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ASFV pD345L protein negatively regulates NF-κB signalling by inhibiting IKK kinase activity
Huan Chen1, Zhenzhong Wang1,2, Xiaoyu Gao1
1MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, China.
Abstract:
The NF-κB 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-κB signalling by blocking the IkappaB kinase (IKKα/β) activity. Specifically, we showed that overexpression of pD345L suppresses cGAS/STING-induced IFNβ and NF-κB activation, resulting in decreased transcription of IFNβ and several proinflammatory cytokines, including IL-1α, IL-6, IL-8, and TNFα. 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 IKKα and the LZ domain of IKKβ and thus interrupts their kinase activity towards the downstream substrate IκBα. Finally, we showed that pD345L-mediated inhibition of NF-κB signalling was independent of its exonuclease activity. Considering these results collectively, we concluded that pD345L blocks IKKα/β kinase activity via protein-protein interactions and thus disrupts cGAS/STING-mediated NF-κB signalling.
Insights
African swine fever virus (ASFV) protein pD345L inhibits the cGAS/STING pathway by blocking IKKα/β kinase activity. This viral protein disrupts innate immune responses, aiding ASFV infection.
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- The NF-κB pathway is crucial for antiviral defense against viruses like African swine fever virus (ASFV).
- ASFV possesses numerous proteins that can evade host innate immune responses, with many viral proteins remaining uncharacterized.
Purpose of the Study:
- To identify novel ASFV proteins involved in subverting host antiviral signaling.
- To elucidate the mechanism by which ASFV protein pD345L interferes with the cGAS/STING-mediated NF-κB pathway.
Main Methods:
- Overexpression of ASFV pD345L in cells.
- Analysis of IFNβ and NF-κB activation using reporter assays.
- Western blotting to assess protein interactions and phosphorylation.
- Site-directed mutagenesis to investigate the role of exonuclease activity.
Main Results:
- ASFV pD345L suppresses cGAS/STING-induced IFNβ and NF-κB activation.
- pD345L inhibits IκB kinase (IKKα/β) activity, acting downstream of IKK and upstream of p65.
- pD345L directly binds to IKKα and IKKβ, disrupting their kinase function.
- The inhibitory effect of pD345L on NF-κB signaling is independent of its exonuclease activity.
Conclusions:
- ASFV protein pD345L is a novel inhibitor of cGAS/STING-mediated NF-κB signaling.
- pD345L blocks IKKα/β kinase activity through protein-protein interactions, thereby dampening the innate immune response.
- This viral mechanism contributes to ASFV's ability to evade host defenses.
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