There is considerable divergence in the sequences of steroid receptor response elements, including the vitamin D response elements (VDREs). Two major VDRE-containing and thus 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3))-regulated genes are the two non-collagenous, osteoblast-derived bone matrix proteins osteocalcin and osteopontin. We observed a stronger induction of osteopontin than osteocalcin mRNA expression by 1,25-(OH)(2)D(3). Subsequently, we have shown that vitamin D receptor/retinoid X receptor alpha (VDR/RXRalpha) heterodimers bind more tightly to the osteopontin VDRE than to the osteocalcin VDRE. Studies using point mutants revealed that the internal dinucleotide at positions 3 and 4 of the proximal steroid half-element are most important for modulating the strength of receptor binding. In addition, studies with VDRE-driven luciferase reporter gene constructs revealed that the central dinucleotide influences the transactivation potential of VDR/RXRalpha with the same order of magnitude as that observed in the DNA binding studies. The synthetic vitamin D analog KH1060 is a more potent stimulator of transcription and inducer of VDRE binding of VDR/RXR in the presence of nuclear factors isolated from ROS 17/2.8 osteoblast-like cells than the natural ligand 1,25-(OH)(2)D(3). Interestingly, however, KH1060 is comparable or even less potent than 1,25-(OH)(2)D(3) in stimulating VDRE binding of in vitro synthesized VDR/RXRalpha. Thus, the extent of 1,25-(OH)(2)D(3)- and KH1060-dependent binding of VDR/RXRalpha is specified by a central dinucleotide in the VDRE, and the ligand-induced effects on DNA binding are in part controlled by the cellular context of nuclear proteins.

*Trans-Activation (Genetics), *Vitamin D Response Element, Animals, Base Sequence, DNA Primers, Electrophoretic Mobility Shift Assay, Humans, Ligands, Osteocalcin/genetics, Protein Binding, RNA, Messenger/genetics, Receptors, Calcitriol/chemistry/*metabolism, Receptors, Retinoic Acid/chemistry/*metabolism, Retinoid X Receptors, Sialoglycoproteins/genetics, Transcription Factors/chemistry/*metabolism, Tumor Cells, Cultured,
Journal of Biological Chemistry
Erasmus MC: University Medical Center Rotterdam

van den Bemd, G.J.C.M, Jhamai, M, Staal, A, van Wijnen, A.J, Lian, J.B, Stein, G.S, … van Leeuwen, J.P.T.M. (2002). A central dinucleotide within vitamin D response elements modulates DNA binding and transactivation by the vitamin D receptor in cellular response to natural and synthetic ligands. Journal of Biological Chemistry, 277(17), 14539–14546. doi:10.1074/jbc.M111224200