Oncohistones: Role of Histone H3 Mutations in the Oncogenesis of Pediatric Cancers

DESCRIPTION（由申请人提供）：全基因组测序技术使人类癌症表观遗传修饰因子的体细胞突变得到了前所未有的发现，提供了癌症表观基因组和遗传改变之间的机制联系。表观遗传调控因子中致癌激活突变的集体数量导致了癌症表观基因组中“驱动突变”的新兴观点。没有什么比最近发现的核心组蛋白高频错义突变更能说明这一点了，例如儿童胶质瘤中的组蛋白H3赖氨酸27到蛋氨酸（H3K27M）和甘氨酸34到精氨酸/缬氨酸（G34R/V）突变，以及儿童成软骨细胞瘤中的H3K36M突变，特别是目前尚不清楚且没有有效治疗方法的侵袭性癌症。我们的生化研究表明，“K-to-M”突变组蛋白可以抑制相关组蛋白甲基转移酶（hmt）的酶活性，如H3K27甲基化的Ezh2和H3K36甲基化的SETD2。奇怪的是，组蛋白突变和HMT突变从未在同一类型的癌症中被发现。这些观察结果使我们假设，H3“K-to-M”突变除了使hmt失活之外，还具有不同的功能，这可能是各自癌症谱系特异性发病机制的关键。在这里，我们提出了多学科和综合的方法，使用遗传学（细胞系和小鼠模型），表观遗传学（ChIP-seq和RNA-seq），蛋白质组学（定量质谱）和化学生物学（“设计染色质”）来获得机制见解，了解“突变”组蛋白编码如何发挥作用，破坏表观遗传景观，进而导致癌症进展。世界一流的癌症、染色质和化学生物学专家团队聚集在一起，探索治疗这些毁灭性儿童癌症的新方法。我们项目的唯一目标是阐明“组蛋白”突变的分子机制，以推进相关儿科癌症的诊断和治疗途径的探索。具体来说，我们将：i)研究组蛋白突变如何影响其他组蛋白和DNA修饰之间的串扰；Ii)利用基于细胞的系统、动物模型和患者肿瘤样本，通过组蛋白突变确定染色质景观的变化；Iii)描述有助于确定肿瘤发生的失调发育程序；iv)专门设计化学定义的染色质模板，用于体外生化反应，旨在详细解剖组蛋白突变如何改变HMT活性。这些研究将为开发治疗策略提供指导，旨在改善组蛋白突变和hmt在这些儿童癌症中的致病作用。此外，新的免疫试剂将产生急需的免疫组织化学（IHC）诊断肿瘤样本。

DESCRIPTION (provided by applicant): Genome-wide sequencing technologies have allowed an unprecedented discovery of somatic mutations in epigenetic modifiers in human cancers, providing mechanistic links between cancer epigenomes and genetic alterations. The collective number of oncogenic activating mutations in epigenetic regulators has led to the emerging view of "driver mutations" underlying cancer epigenomes. Nowhere is this better illustrated than with recent findings of high-frequency missense mutations in core histones, such as histone H3 lysine 27 to methionine (H3K27M) and glycine 34 to arginine/valine (G34R/V) mutations in pediatric gliomas, and H3K36M mutations in pediatric chondroblastomas, particularly aggressive cancers that remain poorly understood and for which there are no effective therapies. Our biochemical studies suggest that the 'K-to-M' mutant histones can inhibit the enzymatic activity of responsible histone methyltransferases (HMTs), such as Ezh2 for H3K27 methylation, and SETD2 for H3K36 methylation. Oddly, histone mutations and HMT mutations are never found in the same type of cancer. These observations lead us to hypothesize that H3 'K-to-M' mutations play distinct functions beyond just inactivation of HMTs, which may be key to the lineage-specific pathogenesis of the respective cancers. Here, we propose multidisciplinary and integrative approaches, using genetics (cell line and mouse models), epigenetics (ChIP-seq and RNA-seq), proteomics (quantitative mass spectrometry) and chemical biology ("designer chromatin") to gain mechanistic insights into how a "mutated" histone code functions towards disrupting epigenetic landscapes that, in turn, lead to cancer progression. A world-class team of experts in cancer, chromatin and chemical biology are assembled to explore novel approaches to these devastating childhood cancers. The single goal of our Program is to illuminate the molecular mechanisms underlying "oncohistone" mutations to advance the diagnosis and exploration of therapeutic avenues for the associated pediatric cancers. Specifically, we will: i) investigate how histone mutations affect the cross-talk between other histone and DNA modifications; ii) identify the changes in chromatin landscape by histone mutations using cell-based systems, animal models and patient tumor samples; iii) characterize misregulated developmental programs that help establish tumorigenesis; and iv) specifically engineer chemically-defined chromatin templates for use in in vitro biochemical reactions aimed at a detailed mechanistic dissection of how histone mutations alter HMT activities. These studies will provide guidance for the development of therapeutic strategies designed to ameliorate the pathogenic effects of histone mutations and HMTs in these childhood cancers. Also, novel immunological reagents will be generated for much-needed immunohistochemistry (IHC) diagnosis of tumor samples.