title: Mechanisms involved in 3',5'-cyclic adenosine monophosphate-mediated inhibition of the ubiquitin-proteasome system in skeletal muscle.
abstract: Although it is well known that catecholamines inhibit skeletal muscle protein degradation, the molecular underlying mechanism remains unclear. This study was undertaken to investigate the role of beta(2)-adrenoceptors (AR) and cAMP in regulating the ubiquitin-proteasome system (UPS) in skeletal muscle. We report that increased levels of cAMP in isolated muscles, promoted by the cAMP phosphodiesterase inhibitor isobutylmethylxanthine was accompanied by decreased activity of the UPS, levels of ubiquitin-protein conjugates, and expression of atrogin-1, a key ubiquitin-protein ligase involved in muscle atrophy. In cultured myotubes, atrogin-1 induction after dexamethasone treatment was completely prevented by isobutylmethylxanthine. Furthermore, administration of clenbuterol, a selective beta(2)-agonist, to mice increased muscle cAMP levels and suppressed the fasting-induced expression of atrogin-1 and MuRF-1, atrogin-1 mRNA being much more responsive to clenbuterol. Moreover, clenbuterol increased the phosphorylation of muscle Akt and Foxo3a in fasted rats. Similar responses were observed in muscles exposed to dibutyryl-cAMP. The stimulatory effect of clenbuterol on cAMP and Akt was abolished in muscles from beta(2)-AR knockout mice. The suppressive effect of beta(2)-agonist on atrogin-1 was not mediated by PGC-1alpha (peroxisome proliferator-activated receptor-gamma coactivator 1alpha known to be induced by beta(2)-agonists and previously shown to inhibit atrogin-1 expression), because food-deprived PGC-1alpha knockout mice were still sensitive to clenbuterol. These findings suggest that the cAMP increase induced by stimulation of beta(2)-AR in skeletal muscles from fasted mice is possibly the mechanism by which catecholamines suppress atrogin-1 and the UPS, this effect being mediated via phosphorylation of Akt and thus inactivation of Foxo3.
authors.affiliation: Departments of Physiology and Biochemistry & Immunology, School of Medicine, University of São Paulo, 14049-900 Ribeirão Preto, Brazil.
authors.forename: Dawit A P
authors.initials: DA
authors.lastname: Gonçalves
authors.forename: Eduardo C
authors.initials: EC
authors.lastname: Lira
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Baviera
authors.forename: Peirang
authors.initials: P
authors.lastname: Cao
authors.forename: Neusa M
authors.initials: NM
authors.lastname: Zanon
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Arany
authors.forename: Nathalie
authors.initials: N
authors.lastname: Bedard
authors.forename: Preeti
authors.initials: P
authors.lastname: Tanksale
authors.forename: Simon S
authors.initials: SS
authors.lastname: Wing
authors.forename: Stewart H
authors.initials: SH
authors.lastname: Lecker
authors.forename: Isis C
authors.initials: IC
authors.lastname: Kettelhut
authors.forename: Luiz C C
authors.initials: LC
authors.lastname: Navegantes
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D058666:Adrenergic beta-2 Receptor Agonists; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002976:Clenbuterol / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D009124:Muscle Proteins; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010726:Phosphodiesterase Inhibitors; C485290:Ppargc1a protein, mouse; D018343:Receptors, Adrenergic, beta-2; D015534:Trans-Activators; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin; D003907:Dexamethasone; D000242:Cyclic AMP; C486691:Fbxo32 protein, mouse; D044843:SKP Cullin F-Box Protein Ligases; C499084:Trim63 protein, mouse; D044767:Ubiquitin-Protein Ligases; D051057:Proto-Oncogene Proteins c-akt; D046988:Proteasome Endopeptidase Complex; D015056:1-Methyl-3-isobutylxanthine; D002976:Clenbuterol