Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Epithelial Na+ channels are expressed widely in absorptive epithelia such as the renal collecting duct and the colon and play a critical role in fluid and electrolyte homeostasis. Recent studies have shown that these channels interact via PY motifs in the C terminals of their alpha, beta, and gamma subunits with the WW domains of the ubiquitin-protein ligase Nedd4. Mutation or deletion of these PY motifs (as occurs, for example, in the heritable form of hypertension known as Liddle's syndrome) leads to increased Na+ channel activity. Thus, binding of Nedd4 by the PY motifs would appear to be part of a physiological control system for down-regulation of Na+ channel activity. The nature of this control system is, however, unknown. In the present paper, we show that Nedd4 mediates the ubiquitin-dependent down-regulation of Na+ channel activity in response to increased intracellular Na+. We further show that Nedd4 operates downstream of Go in this feedback pathway. We find, however, that Nedd4 is not involved in the feedback control of Na+ channels by intracellular anions. Finally, we show that Nedd4 has no influence on Na+ channel activity when the Na+ and anion feedback systems are inactive. We conclude that Nedd4 normally mediates feedback control of epithelial Na+ channels by intracellular Na+, and we suggest that the increased Na+ channel activity observed in Liddle's syndrome is attributable to the loss of this regulatory feedback system.
 ...
PMID:Nedd4 mediates control of an epithelial Na+ channel in salivary duct cells by cytosolic Na+. 961 57

Liddle's syndrome is a form of inherited hypertension linked to mutations in the genes encoding the epithelial Na+ channel (ENaC). These mutations alter or delete PY motifs involved in protein-protein interactions with a ubiquitin-protein ligase, Nedd4. Here we show that Na+ transporting cells, derived from mouse cortical collecting duct, express two Nedd4 proteins with different structural organization and characteristics of ENaC regulation: 1) the classical Nedd4 (herein referred to as Nedd4-1) containing one amino-terminal C2, three WW, and one HECT-ubiquitin protein ligase domain and 2) a novel Nedd4 protein (Nedd4-2), homologous to Xenopus Nedd4 and comprising four WW, one HECT, yet lacking a C2 domain. Nedd4-2, but not Nedd4-1, inhibits ENaC activity when coexpressed in Xenopus oocytes and this property correlates with the ability to bind to ENaC, as only Nedd4-2 coimmunoprecipitates with ENaC. Furthermore, this interaction depends on the presence of at least one PY motif in the ENaC complex and on WW domains 3 and 4 in Nedd4-2. Thus, these results suggest that the novel suppressor protein Nedd4-2 is the regulator of ENaC and hence a potential susceptibility gene for arterial hypertension.
 ...
PMID:A novel mouse Nedd4 protein suppresses the activity of the epithelial Na+ channel. 1114 8

The epithelial Na+ channel (ENaC) forms the pathway for Na+ absorption in the kidney collecting duct and other epithelia. Dominant gain-of-function mutations cause Liddle's syndrome, an inherited form of hypertension resulting from excessive renal Na+ absorption. Conversely, loss-of-function mutations cause pseudohypoaldosteronism type I, a disorder of salt wasting and hypotension. Thus, ENaC has a critical role in the maintenance of Na+ homeostasis and blood pressure control. Altered Na+ absorption in the lung may also contribute to the pathogenesis of cystic fibrosis. Epithelial Na+ absorption is regulated in large part by mechanisms that control the expression of ENaC at the cell surface. Nedd4, a ubiquitin protein ligase, binds to ENaC and targets the channel for endocytosis and degradation. Liddle's syndrome mutations disrupt the interaction between ENaC and Nedd4, resulting in an increase in the number of ENaC channels at the cell surface. Aldosterone and vasopressin also regulate Na+ absorption to defend against hypotension and hypovolemia. Both hormones increase the expression of ENaC at the cell surface. The goal of this review is to summarize recent data on the regulation of ENaC expression at the cell surface.
 ...
PMID:The epithelial Na+ channel: cell surface insertion and retrieval in Na+ homeostasis and hypertension. 1194 47

