MEDU-24. INTERROGATING THE ROLE OF EPIGENETIC REGULATORS IN MYC-DRIVEN MEDULLOBLASTOMA

Abstract

Medulloblastoma (MB), the most common malignant pediatric brain tumor, is characterized by four molecularly and histopathologically distinct groups with different prognoses. With the advent of next generation sequencing, the field has gained new insights into somatically altered genes in MB, many of which are involved in epigenetic gene regulation and chromatin modification. A significant portion of Group 3 MB do not carry any mutations, suggesting that additional, non-mutated, epigenetic regulators may be implicated in shaping chromatin structure and driving tumor pathogenesis. Considering this possibility, we conducted two unbiased screens of epigenetic regulators in G3 MB to identify candidate drivers of medulloblastoma genesis. 1) In collaboration with Dr. Christopher Vakoc, we screened a library of shRNAs targeting 293 known chromatin modifiers in mouse G3 MB cells. Designed to assess reduction in viability, the dropout screen identified putative oncogenes, and of the top hits, SMYD3, a lysine methyltransferase, emerged as the most interesting candidate. SMYD3 is overexpressed and exhibits increased predicted activity in G3 MB compared to other subgroups. Perturbation of SMYD3 using shRNA or CRISPR/Cas9 results in significantly reduced tumor progression and significantly prolonged lifespan in tumor-bearing animals. 2) We also screened a pooled epigenetic CRISPR/Cas9 gRNA library in G3 MB cells where we assessed gRNA enrichment in vivo and thus, identified putative tumor suppressors. Based on biological relevance and computational prediction, PRDM2 was selected as the top candidate. Implicated in other cancers, PRDM2, a histone 3 lysine 9 methyltransferase, exhibits low expression and predicted activity in G3 MB compared to other subgroups. Current work is focused on dissecting the epigenetic, transcriptomic, and phenotypic consequences of PRDM2 perturbation in naïve neural progenitors and G3 MB cells. Taken together, these efforts will help us to understand how changes in chromatin modifiers affect disease pathogenesis and how these changes may represent therapeutic vulnerabilities.