The NHX family of Na+-H+ exchangers in Caenorhabditis elegans
The NHX family of Na+-H+ exchangers in Caenorhabditis elegans
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DOI：
10.1074/jbc.m203200200
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发表时间：
2002-08-09
影响因子：
4.8
通讯作者：
Melvin, JE
中科院分区：
文献类型：
--
作者：
Nehrke, K;Melvin, JE
Na+-H+交换剂通过催化细胞外钠与细胞内质子的电中性交换来防止细胞酸化。迄今为止，已在哺乳动物中鉴定出七种 Na+-H+ 交换剂，尽管该家族的几个成员已被广泛研究和表征，但很明显，我们对其余家族成员的理解存在重大差距。为了在基因组定义和遗传易处理的模型系统中启动 Na+-H+ 交换剂的研究，我们克隆了完整的 cDNA，并分析了来自线虫秀丽隐杆线虫的九个假定同源物（我们将其称为 NHX-1 至 -9）的剪接位点变异。使用绿色荧光蛋白的转录和翻译启动子-转基因融合构建体确定 NHX 蛋白的表达模式和细胞分布。四个假定的交换器在细胞表面表达，而五个交换器与细胞内细胞器的膜相关。各个亚型仅在肠道、接缝细胞、主体合胞体的皮下细胞和排泄细胞中表达，所有这些细胞都是极化上皮细胞，表明这些蛋白质在线虫的上皮膜转运过程中发挥作用。其他亚型被发现普遍表达或以泛神经模式表达，表明在细胞 pH 调节或神经元功能中具有更保守的作用。最后，我们证明重组 NHX-4（普遍存在的线虫 Na+-H+ 交换剂）可介导细胞内酸化后 Na+ 依赖性 pH 恢复。 NHX-4 对 Na+ 的 K-a 类似于 32 mM，不依赖 Cl-，并且对阿米洛利类似物 EIPA 相对不敏感。
Na+-H+ exchangers prevent cellular acidification by catalyzing the electroneutral exchange of extracellular sodium for an intracellular proton. To date, seven Na+-H+ exchangers have been identified in mammals, and although several members of this family have been extensively studied and characterized, it is clear that there are major gaps in our understanding with respect to the remaining family members. To initiate the study of Na+-H+ exchangers in a genomically defined and genetically tractable model system, we have cloned the complete cDNAs and analyzed splice site variation for nine putative homologs from the nematode Caenorhabditis elegans, which we have called NHX-1 through -9. The expression patterns and cellular distributions of the NHX proteins were determined using transcriptional and translational promoter-transgene fusion constructs to green fluorescent protein. Four of the putative exchangers were expressed at the cell surface, whereas five of the exchangers were associated with the membranes of intracellular organelles. Individual isoforms were expressed exclusively in the intestine, seam cells, hypodermal cells of the main body syncytium, and the excretory cell, all of which are polarized epithelial cells, suggesting a role for these proteins in epithelial membrane transport processes in the nematode. Other isoforms were found to express either ubiquitously or in a pan-neural pattern, suggesting a more conserved role in cell pH regulation or neuronal function. Finally, we show that recombinant NHX-4, the ubiquitous nematode Na+-H+ exchanger, mediates Na+-dependent pH recovery after intracellular acidification. NHX-4 has a K-a for Na+ of similar to32 mM, is not Cl--dependent, and is relatively insensitive to the amiloride analog EIPA.