The amiloride-sensitive epithelial sodium channel (ENaC) plays a critical role in fluid and electrolyte homeostasis and consists of alpha, beta, and gamma subunits. The carboxyl terminus of each ENaC subunit contains a PPXY motif that is believed to be important for interaction with the WW domains of the ubiquitin-protein ligases, Nedd4 and Nedd4-2. Disruption of this interaction, as in Liddle's syndrome where mutations delete or alter the PPXY motif of either the beta or gamma subunits, has been shown to result in increased ENaC activity and arterial hypertension. Here we present evidence that N4WBP5A, a novel Nedd4/Nedd4-2-binding protein, is a potential regulator of ENaC. In Xenopus laevis oocytes N4WBP5A increases surface expression of ENaC by reducing the rate of ENaC retrieval. We further demonstrate that N4WBP5A prevents sodium feedback inhibition of ENaC possibly by interfering with the xNedd4-2-mediated regulation of ENaC. As N4WBP5A binds Nedd4/Nedd4-2 via PPXY motif/WW domain interactions and appears to be associated with specific intracellular vesicles, we propose that N4WBP5A functions by regulating Nedd4/Nedd4-2 availability and trafficking. Because N4WBP5A is highly expressed in native renal collecting duct and other tissues that express ENaC, it is a likely candidate to modulate ENaC function in vivo.
 ...
PMID:Regulation of the epithelial sodium channel by N4WBP5A, a novel Nedd4/Nedd4-2-interacting protein. 1205 Jan 53

Mutations that disrupt a PY motif in epithelial Na+ channel (ENaC) subunits increase surface expression of Na+ channels in the collecting duct, resulting in greater Na+ reabsorption. Recently, Nedd4 and Nedd4-2 have been identified as ubiquitin ligases that can interact with ENaC via its PY motifs to regulate channel activity. To further understand the role of human Nedd4-2 (hNedd4-2), we cloned its cDNAs and determined its genomic organization using a bioinformatic approach. The gene is present as a single copy, spans at least 400 kb, and contains >40 exons. Multiple 5'-exons were identified by 5'-rapid amplification of cDNA ends, and tissue-specific expression of these transcripts was noted by RT-PCR and RNase protection assay. Alternate polyadenylation signal sequences led to varying lengths of the 3'-untranslated region. Alternate splicing events within internal exons were also noted. Open reading frame analysis indicates that hNedd4-2 encode multiple protein variants with and without a C2 domain, and with a variable number of WW domains. Coexpression, in Fischer rat thyroid epithelia, of ENaC and Nedd4-2 cDNAs leads to a significant reduction in amiloride-sensitive currents, confirming a role in Na+ transport regulation. In vitro binding studies demonstrated that individual PY motifs of alpha-, beta-, and gamma-ENaC have strong affinity for WW domains 3 and 4 but not 1 and 2. These studies indicate that alternate transcripts of Nedd4-2 may interact with ENaC differently. Understanding the function of variant proteins will increase our knowledge of the role of hNedd4-2 in the regulation of ENaC and define protein domains important for Nedd4-2 function.
 ...
PMID:Alternate promoters and variable splicing lead to hNedd4-2 isoforms with a C2 domain and varying number of WW domains. 1287 68

