Viral targeting of DEAD box protein 3 reveals its role in TBK1/IKKepsilon-mediated IRF activation

Viral Immune Evasion Group, School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland.
The EMBO Journal (Impact Factor: 10.43). 08/2008; 27(15):2147-57. DOI: 10.1038/emboj.2008.143
Source: PubMed


Viruses are detected by different classes of pattern recognition receptors (PRRs), such as Toll-like receptors and RIG-like helicases. Engagement of PRRs leads to activation of interferon (IFN)-regulatory factor 3 (IRF3) and IRF7 through IKKepsilon and TBK1 and consequently IFN-beta induction. Vaccinia virus (VACV) encodes proteins that manipulate host signalling, sometimes by targeting uncharacterised proteins. Here, we describe a novel VACV protein, K7, which can inhibit PRR-induced IFN-beta induction by preventing TBK1/IKKepsilon-mediated IRF activation. We identified DEAD box protein 3 (DDX3) as a host target of K7. Expression of DDX3 enhanced Ifnb promoter induction by TBK1/IKKepsilon, whereas knockdown of DDX3 inhibited this, and virus- or dsRNA-induced IRF3 activation. Further, dominant-negative DDX3 inhibited virus-, dsRNA- and cytosolic DNA-stimulated Ccl5 promoter induction, which is also TBK1/IKKepsilon dependent. Both K7 binding and enhancement of Ifnb induction mapped to the N-terminus of DDX3. Furthermore, virus infection induced an association between DDX3 and IKKepsilon. Therefore, this study shows for the first time the involvement of a DEAD box helicase in TBK1/IKKepsilon-mediated IRF activation and Ifnb promoter induction.

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Available from: Martina Schroeder
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    • "Approximately 60 genes encode DDX helicases in the human genome. Bowie and colleagues first reported that a member of the DDX superfamily is involved in RIG-I signaling (Schrö der et al., 2008; Soulat et al., 2008). Subsequently, other studies have shown that DDX superfamily members such as DDX3, DHX29, DHX36, and DDX60 are involved in RIG-I-dependent type I IFN production in response to viral RNA and DNA (Desmet and Ishii, 2012; Sugimoto et al., 2014; Yoo et al., 2014). "
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    ABSTRACT: RIG-I-mediated type I interferon (IFN) production and nuclease-mediated viral RNA degradation are essential for antiviral innate immune responses. DDX60 is an IFN-inducible cytoplasmic helicase. Here, we report that DDX60 is a sentinel for both RIG-I activation and viral RNA degradation. We show that DDX60 is an upstream factor of RIG-I that activates RIG-I signaling in a ligand-specific manner. DDX60 knockout attenuates RIG-I signaling and significantly reduces virus-induced type I IFN production in vivo. In addition, we show that DDX60 is involved in RIG-I-independent viral RNA degradation. DDX60 and RIG-I adaptor MAVS double-knockout mice reveal a role for DDX60-dependent RNA degradation in antiviral responses. Several viruses induced DDX60 phosphorylation via epidermal growth factor receptor (EGFR), leading to attenuation of the DDX60 antiviral activities. Our results define DDX60 as a sentinel for cytoplasmic antiviral response, which is counteracted by virus-mediated EGF receptor activation. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
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    • "Several DDX proteins have been implicated in innate immunity in which they function either RNA sensors such as RIG-I (retinoic acidinduce gene-I) and MDA5 (melanoma differentiation associated gene 5) or signaling molecules such as DDX3 [17] [22]. RIG-I-like receptors (RLRs), including RIG-I, MDA5 and LGP2 (laboratory of genetics and physiology 2/DExH box polypeptide 58), belong to a class of PRRs for viral PAMPs (pathogen-associated molecular patterns ) in the cytoplasm. "
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    ABSTRACT: DDX41, a receptor belonging to the DExD family, functions as a DNA sensor in the mammalian cytoplasm and mediates the antiviral response in host cells. Here, the olive flounder DDX41 was found to have 2267-bp long and encodes a putative protein of 614 amino acid residues. The olive flounder DDX41 mRNA was presented in all tested tissues, and was distinctly expressed in fish naturally infected with LCDV. High expression levels were observed in the heart, liver, kidney and stomach. Furthermore, the olive flounder DDX41 mRNA expression increased significantly in adherent (monocyte-like) cells following stimulation with a DNA virus. Reporter assays showed that the transcriptional activity of the IFN-I promoter was enhanced in DDX41-overexpressing HINAE cells treated with C-di-GMP (dinucleotides). Overexpression of DDX41 also induced the antiviral and inflammatory cytokine gene expression through cytoplasmic C-di-GMP treatment. These results suggest that DDX41 functions as a cytosolic DNA sensor that is capable of inducing antiviral activity and inflammatory responses in the olive flounder. Copyright © 2015. Published by Elsevier Ltd.
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    • "Cells were stained with DAPI to visualize nuclei and the DNA-rich virus factories surrounding the nucleus, indicating infected cells. Staining with an antibody to NFκB p65 revealed that p65 was dispersed throughout the cytoplasm in mock-infected cells (Fig. 7A, panels a–c), whereas mock-infected cells treated with TNFα displayed dramatic accumulation of p65 in the nucleus (Fig. 7A, panels d–f) (Salminen et al., 2008; Schroder et al., 2008). In contrast, cells infected with ECTV displayed cytoplasmic retention of p65 following stimulation (Fig. 7A, panels g–i). "
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