Keap1 represses nuclear activation of antioxidant responsive elements by Nrf2 through binding to the amino-terminal Neh2 domain

Transcription factor Nrf2 is essential for the antioxidant responsive eleme nt (ARE)-mediated induction of phase LI detoxifying and oxidative stress en zyme genes. Detailed analysis of differential Nrf2 activity displayed in tr ansfected cell lines ultimately led to the identification of a new protein, which we named Keap1, that suppresses Nrf2 transcriptional activity by spe cific binding to its evolutionarily conserved amino-terminal regulatory dom ain. The closest homolog of Keap1 is a Drosophila actin-binding protein cal led Reich, implying that Keap1 might be a Nrf2 cytoplasmic effector. We the n showed that electrophilic agents antagonize Keap1 inhibition of Nrf2 acti vity in vivo, allowing Nrf2 to traverse from the cytoplasm to the nucleus a nd potentiate the ARE response. We postulate that Keap1 and Nrf2 constitute a crucial cellular sensor for oxidative stress, and together mediate a key step in the signaling pathway that leads to transcriptional activation by this novel Nrf2 nuclear shuttling mechanism. The activation of Nrf2 leads i n turn to the induction of phase II enzyme and antioxidative stress genes i n response to electrophiles and reactive oxygen species.