Mammalian H3K4 Methylases, Chromosomal Translocations and Human Leukemia

描述（由申请方提供）：导致基因表达改变的染色体重排是血液恶性肿瘤的主要原因。这项资助申请的重点是MLL家族蛋白质及其嵌合体的分子功能和生化特性的表征，希望能促进我们对基于免疫的白血病分子机制的理解。我们在过去五年中的研究大大扩展了我们对MLL 1及其易位伙伴之一ELL蛋白作用的分子理解。我们和其他人已经确定MLL，MLL相关蛋白及其复合物为组蛋白H3赖氨酸4（H3 K4）甲基化酶。通过我们的生物化学和遗传筛选，我们还确定了H3 K4甲基化酶的适当酶活性所需的分子机制。我们还证明了ELL蛋白，白血病中MLL 1的伙伴之一，是一个真正的RNA聚合酶II延伸因子，调节RNA聚合酶II延伸形式的转录特性。这些研究有助于建立这样的范式，即通过甲基化和转录延伸控制的染色质翻译后修饰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H3 K4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。具体目标1的重点是确定六种哺乳动物H3 K4甲基化酶的基因靶点，并定义这些甲基化酶如何获得其基因靶点特异性，并了解H3 K4甲基化在这些位点的生物学意义。具体目标2的重点是几个MLL易位嵌合体的生化分离和定义其分子组成，希望确定嵌合体之间的分子共性，这可能会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本申请中提出的目标。拟议的研究应（i）有一个根本性的影响，我们的理解如何MLL易位导致血液恶性肿瘤的发病机制;和（ii）有助于我们理解的不同角色，哺乳动物H3 K4甲基化酶机制在发展和分化过程中发挥作用。这些研究提供的信息有可能在某一天证明有助于研究人员试图设计合理的方法，用于治疗某些人类恶性肿瘤的靶向特异性治疗。 公共卫生相关性：本申请的重点是一组蛋白质（MLL 1 -4和Set 1A/B），它们通过甲基化调节活细胞染色质的翻译后修饰。这种修饰可以改变细胞生长、分裂和分化特性。重要的是，这些基因之一，MLL 1是在基于易位的白血病中发现的。因此，详细了解MLL及其家族成员的分子功能对于人类白血病的检测、诊断和治疗至关重要。

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.