title: LQT1 mutations in KCNQ1 C-terminus assembly domain suppress IKs using different mechanisms.
abstract: OBJECTIVE
  Long QT syndrome 1 (LQT1) mutations in KCNQ1 that decrease cardiac IKs (slowly activating delayed rectifier K(+) current) underlie ventricular arrhythmias and sudden death. LQT1 mutations may suppress IKs by preventing KCNQ1 assembly, disrupting surface trafficking, or inhibiting gating. We investigated mechanisms underlying how three LQT1 mutations in KCNQ1 C-terminus assembly domain (R555H/G589D/L619M) decrease IKs in heterologous cells and cardiomyocytes.
  
  
  RESULTS
  In Chinese hamster ovary (CHO) cells, mutant KCNQ1 + KCNE1 channels either produced no currents (G589D/L619M) or displayed markedly reduced IKs with a right-shifted voltage-dependence of activation (R555H). When co-expressed with wild-type (wt) KCNQ1, the mutant KCNQ1s displayed varying intrinsic dominant-negative capacities that were affected by auxiliary KCNE1. All three mutant KCNQ1s assembled with wt KCNQ1 as determined by fluorescence resonance energy transfer (FRET). We developed an optical quantum dot labelling assay to measure channel surface density. G589D/R555H displayed substantial reductions in surface density, which were either partially (G589D) or fully (R555H) rescued by wt KCNQ1. Unexpectedly, L619M showed no trafficking defect. In adult rat cardiomyocytes, adenovirus-expressed homotetrameric G589D/L619M + KCNE1 channels yielded no currents, whereas R555H + KCNE1 produced diminished IKs with a right-shifted voltage-dependence of activation, mimicking observations in CHO cells. In contrast to heterologous cells, homotetrameric R555H channels showed no trafficking defect in cardiomyocytes.
  
  
  CONCLUSIONS
  Distinct LQT1 mutations in KCNQ1 assembly domain decrease IKs using unique combinations of biophysical and trafficking mechanisms. Functional deficits in IKs observed in heterologous cells are mostly, but not completely, recapitulated in adult rat cardiomyocytes. A 'methodological chain' combining approaches in heterologous cells and cardiomyocytes provides mechanistic insights that may help advance personalized therapy for LQT1 mutations.
authors.affiliation: Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, 504 Russ Berrie, New York, NY 10032, USA.
authors.forename: Ademuyiwa S
authors.initials: AS
authors.lastname: Aromolaran
authors.affiliation: Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, 504 Russ Berrie, New York, NY 10032, USA.
authors.forename: Prakash
authors.initials: P
authors.lastname: Subramanyam
authors.affiliation: Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, 504 Russ Berrie, New York, NY 10032, USA.
authors.forename: Donald D
authors.initials: DD
authors.lastname: Chang
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School Worcester, MA 01605, USA.
authors.forename: William R
authors.initials: WR
authors.lastname: Kobertz
authors.affiliation: Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, 504 Russ Berrie, New York, NY 10032, USA hc2405@columbia.edu.
authors.forename: Henry M
authors.initials: HM
authors.lastname: Colecraft
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000235:genetics* / Q000378:metabolism*; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D051381:Rats
chemical_list: C489622:KCNE1 protein, human; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D024642:Potassium Channels, Voltage-Gated; D011188:Potassium
keywords: Cardiac myocyte; Channel trafficking; Ion channel; KCNQ1; Long QT syndrome