Abstract BACKGROUND Ependymomas can arise from all compartments of the central nervous system and ten distinct molecular groups have been identified in children and adults. In children, the most aggressive group is posterior fossa group A ependymoma (PFA). In PFA ependymomas, the aberrant overexpression of EZHIP (EZH inhibitory protein) has been implicated as a relevant driver of the disease. EZHIP suppresses the installing and spreading of the repressive epigenetic mark H3K27me3 via disturbing PRC2 (polycomb repressive complex 2) activity through inhibiting EZH2 (enhancer of zeste 2), which causes overall low levels of H3K27me3 in PFA. METHODS To get a better understanding how EZHIP may drive the disease, how it affects the epigenetic landscape and what the downstream targets of EZHIP are, we performed DNA sequencing, RNA expression profiling and ChIP-seq experiments of H3K27me3, H3K27ac, EZH2, and EZHIP in PFA, PFB, and ST-ZFTA ependymomas (n = 3 tumor cases each). RESULTS After validating the high levels of EZHIP and global reduction of H3K27me3 in PFA, we characterized the epigenetic landscape and EZHIP chromatin binding characteristics in PFA compared to PFB and ST-ZFTA ependymoma. Transcriptome analysis showed that overall more genes are up-regulated in PFA compared with PFB and ZFTA, which might be caused by its relatively high accessibility with a global loss of H3K27me3. EZHIP knockdown experiments confirmed direct changes on H3K27me3, H3K27ac and gene expression. We also found that PLAG1 (pleomorphic adenoma gene 1) expression linearly correlated with EZHIP expression in PFA tumors. ChIP-seq data indeed showed the PLAG1 locus to be bound by EZHIP and marked with increased H3K27ac and decreased H3K27me3 signals in PFA. CONCLUSIONS We identified PLAG1 as a potential downstream target of EZHIP in PFA tumors. Currently, more experiments on PLAG1 are being performed to further explore its role as a potential vulnerability in PFA ependymoma.