Vaccinia virus protein A52R activates p38 mitogen-activated protein kinase and potentiates lipopolysaccharide-induced interleukin-10.
ABSTRACT Vaccinia virus (VV) has many mechanisms to suppress and modulate the host immune response. The VV protein A52R was previously shown to act as an intracellular inhibitor of nuclear factor kappaB (NFkappaB) signaling by Toll-like receptors (TLRs). Co-immunoprecipitation studies revealed that A52R interacted with both tumor necrosis factor receptor-associated factor 6 (TRAF6) and interleukin-1 receptor-associated kinase 2 (IRAK2). The effect of A52R on signals other than NFkappaB was not determined. Here, we show that A52R does not inhibit TLR-induced p38 or c-Jun amino N-terminal kinase (JNK) mitogen activating protein (MAP) kinase activation. Rather, A52R could drive activation of these kinases. Two lines of evidence suggested that the A52R/TRAF6 interaction was critical for these effects. First, A52R-induced p38 MAP kinase activation was inhibited by overexpression of the TRAF domain of TRAF6, which sequestered A52R and inhibited its interaction with endogenous TRAF6. Second, a truncated version of A52R, which interacted with IRAK2 and not TRAF6, was unable to activate p38. Because interleukin 10 (IL-10) production is strongly p38-dependent, we examined the effect of A52R on IL-10 gene induction. A52R was found to be capable of inducing the IL-10 promoter through a TRAF6-dependent mechanism. Furthermore, A52R enhanced lipopolysaccharide/TLR4-induced IL-10 production, while inhibiting the TLR-induced NFkappaB-dependent genes IL-8 and RANTES. These results show that although A52R inhibits NFkappaB activation by multiple TLRs it can simultaneously activate MAP kinases. A52R-mediated enhancement of TLR-induced IL-10 may be important to virulence, given the role of IL-10 in immunoregulation.
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ABSTRACT: Poxviruses have evolved numerous mechanisms to evade host innate immunity. Sensory pathways that are activated by Toll-like and nucleotide receptors, as well as innate cell death pathways, are both targets of antagonism by viral proteins. Recent structural, biochemical and functional studies of poxvirus proteins have identified a family of α-helical proteins that adopt a Bcl-2 fold despite highly divergent polypeptide sequences from cellular proteins that regulate apoptosis. These newly identified proteins have assumed new roles in antagonism of NF-κB and interferon signaling pathways and interfere with the release of pro-inflammatory cytokines. Structures of isolated viral proteins and their complexes with cellular targets provide insight into the diverse ways that the Bcl-2 scaffold can be exploited for antagonism of host immunity.Journal of Structural Biology 11/2012; 181(1). DOI:10.1016/j.jsb.2012.10.015 · 3.37 Impact Factor
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ABSTRACT: Poxviruses are DNA viruses that express numerous proteins to subvert the host immune response. Vaccinia virus protein K7 adopts a Bcl-2 fold and displays structural and functional similarities to Toll-like receptor antagonist A52. Both proteins interact with IRAK2 and TRAF6 and suppress TLR-dependent NF-kappaB activation. However, unlike A52, K7 also forms a complex with RNA helicase DDX3 and antagonizes interferon-beta promoter induction. We have narrowed the K7 binding site to an N-terminal peptide motif of DDX3 ahead of its core RNA-helicase domains. The crystal structure of full-length K7 in complex with the DDX3 peptide reveals a thumblike projection of tandem phenalyalanine residues of DDX3 into a deep hydrophobic cleft. Mutagenesis of these phenylalanines abolishes the effects of DDX3 on interferon-beta promoter induction. The structure of K7-DDX3 reveals a novel binding mode by a viral Bcl-2 protein that antagonizes a key pathway in innate immunity.Structure 11/2009; 17(11):1528-37. DOI:10.1016/j.str.2009.09.005 · 6.79 Impact Factor
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ABSTRACT: Vaccinia virus (VACV), a prototype member of the poxvirus family, has been used from the early times after interferons (IFN) were discovered, as a model virus cell system to analyze the mode of action of IFN. This large DNA-containing virus (around 200 kb) replicates entirely in the cytoplasm of the cell, taking rapidly over the host cell machinery for virus multiplication. In the presence of IFN, this virus exhibits sensitivity or resistance depending on the virus-host model. With the discovery of IFN-induced enzymes, the sensitivity of VACV to IFN was correlated with dsRNA activation of the protein kinase PKR and 2'-5'-OAS/RNaseL systems leading to a translational block by the phosphorylation of the eIF2 alpha factor and RNA breakdown. Following sequencing of the VACV genome and generation of deletion mutants, the resistance phenomenon to IFN was shown to be exerted through inhibition of multiple pathways. This review analyzes current knowledge on the VACV genes encoding proteins acting as decoy receptors to block the activity of type I and type II IFNs, targeting cytokines and chemokines, and antagonizing intracellular signaling pathways (pattern recognition receptors [PRRs] signaling). The molecular dissection of how VACV prevents the IFN response is providing important insights on our understanding of antiviral action and immune surveillance.Journal of interferon & cytokine research: the official journal of the International Society for Interferon and Cytokine Research 09/2009; 29(9):581-98. DOI:10.1089/jir.2009.0073 · 3.90 Impact Factor