The functional role of DDX41 in myelodysplastic syndromes

项目摘要 骨髓增生异常综合征（MDS）是一组以克隆性增生异常为特征的恶性血液病。 造血功能障碍、一种或多种血细胞减少和转化为急性髓性白血病（AML）的风险增加。 已确定多种突变与MDS相关。其中一个突变发生在死亡- 盒解旋酶4（DDX 41）基因。已经报道了至少70种DDX 41种系或体细胞突变，使得 DDX 41是最常突变的MDS易感基因之一。种系DDX 41突变导致其 功能丧失，而体细胞突变通常产生亚形态变化。斑马鱼的最新研究 DDX 41的敲除诱导增加的R环积累和异常造血。另一 使用条件性DDX 41敲除小鼠的研究报告，DDX 41双等位基因突变破坏snoRNA 生物发生并导致造血细胞凋亡。这些和其他研究开始揭示了 DDX 41突变的MDS发病机制。然而，仍然不清楚DDX 41的损失是如何发生的。 造血细胞引起细胞凋亡以及什么样的谱系对其缺乏最敏感。因此有 这对于剖析DDX 41功能的分子和细胞机制至关重要，这可能有助于 开发DDX 41突变型MDS的靶向治疗。G-四链体（G4）是四链的、非典型的 在富含鸟嘌呤的序列中形成的二级DNA结构。我们的初步研究表明， DDX 41导致造血系统中G4的异常上调。我们进一步发现，G4富集了 在红细胞生成过程中。由于DDX 41缺乏引起的G4积累严重破坏红细胞生成， 在体外和离体其他谱系中的作用。重要的是，我们验证了这些体外研究结果，并揭示， 造血特异性DDX 41敲除小鼠的致死性可能是由于红细胞生成缺陷。我们 初步的机制研究还显示，DDX 41缺陷介导的红系细胞G4上调 在红系细胞中，它损害了导致p53依赖性凋亡的各种核糖体蛋白的表达。 基于这些数据，我们假设MDS中DDX 41缺陷导致G4积累和G4缺陷。 核糖体生物发生，其特异性地在红系细胞中诱导p53介导的细胞死亡。为了验证我们的假设， 我们提出三个具体目标。目的1将重点研究DDX 41在不同谱系中的功能， 通过产生谱系特异性DDX 41敲除小鼠来获得造血细胞。在目标2中，我们将研究如何 DDX 41调节红细胞生成中G4的积累。目标3将侧重于以下方面的机理研究： DDX 41-G4-核糖体生物合成-p53途径。成功完成我们提出的研究将提供 DDX 41在正常和异常造血中的功能作用的新机制，这将对 DDX 41突变相关血液恶性肿瘤的新疗法的开发。

Project Summary Myelodysplastic syndromes (MDS) are a group of hematologic malignancies characterized by clonal hematopoiesis, one or more cytopenias, and increased risks to transform into acute myeloid leukemia (AML). Multiple mutations have been identified to be associated with MDS. One of these mutations occurs on DEAD- box helicase 4 (DDX41) gene. At least 70 DDX41 germline or somatic mutations have been reported, making DDX41 one of the most frequently mutated MDS predisposition genes. Germline DDX41 mutations lead to its loss of function whereas somatic mutations often produce hypomorphic changes. Recent studies in zebrafish showed that knockout of DDX41 induces increased R-loop accumulation and aberrant hematopoiesis. Another research using conditional DDX41 knockout mice reported that DDX41 biallelic mutations disrupt snoRNA biogenesis and lead to apoptosis in hematopoietic cells. These and other studies started to shed lights on the mechanisms of DDX41 mutated pathogenesis of MDS. However, it still remains unknown how loss of DDX41 in hematopoietic cells causes apoptosis and what lineages are most sensitive to its deficiency. Therefore, it is essential to dissect the molecular and cellular mechanisms of DDX41’s functions, which could be helpful to develop targeted therapy for DDX41 mutated MDS. G-quadruplexes (G4) are four-stranded, noncanonical secondary DNA structures formed in guanine-rich sequences. We showed in our preliminary study that loss of DDX41 led to aberrant upregulation of G4 in the hematopoietic system. We further revealed that G4 is enriched during erythropoiesis. G4 accumulation due to DDX41 deficiency severely disrupted erythropoiesis with less effects in other lineages in vitro and ex vivo. Importantly, we validated these in vitro findings and revealed that the lethality of hematopoietic-specific DDX41 knockout mice is likely due to the defects in erythropoiesis. Our preliminary mechanistic studies also revealed that DDX41 deficiency-mediated G4 upregulation in erythroid cells compromised the expression of various ribosome proteins that led to p53-dependent apoptosis in erythroid cells. Based on these data, we hypothesize that DDX41 deficiency in MDS leads to G4 accumulation and defects in ribosome biogenesis, which induces p53-mediated cell death specifically in erythroid cells. To test our hypothesis, we propose three specific aims. Aim 1 will focus on the study of the functions of DDX41 in various lineages of hematopoietic cells by generating lineage specific DDX41 knockout mice. In aim 2, we will investigate how DDX41 regulates the accumulation of G4 in erythropoiesis. Aim 3 will focus on the mechanistic studies on DDX41-G4-ribosomal biogenesis-p53 pathway. Successful completion of our proposed research will provide novel mechanisms of DDX41’s functional role in normal and abnormal hematopoiesis, which will be impactful for the development of novel therapies for DDX41 mutation-related hematologic malignancies.