Phosphorylation of eukaryotic translation initiation factor 2Bepsilon by glycogen synthase kinase-3beta regulates beta-adrenergic cardiac myocyte hypertrophy.
Glycogen synthase kinase 3beta (GSK-3beta) negatively regulates cardiac hypertrophy. A potential target mediating the antihypertrophic effect of GSK-3beta is eukaryotic translation initiation factor 2Bepsilon (eIF2Bepsilon). Overexpression of GSK-3beta increased the cellular kinase activity toward GST-eIF2Bepsilon in neonatal rat cardiac myocytes, whereas LiCl (10 mmol/L) or isoproterenol (ISO) (10 micromol/L), a treatment known to inhibit GSK-3beta, decreased it. Immunoblot analyses using anti-S535 phosphospecific eIF2Bepsilon antibody showed that S535 phosphorylation of endogenous eIF2Bepsilon was decreased by LiCl or ISO, suggesting that GSK-3beta is the predominant kinase regulating phosphorylation of eIF2Bepsilon-S535 in cardiac myocytes. Decreases in eIF2Bepsilon-S535 phosphorylation were also observed in a rat model of cardiac hypertrophy in vivo. Overexpression of wild-type eIF2Bepsilon alone moderately increased cell size (+31+/-11%; P<0.05 versus control), whereas treatment of eIF2Bepsilon-transduced myocytes with LiCl (+73+/-22% versus eIF2Bepsilon only; P<0.05) or ISO (+84+/-33% versus eIF2Bepsilon only; P<0.05) enhanced the effect of eIF2Bepsilon. Overexpression of eIF2Bepsilon-S535A, which is not phosphorylated by GSK-3beta, increased cell size (+107+/-35%) as strongly as ISO (+95+/-25%), and abolished antihypertrophic effects of GSK-3beta, indicating that S535 phosphorylation of eIF2Bepsilon critically mediates antihypertrophic effects of GSK-3beta. Furthermore, expression of eIF2Bepsilon-F259L, a dominant-negative mutant, inhibited ISO-induced hypertrophy, indicating that eIF2Bepsilon is required for beta-adrenergic hypertrophy. Interestingly, expression of eIF2Bepsilon-S535A partially increased cytoskeletal reorganization, whereas it did not increase expression of atrial natriuretic factor gene. These results suggest that GSK-3beta is the predominant kinase mediating phosphorylation of eIF2Bepsilon-S535 in cardiac myocytes, which in turn plays an important role in regulating cardiac hypertrophy primarily through protein synthesis.
Hardt
Stefan E
SE
Department of Cell Biology and Molecular Medicine, Cardiovascular Research Institute, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, NJ 07103-2714, USA.
Tomita
Hideharu
H
Katus
Hugo A
HA
Sadoshima
Junichi
J
D000256:Adenoviridae / Q000235:genetics; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D009320:Atrial Natriuretic Factor / Q000096:biosynthesis / Q000235:genetics; D006332:Cardiomegaly / Q000201:enzymology / Q000209:etiology / Q000473:pathology; D002478:Cells, Cultured / Q000187:drug effects / Q000201:enzymology; D020717:Eukaryotic Initiation Factor-2B / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D005822:Genetic Vectors / Q000235:genetics; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000502:physiology*; D000071679:Glycogen Synthase Kinase 3 beta; D006352:Heart Ventricles / Q000166:cytology; D006984:Hypertrophy; D007545:Isoproterenol / Q000494:pharmacology; D018021:Lithium Chloride / Q000494:pharmacology; D008297:Male; D009203:Myocardial Infarction / Q000150:complications; D032383:Myocytes, Cardiac / Q000201:enzymology* / Q000473:pathology; D018995:Myosin Heavy Chains / Q000096:biosynthesis / Q000235:genetics; D010442:Peptide Chain Initiation, Translational / Q000502:physiology; D010768:Phosphoserine / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D051381:Rats; D017208:Rats, Wistar; D011993:Recombinant Fusion Proteins / Q000502:physiology; D014161:Transduction, Genetic; D020257:Ventricular Remodeling / Q000502:physiology
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D020717:Eukaryotic Initiation Factor-2B; D011993:Recombinant Fusion Proteins; D010768:Phosphoserine; D009320:Atrial Natriuretic Factor; D011433:Propranolol; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D038362:Glycogen Synthase Kinase 3; D018995:Myosin Heavy Chains; D018021:Lithium Chloride; D007545:Isoproterenol