RESUMO
Current therapies for medulloblastoma, a highly malignant childhood brain tumour, impose debilitating effects on the developing child, and highlight the need for molecularly targeted treatments with reduced toxicity. Previous studies have been unable to identify the full spectrum of driver genes and molecular processes that operate in medulloblastoma subgroups. Here we analyse the somatic landscape across 491 sequenced medulloblastoma samples and the molecular heterogeneity among 1,256 epigenetically analysed cases, and identify subgroup-specific driver alterations that include previously undiscovered actionable targets. Driver mutations were confidently assigned to most patients belonging to Group 3 and Group 4 medulloblastoma subgroups, greatly enhancing previous knowledge. New molecular subtypes were differentially enriched for specific driver events, including hotspot in-frame insertions that target KBTBD4 and 'enhancer hijacking' events that activate PRDM6. Thus, the application of integrative genomics to an extensive cohort of clinical samples derived from a single childhood cancer entity revealed a series of cancer genes and biologically relevant subtype diversity that represent attractive therapeutic targets for the treatment of patients with medulloblastoma.
Assuntos
Análise Mutacional de DNA , Genoma Humano/genética , Meduloblastoma/classificação , Meduloblastoma/genética , Sequenciamento Completo do Genoma , Carcinogênese/genética , Proteínas de Transporte/genética , Estudos de Coortes , Metilação de DNA , Conjuntos de Dados como Assunto , Epistasia Genética , Genômica , Humanos , Terapia de Alvo Molecular , Proteínas Musculares/genética , Mutação , Oncogenes/genética , Fatores de Transcrição/genética , Proteínas Wnt/genéticaRESUMO
Medulloblastoma is a highly malignant paediatric brain tumour currently treated with a combination of surgery, radiation and chemotherapy, posing a considerable burden of toxicity to the developing child. Genomics has illuminated the extensive intertumoral heterogeneity of medulloblastoma, identifying four distinct molecular subgroups. Group 3 and group 4 subgroup medulloblastomas account for most paediatric cases; yet, oncogenic drivers for these subtypes remain largely unidentified. Here we describe a series of prevalent, highly disparate genomic structural variants, restricted to groups 3 and 4, resulting in specific and mutually exclusive activation of the growth factor independent 1 family proto-oncogenes, GFI1 and GFI1B. Somatic structural variants juxtapose GFI1 or GFI1B coding sequences proximal to active enhancer elements, including super-enhancers, instigating oncogenic activity. Our results, supported by evidence from mouse models, identify GFI1 and GFI1B as prominent medulloblastoma oncogenes and implicate 'enhancer hijacking' as an efficient mechanism driving oncogene activation in a childhood cancer.
Assuntos
Proteínas de Ligação a DNA/genética , Elementos Facilitadores Genéticos/genética , Variação Estrutural do Genoma/genética , Meduloblastoma/genética , Oncogenes/genética , Proteínas Proto-Oncogênicas/genética , Proteínas Repressoras/genética , Fatores de Transcrição/genética , Animais , Criança , Cromossomos Humanos Par 9/genética , Proteínas de Ligação a DNA/metabolismo , Humanos , Meduloblastoma/classificação , Meduloblastoma/patologia , Camundongos , Proteínas Proto-Oncogênicas/metabolismo , Proteínas Repressoras/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Epigenetic alterations, that is, disruption of DNA methylation and chromatin architecture, are now acknowledged as a universal feature of tumorigenesis. Medulloblastoma, a clinically challenging, malignant childhood brain tumour, is no exception. Despite much progress from recent genomics studies, with recurrent changes identified in each of the four distinct tumour subgroups (WNT-pathway-activated, SHH-pathway-activated, and the less-well-characterized Group 3 and Group 4), many cases still lack an obvious genetic driver. Here we present whole-genome bisulphite-sequencing data from thirty-four human and five murine tumours plus eight human and three murine normal controls, augmented with matched whole-genome, RNA and chromatin immunoprecipitation sequencing data. This comprehensive data set allowed us to decipher several features underlying the interplay between the genome, epigenome and transcriptome, and its effects on medulloblastoma pathophysiology. Most notable were highly prevalent regions of hypomethylation correlating with increased gene expression, extending tens of kilobases downstream of transcription start sites. Focal regions of low methylation linked to transcription-factor-binding sites shed light on differential transcriptional networks between subgroups, whereas increased methylation due to re-normalization of repressed chromatin in DNA methylation valleys was positively correlated with gene expression. Large, partially methylated domains affecting up to one-third of the genome showed increased mutation rates and gene silencing in a subgroup-specific fashion. Epigenetic alterations also affected novel medulloblastoma candidate genes (for example, LIN28B), resulting in alternative promoter usage and/or differential messenger RNA/microRNA expression. Analysis of mouse medulloblastoma and precursor-cell methylation demonstrated a somatic origin for many alterations. Our data provide insights into the epigenetic regulation of transcription and genome organization in medulloblastoma pathogenesis, which are probably also of importance in a wider developmental and disease context.
