Feline calicivirus strain 2280 p30 antagonizes type I interferon-mediated antiviral innate immunity through directly degrading IFNAR1 mRNA.

Jin Tian,Yudi Pan,Hongtao Kang,Zhijie Li,Jiapei Huang,Jikai Zhang,Hang Yin,Yin Li,Liandong Qu,Si Chen,Christiane E Wobus

doi:10.1371/journal.ppat.1008944

Abstract

Feline calicivirus (FCV) belongs to the Caliciviridae, which comprises small RNA viruses of both medical and veterinary importance. Once infection has occurred, FCV can persist in the cat population, but the molecular mechanism of how it escapes the innate immune response is still unknown. In this study, we found FCV strain 2280 to be relatively resistant to treatment with IFN-β. FCV 2280 infection inhibited IFN-induced activation of the ISRE (Interferon-stimulated response element) promoter and transcription of ISGs (Interferon-stimulated genes). The mechanistic analysis showed that the expression of IFNAR1, but not IFNAR2, was markedly reduced in FCV 2280-infected cells by inducing the degradation of IFNAR1 mRNA, which inhibited the phosphorylation of downstream adaptors. Further, overexpression of the FCV 2280 nonstructural protein p30, but not p30 of the attenuated strain F9, downregulated the expression of IFNAR1 mRNA. His-p30 fusion proteins were produced in Escherichia coli and purified, and an in vitro digestion assay was performed. The results showed that 2280 His-p30 could directly degrade IFNAR1 RNA but not IFNAR2 RNA. Moreover, the 5’UTR of IFNAR1 mRNA renders it directly susceptible to cleavage by 2280 p30. Next, we constructed two chimeric viruses: rFCV 2280-F9 p30 and rFCV F9-2280 p30. Compared to infection with the parental virus, rFCV 2280-F9 p30 infection displayed attenuated activities in reducing the level of IFNAR1 and inhibiting the phosphorylation of STAT1 and STAT2, whereas rFCV F9-2280 p30 displayed enhanced activities. Animal experiments showed that the virulence of rFCV 2280-F9 p30 infection was attenuated but that the virulence of rFCV F9-2280 p30 was increased compared to that of the parental viruses. Collectively, these data show that FCV 2280 p30 could directly and selectively degrade IFNAR1 mRNA, thus blocking the type I interferon-induced activation of the JAK-STAT signalling pathway, which may contribute to the pathogenesis of FCV infection.

Highlights

Feline calicivirus (FCV) is a non-enveloped RNA virus with a single-stranded positive-sense RNA genome approximately 7.5 kb in size, which is enclosed in an icosahedral capsid with a diameter of 27–40 nm [1, 2]
Our findings reveal a new mechanism evolved by FCV to circumvent the host antiviral response
We performed an RNA-seq assay on the FCV strain 2280 infection at 12 hpi and found that infection led to the downregulated expression of interferon receptor 1 (IFNAR1) (S1 Table), suggesting that FCV 2280 is able to evade the host antiviral response

Summary

Introduction

Feline calicivirus (FCV) is a non-enveloped RNA virus with a single-stranded positive-sense RNA genome approximately 7.5 kb in size, which is enclosed in an icosahedral capsid with a diameter of 27–40 nm [1, 2]. Due to the technical limitations of these experimental systems, no perfect animal model is widely available for the research of virus biology [11]; zebrafish larvae support the replication of HuNoV and may function as a good model to evaluate antiviral reagents [12]. This problem severely hinders the investigation of the calicivirus life cycle, and the function of some viral proteins is not well-known [13]. Murine norovirus (MNV) (genus Norovirus) and FCV have been used as excellent models to explore the calicivirus biology due to their culturability and the availability of mature animal models for virus pathogenesis [14, 15]

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Results

Discussion

Conclusion