A mutation in the beta-subunit of ENaC identified in a patient with cystic fibrosis-like symptoms has a gain-of-function effect

作者：Rauh Robert^*; Soell Daniel; Haerteis Silke; Diakov Alexei; Nesterov Viatcheslav; Krueger Bettina; Sticht Heinrich; Korbmacher Christoph

来源：American Journal of Physiology - Lung Cellular and Molecular Physiology, 2013, 304(1): L43-L55.

DOI：10.1152/ajplung.00093.2012

• gain-of-function mutation
• Xenopus laevis oocyte expression system
• electrophysiology
• computational channel modeling
• sodium transport in cystic fibrosis
• epithelial sodium channel

Rauh R, Soell D, Haerteis S, Diakov A, Nesterov V, Krueger B, Sticht H, Korbmacher C. A mutation in the beta-subunit of ENaC identified in a patient with cystic fibrosis-like symptoms has a gain-of-function effect. Am J Physiol Lung Cell Mol Physiol 304: L43-L55, 2013. First published October 19, 2012; doi:10.1152/ajplung.00093.2012.-In some patients with atypical cystic fibrosis (CF), only one allele of the CF transmembrane conductance regulator (CFTR) gene is affected. Mutations of the epithelial sodium channel (ENaC) may contribute to the pathophysiology of the disease in these patients. To functionally characterize a mutation in the beta-subunit of ENaC (beta V348M) recently identified in a patient with severe CF-like symptoms (Mutesa et al. 2009), we expressed wild-type (wt) alpha beta gamma ENaC or mutant alpha beta V348M gamma ENaC in Xenopus laevis oocytes. The beta V348M mutation stimulated amiloride-sensitive whole-cell current (Delta I-ami) by similar to 40% but had no effect on surface expression or single-channel conductance of ENaC. Instead the mutation increased channel open probability (P-o). Proteolytic activation of mutant ENaC by chymotrypsin was reduced compared with that of wt ENaC (similar to 3.0-fold vs. similar to 4.2-fold), which is consistent with the increased baseline P-o of mutant ENaC. Similarly, the ENaC activator S3969 stimulated mutant ENaC currents to a lesser degree (by similar to 2.6-fold) than wt ENaC currents (by similar to 3.5-fold). The gain-of-function effect of the beta V348M mutation was confirmed by whole-cell current measurements in HEK293 cells transiently transfected with wt or mutant ENaC. Computational channel modeling in combination with functional expression of different beta V348 mutants in oocytes suggests that the beta V348M mutation increases channel P-o by destabilizing the closed channel state. Our findings indicate that the gain-of-function effect of the beta V348M mutation may contribute to CF pathophysiology by inappropriately increasing sodium and fluid absorption in the respiratory tract.

• 出版日期2013-1