title: Thioredoxin reductase regulates AP-1 activity as well as thioredoxin nuclear localization via active cysteines in response to ionizing radiation.
abstract: A recently identified class of signaling factors uses critical cysteine motif(s) that act as redox-sensitive 'sulfhydryl switches' to reversibly modulate specific signal transduction cascades regulating downstream proteins with similar redox-sensitive sites. For example, signaling factors such as redox factor-1 (Ref-1) and transcription factors such as the AP-1 complex both contain redox-sensitive cysteine motifs that regulate activity in response to oxidative stress. The mammalian thioredoxin reductase-1 (TR) is an oxidoreductase selenocysteine-containing flavoprotein that also appears to regulate multiple downstream intracellular redox-sensitive proteins. Since ionizing radiation (IR) induces oxidative stress as well as increases AP-1 DNA-binding activity via the activation of Ref-1, the potential roles of TR and thioredoxin (TRX) in the regulation of AP-1 activity in response to IR were investigated. Permanently transfected cell lines that overexpress wild type TR demonstrated constitutive increases in AP-1 DNA-binding activity as well as AP-1-dependent reporter gene expression, relative to vector control cells. In contrast, permanently transfected cell lines expressing a TR gene with the active site cysteine motif deleted were unable to induce AP-1 activity or reporter gene expression in response to IR. Transient genetic overexpression of either the TR wild type or dominant-negative genes demonstrated similar results using a transient assay system. One mechanism through which TR regulates AP-1 activity appears to involve TRX sub-cellular localization, with no change in the total TRX content of the cell. These results identify a novel function of the TR enzyme as a signaling factor in the regulation of AP-1 activity via a cysteine motif located in the protein.
authors.affiliation: Radiation Oncology Branch, Radiation Oncology Sciences Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Shervin
authors.initials: S
authors.lastname: Karimpour
authors.forename: Junyang
authors.initials: J
authors.lastname: Lou
authors.forename: Lilie L
authors.initials: LL
authors.lastname: Lin
authors.forename: Luis M
authors.initials: LM
authors.lastname: Rene
authors.forename: Lucio
authors.initials: L
authors.lastname: Lagunas
authors.forename: Xinrong
authors.initials: X
authors.lastname: Ma
authors.forename: Sreenivasu
authors.initials: S
authors.lastname: Karra
authors.forename: C Matthew
authors.initials: CM
authors.lastname: Bradbury
authors.forename: Stephanie
authors.initials: S
authors.lastname: Markovina
authors.forename: Prabhat C
authors.initials: PC
authors.lastname: Goswami
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Spitz
authors.forename: Kiichi
authors.initials: K
authors.lastname: Hirota
authors.forename: Dhananjaya V
authors.initials: DV
authors.lastname: Kalvakolanu
authors.forename: Junji
authors.initials: J
authors.lastname: Yodoi
authors.forename: David
authors.initials: D
authors.lastname: Gius
mesh_terms: D003545:Cysteine; D006367:HeLa Cells; D006801:Humans; D015398:Signal Transduction / Q000235:genetics; D054481:Thioredoxin Reductase 1; D013880:Thioredoxin-Disulfide Reductase / Q000235:genetics / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D018808:Transcription Factor AP-1; D013879:Thioredoxins; C516124:TXNRD1 protein, human; D054481:Thioredoxin Reductase 1; D013880:Thioredoxin-Disulfide Reductase; D003545:Cysteine