Proteolytic activation of the human epithelial sodium channel by trypsin IV and trypsin I involves distinct cleavage sites

Research output: Contribution to journalArticle


Proteolytic activation is a unique feature of the epithelial sodium channel (ENaC). However, the underlying molecular mechanisms and the physiologically relevant proteases remain to be identified. The serine protease trypsin I can activate ENaC in vitro but is unlikely to be the physiologically relevant activating protease in ENaC-expressing tissues in vivo. Herein, we investigated whether human trypsin IV, a form of trypsin that is co-expressed in several extrapancreatic epithelial cells with ENaC, can activate human ENaC. In Xenopus laevis oocytes, we monitored proteolytic activation of ENaC currents and the appearance of γENaC cleavage products at the cell surface. We demonstrated that trypsin IV and trypsin I can stimulate ENaC heterologously expressed in oocytes. ENaC cleavage and activation by trypsin IV but not by trypsin I required a critical cleavage site (Lys-189) in the extracellular domain of the γ-subunit. In contrast, channel activation by trypsin I was prevented by mutating three putative cleavage sites (Lys-168, Lys-170, and Arg-172) in addition to mutating previously described prostasin (RKRK(178)), plasmin (Lys-189), and neutrophil elastase (Val-182 and Val-193) sites. Moreover, we found that trypsin IV is expressed in human renal epithelial cells and can increase ENaC-mediated sodium transport in cultured human airway epithelial cells. Thus, trypsin IV may regulate ENaC function in epithelial tissues. Our results show, for the first time, that trypsin IV can stimulate ENaC and that trypsin IV and trypsin I activate ENaC by cleavage at distinct sites. The presence of distinct cleavage sites may be important for ENaC regulation by tissue-specific proteases.


  • Silke Haerteis
  • Annabel Krappitz
  • Matteus Krappitz
  • Jane E Murphy
  • Marko Bertog
  • Bettina Krueger
  • Regina Nacken
  • Hyunjae Chung
  • Morley D Hollenberg
  • Wolfgang Knecht
  • Nigel W Bunnett
  • Christoph Korbmacher
External organisations
  • AstraZeneca, Sweden
  • Friedrich-Alexander University Erlangen-Nürnberg
  • Monash University
  • University of Melbourne
  • University of Calgary
  • University of California, San Francisco
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Cell and Molecular Biology


  • Amino Acid Sequence, Animals, Azetidines/pharmacology, Benzylamines/pharmacology, Binding Sites, Epithelial Cells/metabolism, Epithelial Sodium Channels/chemistry, Extracellular Space/metabolism, Humans, Kidney/metabolism, Molecular Sequence Data, Mutation, Oocytes/metabolism, Protein Structure, Tertiary, Proteolysis/drug effects, Trypsin/metabolism, Xenopus laevis/genetics
Original languageEnglish
Pages (from-to)19067-19078
JournalThe Journal of biological chemistry
Issue number27
Publication statusPublished - 2014 Jul 4
Publication categoryResearch
Externally publishedYes