The Role of DDX41 in Inherited Myelodysplastic Syndromes

项目摘要 骨髓增生异常综合征(MDS)是由造血干/祖细胞受损引起的遗传性疾病 细胞(HSPC)，可转化为急性髓系白血病(AML)。MDS通常发生在老龄化时期 然而，MDS也可作为年轻个体遗传种系突变的结果。 DEAD/H-box解旋酶基因DDX41的突变是与 遗传的MDS。遗传性DDX41突变是杂合性的，通常是移码，这表明 这些突变导致DDX41功能丧失。DDX41突变也在新生MDS和 AML，是典型的错义突变，经常导致氨基酸替换R525H。DDX41是 一种能分解三磷酸腺苷的RNA解旋酶，可作为天然免疫感受器、RNA剪接因子和 核糖体调节剂。DDX41突变改变HSPC功能及其贡献的确切机制(S) 对MDS/AML的影响仍不清楚。因此，拟议的项目将定义DDX41突变在 MDS/AML的发病机制。模拟在人类MDS中观察到的移码突变并确定其作用 对于正常造血中的DDX41，我们产生了造血特异性和条件性Ddx41缺陷 老鼠。我们的初步数据显示，DDX41缺乏(完全敲除)与 HSPC功能和造血功能，而DDX41杂合子增加骨髓HPSC。此外，通过 蛋白质组学和生化相结合的方法我们在白血病中发现了一种新的DDX41相互作用蛋白 细胞，SAMHD1，dNTPase和宿主防御因子，控制dNTP的细胞池。总的来说，我们的 初步数据表明，DDX41在造血和HSPC功能中起关键作用。我们假设 DDX41表达和/或功能减弱导致无效的造血和 MDS和AML的发病机制，部分是由于SAMHD1活性增加和细胞dNTP池改变。 因此，这项建议的目标是建立正常和正常个体的体细胞和生殖系DDX41突变模型。 目的：阐明DDX41基因在HSPC功能中的分子功能。 通过广泛的造血途径，我们将确定DDX41缺乏和R525H的作用 MDS发病和进展为AML的表达(目标1)。由于DNMT3A和DDX41突变 通常在进展为AML的MDS患者中并存，我们将确定DDX41是否 杂合性或R525H表达与DNMT3A缺陷小鼠相结合将导致高危MDS或 公开的AML。减少的细胞dNTP池损害细胞周期进程并导致基因组不稳定； 因此，我们将确定SAMHD1活性在DDX41缺乏的HSPC或突变的MDS中的作用，以及 细胞dNTPs池减少是否导致基因组不稳定和急性髓系白血病的发展(目标2)。通过 阐明DDX41恶性造血的功能，我们预计将揭示新的机制 潜在的继承的和从头开始的MDS。

Project Summary Myelodysplastic syndromes (MDS) are genetic disorders caused by impaired hematopoietic stem/progenitor cells (HSPC), which can transform to acute myeloid leukemia (AML). MDS typically occurs in the ageing population, however MDS can also manifest as a result of inherited germline mutations in younger individuals. Mutations in the DEAD/H-box helicase gene DDX41 are among the most common alterations associated with inherited MDS. Inherited DDX41 mutations are heterozygous and are typically frameshifts, suggesting that these mutations result in loss of DDX41 function. DDX41 mutations are also observed in de novo MDS and AML, and are typically missense mutations frequently resulting in the amino acid substitution R525H. DDX41 is an RNA helicase that hydrolyzes ATP, and can function as an innate immune sensor, RNA splicing factor, and ribosome regulator. The precise mechanism(s) by which DDX41 mutations alter HSPC function and contribute to MDS/AML remains unknown. As such, the proposed project will define the role of DDX41 mutations in the pathogenesis of MDS/AML. To mimic the frameshift mutations observed in human MDS and determine the role of DDX41 in normal hematopoiesis, we generated hematopoietic-specific and conditional Ddx41-deficient mice. Our preliminary data has revealed that DDX41-deficiency (complete knockout) is not compatible with HSPC function and hematopoiesis, whereas DDX41 heterozygosity increases BM HPSC. In addition, through integrative proteomic and biochemical approaches we identified a novel DDX41-interacting protein in leukemic cells, SAMHD1, a dNTPase and host defense factor, which controls cellular pools of dNTPs. Collectively, our preliminary data indicate that DDX41 has a critical role in hematopoiesis and HSPC function. We hypothesize that diminished DDX41 expression and/or function contributes to ineffective hematopoiesis and to the pathogenesis of MDS and AML, in part due to increased SAMHD1 activity and altered cellular dNTP pools. Therefore, the objectives of this proposal are to model somatic and germline DDX41 mutations in normal and malignant hematopoiesis, and to elucidate the molecular function of DDX41 required for HSPC function. Through extensive hematopoietic approaches, we will define the role of DDX41 deficiency and R525H expression in MDS incidence and progression to AML (Aim 1). Since DNMT3A and DDX41 mutations commonly co-occur in MDS patients that have progressed to AML, we will determine whether DDX41 heterozygosity or R525H expression combined with DNMT3A-deficient mice will result in high-risk MDS or overt AML. Reduced cellular dNTP pools impair cell cycle progression and result in genomic instability; therefore, we will determine the role of SAMHD1 activity in DDX41-deficient HSPC or mutant MDS, and whether diminished cellular dNTPs pools lead to genomic instability and development of AML (Aim 2). By elucidating the function of DDX41 malignant hematopoiesis, we predict to uncover novel mechanisms underlying inherited and de novo MDS.