title: A long QT mutation substitutes cholesterol for phosphatidylinositol-4,5-bisphosphate in KCNQ1 channel regulation.
abstract: BACKGROUND
  Phosphatidylinositol-4,5-bisphosphate (PIP2) is a cofactor necessary for the activity of KCNQ1 channels. Some Long QT mutations of KCNQ1, including R243H, R539W and R555C have been shown to decrease KCNQ1 interaction with PIP2. A previous study suggested that R539W is paradoxically less sensitive to intracellular magnesium inhibition than the WT channel, despite a decreased interaction with PIP2. In the present study, we confirm this peculiar behavior of R539W and suggest a molecular mechanism underlying it.
  
  
  RESULTS
  COS-7 cells were transfected with WT or mutated KCNE1-KCNQ1 channel, and patch-clamp recordings were performed in giant-patch, permeabilized-patch or ruptured-patch configuration. Similar to other channels with a decreased PIP2 affinity, we observed that the R243H and R555C mutations lead to an accelerated current rundown when membrane PIP2 levels are decreasing. As opposed to R243H and R555C mutants, R539W is not more but rather less sensitive to PIP2 decrease than the WT channel. A molecular model of a fragment of the KCNQ1 C-terminus and the membrane bilayer suggested that a potential novel interaction of R539W with cholesterol stabilizes the channel opening and hence prevents rundown upon PIP2 depletion. We then carried out the same rundown experiments under cholesterol depletion and observed an accelerated R539W rundown that is consistent with this model.
  
  
  CONCLUSIONS
  We show for the first time that a mutation may shift the channel interaction with PIP2 to a preference for cholesterol. This de novo interaction wanes the sensitivity to PIP2 variations, showing that a mutated channel with a decreased affinity to PIP2 could paradoxically present a slowed current rundown compared to the WT channel. This suggests that caution is required when using measurements of current rundown as an indicator to compare WT and mutant channel PIP2 sensitivity.
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Fabien C
authors.initials: FC
authors.lastname: Coyan
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Fayal
authors.initials: F
authors.lastname: Abderemane-Ali
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Mohamed Yassine
authors.initials: MY
authors.lastname: Amarouch
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Piron
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Mordel
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Céline S
authors.initials: CS
authors.lastname: Nicolas
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France.
authors.forename: Marja
authors.initials: M
authors.lastname: Steenman
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Mérot
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Marionneau
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Toulouse, France.
authors.forename: Annick
authors.initials: A
authors.lastname: Thomas
authors.affiliation: Centre de Biophysique Moléculaire Numérique, University of Liège, Gembloux, Belgium.
authors.forename: Robert
authors.initials: R
authors.lastname: Brasseur
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Baró
authors.affiliation: l'institut du thorax, Institut National de la Santé et de la Recherche Médicale, Nantes, France; Unité Mixte de Recherche 6291, Centre National de la Recherche Scientifique, Nantes, France; Unité de Formation et de Recherche de Médecine, Université de Nantes, Nantes, France.
authors.forename: Gildas
authors.initials: G
authors.lastname: Loussouarn
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000235:genetics / Q000378:metabolism; D053840:Brugada Syndrome; D019556:COS Cells; D000075224:Cardiac Conduction System Disease; D002460:Cell Line; D002522:Chlorocebus aethiops; D002784:Cholesterol / Q000235:genetics / Q000378:metabolism*; D006329:Heart Conduction System / Q000002:abnormalities / Q000378:metabolism; D051657:KCNQ1 Potassium Channel / Q000235:genetics / Q000378:metabolism*; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000235:genetics / Q000378:metabolism*
chemical_list: D051657:KCNQ1 Potassium Channel; D019269:Phosphatidylinositol 4,5-Diphosphate; D002784:Cholesterol; D008274:Magnesium