HGG-47. Comparative analysis of the Histone H3 mutant protein interactome landscape in paediatric high-grade gliomas

Abstract There have been no significant improvements in the treatments for childhood and adolescent High-Grade Glioma (pHGG) and Diffuse Intrinsic Pontine Glioblastoma (DIPG), which have a very poor prognosis. These cancers harbour mutations affecting histone 3 (H3) proteins, 80% of DIPGs harbour histone H3.1 and H3.3 K27M somatic mutations whilst 30% of pHGGs exhibit H3.3 G34R or G34V mutations. Several studies have highlighted the epigenetic changes associated with these mutations, however their precise role in tumourigenesis is still unknown. We hypothesize that H3 mutations promote an aberrant interaction landscape and analysis of these interactome will highlight important pathophysiological consequences in these tumours. Two different affinity chromatographic proteomic analyses were performed using different recombinant H3 wild type (WT) and H3 mutant histone proteins (K27M, G34R and G34V) to purify their binding partners, from cell extracts of control and pHGG/DIPG patients cell lines. The purified samples were then subjected to Liquid Chromatography-Mass Spectrometry (LC-MS) to identify their co-bound partners. The results have isolated unique and common differential interaction partners of the H3 mutants and with cellular proteins in comparison to H3 WT protein, in the pHGG tumour cells. The role these altered protein interactions are being investigating in tumour initiation, progression and/or maintenance of H3 mutated pHGG/DIPG, with the aim to manipulate their function as alternate therapeutic intervention. Results of these analyses/experiments will be presented.