Functional Analysis of Vitamin D Response Elements in the Parathyroid Hormone Gene and a Comparison with the Osteocalcin Gene

We have previously localised two putative vitamin D response elements (VDRE) in the bovine parathyroid hormone (PTH) gene to within −485 to −452 and −451 to −348 base pairs (bp). To confirm the functional significance of these elements, a series of reporter gene constructs were generated and the ability of 1,25-dihydroxyvitamin D3(1,25(OH)2D3) to suppress gene transcription was assessed. These data confirmed the presence of two regions within −485 to −348 bp which confer responsiveness to 1,25(OH)2D3and mediate its down-regulatory effect on PTH gene transcription. Second, we investigated whether the putative bovine PTH VDRE and the osteocalcin VDRE require the same nuclear proteins in their interaction with VDR. In gel shift assays, three specific DNA–protein complexes were formed using CV-1 nuclear extract and PTH VDRE. However, unlabelled osteocalcin VDRE (50-fold) failed to inhibit the formation of these complexes. These results suggest that interactions of VDR with the PTH and osteocalcin genes require different accessory factors.