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Ectromelia Virus Encodes A Novel Family Of Ankyrin/F-box Proteins That Manipulate The SCF Ubiquitin Ligase And NF-κB Activation Open Access
- Other title
SCF ubiqutin ligase
- Type of item
- Degree grantor
University of Alberta
- Author or creator
van Buuren, Nicholas J.
- Supervisor and department
- Examining committee member and department
Schultz, Michael (Biochemistry)
Schang, Luis (Biochemistry)
Coscoy, Laurent (Immunology and Pathogenesis, UC Berkeley)
Ostergaard, Hanne (Medical Microbiology and Immunology)
Ingham, Rob (Medical Microbiology and Immunology)
Department of Medical Microbiology and Immunology
- Date accepted
- Graduation date
Doctor of Philosophy
- Degree level
Ectromelia virus (ECTV) is the causative agent of lethal mousepox, and is highly related to the human pathogen, variola virus, the causative agent of smallpox. Poxviruses contain large dsDNA genomes that encode numerous open reading frames that manipulate cellular signalling pathways. We used bioinformatics to identify a family of four genes encoded by ECTV that contain N-terminal ankyrin repeats in conjunction with a C-terminal F-box domain. The ECTV encoded ankyrin/F-box proteins: EVM002, EVM005, EVM154 and EVM165, all interact with the cellular SCF (Skp1/Cul-1/F-box) ubiquitin ligase complex through an interaction mediated by their C-terminal F-box domain. These four proteins bind to the SCF complex in a similar manner to cellular F-box-containing substrate adaptor proteins. We hypothesize that each of the ECTV encoded ankyrin/F-box proteins recruits a unique family of target proteins to the SCF complex for ubiquitylation. The NF-κB signalling cascade is an important mediator of innate immunity, and is tightly regulated by ubiquitylation. A critical step in the activation of NF-κB is the ubiquitylation and degradation of the inhibitor of kappaB (IκBα), by the cellular SCFβ-TRCP ubiquitin ligase. Upon stimulation with TNFα or IL-1β, orthopoxvirus-infected cells display an accumulation of phosphorylated IκBα, indicating that NF-κB activation is inhibited during poxvirus infection at the point of IκBα degradation. Since degradation of IκBα is catalyzed by the SCFβ-TRCP ubiquitin ligase complex we investigated the role of the ECTV encoded ankyrin/F-box proteins in the regulation of NF-κB activation. Expression of Flag-EVM005 inhibited both IκBα degradation and p65 nuclear translocation in response to TNFα or IL-1β. Regulation of the NF-κB pathway by EVM005 was dependent on the F-box domain, and interaction with the SCF complex. Additionally, we created ECTV knockout viruses devoid of each of the four ankyrin/F-box genes using a novel “Selectable and Excisable Marker” system. The EVM005 deletion virus was shown to inhibit NF-κB activation despite lacking the EVM005 open reading frame; however, this virus was attenuated in two mouse strains. The contribution of EVM005 to virulence is therefore independent from its ability to inhibit NF-κB activation, and is potentially linked to unique target proteins ubiquitylated through the SCF complex during infection.
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- Citation for previous publication
van Buuren, N., B. Couturier, Y. Xiong, and M. Barry. 2008. Ectromelia virus encodes a novel family of F-box proteins that interact with the SCF complex. J Virol 82:9917-27.Rintoul, J., Wang, J., Gammon, D.B., van Buuren, N., Garson, K., Jardine, K., Barry, M., Evans, D.H., and Bell, J.C. 2011. A selectable and excisable marker system for the rapid creation of recombinant poxviruses. Plos One, 6(9): e24643.Mohamed, M. R., M. M. Rahman, J. S. Lanchbury, D. Shattuck, C. Neff, M. Dufford, N. van Buuren, K. Fagan, M. Barry, S. Smith, I. Damon, and G. McFadden. 2009. Proteomic screening of variola virus reveals a unique NF-kappaB inhibitor that is highly conserved among pathogenic orthopoxviruses. PNAS, 106:9045-50.Teale, A., S. Campbell, N. Van Buuren, W. C. Magee, K. Watmough, B. Couturier, R. Shipclark, and M. Barry. 2009. Orthopoxviruses require a functional ubiquitin-proteasome system for productive replication. J Virol 83:2099-108.
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