Abstract
Previous studies have shown that EZH2, an epigenetic developmental regulator, is overexpressed in medulloblastoma. EZH2 is known to repress developmental genes in embryonic stem cells to maintain their stem cell characteristics. To identify the transcriptional networks that may be driving medulloblastoma oncogenesis, we overexpressed EZH2 (EZH2(Ox)) in the C17.2 cerebellar progenitor immortalized cell line. In addition, to understand the effects of EZH2 loss of function on transcriptional networks we deleted the catalytic methyltransferase SET domain of EZH2 (EZH2(ΔS)). Comparing RNA-seq data of the control C17.2, EZH2(Ox), and EZH2(ΔS) cell line using Gene Set Enrichment Analysis (GSEA) showed that the oncogenic character of EZH2Ox cells was significantly increased. EZH2 overexpression triggered oncogenic pathways including inhibition of neural differentiation. Soft Agar, colony formation, and neurosphere size assays all indicated an increase in the tumorigenic potential of EZH2(Ox) cells. The results of our RNA-seq analysis and in vitro oncogenic assays suggest that EZH2 overexpression in the C17.2 cerebellar progenitors are likely to be tumorigenic therefore we isografted EZH2(Ox) cells and the control cells into the cerebellum of athymic nude mice. Four of the six mice with EZH2(Ox) cell isografts grew cerebellar tumors while none of the control mice had tumor growth. Pathology indicated the tumorous cells were large cell anaplastic consistent with group 3 medulloblastoma. Our results suggest that EZH2 is a candidate oncogenic driver in medulloblastoma.