Expression of 25(OH)D3 24-hydroxylase in distal nephron: coordinate regulation by 1,25(OH)2D3 and cAMP or PTH.
Expression of 25(OH)D3 24-hydroxylase in distal nephron: coordinate regulation by 1,25(OH)2D3 and cAMP or PTH.
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远端肾单位中 25(OH)D3 24-羟化酶的表达：1,25(OH)2D3 和 cAMP 或 PTH 的协调调节。
DOI：
10.1152/ajpendo.1999.276.4.e793
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Christakos,S
中科院分区：
文献类型：
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作者：
Yang,W;Friedman,PA;Kumar,R;Omdahl,JL;May,BK;Siu-Caldera,ML;Reddy,GS;Christakos,S
先前的研究使用显微切割的肾单位片段报道，肾25-羟基维生素D3-24-羟化酶（24 OHase）活性的唯一位点是肾近曲小管（PCT）。我们现在报告的24 OHase mRNA，蛋白质和活性的细胞中，没有近端小管的标记，但表达的特征高度特异性的远端小管的存在。在溶剂处理的小鼠远曲小管（DCT）细胞中未检测到24 OHase mRNA，但当DCT细胞用1，25二羟维生素D3[1，25（OH）2D 3]处理时，24 OHase mRNA被显著诱导。用Western blot和HPLC分别检测DCT细胞中24 OHase蛋白和活性。发现8-溴-cAMP（1 mM）或甲状旁腺激素[PTH-（1-34）; 10 nM]可增强1，25（OH）2D 3对24 OHase mRNA的作用。cAMP或PTH对DCT细胞中24 OHase表达的刺激作用表明PCT和DCT中24 OHase表达的差异调节。在cAMP和1，25（OH）2D 3的存在下，观察到维生素D受体（VDR）mRNA的4 - 6倍诱导。VDR蛋白，如通过Western印迹分析所确定的，在cAMP存在下也增强。用大鼠24 OHase启动子缺失构建体在DCT细胞中的瞬时转染分析表明，cAMP增强1，25（OH）2D 3诱导的24 OHase转录，但这种增强不是由24 OHase启动子中的cAMP应答元件（克雷斯）介导的。结论：1）尽管PCT是24 OHase的主要定位部位，但24 OHase的mRNA和活性也可定位于远端肾单位;2）PTH和cAMP均以不同于PCT报道的方式调节1，25（OH）_2D_3对DCT细胞24 OHase表达的诱导;在DCT细胞中，cAMP上调VDR水平，而不影响24 OHase启动子中的克雷斯，是cAMP介导的24 OHase转录调节的一种机制。
Previous studies using microdissected nephron segments reported that the exclusive site of renal 25-hydroxyvitamin D3-24-hydroxylase (24OHase) activity is the renal proximal convoluted tubule (PCT). We now report the presence of 24OHase mRNA, protein, and activity in cells that are devoid of markers of proximal tubules but express characteristics highly specific for the distal tubule. 24OHase mRNA was undetectable in vehicle-treated mouse distal convoluted tubule (DCT) cells but was markedly induced when DCT cells were treated with 1,25 dihydroxyvitamin D3[1,25(OH)2D3]. 24OHase protein and activity were also identified in DCT cells by Western blot analysis and HPLC, respectively. 8-Bromo-cAMP (1 mM) or parathyroid hormone [PTH-(1—34); 10 nM] was found to potentiate the effect of 1,25(OH)2D3on 24OHase mRNA. The stimulatory effect of cAMP or PTH on 24OHase expression in DCT cells suggests differential regulation of 24OHase expression in the PCT and DCT. In the presence of cAMP and 1,25(OH)2D3, a four- to sixfold induction in vitamin D receptor (VDR) mRNA was observed. VDR protein, as determined by Western blot analysis, was also enhanced in the presence of cAMP. Transient transfection analysis in DCT cells with rat 24OHase promoter deletion constructs demonstrated that cAMP enhanced 1,25(OH)2D3-induced 24OHase transcription but this enhancement was not mediated by cAMP response elements (CREs) in the 24OHase promoter. We conclude that1) although the PCT is the major site of localization of 24OHase, 24OHase mRNA and activity can also be localized in the distal nephron;2) both PTH and cAMP modulate the induction of 24OHase expression by 1,25(OH)2D3in DCT cells in a manner different from that reported in the PCT; and3) in DCT cells, upregulation of VDR levels by cAMP, and not an effect on CREs in the 24OHase promoter, is one mechanism involved in the cAMP-mediated modulation of 24OHase transcription.