The Methylation Status and Expression of Epstein-Barr Virus Early Genes BARF1 and BHRF1 in Epstein-Barr Virus-Associated Gastric Carcinomas

Abstract

Epstein-Barr virus (EBV) is an important DNA virus which establishes latent infection in human malignancies. Expression of EBV-encoded genes in the associated tumors is strongly modulated by promoter CpG methylation of EBV genome. This study aimed to explore the methylation status of the promoters of EBV BamHI-A rightward frame 1 (BARF1) and BamHI-H rightward open reading frame 1 (BHRF1) and their influence on transcriptional expression, to further understand the roles of BARF1 and BHRF1 in the occurrence of EBV-associated cancer. We evaluated the methylation status of BARF1 and BHRF1 promoters in 43 EBV-associated gastric carcinoma (EBVaGC) tissues and EBV-positive cell lines. Their expressions were evaluated by real-time quantitative PCR. We found that the promoters of BARF1 and BHRF1 were methylated by varying degrees in different EBV-positive cell lines and were almost hypermethylated in all EBVaGC tissues. The methylation status of BARF1 and BHRF1 promoters were significantly reduced by 5-Aza-CdR along with the increasing gene expressions. Hypermethylation of Ap and Hp mediates the frequent silencing of BARF1 and BHRF1 in EBV-associated tumors, which could be reactivated by a demethylation agent, suggesting that promoter demethylation and activation is important for BARF1 and BHRF1 transcription and their further action.

Role of BamHI-A Rightward Frame 1 in Epstein–Barr Virus-Associated Epithelial Malignancies

“…Interestingly, it has been reported that the BARF1 promoter region remains highly methylated in both epithelial and B-cells [ 61 ]. A similar result was found in EBVaGC tissues [ 67 ]. Conversely, BARF1 was expressed regardless of the promoter methylation status in NPC cells as well as in the latently EBV-infected C15 and C17 NPC xenografts.…”

The viral etiology of EBV-associated gastric cancers contributes to their unique pathology, clinical outcomes, treatment responses and immune landscape

“…Although BamH1 fragment H rightward facing 1 (BHRF1) miRNAs are known to play a role in B cell transformation ( 113 , 114 ), they are almost undetectable in GCs and NPCs ( 115 ). Indeed, the BHRF1 promoter is hypermethylated in almost all EBVaGC tissue, and this epigenetic modification likely contributes to its lack of expression ( Figure 2 ) ( 116 ).…”