Abstract
Cytochrome P450 (P450) enzymes play a critical role in the metabolic activation of a wide variety of environmental carcinogens. Recently, a novel human P450 enzyme, CYP2S1, has been identified. It is inducible by dioxin and other classical aryl hydrocarbon receptor ligands. However, little is known regarding the substrates and the functional role of CYP2S1. Since CYP2S1 is predominantly expressed in human lung and trachea, it is reasonable to speculate that CYP2S1 may play an important role in metabolizing the environmental chemicals to which human respiratory tissues are exposed. In the present study, we examined the activity of human CYP2S1 in the metabolism of nicotine and in the activation of three potent carcinogens in cigarette smoke, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), benzo[a]pyrene (BaP), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). The full-length CYP2S1 cDNA was amplified by nested polymerase chain reaction from a human lung cDNA library and was expressed in both Chinese hamster ovary (CHO) cells and Sf9 insect cells. In contrast to the positive controls, i.e., CHO cells expressing human CYP2A13 (for NNK activation) or human CYP1A1 (for BaP activation), there was no increase in NNK- or BaP-induced toxicity in the CHO cells expressing CYP2S1. The heterologously expressed CYP2S1 proteins showed no detectable activity in metabolizing nicotine and PhIP. These results clearly demonstrate that CYP2S1 does not catalyze the metabolism of nicotine and the metabolic activation of these lung carcinogens.
Footnotes
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This study was supported by National Institutes of Health Grant R01-ES10048 (J.-Y.H.) and National Institute of Environmental Health Sciences Center Grant ES-05022.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.104.002923.
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ABBREVIATIONS: P450, cytochrome P450; NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; BaP, benzo[a]pyrene; PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine; CHO, Chinese hamster ovary; PCR, polymerase chain reaction; CHO-2S1, CYP2S1-expressing CHO cells; DMSO, dimethyl sulfoxide; MTS, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfopheny)-2H-tetrazolium; LC/MS, liquid chromatography/mass spectrometry; FRT, Flp recombination target; CHO-2A13, CYP2A13-expressing CHO cells; CHO-1A1, CYP1A1-expressing CHO cells; AF, aflatoxin.
- Received November 4, 2004.
- Accepted December 15, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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