The role of TAX1BP1 in the innate immune response to virus infection

 描述（由申请方提供）：病毒感染诱导由感知病毒RNA的细胞质模式识别受体RIG-I和MDA-5介导的先天性抗病毒宿主应答。RIG-I/MDA 5触发涉及线粒体衔接分子MAVS、激酶TBK 1/IKKi和转录因子IRF 3和IRF 7的下游信号传导事件。IRF 3和IRF 7直接激活发挥关键抗病毒作用的I型干扰素-（IFN）α和IFN β基因的转录。该途径受到关键抑制蛋白的严格调节，这些蛋白在病毒清除后协调抗病毒信号传导的下调，以确保体内平衡并防止组织损伤和不受控制的炎症。RIG-I/MDA-5通路的激活和抑制之间的平衡失调可能导致I型IFN的不受控制的产生，这可能导致自身免疫性疾病。TAX 1BP 1首先被鉴定为与A20锌指蛋白相互作用的抗凋亡蛋白。TAX 1BP 1被认为是A20的衔接分子，这两种蛋白共同抑制炎症信号通路中NF-B转录因子的刺激诱导的活化。我们已经证明，TAX 1BP 1和A20也合作抑制RIG-I/MDA-5途径，并限制由病毒感染触发的I型IFN的激活。然而，TAX 1BP 1的抗凋亡功能是否在宿主对病毒感染的反应中起作用尚不清楚。目前还不清楚TAX 1BP 1在呼吸道病毒感染（如流感）过程中的体内确切作用，以及TAX 1BP 1减弱病毒诱导的促炎细胞因子和I型IFN产生的特定细胞类型。在初步研究中，我们提供的证据表明，TAX 1BP 1作为一种新的底物的IKKi激酶在病毒感染。IKKi对TAX 1BP 1的磷酸化引发其蛋白酶体降解和病毒感染细胞的凋亡死亡。因此，TAX 1BP 1缺陷细胞对病毒诱导的细胞死亡和细胞病变效应高度敏感，表明TAX 1BP 1的抗凋亡功能通过其降解而被揭示，并进一步支持TAX 1BP 1将抗病毒信号传导与细胞死亡途径偶联的观点。推动这些研究的中心假设是，TAX 1BP 1是病毒感染背景下先天抗病毒信号传导和细胞存活的关键调节因子。我们将通过以下具体目标来实验验证这一假设：（1）确定IKKi诱导的TAX 1BP 1磷酸化和降解的机制;（2）阐明细胞类型特异性TAX 1BP 1在调节流感病毒感染中的作用。完成拟议的研究将为限制病毒复制所必需的宿主机制提供重要的见解，并可能为识别新型抗病毒药物或流感疫苗铺平道路。

 DESCRIPTION (provided by applicant): Virus infection induces an innate antiviral host response mediated by the cytoplasmic pattern recognition receptors RIG-I and MDA-5 that sense viral RNAs. RIG-I/MDA5 trigger downstream signaling events involving the mitochondrial adaptor molecule MAVS, the kinases TBK1/IKKi and the transcription factors IRF3 and IRF7. IRF3 and IRF7 directly activate the transcription of the type I interferon-(IFN) a and ß genes tha play critical antiviral roles. This pathway is tightly regulated by key inhibitory proteins that orchestrate the downregulation of antiviral signaling upon viral clearance to ensure homeostasis and prevent tissue damage and uncontrolled inflammation. Dysregulation of the balance between activation and inhibition of the RIG-I/MDA-5 pathway may result in the uncontrolled production of type I IFN that may lead to autoimmune disease. TAX1BP1 was first identified as an anti-apoptotic protein that interacts with the A20 zinc finger protein. TAX1BP1 has since been characterized as an adaptor molecule for A20, and together these two proteins inhibit the stimulus-induced activation of the NF-¿B transcription factor in inflammatory signaling pathways. We have demonstrated that TAX1BP1 and A20 also cooperate to inhibit the RIG-I/MDA-5 pathway and restrict the activation of type I IFN triggered by virus infection. However, whether the anti-apoptotic function of TAX1BP1 plays a role in the host response to virus infection is unknown. It is also unclear what the precise roles of TAX1BP1 are in vivo during the course of a respiratory virus infection such as influenza and the specific cell types where TAX1BP1 attenuates viral-induced production of proinflammatory cytokines and type I IFN. In preliminary studies we provide evidence that TAX1BP1 serves as a novel substrate of the IKKi kinase during virus infection. The phosphorylation of TAX1BP1 by IKKi triggers its proteasomal degradation and apoptotic death of virus-infected cells. Consequently, TAX1BP1-deficient cells are highly sensitive to virus-induced cell death and cytopathic effects, suggesting that the anti-apoptotic function of TAX1BP1 is unmasked by its degradation and further supporting the notion that TAX1BP1 couples antiviral signaling to cell death pathways. The central hypothesis driving the proposed investigations is that TAX1BP1 is a key regulator of innate antiviral signaling and cell survival in the context of virus infection. We will test this hypothesis experimentally with te following specific aims: (1) determine the mechanisms of IKKi-induced TAX1BP1 phosphorylation and degradation and; (2) elucidate the role of cell-type specific TAX1BP1 in regulating influenza virus infection. Completion of the proposed studies will provide important insight into the host mechanisms that are essential to restrict virus replication and may pave the way for the identification of novel antiviral drugs or vaccines for influenza infection.