KEAP1 is a substrate adaptor protein for a CUL3 (603136)-dependent ubiquitin ligase complex that functions as a sensor for thiol-reactive chemopreventive compounds and oxidative stress (Lo and Hannink, 2006).

Transcription factor NRF2 (600492), which is homologous to the chicken Ech protein, is essential for the expression of detoxifying enzymes and oxidative stress-inducible genes to protect against DNA damage. Using a yeast 2-hybrid screen of a mouse embryo cDNA library with mouse Nrf2 as bait, Itoh et al. (1999) isolated cDNAs encoding a protein they named 'Kelch-like Ech-associated protein-1,' or Keap1, due to its resemblance to the Drosophila Kelch protein. Sequence analysis predicted that the 624-amino acid mouse protein is 94% identical to the 624-amino acid human KIAA0132 protein identified by Nagase et al. (1995). Keap1 contains a central BTB/POZ domain and a C-terminal double glycine repeat (DGR), or Kelch, module. By RT-PCR analysis, Nagase et al. (1995) detected strong expression of KIAA0132 in heart and skeletal muscle, with lower expression in brain, placenta, lung, liver, testis, ovary, small intestine, and colon, and weaker or undetectable expression in other tissues.

Nagase et al. (1995) mapped the KIAA0132 gene (KEAP1) to chromosome 19 by analysis of a human-rodent hybrid cell panel.

Using yeast 2-hybrid and BIAcore analyses of mutant Keap1, Itoh et al. (1999) showed that the Kelch motifs of Keap1 interact with the Neh2 domain of Nrf2 and that this interaction is required for the repression of Nrf2 by Keap1. Fluorescence microscopy demonstrated that Keap1 is expressed in the cytoplasm with Nrf2. In the presence of the electrophilic agent diethylmalate, Nrf2 activity was released from Keap1 and Nrf2 translocated to the nucleus.

Eades et al. (2011) found that microRNA-200A (MIR200A; 612090) bound to the 3-prime UTR of the KEAP1 transcript, leading to degradation of the mRNA. Epigenetic silencing of MIR200A in breast cancer cells resulted in KEAP1 dysregulation, inhibition of NRF2 transcriptional activity, and reduced expression of NQO1 (125860), a detoxifying NRF2 target gene. Overexpression of MIR200A in human breast cancer cells or treatment of a mouse model of breast cancer with a histone deacetylase inhibitor enhanced MIR200A-dependent KEAP1 downregulation and restored NRF2 expression.

Using mass spectrometric analysis and database analysis to identify transcripts encoding proteins other than NRF2 that copurified with KEAP1 from the MD-MB-231 breast carcinoma cell line, Lo and Hannink (2006) identified 2 splice variants of PGAM5 (614939). Protein interaction assays and mutation analysis revealed that the putative N-terminal KEAP1-binding motif of both PGAM5 isoforms interacted with the Kelch domain of KEAP1 in transfected HEK293T cells. Coexpression of KEAP1 with the long isoform of PGAM5 (PGAM5L) resulted in PGAM5L ubiquitination and reduced PGAM5L half-life and total protein content. Coexpression of CUL3 and RBX1 (603814) markedly induced KEAP1-dependent PGAML ubiquitination, and proteasome inhibition blocked KEAP1-dependent PGAM5L degradation. Oxidative stress or treatment of cells with the chemotherapeutic isothiocyanate sulforaphane inhibited KEAP1-dependent PGAM5L ubiquitination and increased steady-state PGAM5L protein levels.

Mills et al. (2018) showed that itaconate, an endogenous metabolite, is required for the activation of the antiinflammatory transcription factor NRF2 (600492) by lipopolysaccharide in mouse and human macrophages. Mills et al. (2018) found that itaconate directly modifies proteins via alkylation of cysteine residues. Itaconate alkylates cysteine residues 151, 257, 288, 273, and 297 on the protein KEAP1 enabling NRF2 to increase the expression of downstream genes with antioxidant and antiinflammatory capacities. The activation of NRF2 is required for the antiinflammatory action of itaconate. Mills et al. (2018) described the use of a cell-permeable itaconate derivative, 4-octyl itaconate, which is protective against lipopolysaccharide-induced lethality in vivo and decreases cytokine production. The authors showed that type I interferons boost the expression of IRG1 (615275) and itaconate production. Itaconate production limits the type I interferon response, indicating a negative feedback loop that involves interferons and itaconate. Mills et al. (2018) concluded that itaconate is a crucial antiinflammatory metabolite that acts via NRF2 to limit inflammation and modulate type I interferons.

