Targeting Metabolic Liabilities of Leukemia-Initiating Cells

项目摘要 表观遗传学和代谢在癌症进展中的功能关系尚未得到仔细研究。 考察许多催化DNA或组蛋白修饰的表观遗传酶容易受到DNA或组蛋白的变化的影响。 代谢的共同底物，但很少有人知道是否以及如何改变表观遗传学影响细胞 癌症进展过程中的代谢。EZH2（组蛋白H3赖氨酸27甲基转移酶）的突变， 常见于骨髓恶性肿瘤，与预后不良相关。我们最近开发了一种新的 通过EZH2的失活和致癌NRAS（G12D）的活化的骨髓肿瘤小鼠模型。而 G12 D单独导致无痛性骨髓增生，EZH2失活显著加速疾病进展 导致骨髓纤维化、白血病转化和死亡。这个模型忠实地概括了 在白血病进展中，我们意外地发现支链氨基酸（BCAA）代谢是最重要的 在EZH2缺陷型白血病起始细胞（LIC）中显著上调代谢途径。BCAT 1，第一个 催化BCAA转氨作用的酶，在造血中被EZH2抑制， 小鼠和人类中EZH2缺陷型骨髓肿瘤。BCAT1的增加促进了BCAA的产生， LIC，导致激活的mTOR信号传导。BCAT 1选择性的遗传和药理学抑制 损害EZH2缺陷型LIC并构成代谢脆弱性。这些发现首次将 EZH2失调与癌症进展中代谢途径的改变。该项目的目标是 通过关注支链氨基酸的作用，阐明控制LIC代谢负债的因果机制 EZH2缺陷型骨髓肿瘤的代谢。核心假设是EZH2缺乏诱导了 通过激活BCAT 1和BCAA代谢来进行代谢重新布线，以产生对LIC的代谢依赖性，以及 BCAT 1的抑制将通过使EZH2缺陷型LIC的代谢能力丧失而选择性地根除LIC， 低收入国家。这一假设是基于我们的初步研究，使用体内模型， 白血病进展和一个新发现的改变表观遗传学和代谢之间的分子联系。 在这些初步数据的指导下，这一假设将通过三个具体目标进行检验：1）定义功能 使用BCAT1敲除和诱导型BCAT1在体内EZH2缺陷诱导的骨髓肿瘤中的作用 表达小鼠模型。2)确定EZH2缺陷型LIC表现出代谢性 对BCAA代谢的依赖。3)确定靶向BCAA代谢在人AML中的作用 利用遗传、药理学和饮食操作来培育干细胞。这些研究不仅将 验证EZH2突变型骨髓肿瘤的选择性代谢倾向，但也发现了新的途径 可以用来有选择地根除低收入国家。这些结果有望推动我们的机制 了解癌症进展中表观遗传学和代谢之间的功能关系， 指导设计更有效的治疗方法，以靶向癌症引发细胞的代谢责任。

PROJECT SUMMARY The functional relationship between epigenetics and metabolism in cancer progression has not been carefully examined. Many epigenetic enzymes catalyzing DNA or histone modifications are susceptible to changes in co-substrates of metabolism, but little is known about whether and how altered epigenetics influences cellular metabolism during cancer progression. Mutations of EZH2, the histone H3 lysine 27 methyltransferase, are frequently found in myeloid malignancies and correlate with poor prognosis. We recently developed a new mouse model of myeloid neoplasms by inactivation of EZH2 and activation of oncogenic NRas (G12D). While G12D alone led to an indolent myeloproliferation, EZH2 inactivation markedly accelerated disease progression resulting in myelofibrosis, leukemic transformation and mortality. With this model that faithfully recapitulates leukemia progression, we unexpectedly identified branched-chain amino acid (BCAA) metabolism as the most significantly upregulated metabolic pathway in EZH2-deficient leukemia-initiating cells (LICs). BCAT1, the first enzyme catalyzing BCAA transamination, is repressed by EZH2 in hematopoiesis and aberrantly activated in EZH2-deficient myeloid neoplasms in mice and humans. Increased BCAT1 promotes BCAA production in LICs, resulting in activated mTOR signaling. Genetic and pharmacological inhibition of BCAT1 selectively impairs EZH2-deficient LICs and constitutes a metabolic vulnerability. These findings for the first time connect dysregulation of EZH2 with altered metabolic pathways in cancer progression. The objective of this project is to elucidate the causal mechanisms controlling metabolic liabilities of LICs by focusing on the role of BCAA metabolism in EZH2-deficient myeloid neoplasms. The central hypothesis is that EZH2 deficiency induces metabolic rewiring by activating BCAT1 and BCAA metabolism to create a metabolic dependency for LICs, and that inhibition of BCAT1 will selectively eradicate LICs by disabling the metabolic liability of EZH2-deficient LICs. This hypothesis has been formulated on the basis of our preliminary studies using an in vivo model of leukemia progression and a newly discovered molecular link between altered epigenetics and metabolism. Guided by these preliminary data, this hypothesis will be tested by three specific aims: 1) Define the functional role of BCAT1 in EZH2-deficiency-induced myeloid neoplasms in vivo using BCAT1 knockout and inducible expression mouse models. 2) Determine the mechanisms by which EZH2-deficient LICs exhibit a metabolic dependency on BCAA metabolism. 3) Determine the effects of targeting BCAA metabolism in human AML stem cells using genetic, pharmacological and dietary manipulations. Together these studies will not only validate a selective metabolic liability for EZH2-mutant myeloid neoplasms, but also uncover new pathways that can be exploited to selectively eradicate LICs. Such results are expected to advance our mechanistic understanding of the functional relationship between epigenetics and metabolism in cancer progression, and to guide the design of more effective therapies to target the metabolic liabilities of cancer-initiating cells.