Regulation of intestinal phosphate cotransporter NaPi IIb by ubiquitin ligase Nedd4-2 and by serum- and glucocorticoid-dependent kinase 1
Regulation of intestinal phosphate cotransporter NaPi IIb by ubiquitin ligase Nedd4-2 and by serum- and glucocorticoid-dependent kinase 1
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DOI：
10.1152/ajpgi.00121.2003
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发表时间：
2004-07-01
影响因子：
4.5
通讯作者：
Lang, F
中科院分区：
文献类型：
--
作者：
Palmada, M;Dieter, M;Lang, F
血清和糖皮质激素诱导激酶1（SGK 1）在肠上皮细胞中高度表达。然而，激酶在调节肠功能中的重要性仍然难以捉摸。在非洲爪蟾卵母细胞中，SGK 1通过磷酸化泛素连接酶Nedd 4 -2刺激上皮Na+通道，Nedd 4 -2通过泛素化调节通道，导致随后的通道蛋白降解。因此，本研究已进行，以探讨是否SGK 1调节运输系统表达的肠上皮细胞，特别是IIb型钠磷酸盐（Na+-P-i）协同转运蛋白（NaPi IIb）。免疫组化显示SGK 1与Nedd 4 - 2共定位于人小肠绒毛上皮细胞。为了进行功能分析，将编码NaPi IIb、SGK同种型和/或Nedd 4 - 2的cRNA注射到X中。I-P），并将转运活性定量为底物诱导电流（I-P）。暴露于3 mM磷酸盐诱导NaPi IIb表达卵母细胞中的I-P。共注射Nedd 4 - 2而非无催化活性的突变体（C938 S）Nedd 4 - 2显著下调I-P，而共注射（S422 D）SGK 1显著刺激I-P，甚至完全逆转Nedd 4 - 2对IP的作用。S422 DSGK 1对NaPi IIb的作用被野生型SGK 3模拟，但不被野生型SGK 2、组成型活性（PKB）-P-T308 D、S473 D或失活（K127 N）SGK 1模拟。此外，（S422 D）SGK 1和SGK 3使Nedd 4 - 2磷酸化。总之，SGK 1至少部分地通过磷酸化刺激NaPi IIb，从而抑制Nedd 4 - 2与其靶点的结合。因此，本研究揭示了一种新的信号通路在调节肠道磷酸盐转运，这可能是重要的磷酸盐平衡的调节。
Serum and glucocorticoid-inducible kinase 1 (SGK1) is highly expressed in enterocytes. The significance of the kinase in regulation of intestinal function has, however, remained elusive. In Xenopus laevis oocytes, SGK1 stimulates the epithelial Na+ channel by phosphorylating the ubiquitin ligase Nedd4-2, which regulates channels by ubiquitination leading to subsequent degradation of the channel protein. Thus the present study has been performed to explore whether SGK1 regulates transport systems expressed in intestinal epithelial cells, specifically type IIb sodium-phosphate (Na+-P-i) cotransporter ( NaPi IIb). Immunohistochemistry in human small intestine revealed SGK1 colocalization with Nedd4 - 2 in villus enterocytes. For functional analysis cRNA encoding NaPi IIb, the SGK isoforms and/or the Nedd4 - 2 were injected into X. laevis oocytes, and transport activity was quantified as the substrate-induced current (I-P). Exposure to 3 mM phosphate induces an I-P in NaPi IIb-expressing oocytes. Coinjection of Nedd4 - 2, but not the catalytically inactive mutant (C938S)Nedd4 - 2, significantly downregulates I-P, whereas the coinjection of (S422D)SGK1 markedly stimulates I-P and even fully reverses the effect of Nedd4 - 2 on IP. The effect of S422DSGK1 on NaPi IIb is mimicked by wild-type SGK3 but not by wild-type SGK2, constitutively active (PKB)-P-T308D, S473D, or inactive (K127N)SGK1. Moreover, (S422D)SGK1 and SGK3 phosphorylate Nedd4 - 2. In conclusion, SGK1 stimulates the NaPi IIb, at least in part, by phosphorylating and thereby inhibiting Nedd4 - 2 binding to its target. Thus the present study reveals a novel signaling pathway in the regulation of intestinal phosphate transport, which may be important for regulation of phosphate balance.