VDR gene polymorphism and falls in the elderly.

Abstract

We previously identified a NF-Y binding site (NF-YDIST) unique to the human PTH (hPTH) promoter adjoining a Sp1 DNA element that is highly conserved in a variety of mammalian PTH promoters. We also showed that a second NF-Y element (NF-YPROX) is located ca. 30 bp downstream from the Sp1/NF-YDIST site in the hPTH promoter. NF-YPROX overlaps with the repressor DNA binding site for the vitamin D receptor (VDR) heterodimer complex and the two factors compete for DNA-binding in vitro. In the present study, addition of recombinant VDR heterodimer to nuclear extracts possessing NF-Y binding activity revealed that the VDR heterodimer also formed a distinct complex on the hPTH Sp1/NF-YDIST element and could compete with NF-Y for binding to this DNA element. The binding activity was specific for the heterodimer and interference footprint analysis indicated the sites of DNA contacted by the complex comprised an everted repeat. Cold competition analysis indicated VDR heterodimer binding to the hPTH Sp1/NF-YDIST site was weaker compared to the downstream VDRE/NF-YPROX element, and interactions with a contiguous DNA sequence containing both binding sites did not reveal evidence of cooperativity. Sp1 and NF-Y can synergistically enhance transcription from the hPTH promoter; however, co-expression of the VDR heterodimer complex resulted in strong 1,25(OH)2 D3 -dependent suppression (>80%) of Sp1/NF-Y synergistic transactivation. This suppressive capability was lost when transient expression of the wild-type VDR in the heterodimer complex was replaced by VDR mutants L417S or E420Q. Thus, synergistic transactivation of the hPTH promoter by Sp1/NF-Y complexes can be suppressed by 1,25(OH)2 D3 and requires hormone interactions with an intact VDR AF-2 domain. The data suggest that VDR heterodimer binding to the hPTH Sp1/NF-YDIST element may be contributing to the overall suppression of enhanced promoter activity.