Differential Regulation of the Epithelial Sodium Channel (ENaC) in Rat Kidney, Lung and Distal Colon in Response to Aldosterone.

Hypertension ◽  
2000 ◽  
Vol 36 (suppl_1) ◽  
pp. 724-724
Author(s):  
Shyama M E Masilamani ◽  
Gheun-Ho Kim ◽  
Mark A Knepper
Keyword(s):  
Sodium Channel ◽  
Epithelial Sodium Channel ◽  
Distal Colon ◽  
Β Subunit ◽  
Dietary Salt ◽  
Α Subunit ◽  
Salt Restriction ◽  
Γ Subunit ◽  
Dietary Salt Restriction ◽  
Epithelial Sodium Channel Enac

P170 The mineralocorticoid hormone, aldosterone increases renal tubule Na absorption via increases in the protein abundances of the α-subunit of the epithelial sodium channel (ENaC) and the 70 kDa form of the γ- subunit of ENaC (JCI 104:R19-R23). This study assesses the affect of dietary salt restriction on the regulation of the epithelial sodium channel (ENaC) in the lung and distal colon, in addition to kidney, using semiquantitative immunoblotting. Rats were placed initially on either a control Na intake (0.02 meq/day), or a low Na intake (0.2 meq/day) for 10 days. The low salt treated rats demonstrated an increase in plasma aldosterone levels at day 10 (control = 0.78 + 0.32 nM; Na restricted = 3.50 + 1.30 nM). In kidney homogenates, there were marked increases in the band density of the α-subunit of ENaC (286 % of control) and the 70 kDa form of γ-subunit of ENaC (262 % of control), but no increase in the abundance of the β-subunit of ENaC. In lung homogenates, there was no significant change in the band densities of the α, β, or γ subunits of ENaC. In distal colon, there was an increase in the band density of the β-subunit of ENaC (311 % of control) and an increase in both the 85 kDa (2355% of control) and 70 kDa (843 % of control) form of the γ subunit of ENaC in response to dietary Na restriction. However, there was no significant difference in the band density of the α-subunit of ENaC. These findings demonstrate tissue specific regulation of the three subunits of ENaC in response to dietary salt restriction.

Altered expression of renal NHE3, TSC, BSC-1, and ENaC subunits in potassium-depleted rats

2002 ◽  
Vol 283 (6) ◽  
pp. F1376-F1388 ◽  
Author(s):  
Marie-Louise Elkjær ◽  
Tae-Hwan Kwon ◽  
Weidong Wang ◽  
Jakob Nielsen ◽  
Mark A. Knepper ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Β Subunit ◽  
Outer Medulla ◽  
Α Subunit ◽  
Altered Expression ◽  
Γ Subunit ◽  
Outer Stripe ◽  
Type 3 ◽  
Epithelial Sodium Channel Enac ◽  
Concentrating Defect

The purpose of this study was to examine whether hypokalemia is associated with altered abundance of major renal Na+ transporters that may contribute to the development of urinary concentrating defects. We examined the changes in the abundance of the type 3 Na+/H+ exchanger (NHE3), Na+-K+-ATPase, the bumetanide-sensitive Na+-K+-2Cl− cotransporter (BSC-1), the thiazide-sensitive Na+-Cl− cotransporter (TSC), and epithelial sodium channel (ENaC) subunits in kidneys of hypokalemic rats. Semiquantitative immunoblotting revealed that the abundance of BSC-1 (57%) and TSC (46%) were profoundly decreased in the inner stripe of the outer medulla (ISOM) and cortex/outer stripe of the outer medulla (OSOM), respectively. These findings were confirmed by immunohistochemistry. Moreover, total kidney abundance of all ENaC subunits was significantly reduced in response to the hypokalemia: α-subunit (61%), β-subunit (41%), and γ-subunit (60%), and this was confirmed by immunohistochemistry. In contrast, the renal abundance of NHE3 in hypokalemic rats was dramatically increased in cortex/OSOM (736%) and ISOM (210%). Downregulation of BSC-1, TSC, and ENaC may contribute to the urinary concentrating defect, whereas upregulation of NHE3 may be compensatory to prevent urinary Na+ loss and/or to maintain intracellular pH levels.

