Therefore, PML disruption by EBNA1 is one mechanism by which EBV may contribute to the development of gastric cancer.182 O6-methylguanine-DNA methyltransferase (MGMT) is a key DNA repair enzyme contributing to the chemoresistance, which protects NPC cells from DNA damage by enhancing the capacity for DNA repair.183 Research findings showed that ubiquitin-conjugating enzyme E2 B (UBE2B) collaborates with E3 ubiquitin ligase RAD18 to mediated MGMT ubiquitination and degradation.184 Rad18 is also responsible for monoubiquitination of PCNA, which initiates several cellular DNA repair processes. Here, RAD18 is linked to nasopharyngeal carcinoma.