文摘
1,25-Dihydroxyvitamin D3 [1,25(OH)2 D3] exerts its biological effects by binding to the vitamin D receptor (VDR), which binds in turn to the vitamin D response elements located in the target gene's promoter. We have previously demonstrated that VDR binds in vitro with high affinity to the 5′-flanking sequence of the human growth hormone (hGH) gene. In this study, we analyzed the response to 1,25(OH)2 D3 of hGH-promoter constructs introduced by transfection into the MCF-7 human adenocarcinoma cell line. We found that the transcriptional activity of some of these constructs was markedly reduced by 1,25(OH)2 D3. Deletion analyses revealed that a 34-bp sequence located between positions −62 and −29 upstream of the transcription start site is sufficient for this repressive response. This conclusion was also confirmed by gel mobility shift assays. Our results indicate that vitamin D inhibits hGH gene transcription, directly or by interference with other transcription factors.
