A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation

Am J Respir Crit Care Med. 2014 Sep 1;190(5):522-32. doi: 10.1164/rccm.201405-0833OC.


Rationale: 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.

Objectives: 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.

Measurements and main 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.

Keywords: epithelial sodium channel; pneumonia; protein kinase C-α; pulmonary edema; tumor necrosis factor.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins
  • Epithelial Sodium Channel Agonists / chemistry
  • Epithelial Sodium Channel Agonists / metabolism*
  • Epithelial Sodium Channels / chemistry
  • Epithelial Sodium Channels / metabolism*
  • Female
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Mutant Strains
  • Peptides, Cyclic / chemistry
  • Peptides, Cyclic / metabolism*
  • Pulmonary Alveoli / metabolism*
  • Pulmonary Alveoli / microbiology
  • Pulmonary Edema / metabolism*
  • Pulmonary Edema / microbiology
  • Streptolysins*
  • Tumor Necrosis Factor-alpha / chemistry
  • Tumor Necrosis Factor-alpha / metabolism*


  • Bacterial Proteins
  • Epithelial Sodium Channel Agonists
  • Epithelial Sodium Channels
  • Peptides, Cyclic
  • Streptolysins
  • Tumor Necrosis Factor-alpha
  • plY protein, Streptococcus pneumoniae
  • AP301 peptide