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: 9110948
• 负责人: Sarah Ching-Lan Hsu
• 金额: $ 3.03万
• 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/9110948
• 关键词: Address; Adult; Architecture; Binding; Blood; Bone Marrow; Bone Marrow Cells; Cell Cycle; Cell Line; Cell Survival; Cell division; Cells; Chimera organism; Chimeric Proteins; Chromatin; Chromosomal translocation; Chromosomes; Cyclin B; DNA; Data; Development; Embryo; Engineering; Epigenetic Process; Exhibits; FUS-1 Protein; Fibroblasts; Flow Cytometry; Gene Chips; Gene Expression; Gene Expression Profile; Gene Expression Profiling; Gene Targeting; Genes; Genetic Transcription; Goals; Health; Hematopoiesis; Hematopoietic; Hematopoietic stem cells; Immunofluorescence Immunologic; Interphase; Interphase Cell; Laboratories; MLL-AF9; MLL2 gene; Malignant - descriptor; Measures; Mediating; Memory; Mitosis; Mitotic; Mitotic Chromosome; Mixed-Lineage Leukemia; Molecular; Mus; Mutation; Nuclear; Oncogenic; Pattern; Population; Property; RNA Polymerase II; Role; Series; Stem cells; Techniques; Tertiary Protein Structure; Testing; bone marrow hyperplasia; chromatin immunoprecipitation; daughter cell; genome-wide; histone methyltransferase; insight; leukemia; leukemogenesis; live cell imaging; metaplastic cell transformation; novel; programs; 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（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传递。在有丝分裂过程中，转录停止，因为大多数转录调节因子从它们的靶基因中被移除。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保持与有丝分裂染色体结合的核因子，称为有丝分裂书签。然而，理解什么使这些因子的有丝分裂保留，以及它们在谱系定型和/或谱系稳定性中的具体作用仍然不完整。 该提案的目标是定义书签因子MLL 1（混合谱系白血病1）占据其有丝分裂靶点的机制，并确定MLL 1中的突变是否以干扰造血的方式改变有丝分裂功能。我们实验室最近的研究表明，MLL 1是一种正常胚胎和成人造血所需的组蛋白甲基转移酶，它在有丝分裂染色体上被全局保留。MLL 1染色质占据模式在有丝分裂中重组，向最高表达的基因转移。然而，控制MLL 1有丝分裂再分布的物理相互作用以及其与正常造血的相关性尚不清楚。MLL 1经常通过染色体易位重排产生致白血病融合蛋白，维持异常基因表达程序并阻断造血分化。初步结果表明，MLL 1融合蛋白，MLL-AF 9，仍然结合到有丝分裂染色体，然而，这是否需要MLL-AF 9维持不适当的转录模式，导致白血病是未知的。 在这个建议中，我将调查的相互作用，直接MLL 1有丝分裂占用，并检查MLL 1和MLL-AF 9在正常和恶性造血有丝分裂功能。在目标1中，我将系统地定义MLL 1的最小区域，这些区域是结合有丝分裂染色质所必需的和足够的，并评估MLL 1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MLL-AF 9和野生型MLL 1在白血病细胞的间期和有丝分裂中的全局占用模式，并定义与正常和白血病特异性转录程序的关系。我将确定是否需要有丝分裂特异性MLL-AF 9功能白血病转化工程MLL-AF 9融合蛋白，在有丝分裂过程中选择性降解。总之，这些实验有望提供深入了解MLL 1进行其有丝分裂功能的机制，以及致癌MLL融合是否表现出干扰有丝分裂书签特性，阻碍正常的分化程序。更一般地说，据我们所知，拟议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。