Cyclopentenone Prostaglandins as Potential Inducers of Phase II Detoxification Enzymes: 15-DEOXY-Δ12,14-PROSTAGLANDIN J2-INDUCED EXPRESSION OF GLUTATHIONE S-TRANSFERASES

Abstract

Exposure of cells to a wide variety of chemoprotective compounds confers resistance to a broad set of carcinogens. For a subset of the chemoprotective compounds, protection is generated by an increase in the abundance of protective enzymes, such as glutathione S-transferases (GSTs). In the present study, we developed a cell culture system that potently responds to phenolic antioxidants and found that antitumor prostaglandins (PGs) are potential inducers of GSTs. We screened primary hepatocytes and multiple cell lines for inducing GST activity upon incubation with the phenolic antioxidant (tert-butylhydroquinone) and found that rat liver epithelial RL34 cells most potently responded. Based on an extensive screening of diverse chemical agents on the induction of GST activity in RL34 cells, the J2 series of PGs, 15-deoxy-Delta(12,14)-prostaglandin J2 (15-deoxy-Delta(12,14)-PGJ2) in particular, were found to be potential inducers of GST. Enhanced gene expression of Class pi GST isozyme (GSTP1) by 15-deoxy-Delta(12,14)-PGJ2 was evident as a drastic elevation of the mRNA level. Hence, we examined the molecular mechanism underlying the 15-deoxy-Delta(12, 14)-PGJ2-induced GSTP1 gene expression. From functional analysis of various deletion mutant genes, we found that the 15-deoxy-Delta(12, 14)-PGJ2 reponse element was localized in a region containing a GSTP1 enhancer I (GPEI) that consists of two imperfect phorbol 12-O-tetradecanoylphorbol-13-acetate response elements. When the GPEI was combined with the minimum GSTP1 promoter, the element indeed showed an enhancer activity in response to 15-deoxy-Delta(12, 14)-PGJ2. Point mutations of either of the two imperfect 12-O-tetradecanoylphorbol-13-acetate response elements in GPEI completely abolished the enhancer activity. Gel mobility shift assays demonstrated that 15-deoxy-Delta(12,14)-PGJ2 specifically stimulated the binding of nuclear proteins including the transcription factor c-Jun, but not Nrf2, to GPEI. These results suggest that 15-deoxy-Delta(12,14)-PGJ2 induces the expression of the rat GSTP1 gene through binding of proteins, including c-Jun, to a specific GPEI.