ANALYSIS OF BINDING OF THE 1,25-DIHYDROXYVITAMIN D-3 RECEPTOR TO POSITIVE AND NEGATIVE VITAMIN-D RESPONSE ELEMENTS

The binding of the 1,25-dihydroxyvitamin D-3 receptor to the vitamin D response elements (VDREs) in the rat osteocalcin (OSC-DRE), mouse ost eopontin (MOP-DRE), rat calbindin D-9k (CaBP-DRE), and human parathyro id hormone genes (PTH-DRE) was studied. Binding of VDR to the three po sitive VDREs is cooperative. The degree of cooperativity is highest wi th the calbindin VDRE compared with either the OSC-DRE or the MOP-DRE. This cooperativity is largely absent in the case of the negative elem ent, the I?TH-I)RE. The VDR binds in order of decreasing affinity to P TH-I)RE > 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 l ike all other VDREs and is not a single six-base sequence. A nuclear f actor has also been found that binds downstream from the GGTTCA elemen t in the PTH promoter. The binding site of this factor overlaps the PT H-DRE nucleotide sequence. (C) 1996 Academic Press, Inc.