scholarly journals TMPRSS4-dependent activation of the epithelial sodium channel requires cleavage of the γ-subunit distal to the furin cleavage site

2012 ◽  
Vol 302 (1) ◽  
pp. F1-F8 ◽  
Author(s):  
Christopher J. Passero ◽  
Gunhild M. Mueller ◽  
Michael M. Myerburg ◽  
Marcelo D. Carattino ◽  
Rebecca P. Hughey ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Cleavage Site ◽  
Epithelial Sodium Channel ◽  
Cleavage Sites ◽  
Furin Cleavage ◽  
Channel Activation ◽  
Α Subunit ◽  
Γ Subunit ◽  
Furin Cleavage Site ◽  
Unique Mechanism

The epithelial sodium channel (ENaC) is activated by a unique mechanism, whereby inhibitory tracts are released by proteolytic cleavage within the extracellular loops of two of its three homologous subunits. While cleavage by furin within the biosynthetic pathway releases one inhibitory tract from the α-subunit and moderately activates the channel, full activation through release of a second inhibitory tract from the γ-subunit requires cleavage once by furin and then at a distal site by a second protease, such as prostasin, plasmin, or elastase. We now report that coexpression of mouse transmembrane protease serine 4 (TMPRSS4) with mouse ENaC in Xenopus oocytes was associated with a two- to threefold increase in channel activity and production of a unique ∼70-kDa carboxyl-terminal fragment of the γ-subunit, similar to the ∼70-kDa γ-subunit fragment that we previously observed with prostasin-dependent channel activation. TMPRSS4-dependent channel activation and production of the ∼70-kDa fragment were partially blocked by mutation of the prostasin-dependent cleavage site (γRKRK186QQQQ). Complete inhibition of TMPRSS4-dependent activation of ENaC and γ-subunit cleavage was observed when three basic residues between the furin and prostasin cleavage sites were mutated (γK173Q, γK175Q, and γR177Q), in addition to γRKRK186QQQQ. Mutation of the four basic residues associated with the furin cleavage site (γRKRR143QQQQ) also prevented TMPRSS4-dependent channel activation. We conclude that TMPRSS4 primarily activates ENaC by cleaving basic residues within the tract γK173-K186 distal to the furin cleavage site, thereby releasing a previously defined key inhibitory tract encompassing γR158-F168 from the γ-subunit.

Evolution of the epithelial sodium channel and the sodium pump as limiting factors of aldosterone action on sodium transport

2011 ◽  
Vol 43 (13) ◽  
pp. 844-854 ◽  
Author(s):  
Romain A. Studer ◽  
Emilie Person ◽  
Marc Robinson-Rechavi ◽  
Bernard C. Rossier
Keyword(s):  
Sodium Channel ◽  
Sodium Transport ◽  
Salt Intake ◽  
Epithelial Sodium Channel ◽  
Cell Junctions ◽  
Limiting Factors ◽  
Last Common Ancestor ◽  
Β Subunit ◽  
Α Subunit ◽  
Additional Function

