title: Alterations in the interactome of serine/threonine protein phosphatase type-1 in atrial fibrillation patients.
abstract: BACKGROUND
  Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, yet current pharmacological treatments are limited. Serine/threonine protein phosphatase type-1 (PP1), a major phosphatase in the heart, consists of a catalytic subunit (PP1c) and a large set of regulatory (R)-subunits that confer localization and substrate specificity to the holoenzyme. Previous studies suggest that PP1 is dysregulated in AF, but the mechanisms are unknown.
  
  
  OBJECTIVE
  The purpose of this study was to test the hypothesis that PP1 is dysregulated in paroxysmal atrial fibrillation (PAF) at the level of its R-subunits.
  
  
  METHODS
  Cardiac lysates were coimmunoprecipitated with anti-PP1c antibody followed by mass spectrometry-based, quantitative profiling of associated R-subunits. Subsequently, label-free quantification (LFQ) was used to evaluate altered R-subunit-PP1c interactions in PAF patients. R-subunits with altered binding to PP1c in PAF were further studied using bioinformatics, Western blotting (WB), immunocytochemistry, and coimmunoprecipitation.
  
  
  RESULTS
  A total of 135 and 78 putative PP1c interactors were captured from mouse and human cardiac lysates, respectively, including many previously unreported interactors with conserved PP1c docking motifs. Increases in binding were found between PP1c and PPP1R7, cold-shock domain protein A (CSDA), and phosphodiesterase type-5A (PDE5A) in PAF patients, with CSDA and PDE5A being novel interactors validated by bioinformatics, immunocytochemistry, and coimmunoprecipitation. WB confirmed that these increases in binding cannot be ascribed to their changes in global protein expression alone.
  
  
  CONCLUSIONS
  Subcellular heterogeneity in PP1 activity and downstream protein phosphorylation in AF may be attributed to alterations in PP1c-R-subunit interactions, which impair PP1 targeting to proteins involved in electrical and Ca(2+) remodeling. This represents a novel concept in AF pathogenesis and may provide more specific drug targets for treating AF.
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas; Department of Molecular Physiology & Biophysics, Baylor College of Medicine, Houston, Texas; Interdepartmental Program in Translational Biology and Molecular Medicine, Baylor College of Medicine, Houston, Texas.
authors.forename: David Y
authors.initials: DY
authors.lastname: Chiang
authors.affiliation: Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, the Netherlands; Netherlands Proteomics Centre, the Netherlands.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lebesgue
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas; Department of Molecular Physiology & Biophysics, Baylor College of Medicine, Houston, Texas; Interdepartmental Program in Translational Biology and Molecular Medicine, Baylor College of Medicine, Houston, Texas.
authors.forename: David L
authors.initials: DL
authors.lastname: Beavers
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas; Department of Molecular Physiology & Biophysics, Baylor College of Medicine, Houston, Texas.
authors.forename: Katherina M
authors.initials: KM
authors.lastname: Alsina
authors.affiliation: Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, the Netherlands; Netherlands Proteomics Centre, the Netherlands.
authors.forename: J Mirjam A
authors.initials: JM
authors.lastname: Damen
authors.affiliation: Institute of Pharmacology, Faculty of Medicine, University Duisburg-Essen, Essen, Germany.
authors.forename: Niels
authors.initials: N
authors.lastname: Voigt
authors.affiliation: Institute of Pharmacology, Faculty of Medicine, University Duisburg-Essen, Essen, Germany.
authors.forename: Dobromir
authors.initials: D
authors.lastname: Dobrev
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas; Department of Molecular Physiology & Biophysics, Baylor College of Medicine, Houston, Texas; Department of Medicine (Cardiology), Baylor College of Medicine, Houston, Texas. Electronic address: wehrens@bcm.edu.
authors.forename: Xander H T
authors.initials: XH
authors.lastname: Wehrens
authors.affiliation: Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, the Netherlands; Netherlands Proteomics Centre, the Netherlands; Janssen Infectious Diseases and Vaccines, Crucell Holland B.V., Leiden, the Netherlands. Electronic address: a.scholten@uu.nl.
authors.forename: Arjen
authors.initials: A
authors.lastname: Scholten
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D013058:Mass Spectrometry; D051379:Mice; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D054645:Protein Phosphatase 1 / Q000096:biosynthesis*; D040901:Proteomics / Q000379:methods
chemical_list: D054645:Protein Phosphatase 1
keywords: PP1 regulatory subunits; atrial fibrillation; label-free quantification; mass spectrometry; protein phosphatase 1; proteomics