Three N-terminal Variants of the AE2 Cl-/HCO3- Exchanger Are Encoded by mRNAs Transcribed from Alternative Promoters

Wang, Zhuo; Schultheis, Patrick J.; Shull, Gary E.

doi:10.1074/jbc.271.13.7835

Cited by 87 publications

(102 citation statements)

References 33 publications

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“…Our recent data on HNF1a being able to transactivate alternate expression [17] strengthen the view that alternative AE2 isoforms might be related to the possibility of liver cells increasing their expression in response to certain stimuli for bicarbonate secretion. Noticeably, the HNF1 consensus sequence found in the human alternate overlapping promoter within intron 2 is also observed in rat [7] and mouse [33] orthologs. Moreover, both alternative messages AE2b 1 and AE2b 2 are expressed in the liver in these three species, the rat included.…”

Section: Possible Role Of N-terminal Variants Of Ae2 In Hepatocytesmentioning

confidence: 80%

“…Moreover, both alternative messages AE2b 1 and AE2b 2 are expressed in the liver in these three species, the rat included. Thus, using RT-PCR we could not only confirm the rat liver expression of AE2b 1 mRNA (previously referred to as just AE2b mRNA [7]) but also ascertain the liver expression of AE2b 2 mRNA (not shown).…”

Section: Possible Role Of N-terminal Variants Of Ae2 In Hepatocytesmentioning

confidence: 97%

“…Although AE genes locate in different chromosomes they all have a similar structure. A frequent feature for AE genes is the usage of alternate promoters that leads to the expression of transcript variants, often in a tissue-and cell-specific manner [1,[7][8][9]. With respect to AE2, three transcript variants have been reported in humans: the full-length message AE2a and the alternative isoforms AE2b 1 and AE2b 2 [9].…”

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confidence: 99%

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Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes

Aranda

Martı́nez

Melero

et al. 2004

Biochemical and Biophysical Research Communications

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AE2 (SLC4A2) is the member of the Na þ -independent anion exchanger (AE) family putatively involved in the secretion of bicarbonate to bile. In humans, three variants of AE2 mRNA have been described: the full-length transcript AE2a (expressed from the upstream promoter in most tissues), and alternative transcripts AE2b 1 and AE2b 2 (driven from alternate promoter sequences in a tissue-restricted manner, mainly in liver and kidney). These transcripts would result in AE protein isoforms with short N-terminal differences. To ascertain their translation, functionality, and membrane sorting, we constructed expression vectors encoding each AE2 isoform fused to GFP at the C-terminus. Transfected HEK293 cells showed expression of functional GFP-tagged AE2 proteins, all three isoforms displaying comparable AE activities. Primary rat hepatocytes transfected with expression vectors and repolarized in a collagen-sandwich configuration showed a microtubule-dependent apical sorting of each AE2 isoform. This shared apical sorting is liver-cell specific, as sorting of AE2 isoforms was basolateral in control experiments on polarized kidney MDCK cells. Hepatocytic apical targeting of AE2 isoforms suggests that they all may participate in the canalicular secretion of bicarbonate to bile.

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Section: Possible Role Of N-terminal Variants Of Ae2 In Hepatocytesmentioning

confidence: 80%

Section: Possible Role Of N-terminal Variants Of Ae2 In Hepatocytesmentioning

confidence: 97%

mentioning

confidence: 99%

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Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes

Aranda

Martı́nez

Melero

et al. 2004

Biochemical and Biophysical Research Communications

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“…An adenoviral vector was designed for the intracellular expression of small hairpin RNA (shRNA-1) toward this C-terminal sequence, which is common to all rat and human N-terminal AE2 variants. 27,28 As a negative control, we used an adenoviral Fig. 1.…”

Section: Direct Biliary Monitorization Model In Infusedmentioning

confidence: 99%

Bicarbonate-rich choleresis induced by secretin in normal rat is taurocholate-dependent and involves AE2 anion exchanger

