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

TLDR

Nrf2 drives ARE‑mediated induction of phase II detoxifying and oxidative stress genes, and its cytoplasmic regulator Keap1 is homologous to the Drosophila actin‑binding protein Kelch. The study proposes that Keap1 and Nrf2 form a sensor for oxidative stress that mediates nuclear shuttling of Nrf2 to activate transcription. Keap1 binds the conserved N‑terminal regulatory domain of Nrf2, inhibiting its activity until electrophilic agents relieve this inhibition, allowing Nrf2 to enter the nucleus. Keap1 was identified as a suppressor of Nrf2 that binds its Neh2 domain; electrophiles antagonize this inhibition, enabling Nrf2 nuclear translocation and subsequent induction of phase II antioxidant genes.

Abstract

Transcription factor Nrf2 is essential for the antioxidant responsive element (ARE)-mediated induction of phase II detoxifying and oxidative stress enzyme genes. Detailed analysis of differential Nrf2 activity displayed in transfected cell lines ultimately led to the identification of a new protein, which we named Keap1, that suppresses Nrf2 transcriptional activity by specific binding to its evolutionarily conserved amino-terminal regulatory domain. The closest homolog of Keap1 is a Drosophila actin-binding protein called Kelch, implying that Keap1 might be a Nrf2 cytoplasmic effector. We then showed that electrophilic agents antagonize Keap1 inhibition of Nrf2 activity in vivo, allowing Nrf2 to traverse from the cytoplasm to the nucleus and 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 in turn to the induction of phase II enzyme and antioxidative stress genes in response to electrophiles and reactive oxygen species.