cAMP and serum and glucocorticoid-inducible kinase (SGK) regulate the epithelial Na+ channel through convergent phosphorylation of Nedd4-2
ABSTRACT 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.
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ABSTRACT: NEDD4-2 (also known as NEDD4L, neural precursor cell expressed developmentally down-regulated 4-like) is a ubiquitin protein ligase of the Nedd4 family which is known to bind and regulate a number of membrane proteins to aid in their internalization and turnover. Several of the NEDD4-2 substrates include ion channels, such as the epithelial and voltage-gated sodium channels. Given the critical function of NEDD4-2 in regulating membrane proteins, this ligase is essential for the maintenance of cellular homeostasis. In this article we review the biology and function of this important ubiquitin-protein ligase and discuss its pathophysiological significance. Copyright © 2014 Elsevier B.V. All rights reserved.Gene 11/2014; DOI:10.1016/j.gene.2014.11.051 · 2.08 Impact Factor
Article: Inhibition of ENaC by Endothelin-1.[Show abstract] [Hide abstract]
ABSTRACT: The amiloride-sensitive epithelial Na(+) channel (ENaC) is a key player in the regulation of Na(+) homeostasis. Its functional activity is under continuous control by a variety of signaling molecules, including bioactive peptides of endothelin family. Since ENaC dysfunction is causative for disturbances in total body Na(+) levels associated with the abnormal regulation of blood volume, blood pressure, and lung fluid balance, uncovering the molecular mechanisms of inhibitory modulation or inappropriate activation of ENaC is crucial for the successful treatment of a variety of human diseases including hypertension. The precise regulation of ENaC is particularly important for normal Na(+) and fluid homeostasis in organs where endothelins are known to act: the kidneys, lung, and colon. Inhibition of ENaC by endothelin-1 (ET-1) has been established in renal cells, and several molecular mechanisms of inhibition of ENaC by ET-1 are proposed and will be reviewed in this chapter. © 2015 Elsevier Inc. All rights reserved.Vitamins & Hormones 01/2015; 98:155-87. DOI:10.1016/bs.vh.2015.01.001 · 1.78 Impact Factor
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ABSTRACT: NEDD4-2 is an ubiquitin-protein ligase that was originally identified as an interactor of the epithelial Na channel (ENaC); this interaction is defective in Liddle's syndrome, causing elevated ENaC activity and salt-sensitive hypertension. In this review we aim to highlight progress achieved in recent years demonstrating that NEDD4-2 is involved in the control of Na transporters that are different from ENaC, but which also play a role in salt-sensitive hypertension. It has been shown that NEDD4-2 interacts with ubiquitylates and negatively regulates the thiazide-sensitive NCC (Na,Cl-cotransporter), both in vitro and in vivo in inducible, nephron-specific Nedd4-2 knockout mice. Moreover, evidence has been provided that NEDD4-2 is also involved in the regulation of human NHE3 (Na,H-exchanger 3) and NKCC2 (Na,K,2Cl-cotransporter 2). The emerging role of NEDD4-2 in the regulation of different Na transporters along the nephron and the identification of human polymorphisms in the NEDD4-2 gene (Nedd4L) related to salt-sensitive hypertension makes this ubiquitin-protein ligase an interesting target for the development of antihypertensive drugs.