Identification and characterization of genetic drivers of central nervous system primitive neuroectodermal tumors, medulloblastoma, and neuroblastoma.

Abstract

Medulloblastoma, central nervous system primitive neuroectodermal tumors (CNS-PNETs), and neuroblastoma are cancers that affect the nervous system primarily in children. Current treatment strategies with severe long-term treatment-related side effects and dismal survival rates warrant further study into therapies with increased efficacy and lower cost to the patient. Targeted therapy represents a route to better treatments, but a barrier to identifying novel targets is the lack of appropriate animal models. To fill this void, we created a mouse model of medulloblastoma and CNS-PNET using Sleeping Beauty (SB) mutagenesis of neural progenitor cells (Nestin+). Importantly, SB-induced tumors resembled human medulloblastoma and CNS-PNET in location and histology. Additionally, we used RNA-Sequencing to determine that they most closely resemble human Sonic Hedgehog (SHH), group 3, and group 4 medulloblastoma and a subgroup of CNS-PNET with FOXR2 activation (CNS NB-FOXR2). Using both DNA and RNA analyses, we identified over 100 genes as candidate drivers in medulloblastoma and/or CNS-PNET. Of these genes, we focused on validating 3 proto-oncogenes, Megf10, Arhgap36, and Foxr2. All 3 drove soft agar colony formation and tumor formation in mice, suggesting they are bona fide oncogenes. In further studies of ARHGAP36, we found that it promoted Shh signaling, did not affect RhoA activation, and that its 5 isoforms had distinct effects both in vitro and in vivo. We found that FOXR2 bound C-MYC and N-MYC and increased C-MYC stability. Additionally, in the context of neuroblastoma, increased FOXR2 expression was mutually exclusive with MYCN amplification, further suggesting an important interaction between FOXR2 and MYC family transcription factors. We also found a novel role for FOXR2 in activating the FAK/SRC signaling pathway. Increased FOXR2 drove FAK/SRC activation and FOXR2 KO decreased FAK/SRC activation. Interestingly, increased FOXR2 expression conveyed resistance to a SRC family kinase inhibitor (Dasatinib) in a MYC-dependent manner, indicating overlap between these two apparently distinct effects. In conclusion, this study identifies several promising therapeutic targets for treatment of patients with medulloblastoma, CNS-PNET, and neuroblastoma.