The Tumor Suppressor Function of Dnmt3a in Chronic Lymphocytic Leukemia

 描述（由申请人提供）：慢性淋巴细胞白血病（CLL）是一种异质性B细胞恶性肿瘤，与迄今为止发现的致癌物、病毒、辐射或潜在遗传缺陷无关。这种疾病的特征是成熟B细胞在造血组织中的积累，目前无法治愈。哺乳动物基因组DNA的胞嘧啶甲基化对于正常的生理过程是至关重要的，因为其有助于大组基因的转录调控。最近对人类CLL样本的全基因组分析揭示了基因组编码部分的全局低甲基化，表明DNA甲基转移酶（Dnmts）参与了疾病的发病机制。为了诱导低甲基化，我们有条件地灭活小鼠造血谱系中的Dnmt3a和Dnmt3b。造血细胞中Dnmt3a而不是Dnmt3b的缺失诱导B细胞和CLL的细胞转化，表明Dnmt3a在CLL发展中的肿瘤抑制功能。这种功能的细胞和分子基础仍不清楚。我们假设Dnmt3a的肿瘤抑制功能依赖于DNA甲基化酶活性，其损失导致启动子低甲基化和上调作为CLL的表观遗传驱动因子的基因。三个具体目标将解决这一问题：在目标1中，我们将识别和表征癌症启动 Dnmt3a缺陷诱导的CLL细胞，并分析其生物学和分子特性。在目的2中，我们将确定Dnmt3a甲基转移酶活性或甲基化非依赖性阻遏物活性是否负责其肿瘤抑制功能。在目的3中，我们将测试所选Dnmt3a靶基因在体内诱导CLL的能力，并评估它们在体外维持人CLL细胞系中的肿瘤表型中的作用。对Dnmt3a的肿瘤抑制功能的仔细分析将为控制小鼠和人CLL发展的生物学和分子事件提供有用的见解。

 DESCRIPTION (provided by applicant): Chronic lymphocytic leukemia (CLL) is a heterogeneous B-cell malignancy with no association with carcinogens, viruses, radiation or underlying genetic defect identified to date. The disease is characterized by an accumulation of mature B-cells in hematopoietic tissues and it is incurable at present. Cytosine methylation of mammalian genomic DNA is critical for normal physiological processes due to its contribution to transcriptional regulation of large sets of genes. Recent genome-wide analysis of human CLL samples revealed a global hypomethylation of the coding portion of the genome, suggesting involvement of DNA methyltransferases (Dnmts) in the pathogenesis of the disease. To induce hypomethylation, we conditionally inactivated Dnmt3a and Dnmt3b in hematopoietic lineages in mice. Loss of Dnmt3a but not Dnmt3b in hematopoietic cells induces cellular transformation of B-cells and CLL, suggesting a tumor suppressor function for Dnmt3a in CLL development. The cellular and molecular basis of this function remains unclear. We hypothesize that the tumor suppressor function of Dnmt3a depends on DNA methylase activity, whose loss results in promoter hypomethylation and up-regulation of genes functioning as epigenetic drivers of CLL. Three Specific Aims will address this: In Aim 1 we will identify and characterize cancer-initiating cells in CLL induced by Dnmt3a deficiency and analyze their biological and molecular properties. In Aim 2 we will determine whether Dnmt3a methyltransferases activity or rather methylation -independent repressor activity is responsible for its tumor suppressor function. In Aim 3 we will test the ability of selected Dnmt3a target genes to induce CLL in vivo and evaluate their roles in maintenance of the tumor phenotype in human CLL cell lines in vitro. A careful analysis of the tumor suppressor function of Dnmt3a will provide useful insight into biological and molecular events governing the development of mouse and human CLL.