Despite large changes in salt intake, the mammalian kidney is able to maintain the extracellular sodium concentration and osmolarity within very narrow margins, thereby controlling blood volume and blood pressure. In the aldosterone-sensitive distal nephron (ASDN), aldosterone tightly controls the activities of epithelial sodium channel (ENaC) and Na,K-ATPase, the two limiting factors in establishing transepithelial sodium transport. It has been proposed that the ENaC/degenerin gene family is restricted to Metazoans, whereas the α- and β-subunits of Na,K-ATPase have homologous genes in prokaryotes. This raises the question of the emergence of osmolarity control. By exploring recent genomic data of diverse organisms, we found that: 1) ENaC/degenerin exists in all of the Metazoans screened, including nonbilaterians and, by extension, was already present in ancestors of Metazoa; 2) ENaC/degenerin is also present in Naegleria gruberi , an eukaryotic microbe, consistent with either a vertical inheritance from the last common ancestor of Eukaryotes or a lateral transfer between Naegleria and Metazoan ancestors; and 3) The Na,K-ATPase β-subunit is restricted to Holozoa, the taxon that includes animals and their closest single-cell relatives. Since the β-subunit of Na,K-ATPase plays a key role in targeting the α-subunit to the plasma membrane and has an additional function in the formation of cell junctions, we propose that the emergence of Na,K-ATPase, together with ENaC/degenerin, is linked to the development of multicellularity in the Metazoan kingdom. The establishment of multicellularity and the associated extracellular compartment (“internal milieu”) precedes the emergence of other key elements of the aldosterone signaling pathway.

scholarly journals The R563Q mutation of the β-subunit of the Epithelial Sodium Channel (ENaC) strongly associates with hypertension

2005 ◽  
Vol 18 (5) ◽  
pp. A84-A84
Author(s):  
B RAYNER ◽  
E OWEN ◽  
D BAINES ◽  
Y TRINDER ◽  
J KING ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Epithelial Sodium Channel ◽  
Β Subunit ◽  
Epithelial Sodium Channel Enac

scholarly journals Defining an inhibitory domain in the gamma subunit of the epithelial sodium channel

2010 ◽  
Vol 299 (4) ◽  
pp. F854-F861 ◽  
Author(s):  
Christopher J. Passero ◽  
Marcelo D. Carattino ◽  
Ossama B. Kashlan ◽  
Mike M. Myerburg ◽  
Rebecca P. Hughey ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Epithelial Sodium Channel ◽  
Xenopus Laevis Oocytes ◽  
Airway Epithelia ◽  
Gamma Subunit ◽  
Γ Subunit ◽  
Inhibitory Region ◽  
Inhibitory Domain ◽  
Complete Deletion ◽  
Epithelial Sodium Channel Enac

Proteases activate the epithelial sodium channel (ENaC) by cleaving the large extracellular domains of the α- and γ-subunits and releasing peptides with inhibitory properties. Furin and prostasin activate mouse ENaC by cleaving the γ-subunit at sites flanking a 43 residue inhibitory tract (γE144-K186). To determine whether there is a minimal inhibitory region within this 43 residue tract, we generated serial deletions in the inhibitory tract of the γ-subunit in channels resistant to cleavage by furin and prostasin. We found that partial or complete deletion of a short segment in the γ-subunit, R158-N171, enhanced channel activity. Synthetic peptides overlapping this segment in the γ-subunit further identified a key 11-mer tract, R158-F168 (RFLNLIPLLVF), which inhibited wild-type ENaC expressed in Xenopus laevis oocytes, and endogenous channels in mpkCCD cells and human airway epithelia. Further studies with amino acid-substituted peptides defined residues that are required for inhibition in this key 11-mer tract. The presence of the native γ inhibitory tract in ENaC weakened the intrinsic binding constant of the 11-mer peptide inhibitor, suggesting that the γ inhibitory tract and the 11-mer peptide interact at overlapping sites within the channel.

scholarly journals 5′ Heterogeneity in epithelial sodium channel α-subunit mRNA leads to distinct NH2-terminal variant proteins

1998 ◽  
Vol 274 (5) ◽  
pp. C1312-C1323 ◽  
Author(s):  
Christie P. Thomas ◽  
Scott Auerbach ◽  
John B. Stokes ◽  
Kenneth A. Volk
Keyword(s):  
Sodium Channel ◽  
Xenopus Oocytes ◽  
Epithelial Sodium Channel ◽  
Open Reading Frame ◽  
Splice Sites ◽  
Α Subunit ◽  
Exon 2 ◽  
Reading Frame ◽  
Subunit Mrna ◽  
Epithelial Sodium Channel Enac

