Ezh2 augments leukemogenecity by reinforcing differentiation block in acute myeloid leukemia.. Mus musculus

EZH2, a catalytic component of the polycomb repressive complex (PRC) 2, trimethylates histone H3 at lysine 27 (H3K27) to repress the transcription of target genes. Although EZH2 is overexpressed in various cancers including hematological malignancies, the role of EZH2 in acute myeloid leukemia (AML) remained to be determined. In this study, we transformed granulocyte macrophage progenitors (GMPs) from Cre-ERT;Ezh2flox/flox mice with the MLL-AF9 leukemic fusion gene and analyzed function of Ezh2 in AML. Deletion of Ezh2 in transformed GMPs severely compromised growth in vitro and significantly attenuated the progression of leukemia in vivo. Notably, Ezh2-deficient AML cells showed an obvious tendency of differentiation, had lower frequency of leukemia-initiating cells, and developed leukemia mimicking chronic myelomonocytic leukemia. Chromatin immunoprecipitation followed by sequencing analyses revealed a significant reduction in levels of trimethylation at H3K27 in Ezh2-deficient AML cells not only at Ink4a/Arf, its known major target, but also at a cohort of genes relevant to the developmental and differentiation processes. De-repressed genes in Ezh2-deficient AML cells included a gene that can promote differentiation of control AML cells. Our findings suggest that Ezh2 keeps differentiation programs poised for activation in leukemic stem cells, thereby augmenting their leukemogenic capacity. Role of Ezh2 in acute myeloid leukemia.

EZH2是多梳抑制复合体2（polycomb repressive complex 2, PRC2）的催化亚基，可对组蛋白H3的赖氨酸27位（H3K27）进行三甲基化修饰，进而抑制靶基因的转录。尽管EZH2在包括血液系统恶性肿瘤在内的多种癌症中存在过表达现象，但EZH2在急性髓系白血病（acute myeloid leukemia, AML）中的作用仍有待明确。本研究使用MLL-AF9白血病融合基因，对来自Cre-ERT;Ezh2flox/flox小鼠的粒细胞-巨噬细胞祖细胞（granulocyte macrophage progenitors, GMPs）进行转化，以此分析Ezh2在AML中的功能。在转化后的GMPs中敲除Ezh2，会严重损害细胞的体外增殖能力，并显著减缓体内白血病的病程进展。值得注意的是，Ezh2缺陷型AML细胞呈现出明显的分化倾向，白血病起始细胞频率更低，且所诱发的白血病表型类似慢性粒单核细胞白血病。染色质免疫共沉淀联合测序分析显示，在Ezh2缺陷型AML细胞中，不仅在其已知的主要靶基因Ink4a/Arf位点，还在一系列与发育及分化过程相关的基因位点上，H3K27三甲基化水平均显著降低。Ezh2缺陷型AML细胞中的去抑制基因，包含可促进对照AML细胞分化的基因。本研究结果表明，Ezh2可维持白血病干细胞中分化程序处于待命激活状态，从而增强其致白血病能力。急性髓系白血病中Ezh2的作用。