Porcine reproductive and respiratory syndrome virus infection inhibits NF-κB signaling pathway through cleavage of IKKβ by Nsp4

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly contagious porcine pathogen that causes serious economic losses to the world swine industry. The inhibitor kappa B kinase β (IKKβ), a catalytic subunit of the IKK complex, plays multiple roles in regulating the nuclear transcription factor kappa B (NF-κB) activity and a variety of cytokines transcription involved in immune responses. Here, we reported that the nonstructural protein 4 (Nsp4) of PRRSV cleaved IKKβ at the E378 site to inhibit the activation of NF-κB signaling pathway. Additionally, we clearly showed that cleavage of IKKβ by PRRSV Nsp4 depends on the 3 C-like serine protease activity of Nsp4 because the catalytically inactivate mutants of Nsp4 lost the function to cleave IKKβ. Furthermore, we found that hydrophobic patch at the KD-ULD junction of IKKβ could be disrupted by PRRSV Nsp4 via the cleavage of the E378 site, resulting in disruption of NF-κB activity. Of note, the two cleavage fragments of IKKβ lose their function to phosphorylate IκBα and activate NF-κB signaling pathway. Our findings provide a clue to better understand the pathogenic mechanism of PRRSV involved in PRRSV evasion of host Antiviral innate immune responses.