Hernando Nati, Déliot Nadine, Gisler Serge M, Lederer Eleanor, Weinman Edward J, Biber Jürg, Murer Heini
Institute of Physiology, University of Zurich, Wintherthurerstrasse 190, CH-8057 Zurich, Switzerland.
Proc Natl Acad Sci U S A. 2002 Sep 3;99(18):11957-62. doi: 10.1073/pnas.182412699. Epub 2002 Aug 21.
Type IIa Na/P(i) cotransporters are expressed in renal proximal brush border and are the major determinants of inorganic phosphate (P(i)) reabsorption. Their carboxyl-terminal tail contains information for apical expression, and interacts by means of its three terminal amino acids with several PSD95/DglA/ZO-1-like domain (PDZ)-containing proteins. Two of these proteins, NaPi-Cap1 and Na/H exchanger-regulatory factor 1 (NHERF1), colocalize with the cotransporter in the proximal brush border. We used opossum kidney cells to test the hypothesis of a potential role of PDZ-interactions on the apical expression of the cotransporter. We found that opossum kidney cells contain NaPi-Cap1 and NHERF1 mRNAs. For NHERF1, an apical location of the protein could be documented; this location probably reflects interaction with the cytoskeleton by means of the MERM-binding domain. Overexpression of PDZ domains involved in interaction with the cotransporter (PDZ-1/NHERF1 and PDZ-3/NaPi-Cap1) had a dominant-negative effect, disturbing the apical expression of the cotransporter without affecting the actin cytoskeleton or the basolateral expression of Na/K-ATPase. These data suggest an involvement of PDZ-interactions on the apical expression of type IIa cotransporters.
IIa型钠/无机磷酸（P(i)）共转运体表达于肾近端刷状缘，是无机磷酸盐（P(i)）重吸收的主要决定因素。其羧基末端尾部包含顶端表达的信息，并通过其三个末端氨基酸与几种含PSD95/DglA/ZO-1样结构域（PDZ）的蛋白质相互作用。其中两种蛋白质，NaPi-Cap1和钠/氢交换调节因子1（NHERF1），与共转运体在近端刷状缘共定位。我们使用负鼠肾细胞来检验PDZ相互作用对共转运体顶端表达潜在作用的假设。我们发现负鼠肾细胞含有NaPi-Cap1和NHERF1的mRNA。对于NHERF1，可证明该蛋白质位于顶端；该位置可能反映了通过MERM结合结构域与细胞骨架的相互作用。与共转运体相互作用的PDZ结构域（PDZ-1/NHERF1和PDZ-3/NaPi-Cap1）的过表达具有显性负效应，扰乱了共转运体的顶端表达，而不影响肌动蛋白细胞骨架或钠钾ATP酶的基底外侧表达。这些数据表明PDZ相互作用参与了IIa型共转运体的顶端表达。
