Poschet Jens F, Skidmore Jennifer, Boucher John C, Firoved Aaron M, Van Dyke Rebecca W, Deretic Vojo
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA.
J Biol Chem. 2002 Apr 19;277(16):13959-65. doi: 10.1074/jbc.M105441200. Epub 2002 Jan 24.
The cystic fibrosis transmembrane conductance regulator (CFTR), which is aberrant in patients with cystic fibrosis, normally functions both as a chloride channel and as a pleiotropic regulator of other ion transporters. Here we show, by ratiometric imaging with luminally exposed pH-sensitive green fluorescent protein, that CFTR affects the pH of cellubrevin-labeled endosomal organelles resulting in hyperacidification of these compartments in cystic fibrosis lung epithelial cells. The excessive acidification of intracellular organelles was corrected with low concentrations of weak base. Studies with proton ATPase and sodium channel inhibitors showed that the increased acidification was dependent on proton pump activity and sodium transport. These observations implicate sodium efflux in the pH homeostasis of a subset of endocytic organelles and indicate that a dysfunctional CFTR in cystic fibrosis leads to organellar hyperacidification in lung epithelial cells because of a loss of CFTR inhibitory effects on sodium transport. Furthermore, recycling of transferrin receptor was altered in CFTR mutant cells, suggesting a previously unrecognized cellular defect in cystic fibrosis, which may have functional consequences for the receptors on the plasma membrane or within endosomal compartments.
囊性纤维化跨膜传导调节因子（CFTR）在囊性纤维化患者中存在异常，它通常既作为氯离子通道，又作为其他离子转运体的多效调节剂发挥作用。在此我们通过对腔内暴露的pH敏感绿色荧光蛋白进行比率成像显示，CFTR会影响细胞ubrevin标记的内体细胞器的pH值，导致囊性纤维化肺上皮细胞中这些区室过度酸化。低浓度弱碱可纠正细胞内细胞器的过度酸化。质子ATP酶和钠通道抑制剂的研究表明，酸化增加依赖于质子泵活性和钠转运。这些观察结果表明钠外流参与了一部分内吞细胞器的pH稳态，并表明囊性纤维化中功能失调的CFTR会导致肺上皮细胞内细胞器过度酸化，这是因为CFTR对钠转运的抑制作用丧失。此外，转铁蛋白受体的循环在CFTR突变细胞中发生改变，这表明囊性纤维化中存在一种先前未被认识到的细胞缺陷，这可能对质膜或内体区室内的受体产生功能影响。
