期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2001
卷号：98
期号：24
页码：13572-13576
DOI：10.1073/pnas.241516798
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The up-regulation of the 25-hydroxyvitamin D3-24-hydroxylase by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is well established and occurs at the transcriptional level through two vitamin D response elements in the promoter of the gene. However, the mechanism of down-regulation of the 24-hydroxylase by parathyroid hormone (PTH) has not yet been elucidated. To study the mechanism of PTH action, we used AOK-B50 cells, a porcine kidney-cell line with stably transfected opossum PTH receptor in which both the 24-hydroxylase mRNA and activity are down-regulated by PTH. Cells dosed with 1,25(OH)2D3 at 0 h, and subsequently at 0, 1, 2, or 4 h with 100 nM of PTH, showed levels of 24-hydroxylase mRNA equivalent to 72.6, 65.3, 57.2, and 37.1%, respectively, of the levels found in cells dosed with 1,25(OH)2D3 only. All cells were collected 7 h after the initial 1,25(OH)2D3 dose. This pattern of expression indicated that PTH does not act by repressing transcription but rather by making the mRNA for 24-hydroxylase susceptible to degradation. At least 1 h is required for PTH to act. Further RNA and protein syntheses are required for PTH to act. However, the sites and mechanism whereby PTH causes 24-hydroxylase mRNA degradation are unknown. Because the untranslated regions of genes can determine the stability of its transcripts, we studied the 5' untranslated region and the 3' untranslated region of the rat 24-hydroxylase gene by using reporter-gene strategy to identify possible PTH sites of action. None was found, suggesting that the destabilization site is elsewhere in the coding region.
