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

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 factor-mediated 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.

Cyclin D1 is a direct transcriptional target of GATA3 in neuroblastoma tumor cells.

Almost all neuroblastoma tumors express excess levels of Cyclin D1 (CCND1) compared to normal tissues and other tumor types. Only a small percentage of these neuroblastoma tumors have high-level amplification of the Cyclin D1 gene. The other neuroblastoma tumors have equally high Cyclin D1 expression without amplification. Silencing of Cyclin D1 expression was previously found to trigger differentiation of neuroblastoma cells. Overexpression of Cyclin D1 is therefore one of the most frequent mechanisms with a postulated function in neuroblastoma pathogenesis. The cause for the Cyclin D1 overexpression is unknown. Here we show that Cyclin D1 overexpression results from transcriptional upregulation. To identify upstream regulators, we searched in mRNA profiles of neuroblastoma tumor series for transcription factors with expression patterns correlating to Cyclin D1. GATA3 most consistently correlated to Cyclin D1 in four independent data sets. We identified a highly conserved GATA3 binding site 27 bp upstream of the Cyclin D1 transcriptional start. Chromatin immune precipitation confirmed binding of GATA3 to the Cyclin D1 promoter. Overexpression of GATA3 induced Cyclin D1 promoter activity, which decreased after site-directed mutagenesis of the GATA3 binding site in the Cyclin D1 promoter. Silencing of GATA3 resulted in reduced Cyclin D1 promoter activity and reduced Cyclin D1 mRNA and protein levels. Moreover, GATA3 silencing caused differentiation that was similar to that caused by Cyclin D1 inhibition. These finding implicate GATA3 in Cyclin D1 overexpression in neuroblastoma.

Pulmonary interstitial glycogenosis in identical twins.

We present the clinical, radiological, and pathological findings of open lung biopsies from monozygotic prematurely born male twins with respiratory distress at ages 6 and 8 weeks postnatally. Radiological examination showed a reticular nodular interstitial pattern on chest radiography. High-resolution computed tomography (HRCT) revealed ground-glass opacification and thickened interstitial septae in both infants. Lung biopsies showed a similar histology. There was diffuse interstitial thickening of the alveolar septa by mesenchymal cells, without prominent hyperplasia of type 2 pneumocytes, and without airspace exudates. Sections were periodic acid-Schiff (PAS)-positive within the cytoplasm of interstitial cells, indicating the presence of glycogen. Thus the diagnosis of pulmonary interstitial glycogenosis was made. Both infants were treated with glucocorticoids and had a favorable outcome. We speculate that pulmonary interstitial glycogenosis could be a histopathological form of chronic lung disease (CLD) of infancy.

Microsatellite instability and frameshift mutations in BAX and transforming growth factor-beta RII genes are very uncommon in acute lymphoblastic leukemia in vivo but not in cell lines.

Mutations in the DNA mismatch repair (MMR) system lead to an instability of simple repetitive DNA sequences involved in several cancer types. This instability is reflected in a high mutation rate of microsatellites, and recent studies in colon cancer indicate that defects in MMR result in frequent frameshift mutations in mononucleotide repeats located in the coding regions of BAX and transforming growth factor-beta (TGF-beta) receptor genes. Circumstantial evidence suggests that the MMR defect may be involved in some lymphoid malignancies, although several allelotype analyses have concluded on the low level of microsatellite instability in acute lymphoblastic leukemias. To further evaluate the implication of MMR defects in leukemogenesis, we have studied a series of 98 children with acute lymphoblastic leukemia and 14 leukemic cell lines using several indicators of MMR defects. Microsatellite markers were compared between blast and normal DNA from the same patients and mutations were sought in mononucleotide repeat sequences of BAX and TGF-beta receptor II (TGF-beta RII). The absence of microsatellite instability (MI) and the absence of mutations in the genes examined from patient's leukemic cells contrasted with the observation that half of the cell lines displayed a high degree of MI and that three of seven of these mutator cell lines harbored mutations in BAX and/or TGF-beta RII. From these results we conclude that MMR defects are very uncommon in freshly isolated blasts but are likely to be selected for during the establishment of cell lines.