Project 2: KSHV induces tumorigenesis by harnessing differentiation in hypoxia

摘要 缺氧是实体瘤的一个特征，也是一个不利的预后因素，因为它对 肿瘤进展和对治疗的抵抗。卡波西肉瘤(KS)好发于低位 身体的四肢，那里的血管通常氧合不良，这表明缺氧也起作用 在KS开发中的角色。事实上，KSHV感染内皮细胞或间充质干细胞(MSCs) 激活缺氧诱导因子(HIF)，这是发育和病理的主要调节因素 血管生成。缺氧和HIF反过来影响KSHV的生物学和KS的发展。然而，鉴于高度的 KS肿瘤的血管表型，我们想知道缺氧反应可能不是 低氧条件下，但KSHV采取的促进MSC向KS表型分化的策略。 KS病变的特点是感染KSHV的梭形细胞增殖，强烈的血管生成和 渗入的炎性细胞。KS梭形细胞的起源仍存在争议。最近我们发现了一系列 有证据表明KS来源于口腔间充质干细胞(MSCs)，通过间充质向骨髓间充质干细胞转化。 内皮细胞转化(MEndT)过程(Li等人，2018年)。这些发现揭示了新的病毒肿瘤发生机制 当致癌病毒劫持多潜能干细胞的分化过程时，可能会发生癌症。 受这一令人兴奋的发现的启发，我们试图阐明KSHV驱动的MEndT和KSHV-MEndT的机制。 肿瘤发生学。我们的初步研究表明，KSHV感染的MSCs和KS病变的转录本 与低氧培养的MSCs基本重叠，增加了KSHV感染利用低氧的可能性 促进MSC分化的反应导致KS。我们将用三个具体的例子来研究这一假设 目标如下。(I)我们将确定KSHV是如何通过劫持缺氧促进MSC分化的 响应系统。(Ii)我们将确定KSHV和低氧改变的信号通路，并研究它们的 在MEndT、血管生成和炎症中的作用，从而阐明KSHV的机制 低氧介导的MEndT。(Iii)我们将描述骨髓间充质干细胞在MEndT期间的表观遗传调控特征，以及 揭示KSHV如何改变导致KS的法规。通过这些研究，我们最终将解决 关于KSHV如何将MSC转化为KS肿瘤的问题。 我们提出的研究具有很高的创新性和生物学意义。首先，这项研究将证明 KS梭形细胞来源的Kaposi肉瘤的本质和细胞起源的范式转换概念 来自KSHV感染的间充质干细胞。其次，这项研究将揭示一种新的机制 KSHV驱动的MEndT诱导的KS肿瘤细胞的出现及其对多焦点和寡克隆的新认识 KS的性质。第三，本研究将阐明KSHV如何利用低氧反应促进MSC 转化为KS，验证低氧作为治疗KS的有效靶点。

Summary Hypoxia is a characteristic feature of solid tumors and an adverse prognostic factor owing to its contributions to tumor progression and resistance to therapy. Kaposi's sarcoma (KS) preferentially develops in the lower extremities of the body, where blood vessels are often poorly oxygenated, suggesting that hypoxia also plays roles in KS development. Indeed, KSHV infection of endothelial cells or mesenchymal stem cells (MSCs) activates hypoxia-induced factor (HIF), a master regulator of both developmental and pathological angiogenesis. In turn, hypoxia and HIFs affect KSHV biology and KS development. However, given the highly vascular phenotype of KS tumor, we wonder that the hypoxia response may not be the consequence of hypoxia condition, but a strategy that KSHV adapts to promote MSC differentiation towards KS phenotypes. KS lesions are characterized by proliferating KSHV-infected spindle cells, intensive angiogenesis and infiltrating inflammatory cells. The origin of KS spindle cells remains contentious. Recently we found a series of evidence suggesting that KS derives from oral mesenchymal stem cells (MSCs) through a mesenchymal-to- endothelial transition (MEndT) process (Li et al., 2018). These findings revealed novel viral tumorigenesis that cancer can arise from pluripotential stem cells when an oncogenic virus hijacks their differentiation process. Inspired by the exciting discovery, we attempt to elucidate the mechanism underlying KSHV-driven MEndT and tumorigenesis. Our preliminary study showed that the transcriptomes of KSHV infected MSCs and KS lesions largely overlap with that of hypoxia cultured MSCs, raising a possibility that KSHV infection harnesses hypoxia response to promote MSC differentiation leading to KS. We will investigate this hypothesis with three specific aims as follows. (i) We will determine how KSHV promotes MSC differentiation through the hijacking hypoxia response system. (ii) We will identify signaling pathways altered by KSHV and hypoxia and investigate their contribution to MEndT, angiogenesis and inflammation, therefore elucidating the mechanism underlying KSHV and hypoxia-mediated MEndT. (iii) We will characterize epigenetic regulation in MSCs during MEndT, and reveal how KSHV alters the regulation leading to KS. Through these studies, we will ultimately address the question of how KSHV transforms MSC to KS tumor. Our proposed studies are highly innovative and of biological significance. First, the study will prove a paradigm-shifting concept on the nature and cellular origin of Kaposi's sarcoma that KS spindle cells derive from KSHV-infected mesenchymal stem cells. Second, the study will reveal a novel mechanism underlying the emergence of KS tumor cells through KSHV-driven MEndT and new insights into the multifocal and oligoclonal nature of KS. Third, this study will elucidate how KSHV harnesses hypoxia response to promote MSC transformation to KS and validate hypoxia as an effective therapeutic target for the treatment of KS.