HEV ORF3 downregulates TLR7 to inhibit the generation of type I interferon via impairment of multiple signaling pathways

Abstract

Hepatitis E is the most common type of acute hepatitis prevalent worldwide. The open reading frame 3 protein of HEV (HEV ORF3) is proposed to create a favorable environment for viral replication and pathogenesis. However, the mechanisms by which HEV overcomes the effects of host immunity, particularly the role of ORF3, remain to be established. Expression of IFNα and IFNβ in supernatant and cell samples was examined via ELISA and quantitative RT-PCR. The protein levels of specific signaling factors in cells overexpressing HEV ORF3 were examined via western blot. Analyses of cells transfected with vectors expressing ORF3 demonstrated that HEV ORF3 significantly impairs the generation of endogenous type I interferon through downregulating TLR3 and TLR7 as well as their corresponding downstream signaling pathways. Moreover, inhibition of NFκB, JAK/STAT and JNK/MAPK signaling pathways contributed significantly to suppression of increased levels of TLR7. Levels of p-P65, p-STAT1 and p-JNK were markedly impaired in ORF3-expressing cells, even upon treatment with the respective agonists. HEV ORF3 inhibits the production of endogenous type I interferon through downregulation of TLR3 and TLR7. Furthermore, suppression of TLR7 is achieved through impairment of multiple signaling pathways, including NFκB, JAK/STAT and JNK/MAPK.

Deep Insight Into Long Non-Coding RNA and mRNA Transcriptome Profiling in HepG2 Cells Expressing Genotype IV Swine Hepatitis E Virus ORF3

“…Signal transducer and activator of transcription 3 (STAT3) expression can also be regulated, leading to a signi cant reduction of the in ammatory response. These ndings might provide strong support for the effect of ORF3 on virus replication [37][38][39][40]. Taken together, several functions of the ORF3 protein have already been reported.…”

Hepatitis E Virus: How It Escapes Host Innate Immunity

“…The ORF3 of HEV1-Sar55 inhibits the production of type I IFNs in human monocytic THP1 and human hepatic Lo2 cells by inhibiting TLR3 and TLR7 expression [ 97 ]. Another group has reported that HEV1–Sar55 ORF3 inhibits the TLR3-mediated NF-κB activity in A549 cells [ 96 ].…”

The Interplay between Host Innate Immunity and Hepatitis E Virus

“…ORF3 as a multifunctional protein has been proposed to create a favorable environment for HEV infection and pathogenesis [99,100,101]. In respect to the regulatory effects on innate immunity, it has been shown to inhibit STAT1 phosphorylation and ISG expression upon HEV infection (Figure 1) [102].…”

“…ORF3 of genotype 1 has been reported to downregulate the expression of tumor necrosis factor receptor 1-associated death domain protein (TRADD) and receptor-interacting protein kinase 1 (RIP1), thus inhibiting TLR3 mediated activation of NF-κB upon poly (I:C) treatment [103]. In line with this, ORF3 inhibits the expression of endogenous IFNα/β through inhibiting the expression of TLR3 and TLR7 [99]. ORF3 also inhibits LPS-induced cytokines and chemotactic factors [56].…”

“…ORF3 also inhibits LPS-induced cytokines and chemotactic factors [56]. It has been further demonstrated that ORF3 inhibits the activation of NF-κB JAK-STAT and JNK-MAPK pathways induced by TNFα, IFN-γ, and Anisomycin, respectively [99]. Counterintuitively, another study has demonstrated that ORF3 enhances IFN production upon poly (I:C) treatment through increased activation of RIG-I in a genotype-dependent manner [22].…”