title: A novel KCNJ2 nonsense mutation, S369X, impedes trafficking and causes a limited form of Andersen-Tawil syndrome.
abstract: BACKGROUND
  Mutations in KCNJ2, a gene encoding the inward rectifier K(+) channel Kir2.1, are associated with Andersen-Tawil syndrome (ATS), which is characterized by (1) ventricular tachyarrhythmias associated with QT (QU)-interval prolongation, (2) periodic paralysis, and (3) dysmorphic features.
  
  
  RESULTS
  We identified a novel KCNJ2 mutation, S369X, in a 13-year-old boy with prominent QU-interval prolongation and mild periodic paralysis. The mutation results in the truncation at the middle of the cytoplasmic C-terminal domain that eliminates the endoplasmic reticulum (ER)-to-Golgi export signal. Current recordings from Chinese hamster ovary cells transfected with KCNJ2-S369X exhibited significantly smaller K(+) currents compared with KCNJ2 wild type (WT) (1 μg each) (-84 ± 14 versus -542 ± 46 picoamperes per picofarad [pA/pF]; -140 mV; P<0.0001). Coexpression of the WT and S369X subunits did not show a dominant-negative suppression effect but yielded larger currents than those of WT+S369X (-724 ± 98 pA/pF>-[84+542] pA/pF; 1 μg each; -140 mV). Confocal microscopy analysis showed that the fluorescent protein-tagged S369X subunits were predominantly retained in the ER when expressed alone; however, the expression of S369X subunits to the plasma membrane was partially restored when coexpressed with WT. Fluorescence resonance energy transfer analysis demonstrated direct protein-protein interactions between WT and S369X subunits in the intracellular compartment.
  
  
  CONCLUSIONS
  The S369X mutation causes a loss of the ER export motif. However, the trafficking deficiency can be partially rescued by directly assembling with the WT protein, resulting in a limited restoration of plasma membrane localization and channel function. This alleviation may explain why our patient presented with a relatively mild ATS phenotype.
authors.affiliation: Department of Cardiovascular Medicine, Kyoto University, Graduate School of Medicine, Kyoto, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Doi
authors.forename: Takeru
authors.initials: T
authors.lastname: Makiyama
authors.forename: Takeshi
authors.initials: T
authors.lastname: Morimoto
authors.forename: Yoshisumi
authors.initials: Y
authors.lastname: Haruna
authors.forename: Keiko
authors.initials: K
authors.lastname: Tsuji
authors.forename: Seiko
authors.initials: S
authors.lastname: Ohno
authors.forename: Masaharu
authors.initials: M
authors.lastname: Akao
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kimura
authors.forename: Minoru
authors.initials: M
authors.lastname: Horie
mesh_terms: D000293:Adolescent; D000595:Amino Acid Sequence; D050030:Andersen Syndrome / Q000235:genetics* / Q000503:physiopathology; D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D018389:Codon, Nonsense; D006224:Cricetinae; D003412:Cricetulus; D004562:Electrocardiography; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010375:Pedigree; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D018389:Codon, Nonsense; C489457:KCNJ2 protein, human; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins