KEAP1 explained

Kelch-like ECH-associated protein 1 is a protein that in humans is encoded by the Keap1 gene.^[1]

Structure

See also: Kelch protein and Kelch motif. Keap1 has four discrete protein domains. The N-terminal Broad complex, Tramtrack and Bric-à-Brac (BTB) domain contains the Cys151 residue, which is one of the important cysteines in stress sensing. The intervening region (IVR) domain contains two critical cysteine residues, Cys273 and Cys288, which are a second group of cysteines important for stress sensing. A double glycine repeat (DGR) and C-terminal region domains collaborate to form a β-propeller structure, which is where Keap1 interacts with Nrf2.

Interactions

Keap1 has been shown to interact with Nrf2, a master regulator of the antioxidant response, which is important for the amelioration of oxidative stress.^{[2] [3] [4]}

Under quiescent conditions, Nrf2 is anchored in the cytoplasm through binding to Keap1, which, in turn, facilitates the ubiquitination and subsequent proteolysis of Nrf2. Such sequestration and further degradation of Nrf2 in the cytoplasm are mechanisms for the repressive effects of Keap1 on Nrf2. Keap1 is not only a tumor suppressor gene, but also a metastasis suppressor gene.^[5]

Recently, several interesting studies have also identified a hidden circuit in NRF2 regulations. In the mouse Keap1 (INrf2) gene, Lee and colleagues ^[6] found that an AREs located on a negative strand can subtly connect Nrf2 activation to Keap1 transcription. When examining NRF2 occupancies in human lymphocytes, Chorley and colleagues identified an approximately 700 bp locus within the KEAP1 promoter region was consistently top rank enriched, even at the whole-genome scale.^[7] These basic findings have depicted a mutually influenced pattern between NRF2 and KEAP1. NRF2-driven KEAP1 expression characterized in human cancer contexts, especially in human squamous cell cancers,^[8] depicted a new perspective in understanding NRF2 signaling regulation.

As a drug target

Because Nrf2 activation leads to a coordinated antioxidant and anti-inflammatory response, and Keap1 represses Nrf2 activation, Keap1 has become a very attractive drug target.^{[9] [10] [11] [12]}

A series of synthetic oleane triterpenoid compounds, known as antioxidant inflammation modulators (AIMs), are being developed by Reata Pharmaceuticals, Inc. and are potent inducers of the Keap1-Nrf2 pathway, blocking Keap1-dependent Nrf2 ubiquitination and leading to the stabilization and nuclear translocation of Nrf2 and subsequent induction of Nrf2 target genes. The lead compound in this series, bardoxolone methyl (also known as CDDO-Me or RTA 402), was in late-stage clinical trials for the treatment of chronic kidney disease (CKD) in patients with type 2 diabetes mellitus and showed an ability to improve markers of renal function in these patients. However, the Phase 3 trial was halted due to safety concerns.

Human health

Mutations in KEAP1 that result in loss-of-function are not linked to familial cancers, though they do predispose individuals to multinodular goiters. The proposed mechanism leading to goiter formation is that the redox stress experienced when the thyroid produces hormones selects for loss of heterozygosity of KEAP1, leading to the goiters.^[13]

