@article {Bessette312, author = {Erin E. Bessette and Michael J. Fasco and Brian T. Pentecost and Laurence S. Kaminsky}, title = {MECHANISMS OF ARSENITE-MEDIATED DECREASES IN BENZO[K]FLUORANTHENE-INDUCED HUMAN CYTOCHROME P4501A1 LEVELS IN HEPG2 CELLS}, volume = {33}, number = {3}, pages = {312--320}, year = {2005}, doi = {10.1124/dmd.104.002212}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are often environmental cocontaminants that could interact to alter PAH carcinogenicity. The heavy metal, arsenite, and the PAH, benzo[k]fluoranthene, were used as prototypes to investigate, in human HepG2 cells, mechanisms whereby the bioactivation of benzo[k]fluoranthene by human CYP1A1 could be diminished by arsenite-mediated decreases in CYP1A1 induction by benzo[k]fluoranthene. To determine whether arsenite down-regulates CYP1A1 transcription, quantitative real-time reverse transcriptase-polymerase chain reaction assays and luciferase reporter gene expression assays were used with HepG2 cells treated with benzo[k]fluoranthene and arsenite, separately and as a mixture. Benzo[k]fluoranthene (0.5 μM) and arsenite (5 μM) markedly decreased benzo[k]fluoranthene-mediated induction of CYP1A1 mRNA by 45\%. Plasmids containing the CYP1A1 promoter region (pHu-1A1-FL) were induced 7.4-fold over vehicle by benzo[k]fluoranthene (0.5 μM), whereas arsenite (1, 2.5, or 5 μM) decreased reporter gene expression by 46\%, 45\%, and 61\%, respectively. The plasmid, pHu-1A1-Δ100-FL, lacked xenobiotic response element (XRE) sites at {\textendash}1061 and {\textendash}981 and showed greater responsiveness relative to pHu-1A1-FL, by 1.7-fold. Benzo[k]fluoranthene (0.5 μM) and arsenite (1, 2.5, or 5 μM) decreased reporter gene expression by 0\%, 27\%, and 39\%, respectively, relative to expression levels produced by benzo[k]fluoranthene alone. Arsenite is stable for at least 48 h in the HepG2 cell medium with respect to its ability to diminish CYP1A1 benzo[k]fluoranthene induction. Arsenite did not affect benzo[k]fluoranthene induction directly through XRE sites, nor did it affect the stability of CYP1A1 mRNA. Thus, arsenite affects the transcriptional regulation of the benzo[k]fluoranthene-mediated induction of CYP1A1 and could diminish PAH carcinogenicity by decreasing bioactivation by CYP1A1. The American Society for Pharmacology and Experimental Therapeutics}, issn = {0090-9556}, URL = {https://dmd.aspetjournals.org/content/33/3/312}, eprint = {https://dmd.aspetjournals.org/content/33/3/312.full.pdf}, journal = {Drug Metabolism and Disposition} }