Function of ADAR1 in Hematopoietic and Leukemia Stem Cells

项目描述（由申请人提供）：本项目旨在确定RNA编辑酶腺苷脱氨酶作用于RNA 1（ADAR 1）在造血干细胞和白血病干细胞中的功能。特别地，将确定这些干细胞中ADAR 1的RNA编辑活性的需求。ADAR 1是胚胎和成人造血的必需蛋白，而白血病细胞更容易受到编码ADAR 1的基因缺失的影响。 尽管在缺乏ADAR 1的情况下，移植的造血干细胞（HSC）在受体中的造血再增殖受到抑制，但归巢和自我更新能力是完整的。 大量的细胞死亡只发生在分化的祖细胞中。此外，在小鼠白血病模型中已经发现，在所有治疗的动物中，ADAR 1的去除在一周内导致大量白血病细胞死亡，包括白血病干细胞/祖细胞。 描述ADAR 1对正常和白血病干细胞（LSC）的差异性影响可能会揭示白血病干细胞的特征，并导致发现白血病治疗的分子靶点。该项目的目标是描述ADAR 1对正常和LSC的不同影响，并开发通过靶向ADAR 1消除白血病干细胞的治疗策略。虽然ADAR 1被鉴定为RNA编辑酶，并且RNA编辑已被证明在干细胞和其他生物过程中发挥关键作用，但迄今为止的多次尝试都无法鉴定导致ADAR 1敲除的正常造血细胞和白血病细胞死亡的编辑靶标。 在缺乏已知的因果编辑转录物的情况下，确定ADAR 1对白血病和LSC的作用需要RNA编辑是具有挑战性的，特别是因为最近已经描述了ADAR 1的编辑独立功能。这里假设ADAR 1的RNA编辑活性不能解释其在白血病细胞中的功能。本研究的目的是寻求ADAR 1的编辑活性是否是LSC增殖和分化所必需的明确答案。因此，本项目将首先产生敲入（KI）小鼠模型，其中从突变的内源性ADAR 1基因表达用于RNA编辑的失活ADAR 1。 然后将在ADAR 1 KI动物中分析失活ADAR 1对造血和LSC的影响。将观察HSC和LSC以及成熟细胞，并与野生型和ADAR 1敲除细胞进行比较。 本研究所获得的知识将有助于了解LSC和白血病的发展，并最终有助于改善白血病的治疗。

DESCRIPTION (provided by applicant): This project is to define the function of RNA editing enzyme adenosine deaminase acting on RNA 1 (ADAR1) in hematopoietic and leukemia stem cells. Particularly the requirement of RNA editing activity of ADAR1 in these stem cells will be determined. ADAR1 is an essential protein for embryonic and adult hematopoiesis, while the leukemia cells are more susceptible to the gene deletion that codes ADAR1. Whereas hematopoietic repopulation in the recipients by transplanted hematopoietic stem cell (HSC) is suppressed in the absence of ADAR1, the homing and self-renewal capacities are intact. Massive cell death only occurred in the differentiating progenitor cells. Moreover, it have been found in a mouse leukemia model removal of ADAR1 causes massive leukemia cell death including the leukemia stem/progenitor cells within one week in all the treated animals. Delineation of the discrepant impacts of ADAR1 on normal and leukemia stem cells (LSC) might shed a light on the characterization of the leukemia stem cells and lead to a discovery of a molecular target for leukemia treatment. The goal of this project is to delineate the different impacts of ADAR1 on normal and LSC and develop a therapeutic strategy to eliminate leukemia stem cells by targeting ADAR1. Although ADAR1 is identified as an RNA editing enzyme and RNA editing has been shown to play critical roles in stem cells and other biological processes, multiple attempts to date have been unable to identify an editing target that accounts for the death of normal hematopoietic and leukemia cells of ADAR1 knockouts. It is challenging to determine RNA-editing is required for ADAR1's effects on leukemia and LSCs in the absence of a known causal edited transcript, particularly because editing-independent functions fo ADAR1 have recently been described. It is hypothesized here that the RNA editing activity of ADAR1 does not account for its function in leukemia cells. This proposal is to seek a definitive answer whether the editing activity of ADAR1 is necessary for the proliferation and differentiation of LSCs. Therefore this project will first generate a Knock-In (KI) mouse model in which an inactive ADAR1 for RNA editing is expressed from mutated endogenous ADAR1 gene. Then the impact of inactive ADAR1 on the hematopoietic and LSCs will be analyzed in the ADAR1 KI animals. HSC and LSC as well as the mature cells will be observed and compared to wild type and ADAR1 knockout cells. The knowledge obtained from this project will help to understand the LSC and leukemia development and eventually contribute to improve the leukemia treatment.