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FGFR1 genetic alterations are associated with brain malignancies, including FGFR1 mutations in familial and sporadic cases of low-grade glioneuronal tumors, suggesting intrinsic mechanisms of selective pressure toward FGFR1 multiple events arising in the context of a quiet genome. To decipher the molecular mechanisms triggered by multiple concurrent FGFR1 mutations, we have mapped the proximal interactome of wild-type, single- and double-mutant FGFR1 proteins through a BioID-MS approach. Our data reveal novel oncogenic functionality for the two hotspot mutations N546K and K656E, linked to evasion of lysosomal degradation. Further, we identified a modulatory tumor-suppressive role for the susceptibility variant R661P, which hampers the oncogenic potential of both hotspot N546K and K656E mutations by rescuing receptor degradation and reducing N546K affinity for the downstream effector PLCγ. Introducing the R661P missense variant was sufficient to abolish self-renewal capacity of oligodendroglioma cells and downregulate genes involved in neurodevelopment and neuro-glial cell fate decisions, both aspects overcome in the double mutants. This study sheds light on contextual oncogenic effects associated with FGFR1 alterations and their recurrence in low-mutation burden and therapy naive tumors. Show less

Oncogenic alterations in fibroblast growth factor receptor (FGFR)-family proteins occur across cancers, including pediatric gliomas. Our genomic analysis of 11,635 gliomas across ages finds that 5.3% of all gliomas harbor FGFR alterations, with an incidence of almost 9% in pediatric gliomas. Alterations in FGFR proteins are differentially enriched by age, tumor grade, and histology, with FGFR1 alterations associated with glioneuronal histologies. Leveraging isogenic systems, we confirm FGFR1 alterations to induce downstream Mitogen Activated Protein Kinase (MAPK) and mTOR signaling pathways, drive gliomagenesis, activate neuronal transcriptional programs and exhibit sensitivity to MAPK pathway and pan-FGFR inhibitors. Finally, we perform a retrospective analysis of clinical responses in children diagnosed with FGFR-altered gliomas and find that treatment with currently available inhibitors is largely associated with stability of disease. This study provides key insights into the biology of FGFR1-altered gliomas, therapeutic strategies to target them and associated challenges that still need to be overcome. Show less