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: 10.75). 08/2008; 27(15):2147-57. DOI: 10.1038/emboj.2008.143
Source: PubMed

ABSTRACT 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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    Cytokine 09/2012; 59(3):560-561. DOI:10.1016/j.cyto.2012.06.221 · 2.87 Impact Factor
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    ABSTRACT: Tyrosine phosphorylation is a hallmark for activation of Signal Transducer and Activator of Transcription (STAT) proteins, but their transcriptional activity also depends on other secondary modifications. Type I interferons (IFNs) can activate both the ISGF3 (STAT1:STAT2:IRF9) complex and STAT3, but with cell-specific, selective triggering of only the ISGF3 transcriptional program.Methods Simultaneous treatment with IFNa2 and Trichostatin A, as well as combined HDAC1/HDAC2 silencing, restores STAT3-dependent reporter gene and endogenous genes expression, strongly suggesting that HDAC1 and HDAC2 are directly involved in repressing IFNa-activated STAT3. We used the IFN-dependent STAT3 transcriptional blockade as read-out for a genome-wide RNAi repressor screen.ResultsQuite significantly, we identified multiple partners of the Sin3a/HDAC transcriptional repressor complex as negative regulators of STAT3 transcriptional activity, regardless to the STAT3 activating stimulus. Sin3a directly interacts with STAT3 and controls its acetylation status, its nuclear accumulation and DNA binding, strongly influencing the transcription of a subset of STAT3-responsive genes. Conversely, Sin3a is required for ISGF3-dependent gene transcription and for an efficient IFN-mediated antiviral protection against influenza A and hepatitis C viruses.Conclusion The Sin3a complex therefore acts as a context-dependent ISGF3/STAT3 transcriptional switch.
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