Identification of the genetic mechanisms linked to the occurrence of H3.3K27M-mutation in pediatric DIPG

Abstract

Diffuse intrinsic pontine gliomas (DIPG) are incurable pediatric high-grade tumors. 85% of all DIPG carry a mutation in one histone H3 gene (H3K27M), resulting in global loss of H3K27 trimethylation (H3K27me3) and gain of H3K27 acetylation (H3K27ac). H3K27M-mutation is associated with increased tumor-aggressiveness. This project aimed to investigate the (epi)genetic and resulting tumor-biological effects caused by H3.3K27M-mutation in isogenic DIPG (isoDIPG) cell lines generated via CRISPR/Cas9 system. Removal of H3.3K27M-mutation restored H3K27me3 levels with reduction of H3K27ac. In opposite, isoDIPG-H3.3K27M cells lost H3K27me3 and other repressive marks accompanied by gain of H3K27ac. Moreover, increased expression of several activating epigenetic key players was observed. These (epi)genetic changes increased tumor-driving gene expression resulting in elevated cell proliferation, clonogenicity, migration/invasion ability and in ovo growth of isoDIPG-H3.3K27M-mutated cells in comparison to their H3WT counterparts. In summary, the present study revealed that presence of H3.3K27M-mutation in isoDIPG cells is a leading cause for the malignant phenotype observed in DIPG cells.