Regulation of hematopoietic stem cell differentiation

描述（由申请人提供）：所有成熟血细胞都来自一种罕见的特殊群体，即造血干细胞（hsc），这些细胞大多处于静止状态。造血干细胞的细胞分裂导致其增殖和逐渐分化为越来越受谱系限制的成熟血细胞，并维持一小部分造血干细胞，这些造血干细胞不分化，而是在生物体的整个生命周期中进行造血。由于造血干细胞功能的重要性，阐明控制造血干细胞自我更新和分化之间平衡的信号是一项首要任务。有趣的是，一些研究表明，生理性造血和诱导造血恶性肿瘤（白血病）之间存在密切的平衡，这种平衡是由能够转化HSC和祖细胞的异常信号控制的。与这一观点一致，我们最近发现E3泛素连接酶Fbw7在急性淋巴细胞白血病（ALL）中是一个重要的肿瘤抑制因子。Fbw7失活突变在很大一部分ALL患者中发现，由于几个重要癌基因的异常稳定性，包括Notch1和c-Myc， Fbw7失活突变诱导转化。我们利用一种新的条件敲除小鼠模型研究了Fbw7在HSC功能中的作用。我们发现Fbw7的缺失以细胞自主的方式特异性和快速地影响HSC细胞室。Fbw7-/-造血干细胞表现出沉默维持缺陷，导致自我更新受损和竞争性再生能力严重丧失。此外，Fbw7-/- HSC的全基因组转录组研究表明，Fbw7调节与静止、自我更新的HSC表型相关的全局转录“特征”。在本应用中，我们：a)鉴定Fbw7靶向的HSC特异性蛋白底物，并在HSC分化和功能中发挥重要作用；b)通过研究Fbw7在胚胎干细胞功能中的作用来解决Fbw7在干细胞自我更新中的普遍功能；c)研究ALL Fbw7错义突变在造血和HSC自我更新中的作用。

DESCRIPTION (provided by applicant): All mature blood cells arise from a rare and specialized population, the hematopoietic stem cells (HSCs), which exist mostly in a quiescent state. Cell division of HSCs results in both their proliferation and progressive differentiation into increasingly lineage-restricted mature blood cells, as well as maintenance of a small pool of HSCs that do not differentiate, but rather carry out hematopoiesis throughout the life of an organism. Due to the significance of HSC function, the elucidation of the signals that govern the balance between HSC self-renewal and differentiation is a paramount task. Interestingly, several studies have suggested an intimate balance between physiological hematopoiesis and induction of hematopoietic malignancy (leukemia) controlled by aberrant signaling that is able to transform HSC and progenitor cells. In agreement with this notion, we have recently identified the E3 ubiquitin ligase Fbw7 as an important tumor suppressor in acute lymphocytic leukemia (ALL). Fbw7 inactivating mutations are found in a large fraction of ALL patients and induce transformation due to the aberrant stability of several important oncogenes, including Notch1 and c-Myc. We have addressed the role of Fbw7 in HSC function using a novel conditional knock-out mouse model. We have found that deletion of Fbw7 specifically and rapidly affected the HSC compartment in a cell-autonomous manner. Fbw7-/- HSCs showed defective maintenance of quiescence, leading to impaired self-renewal and a severe loss of competitive repopulating capacity. Furthermore, genome-wide transcriptome studies of Fbw7-/- HSC indicated that Fbw7 regulates a global transcriptional "signature" associated with the quiescent, self-renewing HSC phenotype. In this application we: a) Identify HSC-specific protein substrates targeted by Fbw7 and playing important roles in HSC differentiation and function, b) address the universal function of Fbw7 in stem cell self-renewal by studying its role in embryonic stem cell function and c) study the effects of ALL Fbw7 missense mutations in hematopoiesis and HSC self- renewal. PUBLIC HEALTH RELEVANCE: All blood cells originate from a rare population of pluripotent hematopoietic stem cells (HSC) that have the ability to both self-renew and differentiate. In this grant we study in detail the biological function of a novel HSC regulator the E3 ubiquitin ligase Fbw7. Our studies have direct translational impact as they address the function of a central regulator of HSC ability to replenish the immune system that at the same time functions as a tumor suppressor in leukemia.