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

基本信息

批准号：
10432699
负责人：
DANIEL A LIM
金额：
$ 24.23万
依托单位：
UNIVERSITY OF CALIFORNIA, SAN FRANCISCO
依托单位国家：
美国
项目类别：
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/10432699
关键词：
Affect Animal Model Architecture Biochemical Brain Brain Neoplasms Brain Stem Cell Nucleus Cell Proliferation Cells Child Childhood Brain Neoplasm Chromatin Complex DNA Diagnosis Diffuse intrinsic pontine glioma EZH2 gene Epigenetic Process Excision Exhibits Foundations Gene Abnormality Gene Expression Genes Genetic Genetic Transcription Genome Genomic Segment Growth H3 K27M mutation Histones 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 Repression Role Structure Testing Transcriptional Regulation Work base cancer cell cancer type chromatin modification driver mutation effective therapy experimental study gene repression genome-wide histone modification mammalian genome mutant neoplastic cell nerve stem cell oncohistone tumor tumor growth

项目摘要

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.

抽象的弥漫性内质性脑桥胶质瘤（DIPG）是一种侵袭性的幼儿肿瘤，会浸润脑干，尽管放射治疗可以减缓肿瘤生长，但大多数 DIPG 儿童在诊断后两年内死亡。为了开发更有效的疗法，有必要了解其分子和细胞机制大约 80% 的 DIPG 肿瘤在组蛋白 3 (H3) 基因之一中携带点突变。导致赖氨酸 27 取代甲硫氨酸 (H3K27M) H3K27M 突变蛋白的表达是一种。致癌驱动因素，增加细胞增殖，并导致异常基因表达是一个动态的。 DNA 和组蛋白的聚合物，H3 赖氨酸 27 (H3K27-me3) 的三甲基化与 H3K27-me3 受 EZH2 催化，H3K27M 突变组蛋白会抑制转录。 EZH2 活性，导致整个基因组中 H3K27-me3 的广泛缺失。例如，在表达 H3K27M 的细胞中，与转录去抑制并不密切相关。突变后，只有约 4% 失去 H3K27-me3 的基因会增加 H3K27M 的表达。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“区室”的染色质？抑制核区室 (LAD) 是大的、特定的基因组区域。位于核外围，LAD 内的基因表现出低转录活性。富集在 LAD 和非 LAD 基因组区域之间的“边界”，表明该染色质的作用在初步研究中，我们已经对调节高阶基因组组织的这一方面进行了修改。在携带 H3K27M 突变的 DIPG 细胞中绘制 LAD，发现 LAD 架构是独特的鉴于我们对生化的了解，与其他类型的癌症和正常细胞相比，它被破坏了。 H3K27M 突变蛋白、EZH2 的功能以及我们对 LAD 边界结构的了解，我们提出测试以下假设的实验：通过抑制 EZH2 并引起全基因组变化 H3K27-me3 水平时，H3K27M 突变蛋白会破坏正常的 LAD 结构，并且这种破坏核区室相关的基因组组织是 DIPG 基因表达异常的基础。这项工作挑战了当前对 H3K27M 致癌作用的理解，而不是建立在当前的基础上。在局部染色质状态变化水平上解释 H3K27M 致癌功能的模型，获得的结果测试一个新的范例，H3K27M 会导致基因组组织发生更大规模的变化细胞核中的组蛋白突变（例如 H3K27M）代表了一种新兴的致癌驱动因素。癌症具有广泛的多样性，包括罕见的和普遍的，因此，了解 H3K27M 如何影响细胞核。区室相关的基因组组织可以为更广泛的类别提供基础知识癌组蛋白突变。