Analysis of binding of the 1,25-dihydroxyvitamin D3 receptor to positive and negative vitamin D response elements.

The binding of the 1,25-dihydroxyvitamin D3 receptor 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.