Oncogenic activation of FOXR1 by 11q23 intrachromosomal deletion-fusions in neuroblastoma

Abstract

Neuroblastoma tumors frequently show loss of heterozygosity of chromosome 11q with a shortest region of overlap in the 11q23 region. These deletions are thought to cause inactivation of tumor suppressor genes leading to haploinsufficiency. Alternatively, micro-deletions could lead to gene fusion products that are tumor driving. To identify such events we analyzed a series of neuroblastomas by comparative genomic hybridization and single-nucleotide polymorphism arrays and integrated these data with Affymetrix mRNA profiling data with the bioinformatic tool R2 (http://r2.amc.nl). We identified three neuroblastoma samples with small interstitial deletions at 11q23, upstream of the forkhead-box R1 transcription factor (FOXR1). Genes at the proximal side of the deletion were fused to FOXR1, resulting in fusion transcripts of MLL-FOXR1 and PAFAH1B2-FOXR1. FOXR1 expression has only been detected in early embryogenesis. Affymetrix microarray analysis showed high FOXR1 mRNA expression exclusively in the neuroblastomas with micro-deletions and rare cases of other tumor types, including osteosarcoma cell line HOS. RNAi silencing of FOXR1 strongly inhibited proliferation of HOS cells and triggered apoptosis. Expression profiling of these cells and reporter assays suggested that FOXR1 is a negative regulator of fork-head box factormediated transcription. The neural crest stem cell line JoMa1 proliferates in culture conditional to activity of a MYC-ER transgene. Over-expression of the wild-type FOXR1 could functionally replace MYC and drive proliferation of JoMa1. We conclude that FOXR1 is recurrently activated in neuroblastoma by intrachromosomal deletion/fusion events, resulting in overexpression of fusion transcripts. Forkhead-box transcription factors have not been previously implicated in neuroblastoma pathogenesis. Furthermore, this is the first identification of intrachromosomal fusion genes in neuroblastoma.

FOXO3a Is a Major Target of Inactivation by PI3K/AKT Signaling in Aggressive Neuroblastoma

“…Finally, the finding that FOXO3a may function as an important tumor suppressor in neuroblastoma will lead us to examine many other pathways that are known to regulate it. Previously, we identified oncogenic activation of FOXR1 in neuroblastoma as another potential inhibitor of FOXO function (46). In conjunction with the current work, this finding suggests a broader role for forkhead biology in the pathogenesis of neuroblastoma.…”

Sequencing of neuroblastoma identifies chromothripsis and defects in neuritogenesis genes

“…One tumour showed an intrachromosomal rearrangement activating FOXR1 transcription ( Supplementary Fig. 2e), which we recently identified as a recurrent but rare event in neuroblastoma 18 . Similar to the findings for aminoacid-changing mutations, there was a strong relation between the frequency of structural variations and the tumour stage (one-way ANOVA P 5 0.03; Fig.…”

Identification of FoxR2 as an Oncogene in Medulloblastoma

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