The cystic fibrosis transmembrane conductance regulator impedes proteolytic stimulation of the epithelial Na+ channel.
Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) that prevent its proper folding and trafficking to the apical membrane of epithelial cells. Absence of cAMP-mediated Cl(-) secretion in CF airways causes poorly hydrated airway surfaces in CF patients, and this condition is exacerbated by excessive Na(+) absorption. The mechanistic link between missing CFTR and increased Na(+) absorption in airway epithelia has remained elusive, although substantial evidence implicates hyperactivity of the epithelial Na(+) channel (ENaC). ENaC is known to be activated by selective endoproteolysis of the extracellular domains of its α- and γ-subunits, and it was recently reported that ENaC and CFTR physically associate in mammalian cells. We confirmed this interaction in oocytes by co-immunoprecipitation and found that ENaC associated with wild-type CFTR was protected from proteolytic cleavage and stimulation of open probability. In contrast, ΔF508 CFTR, the most common mutant protein in CF patients, failed to protect ENaC from proteolytic cleavage and stimulation. In normal airway epithelial cells, ENaC was contained in the anti-CFTR immunoprecipitate. In CF airway epithelial cultures, the proportion of full-length to total α-ENaC protein signal was consistently reduced compared with normal cultures. Our results identify limiting proteolytic cleavage of ENaC as a mechanism by which CFTR down-regulates Na(+) absorption.
Gentzsch
Martina
M
Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA. gentzsch@med.unc.edu.
Dang
Hong
H
Dang
Yan
Y
Garcia-Caballero
Agustin
A
Suchindran
Hamsa
H
Boucher
Richard C
RC
Stutts
M Jackson
MJ
D000818:Animals; D002478:Cells, Cultured; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism
D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012964:Sodium