ABSTRACT
OTX2 is a potent oncogene that promotes tumor growth in Group 3 medulloblastoma. However, the mechanisms by which OTX2 represses neural differentiation are not well characterized. Here, we perform extensive multiomic analyses to identify an OTX2 regulatory network that controls Group 3 medulloblastoma cell fate. OTX2 silencing modulates the repressive chromatin landscape, decreases levels of PRC2 complex genes and increases the expression of neurodevelopmental transcription factors including PAX3 and PAX6. Expression of PAX3 and PAX6 is significantly lower in Group 3 medulloblastoma patients and is correlated with reduced survival, yet only PAX3 inhibits self-renewal in vitro and increases survival in vivo. Single cell RNA sequencing of Group 3 medulloblastoma tumorspheres demonstrates expression of an undifferentiated progenitor program observed in primary tumors and characterized by translation/elongation factor genes. Identification of mTORC1 signaling as a downstream effector of OTX2-PAX3 reveals roles for protein synthesis pathways in regulating Group 3 medulloblastoma pathogenesis.
Subject(s)
Carcinogenesis/genetics , Cerebellar Neoplasms , Medulloblastoma , Otx Transcription Factors/metabolism , PAX3 Transcription Factor/genetics , Animals , Carcinogenesis/metabolism , Cell Differentiation/genetics , Cell Line, Tumor , Cell Proliferation/genetics , Cerebellar Neoplasms/genetics , Cerebellar Neoplasms/metabolism , Gene Expression Regulation, Neoplastic , Humans , Medulloblastoma/genetics , Medulloblastoma/metabolism , Neoplastic Stem Cells/metabolism , Oncogenes , PAX3 Transcription Factor/metabolism , PAX6 Transcription Factor/genetics , PAX6 Transcription Factor/metabolism , Signal Transduction/geneticsABSTRACT
The extensive heterogeneity both between and within the medulloblastoma subgroups underscores a critical need for variant-specific biomarkers and therapeutic strategies. We previously identified a role for the CD271/p75 neurotrophin receptor (p75NTR) in regulating stem/progenitor cells in the SHH medulloblastoma subgroup. Here, we demonstrate the utility of CD271 as a novel diagnostic and prognostic marker for SHH medulloblastoma using IHC analysis and transcriptome data across 763 primary tumors. RNA sequencing of CD271+ and CD271- cells revealed molecularly distinct, coexisting cellular subsets, both in vitro and in vivo MAPK/ERK signaling was upregulated in the CD271+ population, and inhibiting this pathway reduced endogenous CD271 levels, stem/progenitor cell proliferation, and cell survival as well as cell migration in vitro Treatment with the MEK inhibitor selumetinib extended survival and reduced CD271 levels in vivo, whereas, treatment with vismodegib, a well-known smoothened (SMO) inhibitor currently in clinical trials for the treatment of recurrent SHH medulloblastoma, had no significant effect in our models. Our study demonstrates the clinical utility of CD271 as both a diagnostic and prognostic tool for SHH medulloblastoma tumors and reveals a novel role for MEK inhibitors in targeting CD271+ SHH medulloblastoma cells.Significance: This study identifies CD271 as a specific and novel biomarker of SHH-type medulloblastoma and that targeting CD271+ cells through MEK inhibition represents a novel therapeutic strategy for the treatment of SHH medulloblastoma. Cancer Res; 78(16); 4745-59. ©2018 AACR.
Subject(s)
Biomarkers, Tumor/genetics , Medulloblastoma/genetics , Nerve Tissue Proteins/genetics , Prognosis , Receptors, Nerve Growth Factor/genetics , Anilides/administration & dosage , Annexin A5/genetics , Cell Movement/genetics , Cell Proliferation/genetics , Cell Survival/drug effects , Child , Enzyme Inhibitors/administration & dosage , Female , Gene Expression Regulation, Neoplastic , High-Throughput Nucleotide Sequencing , Humans , Kaplan-Meier Estimate , MAP Kinase Kinase Kinase 1/antagonists & inhibitors , Magnetic Resonance Angiography , Male , Medulloblastoma/drug therapy , Medulloblastoma/pathology , Pyridines/administration & dosageABSTRACT
Medulloblastoma (MB) is the most common malignant primary pediatric brain cancer. Among the most aggressive subtypes, Group 3 and Group 4 originate from stem/progenitor cells, frequently metastasize, and often display the worst prognosis, yet we know the least about the molecular mechanisms driving their progression. Here, we show that the transcription factor orthodenticle homeobox 2 (OTX2) promotes self-renewal while inhibiting differentiation in vitro and increases tumor initiation from MB stem/progenitor cells in vivo. To determine how OTX2 contributes to these processes, we employed complementary bioinformatic approaches to characterize the OTX2 regulatory network and identified novel relationships between OTX2 and genes associated with neuronal differentiation and axon guidance signaling in Group 3 and Group 4 MB stem/progenitor cells. In particular, OTX2 levels were negatively correlated with semaphorin (SEMA) signaling, as expression of 9 SEMA pathway genes is upregulated following OTX2 knockdown with some being potential direct OTX2 targets. Importantly, this negative correlation was also observed in patient samples, with lower expression of SEMA4D associated with poor outcome specifically in Group 4 tumors. Functional proof-of-principle studies demonstrated that increased levels of select SEMA pathway genes are associated with decreased self-renewal and growth in vitro and in vivo and that RHO signaling, known to mediate the effects of SEMA genes, is contributing to the OTX2 KD phenotype. Our study provides mechanistic insight into the networks controlled by OTX2 in MB stem/progenitor cells and reveals novel roles for axon guidance genes and their downstream effectors as putative tumor suppressors in MB.
