Histone Methylation: It's in the Numbers

RESEARCH HIGHLIGHTS

Hoxa7–10 cluster, whereas H3K79me1 levels were the same or increased. A genome-wide analysis of H3K79me1 and H3K79me2 levels showed that Lara Crow / NPG Crow Lara genes with decreased H3K79me2 and increased H3K79me1 levels were enriched for MLL–AF9 target genes. Indeed, Af10 deletion affected the ratio of H3K79me1:H3K79me2 at most of the 129 MLL–AF9 target genes and restored H3K79 methyl EPIGENETICS ation levels to those observed in cells that do not express MLL–AF9. The Histone methylation: it’s in the numbers expression of most of the MLL–AF9 target genes was reduced in these The expression of homeobox (HOX) HOXA genes is driven by the conver- cells, although there were some proteins, which are important regula- sion of H3K79me1 to H3K79me2 and exceptions. DOT1L occupancy of tors of developmental transcription H3K79me3, and that H3K79me1 is Hoxa7–10 was reduced in Af10–/– cells programmes, is altered in approxi- insufficient to sustain high levels of expressing MLL–AF9, whereas mately 50% of cases of acute myeloid gene expression. MLL–AF9 occupancy was unaffected. leukaemia (AML). In particular, the Next, the authors investigated In addition, the DOT1L–AF10 com- expression of the HOXA cluster is how H3K79me1 conversion to higher plex had much higher activity than altered in AML with mixed-lineage methylation states was regulated. DOT1L alone in an in vitro histone leukaemia (MLL) rearrangements, Having excluded a role for changes in methyltransferase assay. and misdirection of DOT1L — a his- DOT1L expression, they investigated Finally, the authors showed that tone methyltransferase that catalyses whether a cofactor might enhance NUP98–NSD1-transformed LSKs in histone H3 lysine 79 (H3K79) methy DOT1L recruitment and activity. which Af10 was deleted had reduced lation — to target genes of MLL They found that AF10 knockdown H3K79me2 levels at the Hoxa7–10 fusion proteins is thought to drive reduced H3K79me2 levels (but not cluster and reduced proliferation. gene hyperexpression. H3K79me1 levels), showing that Similar results were obtained by treat- To examine the role of DOT1L AF10 is crucial for the conversion of ment of these cells with EPZ004777, in the regulation of HOXA gene H3K79me1 to H3K79me2. Af10 dele- which significantly reduced Hoxa7–10 expression, Deshpande et al. sorted tion also reduced the proliferation of expression (as well as H3K79me2 lineage– SCA1+ KIT+ (LSK) cells, leukaemia cell lines with MLL fusion levels) and cell proliferation in a dose- which are enriched in haematopoietic proteins and impaired colony forma- dependent manner, indicating that stem cells (HSCs), from the bone tion of MLL–AF9 and MLL–AF6 some non-MLL-rearranged AMLs marrow of mice with inducible transformed cells. Af10 deletion also may also depend on DOT1L–AF10 Dot1l deletion. Chromatin immuno delayed the initiation and decreased for the regulation of HOXA gene precipitation (ChIP) for H3K79 the propagation of leukaemia in sec- expression. monomethylation (H3K79me1), ondary recipient mice of MLL–AF9 This paper identifies a key role H3K79me2 or H3K79me3 in LSKs and MLL–AF6 transformed cells. for the DOT1L complex cofactor and granulocyte-macrophage Moreover, the authors found that AF10 in regulating progressive progenitors (GMPs; which have low Af10-deficient MLL–AF9 leukaemia H3K79 methylation and shows that expression levels of the Hoxa7–10 cells showed an increased sensitivity DOT1L–AF10 regulates HOXA cluster and Meis1) revealed that to the DOT1L inhibitor, EPZ004777, gene expression in various subtypes H3K79me2 and H3K79me3 levels indicating that AF10 could be an of leukaemia, potentially increas- DOT1L–AF10 were reduced at these loci in GMPs effective therapeutic target. ing the opportunity for DOT1L regulates compared with LSKs. On examining ChIP followed by sequencing inhibition. HOXA gene MLL–AF9 leukaemias, they found (ChIP–seq) of Af10-deficient leu- Gemma K. Alderton that HOXA gene promoters had high kaemias revealed that locus-specific ORIGINAL RESEARCH PAPER Deshpande, A. J. expression levels of H3K79me2 and H3K79me3 changes to H3K79 methylation et al. AF10 reguates progressive H3K79 and low levels of H3K79me1. This particularly decreased H3K79me2 methylation and HOX gene expression in diverse AML subtypes. Cancer Cell 26, 896–908 (2014) indicates that the hyperexpression of and H3K79me3 levels at the

NATURE REVIEWS | CANCER VOLUME 15 | JANUARY 2015