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

项目摘要 造血干细胞（HSC）的血细胞谱系发育受到严格调控， 这一过程会导致包括血癌在内的疾病，如最致命的急性骨髓性白血病（AML）， 白血病亚型面对着骨髓中动态的和潜在的致癌性扰动 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 仍然是造血的核心问题。高度保守的内质网膜激酶- 核糖核酸内切酶IRE 1 α（肌醇需要酶-1），通过其mRNA底物X-box的产物起作用 结合蛋白（Xbp）-1，协调一个“未折叠蛋白反应”程序，促进ER蛋白折叠 在真核细胞中。除了在细胞蛋白质稳定中的作用，我最近发现IRE 1 α/Xbp 1通路 是HSC中抗髓性白血病发生的关键细胞内在制动器。在Flt 3的小鼠模型中， AML中最常见的突变- IRE 1 α/Xbp 1的特异性缺失导致WT Flt 3-ITD小鼠中未观察到的致死性AML。与这些发现一致， 我们发现IRE 1 α/Xbp 1靶基因标记的下调与总生存率低相关 在AML患者队列中，揭示了IRE 1 α/Xbp 1信号转导失调的新可能性， 在AML发病机制中起重要作用。IRE 1 α缺陷型HSC转录组的初步分析 揭示了Wnt/β-catenin信号传导的显著上调，这是发育所需的关键途径， “所谓的”白血病干细胞（LSC）的功能，很少有静止和自我更新的细胞启动， 维持并涉及AML复发，但目前的治疗很少靶向。由于IRE 1 α是一种 用于各种细胞扰动（例如，活性氧、缺氧、营养素）的汇聚点和传感器 剥夺，化学物质，细胞因子和代谢物），我们的研究结果提出了一种新的范式，其中激活 IRE 1 α对这些扰动的反应抑制了HSC祖细胞的自我更新潜力， 减轻白血病的发生使用整合IRE 1 α活性报告基因和诱导型Xbp 1的小鼠AML模型 我们将讨论IRE 1 α/Xbp 1通路在 造血（Aim 1）和该途径抑制髓样细胞的分子机制 白血病发生（目的2）。人们越来越认识到，由于它们在反洗钱方面的重要作用， 在发病机制中，根除LSC对于实现长期AML缓解至关重要。作为IRE 1 α/Xbp 1 抑制LSC功能所需的Wnt/β-catenin信号传导，我们将测试靶向 HSC祖细胞中IRE 1 α/Xbp 1通路的激活将限制LSC的发育和功能（目的3）， 为持久的AML治疗提供创新策略。这些研究是我长期研究的组成部分。 致力于运行一个强大的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，最终目标是发现血液癌症的改进疗法。

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.