Enhanced ubiquitination of cytoskeletal proteins in pressure overloaded myocardium is accompanied by changes in specific E3 ligases.
Ubiquitin conjugation of proteins is critical for cell homeostasis and contributes to both cell survival and death. Here we studied ubiquitination of proteins in pressure overloaded (PO) myocardium in the context of cardiomyocyte survival. Analysis using a feline right ventricular pressure overload (RVPO) model revealed a robust and transient increase in ubiquitination of proteins present in the Triton X-100-insoluble fraction in 24 to 48 h PO myocardium, and confocal micrographs indicate this increase in ubiquitination occurs subsarcolemmaly near the intercalated disc area of cardiomyocytes. The ubiquitination was accompanied by changes in E3 ligases including Cbl, E6AP, Mdm2 and cIAP in the same period of PO, although atrophy-related E3 ligases, MuRF1 and MuRF3 were unaltered. Furthermore, Cbl displayed a substantial increase in both levels of expression and tyrosine phosphorylation in 48 h PO myocardium. Confocal studies revealed enrichment of Cbl at the intercalated discs of 48 h PO cardiomyocytes, as evidenced by its colocalization with N-cadherin. Although apoptosis was observed in 48 h PO myocardium by TUNEL staining, cardiomyocytes showing ubiquitin staining were not positive for TUNEL staining. Furthermore, 48 h PO resulted in the phosphorylation of inhibitor of nuclear factor kappa B (IkappaB), suggesting its ubiquitin-mediated degradation and the nuclear localization of NFkappaB for the expression of specific cell survival factors such as cIAPs. Together these data indicate that increased levels of E3 ligases that regulate cell homeostasis and promote cell survival could ubiquitinate multiple cytoskeletal protein targets and that these events that occur during the early phase of PO may contribute to both cardiomyocyte survival and hypertrophy.
Balasubramanian
Sundaravadivel
S
Cardiology Division of the Department of Medicine, Gazes Cardiac Research Institute, Medical University of South Carolina, Charleston, SC 29425-2221, USA.
Mani
Santhoshkumar
S
Shiraishi
Hirokazu
H
Johnston
Rebecca K
RK
Yamane
Kentaro
K
Willey
Christopher D
CD
Cooper
George
G
Tuxworth
William J
WJ
Kuppuswamy
Dhandapani
D
D000818:Animals; D017209:Apoptosis; D002415:Cats; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D018497:Ventricular Dysfunction, Right / Q000139:chemically induced; D017725:Ventricular Pressure
D003598:Cytoskeletal Proteins; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases