RNASeq of 4SU labelled nascent RNA in MV4;11 cell treated with DMSO, I-BET, SGC0946 and combination of I-BET and SGC0946

Central to the molecular pathogenesis of MLL leukaemia is the abnormal co-optation of members of transcription complexes including disrupter of telomeric silencing 1-like (DOT1L) and bromodomain containing protein 4 (BRD4). Consequently, targeted therapies against DOT1L and BRD4 are currently being evaluated in clinical trials. However, the mechanisms by which BRD4 and DOT1L regulate leukaemogenic transcription programs remain unclear. Using quantitative proteomics, chemoproteomics and biochemical fractionation we find that native BRD4 and DOT1L exist in largely separate protein complexes. Genetic disruption or small molecule inhibition of BRD4 and DOT1L shows marked synergistic activity against MLL-FP leukaemia cell lines, primary human leukaemia cells and murine leukaemia models. Mechanistically, we find a previously unrecognised functional collaboration between DOT1L and BRD4 that is especially important at highly transcribed genes in close proximity to superenhancers. DOT1L via H3K79me2 facilitates the deposition of histone H4 acetylation, which in turn regulates the binding of BRD4 to chromatin. These data provide novel insights into the regulation of transcription and specify a molecular framework for therapeutic intervention in this poor prognostic disease. Overall design: RNASeq of 4SU labelled nascent RNA in MV4;11 cell treated with DMSO, I-BET, SGC0946 and combination of I-BET and SGC0946 in duplicate

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Gilan O, Lam EY, Becher I, Lugo D, Cannizzaro E, Joberty G, Ward A, Wiese M, Fong CY, Ftouni S, Tyler D, Stanley K, MacPherson L, Weng CF, Chan YC, Ghisi M, Smil D, Carpenter C, Brown P, Garton N, Blewitt ME, Bannister AJ, Kouzarides T, Huntly BJ, Johnstone RW, Drewes G, Dawson SJ, Arrowsmith CH, Grandi P, Prinjha RK, Dawson MA