MBRS-24. FUNCTIONAL CHARACTERIZATION OF IKBKAP/ELP1 AS A NOVEL SHH MEDULLOBLASTOMA PREDISPOSITION GENE

Medulloblastoma (MB), a common malignant pediatric brain tumor, comprises at least four distinct molecular entities: WNT, SHH, Group 3, and Group 4. SHH-MB is driven by aberrant activation of the Sonic hedgehog (SHH) pathway in granule neuron progenitors (GNPs) and is associated with hereditary cancer predisposition syndromes including Li Fraumeni and Gorlin. We recently identified germline loss of function (LoF) mutations affecting IKBKAP/ELP1, the primary scaffolding subunit of the Elongator complex in a subset of SHH-MB patients. Germline ELP1 mutations account for ~15% of all pediatric SHH-MBs and position ELP1 as the most prevalent hereditary predisposition gene in MB. We genetically engineered Elp1 LoF in mouse GNPs to determine Elp1 function in cerebellar development and SHH-MB. Results of both mechanistic and phenotypic experiments demonstrate that GNPs harboring Elp1 loss exhibit ribosome pausing and protein aggregation, reinforcing the critical role of Elp1 in translational elongation and protein homeostasis. Further, we generated new transgenic mouse models mimicking germline ELP1 LoF mutations observed in SHH-MB patients. Elp1(+/-) transgenic mice exhibit purkinje cell degeneration and an increased DNA damage response. These mice are currently being evaluated for their capacity to recapitulate ELP1-associated SHH-MB. Additional analyses carried out on SHH-MB patient-derived xenografts showed that ELP1-mutant tumor cells specifically exhibit defects in tRNA biogenesis. Therefore, the function of ELP1 as a translational regulator is severely impaired in ELP1-mutant SHH-MBs. Our ongoing molecular and functional studies will provide important insights into the most common MB predisposition gene and will lay the foundation for future preclinical studies.