Diffuse high-grade gliomas (HGGs) of childhood are a devastating spectrum of disease with no effective cures. The two-year survival for paediatric HGG ranges from 30%, for tumours arising in the ...cerebral cortex, to less than 10% for diffuse intrinsic pontine gliomas (DIPGs), which arise in the brainstem. Recent genome-wide studies provided abundant evidence that unique selective pressures drive HGG in children compared to adults, identifying novel oncogenic mutations connecting tumorigenesis and chromatin regulation, as well as developmental signalling pathways. These new genetic findings give insights into disease pathogenesis and the challenges and opportunities for improving patient survival in these mostly incurable childhood brain tumours.
PI3-kinase and PTEN are major positive and negative regulators, respectively, of the PI3-kinase pathway, which regulates growth, survival, and proliferation. These key signaling components are two of ...the most frequently mutated proteins in human cancers, resulting in unregulated activation of PI3K signaling and providing irrefutable genetic evidence of the central role of this pathway in tumorigenesis. PTEN regulates PI3K signaling by dephosphorylating the lipid signaling intermediate PIP(3), but PTEN may have additional phosphatase-independent activities, as well as other functions in the nucleus. In this review, we highlight current work showing cancer-relevant complexities in the regulation of PTEN and PI3K activity, potential novel functions for PTEN, and feedback regulation within the pathway. The significance and complexity of PI3K signaling make it an important but challenging therapeutic target for cancer.
Malignant glioma remains incurable despite tremendous advancement in basic research and clinical practice. The identification of the cell(s) of origin should provide deep insights into leverage ...points for one to halt disease progression. Here we summarize recent studies that support the notion that neural stem cell (NSC), astrocyte, and oligodendrocyte precursor cell (OPC) can all serve as the cell of origin. We also lay out important considerations on technical rigor for further exploring this subject. Finally, we share perspectives on how one could apply the knowledge of cell of origin to develop effective treatment methods. Although it will be a difficult battle, victory should be within reach as along as we continue to assimilate new information and facilitate the collaboration among basic scientists, translational researchers, and clinicians.
The dentate gyrus has an important role in learning and memory, and adult neurogenesis in the subgranular zone of the dentate gyrus may play a role in the acquisition of new memories. The homeobox ...gene Prox1 is expressed in the dentate gyrus during embryonic development and adult neurogenesis. Here we show that Prox1 is necessary for the maturation of granule cells in the dentate gyrus during development and for the maintenance of intermediate progenitors during adult neurogenesis. We also demonstrate that Prox1-expressing intermediate progenitors are required for adult neural stem cell self-maintenance in the subgranular zone; thus, we have identified a previously unknown non-cell autonomous regulatory feedback mechanism that controls adult neurogenesis in this region of the mammalian brain. Finally, we show that the ectopic expression of Prox1 induces premature differentiation of neural stem cells.
Mutations in the
PTEN,
TP53, and
RB1 pathways are obligate events in the pathogenesis of human glioblastomas. We induced various combinations of deletions in these tumor suppressors in astrocytes and ...neural precursors in mature mice, resulting in astrocytomas ranging from grade III to grade IV (glioblastoma). There was selection for mutation of multiple genes within a pathway, shown by somatic amplifications of genes in the PI3K or Rb pathway in tumors in which
Pten or
Rb deletion was an initiating event. Despite multiple mutations within PI3K and Rb pathways, elevated Mapk activation was not consistent. Gene expression profiling revealed striking similarities to subclasses of human diffuse astrocytoma. Astrocytomas were found within and outside of proliferative niches in the adult brain.
► There is selective cooperativity among tumor suppressors for glioma initiation ► Dysregulation at multiple nodes within a pathway is dictated by initiating mutations ► Mouse models recapitulate mutations and expression profiles of human gliomas ► Astrocytomas developed in proliferative and nonproliferative regions of adult brain
Diffuse intrinsic pontine gliomas (DIPGs) are incurable childhood brainstem tumors with frequent histone H3 K27M mutations and recurrent alterations in PDGFRA and TP53. We generated genetically ...engineered inducible mice and showed that H3.3 K27M enhanced neural stem cell self-renewal while preserving regional identity. Neonatal induction of H3.3 K27M cooperated with activating platelet-derived growth factor receptor α (PDGFRα) mutant and Trp53 loss to accelerate development of diffuse brainstem gliomas that recapitulated human DIPG gene expression signatures and showed global changes in H3K27 posttranslational modifications, but relatively restricted gene expression changes. Genes upregulated in H3.3 K27M tumors were enriched for those associated with neural development where H3K27me3 loss released the poised state of apparently bivalent promoters, whereas downregulated genes were enriched for those encoding homeodomain transcription factors.
Display omitted
•H3.3 K27M mutation enhances neural stem cell self-renewal•Neonatal PDGFRα activation and Trp53 loss induces supratentorial and brainstem glioma•H3.3 K27M preferentially accelerates hindbrain tumorigenesis•H3.3 K27M drives bivalent gene activation associated with neurodevelopment in DIPG
Larson et al. show that H3.3 K27M cooperates with active PDGFRα mutant and loss of p53 to induce brainstem gliomas molecularly resembling human DIPG in mice. These tumors show global H3K27 modification but restricted gene expression changes, including upregulation of genes associated with neural development.
