Role of MLL1 and MLL1 leukemogenic fusions in maintaining transcriptional memory

MLL1 和 MLL1 致白血病融合在维持转录记忆中的作用

• 批准号: 8782704
• 负责人: Sarah Ching-Lan Hsu
• 金额: $ 4.68万
• 依托单位: UNIVERSITY OF PENNSYLVANIA
• 依托单位国家: 美国
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8782704
• 关键词: Address; Adult; Architecture; Binding; Biological Assay; Blood; Bone Marrow; Bone Marrow Cells; Cell Cycle; Cell Line; Cell Survival; Cell division; Cells; Chimera organism; Chimeric Proteins; Chromatin; Chromosomal translocation; Chromosomes; Commit; Cyclin B; DNA; Data; Development; Embryo; Engineering; Epigenetic Process; Exhibits; FUS-1 Protein; Fibroblasts; Flow Cytometry; Gene Expression; Gene Expression Profile; Gene Targeting; Genes; Genetic Transcription; Goals; Hematopoiesis; Hematopoietic; Hematopoietic stem cells; Immunofluorescence Immunologic; Interphase; Interphase Cell; Laboratories; Life; MLL-AF9; MLL2 gene; Malignant - descriptor; Measures; Mediating; Memory; Mitosis; Mitotic; Mitotic Chromosome; Molecular; Mus; Mutation; Nuclear; Oncogenic; Pattern; Population; Property; RNA Polymerase II; Relative (related person); Role; Series; Stem cells; Techniques; Tertiary Protein Structure; Testing; bone marrow hyperplasia; cellular imaging; chromatin immunoprecipitation; daughter cell; genome-wide; histone methyltransferase; insight; leukemia; leukemogenesis; metaplastic cell transformation; novel; programs; public health relevance; research study; self-renewal; small hairpin RNA; stem; transcription factor

DESCRIPTION (provided by applicant): Normal development necessitates that cells establish specific gene expression patterns and transmit them stably through cell division. During mitosis, transcription ceases as most transcriptional regulators are removed from their target genes. The mechanism by which newly formed daughter cells reassemble the transcriptional apparatus to reactivate appropriate gene expression programs is thought to involve nuclear factors that remain bound to mitotic chromosomes, termed mitotic bookmarks. However, an understanding of what enables mitotic retention of these factors, as well as their specific role(s) in lineage commitment and/or lineage stability remains incomplete. The goal of this proposal is to define the mechanism by which the bookmarking factor MLL1 (mixed lineage leukemia 1) occupies its mitotic targets, and to determine whether mutations in MLL1 alter mitotic functions in such a way as to perturb hematopoiesis. Recent studies from our lab demonstrate that MLL1, a histone methyltransferase that is required for normal embryonic and adult hematopoiesis, is globally retained on mitotic chromosomes. MLL1 chromatin occupancy patterns are reorganized in mitosis, shifting towards the most highly expressed genes. Yet the physical interactions that control MLL1 mitotic redistribution, as well as its relevance to normal hematopoiesis are unknown. MLL1 is frequently rearranged via chromosomal translocation to generate leukemogenic fusion proteins that sustain aberrant gene expression programs and block hematopoietic differentiation. Preliminary results suggest that the MLL1 fusion protein, MLL-AF9, remains bound to mitotic chromosomes, however, whether this is required for MLL-AF9 to sustain inappropriate transcriptional patterns that result in leukemia is not known. In this proposal I will investigate the interactions that direct MLL1 mitotic occupancy, and examine the mitotic functions of MLL1 and MLL-AF9 in normal and malignant hematopoiesis. In Aim 1, I will systematically define the minimal region(s) of MLL1 that are both necessary and sufficient to bind mitotic chromatin, and assess mitosis-specific functions of MLL1 in hematopoietic progenitor cells. In Aim 2, I will examine the global occupancy patterns of MLL-AF9 and wild-type MLL1 in interphase and mitosis in leukemia cells, and define relationships to both normal and leukemia-specific transcriptional programs. I will determine if mitosis-specific MLL-AF9 function is required for leukemic transformation by engineering MLL-AF9 fusion proteins that are degraded selectively during mitosis. Together these experiments are expected to provide insight into the mechanisms by which MLL1 carries out its mitotic functions, and whether oncogenic MLL fusions exhibit perturbed mitotic bookmarking properties that impede normal programs of differentiation. More generally, the proposed studies are, to our knowledge, the first to directly test a role for epigenetic mitotic memory in cellular transformation.

描述（由申请人提供）：正常发育需要细胞建立特定的基因表达模式并通过细胞分裂稳定地传递它们。在有丝分裂期间，转录停止，因为大多数转录调节因子从其靶基因中去除。新形成的子细胞重新组装转录装置以重新激活适当的基因表达程序的机制被认为涉及与有丝分裂染色体保持结合的核因子，称为有丝分裂书签。然而，对于是什么使这些因子能够保留有丝分裂，以及它们在谱系定型和/或谱系稳定性中的具体作用的理解仍然不完整。 该提案的目标是确定标记因子 MLL1（混合谱系白血病 1）占据其有丝分裂靶点的机制，并确定 MLL1 的突变是否会改变有丝分裂功能，从而扰乱造血功能。我们实验室最近的研究表明，MLL1（一种正常胚胎和成人造血所需的组蛋白甲基转移酶）整体保留在有丝分裂染色体上。 MLL1 染色质占用模式在有丝分裂中重组，转向表达最高的基因。然而，控制 MLL1 有丝分裂重新分布的物理相互作用及其与正常造血的相关性尚不清楚。 MLL1 经常通过染色体易位进行重排，产生白血病融合蛋白，维持异常基因表达程序并阻止造血分化。初步结果表明，MLL1 融合蛋白 MLL-AF9 仍然与有丝分裂染色体结合，然而，这是否是 MLL-AF9 维持导致白血病的不适当转录模式所必需的尚不清楚。 在本提案中，我将研究指导 MLL1 有丝分裂占据的相互作用，并检查 MLL1 和 MLL-AF9 在正常和恶性造血中的有丝分裂功能。在目标 1 中，我将系统地定义 MLL1 的最小区域，这些区域对于结合有丝分裂染色质是必要且充分的，并评估 MLL1 在造血祖细胞中的有丝分裂特异性功能。在目标 2 中，我将检查白血病细胞间期和有丝分裂中 MLL-AF9 和野生型 MLL1 的整体占据模式，并定义与正常和白血病特异性转录程序的关系。我将通过设计在有丝分裂期间选择性降解的 MLL-AF9 融合蛋白来确定白血病转化是否需要有丝分裂特异性 MLL-AF9 功能。这些实验有望共同深入了解 MLL1 执行其有丝分裂功能的机制，以及致癌 MLL 融合是否表现出扰乱的有丝分裂标记特性，从而阻碍正常的分化程序。更一般地说，据我们所知，所提出的研究是第一个直接测试表观遗传有丝分裂记忆在细胞转化中的作用的研究。