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Dissecting Super-enhancer driven Transcriptional Dependencies Reveals Novel Oncogenes and Therapeutic Strategies of Group 3 Subtype Medulloblastoma [ChIP-seq]

ABSTRACT: Medulloblastoma (MB) is the most common malignant pediatric brain tumor and group 3 subtype (G3-MB) exhibits the worst prognosis. Dissecting super-enhancer (SE) driven transcriptional dependencies of cancer has been shown to facilitate identifying novel oncogenic mechanisms and therapeutic targets or strategies. In this study, our integrative SE analyses of primary tissues and patient-derived tumor cell lines of G3-MB revealed their partially conserved SE-associated transcripts were enriched of subtype-specific tumor-dependent genes and MB patients harboring enrichment of those transcripts exhibited worse prognosis. Fourteen such conserved SE-associated genes were identified to be members of SE-driven core transcriptional regulatory network of G3-MB, including three well-recognized master TFs and eleven newly identified effector oncogenes. ARL4D, one of the effector oncogenes, was further demonstrated to exert its oncogenic role via maintaining cell-cycle progression and stemness of G3-MB cells. Moreover, BET inhibition with CDK7 inhibition or proteasome inhibition, two combinatory strategies of targeting SE complex components (BRD4, CDK7) or SE-associated effector oncogene (PSMB5), were shown to exhibit synergistic therapeutic effects against G3-MB. Taken together, our study verifies the oncogenic role and therapeutic potential of SE-driven transcriptional dependencies of G3-MB, resulting in better understanding of its tumor biology and identification of novel SE-associated therapeutic targets or strategies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE185003 | GEO | 2021/10/04

REPOSITORIES: GEO

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Project description:Drug-tolerant “persister” tumor cells underlie the emergence of drug-resistant clones contribute to relapse and disease progression; thus, identifying actionable targets that disable persisters and mitigate relapse are a high priority need. Although the BCL2-targeting agent venetoclax (ABT-199) has shown promising responses in mantle cell and double hit B cell lymphomas, resistance often arises, yet mechanistically how this occurs is unclear. Here we report that ABT-199 resistance can evolve from persister clones that have selective deletions at 18q21 that involve the drug target BCL2 and the apoptotic regulators Noxa (PMAIP1) and TCF4. Notably, reprogramming of super enhancers (SE) in persisters contributes to resistance, where there is a selection for SE-directed overexpression of the apoptotic regulator BCL2A1 and oncogenic transcription factors IKZF1 and FOXC1. At the same time, the SE reprogramming confers an opportunity for overcoming ABT-199 resistance. An unbiased drug screen on a platform that recapitulates the lymphoma microenvironment revealed that persisters are vulnerable to inhibitors of transcription initiation and elongation, and especially so to inhibitors of cyclin-dependent kinase 7 (CDK7) that is essential for transcription initiation. Specifically, CDK7 loss or inhibition eliminated the persister phenotype by disabling SE-driven expression of BCL2A1, IKZF1 and FOXC1. Thus, the co-treatment of ABT-199 with CDK7 inhibitors blocked the evolution of drug resistance, and provoked tumor regression in models of mantle cell lymphoma (MCL) and double hit lymphomas (DHL) that overexpress both MYC and BCL2. Together, these findings establish loss of apoptotic regulators and an adaptive transcriptional response as drug resistance mechanisms in lymphoma, more importantly, establish a rationale for transcription inhibition-based combination strategies to prevent and overcome drug resistance in B cell malignancies toward BCL2 inhibitor.

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Dissecting Super-enhancer driven Transcriptional Dependencies Reveals Novel Oncogenes and Therapeutic Strategies of Group 3 Subtype Medulloblastoma [ChIP-seq]

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