Atrogin-1 inhibits Akt-dependent cardiac hypertrophy in mice via ubiquitin-dependent coactivation of Forkhead proteins
Hui-Hua Li, … , David J. Glass, Cam Patterson
Hui-Hua Li, … , David J. Glass, Cam Patterson
Published October 25, 2007
Citation Information: J Clin Invest. 2007;117(11):3211-3223. https://doi.org/10.1172/JCI31757.
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Research Article Cardiology

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

Hui-Hua Li, Monte S. Willis, Pamela Lockyer, Nathaniel Miller, Holly McDonough, David J. Glass, Cam Patterson

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Figure 5

Lysine 63–linked ubiquitin chains are required for transcriptional coactivation of Foxo3a by atrogin-1.

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Lysine 63–linked ubiquitin chains are required for transcriptional coact...
(A) Cultured cardiomyocytes were transfected with vectors expressing HA-Foxo3a, Myc–atrogin-1, and/or atrogin-1 ΔF-box together with the p27kip1 luciferase reporter and β-gal constructs. At 24 h after transfection, cells were lysed and luciferase activity was measured. Lysates were immunoblotted with anti-HA and Myc. *P < 0.01 vs. atrogin-1 WT. (B) We transfected 293 cells with the indicated plasmids. Equal amounts of protein lysates were immunoprecipitated with anti-Myc or anti-HA antibodies to detect atrogin-1 and Foxo3a, respectively, followed by IB to detect protein-protein interactions. (C) Reporter assays were performed using the p27kip1 promoter in cardiomyocytes cotransfected with plasmids expressing Foxo3a and/or atrogin-1, along with vectors expressing WT ubiquitin or mutant ubiquitins containing mutations of lysine 48 (K48R) or lysine 63 (K63R). At 24 h after transfection, cells were lysed and luciferase activity was measured. Lysates were immunoblotted with anti-HA and Myc. *P < 0.001 vs. WT ubiquitin. Results are expressed relative to the level of expression with the reporter gene alone and representative of 3 independent experiments. Error bars indicate SEM.