Porcine reproductive and respiratory syndrome virus nonstructural protein 4 antagonizes beta interferon expression by targeting the NF-κB essential modulator

• Published in: Journal of virology Vol. 88; no. 18; pp. 10934 - 10945
• Main Authors: Huang, Chen, Zhang, Qiong, Guo, Xue-kun, Yu, Zhi-bin, Xu, Ao-tian, Tang, Jun, Feng, Wen-hai
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.09.2014
• Subjects: Animals; Down-Regulation; Host-Pathogen Interactions; Interferon-beta - genetics; Interferon-beta - metabolism; Intracellular Signaling Peptides and Proteins - antagonists & inhibitors; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Macrophages - metabolism; Macrophages - virology; NF-kappa B - genetics; NF-kappa B - metabolism; Porcine Reproductive and Respiratory Syndrome - genetics; Porcine Reproductive and Respiratory Syndrome - metabolism; Porcine Reproductive and Respiratory Syndrome - virology; Porcine respiratory and reproductive syndrome virus; Porcine respiratory and reproductive syndrome virus - genetics; Porcine respiratory and reproductive syndrome virus - metabolism; Signal Transduction; Swine; Viral Nonstructural Proteins - genetics; Viral Nonstructural Proteins - metabolism; Virus-Cell Interactions
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/JVI.01396-14

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly infectious pathogen that causes severe diseases in pigs and great economic losses to the swine industry worldwide. Type I interferons (IFNs) play a crucial role in antiviral immunity. In the present study, we demonstrated that infection with the highly pathogenic PRRSV strain JXwn06 antagonized type I IFN expression induced by poly(I·C) in both porcine alveolar macrophages (PAMs) and blood monocyte-derived macrophages (BMo). Subsequently, we showed that the inhibition of poly(I·C)-induced IFN-β production by PRRSV was dependent on the blocking of NF-κB signaling pathways. By screening PRRSV nonstructural and structural proteins, we demonstrated that nonstructural protein 4 (nsp4), a viral 3C-like serine protease, significantly suppressed IFN-β expression. Moreover, we verified that nsp4 inhibited NF-κB activation induced by signaling molecules, including RIG-I, VISA, TRIF, and IKKβ. nsp4 was shown to target the NF-κB essential modulator (NEMO) at the E349-S350 site to mediate its cleavage. Importantly, nsp4 mutants with defective protease activity abolished its ability to cleave NEMO and inhibit IFN-β production. These findings might have implications for our understanding of PRRSV pathogenesis and its mechanisms for evading the host immune response. Porcine reproductive and respiratory syndrome virus (PRRSV) is a major agent of respiratory diseases in pigs. Like many other viruses, PRRSV has evolved a variety of strategies to evade host antiviral innate immunity for survival and propagation. In this study, we show that PRRSV nsp4 is a novel antagonist of the NF-κB signaling pathway, which is responsible for regulating the expression of type I interferons and other crucial cytokines. We then investigated the underlying mechanism used by nsp4 to suppress NF-κB-mediated IFN-β production. We found that nsp4 interfered with the NF-κB signaling pathway through the cleavage of NEMO (a key regulator of NF-κB signaling) at the E349-S350 site, leading to the downregulation of IFN-β production induced by poly(I·C). The data presented here may help us to better understand PRRSV pathogenesis.