AIP inhibition of IRF7 and innate antiviral signaling

摘要 干扰素调节因子7（IRF 7）是一种转录因子，被称为I型干扰素的主调节因子。 干扰素（IFN）反应;然而，目前仍不清楚IRF 7是如何负调节以恢复免疫应答的。 病毒感染后的体内平衡得到解决。我们已经鉴定了芳香烃受体相互作用蛋白 (AIP)作为IRF 7的负调节因子，在抑制IRF 7活化中起重要作用。AIP调节 芳烃受体（AhR），一种宿主异生素反应的配体激活受体， 环境毒素，如2，3，7，8-四氯二苯并对二恶英（TCCD）。我们发现AIP与 IRF 7，这种相互作用通过病毒感染进一步增强。Aip-/-鼠胚胎成纤维细胞（MEFs） 与感染病毒的野生型细胞相比，产生显著更多的I型IFN，从而使这些细胞 对病毒感染具有高度抵抗力。AIP拮抗IRF 7的核定位，以阻止IRF 7的转录。 I型IFN基因的激活。然而，关于AIP和AhR在 调节IRF 7和先天免疫应答。特异性的分子机制是什么？ AIP调节IRF 7和抗病毒天然免疫？鉴于AIP和AIP之间已建立的职能联系， AhR，AhR是否抑制IRF 7，以及AhR配体抑制抗病毒信号传导是否需要AIP？在 初步研究，我们已经确定AIP作为非经典IkB激酶TBK 1（TANK-1）的新底物。 结合激酶1）和三个推定的磷酸化位点。此外，委员会认为， 用AhR激动剂L-犬尿氨酸（L-Kyn）处理细胞显著增强了囊泡的复制， 口腔炎病毒，提供证据表明，AhR信号抑制先天性抗病毒反应。AhR与 IRF 7，表明IRF 7可能是先天免疫信号转导中AhR的靶点。吲哚胺2，3-双加氧酶 (IDO)是产生免疫调节色氨酸代谢物的限速酶，包括 AhR配体L-Kyn。IDO在病毒感染过程中被IFN诱导，提示IDO参与了病毒感染的负性调节。 先天免疫信号的调节。推动这些研究的中心假设是AIP和AhR 作为功能单元通过两步负反馈抑制IRF 7和病毒诱导的I型IFN TBK 1和IFN轴引起的机制。我们将通过以下实验来测试我们的假设 具体目的：1）确定AIP磷酸化在抑制IRF 7和先天信号传导中的作用，以及2） 确定AIP在病毒感染期间调节AhR的作用。完成这些研究可能 为环境因素如何影响对病毒感染的先天免疫提供了新的机制性见解 并可能为使用AhR激动剂或拮抗剂作为微调宿主先天性免疫缺陷的方法提供理论基础。 病原体环境中的免疫应答，如自身免疫或病毒引发的细胞因子风暴（例如， 甲型流感或SARS-CoV 2/COVID-19）。

ABSTRACT Interferon regulatory factor 7 (IRF7) is a transcription factor known as the master regulator of the type I interferon (IFN) response; however, it remains unclear how IRF7 is negatively regulated to restore immune homeostasis after viral infections are resolved. We have identified aryl hydrocarbon receptor interacting protein (AIP) as a negative regulator of IRF7 that plays essential roles in the inhibition of IRF7 activation. AIP regulates the aryl hydrocarbon receptor (AhR), a ligand-activated receptor of the host xenobiotic response to environmental toxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCCD). We found that AIP interacts with IRF7 and this interaction is further enhanced by virus infection. Aip–/– murine embryonic fibroblasts (MEFs) produce significantly more type I IFN compared to wild-type cells infected with virus, thus rendering these cells highly resistant to virus infection. AIP antagonizes the nuclear localization of IRF7 to prevent the transcriptional activation of type I IFN genes. However, key questions remain regarding the roles of AIP and AhR in the regulation of IRF7 and innate immune responses. What is the molecular mechanism underlying specificity for AIP regulation of IRF7 and antiviral innate immunity? Given the established functional links between AIP and AhR, does AhR inhibit IRF7, and is AIP required for the inhibition of antiviral signaling by AhR ligands? In preliminary studies, we have identified AIP as a novel substrate of the noncanonical IkB kinase TBK1 (TANK- binding kinase 1), and three putative phosphorylation sites were mapped by mass spectrometry. Furthermore, treatment of cells with the AhR agonist L-kynurenine (L-Kyn) significantly enhanced the replication of vesicular stomatitis virus, providing evidence that AhR signaling inhibits the innate antiviral response. AhR interacts with IRF7 suggesting that IRF7 may be a target of AhR in innate immune signaling. Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the generation of immune regulatory tryptophan metabolites, including the AhR ligand L-Kyn. IDO is induced by IFN during virus infection suggesting that IDO participates in the negative regulation of innate immune signaling. The central hypothesis driving these investigations is that AIP and AhR cooperate as a functional unit to inhibit IRF7 and virus-induced type I IFN by a two-step negative feedback mechanism instigated by TBK1 and the IFN axis. We will test our hypothesis experimentally with the following Specific Aims: 1) Define the role of AIP phosphorylation in the inhibition of IRF7 and innate signaling, and 2) Determine the role of AIP in the regulation of AhR during virus infection. Completion of these studies may provide new mechanistic insight into how environmental factors can influence innate immunity to virus infection and may provide rationale for the use of AhR agonists or antagonists as an approach to fine-tune host innate immune responses in pathogenic settings such as autoimmunity or virus-triggered cytokine storms (e.g. influenza A or SARS-CoV2/COVID-19).