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Recurrent chromosomal translocations producing a chimaeric MLL oncogene give rise to a highly aggressive acute leukaemia associated with poor clinical outcome. The preferential involvement of chromatin-associated factors as MLL fusion partners belies a dependency on transcription control. Despite recent progress made in targeting chromatin regulators in cancer, available therapies for this well-characterized disease remain inadequate, prompting the need to identify new targets for therapeutic intervention. Here, using unbiased CRISPR-Cas9 technology to perform a genome-scale loss-of-function screen in an MLL-AF4-positive acute leukaemia cell line, we identify ENL as an unrecognized gene that is specifically required for proliferation in vitro and in vivo. To explain the mechanistic role of ENL in leukaemia pathogenesis and dynamic transcription control, a chemical genetic strategy was developed to achieve targeted protein degradation. Acute loss of ENL suppressed the initiation and elongation of RNA polymerase II at active genes genome-wide, with pronounced effects at genes featuring a disproportionate ENL load. Notably, an intact YEATS chromatin-reader domain was essential for ENL-dependent leukaemic growth. Overall, these findings identify a dependency factor in acute leukaemia and suggest a mechanistic rationale for disrupting the YEATS domain in disease.

These results reveal the first high-resolution structural analysis of LIMP-2 and, by homology modelling, the structure of SR-BI and CD36, members of the CD36 superfamily of scavenger receptor proteins. Scavenger receptor proteins of the CD36 superfamily regulate lipid metabolism and innate immunity. They recognize normal and modified lipoproteins and pathogen-associated molecular patterns. In this study, Sergio Grinstein and colleagues present the first high-resolution structural analysis of the CD36 family protein LIMP-2 (lysosomal integral membrane protein type 2), and by homology modelling, the structure of the other two superfamily members, SR-BI and CD36. The structure reveals the existence of a large cavity that traverses the entire length of the molecule; it may serve as a tunnel through which cholesterol is delivered from the bound lipoprotein to the outer leaflet of the plasma membrane. Members of the CD36 superfamily of scavenger receptor proteins are important regulators of lipid metabolism and innate immunity. They recognize normal and modified lipoproteins, as well as pathogen-associated molecular patterns. The family consists of three members: SR-BI (which delivers cholesterol to the liver and steroidogenic organs and is a co-receptor for hepatitis C virus), LIMP-2/LGP85 (which mediates lysosomal delivery of β-glucocerebrosidase and serves as a receptor for enterovirus 71 and coxsackieviruses) and CD36 (a fatty-acid transporter and receptor for phagocytosis of effete cells and Plasmodium-infected erythrocytes). Notably, CD36 is also a receptor for modified lipoproteins and β-amyloid, and has been implicated in the pathogenesis of atherosclerosis and of Alzheimer’s disease1. Despite their prominent roles in health and disease, understanding the function and abnormalities of the CD36 family members has been hampered by the paucity of information about their structure. Here we determine the crystal structure of LIMP-2 and infer, by homology modelling, the structure of SR-BI and CD36. LIMP-2 shows a helical bundle where β-glucocerebrosidase binds, and where ligands are most likely to bind to SR-BI and CD36. Remarkably, the crystal structure also shows the existence of a large cavity that traverses the entire length of the molecule. Mutagenesis of SR-BI indicates that the cavity serves as a tunnel through which cholesterol(esters) are delivered from the bound lipoprotein to the outer leaflet of the plasma membrane. We provide evidence supporting a model2 whereby lipidic constituents of the ligands attached to the receptor surface are handed off to the membrane through the tunnel, accounting for the selective lipid transfer characteristic of SR-BI and CD36.

DNA methylation is a key epigenetic process and the faithful maintenance of DNA methylation patterns is essential to the wellbeing of mammalian cells. This means that cells need a mechanism to identify the partially methylated version of CpG once a new DNA strand has been replicated or repaired, so that it can be further methylated by the DNA methyltransferase, DNMT1. As part of this process the protein UHRF1 (or Np95/ICBP90) facilitates the loading of DNMT1 onto the hemimethylated CpG sequences during DNA replication. Three papers in this issue describe crystal structures of the SRA domain of UHRF1 bound to DNA containing a hemi-methylated CpG site. The structures show that methyl-cytosine is flipped out of the DNA helix and inserted into a binding pocket on the SRA domain. Epigenetic inheritance in mammals is characterized by high-fidelity replication of CpG methylation patterns during development1,2. UHRF1 (also known as ICBP90 in humans and Np95 in mouse)3 is an E3 ligase important for the maintenance of global and local DNA methylation in vivo4,5. The preferential affinity of UHRF1 for hemi-methylated DNA over symmetrically methylated DNA by means of its SET and RING-associated (SRA) domain6 and its association with the maintenance DNA methyltransferase 1 (DNMT1) suggests a role in replication of the epigenetic code4,5,7. Here we report the 1.7 A crystal structure of the apo SRA domain of human UHRF1 and a 2.2 A structure of its complex with hemi-methylated DNA, revealing a previously unknown reading mechanism for methylated CpG sites (mCpG). The SRA–DNA complex has several notable structural features including a binding pocket that accommodates the 5-methylcytosine that is flipped out of the duplex DNA. Two specialized loops reach through the resulting gap in the DNA from both the major and the minor grooves to read the other three bases of the CpG duplex. The major groove loop confers both specificity for the CpG dinucleotide and discrimination against methylation of deoxycytidine of the complementary strand. The structure, along with mutagenesis data, suggests how UHRF1 acts as a key factor for DNMT1 maintenance methylation through recognition of a fundamental unit of epigenetic inheritance, mCpG.