et al. 2006

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Canalicular bile is modified along bile ducts through reabsorptive and secretory processes regulated by nerves, bile salts, and hormones such as secretin. Secretin stimulates ductular cystic fibrosis transmembrane conductance regulator (CFTR)-dependent Cl ؊ efflux and subsequent biliary HCO 3 ؊ secretion, possibly via Cl ؊ /HCO 3 ؊ anion exchange (AE). However, the contribution of secretin to bile regulation in the normal rat, the significance of choleretic bile salts in secretin effects, and the role of Cl ؊ /HCO 3 ؊ exchange in secretin-stimulated HCO 3 ؊ secretion all remain unclear. Here, secretin was administered to normal rats with maintained bile acid pool via continuous taurocholate infusion. Bile flow and biliary HCO 3 ؊ and Cl ؊ excretion were monitored following intrabiliary retrograde fluxes of saline solutions with and without the Cl ؊ channel inhibitor 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) or the Cl ؊ /HCO 3 ؊ exchange inhibitor 4,4 -diisothiocyanatostilbene-2,2 -disulfonic acid (DIDS). Secretin increased bile flow and biliary excretion of HCO 3 ؊ and Cl ؊ . Interestingly, secretin effects were not observed in the absence of taurocholate. Whereas secretin effects were all blocked by intrabiliary NPPB, DIDS only inhibited secretin-induced increases in bile flow and HCO 3 ؊ excretion but not the increased Cl ؊ excretion, revealing a role of biliary Cl ؊ /HCO 3 ؊ exchange in secretininduced, bicarbonate-rich choleresis in normal rats. Finally, small hairpin RNA adenoviral constructs were used to demonstrate the involvement of the Na ؉ -independent anion exchanger 2 (AE2) through gene silencing in normal rat cholangiocytes. AE2 gene silencing caused a marked inhibition of unstimulated and secretin-stimulated Cl ؊ /HCO 3 ؊ exchange. In conclusion, maintenance of the bile acid pool is crucial for secretin to induce bicarbonate-rich choleresis in the normal rat and that this occurs via a chloride-bicarbonate exchange process consistent with AE2 function. (HEPATOLOGY 2006;43:266-275.) S ecretin is known to induce bicarbonate-rich hydrocholeresis in many animal species. 1-7 Its interaction with a G-protein-coupled receptor selectively localized to the epithelial bile duct cells 8 results in increased intracellular levels of cyclic adenosine monophosphate (cAMP) [cAMP] i 7,9,10 and protein kinase A activation. 11,12 Phosphorylation and opening of a cAMP-dependent Cl Ϫ channel, the cystic fibrosis transmembrane conductance regulator (CFTR), 13 causes Cl Ϫ efflux to the ductular lumen. This appears to stimulate an apical Na ϩ -independent Cl Ϫ /HCO 3 Ϫ anion exchange (AE), 14 with HCO 3 Ϫ efflux and Cl Ϫ influx, that is facilitated by the outside to inside transmembrane gradient of Cl Ϫ at relatively high intracellular HCO 3 Ϫ concentration. [10][11][12]15,16 Several bicarbonate transporters, most of them encoded by the SLC4 and SLC26 gene families, 17 have been described to exert AE activity. A decade ago, we localized one of those polypeptides, the SLC4A2 or AE2, 18 to the apical membrane in...

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“…The secretion of ϳ160 mM HCl and ϳ17 mM KCl by gastric parietal cells requires the coordinated activities of ion transporters on both apical and basolateral membranes. There is strong evidence that the major mechanism for Cl Ϫ uptake and HCO 3 Ϫ extrusion across the basolateral membrane is Cl Ϫ / HCO 3 Ϫ exchange (38 -42), which probably involves one or more variants of AE2 (31,43 stomachs, whereas the Na ϩ ,K ϩ -ATPase mediates K ϩ uptake and Na ϩ extrusion. Given the copious quantities of fluid secreted by the parietal cell, it is critical that cellular volume homeostasis be maintained.…”

Section: Nkcc1mentioning

confidence: 99%

Mice Lacking the Basolateral Na-K-2Cl Cotransporter Have Impaired Epithelial Chloride Secretion and Are Profoundly Deaf

Flagella¹,

Clarke²,

Miller³

et al. 1999

Journal of Biological Chemistry

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356

349

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In chloride-secretory epithelia, the basolateral Na-K2Cl cotransporter (NKCC1) is thought to play a major role in transepithelial Cl ؊ and fluid transport. Similarly, in marginal cells of the inner ear, NKCC1 has been proposed as a component of the entry pathway for K ؉ that is secreted into the endolymph, thus playing a critical role in hearing. To test these hypotheses, we generated and analyzed an NKCC1-deficient mouse. Homozygous mutant (Nkcc1 ؊/؊ ) mice exhibited growth retardation, a 28% incidence of death around the time of weaning, and mild difficulties in maintaining their balance. Mean arterial blood pressure was significantly reduced in both heterozygous and homozygous mutants, indicating an important function for NKCC1 in the maintenance of blood pressure. cAMP-induced short circuit currents, which are dependent on the CFTR Cl ؊ channel, were reduced in jejunum, cecum, and trachea of Nkcc1 ؊/؊ mice, indicating that NKCC1 contributes to cAMP-induced Cl ؊ secretion. In contrast, secretion of gastric acid in adult Nkcc1 ؊/؊ stomachs and enterotoxin-stimulated fluid secretion in the intestine of suckling Nkcc1 ؊/؊ mice were normal. Finally, homozygous mutants were deaf, and histological analysis of the inner ear revealed a collapse of the membranous labyrinth, consistent with a critical role for NKCC1 in transepithelial K ؉ movements involved in generation of the K ؉ -rich endolymph and the endocochlear potential.

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Three N-terminal Variants of the AE2 Cl-/HCO3- Exchanger Are Encoded by mRNAs Transcribed from Alternative Promoters

Cited by 87 publications

References 33 publications

Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes

Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes

Bicarbonate-rich choleresis induced by secretin in normal rat is taurocholate-dependent and involves AE2 anion exchanger

Mice Lacking the Basolateral Na-K-2Cl Cotransporter Have Impaired Epithelial Chloride Secretion and Are Profoundly Deaf

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