title: Differential N termini in epithelial Na+ channel δ-subunit isoforms modulate channel trafficking to the membrane.
abstract: The epithelial Na(+) channel (ENaC) is a heteromultimeric ion channel that plays a key role in Na(+) reabsorption across tight epithelia. The canonical ENaC is formed by three analogous subunits, α, β, and γ. A fourth ENaC subunit, named δ, is expressed in the nervous system of primates, where its role is unknown. The human δ-ENaC gene generates at least two splice isoforms, δ(1) and δ(2) , differing in the N-terminal sequence. Neurons in diverse areas of the human and monkey brain differentially express either δ(1) or δ(2) , with few cells coexpressing both isoforms, which suggests that they may play specific physiological roles. Here we show that heterologous expression of δ(1) in Xenopus oocytes and HEK293 cells produces higher current levels than δ(2) . Patch-clamp experiments showed no differences in single channel current magnitude and open probability between isoforms. Steady-state plasma membrane abundance accounts for the dissimilarity in macroscopic current levels. Differential trafficking between isoforms is independent of β- and γ-subunits, PY-motif-mediated endocytosis, or the presence of additional lysine residues in δ(2)-N terminus. Analysis of δ(2)-N terminus identified two sequences that independently reduce channel abundance in the plasma membrane. The δ(1) higher abundance is consistent with an increased insertion rate into the membrane, since endocytosis rates of both isoforms are indistinguishable. Finally, we conclude that δ-ENaC undergoes dynamin-independent endocytosis as opposed to αβγ-channels.
authors.affiliation: Research Division, University Hospital N.S. Candelaria, Spain.
authors.forename: Diana
authors.initials: D
authors.lastname: Wesch
authors.forename: Mike
authors.initials: M
authors.lastname: Althaus
authors.forename: Pablo
authors.initials: P
authors.lastname: Miranda
authors.forename: Ignacio
authors.initials: I
authors.lastname: Cruz-Muros
authors.forename: Martin
authors.initials: M
authors.lastname: Fronius
authors.forename: Tomás
authors.initials: T
authors.lastname: González-Hernández
authors.forename: Wolfgang G
authors.initials: WG
authors.lastname: Clauss
authors.forename: Diego
authors.initials: D
authors.lastname: Alvarez de la Rosa
authors.forename: Teresa
authors.initials: T
authors.lastname: Giraldez
mesh_terms: D000368:Aged; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology; D003001:Cloning, Molecular; D034281:Dynamins / Q000037:antagonists & inhibitors; D004705:Endocytosis / Q000502:physiology*; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D006835:Hydrazones / Q000494:pharmacology; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D009865:Oocytes; D018408:Patch-Clamp Techniques / Q000379:methods; D020033:Protein Isoforms / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D053503:Epithelial Sodium Channels; D006835:Hydrazones; C511794:N'-(3,4-dihydroxybenzylidene)-3-hydroxy-2-naphthahydrazide; D020033:Protein Isoforms; D021122:Protein Subunits; D034281:Dynamins