Mammalian PC‐12 cell genetically engineered for human cytochrome P450 2E1 expression

The stable expression of the human cytochrome CYP2E1 (P450 alcohol) was performed in the mammalian cell line PC‐12. This cell line expressed cytochrome b5 (58 ± 12 pmol/mg microsomal protein vs 528 ± 80 pmol/mg in microsomal human liver) and a high level of NADPH: cytochrome P450 reductase (140 ± 20 nmol · min−1· mg microsomal protein−1 vs 68 ± 48 nmol · min−1· mg−1 in microsomal human liver). An expression plasmid was constructed using the cDNA for the human CYP2E1 mRNA and the Rous sarcoma virus (RSV) promoter. This plasmid was co‐transfected with the plasmid RSVneo into PC‐12 cells. Clones were selected for resistance to the neomycin analog, G418, and then screened for expression of the CYP2E1 isozyme by testing for 6‐hydroxylation of chlorzoxazone, a specific substrate for CYP2E1. Expression of CYP2E1 was confirmed in one clone, DB‐7, by Western blot analysis and by measurement of monooxygenase activities which were not detectable in PC‐12 cells. Chlorzoxazone 6‐hydroxylation, n‐butanol oxidation and dimethylnitrosamine N‐demethylation were localized in microsomes (62, 60 and 63 pmol · min−1· mg microsomal protein−1, respectively) and were inhibited by carbon monoxide and diethyldithiocarbamate, both inhibitors of P450 enzymes. Although the level of the enzyme activities was about a tenth of that measured in human liver microsomes, CYP2E1 expressed in DB‐7 cells has catalytic competence similar to human liver CYP2E1. DB‐7 cells metabolized acetaminophen and this metabolic activation was shown to be toxic to these cells by release of lactate dehydrogenase. Construction of recombinant cell lines expressing CYP2E1 provides a useful tool for studying the catalytic properties of this enzyme and the consequent cytotoxic effects of substrates metabolized by this enzyme.