Further reading

• Zhang DD . Mechanistic studies of the Nrf2-Keap1 signaling pathway . Drug Metabolism Reviews . 38 . 4 . 769–89 . 2007 . 17145701 . 10.1080/03602530600971974 . 10.1.1.600.2452 . 7627379 .
• Nagase T, Seki N, Tanaka A, Ishikawa K, Nomura N . Prediction of the coding sequences of unidentified human genes. IV. The coding sequences of 40 new genes (KIAA0121-KIAA0160) deduced by analysis of cDNA clones from human cell line KG-1 . DNA Research . 2 . 4 . 167–74, 199–210 . August 1995 . 8590280 . 10.1093/dnares/2.4.167 . free .
• Itoh K, Wakabayashi N, Katoh Y, Ishii T, Igarashi K, Engel JD, Yamamoto M . Keap1 represses nuclear activation of antioxidant responsive elements by Nrf2 through binding to the amino-terminal Neh2 domain . Genes & Development . 13 . 1 . 76–86 . January 1999 . 9887101 . 316370 . 10.1101/gad.13.1.76 .
• Dhakshinamoorthy S, Jaiswal AK . Functional characterization and role of INrf2 in antioxidant response element-mediated expression and antioxidant induction of NAD(P)H:quinone oxidoreductase1 gene . Oncogene . 20 . 29 . 3906–17 . June 2001 . 11439354 . 10.1038/sj.onc.1204506 . free .
• Sekhar KR, Spitz DR, Harris S, Nguyen TT, Meredith MJ, Holt JT, Gius D, Marnett LJ, Summar ML, Freeman ML, Guis D . 6 . Redox-sensitive interaction between KIAA0132 and Nrf2 mediates indomethacin-induced expression of gamma-glutamylcysteine synthetase . Free Radical Biology & Medicine . 32 . 7 . 650–62 . April 2002 . 11909699 . 10.1016/S0891-5849(02)00755-4 .
• Velichkova M, Guttman J, Warren C, Eng L, Kline K, Vogl AW, Hasson T . A human homologue of Drosophila kelch associates with myosin-VIIa in specialized adhesion junctions . Cell Motility and the Cytoskeleton . 51 . 3 . 147–64 . March 2002 . 11921171 . 10.1002/cm.10025 . free .
• Zipper LM, Mulcahy RT . The Keap1 BTB/POZ dimerization function is required to sequester Nrf2 in cytoplasm . The Journal of Biological Chemistry . 277 . 39 . 36544–52 . September 2002 . 12145307 . 10.1074/jbc.M206530200 . free .
• Sekhar KR, Yan XX, Freeman ML . Nrf2 degradation by the ubiquitin proteasome pathway is inhibited by KIAA0132, the human homolog to INrf2 . Oncogene . 21 . 44 . 6829–34 . October 2002 . 12360409 . 10.1038/sj.onc.1205905 . free .
• Bloom DA, Jaiswal AK . Phosphorylation of Nrf2 at Ser40 by protein kinase C in response to antioxidants leads to the release of Nrf2 from INrf2, but is not required for Nrf2 stabilization/accumulation in the nucleus and transcriptional activation of antioxidant response element-mediated NAD(P)H:quinone oxidoreductase-1 gene expression . The Journal of Biological Chemistry . 278 . 45 . 44675–82 . November 2003 . 12947090 . 10.1074/jbc.M307633200 . free .
• Cullinan SB, Zhang D, Hannink M, Arvisais E, Kaufman RJ, Diehl JA . Nrf2 is a direct PERK substrate and effector of PERK-dependent cell survival . Molecular and Cellular Biology . 23 . 20 . 7198–209 . October 2003 . 14517290 . 230321 . 10.1128/MCB.23.20.7198-7209.2003 .
• Colland F, Jacq X, Trouplin V, Mougin C, Groizeleau C, Hamburger A, Meil A, Wojcik J, Legrain P, Gauthier JM . 6 . Functional proteomics mapping of a human signaling pathway . Genome Research . 14 . 7 . 1324–32 . July 2004 . 15231748 . 442148 . 10.1101/gr.2334104 .
• Kobayashi A, Kang MI, Okawa H, Ohtsuji M, Zenke Y, Chiba T, Igarashi K, Yamamoto M . 6 . Oxidative stress sensor Keap1 functions as an adaptor for Cul3-based E3 ligase to regulate proteasomal degradation of Nrf2 . Molecular and Cellular Biology . 24 . 16 . 7130–9 . August 2004 . 15282312 . 479737 . 10.1128/MCB.24.16.7130-7139.2004 .
• Strachan GD, Morgan KL, Otis LL, Caltagarone J, Gittis A, Bowser R, Jordan-Sciutto KL . Fetal Alz-50 clone 1 interacts with the human orthologue of the Kelch-like Ech-associated protein . Biochemistry . 43 . 38 . 12113–22 . September 2004 . 15379550 . 3670950 . 10.1021/bi0494166 .
• Li X, Zhang D, Hannink M, Beamer LJ . Crystal structure of the Kelch domain of human Keap1 . The Journal of Biological Chemistry . 279 . 52 . 54750–8 . December 2004 . 15475350 . 10.1074/jbc.M410073200 . free .
• Zhang DD, Lo SC, Cross JV, Templeton DJ, Hannink M . Keap1 is a redox-regulated substrate adaptor protein for a Cul3-dependent ubiquitin ligase complex . Molecular and Cellular Biology . 24 . 24 . 10941–53 . December 2004 . 15572695 . 533977 . 10.1128/MCB.24.24.10941-10953.2004 .
• Li X, Zhang D, Hannink M, Beamer LJ . Crystallization and initial crystallographic analysis of the Kelch domain from human Keap1 . Acta Crystallographica. Section D, Biological Crystallography . 60 . Pt 12 Pt 2 . 2346–8 . December 2004 . 15583386 . 10.1107/S0907444904024825 . 2004AcCrD..60.2346L . 10.1.1.631.1273 .
• Furukawa M, Xiong Y . BTB protein Keap1 targets antioxidant transcription factor Nrf2 for ubiquitination by the Cullin 3-Roc1 ligase . Molecular and Cellular Biology . 25 . 1 . 162–71 . January 2005 . 15601839 . 538799 . 10.1128/MCB.25.1.162-171.2005 .
• Hosoya T, Maruyama A, Kang MI, Kawatani Y, Shibata T, Uchida K, Warabi E, Noguchi N, Itoh K, Yamamoto M . 6 . Differential responses of the Nrf2-Keap1 system to laminar and oscillatory shear stresses in endothelial cells . The Journal of Biological Chemistry . 280 . 29 . 27244–50 . July 2005 . 15917255 . 10.1074/jbc.M502551200 . free .