Assuntos
Metilação de DNA/genética , Regulação Neoplásica da Expressão Gênica , Inativação Gênica , Meduloblastoma/genética , Análise de Sequência de DNA/métodos , Animais , Sítios de Ligação , Linhagem Celular Tumoral , Cromatina/genética , Cromatina/metabolismo , Imunoprecipitação da Cromatina , Feminino , Genoma/genética , Histonas/metabolismo , Humanos , Meduloblastoma/patologia , Camundongos , Regiões Promotoras Genéticas/genética , Proteínas de Ligação a RNA/genética , Fatores de Transcrição/metabolismo , Transcrição GênicaRESUMO
Smoothened (SMO) inhibitors recently entered clinical trials for sonic-hedgehog-driven medulloblastoma (SHH-MB). Clinical response is highly variable. To understand the mechanism(s) of primary resistance and identify pathways cooperating with aberrant SHH signaling, we sequenced and profiled a large cohort of SHH-MBs (n = 133). SHH pathway mutations involved PTCH1 (across all age groups), SUFU (infants, including germline), and SMO (adults). Children >3 years old harbored an excess of downstream MYCN and GLI2 amplifications and frequent TP53 mutations, often in the germline, all of which were rare in infants and adults. Functional assays in different SHH-MB xenograft models demonstrated that SHH-MBs harboring a PTCH1 mutation were responsive to SMO inhibition, whereas tumors harboring an SUFU mutation or MYCN amplification were primarily resistant.
Assuntos
Resistencia a Medicamentos Antineoplásicos/genética , Proteínas Hedgehog/genética , Meduloblastoma/genética , Receptores Acoplados a Proteínas G/antagonistas & inibidores , Receptores Acoplados a Proteínas G/genética , Adolescente , Adulto , Animais , Sequência de Bases , Compostos de Bifenilo/uso terapêutico , Neoplasias Cerebelares/tratamento farmacológico , Neoplasias Cerebelares/genética , Criança , Pré-Escolar , RNA Helicases DEAD-box/genética , Variações do Número de Cópias de DNA/genética , Feminino , Perfilação da Expressão Gênica , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Lactente , Fatores de Transcrição Kruppel-Like/genética , Masculino , Meduloblastoma/tratamento farmacológico , Camundongos , Camundongos Endogâmicos NOD , Camundongos SCID , Dados de Sequência Molecular , Proteína Proto-Oncogênica N-Myc , Transplante de Neoplasias , Proteínas Nucleares/genética , Proteínas Oncogênicas/genética , Receptores Patched , Receptor Patched-1 , Fosfatidilinositol 3-Quinases/genética , Fosfatidilinositol 3-Quinases/metabolismo , Regiões Promotoras Genéticas/genética , Proteínas Proto-Oncogênicas c-akt/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Piridinas/uso terapêutico , Receptores de Superfície Celular/genética , Proteínas Repressoras/genética , Transdução de Sinais/genética , Receptor Smoothened , Telomerase/genética , Proteína Supressora de Tumor p53/genética , Adulto Jovem , Proteína Gli2 com Dedos de ZincoRESUMO
Pilocytic astrocytoma, the most common childhood brain tumor, is typically associated with mitogen-activated protein kinase (MAPK) pathway alterations. Surgically inaccessible midline tumors are therapeutically challenging, showing sustained tendency for progression and often becoming a chronic disease with substantial morbidities. Here we describe whole-genome sequencing of 96 pilocytic astrocytomas, with matched RNA sequencing (n = 73), conducted by the International Cancer Genome Consortium (ICGC) PedBrain Tumor Project. We identified