title: Ankyrin G Expression Regulates Apical Delivery of the Epithelial Sodium Channel (ENaC).
abstract: The epithelial sodium channel (ENaC) is the limiting entry point for Na+reabsorption in the distal kidney nephron and is regulated by numerous hormones, including the mineralocorticoid hormone aldosterone. Previously we identified ankyrin G (AnkG), a cytoskeletal protein involved in vesicular transport, as a novel aldosterone-induced protein that can alter Na+transport in mouse cortical collecting duct cells. However, the mechanisms underlying AnkG regulation of Na+transport were unknown. Here we report that AnkG expression directly regulates Na+transport by altering ENaC activity in the apical membrane. Increasing AnkG expression increased ENaC activity while depleting AnkG reduced ENaC-mediated Na+transport. These changes were due to a change in ENaC directly rather than through alterations to the Na+driving force created by Na+/K+-ATPase. Using a constitutively open mutant of ENaC, we demonstrate that the augmentation of Na+transport is caused predominantly by increasing the number of ENaCs at the surface. To determine the mechanism of AnkG action on ENaC surface number, changes in rates of internalization, recycling, and membrane delivery were investigated. AnkG did not alter ENaC delivery to the membrane from biosynthetic pathways or removal by endocytosis. However, AnkG did alter ENaC insertion from constitutive recycling pathways. These findings provide a mechanism to account for the role of AnkG in the regulation of Na+transport in the distal kidney nephron.
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Christine A
authors.initials: CA
authors.lastname: Klemens
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Edinger
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Lindsay
authors.initials: L
authors.lastname: Kightlinger
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Xiaoning
authors.initials: X
authors.lastname: Liu
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261 michael7@pitt.edu.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Butterworth
mesh_terms: D000818:Animals; D017487:Ankyrins / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D004705:Endocytosis / Q000502:physiology; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D017136:Ion Transport; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D051379:Mice; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D017487:Ankyrins; D053503:Epithelial Sodium Channels; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Ankyrin; apical transport; collecting duct; distal nephron; epithelial sodium channel (ENaC); kidney; membrane trafficking; sodium transport; vesicles