The H3K27M oncogenic histone (oncohistone) mutation drives ~80% of incurable childhood brain tumors known as diffuse midline gliomas (DMGs). The major molecular feature of H3K27M mutant DMGs is a global loss of H3K27 trimethylation (H3K27me3), a phenotype conserved inCaenorhabditis elegans(C. elegans). Here, we perform unbiased genome-wide suppressor screens inC. elegansexpressing H3K27M and isolate 20 suppressors, all of which at least partially restore H3K27me3. 19/20 suppressor mutations map to the same histone H3.3 gene in which the K27M mutation was originally introduced. Most of these create single amino acid substitutions between residues R26-Y54, which do not disrupt oncohistone expression. Rather, they are predicted to impair interactions with the Polycomb Repressive Complex 2 (PRC2) and are functionally conserved in human cells. Further, we mapped a single extragenic H3K27M suppressor toubc-20, an E2 ubiquitin-conjugating enzyme, whose loss rescued H3K27me3 to nearly 50% wild-type levels despite continued oncohistone expression and chromatin incorporation. We demonstrate thatubc-20is the major enzyme responsible for generating diubiquitinated histone H2B. Our study provides in vivo support for existing models of PRC2 inhibition via direct oncohistone contact and suggests that the effects of H3K27M may be modulated by H2B ubiquitination.

中文翻译：

---

一种 E2 泛素结合酶将二泛素化的 H2B 与 H3K27M 癌组蛋白功能联系起来


H3K27M 致癌组蛋白（癌组蛋白）突变驱动 ~80% 的无法治愈的儿童脑肿瘤，称为弥漫性中线神经胶质瘤 （DMG）。H3K27M 突变型 DMGs 的主要分子特征是 H3K27 三甲基化 （H3K27me3） 的整体缺失，H3K27me3 是秀丽隐杆线虫 （C. elegans） 中保守的表型。在这里，我们在 C 中进行无偏倚的全基因组抑制因子筛选。elegansexpressing H3K27M 并分离出 20 个抑制因子，所有这些抑制因子都至少部分恢复了 H3K27me3。19/20 抑制基因突变映射到最初引入 K27M 突变的同一组蛋白 H3.3 基因。其中大多数在残基 R26-Y54 之间产生单个氨基酸取代，不会破坏癌组蛋白表达。相反，预计它们会损害与多梳抑制复合物 2 （PRC2） 的相互作用，并且在人类细胞中功能保守。此外，我们绘制了一个基因外 H3K27M 抑制因子 toubc-20，一种 E2 泛素结合酶，尽管持续的癌组蛋白表达和染色质掺入，但其缺失使 H3K27me3 恢复到近 50% 的野生型水平。我们证明 ubc-20 是负责产生二泛素化组蛋白 H2B 的主要酶。我们的研究为通过直接癌组蛋白接触抑制 PRC2 的现有模型提供了体内支持，并表明 H3K27M 的作用可能受到 H2B 泛素化的调节。