Molecular and Cellular Mechanisms of Chronic Myelomonocytic Leukemia (CMML)

描述（由申请人提供）：慢性粒单核细胞白血病（CMML）是一种毁灭性的癌症，目前没有有效的治疗方法。大约20%的CMML病例在初次诊断后不久演变为急性髓细胞性白血病（AML）。致癌NRAS突变是骨髓疾病中最常见的基因突变之一，在17-60%的CMML病例中发现了致癌NRAS突变，包括转化为AML的病例。然而，致癌的内源性NRAS突变如何导致CMML及其向AML的转化仍然是难以捉摸的。最近，我们建立了一种小鼠骨髓移植模型，该模型在内源性Nras基因座中携带致癌G12 D突变，其中约95%的受体小鼠发生与人CMML的MP变体显著相似的骨髓增生性（MP）疾病。我们的初步结果表明，内源性致癌Nras信号促进HSC增殖和流动性，而不是凋亡和衰老。我们建议，在这个模型中，基因改变的HSC启动和维持CMML。此外，与CMML患者中发生的情况类似，异常GM-CSF（粒细胞-巨噬细胞集落刺激因子）信号传导是我们模型的特征，主要调节粒细胞/单核细胞前体的扩增。我们推测，这种异常的信号传导在疾病的发生和发展过程中驱动了不适当的细胞生长和存活，因此可能构成一个有价值的治疗靶点。由于在我们的模型中，CMML发生在长时间的潜伏期后，伴随着多个额外的遗传病变，我们进一步假设，对于人CMML，致癌NRAS与其他基因的突变合作，诱导CMML或导致CMML转化为AML。作为我们长期研究肿瘤发生、发展和恶性转化的分子和细胞机制的一部分，本申请提出：1）确定内源性致癌Nras信号对HSC性质的影响，并检测表达致癌Nras的HSC是否启动和维持CMML; 2）确定异常GM-CSF信号传导是否是建立和/或维持致癌Nras启动的CMML样表型所必需的; 3）使用CMML患者样品鉴定涉及CMML和/或其转化为AML的新的致病性起源，并验证我们的CMML鼠模型中致癌NRAS的协同突变。所提出的研究的成功完成将不仅提供对CMML的发病机制、进展和转化的见解，而且还可能导致对一般致癌NRAS相关骨髓疾病中的HSC调节、异常细胞因子信号传导和协同突变的新见解。

DESCRIPTION (provided by applicant): Chronic myelomonocytic leukemia (CMML) is a devastating cancer for which there is currently no effective therapy. Approximately 20% of CMML cases evolve to acute myelogenous leukemia (AML) soon after their initial diagnosis. Oncogenic NRAS mutations, which are among the most frequently identified genetic mutations in myeloid diseases, are identified in 17-60% of CMML cases, including cases that transform to AML. However, it remains elusive how oncogenic, endogenously arising NRAS mutations leads to CMML and its transformation to AML. Recently, we established a mouse bone marrow transplantation model harboring an oncogenic G12D mutation in the endogenous Nras locus in which ~95% of recipient mice develop a myeloproliferative (MP) disease remarkably resembling the MP variant of human CMML. Our preliminary results suggest that endogenous oncogenic Nras signaling promotes HSC proliferation and mobility rather than apoptosis and senescence. We propose that genetically altered HSCs initiate and maintain CMML in this model. In addition, similar to what occurs in patients with CMML, aberrant GM-CSF (granulocyte-macrophage colony stimulating factor) signaling is a signature of our model, primarily regulating expansion of granulocytic/monocytic precursors. We hypothesize that this aberrant signaling drives inappropriate cell growth and survival during disease initiation and progression, and thus could constitute a valuable therapeutic target. Because CMML occurs after a prolonged latency accompanied by multiple additional genetic lesions in our model, we further hypothesize that, as for human CMML, oncogenic NRAS cooperates with mutations in other genes to either induce CMML or lead to CMML transformation to AML. As a part of our long-term goal to understand the molecular and cellular mechanisms in tumor initiation, progression, and malignant transformation, in this application we propose: 1) To determine the effects of endogenous oncogenic Nras signaling on the properties of HSCs and examine whether HSCs expressing oncogenic Nras initiate and maintain CMML; 2) To determine whether aberrant GM-CSF signaling is essential to establish and/or maintain oncogenic Nras-initiated CMML-like phenotypes; 3) To identify novel pathogenic origins involved in CMML and/or its transformation to AML using CMML patient samples and to validate cooperating mutations of oncogenic NRAS in our murine model of CMML. Successful accomplishment of the proposed studies will not only provide insights into the pathogenesis, progression, and transformation of CMML, but may also lead to novel insights into HSC regulation, aberrant cytokine signaling, and cooperating mutations in oncogenic NRAS- associated myeloid diseases in general.