15-Keto prostaglandin E2 induces heme oxygenase-1 expression through activation of Nrf2 in human colon epithelial CCD 841 CoN cells

Abstract

Prostaglandin E₂ (PGE₂) plays a key role in inflammation-associated carcinogenesis. NAD⁺-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH) catalyzes the oxidation of the 15(S)-hydroxyl group of PGE₂ to generate 15-keto PGE₂. 15-PGDH has been known as a tumor suppressor in various malignancies including colon cancer. However, the molecular mechanisms underlying the tumor-suppressive function of 15-PGDH remain largely unresolved. In this study, we found that 15-keto PGE₂ upregulated the expression of heme oxygenase-1 (HO-1), a representative antioxidative and anti-inflammatory enzyme, at both transcriptional and translational levels, in human colon epithelial CCD 841 CoN cells. A redox-sensitive transcription factor, NF-E2-related factor (Nrf2) plays a critical role in the regulation of HO-1 and other cytoprotective proteins. 15-Keto PGE₂ induced translocation of Nrf2 into the nucleus and antioxidant response element-driven luciferase activity. Furthermore, the silencing of the Nrf2 gene abolished 15-keto PGE₂-induced HO-1 expression in CCD 841 CoN cells. 15-Keto PGE₂ activated AKT signaling, and the pharmacological AKT inhibitor, LY294002 suppressed the 15-keto PGE₂-induced HO-1 expression. 15-Keto PGE₂ generates the reactive oxygen species which is suppressed by the general antioxidant N-acetyl-l-cysteine. N-acetyl-l-cysteine treatment attenuated the 15-keto PGE₂-induced phosphorylation of GSK3β, transcriptional activity of Nrf2, and subsequently HO-1 expression. However, 13,14-dihydro-15-keto PGE₂ lacking the α,β-unsaturated carbonyl moiety failed to induce intracellular production of reactive oxygen species, HO-1 expression and nuclear translocation of Nrf2. In conclusion, 15-keto PGE₂ induces HO-1 expression through Nrf2 activation in human colon epithelial cells.

Keywords: 15-Keto PGE(2); Colon; Heme oxygenase-1; Nrf2; ROS.