Nuclear factor I/CCAAT box transcription factor trans-activating domain is a negative sensor of cellular stress

The adaptive response to cellular stress requires the reprogramming of gene expression. So far, research has focused on induction mechanisms; several transcription factors activated by cellular stress have been shown to trigger the induction of repair and detoxification enzymes. Using the hepatoma cell line HepG2, we report that the trans-activating function of the nuclear factor I/CCAAT box transcription factor (NFI/CTF-1) is, on the contrary, repressed by various stress conditions, including inflammatory cytokine treatment, glutathione depletion, heat and osmotic shocks, and chemical stress. Under the same conditions, other transcription factors were not affected. We show that when Cys-427 within the trans-activating domain of NFI/CTF-1 is mutated into a serine, the repressive effect triggered by cellular stresses is no longer observed. In addition, this effect is abolished in cells transfected with a thioredoxin expression vector. Using the dichlorofluorescein fluorescent probe, we provide direct evidence that the stress conditions elicit an intracellular reactive oxygen species generation, which can, in turn, negatively regulate NFI/CTF-1. In agreement with these observations, we show that the CYP1A1 mRNA and the CYP1A1 gene promoter, which is a target of NFI/CTF-1, are repressed by stress conditions. Thus, through the redox regulation of its trans-activating function, NFI/CTF-1 constitutes a novel biologically relevant negative sensor of several stress stimuli.