The role of ATRX and H3.3 mutations in pediatric glioblastoma

描述（由申请人提供）：脑肿瘤是儿童癌症相关死亡的主要原因。多形性胶质母细胞瘤（GBM）是一种致命的脑癌，儿童和成人均可感染。被诊断为GBM的儿童面临惨淡的结局。即使是积极的治疗策略也是无效的，因为只有不到20%的儿童在诊断后能存活3年以上。小儿GBM的测序发现，p53和组蛋白变体H3.3（由H3F3A和H3F3B编码）中编码atp依赖性染色质重塑酶ATRX的基因同时发生突变。在癌症中，ATRX突变导致ATRX表达或活性丧失，并与基因组不稳定、端粒和着丝粒表型异常以及临床预后不良相关。H3.3突变发现于组蛋白尾部区域，该区域受到广泛的共价修饰。突变体H3.3的强制表达最近已被证明以显性方式诱导染色质甲基化的全局变化，但这些突变的功能后果仍然知之甚少。基于这些发现，我们将验证ATRX和H3.3突变协同作用导致表观遗传不稳定、着丝粒和端粒异常以及GBM肿瘤发生的总体假设。首先，我们将建立新的脑癌小鼠模型来模拟患者ATRX和H3.3突变的影响，这将提供给科学界用于未来的研究，测试某些药物是否可以抑制肿瘤的生长

DESCRIPTION (provided by applicant): Brain tumors are the leading cause of cancer-related deaths in children. Glioblastoma multiforme (GBM) is a deadly form of brain cancer that strikes both children and adults. Children diagnosed with GBM face dismal outcomes. Even aggressive treatment strategies are ineffective, as less than 20% of children will survive more than three years post-diagnosis. Sequencing of pediatric GBM has identified concurrent mutations in the genes encoding an ATP-dependent chromatin remodeling enzyme called ATRX, in p53, and in the histone variant, H3.3 (encoded by H3F3A and H3F3B). In cancer, ATRX mutations result in a loss of ATRX expression or activity and correlate with genome instability, aberrant telomere and centromere phenotypes, and with poor clinical prognosis. H3.3 mutations are found in the histone tail region that is subject to extensive covalent modification. Forced expression of mutant H3.3 has been recently shown to act in a dominant manner to induce global changes in the methylation of chromatin, yet the functional consequences of these mutations are still poorly understood. Based on these findings, we will test the overall hypothesis that ATRX and H3.3 mutations act in a cooperative manner leading to epigenetic instability, centromere and telomere abnormalities, and GBM tumorigenesis. First, we will generate novel mouse models of brain cancer to mimic the effects of patient ATRX and H3.3 mutations, which will be made available to the scientific community for future studies testing whether certain drugs can inhibit the growth of these tumors. In parallel, we will investigate the consequences of ATRX and H3.3 mutations on a mechanistic level. Using cutting edge microscopy and sequencing techniques we will analyze changes in DNA and chromatin organization after forcing normal neural progenitor cells to have ATRX and H3.3 mutations. We will also purify ATRX and both normal and mutant forms of H3.3 and study how these factors might work together to re-organize DNA into chromatin in a test tube. We hope that the detailed understanding of the functions of ATRX and H3.3 in mediating chromatin organization gained from these studies will enable the development of personalized therapies for cancer patients suffering from brain tumors with ATRX and H3.3 mutations.