Ectromelia Virus Encodes a BTB/kelch Protein, EVM150, That Inhibits NF-B Signaling

The NF-B signaling pathway plays a critical role in inflammation and innate immunity. Consequently, many viruses have evolved strategies to inhibit NF-B in order to facilitate replication and evasion of the host immune response. Recently, we de-termined that ectromelia virus, the causative agent of mousepox, contains a family of four BTB/kelch proteins that interact with cullin-3-based ubiquitin ligases. We demonstrate here that expression of EVM150, one of the four BTB/kelch proteins, inhibited NF-B activation induced by tumor necrosis factor alpha (TNF-) and interleukin-1 (IL-1). Although EVM150 inhibited NF-B p65 nuclear translocation, IB degradation was observed, indicating that EVM150 functioned downstream of IB degradation. Significantly, expression of the BTB-only domain of EVM150 blocked NF-B activation, demonstrating that EVM150 functioned independently of the kelch domain and its role as an adapter for cullin-3-based ubiquitin ligases. Further-more, cullin-3 knockdown by small interfering RNA demonstrated that cullin-3-based ubiquitin ligases are dispensable for TNF--induced NF-B activation. Interestingly, nuclear translocation of IRF3 and STAT1 still occurred in the presence of EVM150, indicating that EVM150 prevented NF-B nuclear translocation specifically. In addition to identifying EVM150 as an inhibitor of the NF-B pathway, this study provides new insights into the role of BTB/kelch proteins during virus infection. IMPORTANCE With the exception of virulence studies, little work has been done to determine the role of poxviral BTB/kelch proteins durin