title: Novel cardiac apoptotic pathway: the dephosphorylation of apoptosis repressor with caspase recruitment domain by calcineurin.
abstract: BACKGROUND
  Apoptosis repressor with caspase recruitment domain (ARC) is abundantly expressed in cardiomyocytes. Protein kinase CK2 can phosphorylate ARC at threonine-149, thereby enabling ARC to antagonize apoptosis. ARC phosphorylation occurs in a constitutive manner. Nevertheless, cardiomyocytes still undergo apoptosis that is related to cardiac diseases such as myocardial infarction and heart failure. Whether the occurrence of apoptosis is related to the loss of protection by ARC under pathological conditions remains unknown.
  
  
  RESULTS
  ARC phosphorylation levels are decreased in cardiomyocytes treated with isoproterenol or aldosterone. We explored the molecular mechanism by which ARC phosphorylation levels are decreased. Our results reveal that either direct incubation or coexpression with calcineurin leads to a decrease in ARC phosphorylation levels. Inhibition of calcineurin can attenuate the reduction in ARC phosphorylation levels on treatment with isoproterenol or aldosterone. These data indicate that the reduction in ARC phosphorylation levels is related to its dephosphorylation by calcineurin. Our results further reveal that ARC can prevent isoproterenol- and aldosterone-induced apoptosis, but this function depends on its phosphorylation status. Isoproterenol and aldosterone upregulate Fas ligand expression, and Fas ligand and caspase-8 are required for isoproterenol and aldosterone to induce apoptosis. However, phosphorylated but not dephosphorylated ARC is able to inhibit caspase-8-mediated apoptosis. Phosphorylated ARC exerts its effects against caspase-8 by directly associating with procaspase-8 and inhibiting its interaction with Fas-associated protein with death domain.
  
  
  CONCLUSIONS
  Our study identifies a novel cardiac apoptotic pathway in which ARC is dephosphorylated by calcineurin. This pathway could be a component in the cardiac apoptotic machinery.
authors.affiliation: Division of Cardiovascular Research, National Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China.
authors.forename: Wei-Qi
authors.initials: WQ
authors.lastname: Tan
authors.forename: Jian-Xun
authors.initials: JX
authors.lastname: Wang
authors.forename: Zhi-Qiang
authors.initials: ZQ
authors.lastname: Lin
authors.forename: Yan-Rui
authors.initials: YR
authors.lastname: Li
authors.forename: Yu
authors.initials: Y
authors.lastname: Lin
authors.forename: Pei-Feng
authors.initials: PF
authors.lastname: Li
mesh_terms: D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D019703:Calcineurin / Q000235:genetics* / Q000378:metabolism; D047390:Casein Kinase II / Q000235:genetics / Q000378:metabolism; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D006321:Heart / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology; D009124:Muscle Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D034622:RNA Interference; D051381:Rats
chemical_list: D051017:Apoptosis Regulatory Proteins; D061945:Caspase Inhibitors; D009124:Muscle Proteins; C491788:Nol3 protein, rat; D000450:Aldosterone; D047390:Casein Kinase II; D019703:Calcineurin; D053181:Caspase 8; D020169:Caspases; D007545:Isoproterenol