Bmi-1在造血干细胞中的功能研究

Hematopoietic stem cell (HSC) is a multipotent cell type, which can self-renew and differentiate to all blood cell lineages. The unique features of HSCs support a vital process of replenishing the stem cell pool within an individual. Although HSCs have been identified and studied for many years, the molecular mechanism of HSC function remains poorly understood. An emerging area in stem cell research in recent years have focused on epigenetic regulations, such as DNA methylation and histone modifications, which are crucial in regulating gene expression patterns and maintaining a stem cell identity. Recent studies have revealed the significant role of Bmi-1 in the regulation of HSC function, which is partially associated with the downstream Ink4a-Arf pathway. Since Bmi-1 is a core component of polycomb repressive complex which repress gene expression by introducing histone H2A ubiquitination H2AK119ub1, we hypothesize that Bmi-1 can epigenetically regulated global transcription machinery in HSC by the introduction of H2AK119ub1 at its targeted gene loci. Nevertheless, most of the Bmi-1 studies examine histone modifications in single gene locus, which restricts the scope of understanding the complete function of Bmi-1 in HSC. With the technology advancement of next generation sequencing, we propose analyses of the genome-wide epigenetic and transcriptomic pattern associated with Bmi-1 in HSC. We aim to reveal the association between Bmi-1 mediated H2AK119ub1 and the HSC transcription program, and unravel the epigenetic mechanism that controls HSC self-renewal and multipotency. On the other hand, strong expression of BMI-1 is associated with leukemia development, potentially involved in the establishment of leukemic stem cell. The function of Bmi-1 and its target genes will therefore be studied in an MLL-rearranged leukemia cell model, which delineates the molecular synergism between Bmi-1 and MLL fusion protein in the process of leukemogenesis. Taken together, the new knowledge gained from this project can shed light on the epigenetic mechanism of Bmi-1 in HSC biology, and provide new insight onto the therapeutic targets of leukemia.

造血干细胞是具有多潜能性的细胞可以自我更新并分化成任何血细胞类型。近年表观遗传学发现这些调控对于调节基因表达和维持干细胞特性都非常重要。最近的研究显示Bmi-1在调节造血干细胞功能中有明显作用。由于Bmi-1是polycomb抑制复合体的核心组分，并通过引发组蛋白H2A泛素化(H2AK119ub1)来抑制基因表达。我们设想Bmi-1是通过在它的目标基因位点引入H2AK119ub1来调节造血干细胞的全局转录机制。通过利用下一代测序技术进行H2AK119ub1全基因组特征分析，我们可以揭示Bmi-1介导的H2AK119ub1和造血干细胞转录机制之间的联系，并阐明造血干细胞自我更新和多潜能性的表观遗传学机理。另外我们将在MLL基因重组的白血病细胞模型中研究Bmi-1和它目标基因的功能。这个研究项目将有助于理解造血干细胞生物学的表观遗传机制，同时也为治疗白血病提供了新的治疗靶点。

造血干细胞是具有多潜能性的细胞。在小鼠造血干细胞中操纵多梳组蛋白Bmi-1的表达会改变细胞增殖和集落形成的潜力，这表明Bmi-1在造血干细胞的自我更新和维护起着关键的作用。通过RNA测序数据的分析，我们已经确定了共1263个基因（722个上调和541个下调）在造血干细胞中是被BMI-1监管的。许多失调的基因都涉及到关键的细胞事件，如细胞增殖，分化和各种细胞信号传导途径，包括Wnt信号传导，而影响造血干细胞的功能。Bmi-1的高表达能把造血干细胞的β连环蛋白作出温和的诱导。β连环蛋白的诱导在过去的报道中是与造血干细胞的自我更新有关联的。此外，我们已发现BMI-1能够抑制Amer2的表达。Amer2是Wnt信号的负调节的启动子。这进一步支持了BMI-1可通过Wnt信号传导的调节来控制造血干细胞的自我更新。..另一方面，我们发现BMI-1在多个人白血病细胞系中属于较低的表达水平。要注意的是BMI-1在人白血病细胞系过表达能够抑制其细胞增殖和集落形成的潜力。这意味着BMI-1可能在人白血病细胞是有肿瘤抑制功能的。我们利用BMI-1过表达的白血病细胞进一步研究不同的细胞信号传导途径，发现JAK-STAT信号传导被抑制，导致BMI-1表达能够减少细胞增殖和增加细胞凋亡。我们还注意到IL-7的细胞因子途径被抑制，从而减少了细胞存活基因PAX5, MCL-1，BCL-2和BCL-X L的表达。此外，我们发现BMI-1能上调JAK-STAT的负调节基因SOCS1和SOCS3的表达。所以我们得出的结论是BMI-1通过上调SOCS1和SOCS3的基因表达来抑制JAK-STAT信号传导，导致抑制白血病细胞的增长。..我们的研究在造血干细胞自我更新的调控提出新的见解。这能显著提高对造血干细胞的理解和它的临床应用，例如扩大造血干细胞的数目进行细胞移植。此外，我们已经确定BMI1在白血病的肿瘤抑制功能。这将有利于发展标靶BMI-1为目标的白血病治疗策略。