Wakabayashi S, Fafournoux P, Sardet C, Pouysségur J
Centre de Biochimie, Centre National de la Recherche Scientifique, Nice, France.
Proc Natl Acad Sci U S A. 1992 Mar 15;89(6):2424-8. doi: 10.1073/pnas.89.6.2424.
The amiloride-sensitive Na+/H+ exchanger (NHE1 human isoform) is activated in response to diverse mitogenic and oncogenic signals presumably through phosphorylation. To get insight into the activating mechanism, a set of deletion mutants within the C-terminal cytoplasmic domain of NHE1 has been generated. These mutant forms expressed in antiporter-deficient fibroblasts revealed that deletion of the complete cytoplasmic domain (i) preserves amiloride-sensitive Na+/H+ exchange and activation by intracellular H+, (ii) reduces the affinity of the internal "H(+)-modifier site" in a manner mimicked by cellular ATP depletion, and (iii) abolishes growth factor-induced cytoplasmic alkalinization. We conclude that NHE1 can be separated into two distinct functional domains. One is an N-terminal transporter domain (T) that has all the features required to catalyze amiloride-sensitive Na+/H+ exchange with a built-in H(+)-modifier site. The other is a C-terminal cytoplasmic regulatory domain (R) that (i) determines the set point value of the exchanger and (ii) mediates growth factor signals by interacting with the "H(+)-sensor" in a phosphorylation-dependent manner.
氨氯地平敏感的Na⁺/H⁺交换体（人NHE1亚型）可能通过磷酸化作用对多种促有丝分裂和致癌信号作出反应而被激活。为深入了解其激活机制，已构建了一组NHE1 C端胞质结构域内的缺失突变体。在缺乏反向转运体的成纤维细胞中表达的这些突变体形式表明，完整胞质结构域的缺失：（i）保留了氨氯地平敏感的Na⁺/H⁺交换以及细胞内H⁺的激活作用；（ii）以类似于细胞ATP耗竭的方式降低了内部“H⁺修饰位点”的亲和力；（iii）消除了生长因子诱导的胞质碱化。我们得出结论，NHE1可分为两个不同的功能结构域。一个是N端转运结构域（T），它具有催化氨氯地平敏感的Na⁺/H⁺交换所需的所有特征，并带有一个内置的H⁺修饰位点。另一个是C端胞质调节结构域（R），它：（i）决定交换体的设定点值；（ii）通过以磷酸化依赖的方式与“H⁺传感器”相互作用来介导生长因子信号。
