The role of H3K27M-induced aberrant PRC2 activity in brainstem gliomagenesis

 描述（由申请人提供）：弥漫性内在脑桥神经胶质瘤（DIPG）是一种侵袭性和不可治愈的儿科脑肿瘤，目前研究尚不充分。在过去的30年里，治疗方面没有取得任何进展，放射治疗仍然是治疗的标准。 最近对肿瘤样本进行的全基因组测序显示，80%的患者在氨基酸残基27（K27 M）处存在组蛋白变体H3.3的杂合赖氨酸至甲硫氨酸突变。我们和其他人已经表明，K27 M引起了一个功能获得性突变，该突变抑制了组蛋白甲基转移酶EZH 2。这种抑制导致H3 K27 me 3标记的整体丧失以及残余H3 K27 me 3景观的重构。对有或没有K27 M突变的人类肿瘤的染色质免疫沉淀测序（ChIP-seq）分析显示，Cdkn 2a转录变体p16是H3 K27 me 3增加的靶点。 我们的鼠H3.3K27M神经胶质瘤模型的表达分析概括了这些结果，并且另外揭示了hoxa 4、5和7是最显著下调的基因。 由于肿瘤抑制基因p16在几种癌症中发生突变，但很少出现在DIPG中，我们假设K27 M突变部分通过表观遗传学沉默该位点来驱动肿瘤发生。 Hox基因座的改变由于其在脑干发育过程中的作用而与DIPG有关。 我们的结果表明K27 M突变通过抑制这些基因抑制脑干祖细胞的分化。为了研究这些假设，我建议在我们的鼠H3.3K27M胶质瘤模型中描述Cdkn 2a和Hoxa基因座处的H3 K27 me 3景观。 此外，我将利用我们的条件Cdkn 2a floxed模型，以确定H3.3K27M突变体表达和p16肿瘤抑制通路的致癌转化之间的关系。 该项目的目标是确定突变体H3.3K27M如何通过操纵表观基因组来抑制p16和Hoxa基因来驱动肿瘤发生。 H3 K27 me 3在这些位点的抑制可以增强细胞周期进展并维持原始祖细胞样状态，并且用化疗药物靶向这些基因可以导致更有效的治疗。

 DESCRIPTION (provided by applicant): Diffuse intrinsic pontine glioma (DIPG) is an aggressive and incurable pediatric brain tumor that remains understudied. No progress in treatment has been made in the past 30 years, and radiation remains the standard of care. Recent whole-genome sequencing on tumor samples revealed heterozygous lysine-to-methionine mutations of histone variant H3.3 at amino acid residue 27(K27M) in 80% of patients. We and others have shown that K27M invokes a gain-of-function mutation which inhibits the histone methyltransferase EZH2. This inhibition causes an overall global loss of the H3K27me3 mark as well as a restructuring of the residual H3K27me3 landscape. Chromatin immunopreciptiation-sequencing (ChIP-seq) analysis of human tumors with or without K27M mutations revealed the Cdkn2a transcript variant p16 as a target of increased H3K27me3. Expression analysis of our murine H3.3K27M glioma model recapitulated these results and additionally revealed hoxa4, 5, and 7 among the most significantly downregulated genes. Since the tumor suppressor p16 is mutated in several cancers but rarely appears in DIPG, we hypothesize K27M mutations drive tumorgenesis in part by epigenetically silencing this locus. Alteration of the hox locus has been implicated in DIPG due to its role during brainstem development. Our results suggest K27M mutation inhibits differentiation of brainstem progenitors by repressing these genes. To investigate these hypotheses I propose to characterize the H3K27me3 landscape at the Cdkn2a and Hoxa loci in our murine H3.3K27M glioma model. Additionally, I will take advantage of our conditional Cdkn2a floxed model to determine the relationship between H3.3K27M mutant expression and the p16 tumor suppressor pathway with regard to oncogenic transformation. The goal of this project is to determine how mutant H3.3K27M drives tumorigenesis by manipulating the epigenome to repress the p16 and Hoxa genes. The repression of H3K27me3 at these sites may be enhancing cell cycle progression and maintaining a primitive progenitor-like state and targeting these genes with chemotherapeutics could lead to a more efficacious treatment.