EVM005: an ectromelia-encoded protein with dual roles in NF-?B inhibition and virulence.

ABSTRACT: Poxviruses contain large dsDNA genomes encoding numerous open reading frames that manipulate cellular signalling pathways and interfere with the host immune response. The NF-?B signalling cascade is an important mediator of innate immunity and inflammation, and is tightly regulated by ubiquitination at several key points. A critical step in NF-?B activation is the ubiquitination and degradation of the inhibitor of kappaB (I?B?), by the cellular SCF?-TRCP ubiquitin ligase complex. We show here that upon stimulation with TNF? or IL-1?, Orthopoxvirus-infected cells displayed an accumulation of phosphorylated I?B?, indicating that NF-?B activation was inhibited during poxvirus infection. Ectromelia virus is the causative agent of lethal mousepox, a natural disease that is fatal in mice. Previously, we identified a family of four ectromelia virus genes (EVM002, EVM005, EVM154 and EVM165) that contain N-terminal ankyrin repeats and C-terminal F-box domains that interact with the cellular SCF ubiquitin ligase complex. Since degradation of I?B? is catalyzed by the SCF?-TRCP ubiquitin ligase, we investigated the role of the ectromelia virus ankyrin/F-box protein, EVM005, in the regulation of NF-?B. Expression of Flag-EVM005 inhibited both TNF?- and IL-1?-stimulated I?B? degradation and p65 nuclear translocation. Inhibition of the NF-?B pathway by EVM005 was dependent on the F-box domain, and interaction with the SCF complex. Additionally, ectromelia virus devoid of EVM005 was shown to inhibit NF-?B activation, despite lacking the EVM005 open reading frame. Finally, ectromelia virus devoid of EVM005 was attenuated in both A/NCR and C57BL/6 mouse models, indicating that EVM005 is required for virulence and immune regulation in vivo.

SUBMITTER: van Buuren N 

PROVIDER: S-EPMC4133408 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature