Half-lives of plasma membrane Na+/H+ exchangers NHE1-3:: plasma membrane NHE2 has a rapid rate of degradation
Half-lives of plasma membrane Na+/H+ exchangers NHE1-3:: plasma membrane NHE2 has a rapid rate of degradation
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DOI：
10.1152/ajpcell.2001.281.6.c2039
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发表时间：
2001-12-01
影响因子：
5.5
通讯作者：
Donowitz, M
中科院分区：
文献类型：
--
作者：
Cavet, ME;Akhter, S;Donowitz, M
Na+/H+交换体NHE2和NHE3参与上皮Na+和HCO3-的吸收。为了进一步了解NHE2和NHE3的功能，我们比较了它们的细胞处理过程，并与内务同源异构体NHE1进行了比较。利用生物素化交换剂，我们测定了质膜NHE2在PS120成纤维细胞和cco -2细胞中的半衰期（3 h）比NHE1 （24 h）和NHE3 （14 h）短。Brefeldin A处理3小时后，NHE2转运和质膜水平降低，而NHE1不受影响。NHE2可被溶酶体而非蛋白体降解，这表明溶酶体抑制后内吞NHE2蛋白水平升高，而蛋白体不受抑制。与NHE3不同，NHE2的基础转运活性不受磷脂酰肌醇3-激酶抑制的影响，并且似乎不局限于核旁循环内体。因此，对于NHE2，蛋白质降解和/或蛋白质合成可能在其基础和调控状态中起重要作用。这些结果表明NHE2和NHE3在细胞加工和运输方面存在根本差异。这些差异可能是这些交换剂在上皮细胞中发挥特殊作用的基础。
The Na+/H+ exchangers NHE2 and NHE3 are involved in epithelial Na+ and HCO3- absorption. To increase insights into the functions of NHE2 vs. NHE3, we compared their cellular processing with each other and with the housekeeping isoform NHE1. Using biotinylated exchanger, we determined that the half-life of plasma membrane NHE2 was short (3 h) compared with that of NHE1 (24 h) and NHE3 (14 h) in both PS120 fibroblasts and Caco-2 cells. NHE2 transport and plasma membrane levels were reduced by 3 h of Brefeldin A treatment, whereas NHE1 was unaffected. NHE2 was degraded by the lysosomes but not proteosomes, as demonstrated by increasing levels of endocytosed NHE2 protein after inhibition of the lysosomes, but not with proteosome inhibition. Unlike that of NHE3, basal NHE2 transport activity was not affected by phosphatidylinositol 3-kinase inhibition and did not appear to be localized in the juxtanuclear recycling endosome. Therefore, for NHE2, protein degradation and/or protein synthesis probably play important roles in its basal and regulated states. These results suggest fundamental differences in the cellular processing and trafficking of NHE2 and NHE3. These differences may underlie the specialized roles that these exchangers play in epithelial cells.