ASCL1 is directly activated by the LMO1 and MYCN oncogenes and is a master regulator of the differentiation program in neuroblastoma
ABSTRACT: Neuroblastoma is an embryonal tumor of the peripheral sympathetic nervous system. Elevated expression of the transcription factor LMO1 and the polymorphisms within this gene are associated with the susceptibility to develop neuroblastoma. LMO1 has been implicated as an oncogene in T-cell acute lymphoblastic leukemia; however, the transcriptional targets regulated by this protein in neuroblastoma cells are unknown. Here, we identify the genes and molecular pathways controlled by LMO1 in neuroblastoma cells. ChIP-seq analysis revealed that LMO1-bound regions are frequently co-occupied by GATA3 and MYCN proteins and are associated with active histone marks in neuroblastoma cells. RNA-seq analysis demonstrated that LMO1 regulates gene expression in a tumor type-specific manner. One high-confidence target gene directly regulated by LMO1 and MYCN is ASCL1, which is more highly expressed in adrenergic subtype of neuroblastoma cells as compared to normal neuronal cells. High levels of ASCL1 expression are associated with inferior overall survival in primary human neuroblastoma cases. ChIP-seq analysis identified a regulatory element controlling ASCL1 expression that is bound by LMO1, MYCN and the members of the core regulatory circuitry in neuroblastoma cells. Furthermore, ASCL1 is required for neuroblastoma cell growth and regulates genes responsible for repression of neuronal cell differentiation. Taken together, our results implicate ASCL1 as a critical downstream target of LMO1 in the molecular pathogenesis of neuroblastoma.
Project description:High levels of LMO1 expression synergizes with MYCN to accelerate neuroblastomagenesis, enhance disease penetrance and promote widespread metastasis in zebrafish. Transcriptomic analysis of human neuroblasotma cells with programed expression of LMO1 vs vector control or neuroblastoma cells with differential endogenous LMO1 expression revealed that gene signitures affecting tumor cell-extracellular matrix interaction are significantly associated with high levels of LMO1 expression. Our findings provide compelling evidence for a major pathogenic role of LMO1 in MYCN-driven neuroblastoma.
Project description:A previous genome-wide association study identified common polymorphisms at the LMO1 gene locus that are highly associated with neuroblastoma susceptibility in children and oncogenic addiction to LMO1 in the tumor cells1. Here we sought to discover the causal DNA variant at this locus and the mechanism by which it leads to neuroblastoma tumorigenesis. We first imputed all possible genotypes across the LMO1 locus and then mapped highly associated single nucleotide polymorphism (SNPs) to areas of chromatin accessibility, evolutionary conservation, and transcription factor binding sites. SNP rs2168101 G>T was the most highly associated variant (combined P=7.47x10-29, Odds Ratio 0.65, 95% CI: 0.60-0.70) and resided in a super-enhancer defined by extensive acetylation of histone H3 lysine 27 within the first intron of LMO1. The ancestral G allele that is associated with tumor formation resides in a conserved GATA transcription factor binding motif. We show that the newly evolved protective TATA allele is associated with decreased total LMO1 expression (P=0.028) in neuroblastoma primary tumors and ablates GATA3 binding (P=0.007). We demonstrate monoallelic LMO1 expression from the G-containing strand in tumors heterozygous for this SNP as demonstrated both by RNA sequencing (P<0.0001) and reporter assays (P=0.002). These findings show that a recently evolved polymorphism within a super-enhancer element in the first intron of LMO1 influences neuroblastoma susceptibility through differential GATA transcription factor binding and direct modulation of LMO1 expression in cis, and this leads to an oncogenic dependency in tumor cells.
Project description:Childhood neuroblastomas exhibit plasticity between an undifferentiated neural crest-like “mesenchymal” cell state and a more differentiated sympathetic “adrenergic” cell state. These cell states are governed by autoregulatory transcriptional loops called core regulatory circuitries (CRCs), which drive the early development of sympathetic neuronal progenitors from migratory neural crest cells during embryogenesis. The adrenergic cell identity of neuroblastoma requires LMO1 as a transcriptional co-factor. Both LMO1 expression levels and the risk of developing neuroblastoma in children are associated with a single nucleotide polymorphism G/T that affects a GATA motif in the first intron of LMO1. Here we showed that wild-type zebrafish with the GATA genotype developed adrenergic neuroblastoma, while knock-in of the protective TATA allele at this locus reduced the penetrance of MYCN-driven tumors, which were restricted to the mesenchymal cell state. Whole genome sequencing of childhood neuroblastomas demonstrated that TATA/TATA tumors also exhibited a mesenchymal cell state and were low risk at diagnosis. Thus, conversion of the regulatory GATA to a TATA allele in the first intron of LMO1 reduced the neuroblastoma initiation rate by preventing formation of the adrenergic cell state, a mechanism that was conserved over 400 million years of evolution separating zebrafish and humans.
Project description:The SCL and LMO1 oncogenic transcription factors reprogram thymocytes into self-renewing pre-leukemic stem cells (pre-LSCs). Here we report that SCL directly interacts with LMO1 to activate the transcription of a self-renewal program coordinated by LYL1. Gene expression profiles of thymocytes from SCL-LMO1 transgenic and age-matched non transgenic Cd3Îµ-/- mice were compared to identify candidate genes that confer self-renewal capability to pre-leukemic thymocytes.
Project description:Neuroblastoma is a pediatric cancer of the sympathetic nervous system. MYCN amplification is a key indicator of poor prognosis for the disease, however, mechanisms by which MYCN promotes neuroblastoma tumorigenesis are not fully understood. In this study, we analyzed global miRNA and mRNA expression profiles of tissues at different stages of tumorigenesis from TH-MYCN transgenic mice, a model of MYCN-driven neuroblastoma. Based on a Bayesian learning network model in which we compared pre-tumor ganglia from TH-MYCN+/+ mice to age-matched wild-type controls, we devised a predicted miRNA-mRNA interaction network. Among the miRNA-mRNA interactions operating during human neuroblastoma tumorigenesis, we identified that miR-204 is a tumor suppressor miRNA that inhibits a subnetwork of oncogenes strongly associated with MYCN-amplified neuroblastoma and poor patient outcome. Accordingly, we found that MYCN was bound to the miR-204 promoter and repressed miR-204 transcription, while in contrast, miR-204 directly bound MYCN mRNA and repressed MYCN expression. In support of a tumor suppressor role, miR-204 overexpression significantly inhibited neuroblastoma cell proliferation in vitro and tumorigenesis in vivo. Together these findings identify novel tumorigenic miRNA gene networks and miR-204 as a tumor suppressor that regulates MYCN expression in neuroblastoma tumorigenesis.
Project description:To compare the function of endogenous ASCL1 in different neuroblastoma cell contexts, we have used CRISPR-mediated deletion to compare the effects of ASCL1 deletion in a MYCN-amplified and an ALK-driven neuroblastoma line and assessed the transcriptome wide impact of ASCL1 knockout using RNA-seq
Project description:Cut & Run analysis was performed in an neuroblastoma cell line to analyze DNA bindings of ASCL1-tag-HA in GI-MEN ASCL1-tag-HA cells and GI-MEN ASCL1-tag-HA+4TFs cells; analyze DNA bindings of MYCN, PHOX2B and H3K27ac in, GI-MEN 4TFs cells, and GI-MEN ASCL1-tag-HA+4TFs cells.