Abstract:
Increases in oxidative stress and inflammation and alterations of DNA methylation are frequently detected in bladder cancer patients. Previousely, increased oxidative stress and inflammation was found to associate with hypomethylation of a transposable element, long-interspersed nuclear element-1 (LINE-1). Hypermethylation of promoter of a tumor suppressor gene, runt-related transcription factor 3 (RUNX3), is well recognized in bladder cancer patients. In this study, changes of DNA methylation in LINE-1 and RUNX3 promoter in UM-UC-3 cell line under oxidative stress and inflammation conditions were investigated. Combined bisulfite restriction analysis and methylation-specific PCR were used to measure LINE-1 and RUNX3 promoter methylation, respectively. UM-UC-3 cells were challenged with 10 and 50 µM H₂O₂ for 72 h for induction of oxidative stress. Protein carbonyl content increased in H₂O₂ treated cells and decreased in H₂O₂ -treated cells pretreated with tocopheryl acetate (50 and 300 µM). LINE-1 hypomethylation was observed in H₂O₂ -treated cells, but it was prevented by pretreatment with tocopheryl acetate. However, LINE-1 methylation did not increased after pretreatment with lime powder regimen. Methylation of RUNX3 promoter increased in cells exposed to H₂O₂ and decreased in tocopheryl acetate/H₂O₂ -treated cells. For inflammatory stimulation, cells were treated with 1-20 ng/ml TNF-α for 72 h. No change in LINE-1 methylation was observed. Conclusion, our findings demonstrated that oxidative stress induced hypomethylation of LINE-1 and hypermethylation of RUNX3 promoter in bladder cancer cell line. These evidences support the hypothesis that oxidative stress promotes tumorigenesis of urothelial cells through modulation of DNA methylation. Our data also imply that mechanistic pathways of DNA methylation between gene and non-gene regions might be different.