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ChIPSeq of MV4;11 cell treated with DMSO, I-BET, SGC0946 and combination of I-BET and SGC0946

ABSTRACT: 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.

ORGANISM(S): Homo sapiens

PROVIDER: GSE71776 | GEO | 2016/06/12

SECONDARY ACCESSION(S): PRJNA292067

REPOSITORIES: GEO

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Project description:Bromodomain and Extra Terminal protein (BET) inhibitors are first-in-class targeted therapies that deliver a new therapeutic paradigm by directly targeting epigenetic readers. Early clinical trials have shown significant promise especially in acute myeloid leukaemia (AML)3; therefore the evaluation of resistance mechanisms, an inevitable consequence of cancer therapies, is of utmost importance to optimise the clinical efficacy of these drugs. Using primary murine stem and progenitor cells immortalised with MLL-AF9, we have used an innovative approach to generate 20 cell lines derived from single cell clones demonstrating stable resistance, in vitro and in vivo, to the prototypical BET inhibitor, I-BET. Resistance to I-BET confers cross-resistance to chemically distinct BET inhibitors such as JQ1, as well as resistance to genetic knockdown of BET proteins. Resistance is not mediated through increased drug efflux or metabolism but is demonstrated to emerge from leukaemia stem cells (LSC). Resistant clones display a leukaemic granulocyte-macrophage progenitor (L-GMP) phenotype (Lin-, Sca-, cKit+, CD34+, FcγRII/RIII+) and functionally exhibit increased clonogenic capacity in vitro and markedly shorter leukaemia latency in vivo. Chromatin bound BRD4 is globally reduced in resistant cells, however expression of key target genes such as MYC remains unaltered, highlighting the existence of alternative mechanisms to regulate transcription. We demonstrate that resistance to BET inhibitors is in part a consequence of increased Wnt/β-catenin signaling. Negative regulation of this pathway results in differentiation of resistant cells into mature leukaemic blasts, inhibition of MYC expression and restoration of sensitivity to I-BET in vitro and in vivo. Finally, we show that the sensitivity of primary human AML cells to I-BET correlates with the baseline expression of Wnt/β-catenin target genes. Together these findings provide novel insights into the biology of AML, highlight the potential therapeutic limitations of BET inhibitors and identify strategies that may overcome resistance and enhance the clinical utility of these unique targeted therapies. Total RNA obtained from iBET resistant and sensitive cells

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ChIPSeq of MV4;11 cell treated with DMSO, I-BET, SGC0946 and combination of I-BET and SGC0946

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