Epigenetic Regulation of Medulloblastoma

髓母细胞瘤的表观遗传调控

• 批准号: 8193237
• 负责人: LAURIE L JACKSON-GRUSBY
• 金额: $ 34.89万
• 依托单位: BOSTON CHILDREN'S HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-08 至 2013-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8193237
• 关键词: Address; Alleles; Animals; Awareness; Biological Assay; Brain Neoplasms; Cancer Etiology; Cellular Structures; Childhood; Childhood Brain Neoplasm; Chromosomal Instability; DNA; DNA Methylation; DNA Methylation Inhibition; DNA Methyltransferase; DNA Modification Methylases; Dependence; Disease; Embryonic Development; Epigenetic Process; Event; Fibroblasts; Gene Silencing; Genes; Genetic; Genomics; Goals; Health; Human; Intestinal Neoplasms; Kinetics; Knowledge; Lead; Long-Term Effects; Maintenance; Malignant Neoplasms; Malignant neoplasm of brain; Mediating; Methylation; Modeling; Mus; Mutate; Mutation; Oncogene Deregulation; Pathologic; Pathway interactions; Play; Predisposition; Process; Property; Protein p53; Regulation; Risk; Role; Somatic Cell; Stem cells; TP53 gene; Testing; Therapeutic; Tumor Stem Cells; Tumor Suppressor Genes; Tumor Tissue; cancer risk; cancer stem cell; cancer type; cell growth regulation; cohort; demethylation; embryonic stem cell; genome-wide; imprint; in vivo; insight; medulloblastoma; mouse model; mutant; pluripotency; prevent; promoter; self renewing cell; self-renewal; stem cell population; therapeutic target; tumor; tumor initiation; tumor progression; tumorigenesis

DESCRIPTION (provided by applicant): The overarching goal of this project is to understand two important aspects of epigenetic control during medulloblastoma formation, namely the difference between cancer stem cells and bulk tumor, and the role of DNA methylation dependent gene silencing in tumor progression. Our experimental rationale that connects these two questions is an observation we made that normal mouse embryonic stem cells do not require the sole maintenance DNA methyltransferase Dnmt1, whereas all known somatic cells tested require this gene for survival. The increasing awareness that pluripotency genes, those genes important for embryonic stem cell self-renewal, may play an important functional role in cancer stem cells encourages us to test the importance of this pathway in brain tumor stem cells derived from medulloblastoma. To approach this question, we are utilizing a mouse model harboring mutations in two tumor suppressor genes, Ptch and p53, that when mutated lead to a highly penetrant and lethal medulloblastoma. To examine the role for epigenetic control in cancer stem cells we will first characterize Ptch-P53 medulloblastomas to determine whether they contain a self- renewing cancer stem cell population. We will then test whether the self-renewing cells within these medulloblastomas are Dnmt1 dependent like other somatic cells or are Dnmt1 independent like embryonic stem cells. To address the role of epigenetic silencing, we will utilize a viable hypomorphic allele of Dnmt1 and ask whether genomic DNA hypomethylation induces or suppresses medulloblastoma formation. Depending on tumor context, Dnmt1 hypomorphic mice have revealed important roles for DNA hypomethylation in promoting chromosomal instability and alternatively in preventing aberrant gene silencing. We will determine whether chromosomal or epigenetic mechanisms prevail in medulloblastoma progression using a genetic approach with Dnmt1 hypomorphic mice. Finally, we have recently demonstrated that transient demethylation in embryonic stem cells leads to global loss of imprinting, and loss of p53 expression in derived mouse fibroblasts through an unknown mechanism. We have derived ES cells from medulloblastoma prone Ptch mice in order to carry out transient demethylation in stem cells and test whether epigenetic mechanisms lead to loss of p53 and promote medulloblastoma tumor progression in vivo. These results will extend prior results that global loss of imprinting can promote tumorigenesis, and provide a model to dissect the mechanism through which transient epigenetic changes exert long term effects on cell growth regulation, and tumor predisposition in vivo. PUBLIC HEALTH RELEVANCE: This proposal tests four hypotheses regarding the contribution of epigenetic alterations to medulloblastoma initiation and progression. We ask are cancer stem cells similar to embryonic stem cells in their lack of dependence on the DNA methyltransferase Dnmt1, and does global transient demethylation promote cancer by potentiating cancer stem cell expansion? We test the contribution of epigenetic alterations by asking does gene silencing contribute to tumor initiation or progression, and are imprinted genes a key functional class of epigenetic targets that become deregulated in these pediatric brain tumors? Answers to these questions should yield insight into the origins of the most common pediatric brain tumor, and will likely impact a broader understanding of cancer epigenetics.

