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


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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    • "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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    ABSTRACT: The p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinases (MAPKs) play important roles in the host innate immune response. The protein kinase regulated by RNA (PKR) is implicated in p38 MAPK activation in response to proinflammatory signals in mouse embryonic fibroblasts. To test the role of PKR in the activation of p38 and JNK MAPKs in human cells following viral infection, HeLa cells made stably deficient in PKR by using an RNA interference strategy were compared to cells with sufficient PKR. The phosphorylation of both p38 and JNK in cells with sufficient PKR was activated following either infection with an E3L deletion (DeltaE3L) mutant of vaccinia virus or transfection with double-stranded RNA (dsRNA) in the absence of infection with wild-type vaccinia virus. The depletion of PKR by stable knockdown impaired the phosphorylation of both p38 and JNK induced by either the DeltaE3L mutant virus or dsRNA but not that induced by tumor necrosis factor alpha. The PKR-dependent activation of MAPKs in DeltaE3L mutant-infected cells was abolished by treatment with cytosine beta-d-arabinoside. The complementation of PKR-deficient cells with the human PKR wild-type protein, but not with the PKR catalytic mutant (K296R) protein, restored p38 and JNK phosphorylation following DeltaE3L mutant virus infection. Transient small interfering RNA knockdown established that the p38 and JNK kinase activation following DeltaE3L infection was dependent upon RIG-I-like receptor signal transduction pathway components, including the mitochondrial adapter IPS-1 protein.
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