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The SAGA complex maintains the oncogenic gene expression program in MYCN-amplified neuroblastoma [ChIP-Seq]

ABSTRACT: Pediatric cancers are frequently driven by fusion or amplification events that result in aberrant transcription factor activity. As transcription factors themselves remain challenging to target, an emerging therapeutic approach for these cancers is to target epigenetic complexes that help maintain oncogenic transcriptional programs. It is therefore critical to identify the complete set of epigenetic modulators maintaining the oncogenic epigenetic landscape of pediatric cancers. Here, we used functional genomic screens to identify epigenetic complexes critical for viability in cell line models of MYCN-amplified neuroblastoma, a disease of dysregulated development driven by an aberrant oncogenic transcriptional program. We identified multiple genes within the transcriptional coactivator Spt-Ada-Gcn5-acetyltransferase (SAGA) complex as selective dependencies in MYCN-amplified neuroblastoma. Integrating ChIP-seq, ATAC-seq, and RNA-seq with targeted protein-degradation and gene editing tools, we characterized the DNA recruitment sites of the SAGA complex in neuroblastoma, and the consequences of SAGA complex lysine acetyltransferase (KAT) activity loss on histone acetylation and gene expression. We demonstrate that loss of SAGA KAT activity suppresses MYC and MYCN gene expression programs and impairs cell cycle progression. Further, we showed that the SAGA complex is pharmacologically targetable with a KAT2A/KAT2B proteolysis targeting chimera molecule that demonstrated significant activity in vitro and in vivo. Our findings expand our understanding of the histone modifying complexes that maintain the oncogenic transcriptional state in this disease and suggest therapeutic potential for inhibitors of SAGA KAT activity in MYCN-amplified neuroblastoma.

ORGANISM(S): Homo sapiens

PROVIDER: GSE211953 | GEO | 2024/04/19

REPOSITORIES: GEO

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Project description:In neuroblastoma, amplification of the oncogenic basic helix-loop-helix (bHLH) transcription factor (TF) MYCN is the defining prognosticator of high-risk disease, occurs in one-third of neuroblastoma, and drastically reduces overall survival rates. As a proto-oncogene, targeted MYCN overexpression in peripheral neural crest is sufficient to initiate disease in mouse models. In MYCN amplified neuroblastoma, elevated expression of the factor is crucial to maintain tumor stemness and is associated with increased proliferation and aberrant cell cycle progression, as these tumors lack the ability to arrest in G1 in response to irradiation. MYCN down-regulation broadly reverses these oncogenic phenotypes in a variety of neuroblastoma models and recent thereapeutic strategies to indirectly target MYCN production or protein stability have reduced tumor growth in vivo. These observations motivate an investigation of MYCN binding in MYCN amplified tumors as it remains fundamentally unclear how elevated levels of the factor occupy the genome and alter transcriptional programs in neuroblastoma. Here we present the first dynamic chromatin and transcriptional landscape of direct MYCN perturbation in neuroblastoma. We find that at oncogenic levels, MYCN associates with E-box (CANNTG) binding motifs in an affinity dependent manner across most active cis-regulatory promoters and enhancers. MYCN shutdown globally reduces histone acetylation and transcription, consistent with prior descriptions of MYC proteins as non-linear amplifiers of gene expression. We establish that MYCN load at the promoter and proximal enhancers predicts transcriptional responsiveness to MYCN shutdown and that MYCN enhancer binding occurs prominently at the most strongly occupied and down-regulated genes, suggesting a role for these tissue specific elements in predicating MYCN responsive âtargetâ genes. At these invaded enhancers, we identify the lineage specific bHLH TWIST1 as a key collaborator and dependency of oncogenic MYCN. These data suggest that MYCN enhancer invasion helps shape transcriptional amplification of the neuroblastoma gene expression program to promote tumorigenesis. ChIP-Seq in SHEP21, BE2C, KELLY, and NGP neuroblastoma cell lines for H3K27ac, H3K4me3, RNA PolII, MYCN, BRD4, or TWIST1

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The SAGA complex maintains the oncogenic gene expression program in MYCN-amplified neuroblastoma [ChIP-Seq]

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