title: Ubiquitination is required for effective replication of coxsackievirus B3.
abstract: BACKGROUND
  Protein ubiquitination and/or degradation by the ubiquitin/proteasome system (UPS) have been recognized as critical mechanisms in the regulation of numerous essential cellular functions. The importance of the UPS in viral pathogenesis has become increasingly apparent. Using murine cardiomyocytes, we have previously demonstrated that the UPS plays a key role in the replication of coxsackievirus B3 (CVB3), an important human pathogen associated with various diseases. To further elucidate the underlying mechanisms, we examined the interplay between the UPS and CVB3, focusing on the role of ubiquitination in viral lifecycle.
  
  
  RESULTS
  As assessed by in situ hybridization, Western blot, and plaque assay, we showed that proteasome inhibition decreased CVB3 RNA replication, protein synthesis, and viral titers in HeLa cells. There were no apparent changes in 20S proteasome activities following CVB3 infection. However, we found viral infection led to an accumulation of protein-ubiquitin conjugates, accompanied by a decreased protein expression of free ubiquitin, implicating an important role of ubiquitination in the UPS-mediated viral replication. Using small-interfering RNA, we demonstrated that gene-silencing of ubiquitin significantly reduced viral titers, possibly through downregulation of protein ubiquitination and subsequent alteration of protein function and/or degradation. Inhibition of deubiquitinating enzymes apparently enhances the inhibitory effects of proteasome inhibitors on CVB3 replication. Finally, by immunoprecipitation, we showed that coxsackieviral polymerase 3D was post-translationally modified by ubiquitination and such modification might be a prerequisite for its function in transcriptional regulation of viral genome.
  
  
  CONCLUSIONS
  Coxsackievirus infection promotes protein ubiquitination, contributing to effective viral replication, probably through ubiquitin modification of viral polymerase.
authors.affiliation: The James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research, Department of Pathology and Laboratory Medicine, University of British Columbia, Providence Heart + Lung Institute, St. Paul's Hospital, Vancouver, British Columbia, Canada.
authors.forename: Xiaoning
authors.initials: X
authors.lastname: Si
authors.forename: Guang
authors.initials: G
authors.lastname: Gao
authors.forename: Jerry
authors.initials: J
authors.lastname: Wong
authors.forename: Yahong
authors.initials: Y
authors.lastname: Wang
authors.forename: Jingchun
authors.initials: J
authors.lastname: Zhang
authors.forename: Honglin
authors.initials: H
authors.lastname: Luo
mesh_terms: D003384:Coxsackievirus Infections / Q000378:metabolism; D029822:Enterovirus B, Human / Q000472:pathogenicity / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D054875:Ubiquitination / Q000502:physiology*; D014779:Virus Replication / Q000502:physiology*
chemical_list: D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D025801:Ubiquitin; D012324:RNA-Dependent RNA Polymerase; D046988:Proteasome Endopeptidase Complex