Viral mimicry of p65/RelA transactivation domain to inhibit NF-κB activation

Sensing of virus infection activates NF-κB to induce the expression of interferons, cytokines and chemokines to initiate the antiviral response. Viruses antagonise these antiviral defences by interfering with immune sensing and blocking the actions of antiviral and inflammatory molecules. Here, we show that a viral protein mimics the transactivation domain of the p65 subunit of NF-κB. The C terminus of vaccinia virus (VACV) protein F14 (residues 51-73) activates transcription when fused to a DNA-binding domain-containing protein and F14 associates with NF-κB co-activator CBP, disrupting p65-CBP interaction. Consequently, F14 diminishes CBP-mediated acetylation of p65 and the downstream recruitment of the transcriptional regulator BRD4 to the promoter of the NF-κB-responsive genes CXCL10 and CCL2 , hence inhibiting their expression. Conversely, the recruitment of BRD4 to the promoters of NFKBIA , which encodes the inhibitor of NF-κB (IκBα), and CXCL8 remains unaffected in the presence of either F14 or JQ1, a competitive inhibitor of BRD4 bromodomains, indicating its recruitment is acetylation-independent. Therefore, unlike other viral NF-κB antagonists, F14 is a selective inhibitor of NF-κB-dependent gene expression. A VACV strain lacking F14 showed that it contributes to virulence in an intradermal model of infection. Our results uncover a mechanism by which viruses disarm the antiviral defences through molecular mimicry of a conserved host protein and provide insight into the regulation of NF-κB-dependent gene expression by BRD4. ### Competing Interest Statement The authors have declared no competing interest.