Investigations of the posttranslational mechanism of arsenite-mediated downregulation of human cytochrome P4501A1 levels: the role of heme oxygenase-1.
Arsenite, an environmental cocontaminant of polycyclic aromatic hydrocarbons (PAHs), diminishes the PAH-mediated upregulation of human CYP1A1, the enzyme that bioactivates PAHs to carcinogenic metabolites. Mechanistically, while transcriptional downregulation contributes to these effects, a role for posttranslational regulation has been implicated but not proven. We hypothesize that arsenite induces heme oxygenase-1 (HO-1), which catabolizes CYP1A1 heme or cellular heme pools, thereby downregulating CYP1A1. Arsenite (5 microM), in HepG2 cells, induced HO-1 mRNA 7.4-fold over the 48 h observation period, and it upregulated HO-1 protein expression. Arsenite decreased the induction of CYP1A1 by a PAH, benzo[k]fluoranthene (BKF), by 50%; and transfection of HepG2 cells with siRNA targeting the human HO-1 gene, reduced the arsenite downregulation of BKF-induced CYP1A1 from 54% to 27%, relative to untransfected cells. Reconstituted HO-1 did not significantly catabolize CYP1A1 heme in vitro. Together these findings demonstrate that a posttranslational mechanism involving decreases in the cellular heme pool by arsenite-induced HO-1 may contribute to arsenite-mediated downregulation of CYP1A1.
Bessette
Erin E
EE
Department of Environmental Health Sciences, School of Public Health, University at Albany, State University of New York, Albany, NY 12201-0509, USA.
Fasco
Michael J
MJ
Pentecost
Brian T
BT
Reilly
Andrew
A
Kaminsky
Laurence S
LS
D018053:Arsenites / Q000633:toxicity*; D045744:Cell Line, Tumor; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects*; D004785:Environmental Pollutants / Q000633:toxicity*; D004789:Enzyme Activation / Q000187:drug effects; D005449:Fluorenes / Q000633:toxicity*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D006801:Humans; D013723:Teratogens / Q000633:toxicity*; D013997:Time Factors
D018053:Arsenites; D004785:Environmental Pollutants; D005449:Fluorenes; D013723:Teratogens; D019388:Cytochrome P-450 CYP1A2; D051547:Heme Oxygenase-1; C015001:arsenite; C022921:benzo(k)fluoranthene