3280

HES1

HES-1|HHL|HRY|bHLHb39;hairy and enhancer of split 1, (Drosophila);HES1;hairy and enhancer of split 1, (Drosophila)

class B basic helix-loop-helix protein 39|hairy homolog|hairy-like protein|transcription factor HES-1

3q28-q29

protein-coding

Neuroblastoma is a childhood tumor originating from cells of the developing sympathetic nervous system. The disease exhibits a remarkable phenotypic diversity reflected in the outcome, ranging from spontaneous regression to fataldisease. Mammalian achaete-scute homologue 1 (MASH-1 or HASH-1 in humans), a basic helix-loop-helix transcription (bHLH) factor, is transiently expressed in migrating sympatho-adrenal precursor cells. This gene, which is essential for proper development of the sympathetic nervous system, is expressed in a majorityof primary neuroblastomas and neuroblastoma cell lines indicating an embryonal origin of the tumor. One important negative regulator of MASH-1 expression is the bHLH factor hairy and Enhancer of split homolog-1 (HES-1), which in turn is under positive control of the Notch signaling cascade. When neuroblastoma cells are induced to differentiate, as indicated by neuronal morphology and upregulation of neuronal marker genes, the HASH-1 expression is rapidly downregulated with a concomitant, transient upregulation of HES-1. Furthermore, a constitutively active form of Notch-1 inhibits induced differentiation of neuroblastoma cells. In this review, the role of the Notch-signaling cascade in neuroblastoma, with focus on the bHLH factors HASH-1 and HES-1, will be discussed.

PURPOSE: The molecular pathogenesis of pediatric ependymoma remains unclear. Ourstudy was designed to identify genetic changes implicated in ependymoma progression. PATIENTS AND METHODS: We characterized 59 ependymoma samples (33 atdiagnosis and 26 at relapse) using array-comparative genomic hybridization (aCGH). Specific chromosomal imbalances were confirmed by fluorescent in situ hybridization, and candidate genes were assessed by real-time quantitative polymerase chain reaction (qPCR), immunohistochemistry, sequencing, and in vitrofunctional studies. RESULTS: aCGH analysis revealed a significant increase in genomic imbalances on relapse compared with diagnosis, such as gain of 9qter and1q (54% v 21% and 12% v 0%, respectively) and loss of 6q (27% v 6%). Supervised tumor classification showed that gain of 9qter was associated with tumor recurrence, age older than 3 years, and posterior fossa location. Using a candidate-gene strategy, we found an overexpression of two potential oncogenes at the locus 9qter: Tenascin-C and Notch1. Moreover, Notch pathway analysis (qPCR) revealed overexpression of Notch ligands, receptors, and target genes (Hes-1, Hey2, and c-Myc), and downregulation of Notch repressor Fbxw7. We confirmed by immunohistochemistry the overexpression of Tenascin-C and Hes-1. We detected Notch1 missense mutations in 8.3% of the tumors (only in the posterior fossa location and in case of 9q33-34 gain). Furthermore, inhibition of Notch pathway with a gamma-secretase inhibitor impaired the growth of ependymoma stem cell cultures. CONCLUSION: The activation of the Notch pathway and Tenascin-C seem tobe important events in ependymoma progression and may represent future targets for therapy. We report, to our knowledge for the first time, recurrent oncogenicmutations in pediatric posterior fossa ependymomas.

Midkine is a heparin-binding growth factor highly expressed in various cancers, including neuroblastoma, the most common extracranial pediatric solid tumor. Prognosis of patients with neuroblastoma in which MYCN is amplified remains particularly poor. In this study, we used a MYCN transgenic model for neuroblastoma in which midkine is highly expressed in precancerous lesions of sympathetic ganglia. Genetic ablation of midkine in this model delayed tumor formation and reduced tumor incidence. Furthermore, an RNA aptamer that specifically bound midkine suppressed the growth of neuroblastoma cells in vitroand in vivo in tumor xenografts. In precancerous lesions, midkine-deficient MYCNtransgenic mice exhibited defects in activation of Notch2, a candidate midkine receptor, and expression of the Notch target gene HES1. Similarly, RNA aptamer-treated tumor xenografts also showed attenuation of Notch2-HES1 signaling. Our findings establish a critical role for the midkine-Notch2 signaling axis in neuroblastoma tumorigenesis, which implicates new strategies to treat neuroblastoma.