Epigenomic landscape study reveals molecular subtypes and EBV-associated regulatory epigenome reprogramming in nasopharyngeal carcinomaResearch in context

Summary: Background: Epstein-Barr virus (EBV) latent infection is associated with genome-wide epigenomic changes in several malignancies, but its role in epigenetic dysregulation remains unclear in nasopharyngeal carcinoma (NPC). Methods: To investigate EBV-associated epigenetic dysregulation, we performed a multi-omics study by integrating whole-genome bisulfite sequencing (WGBS), assay for transposase-accessible chromatin using sequencing (ATAC-Seq), whole-exome sequencing (WES), and single-cell RNA sequencing (scRNA-Seq) data. Findings: In addition to the known global DNA hypermethylated subtype, we discovered a novel subtype with global hypomethylation in EBV + NPC. The consistent EBV-specific differentially methylated regions (EBV-DMRs) in the human genome were identified from both subtypes and associated with loss of CTCF binding (P < 2.2e-16). Importantly, CTCF is a master chromatin regulator and CTCF protein was reduced in 45% of NPC cases, especially in those with advanced NPC (Stage IV vs. others: 62% vs. 38%, P = 0.034). This result links EBV with chromatin changes. The ATAC-Seq data suggest regulatory epigenome reprogramming through chromatin accessibility changes in EBV + NPC with altered CTCF binding and the switch of transcription factor binding from differentiation-associated KLF/SP family to the innate and adaptive immunity-related NF-ĸB and IRF families. Detailed chromatin accessibility analysis identified a potential EBV target gene CD74, which mediated EBV-specific cell-cell communications in the tumor microenvironment (TME) and was strongly correlated with T cell exhaustion (r2 = 0.55). Interpretation: Our study reveals the unexpected epigenetic heterogeneity, providing insights into NPC pathogenesis and highlighting the involvement of host factors in virus-associated epigenetic changes. EBV infection is associated with epigenome reprogramming and may promote immune evasion. Funding: This study was funded by the Hong Kong Research Grants Council grant (AoE/M-06/08) to MLL, General Research Fund (17103218 and 17102619) and seed funding for basic research (201611159158) to WD, and General Research Fund (17119618) to HC.