A New Insight Into p53-Inhibiting Genes in Epstein–Barr Virus-Associated Gastric Adenocarcinoma

Background: The p53 mutation is uncommon in EBV-linked gastric carcinoma, but its suppression occurs through mechanisms such as USP7 inhibition via EBNA1 activity. This study aimed to evaluate the effect of EBNA1 on p53-inhibiting gene expression and the impact of USP7 inhibition on p53 suppression. METHODS: MKN-45 cells were transfected with the EBNA1 plasmid. A stable EBNA1 expression cell line was developed through selection based on hygromycin B resistance. MDM4, MDM2, SIRT3, HDAC1, PSMD10, USP7, and p53 expression were checked using real-time PCR. Also, cells containing EBNA1 or control plasmid were treated with GNE-6776, and the expression of the interested genes and cell survival were assessed. RESULTS: MDM4, MDM2, and PSMD10 were significantly upregulated in the MKN-45 cell line following EBNA1 transfection. Morphological changes were observed in the cells harboring EBNA1 after 20 days. In the control cells, USP7 inhibition significantly upregulated the HDAC1, PSMD10, MDM4, and MDM2 genes after 24 h, but downregulated these genes after four days. In the EBNA1-harboring cells, MDM2, MDM4, and PSMD10 genes were significantly upregulated after 24 h, and this effect was sustained for all genes except for MDM4, even after four days. Furthermore, USP7 inhibition induced apoptosis in both cell groups. CONCLUSION: EBNA1 enhances the expression of p53-inhibiting genes. Two events—p53 protein overexpression and apoptosis activation—followed the suppression of the USP7 protein and provided evidence for its possible function. The significance of the EBNA1-USP7 interaction in p53 suppression warrants additional investigation and possibly reconsideration.