title: Molecular determinants for apical expression of the renal type IIa Na+/Pi-cotransporter.
abstract: Type IIa and IIb Na+/Pi-cotransporters have different patterns of expression in vivo: IIa is expressed in apical membranes of renal proximal tubules, and IIb in intestinal and lung epithelia. They are found in different subcellular locations when transfected in epithelial cells: IIa is apically expressed in renal proximal cells (OK), but mostly intracellularly in intestinal cells (CaCo2); IIb is apical in both cell types. To identify the domains responsible for the different expression of both cotransporters (in CaCo2), as well as those responsible for the apical expression of IIa (in OK), mutated cotransporters were fused to the Enhanced Green Fluorescent Protein (EGFP), and their expression analyzed by confocal microscopy. We conclude that the apical expression information for CaCo2 is contained within the C-terminal tail of IIb, but is not contained within IIa. From analysis of mutated IIa cotransporters we identified residues, within the C-terminal tail, involved in the apical expression of these cotransporters in OK cells: internal PR-residues and terminal TRL-residues. These signals are functional in OK but not in CaCo2-cells, supporting the concept that polarized targeting can be protein and cell specific.
authors.affiliation: Institute of Physiology, University of Zürich, Zürich 8057, Switzerland.
authors.forename: Z
authors.initials: Z
authors.lastname: Karim-Jimenez
authors.forename: N
authors.initials: N
authors.lastname: Hernando
authors.forename: J
authors.initials: J
authors.lastname: Biber
authors.forename: H
authors.initials: H
authors.lastname: Murer
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D018938:Caco-2 Cells; D002460:Cell Line; D016764:Cell Polarity; D049452:Green Fluorescent Proteins; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D008958:Models, Molecular; D009893:Opossums; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: D008164:Luminescent Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C493554:SLC34A1 protein, human; C493555:Slc34a1 protein, mouse; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters; D049452:Green Fluorescent Proteins