title: Atrogin-1 inhibits Akt-dependent cardiac hypertrophy in mice via ubiquitin-dependent coactivation of Forkhead proteins.
abstract: Cardiac hypertrophy is a major cause of human morbidity and mortality. Although much is known about the pathways that promote hypertrophic responses, mechanisms that antagonize these pathways have not been as clearly defined. Atrogin-1, also known as muscle atrophy F-box, is an F-box protein that inhibits pathologic cardiac hypertrophy by participating in a ubiquitin ligase complex that triggers degradation of calcineurin, a factor involved in promotion of pathologic hypertrophy. Here we demonstrated that atrogin-1 also disrupted Akt-dependent pathways responsible for physiologic cardiac hypertrophy. Our results indicate that atrogin-1 does not affect the activity of Akt itself, but serves as a coactivator for members of the Forkhead family of transcription factors that function downstream of Akt. This coactivator function of atrogin-1 was dependent on its ubiquitin ligase activity and the deposition of polyubiquitin chains on lysine 63 of Foxo1 and Foxo3a. Transgenic mice expressing atrogin-1 in the heart displayed increased Foxo1 ubiquitylation and upregulation of known Forkhead target genes concomitant with suppression of cardiac hypertrophy, while mice lacking atrogin-1 displayed the opposite physiologic phenotype. These experiments define a role for lysine 63-linked ubiquitin chains in transcriptional coactivation and demonstrate that atrogin-1 uses this mechanism to disrupt physiologic cardiac hypertrophic signaling through its effects on Forkhead transcription factors.
authors.affiliation: Carolina Cardiovascular Biology Center, Department of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7126, USA. hhli1995@yahoo.com
authors.forename: Hui-Hua
authors.initials: HH
authors.lastname: Li
authors.forename: Monte S
authors.initials: MS
authors.lastname: Willis
authors.forename: Pamela
authors.initials: P
authors.lastname: Lockyer
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Miller
authors.forename: Holly
authors.initials: H
authors.lastname: McDonough
authors.forename: David J
authors.initials: DJ
authors.lastname: Glass
authors.forename: Cam
authors.initials: C
authors.lastname: Patterson
mesh_terms: D000818:Animals; D006332:Cardiomegaly / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D004452:Echocardiography; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D010641:Phenotype; D025821:Polyubiquitin / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; C467200:Foxo1 protein, mouse; D007328:Insulin; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; D025821:Polyubiquitin; D007334:Insulin-Like Growth Factor I; C486691:Fbxo32 protein, mouse; D044843:SKP Cullin F-Box Protein Ligases; D051057:Proto-Oncogene Proteins c-akt; D008239:Lysine