Primary activation of interferon A and interferon B gene transcription by interferon regulatory factor 3.
The family of interferon (IFN) regulatory factors (IRFs) encodes DNA-binding transcription factors, some of which function as modulators of virus-induced signaling. The IRF-3 gene is constitutively expressed in many tissues and cell types, and neither virus infection nor IFN treatment enhances its transcription. In infected cells, however, IRF-3 protein is phosphorylated at the carboxyl terminus, which facilitates its binding to the CBP/p300 coactivator. In the present study, we demonstrate that overexpression of IRF-3 significantly enhances virus-mediated transcription of the IFNA and IFNB genes in infected cells as well as IFN synthesis. IRF-3-mediated activation of IFN genes depends in part on carboxyl-terminal phosphorylation of a cluster of Ser/Thr residues, because a mutant with Ser/Thr to Ala substitutions activates the IFN promoter less efficiently. However, overexpression of IRF-3 in human 2FTGH cells alone results in the induction of an antiviral state, which depends on functional IFN signaling, because IRF-3 does not induce an antiviral state in mutant 2FTGH cells defective in either JAK-1 or p48 functions; also no antiviral effect of IRF-3 could be demonstrated in Vero cells that lack the IFNA and IFNB genes. This finding indicates that the observed antiviral activity of IRF-3 in 2FTGH cells results mainly from the induction of IFNs. Furthermore, E1A protein inhibited IRF-3-mediated stimulation of the IFNA4 promoter in transient expression assays; this inhibition could be reversed partially by overexpression of CBP/p300 and was not demonstrated with the mutant of E1A that does not bind p300. These results identify IRF-3 and CBP/p300 as integral components of the virus-induced complex that stimulates type 1 IFN gene transcription. The observation that adenovirus E1A antagonizes IRF-3 mediated activation suggests that E1A and IRF-3 may compete for binding to CBP/p300 and implicates a novel mechanism by which adenovirus may overcome the antiviral effects of the IFN pathway.
Oncology Center, The Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
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Juang
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Lowther
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Kellum
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Lin
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Hiscott
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Pitha
D000256:Adenoviridae / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D017500:Adenovirus E1A Proteins / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D050882:CREB-Binding Protein; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D006801:Humans; D050838:Interferon Regulatory Factor-3; D007372:Interferons / Q000096:biosynthesis / Q000235:genetics*; D007739:L Cells; D051379:Mice; D009522:Newcastle disease virus / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051381:Rats; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation; D014709:Vero Cells; D014762:Viral Interference
D017500:Adenovirus E1A Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; C494233:Irf3 protein, mouse; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D007372:Interferons; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; C494364:Crebbp protein, mouse; C494365:Crebbp protein, rat