Collins J F, Honda T, Knobel S, Bulus N M, Conary J, DuBois R, Ghishan F K
Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, TN 37232.
Proc Natl Acad Sci U S A. 1993 May 1;90(9):3938-42. doi: 10.1073/pnas.90.9.3938.
The present studies demonstrate cloning, sequencing, tissue distribution, and functional expression of a Na+/H+ exchanger which was isolated from a rat intestinal cDNA library. The cloned cDNA recognizes two transcripts in poly(A)+ RNA from the stomach, jejunum, ileum, liver, large intestine, and uterus. Based on deduced amino acid sequences, this clone shares sequence homology with the other known Na+/H+ exchanger isoforms (NHE-1, NHE-3, and NHE-4) except for its 5' end. Overall, the protein exhibits 47.8%, 41.2%, and 56.2% amino acid sequence identity to NHE-1, NHE-3, and NHE-4, respectively. The hydropathy profile of the predicted protein shows 10 transmembrane domains, suggesting a protein with transport characteristics. The tissue distribution differs from that of the other Na+/H+ exchanger isoforms. The cDNA hybridizes to two closely related transcripts in the mRNA of these tissues, which suggests that the predominant transcript of this clone is alternatively spliced. Transfection of this cDNA into Na+/H+ exchanger-deficient mutant fibroblasts (PS120 cells) results in functional Na+/H+ exchange activity. These data suggest that we have cloned a member of the Na+/H+ exchanger family with tissue-specific expression. We suggest the designation of NHE-2 for this Na+/H+ exchanger.
目前的研究展示了从大鼠肠道cDNA文库中分离出的一种Na⁺/H⁺交换体的克隆、测序、组织分布及功能表达。克隆的cDNA在来自胃、空肠、回肠、肝脏、大肠和子宫的聚腺苷酸加尾RNA（poly(A)⁺ RNA）中识别出两种转录本。根据推导的氨基酸序列，该克隆与其他已知的Na⁺/H⁺交换体亚型（NHE - 1、NHE - 3和NHE - 4）具有序列同源性，但其5'端除外。总体而言，该蛋白质与NHE - 1、NHE - 3和NHE - 4的氨基酸序列同一性分别为47.8%、41.2%和56.2%。预测蛋白质的亲水性图谱显示有10个跨膜结构域，表明这是一种具有转运特性的蛋白质。其组织分布与其他Na⁺/H⁺交换体亚型不同。该cDNA在这些组织的mRNA中与两种密切相关的转录本杂交，这表明该克隆的主要转录本存在可变剪接。将此cDNA转染到缺乏Na⁺/H⁺交换体的突变成纤维细胞（PS120细胞）中可产生功能性的Na⁺/H⁺交换活性。这些数据表明我们克隆了一个具有组织特异性表达的Na⁺/H⁺交换体家族成员。我们建议将这种Na⁺/H⁺交换体命名为NHE - 2。
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