Down-Regulation of MHC Class II Expression through Inhibition of CIITA Transcription by Lytic Transactivator Zta during Epstein-Barr Virus Reactivation
Down-Regulation of MHC Class II Expression through Inhibition of CIITA Transcription by Lytic Transactivator Zta during Epstein-Barr Virus Reactivation
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DOI：
10.4049/jimmunol.0802686
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发表时间：
2009-02-15
影响因子：
4.4
通讯作者：
Guo, Ning
中科院分区：
文献类型：
--
作者：
Li, Dan;Qian, Lu;Guo, Ning
通过MHC II类分子将肽呈递给T细胞在免疫系统对病原体的特异性识别中至关重要。MHC Ⅱ类分子的水平直接影响T淋巴细胞的活化。本研究的目的是确定Zta在EBV裂解周期中下调MHC II类分子表达的可能机制。本研究的数据表明，Zta的异位表达可以强烈抑制Raji细胞中MHC II类和CIITA的组成性表达。还观察到Zta对CIITA启动子活性的负面影响。CIITA启动子III的DNA序列的仔细检查揭示了存在两个Zta响应元件（ZRE）基序，其与EBV的DR和左侧重复序列启动子中的ZRE具有完全同源性。通过染色质免疫沉淀测定，证实了Zta与CIITA启动子中的ZRE（221）的结合。ZRE（221）的三个保守核苷酸的定点诱变基本上破坏了Zta介导的CIITA启动子活性的抑制。寡核苷酸pull-down分析表明ZRE（221）突变显著地消除了Zta结合。对缺失DNA结合结构域的Zta突变体的分析表明，Zta的DNA结合活性是CIITA的性状阻遏所必需的。通过Zta基因沉默恢复HLA-DR α和CIITA的表达。这些数据表明，Zta可以作为MHC II类途径的抑制剂，抑制CIITA转录，从而干扰MHC II类分子的表达。免疫学杂志，2009，182：1799-1809.
The presentation of peptides to T cells by MHC class II molecules is of critical importance in specific recognition to a pathogen by the immune system. The level of MHC class II directly influences T lymphocyte activation. The aim of this study was to identify the possible mechanisms of the down-regulation of MHC class II expression by Zta during EBV lytic cycle. The data in the present study demonstrated that ectopic expression of Zta can strongly inhibit the constitutive expression of MHC class II and CIITA in Raji cells. The negative effect of Zta on the CIITA promoter activity was also observed. Scrutiny of the DNA sequence of CIITA promoter III revealed the presence of two Zta-response element (ZRE) motifs that have complete homology to ZREs in the DR and left-hand side duplicated sequence promoters of EBV. By chromatin immunoprecipitation assays, the binding of Zta to the ZRE(221) in the CIITA promoter was verified. Site-directed mutagenesis of three conserved nucleotides of the ZRE(221) substantially disrupted Zta-mediated inhibition of the CIITA promoter activity. Oligonucleotide pull-down assay showed that mutation of the ZRE(221) dramatically abolished Zta binding. Analysis of the Zta mutant lacking DNA binding domain revealed that the DNA-binding activity of Zta is required for the traits repression of CIITA. The expression of HLA-DR alpha and CIITA was restored by Zta gene silencing. The data indicate that Zta may act as an inhibitor of the MHC class II pathway, suppressing CIITA transcription and thus interfering with the expression of MHC class II molecules. The Journal of Immunology, 2009, 182: 1799-1809.