MDB-46. ARE RAB40 SMALL GTPASES DRIVERS OF MEDULLOBLASTOMA PATHOGENESIS?

Abstract

Abstract BACKGROUND Medulloblastoma is the most common solid paediatric neoplasm and is among the leading causes of cancer-related deaths in children. Patients associated with high-risk molecular subgroups convey poor outcomes due to frequent relapse and metastasis, with two thirds of survivors experiencing life-changing developmental deficits. Poor patient outcomes and significant co-morbidities highlight an urgent need for specific, molecularly targeted therapies. The RAB40 subfamily of atypical small GTPases regulate cytoskeletal structure and cell adhesion via their ubiquitin ligase activity. Although previous studies have linked the RAB40 subfamily with cell invasiveness, their role in paediatric brain cancer remains undefined. METHODS Patient methylation and survival data from Cavalli et. al (2017) was analysed via the R2 Genomics Analysis and Visualisation Platform. RAB40 gene and protein expression were determined in eight in vitro models of medulloblastoma via qRT-PCR and western blotting. Cells were transfected with EGFP-Cas9 mRNA and RAB40-targeted CRISPR sgRNA and seeded singly using fluorescence-activated cell sorting. RAB40 knockout clones were identified via western blot and Sanger sequencing. RESULTS Patient data demonstrated that higher RAB40 gene expression correlates with worse outcomes in group 3 and 4 medulloblastoma. RAB40 genes were also significantly more highly expressed in high-risk groups 3 and 4 compared to low-risk WNT group medulloblastoma. RAB40 mRNA was enriched in cell lines derived from high-risk group 3 and 4 medulloblastoma relative to SHH controls. RAB40 knockout models were subsequently generated in HD-MB03, an in vitro model of metastatic Group 3 medulloblastoma using CRISPR/Cas9. CONCLUSIONS Our data supports the hypothesis that RAB40 small GTPases are enriched in high-risk medulloblastoma subgroups, and that their expression correlates with worse patient outcomes. We have generated knockout models which will be used to characterise the impact of RAB40 GTPases on cell growth, adhesion, invasiveness, and chemotherapeutic tolerance.