title: Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes.
abstract: AE2 (SLC4A2) is the member of the Na(+)-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.
authors.affiliation: Laboratory of Molecular Genetics, Division of Gene Therapy and Hepatology, University Hospital/School of Medicine, Center for Applied Medical Research, University of Navarra, Pamplona, Spain.
authors.forename: Victoria
authors.initials: V
authors.lastname: Aranda
authors.forename: Iñigo
authors.initials: I
authors.lastname: Martínez
authors.forename: Saida
authors.initials: S
authors.lastname: Melero
authors.forename: Jon
authors.initials: J
authors.lastname: Lecanda
authors.forename: Jesús M
authors.initials: JM
authors.lastname: Banales
authors.forename: Jesús
authors.initials: J
authors.lastname: Prieto
authors.forename: Juan F
authors.initials: JF
authors.lastname: Medina
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins; D017920:Antiporters; D016764:Cell Polarity; D002478:Cells, Cultured; D027963:Chloride-Bicarbonate Antiporters; D003078:Colchicine / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D064606:SLC4A Proteins
chemical_list: D027321:Anion Transport Proteins; D017920:Antiporters; D027963:Chloride-Bicarbonate Antiporters; D008565:Membrane Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D064606:SLC4A Proteins; C579496:SLC4A2 protein, human; C579494:Slc4a2 protein, rat; D003078:Colchicine