Introduction: The interaction of K27M mutation in histone H3 (H3K27M mutation) with polycomb repressive complex 2 (PRC2) is facilitated by the enhancer of zeste homolog 2 (EZH2). Subsequently, this interaction leads to the global reduction level of H3K27me3. We analyzed the EZH2 expression level in H3K27M mutation-positive tumors and revealed the association of high EZH2 expression with poor survival. Methods: Our study included 12 patients, with an age range of 6–56 years and treated between 2007 and 2016. All patients underwent MRI study for nonenhanced T1, T2, diffusion, gadolinium-enhanced T1-weighted imaging, and fluid-attenuated inversion recovery (FLAIR). Immunohistochemical staining was performed against H3K27M, H3K27me3, EZH2, EED, mutant isocitrate dehydrogenase 1 (IDH1), α-thalassemia X-linked intellectual disability (ATRX), p53, O6-methylguanine-DNA methyltransferase (MGMT), and Ki-67 antibodies. Results: All patients were negative for IDH1R132H and H3K27me3, but H3K27M-positive. Staining against EZH2 was negative in all histological features of grade II cases (3/12) and positive in grade III and IV cases; EZH2 positivity is associated with poor prognosis (p = 0.0082). EZH2 positivity was not associated with EED positivity. Retained ATRX staining was found mostly in grade III and IV cases (6/12). P53 was predominantly positive in cases of astrocytoma and glioblastoma (8/12). The labeling index of Ki-67 was 1.2–31.4% for grade II and III histological features and 11.2–24.8% for grade IV. Conclusion: We suggest that the expression of EZH2 is not associated with the PRC2 pathway and increases in patients with H3K27M-mutant diffuse midline glioma and a poor prognosis. Further studies are necessary to understand the mechanism involved.

中文翻译：

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弥漫性中线胶质瘤 H3K27M 突变患者中 Zeste 同源物 2 (EZH2) 增强子表达增加的免疫染色

简介： zeste 同源物 2 (EZH2) 的增强子促进了组蛋白 H3 中的 K27M 突变（H3K27M 突变）与多梳抑制复合物 2（PRC2）的相互作用。随后，这种相互作用导致 H3K27me3 的全局减少水平。我们分析了 H3K27M 突变阳性肿瘤中的 EZH2 表达水平，并揭示了高 EZH2 表达与较差的存活率之间的关联。方法：我们的研究包括 12 名患者，年龄范围为 6-56 岁，在 2007 年至 2016 年期间接受治疗。所有患者均接受了非增强 T1、T2、弥散、钆增强 T1 加权成像和液体衰减倒置的 MRI 研究恢复（FLAIR）。针对 H3K27M、H3K27me3、EZH2、EED、突变异柠檬酸脱氢酶 1 (IDH1)、α-地中海贫血 X 连锁智力障碍 (ATRX)、p53、O6-甲基鸟嘌呤-DNA 甲基转移酶 (MGMT) 和 Ki-67 抗体。结果：所有患者 IDH1R132H 和 H3K27me3 均为阴性，但 H3K27M 为阳性。EZH2染色在II级病例（3/12）的所有组织学特征中均呈阴性，在III级和IV级病例中呈阳性；EZH2 阳性与不良预后相关（p = 0.0082）。EZH2 阳性与 EED 阳性无关。保留的 ATRX 染色主要见于 III 级和 IV 级病例 (6/12)。P53 在星形细胞瘤和胶质母细胞瘤的病例中主要呈阳性 (8/12)。Ki-67 的标记指数 II 级和 III 级组织学特征为 1.2-31.4%，IV 级为 11.2-24.8%。结论：我们认为 EZH2 的表达与 PRC2 通路无关，并且在 H3K27M 突变弥漫性中线胶质瘤和预后不良的患者中表达增加。