Department of Biochemistry, Tulane University, New Orleans, Louisiana, USA.
Cancer Res. 2010 Dec 15;70(24):10234-42. doi: 10.1158/0008-5472.CAN-10-3294.
Chimeric oncoproteins resulting from fusion of MLL to a wide variety of partnering proteins cause biologically distinctive and clinically aggressive acute leukemias. However, the mechanism of MLL-mediated leukemic transformation is not fully understood. Dot1, the only known histone H3 lysine 79 (H3K79) methyltransferase, has been shown to interact with multiple MLL fusion partners including AF9, ENL, AF10, and AF17. In this study, we utilize a conditional Dot1l deletion model to investigate the role of Dot1 in hematopoietic progenitor cell immortalization by MLL fusion proteins. Western blot and mass spectrometry show that Dot1-deficient cells are depleted of the global H3K79 methylation mark. We find that loss of Dot1 activity attenuates cell viability and colony formation potential of cells immortalized by MLL oncoproteins but not by the leukemic oncoprotein E2a-Pbx1. Although this effect is most pronounced for MLL-AF9, we find that Dot1 contributes to the viability of cells immortalized by other MLL oncoproteins that are not known to directly recruit Dot1. Cells immortalized by MLL fusions also show increased apoptosis, suggesting the involvement of Dot1 in survival pathways. In summary, our data point to a pivotal requirement for Dot1 in MLL fusion protein-mediated leukemogenesis and implicate Dot1 as a potential therapeutic target.
嵌合性癌蛋白是由 MLL 与多种伙伴蛋白融合而成的，它们导致生物学上独特且临床上侵袭性强的急性白血病。然而，MLL 介导的白血病转化的机制尚未完全阐明。Dot1 是唯一已知的组蛋白 H3 赖氨酸 79（H3K79）甲基转移酶，已被证明与多个 MLL 融合伙伴相互作用，包括 AF9、ENL、AF10 和 AF17。在这项研究中，我们利用条件性 Dot1l 缺失模型来研究 Dot1 在 MLL 融合蛋白诱导造血祖细胞永生化中的作用。Western blot 和质谱分析表明，Dot1 缺失细胞中全局 H3K79 甲基化标记缺失。我们发现，Dot1 活性丧失会削弱由 MLL 癌蛋白而非白血病癌蛋白 E2a-Pbx1 永生化的细胞的细胞活力和集落形成能力。尽管这种效应在 MLL-AF9 中最为明显，但我们发现 Dot1 有助于其他不被认为直接招募 Dot1 的 MLL 癌蛋白永生化的细胞的活力。MLL 融合诱导的细胞也表现出增加的细胞凋亡，表明 Dot1 参与了存活途径。总之，我们的数据表明 Dot1 在 MLL 融合蛋白介导的白血病发生中具有关键作用，并暗示 Dot1 是一个潜在的治疗靶点。