High-grade gliomas in children are different from those that arise in adults. Recent collaborative molecular analyses of these rare cancers have revealed previously unappreciated connections among ...chromatin regulation, developmental signaling, and tumorigenesis. As we begin to unravel the unique developmental origins and distinct biological drivers of this heterogeneous group of tumors, clinical trials need to keep pace. It is important to avoid therapeutic strategies developed purely using data obtained from studies on adult glioblastoma. This approach has resulted in repetitive trials and ineffective treatments being applied to these children, with limited improvement in clinical outcome. The authors of this perspective, comprising biology and clinical expertise in the disease, recently convened to discuss the most effective ways to translate the emerging molecular insights into patient benefit. This article reviews our current understanding of pediatric high-grade glioma and suggests approaches for innovative clinical management.
Long-term survival for children with diffuse intrinsic pontine glioma (DIPG) is less than 10%, and new therapeutic targets are urgently required. We evaluated a large cohort of DIPGs to identify ...recurrent genomic abnormalities and gene expression signatures underlying DIPG.
Single-nucleotide polymorphism arrays were used to compare the frequencies of genomic copy number abnormalities in 43 DIPGs and eight low-grade brainstem gliomas with data from adult and pediatric (non-DIPG) glioblastomas, and expression profiles were evaluated using gene expression arrays for 27 DIPGs, six low-grade brainstem gliomas, and 66 nonbrainstem low-grade gliomas.
Frequencies of specific large-scale and focal imbalances varied significantly between DIPGs and nonbrainstem pediatric glioblastomas. Focal amplifications of genes within the receptor tyrosine kinase-Ras-phosphoinositide 3-kinase signaling pathway were found in 47% of DIPGs, the most common of which involved PDGFRA and MET. Thirty percent of DIPGs contained focal amplifications of cell-cycle regulatory genes controlling retinoblastoma protein (RB) phosphorylation, and 21% had concurrent amplification of genes from both pathways. Some tumors showed heterogeneity in amplification patterns. DIPGs showed distinct gene expression signatures related to developmental processes compared with nonbrainstem pediatric high-grade gliomas, whereas expression signatures of low-grade brainstem and nonbrainstem gliomas were similar.
DIPGs comprise a molecularly related but distinct subgroup of pediatric gliomas. Genomic studies suggest that targeted inhibition of receptor tyrosine kinases and RB regulatory proteins may be useful therapies for DIPG.
To discover driver fusions beyond canonical exon-to-exon chimeric transcripts, we develop CICERO, a local assembly-based algorithm that integrates RNA-seq read support with extensive annotation for ...candidate ranking. CICERO outperforms commonly used methods, achieving a 95% detection rate for 184 independently validated driver fusions including internal tandem duplications and other non-canonical events in 170 pediatric cancer transcriptomes. Re-analysis of TCGA glioblastoma RNA-seq unveils previously unreported kinase fusions (KLHL7-BRAF) and a 13% prevalence of EGFR C-terminal truncation. Accessible via standard or cloud-based implementation, CICERO enhances driver fusion detection for research and precision oncology. The CICERO source code is available at https://github.com/stjude/Cicero.
To define copy number alterations and gene expression signatures underlying pediatric high-grade glioma (HGG).
We conducted a high-resolution analysis of genomic imbalances in 78 de novo pediatric ...HGGs, including seven diffuse intrinsic pontine gliomas, and 10 HGGs arising in children who received cranial irradiation for a previous cancer using single nucleotide polymorphism microarray analysis. Gene expression was analyzed with gene expression microarrays for 53 tumors. Results were compared with publicly available data from adult tumors.
Significant differences in copy number alterations distinguish childhood and adult glioblastoma. PDGFRA was the predominant target of focal amplification in childhood HGG, including diffuse intrinsic pontine gliomas, and gene expression analyses supported an important role for deregulated PDGFRalpha signaling in pediatric HGG. No IDH1 hotspot mutations were found in pediatric tumors, highlighting molecular differences with adult secondary glioblastoma. Pediatric and adult glioblastomas were clearly distinguished by frequent gain of chromosome 1q (30% v 9%, respectively) and lower frequency of chromosome 7 gain (13% v 74%, respectively) and 10q loss (35% v 80%, respectively). PDGFRA amplification and 1q gain occurred at significantly higher frequency in irradiation-induced tumors, suggesting that these are initiating events in childhood gliomagenesis. A subset of pediatric HGGs showed minimal copy number changes.
Integrated molecular profiling showed substantial differences in the molecular features underlying pediatric and adult HGG, indicating that findings in adult tumors cannot be simply extrapolated to younger patients. PDGFRalpha may be a useful target for pediatric HGG, including diffuse pontine gliomas.
PDF
