RESUMEN
Ependymomas are common childhood brain tumours that occur throughout the nervous system, but are most common in the paediatric hindbrain. Current standard therapy comprises surgery and radiation, but not cytotoxic chemotherapy as it does not further increase survival. Whole-genome and whole-exome sequencing of 47 hindbrain ependymomas reveals an extremely low mutation rate, and zero significant recurrent somatic single nucleotide variants. Although devoid of recurrent single nucleotide variants and focal copy number aberrations, poor-prognosis hindbrain ependymomas exhibit a CpG island methylator phenotype. Transcriptional silencing driven by CpG methylation converges exclusively on targets of the Polycomb repressive complex 2 which represses expression of differentiation genes through trimethylation of H3K27. CpG island methylator phenotype-positive hindbrain ependymomas are responsive to clinical drugs that target either DNA or H3K27 methylation both in vitro and in vivo. We conclude that epigenetic modifiers are the first rational therapeutic candidates for this deadly malignancy, which is epigenetically deregulated but genetically bland.
Asunto(s)
Islas de CpG/genética , Ependimoma/genética , Epigénesis Genética/genética , Animales , Neoplasias Encefálicas/tratamiento farmacológico , Neoplasias Encefálicas/genética , Metilación de ADN/efectos de los fármacos , Células Madre Embrionarias/metabolismo , Ependimoma/tratamiento farmacológico , Epigenómica , Femenino , Regulación Neoplásica de la Expresión Génica , Silenciador del Gen/efectos de los fármacos , Histonas/efectos de los fármacos , Histonas/metabolismo , Humanos , Lactante , Ratones , Ratones Endogámicos NOD , Ratones SCID , Mutación/genética , Fenotipo , Complejo Represivo Polycomb 2/metabolismo , Pronóstico , Rombencéfalo/patología , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Recent developments in sequencing technologies led to the discovery of a novel form of genomic instability, termed chromothripsis. This catastrophic genomic event, involved in tumorigenesis, is characterized by tens to hundreds of simultaneously acquired locally clustered rearrangements on one chromosome. We hypothesized that leukemias developing in individuals with Ataxia Telangiectasia, who are born with two mutated copies of the ATM gene, an essential guardian of genome stability, would show a higher prevalence of chromothripsis due to the associated defect in DNA double-strand break repair. Using whole-genome sequencing, fluorescence in situ hybridization and RNA sequencing, we characterized the genomic landscape of Acute Lymphoblastic Leukemia (ALL) arising in patients with Ataxia Telangiectasia. We detected a high frequency of chromothriptic events in these tumors, specifically on acrocentric chromosomes, as compared with tumors from individuals with other types of DNA repair syndromes (27 cases total, 10 with Ataxia Telangiectasia). Our data suggest that the genomic landscape of Ataxia Telangiectasia ALL is clearly distinct from that of sporadic ALL. Mechanistically, short telomeres and compromised DNA damage response in cells of Ataxia Telangiectasia patients may be linked with frequent chromothripsis. Furthermore, we show that ATM loss is associated with increased chromothripsis prevalence in additional tumor entities.
Asunto(s)
Proteínas de la Ataxia Telangiectasia Mutada/fisiología , Ataxia Telangiectasia/genética , Proteínas de Neoplasias/fisiología , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Adolescente , Ataxia Telangiectasia/complicaciones , Proteínas de la Ataxia Telangiectasia Mutada/deficiencia , Proteínas de la Ataxia Telangiectasia Mutada/genética , Niño , Preescolar , Cromosomas Humanos/ultraestructura , Cromotripsis , Reparación del ADN/genética , ADN de Neoplasias/genética , Femenino , Genoma Humano , Inestabilidad Genómica , Humanos , Hibridación Fluorescente in Situ , Masculino , Mutación , Proteínas de Neoplasias/deficiencia , Proteínas de Neoplasias/genética , Neoplasias/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras/etiología , Leucemia-Linfoma Linfoblástico de Células T Precursoras/genética , ARN Neoplásico/genética , Análisis de Secuencia de ADN , Análisis de Secuencia de ARN , Acortamiento del Telómero/genética , TranscriptomaRESUMEN
Glioblastomas are highly aggressive brain tumours and are characterised by substantial cellular heterogeneity within a single tumour. A sub-population of glioblastoma stem-like cells (GSCs) that shares properties with neural precursor cells has been described, exhibiting resistance to therapy and therefore being considered responsible for the high recurrence rate in glioblastoma. To elucidate the underlying cellular processes we investigated the role of phosphatases in the GSC phenotype, using an in vitro phosphatome-wide RNA interference screen. We identified a set of genes, the knockdown of which induces a significant decrease in the glioma stem cell marker CD133, indicating a role in the glioblastoma stem-like phenotype. Among these genes, the ecto-nucleotidase ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1) was found to be highly expressed in GSCs compared with normal brain and neural stem cells. Knockdown of ENPP1 in cultured GSCs resulted in an overall downregulation of stem cell-associated genes, induction of differentiation into astrocytic cell lineage, impairment of sphere formation, in addition to increased cell death, accumulation of cells in G1/G0 cell cycle phase and sensitisation to chemotherapeutic treatment. Genome-wide gene expression analysis and nucleoside and nucleotide profiling revealed that knockdown of ENPP1 affects purine and pyrimidine metabolism, suggesting a link between ENPP1 expression and a balanced nucleoside-nucleotide pool in GSCs. The phenotypic changes in E-NPP1-deficient GSCs are assumed to be a consequence of decreased transcriptional function of E2F1. Together, these results reveal that E-NPP1, by acting upstream of E2F1, is indispensable for the maintenance of GSCs in vitro and hence required to keep GSCs in an undifferentiated, proliferative state.