Biosynthesis and Processing of Epithelial Sodium Channels inXenopus Oocytes
The epithelial sodium channel (ENaC) provides the rate-limiting step in the reabsorption of sodium by many epithelia. The number of channels at the cell surface is tightly regulated; most cells express only a few channels. We have examined the biosynthesis and cell surface expression of ENaC in Xeno...
Saved in:
Published in | The Journal of biological chemistry Vol. 273; no. 46; p. 30344 |
---|---|
Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
American Society for Biochemistry and Molecular Biology
13.11.1998
|
Online Access | Get full text |
Cover
Loading…
Summary: | The epithelial sodium channel (ENaC) provides the rate-limiting step in the reabsorption of sodium by many epithelia. The
number of channels at the cell surface is tightly regulated; most cells express only a few channels. We have examined the
biosynthesis and cell surface expression of ENaC in Xenopus oocytes. The subunits of ENaC are readily synthesized in the endoplasmic reticulum, but most of them remain as immature proteins
in pre-Golgi compartments, where they are degraded by the proteasomal pathway without apparent ubiquitination. Even when the
three subunits, α, β, and γ, are expressed in the same cell, only a very small fraction of the total channel population leave
the endoplasmic reticulum, acquire complex oligosaccharides, and reach the plasma membrane. Overexpression of subunits does
not increase the number of channels in the plasma membrane but results in the appearance of cytoplasmic subunits in a form
not membrane bound. The data indicate that maturation and assembly of the subunits are slow and inefficient processes, and
constitute limiting steps for the expression of functional ENaC channels in the plasma membrane. |
---|---|
ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.273.46.30344 |