The Tumor Suppressor Function of Dnmt3a in Chronic Lymphocytic Leukemia

 描述(申请人提供)：慢性淋巴细胞性白血病(CLL)是一种异质性B细胞恶性肿瘤，与致癌物、病毒、辐射或潜在的遗传缺陷无关。这种疾病的特点是成熟的B细胞在造血组织中积聚，目前是无法治愈的。哺乳动物基因组DNA的胞嘧啶甲基化对正常的生理过程至关重要，因为它对大量基因的转录调控起着重要作用。最近对人类CLL样本的全基因组分析显示，基因组编码部分存在全局低甲基化，提示DNA甲基转移酶(DNMT)参与了该病的发病机制。为了诱导低甲基化，我们有条件地灭活了小鼠造血系中的DNMT3A和DNMT3B。在造血细胞中DNMT3A的缺失而不是DNMT3B的缺失可以诱导B细胞和CLL的细胞转化，提示DNMT3A在CLL的发生发展中具有肿瘤抑制作用。这一功能的细胞和分子基础尚不清楚。我们假设DNMT3A的肿瘤抑制功能依赖于DNA甲基酶活性，DNA甲基酶活性的丧失导致启动子低甲基化和作为CLL表观遗传驱动因素的基因上调。三个具体的目标将解决这个问题：在目标1中，我们将识别和描述致癌因素 DNMT3A缺乏诱导的CLL细胞，并对其生物学和分子特性进行分析。在目标2中，我们将确定DNMT3A甲基转移酶活性，或者更确切地说，甲基化非依赖性抑制活性是否对其肿瘤抑制功能负责。在目标3中，我们将测试选定的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细胞系肿瘤表型中的作用。仔细分析DNMT3A的肿瘤抑制功能将有助于深入了解支配小鼠和人类CLL发育的生物学和分子事件。

 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.