Recent studies from our laboratory demonstrated that Egr-1 is upregulated in the rat duodenal mucosa during cysteamine-induced duodenal ulceration and that antisense egr-1 oligonucleotide aggravates the duodenal ulcers. This study was aimed to determine the effects of cysteamine on redox-sensitive Egr-1 transcriptional activity and on other thiol-containing proteins such as redox factor-1 (Ref-1) and thioredoxin (Trx). Here we demonstrate for the first time that cysteamine increases the expression and nuclear translocation of Egr-1, Ref-1, and Trx, and activates binding of Egr-1 to DNA. Moreover, we also show that Egr-1 forms a complex with other redox-sensitive transcription factors (e.g., AP-1, AP-2, NFATc, Sp1, PAX-5, MTF-1, c-Myb, and CREB) in rat duodenal mucosa and that cysteamine enhances the formation of these complexes. The antioxidant ebselen markedly elevated the nuclear Ref-1 expression and Egr-1/DNA binding, and decreased the ulcerogenic effect of cysteamine as did catalase. Thus, redox-sensitive signaling systems seem to play an important role in cysteamine-induced duodenal ulceration.