Small GTPase Rab7 Mediates Aquaporin‐2 Recycling and Apical Trafficking

Abstract

Water permeability of the kidney collecting ducts is regulated by the abundance of the molecular water channel protein aquaporin‐2 (AQP2) in the apical plasma membrane of the collecting duct cells. The apical AQP2 abundance in turn is regulated by trafficking of AQP2‐containing intracellular vesicles to and from the apical membrane by the peptide hormone vasopressin. Here we used confocal microscopy to follow how AQP2 trafficked among biotin‐labeled apical membrane, Rab5+ early endosome, Rab7+ late endosome, and Rab11+ recycling endosome in response to vasopressin. Before vasopressin stimulation, most AQP2 stayed in Rab5+ early endosome and Rab11+ recycling endosome. In response to vasopressin, AQP2 in the Rab11+ recycling endosome trafficked first to the apical membrane followed by AQP2 in the Rab5+ early endosome. Upon vasopressin withdrawal, apical AQP2 returned to the Rab5+ early endosome before joining the Rab11+ recycling endosome. Rab5 knockdown slowed APQ2 internalization upon vasopressin withdrawal. Rab7 knockdown resulted in AQP2 accumulation in the Rab5+ early endosome upon vasopressin withdrawal, consistent with a role of Rab7 in AQP2 sorting to the late endosome. However, Rab7 knockdown also reduced AQP2 in the Rab11+ recycling endosome upon vasopressin withdrawal, suggesting that Rab7 participates in AQP2 sorting from the early endosome to the recycling endosome. In fact, in the Rab7 knockdown cells vasopressin‐stimulated apical AQP2 trafficking was greatly impaired. These results indicate that internalizing AQP2 first arrives at the early endosome where Rab7 sorts it to the recycling endosome where it waits for the next vasopressin signal for apical trafficking. Rab11 knockdown did not affect vasopressin‐induced apical AQP2 trafficking as reported previously. In contrast, Vps35 (vacuolar protein sorting‐associated protein 35) knockdown trapped AQP2 in the Rab11+ recycling endosome and reduced apical AQP2 trafficking. We conclude that Rab7 plays an important role in AQP2 sorting from the early endosome to the recycling endosome where vasopressin excites its apical trafficking mediated by Vps35.Support or Funding InformationThis work was supported by the Ministry of Science and Technology, TAIWAN (MOST 107‐2320‐B‐002‐057‐MY3).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.