5-hydroxymethylcytosine deposition mediates Polycomb Repressive Complex 2 function in MYCN -amplified neuroblastoma

MYCN -amplification is a strong predictor of poor prognosis in neuroblastoma, an embryonal malignancy that accounts for 15% of pediatric cancer deaths. Here, we found that MYCN -amplified neuroblastoma tumors had increased 5-hydroxymethylcytosine (5-hmC) deposition on Polycomb Repressive Complex 2 (PRC2) target genes. 5-hmC and H3K27me3, a catalytic product of PRC2, directly co-localized at the nucleosomal level in MYCN -amplified neuroblastoma. Genes with co-localization of 5-hmC/H3K27me3 were involved in development related pathways and were transcriptionally repressed in MYCN -amplified neuroblastoma. Inhibition of 5-hmC deposition resulted in a loss of H3K27me3 on protein-coding genes and sensitized neuroblastoma to DNA demethylating agents. 5-hmC deposition predisposed H3K27me3 marked genes to transcriptional activation upon PRC2 inhibition with tazemetostat. Low expression of genes marked by 5-hmC/H3K27me3 was associated with poor clinical outcome. Our results suggest that 5-hmC/H3K27me3 co-operate to repress mediators of development highlighting a novel link between DNA and chromatin modifications with potential therapeutic implications in MYCN -amplified neuroblastoma.