title: Phospholamban is concentrated in the nuclear envelope of cardiomyocytes and involved in perinuclear/nuclear calcium handling.
abstract: OBJECTIVE
  Phospholamban (PLB) regulates the cardiac Ca2+-ATPase (SERCA2a) in sarcoplasmic reticulum (SR). However, the localization of PLB at subcellular sites outside the SR and possible contributions to Ca2+cycling remain unknown. We examined the intracellular distribution of PLB and tested whether a pool of PLB exists in the nuclear envelope (NE) that might regulate perinuclear/nuclear Ca2+(nCa2+) handling in cardiomyocytes (CMs).
  
  
  RESULTS
  Using confocal immunofluorescence microscopy and immunoblot analyses of CMs and CM nuclei, we discovered that PLB was highly concentrated in NE. Moreover, the ratio of PLB levels to SERCA levels was greater in NE than in SR. The increased levels of PLB in NE were a consistent finding using a range of antibodies, tissue samples, and species. To address a possible role in affecting Ca2+handling, we used Fluo-4 based confocal Ca2+imaging, with scan-lines across cytosol and nuclei, and evaluated the effects of PLB on cytosolic and nCa2+uptake and release in mouse CMs. In intact CMs, isoproterenol increased amplitude and decreased the decay time of Ca2+transients not only in cytosol but also in nuclear regions. In saponin-permeabilized mouse CMs ([Ca2+]i=400nM), we measured spontaneous Ca2+waves after specific reversal of PLB activity by addition of the Fab fragment of an anti-PLB monoclonal antibody (100μg/ml). This highly selective immunological reagent enhanced Ca2+uptake (faster decay times) and Ca2+release (greater intensity) in both cytosol and across the nuclear regions.
  
  
  CONCLUSIONS
  Besides SR, PLB is concentrated in NE of CMs, and may be involved in modulation of nCa2+dynamics.
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA; Institute of Biomedical Engineering, National Chiao-Tung University, Hsinchu, Taiwan.
authors.forename: Adonis Z
authors.initials: AZ
authors.lastname: Wu
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA; Cardiovascular Division, Institute of Clinical Medicine, Faculty of Medicine, University of Tsukuba, Japan.
authors.forename: Dongzhu
authors.initials: D
authors.lastname: Xu
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Gynecological and Obstetric Ultrasound, First Affiliated Hospital of Harbin Medical University, Heilongjiang, PR China.
authors.forename: Na
authors.initials: N
authors.lastname: Yang
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA; Institute of Biomedical Engineering, National Chiao-Tung University, Hsinchu, Taiwan.
authors.forename: Shien-Fong
authors.initials: SF
authors.lastname: Lin
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Peng-Sheng
authors.initials: PS
authors.lastname: Chen
authors.affiliation: Department of Physiology, Wayne State University, Detroit, MI, USA.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Cala
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA. Electronic address: zhechen@iu.edu.
authors.forename: Zhenhui
authors.initials: Z
authors.lastname: Chen
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002466:Cell Nucleolus / Q000378:metabolism; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008856:Microscopy, Fluorescence; D057054:Molecular Imaging; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D009685:Nuclear Envelope / Q000378:metabolism*; D011817:Rabbits; D013045:Species Specificity; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D007545:Isoproterenol; D000099211:Phospholamban
keywords: Calcium signaling; Cardiomyocyte; Nuclear membranes; Perinuclear Ca(2+) dynamics; Phospholamban; Sarcoplasmic reticulum Ca(2+) ATPase