A new model for understanding a brain tumor epigenetic driver

理解脑肿瘤表观遗传驱动因素的新模型

• 批准号: 10588174
• 负责人: DANIEL A LIM
• 金额: $ 20.19万
• 依托单位: UNIVERSITY OF CALIFORNIA, SAN FRANCISCO
• 依托单位国家: 美国
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-03-15 至 2024-02-29
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10588174
• 关键词: Affect; Animal Model; Architecture; Biochemical; Brain; Brain Neoplasms; Brain Stem; Cell Nucleus; Cell Proliferation; Cells; Child; Childhood Brain Neoplasm; Chromatin; Chromosome Mapping; Complex; DNA; Diagnosis; Diffuse intrinsic pontine glioma; EZH2 gene; Epigenetic Process; Excision; Exhibits; Gene Abnormality; Gene Expression; Genes; Genetic; Genetic Transcription; Genome; Genomic Segment; Growth; H3 K27M mutation; Histones; Infiltration; Knowledge; Lysine; Malignant Neoplasms; Maps; Methionine; Methods; Modeling; Molecular; Mutation; Normal Cell; Nuclear; Nuclear Inner Membrane; Oncogenic; Outcome; Point Mutation; Polycomb; Polymers; Post-Translational Protein Processing; Proteins; Radiation therapy; Role; Structure; Testing; Transcriptional Regulation; Work; cancer cell; cancer type; chromatin modification; derepression; driver mutation; effective therapy; experimental study; gene repression; genome-wide; histone methylation; histone modification; mammalian genome; mutant; neoplastic cell; nerve stem cell; oncohistone; tumor; tumor growth

ABSTRACT Diffuse intrinsic pontine glioma (DIPG) is an aggressive tumor of young children that infiltrates the brainstem, and although radiation therapy can slow tumor growth, most children with DIPG die within two years of diagnosis. To develop more effective therapies, it is necessary to understand the molecular and cellular mechanisms that drive DIPG. Approximately 80% of DIPG tumors carry a point mutation in one of the histone 3 (H3) genes that causes a substitution of lysine 27 for methionine (H3K27M). Expression of H3K27M mutant protein is an oncogenic driver, increasing cell proliferation, and causes aberrant gene expression. Chromatin is a dynamic polymer of DNA and histone proteins, and the trimethylation of H3 lysine 27 (H3K27-me3) correlates with transcriptional repression. H3K27-me3 is catalyzed by EZH2, and the H3K27M mutant histone protein inhibits EZH2 activity, causing widespread loss of H3K27-me3 across the genome. However, this loss of H3K27-me3 does not closely correlate with transcriptional de-repression. For example, in cells expressing the H3K27M mutation, only about 4% of the genes that lose H3K27-me3 increase their expression. Does H3K27M instead affect gene expression by altering “higher-order” aspects of genome organization, such as the interaction of chromatin with specific nuclear “compartments?” The lamina of the inner nuclear membrane is a transcriptionally repressive nuclear compartment. Lamina associated domains (LADs) are large, specific genomic regions located at the nuclear periphery, and genes within LADs exhibit low transcriptional activity. H3K27-me3 is highly enriched at the “borders” between LADs and non-LAD genomic regions, suggesting a role for this chromatin modification in regulating this aspect of higher-order genome organization. In Preliminary Studies, we have mapped LADs in DIPG cells that carry the H3K27M mutation, finding that the LAD architecture is uniquely disrupted as compared to other types of cancer and normal cells. Given our biochemical understanding of H3K27M mutant protein, the function of EZH2, and our knowledge of LAD border structure, we propose experiments that test the following hypothesis: By inhibiting EZH2 and causing genome-wide changes in H3K27-me3 levels, the H3K27M mutant protein disrupts normal LAD structures, and that such disruption of nuclear compartment-associated genome organization underlies the abnormal gene expression of DIPG. This work challenges the current understanding of H3K27M oncogenic effects. Instead of building upon the current model that explains H3K27M oncogenic function at the level of local chromatin state changes, results obtained test a new paradigm, that H3K27M causes a much larger-scale change to the organization of the genome in the nucleus. Mutations in histone proteins such as H3K27M represent an emerging class of oncogenic drivers in a wide diversity of cancer, both rare and prevalent. Thus, understanding how H3K27M affects nuclear compartment-associated genome organization may provide foundational knowledge to the broader class of oncohistone mutations.

抽象的 弥漫性内在庞然神经胶质瘤（DIPG）是浸润脑干的幼儿的侵袭性肿瘤， 尽管放射治疗可以减缓肿瘤的生长，但大多数DIPG儿童在诊断后的两年内死亡。 为了开发更有效的疗法，有必要了解分子和细胞机制 驱动器DIPG。大约80％的DIPG肿瘤在Hisstone 3（H3）基因之一中带有点突变。 导致赖氨酸27代替蛋氨酸（H3K27M）。 H3K27M突变蛋白的表达是一种 致癌驱动力，增加细胞增殖并引起异常基因表达。染色质是动态的 DNA和组蛋白的聚合物，H3赖氨酸27（H3K27-ME3）的三甲基化与 转录表示。 H3K27-ME3由EZH2催化，H3K27M突变体组蛋白抑制 EZH2活性，导致基因组H3K27-ME3的宽度损失。但是，H3K27-ME3的损失 与转录解压缩不密切相关。例如，在表达H3K27M的细胞中 突变，损失H3K27-ME3的基因中只有大约4％会增加其表达。改为H3K27M 通过改变基因组组织的“高阶”方面来影响基因表达，例如 具有特定核“隔间？”的染色质？内核膜的椎板是转录 抑制性核舱。薄片相关域（LAD）是大的特定基因组区域 位于核周围，小伙子内的基因暴露了低转录活性。 H3K27-ME3高度 在小伙子和非LAD基因组区域之间的“边界”中富集，这表明该染色质的作用 在确定高阶基因组组织的这一方面的修改。在初步研究中，我们有 在含有H3K27M突变的DIPG单元格中映射的LAD，发现LAD结构是独特的 与其他类型的癌症和正常细胞相比，被破坏了。考虑到我们对 H3K27M突变蛋白，EZH2的功能以及我们对LAD边框结构的了解，我们建议 检验以下假设的实验：通过抑制EZH2并引起全基因组的变化 H3K27-ME3水平，H3K27M突变蛋白破坏了正常的LAD结构，并且这种破坏 核区室相关的基因组组织是DIPG异常基因表达的基础。这 工作挑战了当前对H3K27M致癌作用的理解。而不是在电流上建立 在局部染色质状态变化的水平上解释H3K27M致癌功能的模型，获得的结果 测试一个新的范式，H3K27M导致基因组组织的更大变化 核。组蛋白（例如H3K27M）的突变代表了一类新兴的致癌驱动因素 罕见和普遍的癌症多样性。这是了解H3K27M如何影响核的 与隔室相关的基因组组织可以为更广泛的类别提供基础知识 关于酒精酮突变。