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

描述(申请人提供)：全基因组测序技术允许在人类癌症的表观遗传修饰物中发现前所未有的体细胞突变，提供癌症表观基因组和基因改变之间的机械联系。表观遗传调节器中致癌激活突变的总数导致了癌症表观基因组背后的“驱动突变”的新兴观点。最近发现的核心组蛋白高频错义突变最能说明这一点，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)的突变，以及儿童软骨母细胞瘤中的H3K36M突变，特别是仍然知之甚少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组蛋白甲基转移酶(HMTs)的酶活性，例如用于H3K27甲基化的Ezh2和用于H3K36甲基化的SETD2。奇怪的是，在同一类型的癌症中从未发现组蛋白突变和HMT突变。这些观察结果使我们假设，H3‘K-M’突变除了HMT的失活外，还发挥着不同的功能，这可能是各自癌症家族特异性发病的关键。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(芯片序列和RNA序列)、蛋白质组学(定量质谱学)和化学生物学(“设计染色质”)来获得关于“突变的”组蛋白密码如何发挥作用的机械性见解，以破坏表观遗传景观，进而导致癌症进展。一个世界级的癌症、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的儿童癌症的新方法。我们计划的唯一目标是阐明“癌组蛋白”突变的分子机制，以促进相关儿科癌症的诊断和治疗途径的探索。具体地说，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)使用基于细胞的系统、动物模型和患者肿瘤样本确定组蛋白突变导致的染色质景观的变化；iii)表征有助于建立肿瘤发生的调控不当的发育计划；以及iv)专门设计用于体外生化反应的化学定义的染色质模板，旨在详细剖析组蛋白突变如何改变HMT活性的机制。这些研究将为制定治疗策略提供指导，旨在改善组蛋白突变和HMT对这些儿童癌症的致病作用。此外，还将产生新的免疫学试剂，用于肿瘤样本急需的免疫组织化学(IHC)诊断。

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.