ASFV pD345L protein negatively regulates NF-κB signalling by inhibiting IKK kinase activity

The NF-kappa B pathway is an essential signalling cascade in the defence against viral infections, including African swine fever virus (ASFV) infection. ASFV encodes more than 151 proteins via its own transcription machinery and possesses a great capacity to evade or subvert antiviral innate immune responses. Although some of these viral proteins have been reported, many remain unknown. Here, we show that pD345L, an ASFV-encoded lambda-like exonuclease, acts as an inhibitor of cGAS/STING-mediated NF-kappa B signalling by blocking the IkappaB kinase (IKK alpha/beta) activity. Specifically, we showed that overexpression of pD345L suppresses cGAS/STING-induced IFN beta and NF-kappa B activation, resulting in decreased transcription of IFN beta and several proinflammatory cytokines, including IL-1 alpha, IL-6, IL-8, and TNF alpha. In addition, we showed that pD345L acts at or downstream of IKK and upstream of p65. Importantly, we found that pD345L associates with the KD and HLH domains of IKK alpha and the LZ domain of IKK beta and thus interrupts their kinase activity towards the downstream substrate I kappa B alpha. Finally, we showed that pD345L-mediated inhibition of NF-kappa B signalling was independent of its exonuclease activity. Considering these results collectively, we concluded that pD345L blocks IKK alpha/beta kinase activity via protein-protein interactions and thus disrupts cGAS/STING-mediated NF-kappa B signalling.

Automated summary

The ASFV-encoded lambda-like exonuclease pD345L acts as an inhibitor of cGAS/STING-mediated NF-kappa B signaling by blocking the IKK alpha/beta activity. It disrupts the activation of IFN beta and proinflammatory cytokines, leading to the inhibition of NF-kappa B signaling.