Atrogin-1/muscle atrophy F-box inhibits calcineurin-dependent cardiac hypertrophy by participating in an SCF ubiquitin ligase complex
Hui-Hua Li, … , Da-Zhi Wang, Cam Patterson
Hui-Hua Li, … , Da-Zhi Wang, Cam Patterson
Published October 15, 2004
Citation Information: J Clin Invest. 2004;114(8):1058-1071. https://doi.org/10.1172/JCI22220.
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Article Cardiology

Atrogin-1/muscle atrophy F-box inhibits calcineurin-dependent cardiac hypertrophy by participating in an SCF ubiquitin ligase complex

Abstract

Calcineurin, which binds to the Z-disc in cardiomyocytes via α-actinin, promotes cardiac hypertrophy in response to numerous pathologic stimuli. However, the endogenous mechanisms regulating calcineurin activity in cardiac muscle are not well understood. We demonstrate that a muscle-specific F-box protein called atrogin-1, or muscle atrophy F-box, directly interacts with calcineurin A and α-actinin-2 at the Z-disc of cardiomyocytes. Atrogin-1 associates with Skp1, Cul1, and Roc1 to assemble an SCFatrogin-1 complex with ubiquitin ligase activity. Expression of atrogin-1 decreases levels of calcineurin A and promotes its ubiquitination. Moreover, atrogin-1 attenuates agonist-induced calcineurin activity and represses calcineurin-dependent transactivation and NFATc4 translocation. Conversely, downregulation of atrogin-1 using adenoviral small interfering RNA (siRNA) expression enhances agonist-induced calcineurin activity and cardiomyocyte hypertrophy. Consistent with these cellular observations, overexpression of atrogin-1 in hearts of transgenic mice reduces calcineurin protein levels and blunts cardiac hypertrophy after banding of the thoracic aorta. These studies indicate that the SCFatrogin-1 ubiquitin ligase complex interacts with and represses calcineurin by targeting calcineurin for ubiquitin-mediated proteolysis, leading to inhibition of cardiac hypertrophy in response to pathologic stimuli.

Authors

Hui-Hua Li, Vishram Kedar, Chunlian Zhang, Holly McDonough, Ranjana Arya, Da-Zhi Wang, Cam Patterson

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Atrogin-1 blocks calcineurin-dependent transcriptional responses and nuc...
Atrogin-1 blocks calcineurin-dependent transcriptional responses and nuclear translocation of NFATc4 but does not inhibit a constitutively active form of NFAT in cardiomyocytes. (A) The calcineurin-dependent transcriptional response was measured in cardiomyocytes by cotransfection of a pIL2-Luc reporter plasmid and active calcineurin A (CnA*) together with atrogin-1 or the empty expression vector as control, and luciferase activity was measured. (B) A pIL2-Luc reporter plasmid and active calcineurin A together with plasmids expressing siRNA-atrogin-1 or siRNA-control were transfected in cardiomyocytes, and luciferase activity was measured. (C) An NFAT-dependent pIL2-Luc reporter plasmid, an expression vector encoding active NFAT (ΔNFAT), and atrogin-1 or the empty expression vector as control were transfected in cardiomyocytes, and luciferase activity was measured. (D) Cardiomyocytes transfected with the indicated plasmids were immunostained 36 hours after transfection with an antibody against NFATc4 (red), and nuclei were counterstained with DAPI (blue). (E) Cardiomyocytes transfected with the indicated plasmids were separated into cytoplasmic and nuclear fractions. Equal amounts of protein were analyzed by immunoblotting with NFATc4, GAPDH, and Oct1 antibodies. GAPDH and Oct1 served as cytoplasmic and nuclear markers, respectively. A representative blot is shown for each condition. CsA, cyclosporin A.