RAD18 and gastric cancer: 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.