FOXR2 Stabilizes MYCN Protein and Identifies Non--Amplified Neuroblastoma Patients With Unfavorable Outcome.

PURPOSE

Clinical outcomes of patients with neuroblastoma range from spontaneous tumor regression to fatality. Hence, understanding the mechanisms that cause tumor progression is crucial for the treatment of patients. In this study, we show that activation identifies a subset of neuroblastoma tumors with unfavorable outcome and we investigate the mechanism how FOXR2 relates to poor outcome in patients.

MATERIALS AND METHODS

We analyzed three independent transcriptional data sets of in total 1030 primary neuroblastomas with full clinical annotation. We performed immunoprecipitation for FOXR2 and MYCN and silenced FOXR2 expression in two neuroblastoma cell lines to examine the effect on cellular processes, transcriptome, and MYCN protein levels. Tumor samples were analyzed for protein levels of FOXR2 and MYCN.

RESULTS

In three combined neuroblastoma data sets, 9% of tumors show expression of but have low levels of mRNA. expression identifies a group of patients with unfavorable outcome, showing 10-year overall survival rates of 53%-59%, and proves to be an independent prognostic factor compared with established risk factors. Transcriptionally, -expressing tumors are very similar to -amplified tumors, suggesting that they might share a common mechanism of tumor initiation. FOXR2 knockdown in -expressing neuroblastoma cell lines resulted in cell cycle arrest, reduced cell growth, cell death, and reduced MYCN protein levels, all indicating that FOXR2 is essential for these tumors. Finally, we show that FOXR2 binds and stabilizes MYCN protein and MYCN protein levels are highly increased in FOXR2-expressing tumors, in several cases comparable with -amplified samples.

CONCLUSION

The stabilization of MYCN by FOXR2 represents an alternative mechanism to amplification to increase MYCN protein levels. As such, expression identifies another subset of neuroblastoma patients with unfavorable clinical outcome.