Oxidant-induced cell death and Nrf2-dependent antioxidative response are controlled by Fra-1/AP-1

AP-1 (Jun/Fos) transcription factors play key roles in various biological processes, including cell death. Here we report a novel role for Fra-1 in oxidant-induced cell death controlled by modulating antioxidant gene expression. Fra-1-deficient (Fra-1^Δ/Δ) mouse embryonic fibroblasts (MEFs) and primary lung fibroblasts (PLFs) were remarkably resistant to H₂O₂-and diquat-induced cell death, compared to their wild-type (Fra-1^+/+) counterparts. Fra-1 deficiency ablated oxidant-induced mitochondrion-dependent apoptosis. Fra-1^Δ/Δ cells had elevated basal levels of antioxidant enzymes and intracellular glutathione (GSH), which were further stimulated by oxidants. Loss of Fra-1 led to an increased half-life of transcription factor Nrf2 and increased recruitment of this protein to the promoters of antioxidant genes and increased their expression. Depletion of intracellular GSH or RNA interference (RNAi)-mediated knockdown of Nqo1, Hmox1, and Nrf2 restored oxidant-induced cell death in Fra-1^δ/Δ cells. Thus, Fra-1 appears to increase susceptibility to oxidants and promotes cell death by attenuating Nrf2-driven antioxidant responses.