P02.03.A INTEGRATIVE (EPI)GENETIC ANALYSIS OF INVASION-PROMOTING GENES IN HIGH-GRADE GLIOMA CELLS

Abstract

Abstract BACKGROUND DNA methylation-based analyses of brain tumors including glioma is currently the gold standard for diagnostic classification. Aberrant epigenetic alterations can lead to inappropriate gene expression and thereby promote tumorigenesis. Glioblastoma (GBM), CNS WHO grade 4, is characterized by a very diffuse infiltrative growth into the adjacent brain parenchyma. Due to these highly invasive but also genetically heterogeneous and plastic cellular phenotypes, standard treatment, including maximum resection, radio- and chemotherapy, has limited efficacy. It can be assumed that intertumoral or molecular heterogeneity of gliomas on transcriptional level is caused by altered epigenetic changes within the individual tumor cells. Considering this, we hypothesize that tumor cell invasion being one of the critical hallmarks of highly malignant gliomas goes along with altered DNA methylation status and following from this changes in invasion-promoting transcript expression. MATERIAL AND METHODS We performed several in vitro screening approaches to describe the genetic, epigenetic and transcriptional status of invasion glioma cells. Within our first approach, we isolated fractions of glioma cells with increased invasive properties and performed Illumina® array-based methylation profiling as well as RNA sequencing analysis to identify methylation-driven, invasion-associated gene sets. During a second approach, the inducible CRISPR/Cas9 Synergistic Activation Mediator (SAM) system and a genome-wide sgRNA library were introduced in a serum-free glioma cell line. During CRISPR/Cas9 SAM mediated single-gene activation cells were subjected to a transwell invasion assay and sgRNA representation within the invasive glioma cell fraction was determined by next-generation-sequencing (NGS). RESULTS In this study, we integrated Illumina HumanMethylation850K methylation data, RNA-sequencing data and invasion-promoting sgRNA representation data. By systemic screening we identified an invasion-promoting gene signature and the correlating promotor DNA-methylation status. Future studies will be directed to further investigate the impact of identified genes in invasion of high-grade glioma cells. CONCLUSION This integrative experimental approach complements existing genome-wide inhibitory screens as well as incorporates for the first time DNA-methylation profiles and transcriptome analysis with gene-sets identified by CRISPR/Cas9 activation screen and thereby holds the potential to identify novel invasion-essential candidate genes.