title: Interactions between hERG and KCNQ1 α-subunits are mediated by their COOH termini and modulated by cAMP.
abstract: KCNQ1 and hERG encode the voltage-gated potassium channel α-subunits of the cardiac repolarizing currents I(Ks) and I(Kr), respectively. These currents function in vivo with some redundancy to maintain appropriate action potential durations (APDs), and loss-of-function mutations in these channels manifest clinically as long QT syndrome, characterized by the prolongation of the QT interval, polymorphic ventricular tachycardia, and sudden cardiac death. Previous cellular electrophysiology experiments in transgenic rabbit cardiomyocytes and heterologous cell lines demonstrated functional downregulation of complementary repolarizing currents. Biochemical assays indicated direct, protein-protein interactions between KCNQ1 and hERG may underlie the interplay between I(Ks) and I(Kr). Our objective was to investigate hERG-KCNQ1 interactions in the intact cellular environment primarily through acceptor photobleach FRET (apFRET) experiments. We quantitatively assessed the extent of interactions based on fluorophore location and the potential regulation of interactions by physiologically relevant signals. apFRET experiments established specific hERG-KCNQ1 associations in both heterologous and primary cardiomyocytes. The largest FRET efficiency (E(f); 12.0 ± 5.2%) was seen between ion channels with GFP variants fused to the COOH termini. Acute treatment with forskolin + IBMX or a membrane-permeable cAMP analog significantly and specifically reduced the extent of hERG-KCNQ1 interactions (by 41 and 38%, respectively). Our results demonstrate direct interactions between KCNQ1 and hERG occur in both intact heterologous cells and primary cardiomyocytes and are mediated by their COOH termini. Furthermore, this interplay between channel proteins is regulated by intracellular cAMP.
authors.affiliation: Cardiovascular Research Center, Division of Cardiology, Department of Medicine, Rhode Island Hospital, Alpert Medical School of Brown University, Providence, RI 02903, USA.
authors.forename: Louise E
authors.initials: LE
authors.lastname: Organ-Darling
authors.forename: Amanda N
authors.initials: AN
authors.lastname: Vernon
authors.forename: Jacqueline R
authors.initials: JR
authors.lastname: Giovanniello
authors.forename: Yichun
authors.initials: Y
authors.lastname: Lu
authors.forename: Karni
authors.initials: K
authors.lastname: Moshal
authors.forename: Karim
authors.initials: K
authors.lastname: Roder
authors.forename: Weiyan
authors.initials: W
authors.lastname: Li
authors.forename: Gideon
authors.initials: G
authors.lastname: Koren
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000008:administration & dosage; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D005576:Colforsin / Q000008:administration & dosage; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000819:agonists / Q000737:chemistry*; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000737:chemistry* / Q000502:physiology; D005260:Female; D057809:HEK293 Cells; D006321:Heart / Q000187:drug effects / Q000502:physiology; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000737:chemistry* / Q000502:physiology; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000008:administration & dosage; D011817:Rabbits
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D051657:KCNQ1 Potassium Channel; D010726:Phosphodiesterase Inhibitors; D005576:Colforsin; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine