Analysis of Binding of the 1,25-Dihydroxyvitamin D3Receptor to Positive and Negative Vitamin D Response Elements

The binding of the 1,25-dihydroxyvitamin D3receptor to the vitamin D response elements (VDREs) in the rat osteocalcin (OSC–DRE), mouse osteopontin (MOP–DRE), rat calbindin D-9k (CaBP–DRE), and human parathyroid hormone genes (PTH–DRE) was studied. Binding of VDR to the three positive VDREs is cooperative. The degree of cooperativity is highest with the calbindin VDRE compared with either the OSC–DRE or the MOP–DRE. This cooperativity is largely absent in the case of the negative element, the PTH–DRE. The VDR binds in order of decreasing affinity to PTH–DRE > OSC–DRE = MOP–DRE > CaBP–DRE. Thus, the greatest affinity is associated with the lowest degree of cooperativity. Further study has revealed that the PTH–VDRE actually consists of two repeat elements like all other VDREs and is not a single six-base sequence. A nuclear factor has also been found that binds downstream from the GGTTCA element in the PTH promoter. The binding site of this factor overlaps the PTH–DRE nucleotide sequence.