Transcriptional regulation of the human quinone reductase gene by antiestrogen-liganded estrogen receptor-α and estrogen receptor-β

We have previously reported that antiestrogens stimulate quinone reductase (NAD(P)H:(quinone-acceptor) oxidoreductase (QR or NQO1); EC 1.6.99.2) enzymatic activity, an action that may provide protective effects against the toxicity and mutagenicity caused by quinones. We have now investigated the transcriptional regulation of the QR gene by antiestrogens. In transfection experiments employing the 5'-flanking (863-base pair) region of the human QR gene promoter with its electrophile/antioxidant response element (EpRE/ARE) or deleted or mutated constructs, we observe that antiestrogens induced an increase in QR gene promoter reporter activity in estrogen receptor (ER) negative breast cancer and endometrial cancer cells transfeeted with ER, and this induction by antiestrogens was repressed by estradiol. The stimulation of QR transcriptional activity required the 31- base pair electrophile-responsive region from the human QR gene promoter and a functional ER. Intriguingly, antiestrogens were stronger activators of the QR EpRE via the ER subtype ERβ than ERα. Oligonucleotide gel mobility and antibody shift assays reveal that the ER binds to the EpRE but is only a minor component of the proteins bound to the EpRE in ER-containing MCF-7 breast cancer cells. While binding of ERβ to the estrogen response element was weaker when compared with ERα, ERβ and ERα showed similar binding to the EpRE. Together these findings provide evidence that QR gene regulation by the antiestrogen-occupied ER is mediated by the EpRE-containing region of the human QR gene and indicate that the ER is one of the complex of proteins that binds to the EpRE. In addition, that ERβ is a more potent activator at EpRE elements than is ERα suggests that the different levels of these two receptors in various estrogen target cells could impact importantly on the antioxidant potency of antiestrogens in different target cells. These findings have broad implications regarding the potential beneficial effects of antiestrogens since EpREs mediate the transcriptional induction of numerous genes, including QR, which encode chemoprotective detoxification enzymes.