Oxidative stress regulates the expression and activity of transcription factor activator protein-1 in rat conceptus

The transcription factor activator protein-1 (AP-1), composed of the Fos and Jun families of proto-oncogenes, is induced in response to extracellular signals as part of an immediate-early gene response. We hypothesize that teratogens such as oxidative stress induce AP-1 activity in the rat conceptus and that this AP-1 response may either trigger abnormal development or protect the embryo against insult. To test this hypothesis, the AP-1 response was assessed in whole embryos in culture. There was a significant elevation in the oxidized to reduced glutathione ratio in the embryo and yolk sac within 0.25 hr of the initiation of culture, peaking at 0.5 hr; this is indicative of heightened oxidative stress. At 0.5 hr protein oxidation was also enhanced, as demonstrated by increased protein reactivity with 2,4-dinitrophenylhydrazine. In the conceptus, the steady-state concentrations of c-fos, c-jun, junB and junD mRNAs were induced, peaking at 0.5 hr and returning to base line by 1 to 2 hr in the embryo and by 1 to 6 hr in the yolk sac. Electrophoretic mobility shift assays showed enhanced AP-1 DNA-binding activity in both the embryo (elevated by 0.5 hr and persisting for 1 hr) and the yolk sac (persisting for 3 hr). Thus, there are tissue-specific differences in the duration of the AP-1 response in the conceptus. Addition of the antioxidants catalase and superoxide dismutase, but not vitamin E, prevented the rise in the oxidized to reduced glutathione ratio and also inhibited the induction of AP-1 mRNAs and DNA-binding activity. The AP-1 response to oxidative stress may determine how the conceptus responds to insult.