title: Isoforms of SLC26A6 mediate anion transport and have functional PDZ interaction domains.
abstract: The solute carrier gene family SLC26 consists of tissue-specific anion exchanger genes, three of them associated with distinct human recessive disorders. By a genome-driven approach, several new SLC26 family members have been identified, including a kidney- and pancreas-specific gene, SLC26A6. We report the functional characterization of SLC26A6 and two new alternatively spliced variants, named SLC26A6c and SLC26A6d. Immunofluorescence studies on transiently transfected cells indicated membrane localization and indicated that both NH(2)- and COOH-terminal tails of the SLC26A6 variants are located intracellularly, suggesting a topology with an even number of transmembrane domains. Functional expression of the three proteins in Xenopus oocytes demonstrated Cl(-) and SO(4)(2-) transport activity. In addition, the transport of SO(4)(2-) and Cl(-) was inhibited by DIDS and HCO(3)(-). We demonstrated also that the COOH terminus of SLC26A6 binds to the first and second PDZ domains of the Na(+)/H(+) exchanger (NHE)3 kinase A regulatory protein (E3KARP) and NHE3 regulatory factor (NHERF) proteins in vitro. Truncation of the last three amino acids (TRL) of SLC26A6 abrogated the interaction but did not affect transport function. These results demonstrate that SLC26A6 and its two splice variants can function as anion transporters linked to PDZ-interaction pathways. Our results support the general concept of microdomain organization for ion transport and suggest a mechanism for cystic fibrosis transmembrane regulator (CFTR)-mediated SLC26A6 upregulation in pancreatic duct cells.
authors.affiliation: Department of Medical Genetics, Biomedicum Helsinki, University of Helsinki, Finland. hannes.lohi@helsinki.fi
authors.forename: Hannes
authors.initials: H
authors.lastname: Lohi
authors.forename: Georg
authors.initials: G
authors.lastname: Lamprecht
authors.forename: Daniel
authors.initials: D
authors.lastname: Markovich
authors.forename: Anders
authors.initials: A
authors.lastname: Heil
authors.forename: Minna
authors.initials: M
authors.lastname: Kujala
authors.forename: Ursula
authors.initials: U
authors.lastname: Seidler
authors.forename: Juha
authors.initials: J
authors.lastname: Kere
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D027963:Chloride-Bicarbonate Antiporters / Q000235:genetics / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D005057:Eukaryotic Cells / Q000378:metabolism*; D005260:Female; D006801:Humans; D017136:Ion Transport / Q000235:genetics*; D009865:Oocytes; D010750:Phosphoproteins / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D017923:Sodium-Hydrogen Exchangers; D000076988:Sulfate Transporters; D013431:Sulfates / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D017920:Antiporters; C505032:CFTR protein, human; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D003598:Cytoskeletal Proteins; D010750:Phosphoproteins; D020033:Protein Isoforms; C466900:Slc26a6 protein, mouse; D017923:Sodium-Hydrogen Exchangers; D000076988:Sulfate Transporters; D013431:Sulfates; C093376:sodium-hydrogen exchanger regulatory factor; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid