High-affinity binding sites to the vitamin D receptor DNA binding domain in the human growth hormone promoter

The regulation of the human growth hormone (hGH) gene by 1,25(OH)2D3 is a mechanism which is poorly understood. The objective of this study was to investigate whether the hGH gene has DNA recognition elements for the DNA binding domain of the vitamin D receptor. Using gel retardation assays and footprinting techniques, two high-affinity binding sites, denominated F1 and F2, were identified in the 5'-flanking sequence of hGH. The distal site, F1, located at -59 bp is made up of an imperfect direct repeat separated by 3 bp and showed a high degree of similarity with other known vitamin D response elements (VDREs). The proximal site, F2, located at -36 bp showed a single 7-bp sequence, which is different from other known VDREs. The location of both sites (F1 near the GHF-1/Pit-1 response element, F2 contacting the TATA box) suggests that the vitamin D receptor by itself or through interference with other transcriptional factors may modulate hGH expression.