The role of fusion protein, OTT-MKL1, in acute megakaryoblastic leukemia

描述（由申请人提供）：急性巨核母细胞白血病（AMKL）是急性髓系白血病的一种亚型，其特征是胎儿肝脏和/或骨髓中巨核母细胞增加。白血病通常出现在婴儿身上，预后很差。与AMKL相关的主要细胞遗传学异常之一是1号和22号染色体之间的易位，导致融合蛋白OTT-MKL1 （OM）的产生。在我们的实验室中，我们发现OTT和MKL1在正常巨核形成过程中存在差异调控，在分化过程中OTT表达下调，而MKL1表达上调，我们已经开始阐明OTT和MKL1的功能。然而，OM在巨核细胞分化和/或白血病发生中的分子功能在很大程度上是未知的。我们观察到，在各种细胞系和原代细胞中，OM表达可迅速诱导细胞死亡。此外，在先前发表的表达OM融合转基因的小鼠模型中，AMKL在这些小鼠中的发展缓慢且罕见。这些结果表明，OM诱导的白血病是一个多步骤的过程，需要在癌细胞中获得额外的突变，以使OM诱导的初始细胞死亡和随后的增殖存活。因此，我假设额外的协同基因组病变促进了OM诱导的AMKL，这些突变定义了促进AMKL的因素网络。我建议阐明OM破坏正常巨核细胞分化并诱导白血病的机制。我将根据AMKL患者样本的深度测序数据确定潜在的OM协同突变，并使用具有工程诱导OM转基因表达的小鼠和人类造血细胞验证这些突变。我将使用shRNA和小分子筛选方法来补充我的突变分析，从功能上定义受OM融合基因影响的基因和信号网络。这些研究将提供OM的关键分子细节及其在AMKL中的白血病发生作用，以了解该疾病并开发针对该疾病的靶向治疗方法。

DESCRIPTION (provided by applicant): Acute megakaryoblastic leukemia (AMKL) is a subtype of acute myeloid leukemia characterized by increased megakaryoblasts in the fetal liver and/or bone marrow. The leukemia usually presents in infants, and has a very poor prognosis. One of the main cytogenetic abnormalities associated with AMKL is a translocation between chromosomes 1 and 22, resulting in the fusion protein, OTT-MKL1 (OM). In our laboratory, we discovered that OTT and MKL1 are differentially regulated in normal megakaryopoiesis as OTT expression is downregulated whereas MKL1 expression is upregulated during the differentiation, and we have begun to elucidate the functions of OTT and MKL1. However, the molecular function of OM in megakaryocyte differentiation and/or in leukemogenesis is largely unknown. We have observed a rapid induction of cell death upon OM expression in various cell lines and primary cells. Furthermore, in a previously published mouse model expressing the OM fusion transgene, development of AMKL in these mice is slow and rare. These results suggest that OM induced leukemia is a multistep process that requires acquisition of additional mutations in cancer cells for survival of the initial cell death induced by OM and for subsequent proliferation. Therefore, I hypothesize that additional collaborating genomic lesions promote OM- induced AMKL and these mutations define a network of factors that promote AMKL. I propose to elucidate the mechanisms by which OM disrupts normal megakaryocytic differentiation and induces leukemia. I will identify potential OM-collaborating mutations based on deep sequencing data from an AMKL patient sample and validate these mutations using primary murine and human hematopoietic cells with engineered inducible OM transgene expression. I will complement my mutation analysis using shRNA and small molecule screening approaches to functionally define genes and signal networks affect by the OM fusion gene. These studies will provide critical molecular details of OM and its leukemogenic role in AMKL to understand the disease and for development of targeted therapies for this disease. ) PUBLIC HEALTH RELEVANCE: Chromosome translocation is a common structural abnormality in cancer cells that results from joining of two separate chromosomes at a specific breakpoint to generate a fusion gene whose product promotes oncogenesis. Acute megakaryoblastic leukemia is associated with a recurrent translocation that results in a fusion protein. My project aims to determine molecular mechanisms responsible for the fusion protein to induce acute megakaryoblastic leukemia. )