DIPG-14. PROTEOGENOMICS PROFILING REVEALS ENRICHED NON-HISTONE PROTEIN METHYLTRANSFERASES AS NEW THERAPEUTIC TARGETS IN DIPG

Abstract

Abstract Diffuse intrinsic pontine glioma (DIPG) is a devastating brain tumour arising in the brainstems of children. Despite advances in genomics and treatments, the survival rate remains zero, with a median of less than a year, making it the leading cause of death among children with brain tumours. A mutation in histone H3 protein (H3K27M) has been identified as a genetic initiation event and affects global K27 trimethylation on histone H3 proteins and DNA methylation in DIPG. The epigenetic changes caused by the H3K27M mutation suggest the existence of an H3K27M-specific transcriptome and proteome. To deepen our knowledge of DIPG, we conducted a proteogenomic analysis of DIPG tissues by using high-resolution mass spectrometry for comprehensive proteome profiling, including total proteome, phosphoproteome, and methylproteome. Integrating proteomics data with DNA methylation and transcriptomics (bulk RNAseq and single-cell RNAseq) provided new insights into DIPG tumorigenesis. Our multi-omics analyses reveal enriched translation machinery, negative regulation of apoptosis process, and non-histone protein methyltransferase proteins, suggesting their previously unknown roles in DIPG cell growth and survival. Furthermore, our findings indicate that DIPG tissues have lower global mean protein phosphorylation and higher global mean protein methylation compared to normal brains, implying that DIPG may use methyl-signaling rather than phospho-signaling for tumour growth. The translation elongation proteins EEF1A1 and EEF1A2 are the most highly methylated proteins in DIPG. Methylation modifications such as K55me2, K79me3, and K165me2 of EEF1A1 are significantly higher in DIPG tissues compared to normal brains. These enriched methylpeptides are substrates of the non-histone methyltransferases METTL13 and METTL21B, which are enriched in the multi-omics analysis. Knocking down these methyltransferases in DIPG cells significantly decreases their target protein methylation, reduces global protein synthesis, and inhibits cell growth in vitro. Thus, proteogenomic analysis of DIPG reveals tumour-enriched non-histone methyltransferases, METTL13 and METTL21B as new therapeutic targets.