Functional characterization of a partial loss-of-function mutation of the epithelial sodium channel (ENaC) associated with atypical cystic fibrosis.
Loss-of-function mutations of the epithelial sodium channel (ENaC) may contribute to pulmonary symptoms resembling those of patients with atypical cystic fibrosis (CF). Recently, we identified a loss-of-function mutation in the alpha-subunit of ENaC (alphaF61L) in an atypical CF patient without mutations in CFTR. To investigate the functional effect of this mutation, we expressed human wild-type alpha beta gamma-ENaC or mutant alpha(F61L) beta gamma-ENaC in Xenopus laevis oocytes. The alphaF61L mutation reduced the ENaC mediated whole-cell currents by approximately 90%. In contrast, the mutation decreased channel surface expression only by approximately 40% and did not alter the single-channel conductance. These findings indicate that the major effect of the mutation is a reduction of the average channel open probability (P(o)). This was confirmed by experiments using the betaS520C mutant ENaC which can be converted to a channel with a P(o) of nearly one, and by experiments using chymotrypsin to proteolytically activate the channel. These experiments revealed that the mutation reduced the average P(o) of ENaC by approximately 75%. Na(+) self inhibition of the mutant channel was significantly enhanced, but the observed effect was too small to account for the large reduction in average channel P(o). The ENaC-activator S3969 partially rescued the loss-of-function phenotype of the alphaF61L mutation. We conclude that the alphaF61L mutation may contribute to respiratory symptoms in atypical CF patients.
Huber
Regina
R
Institut für Zelluläre und Molekulare Physiologie, Erlangen, Germany.
Krueger
Bettina
B
Diakov
Alexei
A
Korbmacher
Judit
J
Haerteis
Silke
S
Einsiedel
Jürgen
J
Gmeiner
Peter
P
Azad
Abul Kalam
AK
Cuppens
Harry
H
Cassiman
Jean-Jaques
JJ
Korbmacher
Christoph
C
Rauh
Robert
R
D000818:Animals; D002918:Chymotrypsin / Q000378:metabolism; D003550:Cystic Fibrosis / Q000235:genetics* / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D006801:Humans; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014982:Xenopus laevis
D053503:Epithelial Sodium Channels; D012964:Sodium; D002918:Chymotrypsin