cAMP and Serum and Glucocorticoid-inducible Kinase (SGK) Regulate the Epithelial Na+ Channel through Convergent Phosphorylation of Nedd4-2

The epithelial Na + channel (ENaC) functions as a pathway for epithelial Na + transport, contributing to Na + homeostasis and blood pressure control. Vasopressin increases ENaC expression at the cell surface through a pathway that includes cAMP and cAMP-dependent protein kinase (PKA), but the mechan...

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Bibliographic Details
Published in:The Journal of biological chemistry 2004-10, Vol.279 (44), p.45753-45758
Main Authors: Snyder, Peter M, Olson, Diane R, Kabra, Rajesh, Zhou, Ruifeng, Steines, Jennifer C
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
COS Cells
Cyclic AMP - physiology
Cyclic AMP-Dependent Protein Kinases - physiology
Endosomal Sorting Complexes Required for Transport
Epithelial Sodium Channels
Humans
Immediate-Early Proteins
Ion Transport
Molecular Sequence Data
Nedd4 Ubiquitin Protein Ligases
Nuclear Proteins - physiology
Phosphorylation
Protein-Serine-Threonine Kinases - physiology
Sodium - metabolism
Sodium Channels - physiology
Ubiquitin-Protein Ligases - metabolism
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Summary:The epithelial Na + channel (ENaC) functions as a pathway for epithelial Na + transport, contributing to Na + homeostasis and blood pressure control. Vasopressin increases ENaC expression at the cell surface through a pathway that includes cAMP and cAMP-dependent protein kinase (PKA), but the mechanisms that link PKA to ENaC are unknown. Here we found that cAMP regulates Na + transport in part by inhibiting the function of Nedd4-2, an E3 ubiquitin-protein ligase that targets ENaC for degradation. Consistent with this model, we found that cAMP inhibited Nedd4-2 by decreasing its binding to ENaC. Moreover, decreased Nedd4-2 expression (RNA interference) or overexpression of a dominant negative Nedd4-2 construct disrupted ENaC regulation by cAMP. Nedd4-2 was a substrate for phosphorylation by PKA in vitro and in cells; three Nedd4-2 residues were phosphorylated by PKA and were required for cAMP to inhibit Nedd4-2 (relative functional importance Ser-327 > Ser-221 > Thr-246). Previous work found that these residues are also phosphorylated by serum and glucocorticoid-inducible kinase (SGK), a downstream mediator by which aldosterone regulates epithelial Na + transport. Consistent with a functional interaction between these pathways, overexpression of SGK blunted ENaC stimulation by cAMP, whereas inhibition of SGK increased stimulation. Conversely, cAMP agonists decreased ENaC stimulation by SGK. The data suggest that cAMP regulates ENaC in part by phosphorylation and inhibition of Nedd4-2. Moreover, Nedd4-2 is a central convergence point for kinase regulation of Na + transport.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M407858200