Nrf2: control of sensitivity to carcinogens.

Induction of enzymes that enhance the detoxication of chemical carcinogens has been a broadly effective strategy for chemoprevention of experimental carcinogenesis in rodent models. Several inducing agents are now in clinical trials to evaluate utility for prevention of cancers associated with unavoidable high exposures to environmental carcinogens. The successes of these pre-clinical and clinical interventions lead to studies to define the molecular basis for protection by these agents, which now include phenolic antioxidants, dithiolethiones, isothiocyanates, and triterpenoids. In the mid-1990s, the NF-E2-related factor 2 (Nrf2) transcription factor was identified as a key regulator of the inducible expression of enzymes such as glutathione S-transferases and NAD(P)H: quinone oxidoreductase in catalyzing the detoxication of reactive electrophiles and oxidants that contribute to the formation of mutations and ultimately cancers. Nrf2 is now recognized to regulate a broad cytoprotective, transcriptional response leading to prevention of damage to DNA, proteins and lipids; recognition, repair and removal of macromolecular damage; and tissue renewal following toxic assaults. Highlighting the importance of this pathway as a determinant of susceptibility to carcinogenesis, multiple studies now demonstrate enhanced incidence, multiplicity, and/or tumor burden in Nrf2-disrupted mice compared to wild-type in models of inflammation and colon cancer, bladder cancer, lung disease and cancer, stomach cancer, mammary cancer, skin cancer, and hepatocarcinogenesis.