Nrf2 and C/EBPβ-mediated transactivation of hepatic glutathione S-transferase gene by cancer chemopreventive isothiocyanates Free

1871

Cancer chemopreventive agents transcriptionally induce a battery of genes whose protein products can protect cells from chemical-induced carcinogenesis. Dithiolethiones occuring in cruciferous exerts chemopreventive responses through glutathione S-transferase (GST) induction. A significant number of isothiocyanates (NCSs), which play a role in the prevention of human cancer, are also present in cruciferous vegetables. This study was designed to investigate the expression of GST gene in response to arylalkyl NCSs including phenyl, benzyl, phenethyl, o-, m-, p-tolyl NCS and the basis for GST enzyme induction. Northern blot analysis revealed that phenethyl, m-tolyl or p-tolyl NCS (1.17 mmol/kg) was efficacious in inducing hepatic GSTA2/3 in rats with elevation of the mRNA levels by 10- to 13-folds 24 h after treatment as compared to control, whereas phenyl, benzyl or o-tolyl NCS was minimally active. Treatment of rats with m-tolyl or p-tolyl NCS for 3 consecutive days also resulted in marked and persistent increases in GST protein and mRNAs. To investigate the mechanistic basis for the enzyme induction, studies were extended to assess GST transactivation by NCSs in H4IIE rat hepatocyte-derived cells transfected with the pGL-1651 plasmid containing the 1.65 kb flanking region of the GSTA2 gene. Phenethyl NCS (0.1 μM) or m-tolyl NCS (30 μM) induced luciferase expression from the pGL-1651 plasmid by 12-folds as compared to control. Deletion of either the ARE or the CCAAT/enhancer-binding protein (C/EBP)-binding site in the promoter region abolished the reporter gene activity, indicating that GSTA2 gene transactivation by NCSs requires Nrf2 and C/EBPβ activation. These results demonstrated that NCSs including phenethyl, m-tolyl or p-tolyl NCS induce GSTs in the rat liver and that the GST induction by NCSs requires Nrf2 and C/EBPβ activation, implying that cancer chemopreventive effects of certain NSCs may be mediated with the induction of phase II GST detoxifying enzyme.