Capuano Paola, Bacic Desa, Roos Marcel, Gisler Serge M, Stange Gerti, Biber Jürg, Kaissling Brigitte, Weinman Edward J, Shenolikar Shirish, Wagner Carsten A, Murer Heini
Institute of Physiology, Univ. of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Am J Physiol Cell Physiol. 2007 Feb;292(2):C927-34. doi: 10.1152/ajpcell.00126.2006. Epub 2006 Sep 20.
Phosphate reabsorption in the renal proximal tubule occurs mostly via the type IIa Na(+)-phosphate cotransporter (NaP(i)-IIa) in the brush border membrane (BBM). The activity and localization of NaP(i)-IIa are regulated, among other factors, by parathyroid hormone (PTH). NaP(i)-IIa interacts in vitro via its last three COOH-terminal amino acids with the PDZ protein Na(+)/H(+)-exchanger isoform 3 regulatory factor (NHERF)-1 (NHERF1). Renal phosphate reabsorption in Nherf1-deficient mice is altered, and NaP(i)-IIa expression in the BBM is reduced. In addition, it has been proposed that NHERF1 and NHERF2 are important for the coupling of PTH receptors (PTHRs) to phospholipase C (PLC) and the activation of the protein kinase C pathway. We tested the role of NHERF1 in the regulation of NaP(i)-IIa by PTH in Nherf1-deficient mice. Immunohistochemistry and Western blotting demonstrated that stimulation of apical and basolateral receptors with PTH-(1-34) led to internalization of NaP(i)-IIa in wild-type and Nherf1-deficient mice. Stimulation of only apical receptors with PTH-(3-34) failed to induce internalization in Nherf1-deficient mice. Expression and localization of apical PTHRs were similar in wild-type and Nherf1-deficient mice. Activation of the protein kinase C- and A-dependent pathways with 1,2-dioctanoyl-sn-glycerol or 8-bromo-cAMP induced normal internalization of NaP(i)-IIa in wild-type, as well as Nherf1-deficient, mice. Stimulation of PLC activity due to apical PTHRs was impaired in Nherf1-deficient mice. These data suggest that NHERF1 in the proximal tubule is important for PTH-induced internalization of NaP(i)-IIa and, specifically, couples the apical PTHR to PLC.
肾近端小管中的磷酸盐重吸收主要通过刷状缘膜（BBM）中的IIa型钠-磷酸盐共转运体（NaP(i)-IIa）进行。NaP(i)-IIa的活性和定位受甲状旁腺激素（PTH）等多种因素调节。NaP(i)-IIa在体外通过其COOH末端的最后三个氨基酸与PDZ蛋白钠/氢交换体亚型3调节因子（NHERF）-1（NHERF1）相互作用。Nherf1基因缺陷小鼠的肾磷酸盐重吸收发生改变，BBM中NaP(i)-IIa的表达降低。此外，有人提出NHERF1和NHERF2对于甲状旁腺激素受体（PTHRs）与磷脂酶C（PLC）的偶联以及蛋白激酶C途径的激活很重要。我们测试了NHERF1在Nherf1基因缺陷小鼠中对PTH调节NaP(i)-IIa的作用。免疫组织化学和蛋白质印迹表明，用PTH-(1-34)刺激顶端和基底外侧受体可导致野生型和Nherf1基因缺陷小鼠中NaP(i)-IIa的内化。仅用PTH-(3-34)刺激顶端受体未能在Nherf1基因缺陷小鼠中诱导内化。野生型和Nherf1基因缺陷小鼠中顶端PTHRs的表达和定位相似。用1,2-二辛酰-sn-甘油或8-溴-cAMP激活蛋白激酶C和A依赖性途径可诱导野生型以及Nherf1基因缺陷小鼠中NaP(i)-IIa正常内化。Nherf1基因缺陷小鼠中由于顶端PTHRs导致的PLC活性刺激受损。这些数据表明近端小管中的NHERF1对于PTH诱导的NaP(i)-IIa内化很重要，并且具体地将顶端PTHR与PLC偶联。
