title: Aquaporin-2: COOH terminus is necessary but not sufficient for routing to the apical membrane.
abstract: Renal regulation of mammalian water homeostasis is mediated by the aquaporin-1 (AQP1) water channel, which is expressed in the apical and basolateral membranes of proximal tubules and descending limbs of Henle, and aquaporin-2 (AQP2), which is redistributed from intracellular vesicles to the apical membrane (AM) of collecting duct cells with vasopressin. In transfected Madin-Darby canine kidney cells, AQP1 and AQP2 are regulated similarly, which indicates that routing elements reside in their primary sequences. We studied the role of the AQP2 COOH terminus in apical routing and AQP2 shuttling. An AQP1 chimera (AQP1 with an AQP2 tail: AQP1/2-N220) was located only in the AM independent of forskolin treatment. Forskolin increased the apical expression of AQP1 and AQP1/2-N220 less than twofold; that of AQP2 increased more than fourfold with concomitant changes in osmotic water permeabilities. The dimeric AQP2 tail coupled to placental alkaline phosphatase (AQP2-Plap) was retained in intracellular vesicles different from those of homotetrameric wild-type AQP2; the same protein without the AQP2 tail (TMR-Plap) was only expressed in the AM. The study shows that the AQP2 COOH tail is necessary but not sufficient for routing to the AM and suggests that other parts of AQP2 are needed for AQP2 accumulation in intracellular vesicles.
authors.affiliation: Department of Cell Physiology, University Medical Center St. Radboud, Nijmegen 6500 HB, The Netherlands. peterd@sci.kun.nl
authors.forename: Peter M T
authors.initials: PM
authors.lastname: Deen
authors.forename: Bas W M
authors.initials: BW
authors.lastname: Van Balkom
authors.forename: Paul J M
authors.initials: PJ
authors.lastname: Savelkoul
authors.forename: Erik-Jan
authors.initials: EJ
authors.lastname: Kamsteeg
authors.forename: Marcel
authors.initials: M
authors.lastname: Van Raak
authors.forename: Michael L
authors.initials: ML
authors.lastname: Jennings
authors.forename: Theodoor R
authors.initials: TR
authors.lastname: Muth
authors.forename: Vanathy
authors.initials: V
authors.lastname: Rajendran
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Caplan
mesh_terms: D000818:Animals; D051398:Aquaporin 1; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001127:Arginine Vasopressin / Q000494:pharmacology; D001789:Blood Group Antigens; D002451:Cell Compartmentation / Q000502:physiology; D002458:Cell Fractionation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000166:cytology; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014867:Water / Q000378:metabolism
chemical_list: C496020:AQP1 protein, human; C496023:AQP2 protein, human; C496022:Aqp1 protein, rat; C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001789:Blood Group Antigens; D011993:Recombinant Fusion Proteins; D014662:Vasoconstrictor Agents; D014867:Water; D001127:Arginine Vasopressin; D051398:Aquaporin 1; D005576:Colforsin