Disease relevance of SCNN1A

• Therefore, possession of the SCNN1A G(2139) allele significantly increased the risk of hypertension [1].
• In contrast, defects in the epithelial Na(+) channel (SCNN1) have been associated with phenotypes dominated by renal disease (systemic pseudohypoaldosteronism type I and Liddle syndrome) [2].
• A 116 kDa protein from a human lung adenocarcinoma cell line (H441) was specifically bound by the human alpha-ENaC C-terminal fusion protein and by a shorter 18-amino acid proline-rich peptide derived from the larger fusion protein [3].
• In premature infants, low ENaC activity and low expression level of alpha-ENaC have been associated with respiratory failure [4].

High impact information on SCNN1A

• These two chromosomal regions harbour the genes encoding the three subunits of the human amiloride sensitive epithelial sodium channel (hENaC): SCNN1B and SCNN1G on 16p and SCNN1A on 12p [5].
• Preservation of surface epithelium in UC was indicated by unchanged ENaC alpha-subunit expression, which points also against a mere immaturity or epithelial cell loss [6].
• We report two non-classic CF patients without CFTR mutations who have novel deleterious mutations in the beta-subunits of SCNN1 in the absence of overt renal disease [2].
• F-actin was found to co-immunoprecipitate with alpha-ENaC from whole cell lysates of this cell line [7].
• We have investigated the hypothesis that the actin cytoskeleton directly binds to the carboxyl terminus of alpha-ENaC using a combination of confocal microscopy, co-immunoprecipitation, and protein binding studies [7].

Biological context of SCNN1A

• The human lung alpha chain (SCNN1A) has also been cloned and its gene localized on chromosome 12p13 [8].
• Family-based and case-control analyses and sequencing of SCNN1A and TNFRSF1A uncovered an association of the TNFRSF1A intron 1 haplotype with disease severity [9].
• Analysis of deletion constructs confirmed that a single imperfect glucocorticoid response element (GRE) is necessary and sufficient to confer the aldosterone responsiveness to the alpha ENaC gene promoter in MDCK-C7 and HT-29 cells [10].
• To determine whether aldosterone increases alpha ENaC gene transcription, a portion of the alpha ENaC 5'- flanking region coupled to luciferase was transfected into MDCK-C7 cells, a collecting duct cell line with aldosterone-stimulated Na(+) transport [10].
• The aldosterone-stimulated alpha ENaC expression was blocked by actinomycin D, and aldosterone had no effect on alpha ENaC mRNA decay, confirming a transcriptional effect [10].

Anatomical context of SCNN1A

• Interestingly, coexpression of h alpha ENaC+22 or h alpha ENaC+Alu, respectively, with wild type hENaC alpha, beta, and gamma subunits enhanced the expression of amiloride-sensitive current in oocytes [11].
• Steroids and exogenous gamma-ENaC subunit modulate cation channels formed by alpha-ENaC in human B lymphocytes [12].
• In adrenalectomized mice, aldosterone, dexamethasone, and MPA increased alpha-ENaC mRNA levels in kidney cortex [13].
• NAC did not alter total cell mRNA and protein levels of alpha-epithelial Na(+) channel (EnaC) subunit, but reduced abundance of alpha-ENaC subunits in the apical cell membrane as quantified by biotinylation [14].
• It has the highest identity (82%) with a rat H(+)-gated Na channel specific for sensory neurons (DRASIC) and a low identity (29%) with an epithelial isoform (alpha-ENaC) of this superfamily [15].

Associations of SCNN1A with chemical compounds

• These results confirm that alpha ENaC is an aldosterone-induced transcript in the collecting duct and delineates the molecular mechanism for this effect [10].
• Assays of transcriptional activity showed that dexamethasone caused concentration-dependent activation of the human alpha-ENaC promoter (EC50 approximately 5 nM) but, despite its clear effect on GNa, T2 had no effect upon the transcriptional response to dexamethasone [16].
• Thyroid hormone potentiates glucocorticoid-evoked airway Na+ transport without affecting alpha-ENaC transcription [16].
• Although hENaCdelta homomer was also significantly activated by capsazepine, unexpectedly, capsazepine had no effect on hENaCalpha and caused a slight decrease on the hENaCalphabetagamma current [17].
• Aldosterone did not, however, affect alpha-ENaC expression in the cortical collecting duct (CCD), which showed weak and dispersed labeling similar to that in rats treated with lithium alone [18].

Other interactions of SCNN1A

• PPARgamma activation enhances cell surface ENaCalpha via up-regulation of SGK1 in human collecting duct cells [19].
• We have identified the wild-type and three splice variants of the human alpha ENaC (h alpha ENaC) from the human lung cell line H441, using RT-PCR [20].
• A prostasin-preferred poly-basic cleavage site was found in the extracellular domains of the ENaC alpha- and beta-subunits, and may present a mechanism for prostasin activation [21].
• UC was associated with substantial decreases in the expression of the ENaC beta- and gamma-subunit proteins and mRNAs, whereas the decrease in ENaC alpha-subunit protein detected by immunolocalization was less marked [22].
• The NPPA T2238C and SCNN1A A663T were associated with decreased fasting insulin levels after adjusting for body mass index (P=0.015 and 0.028) [23].

Analytical, diagnostic and therapeutic context of SCNN1A

• Subsequently, ENaC alpha-, beta-, and gamma-subunits were analyzed immunohistochemically and in Western and Northern blots (corrected for the inflammatory increase in subepithelial protein content) [6].
• To assess the relative expression of the two most abundant alpha-ENaC transcripts (alpha-ENaC1 and alpha-ENaC2) during lung development, we performed nonradioactive in situ hybridization using probes specific to the alternative 5'-UTRs [24].
• Immunohistochemistry confirmed increased expression of alpha-ENaC in the late distal convoluted tubule and connecting tubule and also revealed increased apical targeting of all three ENaC subunits (alpha, beta, and gamma) in aldosterone-treated rats compared with rats treated with lithium alone [18].
• Immunoblotting showed increased protein expression of alpha-ENaC, the 70-kDa form of gamma-ENaC, and the Na-Cl cotransporter (NCC) in kidney cortex in aldosterone-treated rats, whereas spironolactone decreased alpha-ENaC and NCC compared with control rats treated with lithium alone [18].
• Utilizing transient transfection reporter assays and site-directed mutagenesis analyses, we found that the glucocorticoid response element (GRE), located at -1334 to -1306 base pairs of the alpha-ENaC 5'-flanking region, is the major enhancer for the stimulated alpha-ENaC expression in A549 lung epithelial cells [25].

References