Post-translational regulation of AP-1 transcription factor DNA-binding activity in the rat conceptus.

Activator protein-1 (AP-1) transcription factor DNA binding is induced during transient oxidative stress in the midorganogenesis rat conceptus in culture. L-2-Oxothiazolidine-4-carboxylate (OTC), a cysteine prodrug, prevented oxidative stress and the induction of AP-1 binding activity in the embryo but not in the yolk sac. Because AP-1 activity may be a significant determinant of developmental outcome after insult, we investigated the regulation of AP-1 activity in the conceptus. Supershift assays indicated that basal AP-1 binding in the embryo was due primarily to JunD, whereas in the yolk sac c-Jun and JunD were important. Under oxidative stress, c-Fos and c-Jun contributed to the AP-1 binding in the embryo; in the yolk sac, a c-Fos-shifted complex emerged. OTC protection from oxidative stress did not change the AP-1 composition, suggesting that increased AP-1 activity was due to post-translational modifications. Changes in AP-1 activity in embryos under oxidative stress or with OTC protection were not the result of alterations in the net phosphorylation state of Fos or Jun proteins or of changes in activities of the extracellular signal-regulated kinases 1 and 2 or stress-activated protein kinases. However, immunodepletion of redox factor 1 (Ref-1), a nuclear factor that promotes AP-1 binding, eliminated AP-1 activity from embryonic nuclear extracts under both basal and oxidative stress conditions. Therefore, Ref-1 plays a critical role in regulating AP-1 activity in the conceptus; it is plausible that Ref-1-mediated modulation of the AP-1 stress response is a determinant of embryonic fate.