Deciphering the pathogenesis of pediatric high-grade gliomas

描述(由申请人提供)：该项目的长期目标是阐明儿童高级别胶质瘤(HGG)的分子发病机制。胶质母细胞瘤是人类最常见和最致命的原发脑肿瘤类型，占所有功能性组织脑瘤病例的52%。尽管几十年的协同治疗努力，胶质瘤仍然是无法治愈的。主要问题是，这种疾病背后的真正发病机制基本上是未知的。最近的研究已经将组蛋白H3.3的SETD2和Gly34Arg/Val(G34R/V)突变与儿童和青年HGG联系在一起，但改变的SETD2和H3.3导致儿童和青年HGG恶变的分子机制(S)尚未阐明。由于SETD2编码唯一已知的组蛋白H3裂解36三甲基化(H3K36me3)特异性甲基转移酶，而H3.3G34R/V突变导致H3K36me3水平显著下降，这些观察表明儿童和年轻人HGG的真正罪魁祸首是由H3K36me3调控的机制。引人注目的是，我们最近通过招募错配识别蛋白hMutS？来证明H3K36me3对于一种名为DNA错配修复(MMR)的关键基因组维持系统是必不可少的。通过与hMutS？的直接相互作用对染色质产生突变，缺失SETD2/H3K36me3的细胞表现出在MMR基因缺陷的细胞中常见的突变子表型。因此，我们假设异常的SETD2和H3.3通过阻断H3K36的三甲基化而使MMR功能失活，从而促进儿童和年轻人HGG肿瘤的发生。为了检验这一假设，在本申请中提出了两个具体目标。具体目的1是直接测定SETD2或H3.3G34R/V突变的儿童HGGs的H3K36me3水平和突变子表型。具体目标2是测量基因组的不稳定性和H3K36me3与hMutS？在表达G34R/V H3.3的胶质瘤细胞系中表达。这项研究的成功完成将揭示儿童HGGs的真正发病机制，为癌症检测提供一种新的生物标志物。更重要的是，由于MMR缺陷的肿瘤细胞对包括替莫唑胺在内的许多化疗药物具有高度耐药性，替莫唑胺是胶质瘤治疗中广泛使用并导致耐药性的药物，本研究也将为改善胶质瘤的治疗提供新的策略。

DESCRIPTION (provided by applicant): The long-term goal of this project is to elucidate the molecular pathogenesis underlying pediatric high- grade gliomas (HGGs). Glioblastoma is the most common and lethal type of primary brain tumor in humans, which accounts for 52% of all functional tissue brain tumor cases. Despite decades of concerted therapeutic efforts, gliomas remain incurable. The major problem is that the real pathogenesis underlying this disease is essentially unknown. Recent studies have linked pediatric and young adult HGGs with mutations in SETD2 and Gly34Arg/Val (G34R/V) substitutions in histone H3.3, but the molecular mechanism(s) by which the altered SETD2 and H3.3 drive malignancy of pediatric and young adult HGGs are not elucidated. Because SETD2 encodes the only known methyltransferase specific for histone H3 lysine36 trimethylation (H3K36me3), and H3.3G34R/V mutations lead to significant decrease in H3K36me3 levels, these observations have pointed the true culprit of pediatric and young adult HGGs to a mechanism that is regulated by H3K36me3. Strikingly, we have recently shown that H3K36me3 is essential for a critical genome-maintenance system called DNA mismatch repair (MMR) by recruiting mismatch recognition protein hMutS? to chromatin through its direct interaction with hMutS?, and that cells depleted of SETD2/H3K36me3 display a mutator phenotype usually seen in cells defective in MMR genes. We therefore hypothesize that abnormal SETD2 and H3.3 promote pediatric and young adult HGG tumorigenesis by inactivating the MMR function via blocking H3K36 trimethylation. To test this hypothesis, two specific aims are proposed in this application. Specific Aim 1 is to directly determine H3K36me3 levels and mutator phenotype in pediatric HGGs with SETD2 or H3.3G34R/V mutations. Specific Aim 2 is to measure genomic instability and the dynamic interaction between H3K36me3 and hMutS? in glioma cell lines expressing G34R/V H3.3. A successful completion of the proposed study will reveal the real pathogenesis of pediatric HGGs, providing a novel biomarker for cancer detection. More importantly, since tumor cells defective in MMR are highly resistant to many chemotherapeutic drugs including temozolomide, which is widely used for and causes resistance in glioma therapy, this study will also offer new strategies to improve glioma therapy.