title: A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation.
abstract: BACKGROUND
  Alveolar liquid clearance is regulated by Na(+) uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na(+)-K(+)-ATPase in type II alveolar epithelial cells. Dysfunction of these Na(+) transporters during pulmonary inflammation can contribute to pulmonary edema.
  
  
  OBJECTIVE
  In this study, we sought to determine the precise mechanism by which the TIP peptide, mimicking the lectin-like domain of tumor necrosis factor (TNF), stimulates Na(+) uptake in a homologous cell system in the presence or absence of the bacterial toxin pneumolysin (PLY).
  
  
  METHODS
  We used a combined biochemical, electrophysiological, and molecular biological in vitro approach and assessed the physiological relevance of the lectin-like domain of TNF in alveolar liquid clearance in vivo by generating triple-mutant TNF knock-in mice that express a mutant TNF with deficient Na(+) uptake stimulatory activity.
  
  
  RESULTS
  TIP peptide directly activates ENaC, but not the Na(+)-K(+)-ATPase, upon binding to the carboxy-terminal domain of the α subunit of the channel. In the presence of PLY, a mediator of pneumococcal-induced pulmonary edema, this binding stabilizes the ENaC-PIP2-MARCKS complex, which is necessary for the open probability conformation of the channel and preserves ENaC-α protein expression, by means of blunting the protein kinase C-α pathway. Triple-mutant TNF knock-in mice are more prone than wild-type mice to develop edema with low-dose intratracheal PLY, correlating with reduced pulmonary ENaC-α subunit expression.
  
  
  CONCLUSIONS
  These results demonstrate a novel TNF-mediated mechanism of direct ENaC activation and indicate a physiological role for the lectin-like domain of TNF in the resolution of alveolar edema during inflammation.
authors.affiliation: 1 Vascular Biology Center.
authors.forename: István
authors.initials: I
authors.lastname: Czikora
authors.forename: Abdel
authors.initials: A
authors.lastname: Alli
authors.forename: Hui-Fang
authors.initials: HF
authors.lastname: Bao
authors.forename: David
authors.initials: D
authors.lastname: Kaftan
authors.forename: Supriya
authors.initials: S
authors.lastname: Sridhar
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Apell
authors.forename: Boris
authors.initials: B
authors.lastname: Gorshkov
authors.forename: Richard
authors.initials: R
authors.lastname: White
authors.forename: Astrid
authors.initials: A
authors.lastname: Zimmermann
authors.forename: Albrecht
authors.initials: A
authors.lastname: Wendel
authors.forename: Meike
authors.initials: M
authors.lastname: Pauly-Evers
authors.forename: Jürg
authors.initials: J
authors.lastname: Hamacher
authors.forename: Irène
authors.initials: I
authors.lastname: Garcia-Gabay
authors.forename: Bernhard
authors.initials: B
authors.lastname: Fischer
authors.forename: Alexander
authors.initials: A
authors.lastname: Verin
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Bagi
authors.forename: Jean Francois
authors.initials: JF
authors.lastname: Pittet
authors.forename: Waheed
authors.initials: W
authors.lastname: Shabbir
authors.forename: Rosa
authors.initials: R
authors.lastname: Lemmens-Gruber
authors.forename: Trinad
authors.initials: T
authors.lastname: Chakraborty
authors.forename: Ahmed
authors.initials: A
authors.lastname: Lazrak
authors.forename: Michael A
authors.initials: MA
authors.lastname: Matthay
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Eaton
authors.forename: Rudolf
authors.initials: R
authors.lastname: Lucas
mesh_terms: D000818:Animals; D001426:Bacterial Proteins; D062708:Epithelial Sodium Channel Agonists / Q000737:chemistry / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D010456:Peptides, Cyclic / Q000737:chemistry / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000378:metabolism* / Q000382:microbiology; D011654:Pulmonary Edema / Q000378:metabolism* / Q000382:microbiology; D013301:Streptolysins; D014409:Tumor Necrosis Factor-alpha / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D062708:Epithelial Sodium Channel Agonists; D053503:Epithelial Sodium Channels; D010456:Peptides, Cyclic; D013301:Streptolysins; D014409:Tumor Necrosis Factor-alpha; C032290:plY protein, Streptococcus pneumoniae; C583752:AP301 peptide
keywords: epithelial sodium channel; pneumonia; protein kinase C-α; pulmonary edema; tumor necrosis factor