Nrf2-dependent induction of NQO1 in mouse aortic endothelial cells overexpressing catalase

Overexpression of catalase has been shown to accelerate benzo(a)pyrene (BaP) detoxification in mouse aortic endothelial cells (MAECs). NAD(P)H:quinone oxidoreductase-1 (NQO1) is an enzyme that catalyzes BaP-quinone detoxification. Aryl hydrocarbon receptor (AhR) and nuclear factor erythroid 2-related factor-2 (Nrf2) are transcription factors that control NQO1 expression. Here, we investigated the effects of catalase overexpression on NQO1, Nrf2, and AhR expression. The levels of NQO1 mRNA and protein were comparable in MAECs isolated from wild-type and transgenic mice that overexpress human catalase (hCatTg). BaP treatment increased NQO1 mRNA and protein levels in both groups, with a significantly greater induction in hCatTg MAECs than in wild-type cells. BaP-induced NQO1 promoter activity was dramatically higher in hCatTg MAECs than in wild-type cells. Our data also showed that the basal level of AhR and the BaP-induced level of Nrf2 were significantly higher in hCatTg MAECs than in wild-type cells. Inhibition of specificity protein-1 (Sp1) binding to the AhR promoter region by mithramycin A reversed the enhancing effect of catalase overexpression on AhR expression. Knockdown of AhR by RNA interference diminished BaP-induced expression of Nrf2 and NQO1. Knockdown of Nrf2 significantly decreased NQO1 mRNA and protein levels in cells with or without BaP treatment. NQO1 promoter activity was abrogated by mutation of the Nrf2-binding site in this promoter. In contrast, mutation of the AhR-binding site in the NQO1 promoter did not affect the promoter activity. These results suggest that catalase overexpression upregulates BaP-induced NQO1 expression by enhancing the Sp1-AhR-Nrf2 signaling cascade.