Autocrine cell suicide in a Burkitt lymphoma cell line (Daudi) induced by interferon α: involvement of tumor necrosis factor as ligand for the CD95 receptor

The CD95 receptor, a member of the tumor necrosis factor (TNF) receptor superfamily, mediates signals for cell death on specific ligand or antibody engagement. It was hypothesized that interferon α (IFN-α) induces apoptosis through activation of the CD95-mediated pathway and that CD95 and ligands of the death domain may belong to the group of IFN-stimulated genes. Therefore, the effect of IFN-α on CD95-CD95L expression, on the release of TNF-α, and on TNF receptor 1 expression in an IFN-sensitive human Burkitt lymphoma cell line (Daudi) was investigated. After 5 days' incubation, apoptosis in 81% of IFN-α–treated Daudi cells was preceded by a release of TNF-α and an induction of CD95 receptor expression. Although supernatants of IFN-treated Daudi cells induced apoptosis of CD95-sensitive Jurkat cells, CD95L was undetectable on protein or on messenger RNA levels, and the weak initial expression of TNF receptor 1 increased only slightly during IFN treatment. Surprisingly, binding of TNF-α to CD95 was observed and confirmed by 3 different techniques—enzyme-linked immunosorbent assay using immobilized CD95:Fc–immunoglobulin G, immunoprecipitation assay using CD95 receptor precipitates of Daudi cells, and binding of sodium iodide 125–TNF-α to Daudi cells, which was strongly stimulated by IFN-α and inhibited by CD95L, CD95:Fc, unlabeled TNF-α, and anti–TNF-α antibody. Preincubation of Daudi cells with antagonists of the CD95-mediated pathway resulted in an inhibition of IFN-α–mediated cell death. The present investigation shows that IFN-α induces autocrine cell suicide of Daudi cells by a cross-talk between the CD95 receptor and TNF-α. The CD95 receptor can be considered a third TNF receptor, in addition to p55 and p75.