Mutations that disrupt a PY motif in epithelial Na(+) channel (ENaC) subunits increase surface expression of Na(+) channels in the collecting duct, resulting in greater Na(+) reabsorption. Nedd4 and Nedd4-2 have been identified as ubiquitin ligases that can interact with ENaC via its PY motifs to regulate channel activity. We recently reported that human Nedd4-2 (hNedd4-2) is expressed as many isoforms because of alternative promoter usage and/or variable splicing. To understand the relevance of hNedd4-2 isoforms for collecting duct Na(+) transport, we studied the interaction with ENaC and the intracellular localization and function of the following three naturally occurring hNedd4-2 isoforms: full-length Nedd4-2 (Nedd4-2), Nedd4-2 lacking the NH(2)-terminal C2 domain (Nedd4-2DeltaC2), and Nedd4-2 lacking the C2 domain and WW domains 2 and 3 (Nedd4-2DeltaWW2,3). Nedd4-2 and Nedd4-2DeltaC2 associate with ENaC and robustly reduce Na(+) transport in Xenopus oocytes, whereas the interaction with and functional effect of Nedd4-2DeltaWW2,3 on ENaC is weak. Nedd4-2 is expressed in the mouse collecting duct, and overexpression of Nedd4-2 reduces endogenous ENaC activity in a collecting duct cell line. This reduction in ENaC activity can be reversed early with exposure to dexamethasone, an effect that is associated with an increase in sgk1 abundance. The C2 domain is required to target Nedd4-2 to the plasma membrane in response to elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) in MDCK cells, although it does not appear to mediate the inhibitory effect of [Ca(2+)](i) on Na(+) transport. Our data illustrate that naturally occurring hNedd4-2 isoforms differentially associate with ENaC to regulate its activity.
 ...
PMID:Nedd4-2 isoforms differentially associate with ENaC and regulate its activity. 1581 30

The epithelial Na(+) channel (ENaC) is a pathway for Na(+) transport across epithelia, including the kidney collecting duct, lung, and distal colon. ENaC is critical for Na(+) homeostasis and blood pressure control; defects in ENaC function and regulation are responsible for inherited forms of hypertension and hypotension and may contribute to the pathogenesis of cystic fibrosis and other lung diseases. An emerging theme is that epithelial Na(+) transport is regulated in large part through trafficking mechanisms that control ENaC expression at the cell surface. ENaC trafficking is regulated at multiple steps. Delivery of channels to the cell surface is regulated by aldosterone (and corticosteroids) and vasopressin, which increase ENaC synthesis and exocytosis, respectively. Conversely, endocytosis and degradation is controlled by a sequence located in the C terminus of alpha, beta, and gammaENaC (PPPXYXXL). This sequence functions as an endocytosis motif and as a binding site for Nedd4-2, an E3 ubiquitin protein ligase that targets ENaC for degradation. Mutations that delete or disrupt this motif cause accumulation of channels at the cell surface, resulting in Liddle's syndrome, an inherited form of hypertension. Nedd4-2 is a central convergence point for ENaC regulation by aldosterone and vasopressin; both induce phosphorylation of a common set of three Nedd4-2 residues, which blocks Nedd4-2 binding to ENaC. Thus, aldosterone and vasopressin regulate epithelial Na(+) transport in part by altering ENaC trafficking to and from the cell surface.
 ...
PMID:Minireview: regulation of epithelial Na+ channel trafficking. 1615 Aug 99

Aldosterone increases sodium absorption across renal collecting duct cells primarily by increasing the apical membrane expression of ENaC, the sodium entry channel. Nedd4-2, a ubiquitin-protein isopeptide ligase, tags ENaC with ubiquitin for internalization and degradation, but when it is phosphorylated by the aldosterone-induced kinase, SGK1, Nedd4-2 is inhibited and apical ENaC density and sodium absorption increase. We evaluated the hypothesis that 14-3-3 proteins participate in the aldosterone-mediated regulation of ENaC by associating with phosphorylated Nedd4-2. Mouse cortical collecting duct (mCCD) epithelia cultured on filters expressed several 14-3-3 isoforms; this study focused on an isoform whose expression was induced 3-fold by aldosterone, 14-3-3beta. In polarized mCCD epithelia, aldosterone elicited significant, time-dependent increases in the expression of alpha-ENaC, SGK1, phospho-Nedd4-2, and 14-3-3beta without altering total Nedd4-2. Aldosterone decreased the interaction of alpha-ENaC with Nedd4-2, and with similar kinetics increased the association of 14-3-3beta with phospho-Nedd4-2. Short interfering RNA-induced knockdown of 14-3-3beta blunted the aldosterone-induced increase in alpha-ENaC expression, returned alpha-ENaC-Nedd4-2 binding toward prealdosterone levels, and blocked the aldosterone-stimulated increase in transepithelial sodium transport. Incubation of cell extracts with a selective phospho-Nedd4-2 antibody blocked the aldosterone-induced association of 14-3-3beta with Nedd4-2, implicating SGK1 phosphorylation at Ser-328 as the primary site of 14-3-3beta binding. Our studies show that aldosterone increases the expression of 14-3-3beta, which interacts with phospho-Nedd4-2 to block its interaction with ENaC, thus enhancing sodium absorption by increasing apical membrane ENaC density.
 ...
PMID:14-3-3 isoforms are induced by aldosterone and participate in its regulation of epithelial sodium channels. 1661 46

