title: Small heat-shock protein Hsp20 phosphorylation inhibits beta-agonist-induced cardiac apoptosis.
abstract: Activation of the sympathetic nervous system is a common compensatory feature in heart failure, but sustained beta-adrenergic activation induces cardiomyocyte death, leading to cardiac remodeling and dysfunction. In mouse cardiomyocytes, we recently reported that prolonged exposure to beta-agonists is associated with transient increases in expression and phosphorylation of a small heat-shock protein, Hsp20. To determine the functional significance of Hsp20, we overexpressed this protein and its constitutively phosphorylated (S16D) or nonphosphorylated (S16A) mutant in adult rat cardiomyocytes. Hsp20 protected cardiomyocytes from apoptosis triggered by activation of the cAMP-PKA pathway, as indicated by decreases in the number of pyknotic nuclei, terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling, and DNA laddering, which were associated with inhibition of caspase-3 activity. These protective effects were further increased by the constitutively phosphorylated Hsp20 mutant (S16D), which conferred full protection from apoptosis. In contrast, the nonphosphorylatable mutant (S16A) exhibited no antiapoptotic properties. Immunostaining studies and immunoprecipitations with Hsp20 or actin antibodies demonstrated that Hsp20 translocated to cytoskeleton and associated with actin on isoproterenol stimulation. These findings suggest that Hsp20 and its phosphorylation at Ser16 may provide cardioprotection against beta-agonist-induced apoptosis. Thus, Hsp20 may represent a novel therapeutic target in the treatment of heart failure.
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0575, USA.
authors.forename: Guo-Chang
authors.initials: GC
authors.lastname: Fan
authors.forename: Guoxiang
authors.initials: G
authors.lastname: Chu
authors.forename: Bryan
authors.initials: B
authors.lastname: Mitton
authors.forename: Qiujing
authors.initials: Q
authors.lastname: Song
authors.forename: Qunying
authors.initials: Q
authors.lastname: Yuan
authors.forename: Evangelia G
authors.initials: EG
authors.lastname: Kranias
mesh_terms: D000318:Adrenergic beta-Agonists / Q000633:toxicity*; D019943:Amino Acid Substitution; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004789:Enzyme Activation; D005786:Gene Expression Regulation / Q000187:drug effects; D050886:HSP20 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D051379:Mice; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015290:Second Messenger Systems / Q000502:physiology
chemical_list: D000318:Adrenergic beta-Agonists; D050886:HSP20 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D007545:Isoproterenol