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UBC Theses and Dissertations

Role of the ubiquitin/proteasome system in coxsackievirus induced-myocarditis Gao, Guang


Viral myocarditis, an inflammatory disease of the myocardium, can lead to the development of dilated cardiomyopathy (DCM), a common cause of heart failure. Coxsackievirus B3 (CVB3) in the family of Picornaviridae is one of the primary causative agents of viral myocarditis. The ubiquitin/proteasome system (UPS), a primary intracellular protein degradation system in eukaryotic cells, has emerged as a key modulator in viral infectivity and virus-mediated pathogenesis. Our laboratory has previously demonstrated a potential role of the UPS in CVB3 infection. However, the effect of proteasome inhibition on CVB3-induced myocarditis in vivo has not been assessed and the underlying mechanism by which the UPS regulates CVB3 replication remains unclear. In this dissertation, my hypothesis is that the UPS plays a critical role in the pathogenesis of CVB3-induced myocarditis through promoting CVB3 replication and by regulating host protein degradation. To test this hypothesis, I proposed three aims. In aim 1, using a myocarditis-susceptible mouse model, I demonstrated that treatment with a proteasome inhibitor MLN353 significantly attenuates CVB3-induced myocardial damage, suggesting that proteasome inhibition may provide a therapeutic means for viral myocarditis. During this study, however, the potential toxicity of general inhibition of proteasome was recognized, which prompted me to search for the specific targets within the UPS utilized by CVB3. In aim 2, collaborating with others, I showed that protein ubiquitination is enhanced and CVB3 protein 3D is ubiquitinated during viral infection. Gene-silencing of ubiquitin significantly reduces viral titers. However, this reduction is not as potent as by proteasome inhibition, suggesting that ubiquitin-independent proteasomal degradation may also play a role during CVB3 infection. In aim 3, I showed that REG gamma, which mediates ubiquitin-independent protein degradation, enhances CVB3 replication via facilitating p53 degradation. During CVB3 infection, REG gamma is sumoylated and translocated. Taken together, the results suggest a therapeutic value of proteasome inhibition in the treatment of viral myocarditis. The data also demonstrate important roles of both the ubiquitin-dependent and -independent pathways in the regulation of CVB3 infection. Identification of the specific substrates within the UPS during CVB3 infection and the potential mechanisms involved allows for more precise targeting in drug therapy.

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