genes in a ligand-dependent manner. In order to investigate the details of DNA binding properties of vitamin D receptor, we have developed the overexpression and purification system of vitamin D receptor DNA binding domain. The purified peptide could specifically bind to the osteopontin-derived vitamin D responsible element (VDRE) but not to the osteocalcin and the calbindin D-9k-derived VDREs, as determined by bandshift analysis. The osteopontin VDRE contains a direct repeat of GGTTCA motif separated by 3 nucleotides, whereas the osteocalcin and calbindin D-9k VDREs have inadequate direct repeat. Further analyses using synthetic oligonucleotides revealed that vitamin D receptor DNA binding domain could discriminate the spacing number between the consensus steroid-responsible element motif and had different affinities to direct repeats that consisted of various related sequences. These studies give insight into ways in which vitamin D receptor mediates the signal of 1 alpha,25-dihydroxyvitamin D3.