Transcription Regulation of Rat Glutathione S-Transferase Ya Subunit Gene Expression by Chemopreventive Agents

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Abstract
Purpose. To study the transcription regulation of rat glutathione S-transferase Ya (rGSTya) subunit gene expression by chemopreventive agents. Methods. The effects of chemopreventive agents; tamoxifen, genistein, oltipraz, indole-3-carbinol, and various isothiocyanates—sulforaphane, PMITC, PEITC, PBITC, and PPITC, on the transcriptional activation of rGSTya were investigated in cell culture. These were accomplished with a stable human hepatoma Hep G2 cell line transfected with a 1.6 kilobase (kb) 5′-flanking region of the rGSTya fused with the chloramphenicol acetyltransferase (CAT) reporter gene. Concentration-effect relationship and the kinetics of gene activation following treatments of the cells with different chemopreventive agents were carried out by quantitating CAT reporter protein using ELISA. Northern blot analysis of total RNA on the expression of CAT mRNA as well as potential transcription factors such as c-Jun, c-Fos, and LFR-1 were performed. Results. Treatment of the cells with increasing concentrations of different chemopreventive agents resulted in corresponding increases in the gene expression of CAT reporter protein. Kinetically, induction of CAT protein was seen as early as 3 hr and peaked at about 20 hr. Northern blot analysis revealed an increase in CAT mRNA transcripts and these mRNA inductions in general were in agreement with those quantitated by the production of CAT reporter protein. Induction of the transcription factor, c-Jun mRNA was observed with sulforaphane. Conclusions. These results show that different chemopreventive agents transcriptionally activate rGSTya CAT in a time and dose-dependent fashion.