Cancer epigenetics: Understanding histone methylation in leukemia stem cells

描述（由申请人提供）：我的长期研究兴趣是研究肿瘤发生的表观遗传机制。表观遗传学是由DNA序列无关的改变（如染色质修饰）引起的表型变化的现象。文献记载了一系列癌症的解除管制，似乎特别干扰适当的组蛋白修饰。我们的重点是在人类白血病中发现的复发性染色体易位，其目标是调节特定染色质修饰的分子参与者-组蛋白H3三甲基化赖氨酸4（缩写为H3K4Me3）。H3K4Me3是与常染色质结构和活性转录相关的重要组蛋白标记。MLL是一种h3k4me3特异性甲基转移酶，是一种著名的白血病致癌基因，MLL的功能获得性突变是人类白血病最常见的畸变之一。与这些观察结果一致，我们最近的研究表明，白血病易位NUP98-JARID1A破坏和/或对h3k4me3特异性组蛋白去甲基化酶JARID1产生主要的负面影响。因此，H3K4Me3标记在许多癌基因上的异常积累导致它们的反激活。我们的初步数据还表明，这种新的表观遗传机制将正常造血干细胞（hsc）转化为白血病起始干细胞（LSCs）。JARID1A最初被分离为与肿瘤抑制因子RB相互作用的因子。我们假设JARID1家族组蛋白去甲基化酶，在人类白血病中被发现下调，属于白血病中一类新的肿瘤抑制因子。

DESCRIPTION (provided by applicant): My long-term research interest is to investigate epigenetic mechanisms in oncogenesis. Epigenetics is a phenomenon for phenotypic changes caused by DNA sequence-independent alterations such as chromatin modification. The literature has documented a collection of cancerous deregulations that appear specifically to interfere with proper histone modification. Our focus is recurrent chromosomal translocation found in human leukemia, which targets molecular players that regulate a specific chromatin modification- histone H3 tri-methylated at lysine 4 (abbreviated as H3K4Me3). H3K4Me3 is a prominent histone mark associated with euchromatin structure and active transcription. MLL, an H3K4me3-specific methyltransferase enzyme, is a famed leukemia oncogene, and gain-of-function mutation of MLL represents one of the most common aberrations in human leukemia. In keep with these observations, our recent studies demonstrate that a leukemic translocation NUP98-JARID1A disrupts and/or imparts dominant negative effect on H3K4Me3-specific histone demethylases JARID1. As a result, aberrant accumulation of H3K4Me3 marks on a number of oncogenes leads to their transactivation. Our preliminary data also suggests that such a novel epigenetic mechanism transforms normal hematopoietic stem cells (HSCs) to leukemia-initiating stem cells (LSCs). JARID1A was initially isolated as factor to interact with tumor suppressor RB. We hypothesize that JARID1 family histone demethylases, which were found down regulated among human leukemia, belong to a novel class of tumor suppressors in leukemias. During the mentored phase, I will utilize genomic approaches to identify the histone methylation "signatures" that are associated with LSCs and HSCs. A parallel objective in this phase is to establish targeted mouse ES cells that harbor JARID1A/1B inactivation alleles, as well as to develop techniques for in vitro histone enzymology. In the independent phase, I will examine in vivo functions of JARID1 histone demethylases in tumor suppression and/or normal development using knockout mouse models. Active JARID1 enzymes (in form of protein complexes) and their mediated histone demethylation in vitro will also be characterized. An excellent environment and complementary training program provided by laboratories of Dr. David Allis (mentor), Dr. Shahin Rafii (co-mentor), collaborators, and an Advisory Committee will facilitate my research in the mentored phase and ensure a smooth transition to an independent investigator. The proposed research at the independent phase (Year 3-5) will pave the road to launch my future investigation to reveal novel epigenetic mechanisms in oncogenesis and identify 'druggable' targets for novel therapeutics. PUBLIC HEALTH RELEVANCE: Epigenetics is a phenomenon of phenotypic changes caused by alterations that occur on a specific type of DNA-associated protein termed as histone. Epigenetic mechanisms play critical roles in regulating gene expression and defining cellular states, as well as contributing to the onset and development of human pathologies such as cancers. In this project, we focus on some types of leukemia that accounts for a large percentage of human blood cancer patients. However these cases are currently incurable. Investigating the role of affected histone modifier enzymes in tumor prevention will shed light on novel oncogenic mechanisms. It also has clinical significance for cancer diagnosis and therapies. In vitro enzymology established in the study can be adopted in the future for studies of other cancerous alternations and also for screening small molecular inhibitors. For example, one therapeutic idea is to target an unwanted 'hyperactive' histone methyltransferase activity in cancer cells. Importantly, many chromatin modifier enzymes are considered as feasible targets for screening inhibitor chemicals. In summary, studying the molecular basis of epigenetic regulation will promote greater understanding of the development of normal tissue and/or tumors, which in turn, helps to design some novel effective therapeutic intervention for human cancers.