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: 10729751
• 负责人: Marta Maria Gaglia
• 金额: $ 34.91万
• 依托单位: UNIVERSITY OF WISCONSIN-MADISON
• 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 2026-11-30
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10729751
• 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; Cytoplasm; DNA; Data; Development; Disease; Enzymes; Genetic Transcription; Herpesviridae; Herpesviridae Infections; Human Herpesvirus 8; Immune Evasion; Immune response; Infection; Innate Immune Response; Interferon Type I; Interferons; Kaposi Sarcoma; Lytic Phase; Maintenance; Mediating; Mediator; Molecular; Nature; Oncogenic Viruses; Pathway interactions; Peptide Hydrolases; 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.

项目摘要。在溶解性感染过程中，艾滋病相关肿瘤病毒卡波西肉瘤相关的 疱疹病毒（KSHV）阻断细胞激活抗病毒I型干扰素（IFN）应答。这块 先天性免疫反应促进有效的病毒复制，这反过来又有助于发展 卡波西肉瘤。因此，阐明了KSHV逃避宿主先天免疫的机制， 反应可能提供关于如何靶向这种和其他KSHV诱导的肿瘤的见解。但由于 I型IFN诱导途径的复杂性和冗余性，KSHV如何阻断这种早期抗病毒 反应还不完全清楚。在以前的研究中，我们发现宿主蛋白酶caspase-8是一种 KSHV抑制I型IFN的主要介质。KSHV从延迟重新激活仅触发最小I型 IFN诱导，但有更强的转录诱导和分泌I型IFN时， 半胱天冬酶-8也被抑制。这种更强的IFN诱导，反过来，减少KSHV再活化。这些结果 表明半胱天冬酶-8活性是抑制IFN诱导所必需，并因此促进KSHV复制。 这一发现令人惊讶，因为caspase-8激活通常被认为是抗病毒的，因为它诱导 细胞凋亡然而，我们没有检测到广泛的细胞死亡期间，从潜伏期重新激活 尽管caspase-8激活，表明caspase-8被KSHV劫持和重新利用，以抑制I型 IFN应答。目前，导致caspase-8活性的分子机制和 在KSHV感染期间，caspase-8靶向控制I型IFN的作用仍不清楚。我们有新 初步数据表明，caspase-8被病原体感应途径Toll样受体激活 (TLR)途径，作为细胞对感染的反应。半胱天冬酶-8然后抑制不同的病原体 传感途径，cGAS介导的DNA传感。因此，我们假设KSHV是在利用 TLR介导的细胞对感染的反应，激活caspase-8。KSHV能够将其重定向到 活性抑制DNA传感而不是激活细胞凋亡。我们将测试这个假设，并确定如何 caspase-8在KSHV感染的细胞中被TLR信号激活而不触发细胞死亡（Aim 1）， 所述宿主蛋白被半胱天冬酶-8切割以阻断cGAS诱导的I型IFN应答（目的2）。 此外，我们还将研究半胱天冬酶活性是否以及如何与其他先前的， 描述了KSHV的免疫逃避机制（目的3）。由于半胱天冬酶-8是一个药物靶点， 了解KSHV如何使用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用于KSHV治疗。这很重要，因为没有目标 卡波西肉瘤仍然是撒哈拉以南非洲地区主要的癌症类型之一， 非洲和第二个最常见的艾滋病相关恶性肿瘤在美国。该项目还将揭示 半胱天冬酶信号转导的基本方面，可能在与IFN相关的其他疾病中发挥作用。