Our previous study of interleukin-2 (IL-2) signaling found that redox factor-1 (Ref-l) mRNA was upregulated by IL-2. in this study,we further studied the function of Ref-l in the potential redox regulation of IL-2 signaling in BA/F3 beta cells. Western blot analysis confirmed that IL-2 stimulation increases Ref-l protein. Flow cytometric assay by using 2',7'-dichlorofluorescin diacetate indicated that IL-2 stimulation results in an oxidative shift of intracellular environment. However, IL-2-induced activator protein-1 (AP-1) is oxidation-sensitive. Gel shift assays of nuclear extracts immunodepleted of Ref-l protein demonstrated that IL-2-induced AP-1 DNA binding is dependent on the presence of Ref-l. This was further confirmed by the restoration of AP-1 DNA binding upon the re-addition of immunoprecipitated Ref-l. Additionally, reporter gene assays showed that AP-1 transcriptional activity was enhanced by the overexpression of Ref-l and attenuated by the introduction of antisense Ref-l. These results suggest that the induction of Ref-l ensures AP-1 activation in the intracellular oxidative environment of IL-2-stimulated BA/F3 beta cells,