Cyclopentenone Prostaglandins as Potential Inducers of Phase II Detoxification Enzymes

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-⌬ 12,14 -prostaglandin J2 (15-deoxy-⌬ 12,14 -PGJ2) in particular, were found to be potential inducers of GST. Enhanced gene expression of Class GST isozyme (GSTP1) by 15-deoxy-⌬ 12,14 -PGJ2 was evident as a drastic elevation of the mRNA level. Hence, we examined the molecular mechanism underlying the 15-deoxy-⌬ 12,14 -PGJ2-induced GSTP1 gene expression. From functional analysis of various deletion mutant genes, we found that the 15-deoxy-⌬ 12,14 -PGJ2 reponse element was localized in a region containing a GSTP1 enhancer I (GPEI) that consists of two imperfect phorbol 12-Otetradecanoylphorbol-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-⌬ 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-⌬ 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-⌬ 12,14 -PGJ2 induces the expression of the rat GSTP1 gene through binding of proteins, including c-Jun, to a specific GPEI.

A Sulforaphane Analogue That Potently Activates the Nrf2-dependent Detoxification Pathway

“…We have recently developed a cell culture system, using rat liver epithelial RL34 cells, that potently responds to the already-known phase II inducers, such as phenolic antioxidants and ␣, ␤-unsaturated aldehydes, resulting in the induction of the GST activity (16). In the present study, using the RL34 cells, we determined the GST induction potencies of food plants and found that the wasabi extracts induce GST activity with great potency.…”

Functional characterization and expression of molluscan detoxification enzymes and transporters involved in dietary allelochemical resistance

“…Additionally, prostaglandins have been found to substantially induce mammalian GST pi (GSTPl) gene transcription, mediated by a prostaglandin response element localized in the enhancer region of GSTP1 (Kawamoto et al 2000). The cyclopentenone-type prostaglandins (e.g.…”

“…Cyclopentenone prostaglandins of the A and J series have been shown to be inducers of GST activity and mRNA/protein expression in mammalian (Kawamoto et al 2000, Uchida 2000 and invertebrate cell lines (Stanley et al 2008). Furthermore, select vertebrate alpha-, mu-and pi-class GSTs were found to enhance PGA 2 conjugation with glutathione, suggesting that the overexpression of GST forms could modulate the cytotoxic effects of cyPGs (Bogaards et al 1997).…”

Molecular Basis for the Direct Inhibition of AP-1 DNA Binding by 15-Deoxy-Δ12,14-prostaglandin J2

“…The levels of 15d-PGJ 2 measured in cell-free exudates or extracellular media in several experimental models of inflammation are in the nanomolar range (2, 3). However, most of the biological effects of cyPG have been observed using micromolar concentrations (13,(32)(33)(34). Several considerations have been made to reconcile these discrepancies.…”