Oxidative Stress Suppresses the Expression of 15-Hydroxyprostaglandin Dehydrogenase via Upregulation of DNMT3a/Snail in Human Colon Epithelial Cells

Abstract

Overproduction of prostaglandin E2 (PGE2) is implicated in pathogenesis of inflammation-associated carcinogenesis. 15-Hydroxyprostaglandin dehydrogenase (15-PGDH) is a key enzyme that catalyzes the conversion of PGE2 to a biologically inactive 15-keto-PGE2 metabolite. 15-PGDH has been considered to be a tumor suppressor as its expression is frequently repressed in human malignancies via hypermethylation of its promoter. In our previous study, oxidative stress caused by Helicobacter pylori infection is associated with down-regulation of 15-PGDH. This prompted us to investigate whether 15-PGDH expression could also be down-regulated by oxidative stress in human colon epithelial CCD841 cells. When CCD841 cells were treated with H2O2, the expression level of 15-PGDH was significantly reduced in both concentration and time dependent manners. H2O2 induced methylation of the 15-PGDH promoter in a time dependent manner as determined by methyl specific PCR. H2O2-induced down-regulation of 15-PGDH expression was abrogated by the DNA methyltransferase (DNMT) 3a inhibitor, 5-Aza-2′-deoxycytidine (5-Aza). H2O2 generated the reactive oxygen species (ROS), which is attenuated by general antioxidant, N-acetylcysteine (NAC) as determined by DCF-DA staining. In addition, NAC abrogated the down-regulation of 15-PGDH and up-regulation of DNMT 3a expression induced by H2O2. Moreover, NAC reduced the methylation level of 15-PGDH promoter induced by H2O2. H2O2 treatment also elevated expression of Snail and silencing of snail restored the 15-PGDH expression suppressed by H2O2. Taken together, these finding suggest that ROS down-regulates the expression of 15-PGDH through hypermethylation of CpG island in the 15-PGDH promoter through induction of DNMT3a.