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Duplication of 7q34 in pediatric low-grade astrocytomas detected by high-density single-nucleotide polymorphism-based genotype arrays results in a novel BRAF fusion gene.

ABSTRACT: In the present study, DNA from 28 pediatric low-grade astrocytomas was analyzed using Illumina HumanHap550K single-nucleotide polymorphism oligonucleotide arrays. A novel duplication in chromosome band 7q34 was identified in 17 of 22 juvenile pilocytic astrocytomas and three of six fibrillary astrocytomas. The 7q34 duplication spans 2.6 Mb of genomic sequence and contains approximately 20 genes, including two candidate tumor genes, HIPK2 and BRAF. There were no abnormalities in HIPK2, and analysis of two mutation hot-spots in BRAF revealed a V600E mutation in only one tumor without the duplication. Fluorescence in situ hybridization confirmed the 7q34 copy number change and was suggestive of a tandem duplication. Reverse transcription polymerase chain reaction-based sequencing revealed a fusion product between KIAA1549 and BRAF. The predicted fusion product includes the BRAF kinase domain and lacks the auto-inhibitory N-terminus. Western blot analysis revealed phosphorylated mitogen-activated protein kinase (MAPK) protein in tumors with the duplication, consistent with BRAF-induced activation of the pathway. Further studies are required to determine the role of this fusion gene in downstream MAPK signaling and its role in development of pediatric low-grade astrocytomas.

SUBMITTER: Sievert AJ

PROVIDER: S-EPMC2850204 | biostudies-literature |

REPOSITORIES: biostudies-literature

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BRAF gene duplication constitutes a mechanism of MAPK pathway activation in low-grade astrocytomas.

Project description:The molecular pathogenesis of pediatric astrocytomas is still poorly understood. To further understand the genetic abnormalities associated with these tumors, we performed a genome-wide analysis of DNA copy number aberrations in pediatric low-grade astrocytomas by using array-based comparative genomic hybridization. Duplication of the BRAF protooncogene was the most frequent genomic aberration, and tumors with BRAF duplication showed significantly increased mRNA levels of BRAF and a downstream target, CCND1, as compared with tumors without duplication. Furthermore, denaturing HPLC showed that activating BRAF mutations were detected in some of the tumors without BRAF duplication. Similarly, a marked proportion of low-grade astrocytomas from adult patients also had BRAF duplication. Both the stable silencing of BRAF through shRNA lentiviral transduction and pharmacological inhibition of MEK1/2, the immediate downstream phosphorylation target of BRAF, blocked the proliferation and arrested the growth of cultured tumor cells derived from low-grade gliomas. Our findings implicate aberrant activation of the MAPK pathway due to gene duplication or mutation of BRAF as a molecular mechanism of pathogenesis in low-grade astrocytomas and suggest inhibition of the MAPK pathway as a potential treatment.

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Tandem duplication producing a novel oncogenic BRAF fusion gene defines the majority of pilocytic astrocytomas.

Project description:Brain tumors are the most common solid tumors of childhood, and pilocytic astrocytomas (PA) are the most common central nervous system tumor in 5 to 19 year olds. Little is known about the genetic alterations underlying their development. Here, we describe a tandem duplication of approximately 2 Mb at 7q34 occurring in 66% of PAs. This rearrangement, which was not observed in a series of 244 higher-grade astrocytomas, results in an in-frame fusion gene incorporating the kinase domain of the BRAF oncogene. We further show that the resulting fusion protein has constitutive BRAF kinase activity and is able to transform NIH3T3 cells. This is the first report of BRAF activation through rearrangement as a frequent feature in a sporadic tumor. The frequency and specificity of this change underline its potential both as a therapeutic target and as a diagnostic tool.

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Tandem duplication producing a novel oncogenic BRAF fusion gene defines the majority of pilocytic astrocytomas

2009-04-15 | GSE11265 | GEO

Tandem duplication producing a novel oncogenic BRAF fusion gene defines the majority of pilocytic astrocytomas

Project description:Pilocytic astrocytomas (PAs), WHO Grade I, are one of the most frequently occurring childhood brain tumors. We have used microarray comparative genomic hybridization (aCGH) to study copy number changes on chromosome 7 in a series of PAs (n=44). Keywords: Comparative Genomic Hybridization Single hybridization per case. 44 pilocytic astrocytomas WHO grade I were analyzed. Target (tumor) labelled with Cy5 and reference with Cy3. Mixture of 20 normal male or female genomic DNA was used in sex-mismatched hybridization.

2009-04-15 | E-GEOD-11265 | biostudies-arrayexpress

Chromosome band 7q34 deletions resulting in KIAA1549-BRAF and FAM131B-BRAF fusions in pediatric low-grade Gliomas.

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Duplication of 7q34 is specific to juvenile pilocytic astrocytomas and a hallmark of cerebellar and optic pathway tumours.

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KIAA1549: BRAF Gene Fusion and FGFR1 Hotspot Mutations Are Prognostic Factors in Pilocytic Astrocytomas.

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