PAR bZIP (cells knockout for PAR bZIP transcription factors) proteins, thyrotroph embryonic factor (TEF), albumin D-site-binding protein (DBP), and hepatic leukemia factor (HLF), are a family of transcription factors that have been shown to contribute to the expression of genes involved in detoxification and drug metabolism. Recently, we showed that PAR bZIP proteins were able to regulate the BH3-only gene bcl-gS in tumor cells. Here, we have extended the role of these transcription factors in the control of apoptosis executors by analyzing the expression of BH3-only genes in PAR bZIP triple knockout mouse fibroblasts. We found that bik was the only BH3-only gene downregulated in knockout cells. Consistently, transfection of TEF or DBP induces the expression of endogenous bik, regardless of the presence of active p53. Moreover, both promoter-reporter and chromatin immunoprecipitation assays indicate that PAR bZIP proteins activate the bik promoter directly. Treatment with different stress stimuli reveals a higher survival of knockout fibroblasts compared with that of wild-type cells, especially after incubation with H(2)O(2), which suggest that PAR bZIP proteins participate in oxidative stress-induced apoptosis. Furthermore, the apoptotic cell death promoted by treatment with H(2)O(2) can be impaired by reducing the expression of Bik in wild-type fibroblasts or enhanced by the overexpression of Bik in knockout cells. These findings reveal a novel transcriptional pathway relevant in transducing the apoptotic response to oxidative stress.