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XB-ART-50471
Am J Physiol Cell Physiol 2014 Oct 15;3078:C701-9. doi: 10.1152/ajpcell.00134.2014.
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ERp29 regulates epithelial sodium channel functional expression by promoting channel cleavage.

Grumbach Y , Bikard Y , Suaud L , Chanoux RA , Rubenstein RC .


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The epithelial Na(+) channel (ENaC) plays a key role in the regulation of blood pressure and airway surface liquid volume. ERp29 is a 29-kDa thioredoxin-homologous endoplasmic reticulum (ER) protein that has only a single cysteine instead of the usual thioredoxin CXXC motif. Our group previously demonstrated that ERp29 promotes biogenesis of the cystic fibrosis transmembrane conductance regulator (CFTR). On the basis of similarities of CFTR and ENaC trafficking, we hypothesized that ERp29 would also regulate ENaC biogenesis and functional expression. In epithelial cells, overexpression of wild-type (wt) ERp29 increased ENaC functional expression [amiloride-sensitive short-circuit current (Isc)] in Ussing chamber experiments, as well as the abundance of the cleaved form of γ-ENaC in whole cell lysates. In contrast, siRNA-mediated depletion of ERp29 or overexpression of a mutant ERp29 lacking its single cysteine (C157S ERp29) decreased ENaC functional expression. Cells in which wt ERp29 was overexpressed had a smaller fractional increase in amiloride-sensitive Isc when trypsin was applied to the apical surface to activate uncleaved ENaC, while cells in which C157S ERp29 was overexpressed or ERp29 was depleted had a significantly greater fractional increase in amiloride-sensitive Isc in response to trypsin. Interestingly, these observations were not associated with altered expression of β-ENaC at the apical surface. Instead, ERp29 appeared to promote the interaction of β-ENaC with the Sec24D cargo recognition component of the coat complex II ER exit machinery. Together, these data support the hypothesis that ERp29 directs ENaC toward the Golgi, where it undergoes cleavage during its biogenesis and trafficking to the apical membrane.

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Species referenced: Xenopus laevis
Genes referenced: cftr erp29 prss1 sec24d

References [+] :
Adebamiro, Endogenous protease activation of ENaC: effect of serine protease inhibition on ENaC single channel properties. 2005, Pubmed