Sneddon W B, Barry E L, Coutermarsh B A, Gesek F A, Liu F, Friedman P A
Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, N.H., USA.
Cell Physiol Biochem. 1998;8(5):261-77. doi: 10.1159/000016288.
The renal distal convoluted tubule (DCT) is the major site of parathyroid hormone (PTH) and 1alpha,25-dihydroxyvitamin D3 [1, 25(OH)2D3]-regulated calcium absorption. 1,25(OH)2D3 augments PTH-stimulated calcium transport by DCT cells, while having no effect of its own. 1,25(OH)2D3 mediates its effects on gene expression by binding to a nuclear vitamin-D receptor (VDR), which then associates with the retinoid-X receptor (RXR) as a heterodimer. We studied the effects of 1,25(OH)2D3, 9-cis- and all-trans-retinoic acid on PTH/PTHrP receptor expression. mRNAs for the PTH/PTHrP, VDR, and RXR receptors were detected in immortalized DCT cells by reverse transcriptase-polymerase chain reaction. Changes in PTH/PTHrP receptor mRNA expression were quantified by slot blot hybridization. 1,25(OH)2D3 maximally increased PTH/PTHrP receptor mRNA levels by 70%. The stimulation was specific since 1,25(OH)2D3 treatment had no effect on the expression of adrenergic receptor or Na+/H+ exchanger mRNA levels. Likewise, the inactive form, 25(OH)2D3 had no effect on PTH/PTHrP receptor mRNA expression. In combination with the putative RXR ligand, 9-cis-retinoic acid, 1,25(OH)2D3 increased PTH/PTHrP receptor mRNA levels 4-fold. 9-cis-Retinoic acid had no effect of its own on steady-state PTH/PTHrP receptor mRNA expression. The putative ligand for the retinoic acid receptor, all-trans-retinoic acid, increased PTH/PTHrP receptor mRNA expression alone and in combination with 1,25(OH)2D3. 9-cis-Retinoic acid alone, and in combination with 1,25(OH)2D3, also increased specific PTH/PTHrP receptor binding to plasma membranes isolated from DCT cells. These results indicate that 1,25(OH)2D3 upregulated PTH/PTHrP receptor expression at both mRNA and protein levels in a manner consistent with VDR/RXR heterodimers transactivating the PTH/PTHrP receptor gene by binding a vitamin D response element in the PTH/PTHrP gene.
肾远曲小管（DCT）是甲状旁腺激素（PTH）和1α，25 - 二羟基维生素D3 [1,25(OH)2D3]调节钙吸收的主要部位。1,25(OH)2D3增强PTH刺激的DCT细胞钙转运，而其自身无作用。1,25(OH)2D3通过与核维生素D受体（VDR）结合来介导其对基因表达的作用，VDR随后与视黄酸X受体（RXR）形成异二聚体。我们研究了1,25(OH)2D3、9 - 顺式和全反式视黄酸对PTH/PTHrP受体表达的影响。通过逆转录 - 聚合酶链反应在永生化DCT细胞中检测到PTH/PTHrP、VDR和RXR受体的mRNA。通过狭缝印迹杂交对PTH/PTHrP受体mRNA表达的变化进行定量。1,25(OH)2D3使PTH/PTHrP受体mRNA水平最大增加70%。这种刺激是特异性的，因为1,25(OH)2D3处理对肾上腺素能受体或Na+/H+交换体mRNA水平的表达没有影响。同样，无活性形式的25(OH)2D3对PTH/PTHrP受体mRNA表达也没有影响。与假定的RXR配体9 - 顺式视黄酸联合使用时，1,25(OH)2D3使PTH/PTHrP受体mRNA水平增加4倍。9 - 顺式视黄酸自身对稳态PTH/PTHrP受体mRNA表达没有影响。视黄酸受体的假定配体全反式视黄酸单独以及与1,25(OH)2D3联合使用时均增加PTH/PTHrP受体mRNA表达。9 - 顺式视黄酸单独以及与1,25(OH)2D3联合使用时，也增加了从DCT细胞分离的质膜上特异性PTH/PTHrP受体的结合。这些结果表明，1,25(OH)2D3在mRNA和蛋白质水平上调PTH/PTHrP受体表达，其方式与VDR/RXR异二聚体通过结合PTH/PTHrP基因中的维生素D反应元件反式激活PTH/PTHrP受体基因一致。
