【作者】 王健；

【导师】 耿运琪； 乔文涛；

【作者基本信息】 南开大学 ， 生物学， 2010， 博士

【摘要】 核因子KB,即NF-κB,是细胞中一类重要转录因子,在细胞生存、发育、分化以及免疫、炎症反应过程中参与基因的表达与调控。许多病毒也进化出相应的策略调节细胞的NF-κB信号通路,由此改变相关细胞事件,保证其完成生活周期。对相关现象及其中分子机制的解析是分子病毒学研究的重要内容。本文对牛泡沫病毒(BFV)与宿主NF-κB信号通路间关系展开研究,发现BFV感染宿主细胞后,可通过其正调控蛋白BTas激活细胞NF-κB信号通路；NF-κB通路的活化反过来又会增强BFV的转录,其中的Rel B作为BTas的转录辅因子完成正调控功能。这些发现为全面认识反转录病毒与细胞NF-κB信号通路之间的关系提供了重要证据。相关实验数据如下：使用NF-κB报告基因系统以及p65细胞定位分析,发现BFV可以通过其反式激活因子BTas激活NF-κB信号通路；竞争抑制实验发现IκBα和IKKβ参与BFV(BTas)激活NF-κB过程；使用IκBα磷酸化抗体检测发现BFV(BTas)能够在体内引起IκBα的磷酸化及后续降解。同时,我们还发现BTas除了能够通过经典途径(IκBα的降解以及p65入核)激活NF-κB信号通路之外,还能通过诱导p100的剪切激活NF-κB替代途径；免疫沉淀分析表明BTas能够与IKKa和IKKp在体内相互作用。这些结果支持BTas通过与IKK复合物的相互作用调节其活性,进而促进IκBα的磷酸化,最终激活NF-κB信号通路。此外,我们使用BFV LTR报告基因系统发现BTas介导的LTR转录受到细胞NF-κB的正调控。对病毒利用NF-κB信号通路促进自身复制相关分子机制的研究表明：BFV LTR没有功能性κB位点,表明细胞NF-κB效应分子不能直接活化BFV的转录。但我室前期酵母双杂交实验提示BTas与NF-κB家族的RelB蛋白可能存在着相互作用。本文通过体内、体外实验验证了两者的相互作用,两者的相互作用区域分别位于RelB的Rel同源域(RHD)以及BTas的C端一侧；过表达及RNA干扰实验证实RelB可以增强BTas介导的LTR转录,这一过程需要RelB与BTas在细胞核内的相互作用以及RelB的转录激活域(TAD)。进一步通过染色体免疫共沉淀实验和EMSA实验证明在BFV复制过程中,细胞内源的RelB蛋白可通过BTas介导间接结合在LTR之上,由此促进BFV的转录及复制。上述结果表明BFV在复制过程中利用宿主细胞RelB蛋白作为其反式激活因子BTas的辅助因子,增强病毒基因的转录并最终促进了病毒的复制。此外,我们还发现BFV (BTas)通过调节细胞NF-κB信号通路增加了细胞内RelB蛋白表达。综上所述,本文的研究结果部分阐明了BFV感染宿主细胞后两者之间形成的正反馈循环：BFV感染激活细胞NF-κB信号通路,细胞NF-κB的活化反过来又会通过上调RelB蛋白的表达增强BTas介导的BFV的转录,最终促进病毒的复制。更多还原

【Abstract】 In mammals, nuclear factor-KB (NF-κB) belongs to a family of transcription factors that plays a pivotal role in regulating the expression of various genes related to immune response, cell survival and development. Multiple families of viruses have evolved sophisticated strategies to regulate NF-κB signaling, which plays a pivotal role in diverse cellular events, including virus-host interactions. In this study, we found that bovine foamy virus (BFV) is able to activate the NF-κB pathway through the action of its transactivator, BTas through reporter gene analysis and p65 nuclear translocation assay. Subsequently, the Luc analysis using dominant negative mutation and WB assay using specific antibody against phosphorlated IκBαdemonstrate both cellular IKKβand IκBαalso participate in this activation. In addition, we found that BTas induces the processing of p100 by IFA and WB assay, which implies that BTas can activate NF-κB through a noncanonical pathway as well. Co-immunoprecipitation analysis shows that BTas interacts with IKK catalytic subunits (IKKαand IKKβ), which may be responsible for regulation of IKK kinase activity and persistent NF-κB activation. Furthermore, our results of Luc analysis indicate that the level of BTas-mediated LTR transcription correlates with the activity of cellular NF-κB. Together, these findings suggest that BFV activates the NF-κB pathway through BTas to enhance viral transcription.Although the activation of cellular NF-κB pathway can significantly enhance the BFV transcription (BTas-induced LTR transcription), our results also showed that BFV LTR lacks a functional KB-site. Thus, we speculated NF-κB might adopt a mechanism other than direct binding to the viral LTR to enhance BFV transcription. To address the mechanism of utilizing NF-κB pathway for BFV transcription, we employed a yeast two hybrid assay to screen the BTas interaction proteins. The result demonstrated that RelB, a member of NF-κB protein family, interacts with BTas. Subsequently, we confirmed the RelB/BTas interaction in vitro and in vivo using Co-IP, IFA and GST-pulldown assays, and identified the interaction domain located in the RHD of RelB and C-terminal half of BTas. Furthermore, we found that RelB is able to enhance the BFV transcription (BTas-induced LTR transactivation) through Luc analysis, and this process requires the RelB/BTas interaction in the nucleus. The further study demonstrated that RelB binds to the viral LTR during BFV replication using ChIP assay, and knockdown of cellular endogenous RelB is able to affect BFV transcription and replication. Together, these results suggest that BFV engages cellular RelB protein as a cotransactivator to enhance its transcription and replication; this process is mediated by binding of RelB to the LTR through interaction with the virally encoded protein, BTas. In addition, our findings reveal that BFV infection up-regulates cellular RelB expression through BTas-induced NF-κB activation. Collectively, we describe a positive virus-host feed-back circuit, in which BFV utilizes the host’s signaling pathway for its efficient replication.更多还原