Thioredoxin reductase regulates AP-1 activity as well as thioredoxin nuclear localization via active cysteines in response to ionizing radiation.
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.
Karimpour
Shervin
S
Radiation Oncology Branch, Radiation Oncology Sciences Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Lou
Junyang
J
Lin
Lilie L
LL
Rene
Luis M
LM
Lagunas
Lucio
L
Ma
Xinrong
X
Karra
Sreenivasu
S
Bradbury
C Matthew
CM
Markovina
Stephanie
S
Goswami
Prabhat C
PC
Spitz
Douglas R
DR
Hirota
Kiichi
K
Kalvakolanu
Dhananjaya V
DV
Yodoi
Junji
J
Gius
David
D
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*
D018808:Transcription Factor AP-1; D013879:Thioredoxins; C516124:TXNRD1 protein, human; D054481:Thioredoxin Reductase 1; D013880:Thioredoxin-Disulfide Reductase; D003545:Cysteine