PDTM-31. INVESTIGATING THE EFFECT OF H3G34V MUTATION ON DISTINCT GENOMIC H3K36 METHYLATION PATTERNS IN PEDIATRIC GLIOMA

BACKGROUND Histone H3.3 mutation (H3F3A) occurs in 50% of cortical pediatric high-grade gliomas (pHGGs). This mutation replaces glycine 34 with arginine or valine (G34R/V), impairing SETD2 activity (H3K36-specific trimethyltransferase). Consequently, reduced H3K36me is observed on H3G34V nucleosomes relative to wild-type, contributing to genomic instability and driving a distinct gene expression signature associated with tumorigenesis. However, it is not known if this differential H3K36me3 enrichment is due to H3G34V mutant protein alone. Therefore, we set to elucidate the effect of H3G34V mutation in pediatric glioma on genomic H3K36me3 enrichment in vitro. METHODS Doxycycline-inducible short hairpin RNA (shRNA) against H3F3A was delivered via lentivirus to established H3G34V mutant pediatric glioma cell line KNS42, and H3G34V introduced into H3.3 wild type normal human astrocytes (NHA). Transfections were confirmed by western blot, fluorescent imaging, and flow cytometry, with resulting H3.3WT and H3K36me3 expression determined by western blot. H3.3WT, H3K36me3, and H3G34V ChIP-Seq was performed to evaluate effects of H3G34V mutation on genomic enrichment patterns. RESULTS Complete knockdown of H3G34V was achieved with DOX-induced shRNA, with no change in total H3.3, suggesting disproportionate allelic frequency of genes encoding H3.3 (H3F3A and H3F3B). Modest increase in H3K36me3 expression occurred after H3F3A-knockdown from KNS42, suggesting H3G34V alone impacts observed H3K36me3 levels. H3G34V knock-in to NHAs was verified via western blot. Distinct H3K36me3 genomic enrichment was observed with H3G34V on ChIP-Seq. CONCLUSIONS We demonstrate that DOX-inducible knockdown of H3F3A in an H3G34V mutant pediatric glioma cell line, and H3G34V mutation transduction in wild-type NHAs, directly impacts H3K36me3 expression level. Further evaluation by ChIP-Seq analysis for restoration of wild-type genomic H3K36me3 enrichment patterns with H3G34V knockdown, and mutant H3K36me3 patterns with H3G34V transduction, is currently underway.