LONGITUDINAL EXPOSURE OF HUMAN T-LYMPHOCYTES TO WEAK OXIDATIVE STRESSSUPPRESSES TRANSMEMBRANE AND NUCLEAR SIGNAL-TRANSDUCTION

Products of polyamine oxidase activity, at micromolar levels and durin g a period of 2 to 3 days, down-regulate IL-2 mRNA levels and activity in human lymphocytes. We studied whether this suppression was associa ted with signal transduction abnormalities. We found that polyamine ox idase activity suppresses both anti-CD3-induced IL-2 production and pr otein tyrosine phosphorylation. Polyamine oxidase activity also caused a reduction in intracellular calcium mobilization after mitogenic sti mulation. The most distal step of CD3-mediated signal transduction is dependent upon transcription factors that regulate a set of genes, inc luding IL-2. We found that polyamine oxidase-treated cells exhibited v ery low DNA binding activity of two such factors: NFAT and NF-kappa B. On the other hand, AP-1 DNA binding activity was enhanced in polyamin e oxidase-treated cells, suggesting a possible role for AP-1 in the hu man lymphocyte stress response. In accordance with the oxidation depen dence of this suppressive mechanism, N-acetylcysteine (NAC; an antioxi dant) significantly reversed the polyamine oxidase effects on lymphoki ne production and signal transduction. These results suggest that NAC contributes, under oxidizing conditions, to the preservation of immune function. In summary, our data suggest that chronic low-level oxidati ve stress; via suppression of mitogen-induced transmembrane signaling (protein-tyrosine phosphorylation and calcium mobilization), causes a decrease in the DNA binding activity of transcription factors that reg ulate the IL-2 gene. This results in decreased IL-2 production.