PROTEOMIC ANALYSIS OF GENETICALLY STRATIFIED MENINGIOMA

Abstract WHO grade II and III as well as some WHO grade I meningioma are clinically aggressive. Approximately 60% sporadic meningiomas harbour mutations in the NF2 gene, others in genes including TRAF7, KLF4, AKT1, SMO and PIK3CA . However, the molecular mechanisms behind meningioma tumourigenesis are still unclear. We aim to identify novel biomarkers and therapeutic targets of meningioma by characterising the proteomic landscape. We performed (phosho)proteomic profiling of grade I, II and III meningiomas and three different mutational groups: AKT1 E17K /TRAF7, KLF4 K409Q /TRAF7 and NF2 -/-. We validated differential expression of proteins and phosphoproteins by Western blot on a meningioma validation set and by immunohistochemistry. Looking at all grades bioinformatics analysis revealed commonly upregulated proteins and phosphoproteins to be enriched in Gene Ontology terms associated with RNA metabolism. Validation studies confirmed significant overexpression of proteins such as EGFR and CKAP4 and upregulation and activation of the NIMA-related kinase, NEK9, involved in mitotic progression. Novel proteins described included the nuclear proto-oncogene SET, the splicing factor SF2/ASF and the higher-grade specific protein, Hexokinase 2. For the mutation subtypes we have quantified 4162 proteins across all mutational meningioma subgroups with proteomic profiles of mutational subgroups. Comparative analysis showed 10 proteins were commonly significantly upregulated among all mutational subtypes vs. normal meninges, indicating proteomic landscapes of mutational subtypes to be highly variable. 257 proteins were commonly significantly downregulated and enriched with molecular functions including aldehyde dehydrogenase and oxido-reductase. Mutational subtype-specific analysis identified 162 proteins significantly upregulated in AKT1 E17K /TRAF7 vs. remaining sample groups to be enriched in the oxidative phosphorylation pathway. Less proteins were commonly significantly upregulated in KLF4 K409Q /TRAF7 and NF2 -/- mutant meningioma subtypes respectively. Several of these up-regulated proteins including ANNEXIN-3, CRABP2, CLIC3 were verified. Analyses of 6600 phospho-sites predicted regulatory kinases. Further validation and functional verification of potential candidates is ongoing.