Thioredoxin nuclear translocation and interaction with redox factor-1 activates the activator protein-1 transcription factor in response to ionizing radiation

Thioredoxin (TRX) is a cytoplasmic, redox-sensitive signaling factor believ ed to participate in the regulation of nuclear transcription factors mediat ing cellular responses to environmental stress. Activation of the activator protein (AP)-1 transcription factor is thought to be mediated in part by r edox-sensitive interactions between the nuclear signaling protein redox fac tor-1 (Ref-1) and TRX. In this study, the role of TRX and Ref-1 in the acti vation of the AP-1 complex was examined in HeLa and Jurkat cell lines expos ed to ionizing radiation (IR). After exposure to IR, nuclear levels of immu noreactive TRX increased, accompanied by an increase in AP-1 DNA binding ac tivity. It was shown that a physical interaction between Ref-1 and TRX occu rs within the nucleus and is enhanced after exposure to IR. Furthermore, TR X immunoprecipitated from irradiated cells was capable of activating AP-1 D NA binding activity in nonirradiated nuclear extracts. In addition, immunod epletion of Ref-1 from nuclear extracts demonstrated that the increase in A P-I DNA binding activity after IR was also dependent upon the presence of R ef-1 from irradiated cells. Finally, the ability of both TRX and Ref-1 from irradiated cells to stimulate AP-1 DNA binding in nonirradiated nuclear ex tracts was abolished by chemical oxidation and restored by chemical reducti on. These results indicate that, in response to IR, TRX and Ref-1 undergo c hanges in redox state that contribute to the activation of AP-1 DNA binding activity. These experiments suggest that a redox-sensitive signaling pathw ay leading from TRX to Ref-1 to the AP-1 complex participates in the up-reg ulation of DNA binding activity in response to ionizing radiation.