Oxidative and Electrophilic Stresses Activate Nrf2 through Inhibition of Ubiquitination Activity of Keap1

Abstract

The Keap1-Nrf2 system is the major regulatory pathway of cytoprotective gene expression against oxidative and/or electrophilic stresses. Keap1 acts as a stress sensor protein in this system. While Keap1 constitutively suppresses Nrf2 activity under unstressed conditions, oxidants or electrophiles provoke the repression of Keap1 activity, inducing the Nrf2 activation. However, the precise molecular mechanisms behind the liberation of Nrf2 from Keap1 repression in the presence of stress remain to be elucidated. We hypothesized that oxidative and electrophilic stresses induce the nuclear accumulation of Nrf2 by affecting the Keap1-mediated rapid turnover of Nrf2, since such accumulation was diminished by the protein synthesis inhibitor cycloheximide. While both the Cys273 and Cys288 residues of Keap1 are required for suppressing Nrf2 nuclear accumulation, treatment of cells with electrophiles or mutation of these cysteine residues to alanine did not affect the association of Keap1 with Nrf2 either in vivo or in vitro. Rather, these treatments impaired the Keap1-mediated proteasomal degradation of Nrf2. These results support the contention that Nrf2 protein synthesized de novo after exposure to stress accumulates in the nucleus by bypassing the Keap1 gate and that the sensory mechanism of oxidative and electrophilic stresses is closely linked to the degradation mechanism of Nrf2.

Nrf2 target genes are induced under marginal selenium-deficiency

“…High concentrations of certain selenium compounds or metabolites may directly activate the Nrf2 pathway by modifying critical thiols in Keap1. Reactive thiol groups can also be modified by oxidation [22,29] a situation which prevails in selenium-deficiency [52,55]. Whether a higher oxidative status in the moderately selenium-deficient mice was responsible for the induced Nrf2 target gene expression needs to be clarified.…”

Dietary myo-inositol modulates immunity through antioxidant activity and the Nrf2 and E2F4/cyclin signalling factors in the head kidney and spleen following infection of juvenile fish with Aeromonas hydrophila

“…Oxidative damage occurs in part when antioxidant enzyme gene transcription does not produce sufficient enzymes to combat the excessive ROS in organisms [18,19]. Gene transcription of antioxidant enzymes is typically regulated by the Nrf2 (NF-E2-related factor 2) signalling pathway in fish [20]. Therefore, maintaining the normal antioxidant status and Nrf2 signalling in the head kidney and spleen is very important.…”

Role of Nrf2 Dysfunction in Uremia-Associated Intestinal Inflammation and Epithelial Barrier Disruption

“…In the cytoplasm, Keap1 (Kelchlike ECH-associated protein 1) binds to Nrf2 and facilitates its ubiquitination and thereby prevents its translocation to the nucleus. Increase in intracellular reactive oxygen species enhances nuclear translocation of Nrf2 and expression of its target genes by modifying the reactive cysteine residues on Keap1, thus limiting its ability to bind Nrf2 [29,30]. Oxidative stress and inflammation in CKD are associated with marked elevation of Keap1 abundance, impaired Nrf2 activity, and significant down-regulation of Nrf2 target gene products in the kidney and vascular tissues [31,32].…”