Oltipraz is a bifunctional inducer activating both phase I and phase II drug-metabolizing enzymes via the xenobiotic responsive element.
Oltipraz, a promising cancer chemopreventive agent, has been recognized as a monofunctional inducer selectively activating phase II carcinogen-detoxifying enzymes via the antioxidant responsive element (ARE). However, we report here that oltipraz also induces rat glutathione S-transferase A5 (GSTA5), a potent phase II detoxifying enzyme, by means of the xenobiotic responsive element (XRE). Although an ARE sequence exists in the 5' upstream of the rGSTA5 gene, this cis-acting regulatory element loses its responsiveness to oltipraz treatment because of extensive mutations in its distal-half site. Our data indicate that a XRE sequence, located downstream of the transcription initiation site of the gene, is another oltipraz-responsive element. Electrophoretic mobility shift assay showed that oltipraz steadily induces XRE-aryl hydrocarbon receptor (AhR) binding, which can be blocked specifically by excess XRE oligonucleotides or by AhR antibody. By cloning different XREs into the pGL3-promoter vector, we found that oltipraz can activate XRE enhancers from several phase II drug metabolism enzymes, including rGSTA5, rGSTA2, NAD(P)H:quinone reductase, and it also activates XRE from the phase I metabolism enzyme CYP1A1. Oltipraz's effect on XRE is AhR-dependent and is independent of the presence of active CYP1A1. Reverse transcriptase-polymerase chain reaction experiments revealed that oltipraz induces gene expression of both phase I and II drug-metabolizing enzymes in rat hepatoma cells. Thus, we conclude that, like ARE, the XRE pathway constitutes an important part of the molecular mechanism contributing to oltipraz-induced expression of the phase II metabolism enzymes. Oltipraz is a bifunctional inducer, modulating both phase I and II drug-metabolizing enzymes to enhance carcinogen detoxification.
Miao
Weimin
W
Montreal Center for Experimental Therapeutics in Cancer, Lady Davis Institute for Medical Research, The Sir Mortimer B Davis-Jewish General Hospital, 3755 Cote Sainte Catherine Road, Montreal, Quebec, Canada H3T 1E2.
Hu
Lianggao
L
Kandouz
Mustapha
M
Batist
Gerald
G
D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology; D001483:Base Sequence; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism*; D008658:Inactivation, Metabolic; D008969:Molecular Sequence Data; D011719:Pyrazines / Q000494:pharmacology*; D051381:Rats; D013871:Thiones; D013876:Thiophenes; D015262:Xenobiotics / Q000378:metabolism
D016588:Anticarcinogenic Agents; D011719:Pyrazines; D013871:Thiones; D013876:Thiophenes; D015262:Xenobiotics; C026209:oltipraz; D004247:DNA; D005982:Glutathione Transferase