急性髓系白血病细胞干性维持及分化促进干预机制研究

Contemporary therapeutic methods are ineffective to eradicate the specific leukemia cellular subsets that possess the malignant stemness and thus are capable of re-initiating a full-blown clinical leukemia in vivo, and this inability prevents the further improvement of clinical management of this deadly disease. Interestingly, a few recent studies indicate that the leukemic stemness is not only owned by so-called apical leukemia stem cells, but also by those inferior subsets within the leukemic hierarchy of differentiation, and this phenomenon represents a new research hot-point concerning how the leukemic stemness is molecularly modulated. Our preliminary studies on two mouse acute myeloid leukemic models (M2b and M3 subtypes) confirmed the existence of this stemness complexity. We also found that the self-renewal and de-differentiation both contribute to the maintenance of leukemic stemness, whereas that the leukemic stemness declines in a graded manner in parallel to a step-wise differentiation process of leukemia cells. Importantly, the discrete mechanisms are found to mediate the graded leukemic decline in association with the specific differentiation phases. In this proposed study, starting from a systemic analysis of how the leukemic stemness declines along with the in vivo spontaneous differentiation of leukemia cells in two leukemia models, we attempt to figure out how the specific signal transducers and transcriptional regulators (including classic transcription factors and epigenetic regulators) recognize the chromatin regulatory elements such as super-enhancers to constitute the core regulatory pathways for self-renewal and differentiation processes, and how these two types of mechanisms interplay to determine the fate of the leukemia cells that lie at a specific tier of the differentiation hierarchy: self-renewal, differentiation or de-differentiation. We believe that conduction of this proposed study will greatly improve our understanding about the essential mechanisms that regulate the leukemic stemness and differentiation, which in turn will hatch the development of a general strategy of the eradication of leukemic stemness by manipulating the spontaneous differentiation tendency of leukemia cells.

具有恶性干性的白血病细胞对现行治疗的抵抗是妨碍根治白血病的重要因素。近期研究提示：白血病细胞干性不仅仅存在于处于白血病分化阶层顶端的经典白血病干细胞，成为白血病细胞干性研究中新的关注点。我们对2个小鼠白血病模型（M2b和M3）的分析证实白血病细胞干性分布于多个处于不同分化阶段的细胞亚群，并且自我更新和去分化均可维持白血病细胞干性。然而，白血病细胞干性随白血病细胞自发（或诱导）分化的过程呈阶段性衰减，调控各阶段性干性衰减的分子机制截然不同。在本项目中，我们拟以系统性分析白血病细胞干性如何随自发分化而衰减为着手点，试图弄清何种信号转导分子、转录调控因子通过识别超增强子等转录调控元件组成白血病干性维持或促进分化的机制，及这2种机制如何相互博弈以决定各分化阶段白血病细胞的命运。我们相信这项研究将有助于理解白血病细胞干性维持机制的复杂性和研发“促进自发分化以清除白血病细胞干性”的一般性治疗策略。

白血病干细胞的分化通常被认为是单向的、与自我更新互不兼容的过程。但是，分化如何影响白血病干细胞的干性仍有许多不清楚的地方。首先，我们的第一项研究显示：位于小鼠急性早幼粒性白血病（APL）分化阶层顶端的的白血病干细胞在分化到终末分化的阶段以前，会经历一个部分分化的阶段。在这个阶段的白血病细胞可以通过去分化重建白血病，虽然概率会有所降低。机制上，我们发现全反式维甲酸可轻易地诱导白血病干细胞向部分分化细胞的转变，而单核细胞分化相关的转录因子Irf8能够有效地消除部分分化细胞去分化和增殖的潜力使其达到终末分化阶段，并且联合全反式维甲酸和Irf8的上调能够完全清除白血病细胞的致病潜能。其二，在另一种携带最常见致癌染色体异常—— AML1/ETO融合蛋白的急性髓系白血病亚型(AML-M2b)的研究中。我们发现可将AE9a小鼠白血病细胞分为三个不同等级分化的CD43++c-Kit+、CD43+c-Kit-、CD43-c-Kit-群体。白血病干细胞的自发分化方向以红系分化为主，可能的分子机制为AE9a的自发降解。在第三项研究中，我们发现组蛋白去甲基化酶JMJD3的异常低表达介导了APL和M2b AML的发生，反之，JMJD3的高表达可通过与关键转录因子C/EBPbeta形成转录调控复合物以诱导激活“应急性粒系分化”程序，从而导致白血病干性的泄漏。这些工作为进一步解析白血病发病、干性维持和分化机制，以及研制新型诱导分化疗法提供了一定基础。