Abstract

The regulation of the human cytochrome Cyp1A2 gene by 3-methylcholanthrene was studied through the transfection of 5'-flanking sequences into human cells. The Cyp1A2 promoter sequence and 3700 bases 5' to the cap site were linked to the procaryotic chloramphenicol acetyltransferase gene. Transfection of this construct into HepG2 cells generated a 2-3-fold increase in Cyp1A2-directed chloramphenicol acetyltransferase activity when the cells were treated with 3-methylcholanthrene. Deletion of flanking sequence to -1079 resulted in a loss of 3-methylcholanthrene-induced chloramphenicol acetyltransferase activity. When 5'-flanking sequences of the Cyp1A2 gene were inserted into a plasmid containing the chloramphenicol acetyltransferase gene under control of the simian virus 40 promoter, 3-methylcholanthrene-enhanced chloramphenicol acetyltransferase activity was observed. The strongest 3-methylcholanthrene-induced chloramphenicol acetyltransferase activity, a 4-fold increase, was observed for a DNA fragment located at -3202 to -1595. When this Cyp1A2 responsive element was transfected into human breast carcinoma MCF-7 cells, 3-methylcholanthrene did not stimulate chloramphenicol acetyltransferase activity. In comparison, when a DNA fragment that contained a copy of the human Cyp1A1 xenobiotic-responsive element was analyzed for enhancer activity, 3-methylcholanthrene initiated chloramphenicol acetyltransferase activity in both HepG2 cells and MCF-7 cells. These results suggest that the 3-methylcholanthrene-responsive Cyp1A2 element may be regulated in a tissue-specific manner.