Abstract 16322: A Novel Desmosomal Interaction Reveals Arrhythmogenic Cardiomyopathy as a Disease of Aberrant Desmosomal Protein Turnover
Arrhythmogenic cardiomyopathy (AC) is a genetic-based heart disease characterized by ventricular dysfunction, fibrofatty replacement of the myocardium and ventricular arrhythmias leading to sudden cardiac death in young people. AC is termed a cardiac disease of the desmosome; however, only 40% of patients carry genetic mutations in known desmosomal cell-cell junction genes, suggesting that novel mechanisms and players remain to be uncovered. To address this challenge, we set out to identify novel desmosomal associated proteins by performing a yeast-two-hybrid screen with the desmosomal gene, desmoplakin (DSP), as bait in an adult human heart cDNA library. We identified COP9 signalosome subunit 6 (CSN6), as a novel desmosomal (DSP)-interacting protein, which localizes at the intercalated disc in both adult mouse and human heart. An increasing body of evidence suggests that the CSN complex regulates protein degradation via ubiquitination; however, the specific role of CSN6 in the heart and AC has yet to be defined. We show that CSN6 levels are dramatically reduced at the intercalated disc in hearts of a mouse model of AC (cardiac-specific DSP knockout mice (DSP-cKO)) and human AC patient harboring desmosomal mutations in DSP and plakophilin-2 (PKP2). Yeast-two-hybrid assays revealed that the DSP mutation in the human AC patient abrogates the binding of DSP with CSN6, reinforcing the importance of the link between DSP and CSN6 in human AC. We further show that DSP-cKO hearts display underlying defects in protein degradation associated with loss of CSN6 including increased neddylation, ubiquitination, and ubiquitin-mediated autophagy profiles. A striking increase in markers for the autophagy/lysosome degradation system could also be detected specifically at the intercalated disc in DSP-cKO mouse hearts. Most importantly, characterization of hearts from CSN6 heterozygous knockout mice and analysis of CSN6 knockdown in neonatal ventricular cardiomyocytes in vitro revealed that loss of CSN6 is sufficient to trigger and recapitulate the desmosomal protein turnover defects observed in our mouse model of AC. Our studies highlight the importance of CSN6 at the cardiac desmosome and reveal new mechanisms underlying AC.
- © 2013 by American Heart Association, Inc.