The Antioxidant Defense System Keap1-Nrf2 Comprises a Multiple Sensing Mechanism for Responding to a Wide Range of Chemical Compounds

Abstract

Animals have evolved defense systems for surviving in a chemically diverse environment. Such systems should demonstrate plasticity, such as adaptive immunity, enabling a response to even unknown chemicals. The antioxidant transcription factor Nrf2 is activated in response to various electrophiles and induces cytoprotective enzymes that detoxify them. We report here the discovery of a multiple sensing mechanism for Nrf2 activation using zebrafish and 11 Nrf2-activating compounds. First, we showed that six of the compounds tested specifically target Cys-151 in Keap1, the ubiquitin ligase for Nrf2, while two compounds target Cys-273. Second, in addition to Nrf2 and Keap1, a third factor was deemed necessary for responding to three of the compounds. Finally, we isolated a zebrafish mutant defective in its response to seven compounds but not in response to the remaining four. These results led us to categorize Nrf2 activators into six classes and hypothesize that multiple sensing allows enhanced plasticity in the system.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

This study was supported by Grants-in-Aid from the Japan Science and Technology Corp. (ERATO) (M.Y.) and the Ministry of Education, Science, Sports, and Culture of Japan (M.K. and M.Y.).

We thank T. Kensler and K. Uchida for kind providing D3T and Ebs, respectively, and Y. Kishimoto for technical advice. We also thank T. Kinoshita, H. Niu, M. Oikawa, T. Shimokoube, and Y. Terashita for help in mutant screening and fish maintenance; R. Ide, T. Suzuki, M. Takeuchi, K. Tong, and T. Tsujita for help with experiments and for discussions; and K. Igarashi, H. Kakeya, A. Kobayashi, H. Motohashi, D. Sumi, and T. O'Connor for critical reading of the manuscript.