The mengovirus leader protein blocks interferon-α/β gene transcription and inhibits activation of interferon regulatory factor 3

Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen Centre for Molecular Life Sciences, Nijmegen, The Netherlands.
Cellular Microbiology (Impact Factor: 4.92). 01/2008; 9(12):2921-30. DOI: 10.1111/j.1462-5822.2007.01006.x
Source: PubMed


Viral infection of mammalian cells triggers the synthesis and secretion of type I interferons (i.e. IFN-alpha/beta), which induce the transcription of genes that cause cells to adopt an antiviral state. Many viruses have adapted mechanisms to evade IFN-alpha/beta-mediated responses. The leader protein of mengovirus, a picornavirus, has been implicated as an IFN-alpha/beta antagonist. Here, we show that the leader inhibits the transcription of IFN-alpha/beta and that both the presence of a zinc finger motif in its N-terminus and phosphorylation of threonine-47 are required for this function. Transcription of IFN-alpha/beta genes relies on the activity of a number of transcription factors, including interferon regulatory factor 3 (IRF-3). We show that the leader interferes with the transactivation activity of IRF-3 by interfering with its dimerization. Accordingly, mutant viruses with a disturbed leader function were impaired in their ability to suppress IFN-alpha/beta transcription in vivo. By consequence, the leader mutant viruses had an impaired ability to replicate and spread in normal mice but not in IFNAR-KO mice, which are incapable of mounting an IFN-alpha/beta-dependent antiviral response. These results suggest that the leader, by suppressing IRF3-mediated IFN-alpha/beta production, plays an important role in replication and dissemination of mengovirus in its host.

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Available from: Kjerstin H W Lanke, Jun 11, 2015
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    • "Upon infection with WT EMCV, induction of Ifit1 and Ifnb1 was limited (Figure 6A,B). It was markedly greater in response to infection with EMCV Zn C19AC22A , which encodes the non-functional mutant L protein (Figure 6A,B), consistent with the fact that the L protein inhibits IFN induction (Hato et al., 2007). In contrast, infection with EMCVΔL lacking both L protein and EMCV L region RNA induced lower levels of Ifnb1 or Ifit1 than infection with EMCV Zn C19AC22A at two different multiplicities of infection (MOI) (Figure 6A,B). "
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    • "Figure 1A shows IFN-b responses in WT and knockout MEFs triggered by transfection of vRNA of WT mengovirus (a strain of EMCV) or infection of a mutant mengovirus (mengo-Zn). This virus generates high levels of IFN-b because its IFN antagonist has been compromised (Hato et al., 2007). Both methods resulted in a MDA5- and MAVS-dependent, but RIG-I-independent, IFN-b induction, demonstrating the suitability of the transfection method to identify the RLR(s) responsible for detecting picornaviruses. "
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    • "RNA was treated with DNase I prior to reverse transcription and amplification by PCR. Primer sequences have been described (Hato et al., 2007). "
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    ABSTRACT: Picornaviruses encompass a large family of RNA viruses. Some picornaviruses possess a leader (L) protein at the N-terminus of their polyprotein. The L proteins of encephalomyocarditis virus, a cardiovirus, and foot-and-mouth disease virus (FMDV), an aphthovirus, are both dispensable for replication and their major function seems to be the suppression of antiviral host cell responses. Previously, we showed that the L protein of mengovirus, a strain of encephalomyocarditis virus, inhibits antiviral responses by inhibiting type I interferon (IFN-alpha/beta) gene transcription. The L protein of the FMDV is a protease (L(pro)) that cleaves cellular factors to reduce cytokine and chemokine mRNA production and to inhibit cap-dependent cellular host mRNA translation, thereby limiting the production of proteins with antiviral activity. In this study, we constructed a viable chimeric mengovirus that expresses FMDV L(pro) in place of the authentic L protein in order to compare the efficiency of the immune evasion mechanisms mediated by L and L(pro) respectively. We show that in this mengovirus background the L protein is more potent than FMDV L(pro) in suppressing IFN-alpha/beta responses. Yet, FMDV L(pro) is important to antagonize infection-limiting responses both in vitro and in vivo.
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