Function of ADAR1 in Hematopoietic and Leukemia Stem Cells

描述(申请人提供)：本项目旨在明确作用于RNA1的RNA编辑酶腺苷脱氨酶(ADAR1)在造血干细胞和白血病干细胞中的功能。特别是，将确定这些干细胞中ADAR1的RNA编辑活性的要求。ADAR1是胚胎和成人造血所必需的蛋白质，而白血病细胞更容易受到编码ADAR1的基因缺失的影响。然而，在ADAR1缺失的情况下，移植的造血干细胞(HSC)在受者体内的造血再繁殖受到抑制，归巢和自我更新能力保持不变。大量细胞死亡仅发生在分化的祖细胞中。此外，在小鼠白血病模型中发现，在所有治疗的动物中，ADAR1的移除会导致包括白血病干/祖细胞在内的大量白血病细胞在一周内死亡。阐明ADAR1对正常和白血病干细胞(LSC)的不同影响，可能有助于揭示白血病干细胞的特性，并有助于发现白血病治疗的分子靶点。该项目的目标是描述ADAR1对正常和LSC的不同影响，并开发一种通过靶向ADAR1来消除白血病干细胞的治疗策略。尽管ADAR1被确定为一种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，但到目前为止，多次尝试都无法确定导致ADAR1基因敲除的正常造血和白血病细胞死亡的编辑靶点。在缺乏已知的因果编辑转录本的情况下，确定ADAR1对白血病和LSCs的S效应所需的RNA编辑是具有挑战性的，特别是因为最近已经描述了ADAR1的编辑独立功能。这里假设ADAR1的RNA编辑活性不能解释它在白血病细胞中的功能。这一建议是为了寻求ADAR1的编辑活动是否对LSC的增殖和分化是必要的确定答案。因此，本项目将首先建立一个敲入(KI)小鼠模型，在该模型中，用于RNA编辑的非活性ADAR1是由突变的内源性ADAR1基因表达的。然后分析失活的ADAR1对ADAR1Ki动物的造血细胞和LSCs的影响。将观察HSC和LSC以及成熟细胞，并将其与野生型和ADAR1基因敲除细胞进行比较。本项目所获得的知识将有助于了解LSC与白血病的发展，并最终有助于提高白血病的治疗水平。

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.