title: AMP-activated protein kinase phosphorylates cardiac troponin I and alters contractility of murine ventricular myocytes.
abstract: BACKGROUND
  AMP-activated protein kinase (AMPK) is an important regulator of energy balance and signaling in the heart. Mutations affecting the regulatory γ2 subunit have been shown to cause an essentially cardiac-restricted phenotype of hypertrophy and conduction disease, suggesting a specific role for this subunit in the heart.
  
  
  OBJECTIVE
  The γ isoforms are highly conserved at their C-termini but have unique N-terminal sequences, and we hypothesized that the N-terminus of γ2 may be involved in conferring substrate specificity or in determining intracellular localization.
  
  
  RESULTS
  A yeast 2-hybrid screen of a human heart cDNA library using the N-terminal 273 residues of γ2 as bait identified cardiac troponin I (cTnI) as a putative interactor. In vitro studies showed that cTnI is a good AMPK substrate and that Ser150 is the principal residue phosphorylated. Furthermore, on AMPK activation during ischemia, Ser150 is phosphorylated in whole hearts. Using phosphomimics, measurements of actomyosin ATPase in vitro and force generation in demembraneated trabeculae showed that modification at Ser150 resulted in increased Ca(2+) sensitivity of contractile regulation. Treatment of cardiomyocytes with the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) resulted in increased myocyte contractility without changing the amplitude of Ca(2+) transient and prolonged relaxation despite shortening the time constant of Ca(2+) transient decay (tau). Compound C prevented the effect of AICAR on myocyte function. These results suggest that AMPK activation increases myocyte contraction and prolongs relaxation by increasing myofilament Ca(2+) sensitivity.
  
  
  CONCLUSIONS
  We conclude that cTnI phosphorylation by AMPK may represent a novel mechanism of regulation of cardiac function.
authors.affiliation: Department of Cardiovascular Medicine, University of Oxford, UK.
authors.forename: Sandra Marisa
authors.initials: SM
authors.lastname: Oliveira
authors.forename: Yin-Hua
authors.initials: YH
authors.lastname: Zhang
authors.forename: Raquel Sancho
authors.initials: RS
authors.lastname: Solis
authors.forename: Henrik
authors.initials: H
authors.lastname: Isackson
authors.forename: Mohamed
authors.initials: M
authors.lastname: Bellahcene
authors.forename: Arash
authors.initials: A
authors.lastname: Yavari
authors.forename: Katalin
authors.initials: K
authors.lastname: Pinter
authors.forename: Joanna K
authors.initials: JK
authors.lastname: Davies
authors.forename: Ying
authors.initials: Y
authors.lastname: Ge
authors.forename: Houman
authors.initials: H
authors.lastname: Ashrafian
authors.forename: Jeffery W
authors.initials: JW
authors.lastname: Walker
authors.forename: David
authors.initials: D
authors.lastname: Carling
authors.forename: Hugh
authors.initials: H
authors.lastname: Watkins
authors.forename: Barbara
authors.initials: B
authors.lastname: Casadei
authors.forename: Charles
authors.initials: C
authors.lastname: Redwood
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling; D004789:Enzyme Activation; D020536:Enzyme Activators / Q000494:pharmacology; D006352:Heart Ventricles / Q000201:enzymology; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D009218:Myosins / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D012265:Ribonucleotides / Q000494:pharmacology; D012694:Serine; D013997:Time Factors; D019210:Troponin I / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D016277:Ventricular Function, Left / Q000187:drug effects
chemical_list: D020536:Enzyme Activators; D047428:Protein Kinase Inhibitors; D011720:Pyrazoles; D011743:Pyrimidines; D012265:Ribonucleotides; D019210:Troponin I; C516138:dorsomorphin; D000620:Aminoimidazole Carboxamide; D012694:Serine; C526223:PRKAG2 protein, human; D055372:AMP-Activated Protein Kinases; D009218:Myosins; C031143:AICA ribonucleotide