Molecular and Cellular Mechanisms of Chronic Myelomonocytic Leukemia (CMML)

描述(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，目前还没有有效的治疗方法。大约20%的CMML病例在最初诊断后不久演变为急性髓系白血病(AML)。致癌NRAS突变是髓系疾病中最常见的基因突变之一，在17-60%的CMML病例中被发现，包括转化为AML的病例。然而，致癌的、内源性的NRAS突变如何导致CMML及其向AML的转化仍然难以捉摸。最近，我们建立了一种内源性NRAS基因G12D突变的小鼠骨髓移植模型，在该模型中，约95%的受鼠患上了与人类CMML的MP变异体非常相似的骨髓增生性疾病。我们的初步结果表明，内源性NRAS信号促进了HSC的增殖和迁移，而不是促进了细胞的凋亡和衰老。我们认为，在这个模型中，基因改变的HSCs启动和维持CMML。此外，类似于CMML患者的情况，异常的GM-CSF(粒细胞-巨噬细胞集落刺激因子)信号是我们模型的特征，主要调控粒/单核细胞前体的扩张。我们推测，在疾病的起始和发展过程中，这种异常的信号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发生在潜伏期延长并伴有多个额外的遗传损害之后，我们进一步假设，对于人类CMML，致癌的NRAS与其他基因的突变合作，要么诱发CMML，要么导致CMML向AML的转化。作为我们了解肿瘤发生、发展和恶变的分子和细胞机制的长期目标的一部分，在本应用中，我们建议：1)确定内源性致癌NRAS信号对造血干细胞特性的影响，并检测表达致癌NRAS的造血干细胞是否启动和维持CMML；2)确定GM-CSF信号是否对于建立和/或维持致癌NRAS启动的CMML样表型至关重要；3)利用CMML患者样本确定CMML和/或其向AML转化所涉及的新的致病来源，并在我们的CMML小鼠模型中验证致癌NRAS的协同突变。这些研究的成功完成不仅将为CMML的发病机制、进展和转化提供新的见解，而且还可能导致对HSC调节、异常细胞因子信号转导和肿瘤基因NRAS相关髓系疾病的协同突变的新见解。

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.