Regulation of Nrf2 by a keap1-dependent E3 ubiquitin ligase

Abstract

Oxidative damage to biological macromolecules has been implicated in diverse pathophysiological processes, including cancer, neurodegeneration, aging and cardiovascular disease. The Nrf2 transcription factor regulates expression of ROS (reactive oxygen species)-scavenging enzymes and enables mammalian cells to counteract oxidative stress and maintain redox homeostasis. The Keap1 protein functions as a substrate adaptor for a Cul3-RING dependent E3 ubiquitin ligase complex and targets Nrf2 for proteasome-mediated degradation under homeostatic conditions. The Keap1-Cul3-RING ubiquitin ligase is inactivated following exposure of cells to oxidative stress or electrophilic chemicals, resulting in accumulation of Nrf2 and activation of Nrf2-dependent cytoprotective gene expression. The Keap1-Cul3-RING ubiquitin ligase complex is modulated at multiple levels. Neddylation of Cul3 on Lys 712 and CAND1-dependent cyclical assembly and disassembly of the Keap1-Cul3-RING ubiquitin ligase are required for optimal activity of the ligase. A number of critical amino acid residues located within the substrate-binding pocket of Kelch [beta]-propeller domain of Keap1 make key contacts with the conserved (D/N)xE(T/S)GE motifs in the substrate protein. A distinct subpopulation of the Keap1-Nrf2 complex is anchored at mitochondria by PGAM5 and may thereby facilitate communication between the nuclear anti-oxidant genes that are regulated by Nrf2 and ROS produced by mitochondria.