Unknown,Transcriptomics,Genomics,Proteomics

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Brg1 activates enhancer repertoires to establish B cell identity and modulate cell growth

ABSTRACT: Early B cell development is orchestrated by the combined activities of the transcriptional regulators E2A, EBF1, Foxo1 and Ikaros. However, how the genome-wide binding patterns of these regulators are modulated during B-lineage development remains to be determined. Here, we found that in lymphoid progenitors the chromatin remodeler Brg1 specified the B cell fate. In committed pro-B cells Brg1 regulated Igh locus contraction and controlled c-Myc expression to modulate the expression of genes that regulate ribosome biogenesis. In committed pro-B cells Brg1 also suppressed a pre-B lineage-specific pattern of gene expression. Finally, we found that Brg1 acted mechanistically to establish B cell fate and modulate cell growth by facilitating access of lineage-specific transcription factors to poised enhancer repertoires. 8 ATAC-Seq samples from sorted ALP and BLP (duplicates, control and Brg1-deleted), 4 ATAC-Seq samples from cultured pro-B cells (duplicates, control and Brg1-deleted), 2 Ikaros ChIP-seq samples (performed in Rag1-/- pro-B cells and in E2A-/- pre-pro-B cells), 1 Brg1 ChIP-seq sample and accompanying Input sample (both in Rag1-/- pro-B cells), 4 RNA-Seq samples from cultured pro-B cells (duplicates, control and Brg1-deleted), 6 RNA-Seq samples from cultured Rag1-/- pro-B cells (triplicates, control and Brg1-knock down).

ORGANISM(S): Mus musculus

SUBMITTER: Claudia Bossen

PROVIDER: E-GEOD-66978 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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 rates1,2. As a proto-oncogene, targeted MYCN overexpression in peripheral neural crest is sufficient to initiate disease in mouse models3. In MYCN amplified neuroblastoma, elevated expression of the factor is crucial to maintain tumor stemness4,5 and is associated with increased proliferation and aberrant cell cycle progression, as these tumors lack the ability to arrest in G1 in response to irradiation6-9. MYCN down-regulation broadly reverses these oncogenic phenotypes in a variety of neuroblastoma models10-12 and recent thereapeutic strategies to indirectly target MYCN production or protein stability have reduced tumor growth in vivo13-15. 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 â??targetâ?? 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. ATAC-Seq in SHEP21, BE2C, KELLY, NGP, and MM1S cell lines

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Brg1 activates enhancer repertoires to establish B cell identity and modulate cell growth

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