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

 描述(申请人提供)：病毒感染诱导固有的抗病毒宿主反应，由感受病毒RNA的细胞质模式识别受体RIG-I和MDA-5介导。RIG-I/MDA5触发下游信号事件，涉及线粒体适配器分子MAVS、激酶TBK1/Ikki以及转录因子IRF3和IRF7。IRF3和IRF7直接激活起重要抗病毒作用的I型干扰素α和β基因的转录。这一途径受到关键抑制蛋白的严格调控，这些蛋白在病毒清除时协调抗病毒信号的下调，以确保体内平衡，防止组织损伤和失控的炎症。RIG-I/MDA-5途径激活和抑制之间的平衡失调可能导致I型干扰素的不受控制的产生，从而可能导致自身免疫性疾病。TAX1BP1首先被鉴定为一种与A20锌指蛋白相互作用的抗凋亡蛋白。自那以后，TAX1BP1被鉴定为A20的适配分子，这两种蛋白共同抑制刺激诱导的炎症信号通路中核因子-B转录因子的激活。我们已经证明，TAX1BP1和A20还协同抑制RIG-I/MDA-5途径，并限制病毒感染触发的I型干扰素的激活。然而，TAX1BP1的抗凋亡功能是否在宿主对病毒感染的反应中发挥作用尚不清楚。目前还不清楚TAX1BP1在呼吸道病毒感染(如流感)过程中在体内的确切作用，以及TAX1BP1在哪些特定细胞类型中减弱病毒诱导的促炎细胞因子和I型干扰素的产生。在初步研究中，我们提供了TAX1BP1在病毒感染过程中作为一种新的Ikki激酶底物的证据。TAX1BP1被Ikki磷酸化，引发其蛋白酶体降解和病毒感染细胞的凋亡性死亡。因此，TAX1BP1缺陷的细胞对病毒诱导的细胞死亡和细胞病变效应高度敏感，这表明TAX1BP1的抗凋亡功能被其降解所掩盖，并进一步支持了TAX1BP1将抗病毒信号耦合到细胞死亡途径的观点。推动这项研究的中心假设是，在病毒感染的背景下，TAX1BP1是先天抗病毒信号和细胞生存的关键调节因子。我们将通过实验验证这一假说，具体目的如下：(1)确定Ikki诱导的TAX1BP1磷酸化和降解的机制；(2)阐明细胞类型特异性TAX1BP1在调节流感病毒感染中的作用。拟议研究的完成将提供对限制病毒复制至关重要的宿主机制的重要洞察，并可能为识别新型抗病毒药物或流感感染疫苗铺平道路。

 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.