title: Src subfamily kinases regulate nuclear export and degradation of transcription factor Nrf2 to switch off Nrf2-mediated antioxidant activation of cytoprotective gene expression.
abstract: Nrf2 (NF-E2-related factor 2) is a nuclear transcription factor that in response to chemical and radiation stress regulates coordinated induction of a battery of cytoprotective gene expressions leading to cellular protection. In this study, we investigated the role of Src kinases in the regulation of Nrf2 and downstream signaling. siRNA-mediated inhibition of Fyn, Src, Yes, and Fgr, but not Lyn, in mouse hepatoma Hepa-1 cells, led to nuclear accumulation of Nrf2 and up-regulation of Nrf2 downstream gene expression. Mouse embryonic fibroblasts with combined deficiency of Fyn/Src/Yes/Fgr supported results from siRNA. In addition, steady-state overexpression of Fyn, Src, and Yes phosphorylated Nrf2Tyr568 that triggered nuclear export and degradation of Nrf2 and down-regulation of Nrf2 downstream gene expression. Exposure of cells to antioxidant, oxidant, or UV radiation increased nuclear import of Fyn, Src, and Yes kinases, which phosphorylated Nrf2Tyr568 resulting in nuclear export and degradation of Nrf2. Further analysis revealed that stress-activated GSK3β acted upstream to the Src kinases and phosphorylated the Src kinases, leading to their nuclear localization and Nrf2 phosphorylation. The overexpression of Src kinases in Hepa-1 cells led to decreased Nrf2, increased apoptosis, and decreased cell survival. Mouse embryonic fibroblasts deficient in Src kinases showed nuclear accumulation of Nrf2, induction of Nrf2 and downstream gene expression, reduced apoptosis, and increased cell survival. The studies together demonstrate that Src kinases play a critical role in nuclear export and degradation of Nrf2, thereby providing a negative feedback mechanism to switch off Nrf2 activation and restore normal cellular homeostasis.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, Maryland 21201.
authors.forename: Suryakant K
authors.initials: SK
authors.lastname: Niture
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, Maryland 21201.
authors.forename: Abhinav K
authors.initials: AK
authors.lastname: Jain
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, Maryland 21201.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Shelton
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, Maryland 21201. Electronic address: ajaiswal@som.umaryland.edu.
authors.forename: Anil K
authors.initials: AK
authors.lastname: Jaiswal
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D000975:Antioxidants / Q000378:metabolism* / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D014466:Ultraviolet Rays / Q000009:adverse effects; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; C495636:Nfe2l2 protein, mouse; D016877:Oxidants; D019061:src-Family Kinases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3