Porcine transmissible gastroenteritis virus inhibits NF-κB activity via nonstructural protein 3 to evade host immune system

Abstract

Background Transmissible gastroenteritis virus (TGEV), a member of the family Coronaviridae , causes lethal watery diarrhea in piglets. Previous studies have revealed that the coronaviruses develop various strategies to evade the host innate immunity through the inhibition of nuclear factor kappa B (NF-κB) signaling pathway. However, the ability of TGEV to inhibit the host innate immune response by modulating the NF-κB signaling pathway is not clear. Methods In this study, a dual luciferase reporter assay was used to confirm the inhibition of NF-κB by TGEV infection and to identify the major viral proteins involved in the inhibition of NF-κB signaling. Real-time quantitative PCR was used to quantify the mRNA expression of inflammatory factors. The deubiquitination of Nsp3 domains and its effect on IκBα and p65 were analyzed by western blotting. The ubiquitination level of IκBα was analyzed by immunoprecipitation. Results In ST and IPEC-J2 cells, TGEV exhibited a dose-dependent inhibition of NF-κB activity. Individual TGEV protein screening revealed the high potential of non-structural protein 3 (Nsp3) to inhibit NF-κB signaling, and leading to the downregulation of the NF-κB-induced cytokine production. We demonstrated that the inhibitory effect of Nsp3 was mainly mediated through the suppression of IκBα degradation as well as the inhibition of p65 phosphorylation and nuclear translocation. Furthermore, the amino acid residues at positions 590–1,215 in Nsp3 were demonstrated to inhibit the degradation of IκBα by inhibiting the IκBα ubiquitination. Conclusion TGEV infection can inhibit the activation of the NF-κB signaling pathway, which is mainly mediated by Nsp3 through the canonical pathway. The amino acid residues at positions 590–1,215 in Nsp3 compose the critical domain that mediates NF-κB inhibition. We speculate that this inhibitory effect is likely to be related to the structure of PLP2 with deubiquitinating enzyme activity of the amino acid residues at positions 590–1,215 in Nsp3. Our study provides a better understanding of the TGEV-mediated innate immune modulation and lays the basis for studies on the pathogenesis of coronavirus.

Antiviral activities of mycophenolic acid and IMD‐0354 against SARS‐CoV‐2

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A Comparative Transcriptomic Analysis Reveals That HSP90AB1 Is Involved in the Immune and Inflammatory Responses to Porcine Deltacoronavirus Infection

“…The MAPK and NF-κB signaling pathways are also important signaling pathways related to viral infections [ 48 , 49 ]. Accumulating evidence suggests that activation of the MAPK and NF-κB signaling pathways regulates proinflammatory cytokine production [ 50 , 51 ].…”

Role of intestinal extracellular matrix-related signaling in porcine epidemic diarrhea virus infection

“…Importantly, these viruses inhibit NF-κB activation in the early stage of infection. For example, TGEV and PEDV exhibit rapid replication with almost logarithmic growth from 6 hpi, whereas NF-κB is not activated until 24 hpi, by which time most of the host cells have already been infected [50,51]. Under such circumstances, the cytokines induced by NF-κB activation not only are unable to induce the antiviral response but also aggravate tissue damage, thereby facilitating viral spread at the site of infection.…”