Adenovirus gene therapy is a promising tool in the clinical treatment of many genetic and acquired diseases. However, it has also caused pathogenic effects in organs such as the liver. The redox-sensitive transcription factors AP-1 and NF-kappaB have been implicated in these effects. To study the mechanisms of adenovirus-mediated AP-1 and NF-kappaB activation and the possible involvement of oxidative stress in adenovirus transduction, rats were injected with either replication-defective recombinant adenovirus with DNA containing the cytomegalovirus promoter region only (AdCMV), adenovirus containing human manganese-containing superoxide dismutase (MnSOD) cDNA (AdMnSOD), or vehicle. Compared to vehicle and AdCMV transduction, MnSOD gene transfer yielded a fivefold increase in liver MnSOD activity 7 days postinjection. Gel shift assay showed that AdCMV transduction induced DNA binding activity for AP-1 but not NF-kappaB. MnSOD overexpression abolished this activation. Western blotting analysis of c-Fos and c-Jun suggested that up-regulation of c-fos and c-jun gene expression does not directly contribute to the induction of AP-1 activation. Glutathione/glutathione disulfide ratios were decreased by adenovirus transduction and restored by MnSOD overexpression. The AP-1 binding activity that was induced by AdCMV was decreased by immunoprecipitation of Ref-1 protein. Ref-1 involvement was confirmed by restoration of AP-1 binding activity after the immunoprecipitated Ref-1 protein had been added back. AP-1 DNA binding activity was also elevated in control and AdMnSOD-injected rats after addition of the immunoprecipitated Ref-1 protein. These data indicate that cellular transduction by recombinant adenovirus stimulates AP-1 DNA binding activity. Furthermore, our results suggest that MnSOD overexpression decreases AP-1 DNA binding activity by regulating intracellular redox status, with the possible involvement of Ref-1 in this redox-sensitive pathway.