Mammalian H3K4 Methylases, Chromosomal Translocations and Human Leukemia

描述（由申请人提供）：染色体重排导致基因表达改变是血液学恶性肿瘤的主要原因。这项资助申请的重点是MLL蛋白家族及其嵌合体的分子功能和生化特性的表征，希望能促进我们对重排白血病分子机制的理解。在过去的五年里，我们的研究大大扩展了我们对MLL1及其易位伙伴之一ELL蛋白的作用的分子理解。我们和其他人已经鉴定出MLL、MLL相关蛋白及其复合物是组蛋白H3赖氨酸4 （H3K4）甲基化酶。通过我们的生化和遗传筛选，我们还确定了H3K4甲基化酶的适当酶活性所需的分子机制。我们还证明，白血病中MLL1的伙伴之一ELL蛋白是一种真正的RNA聚合酶II延长因子，调节RNA聚合酶II延长形式的转录特性。这些研究有助于创建一个范例，即染色质的翻译后修饰通过甲基化和转录延伸控制参与白血病的病因学。在这些发现的基础上，本提案的目标是表征哺乳动物H3K4甲基化酶的基因靶点，并通过mll嵌合体了解基于易位的白血病的分子机制。这些目标将通过两个具体目标积极实现。Specific Aim 1的重点是鉴定六种哺乳动物H3K4甲基化酶的基因靶标，并定义这些甲基化酶如何获得其基因靶标特异性，并了解这些位点上H3K4甲基化的生物学意义。特异性目的2侧重于几种mll易位嵌合体的生化分离，并确定它们的分子组成，以期确定嵌合体之间的分子共性，这可能导致白血病表型的发病机制。我们将利用各种生物化学，分子和遗传工具来解决在这个应用程序中提出的目标。拟议的研究应该(i)对我们对MLL易位如何导致血液恶性肿瘤发病机制的理解产生根本性影响；（ii）有助于我们理解哺乳动物H3K4甲基化酶机制在发育和分化过程中所起的不同作用。这些研究提供的信息有可能在某一天证明有助于研究者尝试设计合理的方法来使用靶向特异性疗法治疗某些人类恶性肿瘤。

DESCRIPTION (provided by applicant): Chromosomal rearrangements resulting in alteration of gene expression are a major cause of hematological malignancies. This grant application is focused on the characterization of the molecular functions and biochemical properties of the MLL family of proteins and its chimeras in the hope of advancing our understanding of the molecular mechanisms of rearrangement-based leukemia. Our studies during the past five years have considerably expanded our molecular understanding of the role of MLL1 and one of its translocation partners, the ELL protein. We and others have identified MLL, MLL-related proteins and their complexes as histone H3 lysine 4 (H3K4) methylases. Through our biochemical and genetic screens, we have also identified the molecular machinery required for the proper enzymatic activity of the H3K4 methylases. We have also demonstrated that the ELL protein, one of the MLL1 partners in leukemia, is a bona fide RNA polymerase II elongation factor regulating the transcriptional properties of the elongating form of RNA polymerase II. These studies have helped to create the paradigm that posttranslational modifications of chromatin by methylation and transcriptional elongation control participate in the etiology of leukemia. Building on these discoveries, the goals of this proposal are to characterize the gene targets of the mammalian H3K4 methylases and to understand the molecular mechanism of translocation-based leukemia via MLL-chimeras. These goals will be aggressively pursued via two specific aims. Specific Aim 1 is focused on identifying the gene targets of the six mammalian H3K4 methylases and to define how these methylases acquire their gene target specificity and understand the biological significance of H3K4 methylation at such sites. Specific Aim 2 is focused on the biochemical isolation of several of the MLL-translocation chimeras and on defining their molecular composition in the hope of identifying a molecular commonality among the chimeras, which may result in the pathogenesis of a leukemic phenotype. We will take advantage of a variety of biochemical, molecular and genetic tools to address the aims proposed in this application. The proposed studies should (i) have a fundamental impact on our understanding of how MLL translocations result in the pathogenesis of hematological malignancies; and (ii) be instrumental for our understanding of the diverse roles that the mammalian H3K4 methylase machinery plays during development and differentiation. The information provided by these studies have the potential of some day proving helpful to investigators attempting to design rational approaches for the treatment of certain human malignancies using target specific therapeutics. PUBLIC HEALTH RELEVANCE: The focus of this application is on a group of proteins (MLL1-4 and Set1A/B) that regulate the posttranslational modification of the chromatin of living cells by methylation. This modification can alter cell growth, division, and differentiation properties. Importantly, one of these genes, the MLL1 is found in translocation-based leukemia. Therefore, detailed knowledge of the molecular functions of MLL and its family members will be critical for the detection, diagnosis and treatment of human leukemia.