Juang Y T, Lowther W, Kellum M, Au W C, Lin R, Hiscott J, Pitha P M
Oncology Center, The Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
Proc Natl Acad Sci U S A. 1998 Aug 18;95(17):9837-42. doi: 10.1073/pnas.95.17.9837.
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.
干扰素（IFN）调节因子（IRF）家族编码DNA结合转录因子，其中一些作为病毒诱导信号的调节因子发挥作用。IRF-3基因在许多组织和细胞类型中组成性表达，病毒感染和IFN处理均不会增强其转录。然而，在受感染的细胞中，IRF-3蛋白在羧基末端被磷酸化，这有利于其与CBP/p300共激活因子结合。在本研究中，我们证明IRF-3的过表达显著增强了受感染细胞中病毒介导的IFNA和IFNB基因的转录以及IFN的合成。IRF-3介导的IFN基因激活部分取决于一组Ser/Thr残基的羧基末端磷酸化，因为Ser/Thr被Ala取代的突变体激活IFN启动子的效率较低。然而，单独在人2FTGH细胞中过表达IRF-3会诱导抗病毒状态，这取决于功能性IFN信号传导，因为IRF-3在JAK-1或p48功能缺陷的突变2FTGH细胞中不会诱导抗病毒状态；在缺乏IFNA和IFNB基因的Vero细胞中也未证明IRF-3具有抗病毒作用。这一发现表明，在2FTGH细胞中观察到的IRF-3的抗病毒活性主要源于IFN的诱导。此外，在瞬时表达试验中，E1A蛋白抑制了IRF-3介导地对IFNA4启动子的刺激；CBP/p300的过表达可部分逆转这种抑制作用，而不与p300结合的E1A突变体则未表现出这种抑制作用。这些结果确定IRF-3和CBP/p300是刺激1型IFN基因转录的病毒诱导复合物的组成成分。腺病毒E1A拮抗IRF-3介导的激活这一观察结果表明，E1A和IRF-3可能竞争与CBP/p300的结合，并暗示了腺病毒可能克服IFN途径抗病毒作用的一种新机制。
