Probing the role of the IRE1alpha-XBP1 pathway in normal and malignant hematopoiesis

项目摘要 来自造血干细胞(HSC)的血细胞谱系的发育受到严格的调控，而缺陷 这一过程会导致包括血癌在内的疾病，如最致命的急性髓细胞白血病(AML) 白血病亚型。面对他们骨髓中动态的和潜在的致癌扰动 微环境，HSC祖细胞如何平衡自我更新与分化并保持其完整性 仍然是造血学的中心问题。高度保守的内质网-膜蛋白激酶- 内切核酸酶IRE1α(需要肌醇的酶-1)，通过其底物X-box的产物起作用 结合蛋白(XBP)-1，协调促进内质网蛋白折叠的“未折叠蛋白反应”程序 在真核细胞中。除了在细胞蛋白平衡中的作用外，我最近还发现IRE1XBP1通路 是阻止造血干细胞髓系白血病发生的关键细胞内源性刹车。在Flt3的小鼠模型中 膜旁区域的内部串联复制(Flt3-ITD)是AML、HSC中最常见的突变 IRE1α/XBP1的特异性缺失导致了一种在WT Flt3-ITD小鼠中未见的致死性急性髓细胞白血病。与这些发现一致的是， 我们发现IRE1α/XBP1靶基因信号下调与总体存活率较低有关 在一组急性髓细胞白血病患者中，揭示了一种新的可能性，即IRE1α/XBP1信号失控 在急性髓系白血病的发病机制中起重要作用。IRE1型α缺陷型造血干细胞转录组初步分析 发现Wnt/β-连环蛋白信号显著上调，这是发育和发育所需的关键途径 所谓的白血病干细胞(LSCs)的功能，少数静止的和自我更新的细胞启动， 维持并与AML复发有关，但很少被目前的治疗方法所针对。因为IRE1α是一个 针对各种细胞扰动(例如，活性氧、低氧、营养物质)的汇聚点和传感器 剥夺、化学物质、细胞因子和代谢物)，我们的发现提出了一种新的范式，其中激活 IRE1α的表达抑制了造血干细胞祖细胞的自我更新潜能 减少白血病的发生。利用整合IRE1α活性报告基因和诱导型XBP1基因的小鼠急性髓细胞白血病模型 我最近开发的转基因，我们将讨论IRE1α/XBP1途径是如何在 造血(Aim1)及其抑制髓系细胞的分子机制 白血病发生(目标2)。由于它们在急性髓系白血病中的重要作用，人们越来越认识到 发病机制、根治LSCs将是实现AML长期缓解的关键。作为IRE1α/XBP1. 抑制LSC功能所需的Wnt/β-catenin信号，我们将测试靶向 造血干细胞祖细胞中IRE1XBP1通路的激活将限制胚胎干细胞的发育和功能(目标3)， 为经久耐用的急性髓细胞白血病治疗提供创新策略。这些研究对我的长期工作是不可或缺的 致力于运营一个强大而成功的独立研究实验室，专注于了解正常和 恶性血细胞的发展，最终目标是发现血癌的改进疗法。

Project Summary Development of blood cell lineages from hematopoietic stem cells (HSC) is stringently regulated, and defects in this process cause diseases including blood cancers like acute myelogenous leukemia (AML), the most lethal leukemia subtype. Faced with dynamic and potentially oncogenic perturbations in their bone marrow microenvironment, how HSC progenitors balance self-renewal with differentiation and preserve their integrity remains a central question in hematopoiesis. The highly conserved endoplasmic reticulum-membrane kinase- endoribonuclease IRE1α (inositol-requiring enzyme-1), acting through the product of its mRNA substrate X-box binding protein (Xbp)-1, orchestrates an “unfolded protein response” program that facilitates ER protein folding in eukaryotic cells. Beyond this role in cellular proteostasis, I recently discovered that the IRE1α/Xbp1 pathway is a critical cell-intrinsic brake against myeloid leukemogenesis in HSCs. In a mouse model of the Flt3 internal tandem duplication of the juxtamembrane region (Flt3-ITD), the most frequent mutation in AML, HSC- specific loss of IRE1α/Xbp1 caused a lethal AML not seen in WT Flt3-ITD mice. Consistent with these findings, we found that downregulation of an IRE1α/Xbp1 target gene signature was associated with poor overall survival in a cohort of AML patients, revealing the novel possibility that dysregulated IRE1α/Xbp1 signaling importantly contributes to AML pathogenesis. Preliminary transcriptome analysis of IRE1α-deficient HSCs revealed a marked upregulation of Wnt/β-catenin signaling, a key pathway required for the development and function of the “so-called” leukemia stem cells (LSCs), few quiescent and self-renewing cells that initiate, maintain and are implicated in AML relapse but are rarely targeted by current therapies. As IRE1α is a convergence point and sensor for various cellular perturbations (e.g. reactive oxygen species, hypoxia, nutrient deprivation, chemicals, cytokines and metabolites), our findings suggest a novel paradigm in which activation of IRE1α in response to these perturbations restrains the self-renewal potential of HSC progenitors to mitigate leukemogenesis. Using mouse AML models integrating IRE1α activity reporter and inducible Xbp1 transgene that I recently developed, we will address how the IRE1α/Xbp1 pathway is regulated during hematopoiesis (Aim1) and the molecular mechanisms by which this pathway suppresses myeloid leukemogenesis (Aim 2). There is increasing appreciation that because of their important role in AML pathogenesis, eradication of LSCs will be critical to achieve long-term AML remission. As IRE1α/Xbp1 suppresses the Wnt/β-catenin signaling required for LSC function, we will test the hypothesis that targeted activation of the IRE1α/Xbp1 pathway in HSC progenitors will limit LSC development and function (Aim 3), providing an innovative strategy for durable AML therapy. These studies are integral to my long-term commitment to run a strong successful independent research laboratory focused on understanding normal and malignant blood cell development with the ultimate goal of discovering improved therapies for blood cancers.