Histone H3 Lysine 79 Methyltransferase Dot1 Is Required for Immortalization by MLL Oncogenes

Abstract

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.

MLL1 and DOT1L cooperate with meningioma-1 to induce acute myeloid leukemia

“…HOXA9 is overexpressed in about 50% of AML (36), and most recent data has suggested that normal as well as malignant later HOXA cluster expression may require DOT1L independent of the expression of a leukemogenic fusion protein that could mediate direct recruitment (23,37,38). We find that functional DOT1L is not universally required for high HOXA9 expression.…”

The diverse functions of Dot1 and H3K79 methylation

“…In addition to MLL-AF10 and CALM-AF10, DOT1L is involved in transformation by other MLL fusion proteins, such as MLL-ENL (Mueller et al 2007), MLL-AF4 (Krivtsov et al 2008), and MLL-AF9 (Chang et al 2010;Nguyen et al 2011a). Consistent with the fact that DOT1L is involved in MLL-related transformation, DOT1L associates with a number of MLL fusion proteins and participates in the activation of a leukemic transcriptional program (Bitoun et al 2007;Mueller et al 2007Mueller et al , 2009).…”

Epigenetic alterations in acute myeloid leukemias

“…DOT1L, the only known histone H3 Lys79 methyltransferase, has been shown to have a broad role in transformation mediated by MLL fusion proteins through interactions with multiple MLL fusion partners, and its gene disruption in mice has pointed to a pivotal role of DOT1L in hematopoiesis, cardiac function, and the development of leukemia. Mistargeting of DOT1L to HOX9A and MEIS1 through its interaction with MLL fusion partners leads to the constitutive transcriptional activation of these genes through aberrant hypermethylation of histone H3 Lys79, which in turns results in leukemic transformation [66,67].…”