Nrf2 and p53 cooperatively protect against BBN-induced urinary bladder carcinogenesis

Nuclear factor-erythroid 2 (NF-E2)-related factor 2 (Nrf2), a transcription factor that regulates inducible expression of detoxifying enzymes, is critical in preventing N-nitrosobutyl(4-hydroxybutyl)amine (BBN)-induced urinary bladder carcinogenesis. To explore whether Nrf2 and the tumor suppressor p53 cooperatively act in tumor prevention, we investigated the susceptibility of Nrf2^-/-::p53^+/- mice to BBN-induced urinary bladder carcinogenesis. The incidence of BBN-induced urinary bladder carcinoma was 63.0% in Nrf2^-/- mice (P = 0.115), 75.8% in p53^+/- mice (P < 0.01) and 89.6% in Nrf2^-/-::p53^+/- mice (P < 0.01) compared with 37.9% in wild-type. Higher incidence of carcinoma was observed in Nrf2^-/-::p53^+/- mice when compared with either Nrf2^-/- (P < 0.01) or p53^+/- mice (P = 0.382). Similarly, muscular invasive carcinoma incidence was higher in Nrf2^-/-::p53^+/- mice (62.0%) than either wild-type (6.9%, P < 0.01), p53^+/- (38.0%, P = 0.110) or Nrf2^-/- mice (3.7%, P < 0.01). Furthermore, urinary concentrations of N-nitrosobutyl(3-carboxypropyl)amine, a proximate carcinogen of BBN, were only increased when Nrf2 but not p53 was disrupted. These results demonstrate that tumor susceptibility is synergistically exacerbated in Nrf2^-/-::p53^+/- mice due to poor detoxification and accelerated proliferation in comparison with either single mutant alone. BBN administration increased p53-mediated expression of p21, Mdm2 and Bax, and the inducible expression of p21 was significantly enhanced in Nrf2^-/- mice. Conversely, modest increases in NAD(P)H dehydrogenase, quinone 1 (NQO1) and uridine diphosphate (UDP) glucuronosyltransferase 1A6 (UGT1A6) expression were observed in p53^+/- compared with those of wild-type mice after BBN exposure. These results thus reveal potential interactions between p53 and Nrf2 and their gene batteries, and indicate that both factors cooperatively contribute to tumor prevention.