TRANSCRIPTION REGULATION OF RAT GLUTATHIONE-S-TRANSFERASE YA SUBUNIT GENE-EXPRESSION BY CHEMOPREVENTIVE AGENTS

Purpose. To study the transcription regulation of rat glutathione S-tr ansferase Ya (rGSTya) subunit gene expression by chemopreventive agent s. Methods. The effects of chemopreventive agents; tamoxifen, genistei n, oltipraz, indole-3-carbinol, and various isothiocyanates-sulforapha ne, PMITC, PEITC, PBITC, and PPITC, on the transcriptional activation of rGSTya were investigated in cell culture. These were accomplished w ith a stable human hepatoma Hep G2 cell line transfected with a 1.6 ki lobase (kb) 5'-flanking region of the rGSTya fused with the chloramphe nicol acetyltransferase (CAT) reporter gene, Concentration-effect rela tionship and the kinetics of gene activation following treatments of t he cells with different chemopreventive agents were carried out by qua ntitating CAT reporter protein using ELISA. Northern blot analysis of total RNA on the expression of CAT mRNA as well as potential transcrip tion factors such as c-Jun, c-Fos, and LFR-1 were performed. Results. Treatment of the cells with increasing concentrations of different che mopreventive agents resulted in corresponding increases in the gene ex pression of CAT reporter protein. Kinetically, induction of CAT protei n was seen as early as 3 hr and peaked at about 20 hr. Northern blot a nalysis revealed an increase in CAT mRNA transcripts and these mRNA in ductions in general were in agreement with those quantitated by the pr oduction of CAT reporter protein. Induction of the transcription facto r, c-Jun mRNA was observed with sulforaphane. Conclusions. These resul ts show that different chemopreventive agents transcriptionally activa te rGSTya CAT in a time and dose-dependent fashion.