Molecular mechanisms underlying mineralocorticoid receptor (MR)-mediated gene expression are not fully understood. Various transcription factors are post-translationally modified by small ubiquitin-related modifier-1 (SUMO-1). We investigated the role of the SUMO-1-conjugating enzyme Ubc9 in MR transactivation. Yeast two-hybrid, GST-pulldown, and coimmunoprecipitation assays showed that Ubc9 interacted with N-terminal MR-(1-670). Endogenous Ubc9 is associated with stably expressing MR in 293-MR cells. Transient transfection assays in COS-1 cells showed that Ubc9 increased MR transactivation of reporter constructs containing MRE, ENaC, or MMTV promoter in a hormone-sensitive manner. Moreover, reduction of Ubc9 protein levels by small interfering RNA attenuated hormonal activation of a reporter construct as well as an endogenous target gene by MR. A sumoylation-inactive mutant Ubc9(C93S) similarly interacted with MR and potentiated aldosterone-dependent MR transactivation. An MR mutant in which four lysine residues within sumoylation motifs were mutated into arginine (K89R/K399R/K494R/K953R) failed to be sumoylated, but Ubc9 similarly enhanced transactivation by the mutant MR, indicating that sumoylation activity is dispensable for coactivation capacity of Ubc9. Coexpression of Ubc9 and steroid receptor coactivator-1 (SRC-1) synergistically enhanced MR-mediated transactivation in transient transfection assays. Indeed, chromatin immunoprecipitation assays demonstrated that endogenous MR, Ubc9, and SRC-1 were recruited to an endogenous ENaC gene promoter in a largely aldosterone-dependent manner. Coimmunoprecipitation assays showed a complex of MR, Ubc9, and SRC-1 in mammalian cells, and the endogenous proteins were colocalized in the nuclei of the mouse collecting duct cells. These findings support a physiological role of Ubc9 as a transcriptional MR coactivator, beyond the known SUMO E2-conjugating enzyme.
 ...
PMID:Coactivation of the N-terminal transactivation of mineralocorticoid receptor by Ubc9. 1710 32

We previously reported the existence of multiple isoforms of human Nedd4-2 (Am J Physiol Renal Physiol 285: F916-F929, 2003). When overexpressed in M-1 collecting duct epithelia, full-length Nedd4-2 (Nedd4-2), Nedd4-2 lacking the NH(2)-terminal C2 domain (Nedd4-2DeltaC2), and Nedd4-2 lacking WW domains 2 and 3 (Nedd4-2DeltaWW2,3) variably reduce benzamil-sensitive Na(+) transport. We investigated the effect of each of the Nedd4-2 isoforms on cell surface expression and ubiquitination of ENaC subunits. We find that alphaENaC when transfected alone or with beta and gammaENaC is expressed at the cell surface and this membrane expression is variably reduced by coexpression with each of the Nedd4-2 isoforms. Nedd4-2 reduces the half-life of ENaC subunits and enhances the ubiquitination of alpha, beta, and gammaENaC subunits when expressed alone or together suggesting that each subunit is a target for Nedd4-2-mediated ubiquitination. As has been reported recently, we confirm that the surface-expressed pool of ENaC is multi-ubiquitinated. Inhibitors of the proteasome increase ubiquitination of ENaC subunits and stimulate Na(+) transport in M-1 cells consistent with a role for the ubiquitin-proteasome pathway in regulating Na(+) transport in the collecting duct.
 ...
PMID:Nedd4-2 isoforms ubiquitinate individual epithelial sodium channel subunits and reduce surface expression and function of the epithelial sodium channel. 1832 22


1 2 3 Next >>