PEDV nsp16 negatively regulates innate immunity to promote viral proliferation

Abstract

Type-I IFNs (IFN-I) provide a key mediator of innate antiviral response during virus proliferation. Porcine epidemic diarrhea virus (PEDV), which causes diarrhea in swine of all ages, is a worldwide-distributed alphacoronavirus with economic importance. Here, we screened PEDV RNA modification enzymes involved in regulating antiviral response. Whereas the PEDV nsp13 barely regulates type I IFN, inflammatory cytokines (IL-6, TNF-a) and MHCII, nsp16 and nsp14 (to a lesser extent) down-regulate these antiviral effectors. Importantly, we found nsp16 KDKE tetrad appears to play a key role in interferon inhibition by mutating the D129 catalytic residue. Mechanistically, nsp16 down-regulates the activities of RIG-I and MDA5 mediated IFN-β and ISRE. In turn, the mRNA levels of IFIT family members (IFIT1, IFIT2, IFIT3) was inhibited in cells overexpressing nsp16. In addition, nsp10 enhanced the inhibitory effect of nsp16 on IFN-β. Altogether these results indicate PEDV nsp16 negatively regulates innate immunity to promote viral proliferation. Findings from this study provides novel perspective to advance the understanding in the pathogenesis of PEDV.

Emerging coronaviruses: Genome structure, replication, and pathogenesis

“…Cofactor with nsp7 and nsp12, primase [28][29][30] nsp9 Dimerization and RNA binding 31,32 nsp10 Scaffold protein for nsp14 and nsp16 [33][34][35][36] nsp11 Unknown 37 nsp12 Primer dependent RdRp 28,38,39 nsp13 RNA helicase, 5′ triphosphatase [40][41][42] nsp14 Exoribonuclease, N7-MTase 12,[43][44][45] nsp15 Endoribonuclease, evasion of dsRNA sensors [46][47][48] nsp16 2′-O-MTase; avoiding MDA5 recognition, negatively regulating innate immunity 34,35,49 Abbreviations: 3CL pro , chymotrypsin-like protease; DMV, double-membrane vesicle; dsRNA, double-stranded RNA viruses; IFN, interferon; mRNA, messenger RNA; M pro , main protease.…”

Porcine Epidemic Diarrhea Virus and the Host Innate Immune Response

“…The biological processes involved References S (S1 and S2) receptor binding and subsequent membrane fusion; replication cycle and propagation; cell apoptosis induction [48][49][50]128 [112,[123][124][125][126]132]…”

“…The evasive strategies utilized by PEDV are classified into four major types: 1) inhibition of RLRs-mediated IFN production pathways, 2)inhibition of the activation of transcription factors responsible for IFN induction, 3) disruption of the signal cascades induced by IFN, and 4) hiding its viral RNA to avoid the exposure of viral RNA to immune sensors. In the past decade, accumulating evidence demonstrates that PEDV N protein, nsp1, PLP2, nsp5, nsp15, and nsp16 antagonize type I IFN or type III IFNs production [58,65,78,80,100,132,135,168]. This explains why only weak IFNs' and cytokines' expression is detected in PEDV-infected cells [169,170].…”

“…However, whether DMVs alone are sufficient to shield RNA from PRRs remains unknown. Besides, the replication organelles, the endoribonuclease activity and viral 5′ end RNA capping/protection mechanisms are also the critical ways of avoiding RNA recognition or protecting it from degradation [132,135].…”

“…For example, SARS-CoV nsp16 acts as a 2′-O-MTase to prevent innate immune recognition and promote viral proliferation [113,121,123]. PEDV nsp14 and nsp16 have been identified as the viral IFN antagonists [65,132]. The overexpression of nsp14 or nsp16 remarkably inhibits IFN-β production, but nsp16 appears to play a more important role in innate immunity regulation than nsp14 [132].…”