Lower Induction of P53 and Decreased Apoptosis in NQO1-null Mice Lead to Increased Sensitivity to Chemical-induced Skin Carcinogenesis

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a cytosolic protein that catalyzes metabolic detoxification of quinones and protects cells against redox cycling and oxidative stress. NQO1-null mice deficient in NQO1 protein showed increased sensitivity to 7,12-dimethylbenz(a)anthracene- and benzo(a)pyrene-induced skin carcinogenesis. In the present studies, we show that benzo(a)pyrene metabolite benzo(a)pyrene-trans-7,8-dihydrodiol-9,10-epoxide and not benzo(a)pyrene quinones contributed to increased benzo(a) pyrene-induced skin tumors in NQO1-null mice. An analysis of untreated skin revealed an altered intracellular redox state due to accumulation of NADH and reduced levels of NAD/NADH in NQO1-null mice as compared with wild-type mice. Treatment with benzo(a)pyrene failed to significantly increase p53 and apoptosis in the skin of NQO1-null mice when compared with wild-type mice. These results led to the conclusion that altered intracellular redox state along with lack of induction of p53 and decreased apoptosis plays a significant role in increased sensitivity of NQO1-null mice to benzo(a)pyrene-induced skin cancer.