Determining how Kaposi's sarcoma-associated herpesvirus hijacks caspase function to inhibit anti-viral responses

确定卡波西肉瘤相关疱疹病毒如何劫持半胱天冬酶功能以抑制抗病毒反应

• 批准号: 10403006
• 负责人: Marta Maria Gaglia
• 金额: $ 37.76万
• 依托单位: TUFTS UNIVERSITY BOSTON
• 依托单位国家: 美国
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-12-01 至 2022-09-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10403006
• 关键词: AIDS related cancer; Acquired Immunodeficiency Syndrome; Affect; Africa South of the Sahara; Antiviral Response; Apoptosis; Apoptotic; Autoimmune Diseases; Biology; CASP8 gene; Caspase; Cell Death; Cells; Cessation of life; Communicable Diseases; Complex; DNA; Data; Development; Disease; Enzymes; Genetic Transcription; Herpesviridae Infections; Human Herpesvirus 8; Immune Evasion; Immune response; Infection; Innate Immune Response; Interferon Type I; Interferons; Kaposi Sarcoma; Lead; Lytic Phase; Maintenance; Mediating; Mediator of activation protein; Molecular; Nature; Oncogenic Viruses; Pathway interactions; Peptide Hydrolases; Play; Production; Proteins; Receptor Signaling; Regulation; Regulatory Pathway; Reporting; Role; Signal Transduction; Stimulus; TLR3 gene; Testing; Toll-Like Receptor Pathway; Toll-like receptors; Tumor Immunity; Up-Regulation; Viral; Virus; Virus Replication; Work; cancer type; druggable target; experience; inhibitor; insight; mutant; new therapeutic target; overexpression; pathogen; prevent; reactivation from latency; receptor; response; targeted treatment; tumor; virus host interaction

Project summary. During lytic infection, the AIDS-associated tumor virus Kaposi’s sarcoma-associated herpesvirus (KSHV) blocks cells from activating the anti-viral type I interferon (IFN) responses. This block of the innate immune response facilitates efficient viral replication, which in turn contributes to development of Kaposi’s sarcoma. Thus, elucidating the mechanisms by which KSHV evades the host innate immune response may provide insights on how to target this and other KSHV-induced tumors. However, because of the complex and redundant nature of the type I IFN induction pathway, how KSHV blocks this early antiviral response is still incompletely understood. In a previous study, we found that the host protease caspase-8 is a major mediator of type I IFN inhibition by KSHV. KSHV reactivation from latency only triggers minimal type I IFN induction, but there is a much stronger transcriptional induction and secretion of type I IFNs when caspase-8 is also inhibited. This stronger IFN induction, in turn, reduces KSHV reactivation. These results indicate that caspase-8 activity is necessary to inhibit IFN induction, and thus promotes KSHV replication. This finding was surprising because caspase-8 activation is generally considered antiviral as it induces apoptotic cell death. However, we do not detect wide-spread cell death during reactivation from latency despite caspase-8 activation, suggesting that caspase-8 is hijacked and repurposed by KSHV to inhibit type I IFN responses. At present, the molecular mechanisms that lead to caspase-8 activity and the pathways that are targeted by caspase-8 to control type I IFN during KSHV infection remain unclear. We have new preliminary data suggesting that caspase-8 is activated by a pathogen sensing pathway, the Toll-like receptor (TLR) pathway, as a cellular response to infection. Caspase-8 then proceeds to inhibit a different pathogen sensing pathway, cGAS-mediated DNA sensing. Therefore, we hypothesize that KSHV is taking advantage of a TLR-mediated cellular response to infection that activates caspase-8. KSHV is then able to redirect this activity to inhibit DNA sensing instead of activating apoptosis. We will test this hypothesis and determine how caspase-8 is activated by TLR signaling in KSHV-infected cells without triggering cell death (Aim 1), and which host protein(s) are cleaved by caspase-8 to block cGAS-induced type I IFN responses (Aim 2). Moreover, we will also investigate whether and how caspase activity is connected to other previously described mechanisms of immune evasion by KSHV (Aim 3). As caspase-8 is a druggable target, understanding how caspase-8 is used by KSHV to regulate type I IFNs and promote its replication will reveal whether and how this enzyme could be exploited for KSHV therapy. This is important as there are no target therapies for this virus, and Kaposi’s sarcoma remains one of the leading types of cancers in sub-Saharan Africa and the second most common AIDS-associated malignancy in the US. This project will also uncover fundamental aspects of caspase signaling that may play a role in other diseases connected to IFN.

项目总结。在裂解感染期间，艾滋病相关肿瘤病毒卡波西肉瘤相关 疱疹病毒(KSHV)阻止细胞激活抗病毒I型干扰素(干扰素)反应。这一块 先天免疫反应促进了病毒的有效复制，这反过来又促进了 卡波西肉瘤。因此，阐明KSHV逃避寄主天然免疫的机制 反应可能为如何靶向该肿瘤和其他KSHV诱导的肿瘤提供洞察力。然而，由于 I型干扰素诱导途径的复杂性和冗余性，以及KSHV如何阻断这种早期的抗病毒作用 人们对此的反应仍不完全清楚。在先前的研究中，我们发现宿主蛋白酶caspase-8是一种 KSHV抑制I型干扰素的主要介体。KSHV从延迟重新激活仅触发最小类型I 干扰素诱导，但有更强的转录诱导和I型干扰素的分泌 Caspase-8也被抑制。这种更强的干扰素诱导，反过来又减少了KSHV的重新激活。这些结果 提示Caspase-8活性是抑制干扰素诱导所必需的，从而促进了KSHV的复制。 这一发现令人惊讶，因为caspase-8的激活通常被认为是抗病毒的，因为它诱导 细胞凋亡性死亡然而，在潜伏期重新激活期间，我们没有检测到广泛的细胞死亡 尽管caspase-8被激活，表明caspase-8被KSHV劫持和改变用途以抑制I型 干扰素应答。目前，导致caspase-8活性的分子机制和途径 在KSHV感染期间，caspase-8靶向控制I型干扰素的作用尚不清楚。我们有新的 初步数据表明caspase-8被病原体感知通路Toll样受体激活 (TLR)途径，作为细胞对感染的反应。然后，Caspase-8继续抑制另一种病原体 传感途径，cGAS介导的DNA传感。因此，我们假设KSHV正在利用 TLR介导的细胞对感染的反应激活caspase-8。KSHV然后能够重定向此 抑制DNA传感而不是激活细胞凋亡的活性。我们将检验这一假设，并确定如何 在KSHV感染的细胞中，Caspase-8被TLR信号激活，而不会触发细胞死亡(目标1)，以及 哪些宿主蛋白(S)被caspase-8切割以阻断cGAS诱导的I型干扰素反应(目标2)。 此外，我们还将调查caspase活性是否以及如何与以前的其他 描述了KSHV逃避免疫的机制(目标3)。由于caspase-8是一个可下药的靶点， 了解KSHV如何利用caspase-8来调节I型IFN并促进其复制将揭示 这种酶是否以及如何被开发用于KSHV治疗。这一点很重要，因为没有目标 这种病毒的治疗方法和卡波西肉瘤仍然是撒哈拉以南地区最主要的癌症类型之一 非洲和美国第二常见的与艾滋病相关的恶性肿瘤。该项目还将揭示 Caspase信号的基本方面，可能在与干扰素相关的其他疾病中发挥作用。