Notes and References

1. Web site: Entrez Gene: KEAP1 kelch-like ECH-associated protein 1.
2. Cullinan SB, Zhang D, Hannink M, Arvisais E, Kaufman RJ, Diehl JA . Nrf2 is a direct PERK substrate and effector of PERK-dependent cell survival . Molecular and Cellular Biology . 23 . 20 . 7198–209 . October 2003 . 14517290 . 230321 . 10.1128/mcb.23.20.7198-7209.2003 .
3. Shibata T, Ohta T, Tong KI, Kokubu A, Odogawa R, Tsuta K, Asamura H, Yamamoto M, Hirohashi S . 6 . Cancer related mutations in NRF2 impair its recognition by Keap1-Cul3 E3 ligase and promote malignancy . Proceedings of the National Academy of Sciences of the United States of America . 105 . 36 . 13568–73 . September 2008 . 18757741 . 2533230 . 10.1073/pnas.0806268105 . 2008PNAS..10513568S . free .
4. Wang XJ, Sun Z, Chen W, Li Y, Villeneuve NF, Zhang DD . Activation of Nrf2 by arsenite and monomethylarsonous acid is independent of Keap1-C151: enhanced Keap1-Cul3 interaction . Toxicology and Applied Pharmacology . 230 . 3 . 383–9 . August 2008 . 18417180 . 2610481 . 10.1016/j.taap.2008.03.003 .
5. Lignitto L, LeBoeuf SE, Homer H, Jiang S, Askenazi M, Karakousi TR, Pass HI, Bhutkar AJ, Tsirigos A, Ueberheide B, Sayin VI, Papagiannakopoulos T, Pagano M . 6 . Nrf2 Activation Promotes Lung Cancer Metastasis by Inhibiting the Degradation of Bach1 . Cell . 178 . 2 . 316–329.e18 . July 2019 . 31257023 . 10.1016/j.cell.2019.06.003 . 6625921 . free .
6. Lee OH, Jain AK, Papusha V, Jaiswal AK . An auto-regulatory loop between stress sensors INrf2 and Nrf2 controls their cellular abundance . The Journal of Biological Chemistry . 282 . 50 . 36412–20 . December 2007 . 17925401 . 10.1074/jbc.M706517200 . free .
7. Chorley BN, Campbell MR, Wang X, Karaca M, Sambandan D, Bangura F, Xue P, Pi J, Kleeberger SR, Bell DA . 6 . Identification of novel NRF2-regulated genes by ChIP-Seq: influence on retinoid X receptor alpha . Nucleic Acids Research . 40 . 15 . 7416–29 . August 2012 . 22581777 . 10.1093/nar/gks409 . 3424561 . free .
8. Tian Y, Liu Q, Yu S, Chu Q, Chen Y, Wu K, Wang L . NRF2-Driven KEAP1 Transcription in Human Lung Cancer . Molecular Cancer Research . 18 . 10 . 1465–1476 . October 2020 . 32571982 . 10.1158/1541-7786.MCR-20-0108 . 219989242 . free .
9. Abed DA, Goldstein M, Albanyan H, Jin H, Hu L . Discovery of direct inhibitors of Keap1-Nrf2 protein-protein interaction as potential therapeutic and preventive agents . Acta Pharmaceutica Sinica B . 5 . 4 . 285–99 . July 2015 . 26579458 . 4629420 . 10.1016/j.apsb.2015.05.008 .
10. Lu MC, Ji JA, Jiang ZY, You QD . The Keap1-Nrf2-ARE Pathway As a Potential Preventive and Therapeutic Target: An Update . Medicinal Research Reviews . 36 . 5 . 924–63 . September 2016 . 27192495 . 10.1002/med.21396 . 30047975 .
11. Deshmukh P, Unni S, Krishnappa G, Padmanabhan B . The Keap1-Nrf2 pathway: promising therapeutic target to counteract ROS-mediated damage in cancers and neurodegenerative diseases . Biophysical Reviews . 9 . 1 . 41–56 . February 2017 . 28510041 . 5425799 . 10.1007/s12551-016-0244-4 .
12. Kerr F, Sofola-Adesakin O, Ivanov DK, Gatliff J, Gomez Perez-Nievas B, Bertrand HC, Martinez P, Callard R, Snoeren I, Cochemé HM, Adcott J, Khericha M, Castillo-Quan JI, Wells G, Noble W, Thornton J, Partridge L . 6 . Direct Keap1-Nrf2 disruption as a potential therapeutic target for Alzheimer's disease . PLOS Genetics . 13 . 3 . e1006593 . March 2017 . 28253260 . 5333801 . 10.1371/journal.pgen.1006593 . free .
13. Wu. Warren L.. Papagiannakopoulos. Thales. 2020-03-09. The Pleiotropic Role of the KEAP1/NRF2 Pathway in Cancer. Annual Review of Cancer Biology. en. 4. 1. 413–435. 10.1146/annurev-cancerbio-030518-055627. 2472-3428. free. vanc.