recurrent activating mutations in FGFR1 and PTPN11 and new NTRK2 fusion genes in non-cerebellar tumors. New BRAF-activating changes were also observed. MAPK pathway alterations affected all tumors analyzed, with no other significant mutations identified, indicating that pilocytic astrocytoma is predominantly a single-pathway disease. Notably, we identified the same FGFR1 mutations in a subset of H3F3A-mutated pediatric glioblastoma with additional alterations in the NF1 gene. Our findings thus identify new potential therapeutic targets in distinct subsets of pilocytic astrocytoma and childhood glioblastoma.
Assuntos
Astrocitoma/genética , Neoplasias Encefálicas/genética , Mutação , Receptor Tipo 1 de Fator de Crescimento de Fibroblastos/genética , Receptor trkB/genética , Animais , Astrocitoma/metabolismo , Sequência de Bases , Neoplasias Encefálicas/metabolismo , Linhagem Celular , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/metabolismo , Pontos de Quebra do Cromossomo , Cromossomos Humanos Par 6 , Cromossomos Humanos Par 9 , Fatores de Crescimento de Fibroblastos/metabolismo , Humanos , Sistema de Sinalização das MAP Quinases , Camundongos , Modelos Moleculares , Proteínas de Fusão Oncogênica/química , Proteínas de Fusão Oncogênica/genética , Conformação Proteica , Proteínas Proto-Oncogênicas B-raf/química , Proteínas Proto-Oncogênicas B-raf/genética , Receptor Tipo 1 de Fator de Crescimento de Fibroblastos/metabolismo , Receptor trkB/metabolismoRESUMO
Medulloblastoma is an aggressively growing tumour, arising in the cerebellum or medulla/brain stem. It is the most common malignant brain tumour in children, and shows tremendous biological and clinical heterogeneity. Despite recent treatment advances, approximately 40% of children experience tumour recurrence, and 30% will die from their disease. Those who survive often have a significantly reduced quality of life. Four tumour subgroups with distinct clinical, biological and genetic profiles are currently identified. WNT tumours, showing activated wingless pathway signalling, carry a favourable prognosis under current treatment regimens. SHH tumours show hedgehog pathway activation, and have an intermediate prognosis. Group 3 and 4 tumours are molecularly less well characterized, and also present the greatest clinical challenges. The full repertoire of genetic events driving this distinction, however, remains unclear. Here we describe an integrative deep-sequencing analysis of 125 tumour-normal pairs, conducted as part of the International Cancer Genome Consortium (ICGC) PedBrain Tumor Project. Tetraploidy was identified as a frequent early event in Group 3 and 4 tumours, and a positive correlation between patient age and mutation rate was observed. Several recurrent mutations were identified, both in known medulloblastoma-related genes (CTNNB1, PTCH1, MLL2, SMARCA4) and in genes not previously linked to this tumour (DDX3X, CTDNEP1, KDM6A, TBR1), often in subgroup-specific patterns. RNA sequencing confirmed these alterations, and revealed the expression of what are, to our knowledge, the first medulloblastoma fusion genes identified. Chromatin modifiers were frequently altered across all subgroups. These findings enhance our understanding of the genomic complexity and heterogeneity underlying medulloblastoma, and provide several potential targets for new therapeutics, especially for Group 3 and 4 patients.
