Plasmin activates epithelial Na+ channels by cleaving the gamma subunit
Christopher J Passero1, Gunhild M Mueller, Helbert Rondon-Berrios
1Department of Medicine, Renal-Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
The Journal of Biological Chemistry
|November 5, 2008
Summary
Plasmin activates the epithelial sodium channel (ENaC) by cleaving its gamma subunit at a distal site. This cleavage is crucial for full ENaC activation and may play a role in conditions like proteinuria.
Area of Science:
- Biochemistry
- Molecular Biology
- Physiology
Background:
- Proteolytic processing of epithelial sodium channel (ENaC) subunits is essential for channel maturation and activation.
- While alpha and gamma subunits undergo processing, the gamma subunit requires a second distal cleavage for full activation.
Purpose of the Study:
- To investigate the role of the serine protease plasmin in ENaC activation.
- To identify the specific cleavage site on the gamma subunit targeted by plasmin.
Main Methods:
- Site-directed mutagenesis to create a gammaK194A mutant.
- Measurement of ENaC activity in the presence and absence of plasmin.
- Analysis of gamma subunit cleavage fragments using Western blotting.
Main Results:
- Plasmin activates ENaC and induces cleavage of the gamma subunit at gammaLys194.
- A gammaK194A mutation abolished plasmin-dependent ENaC activation and the production of a 70-kDa gamma subunit fragment.
- Plasmin-dependent ENaC activation may be relevant in proteinuria-associated disorders.
Conclusions:
- Plasmin-dependent cleavage at gammaLys194 is a key step in full ENaC activation.
- This mechanism highlights a novel pathway for ENaC regulation.
- The findings suggest a potential role for plasmin in ENaC-mediated fluid balance during proteinuria.
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