PREEXPOSURE TO OXIDATIVE STRESS DECREASES THE NUCLEAR FACTOR-KAPPA-B-DEPENDENT TRANSCRIPTION IN T-LYMPHOCYTES

Reactive oxygen species (ROS) are used as signaling molecules in T cel l activation, One of the main targets of ROS is the transcription fact or nuclear factor-kappa B (NF-kappa B). NF-kappa B-dependent transcrip tion is inhibited by antioxidants, and the activation is induced or po tentiated by ROS, However, chronic oxidative stress is known to reduce the activation of T cells and NF-kappa B. To analyze these phenomena in more detail, we have exposed Jurkat T cells in vitro to oxidative s tress (H2O2) at various times before or simultaneously with signals kn own to activate NF-kappa B (phorbol dibutyrate (PDBu) and TNF). Simult aneously applied H2O2 strongly potentiated the PDBu- or TNF-induced tr anscriptional activity of NF-kappa B. In contrast to this, H2O2 given 3 to 20 h before the activating signal reduced NF-kappa B-dependent tr anscriptional activity. This was not due to the oxidation-induced modi fication of NF-kappa B; cytoplasmic NF-kappa B was able to bind to DNA after dissociation from I kappa B alpha by detergent treatment, H2O2 pre-exposure effectively inhibited the PDBu- or TNF-induced phosphoryl ation and degradation of I kappa B alpha, but H2O2 given simultaneousl y with PDBu or TNF enhanced the degradation, Oxidative stress was also followed by a strongly decreased ability to form intracellular ROS, T aken together, these data indicate that I kappa B alpha phosphorylatio n is the target of action of ROS, and as the ROS-forming capacity is w eaker after chronic oxidative stress, I kappa B alpha is not effective ly phosphorylated and degraded, thus leading to decreased NF-kappa B-d ependent transcription.