Functional characterization of human E3 ubiquitin ligase RAD18 in regulation of sister chromatid exchange

Abstract

Post-replication repair can bypass stalled replication forks caused by DNA lesions and prevents collapse of forks therefore playing an important role in maintenance of genome integrity Previously we performed transcriptome analysis to compare expression profiles between cisplatin-resistant NPC nasopharyngeal carcinoma (NPC) cell lines HONE6 and HONE15 and their parental cell line HONE1 It revealed that Fanconi anemia (FA) homologous recombination (HR) and post-replication repair (PRR)-related genes are highly expressed in these cisplatin-resistant cells Here we further characterized HONE6 and HONE15 cells We found that cisplatin-resistant HONE6 and HONE15 cell lines are not only resistant to cisplatin but also exhibit higher resistance to other DNA damaging agents including methyl methanesulfonate (MMS) and 4-Nitroquinoline 1-oxide (4NQO) We also verified that several genes in the FA HR and PRR pathways are highly expressed in HONE6 and HONE15 cells Since RAD18 in the PRR pathway is highly expressed in HONE6 and HONE15 cells we determined cell survival and sister chromatid exchange (SCE) in the RAD18-depleted cells Surprisingly the depletion of RAD18 sensitized cells to MMS in HONE1 but not in HONE6 cells Additionally the depletion of RAD18 increased SCE in HONE1 but showed no significant differences in HONE6 cells It could be due to the fact that HONE6 cells have already exhibited elevated SCE indicating that high frequency of chromosomal breaks and recombination have occurred in HONE6 cells Our results reveal that the chemoresistant NPC cells enhance the multiple DNA repair pathways and the enhancement could contribute cells chemoresistant phenotype

Date of Award	2020
Original language	English
Supervisor	Hung-Jiun Liaw (Supervisor)