Dual interactions of K27M mutant nucleosomes with PRC2 and MLL1 shape the cancer epigenetic landscape (ATAC-seq)

Cancer associated mutations in genes encoding histones dramatically reshape chromatin patterns and support tumorigenesis, despite their low prevalence. Lysine to Methionine substitution of residue 27 on histone H3 (K27M) is a driver mutation in high-grade pediatric gliomas, known to abrogate Polycomb activity. We applied single-molecule systems to image individual nucleosomes and delineate the combinatorial chromatin patterns associated with K27M expression. We find that K27M-mutant nucleosomes not only sequester PRC2, but also bind preferentially to MLL1, thus leading to genome-wide redistribution of H3K4me3. K27M-mediated deregulation of both repressive and activating chromatin marks maintains ‘bivalent’ chromatin, supporting a poorly differentiated cellular state. This study provides evidence for widespread effects of the K27M oncohistone on multiple core epigenetic pathways, and highlights the use of single-molecule tools to reveal mechanisms of chromatin deregulation in cacner. ATAC-seq analysis conducted on SU-DIPG13, SU-DIPG6 and SU-DIPG48 cells

组蛋白编码基因中的癌症相关突变，尽管发生率较低，却可显著重塑染色质构型并促进肿瘤发生。组蛋白H3第27位赖氨酸突变为甲硫氨酸（K27M）是高级别儿童胶质瘤的驱动突变，已知该突变可使多梳蛋白的活性丧失。本研究采用单分子成像技术对单个核小体进行成像，并解析与K27M表达相关的组合式染色质构型。研究发现，携带K27M突变的核小体不仅会螯合多梳抑制复合体2（PRC2），还会优先结合混合谱系白血病蛋白1（MLL1），进而导致全基因组范围内组蛋白H3第4位赖氨酸三甲基化（H3K4me3）的分布发生重编程。K27M介导的抑制性与激活型染色质标记失调，会维持“二价”染色质状态，助力细胞维持低分化表型。本研究为K27M致癌组蛋白对多条核心表观遗传通路的广泛调控影响提供了实验证据，并凸显了单分子工具在解析癌症中染色质失调机制方面的应用价值。本研究对SU-DIPG13、SU-DIPG6及SU-DIPG48细胞开展了转座酶可及性测序（ATAC-seq）分析。