Bollong et al. (2018) identified a small-molecule inhibitor of the glycolytic enzyme PGK1 (311800), and revealed a direct link between glycolysis and NRF2 signaling. Inhibition of PGK1 resulted in accumulation of the reactive metabolite methylglyoxal, which selectively modified KEAP1 to form a methylimidazole crosslink between proximal cysteine and arginine residues. This posttranslational modification resulted in the dimerization of KEAP1, the accumulation of NRF2, and activation of the NRF2 transcriptional program. Bollong et al. (2018) concluded that their results demonstrated the existence of direct interpathway communication between glycolysis and the KEAP1-NRF2 transcriptional axis, and provided insight into the metabolic regulation of the cellular stress response.

Cai et al. (2023) found that acetaminophen (APAP) treatment downregulated Usp25 (604736) expression in a mouse model of acute APAP liver toxicity, whereas Usp25 knockout protected liver from APAP-induced injury. Further analysis in mouse indicated that Usp25 negatively regulated Nrf2 through Keap1 in the Keap1-Nrf2 axis in defense against oxidative assaults. Analysis in human cells showed that USP25 interacted with KEAP1, with the interaction mediated by the DGR domain of KEAP1 and the C-terminal domain of USP25. By interacting with KEAP1, USP25 deubiquitinated KEAP1 and thereby protected it from subsequent degradation. In the absence of Usp25 in mouse, Keap1 was downregulated and Nrf2 was stabilized, leading to protection from APAP-induced liver injury. Pharmacologic inhibition of Usp25 effectively attenuated APAP-induced liver injury in mice and reduced mortality from a lethal dose of APAP.

Padmanabhan et al. (2006) resolved the crystal structure of the 6-bladed Kelch repeat and the C-terminal region of mouse Keap1. Extensive inter- and intrablade hydrogen bonds maintained the structural integrity and proper association of Keap1 with Nrf2. A peptide containing the ETGE motif of Nrf2 bound the beta propeller of Keap1 at the entrance of the central cavity on the bottom side via electrostatic interactions with conserved arginines. Padmanabhan et al. (2006) identified 2 mutations in cell lines from lung cancer patients that disrupted the interaction between Keap1 and Nrf2, thus reducing the ability of Keap1 to repress Nrf2 transcriptional activity.

Using molecular evolutionary analysis, Castiglione et al. (2025) showed that the codon for a conserved ancestral residue that likely had functional effects, arg15 (R15), was replaced with a premature stop codon (TGA) in horse Keap1, predicting a truncated and nonfunctional Keap1 protein. This mutation was completely conserved across the Equus genus. However, horse Keap1 maintained its regulatory function as an inducible Nrf2 repressor, despite the presence of the stop codon. Mass spectrometric analysis confirmed read-through of the premature stop codon, which was translated as cys15 (C15), giving rise to a full-length Keap1 protein. Further analysis demonstrated that multiple components of the UGA recoding machinery were functionally altered in horses. The resulting Keap1 with the R15C change had increased Nrf2 activity and cellular resistance to oxidative damage, suggesting that R15C evolved as an adaptation to improve antioxidant function and redox homeostasis in horses. Cell-based assays showed that horse cells displayed enhanced Nrf2 activity and redox homeostasis relative to multiple other species, as the R15C Keap1 protein accelerated oxygen metabolism and ATP production by enhancing Nrf2 activity.

Transcription factor NRF2 (600492) regulates a battery of detoxifying and antioxidant genes, and KEAP1 represses NRF2 function. Wakabayashi et al. (2003) found that Keap1-deficient mice died postnatally, probably from malnutrition resulting from hyperkeratosis in the esophagus and forestomach. Nrf2 activity affects the expression levels of several squamous epithelial genes. Biochemical data showed that, without Keap1, Nrf2 constitutively accumulates in the nucleus to stimulate transcription of cytoprotective genes. Breeding to Nrf2-deficient mice reversed the phenotypic Keap1 deficiencies. These experiments showed that Keap1 acts upstream of Nrf2 in the cellular response to oxidative and xenobiotic stress.

Wakabayashi et al. (2003) observed that the transient scaling phenotype of Keap1 -/- mouse skin is similar to that of autosomal recessive congenital ichthyosis (ARCI). In a Finnish kindred, Virolainen et al. (2000) identified an ARCI locus corresponding to 19p13.2-p13.1 (see ARCI5; 604777). The human KEAP1 locus is located at the same chromosomal position as this autosomal recessive congenital ichthyosis locus. Thus, KEAP1 may have some relationship to congenital ichthyosis. The scaling of the reported Finnish cases was mild, as in the scaling phenotype of the Keap1 mutants, but the neonatal onset of the disorder in Keap1 mutants differed from the human disorder.