Characterization of ELP1 as a novel SHH medulloblastoma predisposition gene

项目总结 髓母细胞瘤(MB)是儿童最常见的恶性脑肿瘤之一。虽然 积极的治疗改善了结果，太多受影响的儿童仍然死于他们的疾病，以及 幸存者经常遭受治疗的严重长期副作用。广泛的分子和生物学 已经描述了MB潜在的异质性，最终导致了共识分子的识别 亚群--WNT、SHH、第3群和第4群--每个亚群都与不同的基因组有关 景观、患者人口统计和临床结果。尽管体细胞改变的基因和 生物途径是对甲基溴遗传易感性的良好注释和全面理解 已经落在后面了。我们最近研究了所有蛋白质编码的生殖系功能丧失(LoF) 一系列&gt；1000 MB患者的基因。这种不偏不倚的方法揭示了极大的有害 ELP1中的生殖系变异是儿童SHH-MB患者特有的，是 影响已知MB相关基因的致病变异。ELP1编码一个支架亚单位 Elongator，一种多亚单位蛋白复合体(ELP1-6)，可以化学修饰细胞内摆动的U34尿氨酸 TRNAs的反密码子环能够有效地翻译延长和维持生理性的 蛋白质折叠动力学。ELP1相关肿瘤经常与体细胞性ptch1并存 PPM1D和MDM4的突变和扩增，提示胚系ELP1 LoF变异体协同作用 通过结构性激活SHH和/或TP53信号来促进MB的发育。ELP1关联 Shh-MBS的特征是具有不稳定的Elongator复合体，丢失Elongator依赖的tRNA 修饰、依赖密码子的翻译重编程和未折叠蛋白的诱导 反应，与蛋白质动态平衡的丧失一致。基于这些发现，我们假设 ELP1是一个新的癌症易感基因，其目的是从功能上阐明肿瘤的发生、发展和转归。 致病性ELP1 LOF促进SHH-MB的生化和分子机制。为了测试这一点 假设，我们建议(I)评估小脑发育期间对Elp1的需求；(Ii) 验证Elp1在SHH-MB中的肿瘤抑制作用；以及(Iii)确定MB相关的影响 Elp1LoF对翻译和蛋白质组的影响。这些研究将在一系列新颖的ELP1/- 转基因小鼠，来自发育中的小鼠小脑的原代细胞，在遗传上是忠诚的 Shh-MB患者来源的异种移植物。该研究项目的成功实施将有效地将 胚系ELP1 LOF对SHH-MB发病机制的生化和分子机制的研究。 拟议研究的结果将引起广泛的兴趣，扩展到科学家和临床医生 对癌症易感性的兴趣，以及研究癌症基础的基础研究人员 翻译调控和蛋白质动态平衡及其在人类疾病中的作用。

PROJECT SUMMARY Medulloblastoma (MB) is among the most common malignant childhood brain tumors. Although aggressive treatments have improved outcomes, too many affected children still die of their disease, and survivors often suffer from severe long-term side effects of therapy. Extensive molecular and biological heterogeneity underlying MB has been described, culminating in the recognition of consensus molecular subgroups – WNT, SHH, Group 3, and Group 4 – each of which is associated with divergent genomic landscapes, patient demographics, and clinical outcomes. Although somatically altered genes and biological pathways are well annotated, comprehensive understanding of genetic predisposition to MB has lagged behind. We recently investigated germline loss-of-function (LoF) across all protein-coding genes in a series of >1,000 MB patients. This unbiased approach uncovered highly significant deleterious germline variants in ELP1 that were specific to childhood SHH-MB patients and twice as common as pathogenic variants affecting known MB-associated genes. ELP1 encodes a scaffolding subunit of Elongator, a multi-subunit protein complex (ELP1-6) that chemically modifies wobble U34 uridines in the anticodon loop of tRNAs to enable efficient translational elongation and maintenance of physiological protein folding dynamics. ELP1-associated tumors exhibited frequent co-occurrence of somatic PTCH1 mutations and amplifications of PPM1D and MDM4, suggesting germline ELP1 LoF variants cooperate with constitutive activation of SHH and/or TP53 signaling to promote MB development. ELP1-associated SHH-MBs were characterized by a destabilized Elongator complex, loss of Elongator-dependent tRNA modifications, codon-dependent translational reprogramming, and induction of the unfolded protein response, consistent with loss of protein homeostasis. Based on these findings, we hypothesize that ELP1 is a novel cancer predisposition gene and aim to functionally elucidate the developmental, biochemical, and molecular mechanisms by which pathogenic ELP1 LoF promotes SHH-MB. To test this hypothesis, we propose to (i) evaluate the requirement for Elp1 during cerebellar development; (ii) validate the tumor suppressive role of Elp1 in SHH-MB; and (iii) determine the impact of MB-associated Elp1 LoF on translation and the proteome. These studies will be conducted in a series of novel Elp1+/- transgenic mice, primary cells derived from the developing mouse cerebellum, and genetically faithful SHH-MB patient-derived xenografts. Successful execution of this research program will effectively link germline ELP1 LoF to the biochemical and molecular mechanisms governing SHH-MB pathogenesis. Outcomes of the proposed research will be of broad interest, extending to scientists and clinicians with an interest in cancer predisposition, as well as basic researchers studying the fundamentals of translational regulation and protein homeostasis and their role in human disease.