描述（由申请人提供）：本项目的总体目标是了解成神经管细胞瘤形成过程中表观遗传控制的两个重要方面，即癌症干细胞和大块肿瘤之间的差异，以及DNA甲基化依赖基因沉默在肿瘤进展中的作用。我们将这两个问题联系起来的实验原理是，我们观察到正常的小鼠胚胎干细胞不需要唯一的维持DNA甲基转移酶Dnmt1，而所有已知的体细胞都需要这种基因来维持生存。越来越多的人意识到多能性基因，即那些对胚胎干细胞自我更新很重要的基因，可能在癌症干细胞中发挥重要的功能作用，这鼓励我们在髓母细胞瘤衍生的脑肿瘤干细胞中测试这一途径的重要性。为了解决这个问题，我们利用了一个小鼠模型，其中包含两个肿瘤抑制基因Ptch和p53的突变，当突变时导致高渗透和致命的髓母细胞瘤。为了研究表观遗传控制在癌症干细胞中的作用，我们将首先表征Ptch-P53髓母细胞瘤，以确定它们是否包含自我更新的癌症干细胞群。然后，我们将测试这些髓母细胞瘤中的自我更新细胞是像其他体细胞一样依赖Dnmt1还是像胚胎干细胞一样不依赖Dnmt1。为了解决表观遗传沉默的作用，我们将利用Dnmt1的一个可行的低形态等位基因，并研究基因组DNA低甲基化是否诱导或抑制成神经管细胞瘤的形成。根据不同的肿瘤背景，Dnmt1亚型小鼠已经揭示了DNA低甲基化在促进染色体不稳定性和防止异常基因沉默方面的重要作用。我们将使用Dnmt1亚型小鼠的遗传方法来确定髓母细胞瘤进展中染色体或表观遗传机制是否占上风。最后，我们最近证明，胚胎干细胞中的短暂去甲基化通过未知的机制导致小鼠成纤维细胞中印迹的全局丢失和p53表达的丢失。我们从易患成神经管细胞瘤的Ptch小鼠中获得ES细胞，以便在干细胞中进行短暂的去甲基化，并在体内测试表观遗传机制是否导致p53缺失并促进成神经管细胞瘤肿瘤进展。这些结果将扩展先前的研究结果，即印迹的整体缺失可以促进肿瘤发生，并提供一个模型来分析瞬时表观遗传变化对体内细胞生长调节和肿瘤易感性的长期影响的机制。公共卫生相关性：本提案测试了关于表观遗传改变对成神经管细胞瘤发生和进展的贡献的四种假设。我们的问题是，癌症干细胞是否与胚胎干细胞相似，它们缺乏对DNA甲基转移酶Dnmt1的依赖，以及全局瞬时去甲基化是否通过增强癌症干细胞的扩增来促进癌症？我们通过询问基因沉默是否有助于肿瘤的发生或进展，以及在这些儿童脑肿瘤中，印迹基因是否是表观遗传靶标的关键功能类别来测试表观遗传改变的贡献？这些问题的答案将有助于深入了解最常见的儿童脑肿瘤的起源，并可能影响对癌症表观遗传学的更广泛理解。