ROLE OF REACTIVE OXYGEN INTERMEDIATES IN ACTIVATION-INDUCED CD95 (APO-1 FAS) LIGAND EXPRESSION/

Activation-induced cell death of T lymphocytes requires the inducible expression of CD95 (APO-1/Fas) ligand, which triggers apoptosis in CD9 5-bearing target cells by an autocrine or paracrine mechanism. Althoug h execution of the CD95 death pathway is largely independent of reacti ve oxygen intermediates, activation-induced cell death is blocked by a variety of antioxidants. In the present study, we investigated the in volvement of redox processes in the regulation of CD95 ligand (CD95L) expression in Jurkat T cells. We show that various antioxidants potent ly inhibited the transcriptional activation of CD95L following T cell receptor litigation or stimulation of cells with phorbol ester and ion omycin. Conversely, a prooxidant such as hydrogen peroxide alone was a ble to increase CD95L expression. As detected by Western blot and cyto toxicity assays, functional expression of CD95L protein was likewise d iminished by antioxidants. Inhibition of CD95L expression was associat ed with a decreased DNA binding activity of nuclear factor (NF)-kappa B, an important redox-controlled transcription factor. Moreover, inhib ition of NF-kappa B activity by a transdominant I kappa B mutant atten uated CD95L expression. Our data suggest that, although reactive oxyge n intermediates do not act as mediators in the execution phase of CD95 -mediated apoptosis, they are involved in the transcriptional regulati on of CD95L expression.