title: AMP-activated protein kinase downregulates Kv7.1 cell surface expression.
abstract: The potassium channel Kv7.1 is expressed in the heart, where it contributes to the repolarization of the cardiac action potential. Additionally, Kv7.1 is expressed in epithelial tissues playing a role in salt and water transport. We recently demonstrated that surface-expressed Kv7.1 is internalized in response to polarization of the epithelial Madin-Darby canine kidney (MDCK) cell line and that this was mediated by activation of protein kinase C (PKC). In this study, the pathway downstream of PKC, which leads to internalization of Kv7.1 upon cell polarization, is elucidated. We show by confocal microscopy that Kv7.1 is endocytosed upon initiation of the polarization process and sent for degradation by the lysosomal pathway. The internalization could be mimicked by pharmacological activation of the AMP-activated protein kinase (AMPK) using three different AMPK activators. We demonstrate that the downstream effector of AMPK is the E3 ubiquitin ligase Nedd4-2. Additionally, we show that AMPK activation results in a downregulation of Kv7.1 currents in Xenopus oocytes through a Nedd4-2-dependent mechanism. In summary, surface-expressed Kv7.1 channels are endocytosed and sent for degradation in lysosomes by an AMPK-mediated activation of Nedd4-2 during the initial phase of the MDCK cell polarization process.
authors.affiliation: The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, The Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, Copenhagen, Denmark.
authors.forename: Martin N
authors.initials: MN
authors.lastname: Andersen
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Krzystanek
authors.forename: Thomas
authors.initials: T
authors.lastname: Jespersen
authors.forename: Søren-Peter
authors.initials: SP
authors.lastname: Olesen
authors.forename: Hanne B
authors.initials: HB
authors.lastname: Rasmussen
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000200:Action Potentials; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D016764:Cell Polarity; D004285:Dogs; D015536:Down-Regulation; D004705:Endocytosis; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000096:biosynthesis* / Q000235:genetics; D008247:Lysosomes / Q000378:metabolism; D018613:Microscopy, Confocal; D000075702:Nedd4 Ubiquitin Protein Ligases; D009865:Oocytes / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport; D014162:Transfection; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D029867:Xenopus Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618482:Nedd4 protein, Xenopus; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human; C000618460:nedd4l protein, Xenopus; D044767:Ubiquitin-Protein Ligases; D011493:Protein Kinase C; D055372:AMP-Activated Protein Kinases; D002118:Calcium