Article

Vaccinia Virus Subverts a Mitochondrial Antiviral Signaling Protein-Dependent Innate Immune Response in Keratinocytes through Its Double-Stranded RNA Binding Protein, E3

Department of Medicine, Dermatology Service, Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Journal of Virology (Impact Factor: 4.44). 09/2008; 82(21):10735-46. DOI: 10.1128/JVI.01305-08
Source: PubMed
ABSTRACT
Skin keratinocytes provide a first line of defense against invading microorganisms in two ways: (i) by acting as a physical
barrier to pathogen entry and (ii) by initiating a vigorous innate immune response upon sensing danger signals. How keratinocytes
detect virus infections and generate antiviral immune responses is not well understood. Orthopoxviruses are dermatotropic
DNA viruses that cause lethal disease in humans. Virulence in animal models depends on the virus-encoded bifunctional Z-DNA/double-stranded
RNA (dsRNA)-binding protein E3. Here, we report that infection of mouse primary keratinocytes with a vaccinia ΔE3L mutant
virus triggers the production of beta interferon (IFN-β), interleukin-6 (IL-6), CCL4, and CCL5. None of these immune mediators
is produced by keratinocytes infected with wild-type vaccinia virus. The dsRNA-binding domain of E3 suffices to prevent activation
of the innate immune response. ΔE3L induction of IFN-β, IL-6, CCL4, and CCL5 secretion requires mitochondrial antiviral signaling
protein (MAVS; an adaptor for the cytoplasmic viral RNA sensors RIG-I and MDA5) and the transcription factor IRF3. IRF3 phosphorylation
is induced in keratinocytes infected with ΔE3L, an event that depends on MAVS. The response of keratinocytes to ΔE3L is unaffected
by genetic ablation of Toll-like receptor 3 (TLR3), TRIF, TLR9, and MyD88.

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    • "Alternatively, it may block the activation of its downstream effector(s). We have previously shown that E3 ZBD plays an inhibitory role in TLR9/MyD88/IRF7-mediated myxoma virussensing in pDCs [17], whereas E3 dsRBD attenuated the cytosolic dsRNA-sensing pathway mediated by MAVS/IRF3 [35]. It has been recently shown that ZBD of E3 antagonizes PKR in primary MEF [82]. "
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    • "Consistently, the attenuated phenotype of E3L-deleted virus following intratracheal infection of wild-type mice was partially reversed upon infection of mice lacking PKR (Rice et al. 2011). The fact that deletion of PKR does not fully rescue the pathogenicity of the E3L-deleted virus (Rice and Kerr 1984; Xiang et al. 2002) indicates that E3L likely targets other components of the cellular antiviral defense, such as the mitochondrial anti-viral signaling (MAVS) pathway for interferon induction (Deng et al. 2008 ). In support of this idea, the E3L-deleted virus was pathogenic in mice lacking both PKR and the anti-viral endoribonuclease RNAse L (Rice et al. 2011). "
    [Show abstract] [Hide abstract] ABSTRACT: Responding to viral infection, the interferon-induced, double-stranded RNA (dsRNA)-activated protein kinase PKR phosphorylates translation initiation factor eIF2α to inhibit cellular and viral protein synthesis. To overcome this host defense mechanism, many poxviruses express the protein E3L, containing an N-terminal Z-DNA binding (Zα) domain and a C-terminal dsRNA-binding domain (dsRBD). While E3L is thought to inhibit PKR activation by sequestering dsRNA activators and by directly binding the kinase, the role of the Zα domain in PKR inhibition remains unclear. Here, we show that the E3L Zα domain is required to suppress the growth-inhibitory properties associated with expression of human PKR in yeast, to inhibit PKR kinase activity in vitro, and to reverse the inhibitory effects of PKR on reporter gene expression in mammalian cells treated with dsRNA. Whereas previous studies revealed that the Z-DNA binding activity of E3L is critical for viral pathogenesis, we identified point mutations in E3L that functionally uncouple Z-DNA binding and PKR inhibition. Thus, our studies reveal a molecular distinction between the nucleic acid binding and PKR inhibitory functions of the E3L Zα domain, and they support the notion that E3L contributes to viral pathogenesis by targeting PKR and other components of the cellular anti-viral defense pathway.
    Preview · Article · Dec 2013 · RNA
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    • "In respect to pathogens, several viral components are known to regulate innate immunity. NS1 of the influenza A virus (7), E3 of the vaccinia virus (8), and VP39 of the ebola virus (9) bind to viral dsRNA and interfere the binding with TLR3. NS3-4A (10) of the hepatitis C virus inhibits TLR3 signaling by degrading Toll-interleukin 1 receptor domain-containing adapter inducing interferon-β (TRIF). "
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