Institute of Biochemistry and Molecular Biology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Am J Physiol Renal Physiol. 2020 Apr 1;318(4):F956-F970. doi: 10.1152/ajprenal.00297.2019. Epub 2020 Feb 24.
Aquaporin-2 (AQP2) is a vasopressin-regulated water channel protein responsible for osmotic water reabsorption by kidney collecting ducts. In response to vasopressin, AQP2 traffics from intracellular vesicles to the apical plasma membrane of collecting duct principal cells, where it increases water permeability and, hence, water reabsorption. Despite continuing efforts, gaps remain in our knowledge of vasopressin-regulated AQP2 trafficking. Here, we studied the functions of two retromer complex proteins, small GTPase Rab7 and vacuolar protein sorting 35 (Vps35), in vasopressin-induced AQP2 trafficking in a collecting duct cell model (mpkCCD cells). We showed that upon vasopressin removal, apical AQP2 returned to Rab5-positive early endosomes before joining Rab11-positive recycling endosomes. In response to vasopressin, Rab11-associated AQP2 trafficked to the apical plasma membrane before Rab5-associated AQP2 did so. Rab7 knockdown resulted in AQP2 accumulation in early endosomes and impaired vasopressin-induced apical AQP2 trafficking. In response to vasopressin, Rab7 transiently colocalized with Rab5, indicative of a role of Rab7 in AQP2 sorting in early endosomes before trafficking to the apical membrane. Rab7-mediated apical AQP2 trafficking in response to vasopressin required GTPase activity. When Vps35 was knocked down, AQP2 accumulated in recycling endosomes under vehicle conditions and did not traffic to the apical plasma membrane in response to vasopressin. We conclude that Rab7 and Vps35 participate in AQP2 sorting in early endosomes under vehicle conditions and apical membrane trafficking in response to vasopressin.
水通道蛋白-2（AQP2）是一种加压素调节的水通道蛋白，负责肾脏集合管的渗透水重吸收。响应加压素，AQP2 从细胞内囊泡转运到集合管主细胞的顶质膜，在那里它增加水通透性，从而增加水重吸收。尽管我们一直在努力，但在加压素调节的 AQP2 转运方面仍存在知识空白。在这里，我们研究了两个返回体复合物蛋白，小 GTPase Rab7 和液泡蛋白分选 35（Vps35），在集合管细胞模型（mpkCCD 细胞）中加压素诱导的 AQP2 转运中的功能。我们表明，在加压素去除后，顶质膜 AQP2 在与 Rab11 阳性再循环内体结合之前返回 Rab5 阳性早期内体。响应加压素，Rab11 相关的 AQP2 在 Rab5 相关的 AQP2 之前转运到顶质膜。Rab7 敲低导致 AQP2 在早期内体中积累，并损害加压素诱导的顶质膜 AQP2 转运。响应加压素，Rab7 与 Rab5 短暂共定位，表明 Rab7 在早期内体中参与 AQP2 分选，然后转运到顶质膜。Rab7 介导的加压素反应性顶质膜 AQP2 转运需要 GTPase 活性。当 Vps35 被敲低时，AQP2 在载体条件下在再循环内体中积累，并且在加压素响应时不会转运到顶质膜。我们得出结论，Rab7 和 Vps35 参与了载体条件下早期内体中的 AQP2 分选和加压素反应性顶质膜转运。
