Keap1 regulates the oxidation-sensitive shuttling of Nrf2 into and out of the nucleus via a Crm1-dependent nuclear export mechanism.
Keap1 is a negative regulator of Nrf2, a transcription factor essential for antioxidant response element (ARE)-mediated gene expression. We find that Keap1 sequesters Nrf2 in the cytoplasm, not by docking it to the actin cytoskeleton but instead through an active Crm1/exportin-dependent nuclear export mechanism. Deletion and mutagenesis studies identified a nuclear export signal (NES) in the intervening region of Keap1 comprised of hydrophobic leucine and isoleucine residues in agreement with a traditional NES consensus sequence. Mutation of the hydrophobic amino acids resulted in nuclear accumulation of both Keap1 and Nrf2, as did treatment with the drug leptomycin B, which inactivates Crm1/exportin. ARE genes were partially activated under these conditions, suggesting that additional oxidation-sensitive elements are required for full activation of the antioxidant response. Based on these data, we propose a new model for regulation of Nrf2 by Keap1. Under normal conditions, Keap1 and Nrf2 are complexed in the cytoplasm where they are targeted for degradation. Oxidative stress inactivates Keap1's NES, allowing entry of both Keap1 and Nrf2 into the nucleus and transcriptional transactivation of ARE genes.
Velichkova
Michaella
M
University of California at San Diego, Division of Biological Sciences, Section of Cell and Developmental Biology, 2129 Bonner Hall, MC 0368, 9500 Gilman Drive, La Jolla, CA 92093-0368, USA. velichko@biomail.ucsd.edu
Hasson
Tama
T
D021581:Active Transport, Cell Nucleus; D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D003599:Cytoskeleton / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006801:Humans; D028884:Karyopherins / Q000378:metabolism / Q000502:physiology*; D000072019:Kelch-Like ECH-Associated Protein 1; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D051267:NF-E2-Related Factor 2; D019913:Nuclear Localization Signals / Q000235:genetics / Q000502:physiology; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism / Q000502:physiology*; D020218:Response Elements; D015534:Trans-Activators / Q000032:analysis / Q000378:metabolism*; D000097606:Exportin 1 Protein
D048868:Adaptor Proteins, Signal Transducing; D000975:Antioxidants; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D005231:Fatty Acids, Unsaturated; D028884:Karyopherins; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; D019913:Nuclear Localization Signals; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D000097606:Exportin 1 Protein; C117301:Keap1 protein, mouse; C495635:NFE2L2 protein, human; C495636:Nfe2l2 protein, mouse; C495637:Nfe2l2 protein, rat; C038753:leptomycin B