Differential effects of flavonoid compounds on tumor promoter-induced activation of the human CYP1A2 enhancer.
Flavonoids, a family of naturally occurring polyphenolic compounds found in many fruits, nuts, vegetables, and beverages, appear to inhibit tumor promotion as part of their chemopreventive properties. To investigate at the molecular level the ability of flavonoids to inhibit tumor-promoting activity, we developed a cell line designed to screen for flavonoids that block the tumor promoter-mediated induction of activator protein-1 (AP-1) transcriptional activity. This cell line, T2Luc, is a HepG2-derived cell line stably integrated with a region of the human CYP1A2 5'-flanking gene containing two AP-1 binding sites linked to the thymidine kinase promoter-driven firefly luciferase reporter gene. Treatment of T2Luc with a commercial extract of green tea alone had no effect on luciferase activity, but did block the induction of luciferase when cells were further challenged with the tumor promoter phorbol 12-O-tetradecanoate 13-acetate (TPA). In contrast, treatment of cells with the flavonoid quercetin alone activated luciferase activity in a concentration-dependent manner and enhanced the TPA-induced transcription of luciferase. Gel mobility shift assays using nuclear extracts from cells treated with green tea extracts or TPA alone revealed induced binding of AP-1 proteins to the CYP1A2 3'AP-1 site. Pretreatment with green tea extracts did not inhibit the TPA-induced formation of AP-1 complexes. Quercetin treatment alone slightly enhanced binding of AP-1 complexes to this site. Our results suggest that these dietary chemopreventive agents may work through different pathways to modulate gene expression.
Shih
H
H
Section of Medical Toxicology, University of Colorado Health Sciences Center, B146, 4200 East 9th Avenue, Denver, Colorado, 80262, USA.
Pickwell
G V
GV
Quattrochi
L C
LC
D000818:Animals; D001483:Base Sequence; D002273:Carcinogens / Q000037:antagonists & inhibitors*; D002460:Cell Line; D019388:Cytochrome P-450 CYP1A2 / Q000235:genetics*; D017931:DNA Primers / Q000235:genetics; D004742:Enhancer Elements, Genetic / Q000187:drug effects*; D005419:Flavonoids / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter / Q000187:drug effects; D006801:Humans; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D010936:Plant Extracts / Q000494:pharmacology; D011794:Quercetin / Q000494:pharmacology; D013662:Tea; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors; D018808:Transcription Factor AP-1 / Q000378:metabolism
D002273:Carcinogens; D017931:DNA Primers; D005419:Flavonoids; D010936:Plant Extracts; D013662:Tea; D018808:Transcription Factor AP-1; D011794:Quercetin; D008156:Luciferases; D019388:Cytochrome P-450 CYP1A2; D013755:Tetradecanoylphorbol Acetate