The amiloride-sensitive epithelial sodium channel (ENaC) is composed of three subunits: α, β, and γ. The human α-ENaC subunit is expressed as at least two transcripts (N. Voilley, E. Lingueglia, G. Champigny, M. G. Mattei, R. Waldmann, M. Lazdunski, and P. Barbry. Proc. Natl. Acad. Sci. USA91: 247–251, 1994). To determine the origin of these transcripts, we characterized the 5′ end of the α-ENaC gene. Four transcripts that differ at their first exon were identified. Exon 1A splices to exon 2 to form the 5′ end of α-ENaC1, whereas exon 1B arises separately and continues into exon 2 to form α-ENaC2. Other variant mRNAs, α-ENaC3 and α-ENaC4, are formed by activating 5′ splice sites within exon 1B. Although α-ENaC3 and -4 did not change the open reading frame for α-ENaC, α-ENaC2 contains upstream ATGs that add 59 amino acids to the previous (α-ENaC1) protein. To address the significance of these isoforms, both proteins were expressed in Xenopus oocytes. The cRNA for each α-ENaC transcript when combined with β- and γ-ENaC cRNA reconstituted a low-conductance ion channel with amiloride-sensitive currents of similar characteristics. We have thus identified variant α-ENaC mRNAs that lead to functional ENaC peptides.

Urine exosomes from healthy and hypertensive pregnancies display elevated level of α-subunit and cleaved α- and γ-subunits of the epithelial sodium channel—ENaC

2017 ◽  
Vol 469 (9) ◽  
pp. 1107-1119 ◽  
Author(s):  
Maria R. Nielsen ◽  
Britta Frederiksen-Møller ◽  
Rikke Zachar ◽  
Jan S. Jørgensen ◽  
Mie R. Hansen ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Elevated Level ◽  
Epithelial Sodium Channel ◽  
Α Subunit ◽  
Urine Exosomes ◽  
Epithelial Sodium Channel Enac

scholarly journals The Endoplasmic Reticulum–associated Degradation of the Epithelial Sodium Channel Requires a Unique Complement of Molecular Chaperones

2010 ◽  
Vol 21 (6) ◽  
pp. 1047-1058 ◽  
Author(s):  
Teresa M. Buck ◽  
Alexander R. Kolb ◽  
Cary R. Boyd ◽  
Thomas R. Kleyman ◽  
Jeffrey L. Brodsky
Keyword(s):  
Sodium Channel ◽  
Molecular Chaperones ◽  
Essential Role ◽  
Epithelial Sodium Channel ◽  
Single Copy ◽  
Salt Balance ◽  
Expression Systems ◽  
Γ Subunit ◽  
Water And Salt Balance ◽  
Epithelial Sodium Channel Enac

The epithelial sodium channel (ENaC) is composed of a single copy of an α-, β-, and γ-subunit and plays an essential role in water and salt balance. Because ENaC assembles inefficiently after its insertion into the ER, a substantial percentage of each subunit is targeted for ER-associated degradation (ERAD). To define how the ENaC subunits are selected for degradation, we developed novel yeast expression systems for each ENaC subunit. Data from this analysis suggested that ENaC subunits display folding defects in more than one compartment and that subunit turnover might require a unique group of factors. Consistent with this hypothesis, yeast lacking the lumenal Hsp40s, Jem1 and Scj1, exhibited defects in ENaC degradation, whereas BiP function was dispensable. We also discovered that Jem1 and Scj1 assist in ENaC ubiquitination, and overexpression of ERdj3 and ERdj4, two lumenal mammalian Hsp40s, increased the proteasome-mediated degradation of ENaC in vertebrate cells. Our data indicate that Hsp40s can act independently of Hsp70 to select substrates for ERAD.

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