EVM005: An Ectromelia-Encoded Protein with Dual Roles in NF-κB Inhibition and Virulence

Poxviruses contain large dsdna genomes encoding numerous open reading frames that manipulate cellular signalling pathways and interfere with the host immune response. the nf-κb 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-κb activation is the ubiquitination and degradation of the inhibitor of kappab (iκbα),by the cellular scfβ-trcp ubiquitin ligase complex. we show here that upon stimulation with tnfα or il-1β,orthopoxvirus-infected cells displayed an accumulation of phosphorylated iκbα,indicating that nf-κb 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 iκbα is catalyzed by the scfβ-trcp ubiquitin ligase,we investigated the role of the ectromelia virus ankyrin/f-box protein,evm005,in the regulation of nf-κb. expression of flag-evm005 inhibited both tnfα- and il-1β-stimulated iκbα degradation and p65 nuclear translocation. inhibition of the nf-κb 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-κb 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. © 2014 van buuren et al.