Epithelial Na+ channels are fully activated by furin- and prostasin-dependent release of an inhibitory peptide from the gamma-subunit.
Epithelial sodium channels (ENaC) are expressed in the apical membrane of high resistance Na(+) transporting epithelia and have a key role in regulating extracellular fluid volume and the volume of airway surface liquids. Maturation and activation of ENaC subunits involves furin-dependent cleavage of the ectodomain at two sites in the alpha subunit and at a single site within the gamma subunit. We now report that the serine protease prostasin further activates ENaC by inducing cleavage of the gamma subunit at a site distal to the furin cleavage site. Dual cleavage of the gamma subunit is predicted to release a 43-amino acid peptide. Channels with a gamma subunit lacking this 43-residue tract have increased activity due to a high open probability. A synthetic peptide corresponding to the fragment cleaved from the gamma subunit is a reversible inhibitor of endogenous ENaCs in mouse cortical-collecting duct cells and in primary cultures of human airway epithelial cells. Our results suggest that multiple proteases cleave ENaC gamma subunits to fully activate the channel.
Bruns
James B
JB
Renal-Electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
Carattino
Marcelo D
MD
Sheng
Shaohu
S
Maarouf
Ahmad B
AB
Weisz
Ora A
OA
Pilewski
Joseph M
JM
Hughey
Rebecca P
RP
Kleyman
Thomas R
TR
D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology*; D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D045683:Furin / Q000378:metabolism*; D006801:Humans; D051379:Mice; D009399:Nephrons / Q000166:cytology; D010446:Peptide Fragments / Q000378:metabolism* / Q000494:pharmacology; D021122:Protein Subunits / Q000378:metabolism; D012137:Respiratory System / Q000166:cytology; D012697:Serine Endopeptidases / Q000378:metabolism*; D014162:Transfection; D014981:Xenopus; D000099271:Prostasin
D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels; D045683:Furin; D010446:Peptide Fragments; D021122:Protein Subunits; D012697:Serine Endopeptidases; D000099271:Prostasin