title: Characterization and subcellular localization of KCNQ1 with a heterozygous mutation in the C terminus.
abstract: Numerous mutations in KCNQ1, a gene encoding the alpha -subunit of cardiac delayed rectifier potassium channels, have been found in long QT syndrome (LQTS). Among them, several mutations in the C terminus have been shown to cause autosomal recessive or subclinical autosomal dominant LQTS. Here, we report a heterozygous mutation, T587M, which is also in the KCNQ1 C-terminal domain. The same mutation was found in three independent probands that were clearly symptomatic with family history of cardiac sudden death. Functional assay using a heterologous expression system with a mammalian cell line (COS7 cells) revealed that the mutant displayed neither functional channels when expressed alone nor dominant-negative effect when co-expressed with wild-type (WT) KCNQ1. To examine the cellular trafficking of KCNQ1, green fluorescent protein (GFP) was tagged to the cytoplasmic C terminus of WT or mutant KCNQ1. This procedure did not affect the essential properties of expressed WT KCNQ1 channels. On confocal microscopic images, GFP-tagged WT KCNQ1 showed a plasma membrane fluorescence pattern, whereas the GFP-tagged mutant showed a perinuclear fluorescence pattern. Co-expression of the mutant with GFP-tagged WT KCNQ1 did not influence its normal cellular transport. Therefore, the T587M mutant cannot traffic to the plasma membrane and may form no subunit assembly with WT KCNQ1. These findings provide a novel molecular basis for the clinical finding that this C-terminal mutation produced a severe form of RWS-type LQTS.
authors.affiliation: First Department of Internal Medicine, Niigata University School of Medicine, Niigata, 951-8510, Japan.
authors.forename: F
authors.initials: F
authors.lastname: Yamashita
authors.forename: M
authors.initials: M
authors.lastname: Horie
authors.forename: T
authors.initials: T
authors.lastname: Kubota
authors.forename: H
authors.initials: H
authors.lastname: Yoshida
authors.forename: Y
authors.initials: Y
authors.lastname: Yumoto
authors.forename: A
authors.initials: A
authors.lastname: Kobori
authors.forename: T
authors.initials: T
authors.lastname: Ninomiya
authors.forename: Y
authors.initials: Y
authors.lastname: Kono
authors.forename: T
authors.initials: T
authors.lastname: Haruna
authors.forename: K
authors.initials: K
authors.lastname: Tsuji
authors.forename: T
authors.initials: T
authors.lastname: Washizuka
authors.forename: M
authors.initials: M
authors.lastname: Takano
authors.forename: H
authors.initials: H
authors.lastname: Otani
authors.forename: S
authors.initials: S
authors.lastname: Sasayama
authors.forename: Y
authors.initials: Y
authors.lastname: Aizawa
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D004252:DNA Mutational Analysis; D004594:Electrophysiology; D005192:Family Health; D005260:Female; D049452:Green Fluorescent Proteins; D006579:Heterozygote; D006801:Humans; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D008133:Long QT Syndrome / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D008297:Male; D018613:Microscopy, Confocal; D009154:Mutation; D020125:Mutation, Missense; D010641:Phenotype; D015221:Potassium Channels / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D024642:Potassium Channels, Voltage-Gated; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D008164:Luminescent Proteins; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins