title: Pathogenesis of nephrogenic diabetes insipidus by aquaporin-2 C-terminus mutations.
abstract: BACKGROUND
  We previously reported three aquaporin-2 (AQP2) gene mutations known to cause autosomal-dominant nephrogenic diabetes insipidus (NDI) (Am J Hum Genet 69:738, 2001). The mutations were found in the C-terminus of AQP2 (721delG, 763 to 772del, and 812 to 818del). The wild-type AQP2 is a 271 amino acid protein, whereas these mutant genes were predicted to encode 330 to 333 amino acid proteins due to the frameshift mutations leading to the creation of a new stop codon 180 nucleotides downstream. The Xenopus oocyte expression study suggested that the trafficking of the mutant AQP2s was impaired.
  
  
  METHODS
  To determine the cellular pathogenesis of these NDI-causing mutations in mammalian epithelial cells, Madin-Darby canine kidney (MDCK) cells were stably transfected with the wild-type AQP2, or the 763 to 772del mutant AQP2, or both. Cells were grown on the membrane support to examine the localization of AQP2 proteins by immunofluorescence microscopy.
  
  
  RESULTS
  Confocal immunofluorescence microscopy showed that the wild-type AQP2 was expressed in the apical region, whereas the mutant AQP2 was apparently located at the basolateral region. Furthermore, the wild-type and mutant AQP2s were colocalized at the basolateral region when they were cotransfected, suggesting the formation of mixed oligomers and thereby mistargeting.
  
  
  CONCLUSIONS
  Mixed oligomers of the wild-type and the 763 to 772del mutant AQP2s are mistargeted to the basolateral membrane due to the dominant-negative effect of the mutant. This defect is very likely to explain the pathogenesis of autosomal-dominant NDI. The mistargeting of the apical membrane protein to the basolateral membrane is a novel molecular pathogenesis of congenital NDI.
authors.affiliation: Department of Homeostasis Medicine and Nephrology, Tokyo Medical and Dental University Graduate School, Tokyo, Japan.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Asai
authors.forename: Michio
authors.initials: M
authors.lastname: Kuwahara
authors.forename: Hidetake
authors.initials: H
authors.lastname: Kurihara
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Sakai
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Terada
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Marumo
authors.forename: Sei
authors.initials: S
authors.lastname: Sasaki
mesh_terms: D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018500:Diabetes Insipidus, Nephrogenic / Q000235:genetics*; D004285:Dogs; D017353:Gene Deletion; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009154:Mutation; D014162:Transfection
chemical_list: C496023:AQP2 protein, human; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins