Fas Resistance of Leukemic Eosinophils Is Due to Activation of NF-κB by Fas Ligation

Abstract

TNF family receptors can lead to the activation of NF-κB and this can be a prosurvival signal in some cells. Although activation of NF-κB by ligation of Fas (CD95/Apo-1), a member of the TNFR family, has been observed in a few studies, Fas-mediated NF-κB activation has not previously been shown to protect cells from apoptosis. We examined the Fas-induced NF-κB activation and its antiapoptotic effects in a leukemic eosinophil cell line, AML14.3D10, an AML14 subline resistant to Fas-mediated apoptosis. EMSA and supershift assays showed that agonist anti-Fas (CH11) induced nuclear translocation of NF-κB heterodimer p65(RelA)/p50 in these cells in both a time- and dose-dependent fashion. The influence of NF-κB on the induction of apoptosis was studied using pharmacological proteasome inhibitors and an inhibitor of IκBα phosphorylation to block IκBα dissociation and degradation. These inhibitors at least partially inhibited NF-κB activation and augmented CH11-induced cell death. Stable transfection and overexpression of IκBα in 3D10 cells inhibited CH11-induced NF-κB activation and completely abrogated Fas resistance. Increases in caspase-8 and caspase-3 cleavage induced by CH11 and in consequent apoptotic killing were observed in these cells. Furthermore, while Fas-stimulation of resistant control 3D10 cells led to increases in the antiapoptotic proteins cellular inhibitor of apoptosis protein-1 and X-linked inhibitor of apoptosis protein, Fas-induced apoptosis in IκBα-overexpressing cells led to the down-modulation of both of these proteins, as well as that of the Bcl-2 family protein, Bcl-xL. These data suggest that the resistance of these leukemic eosinophils to Fas-mediated killing is due to induced NF-κB activation.

Suppressors of Cytokine Signaling Promote Fas-Induced Apoptosis through Downregulation of NF-κB and Mitochondrial Bfl-1 in Leukemic T Cells

“…In support of this notion, the critical role of NF-kB in the resistance against apoptotic signal in various cell types has been demonstrated. For example, blocking NF-kB activation is found to convert the survival agent into an apoptotic effector in Jurkat leukemic T cells (23), and Fas resistance of leukemic eosinophils is shown to be due to the activation of NF-kB induced by Fas receptor ligation (47). In this regard, we have noted a transient induction of NF-kB activation upon Fas ligation in Jurkat T cells, which is then downregulated as apoptosis proceeds (Fig.…”

Interaction of Fas Ligand and Fas Expressed on Osteoclast Precursors Increases Osteoclastogenesis

“…It suggested that delayed or inefficient induction of apoptosis via Fas should be sufficient to allow the activation of NF-B pathway. In contrast, inhibition of NF-B activation completely abrogated the resistance of leukemic eosinophils to Fas-mediated killing (40). The cells of osteoclast lineage increased the sensitivity to Fas-mediated killing (Fig.…”

Eosinophil-specific deletion of IκBα in mice reveals a critical role of NF-κB–induced Bcl-xL for inhibition of apoptosis

“…Although signaling through the receptors for TNF-a or FasL mainly induces active apoptosis of eosinophils in vitro, 52 it was also reported that FasL-or TNF-a-mediated signals can promote survival of eosinophils by activation of NF-kB-dependent target genes. 52,53 Similarly, TNF-a was shown to activate the NF-kB pathway in ex vivo isolated human eosinophils, and it was proposed that a NF-kB-induced protein protects the cell from caspase-dependent apoptosis. 54,55 In addition, it was shown that NF-kB-induced secretion of IL-6 promotes autocrine activation of PI3K and subsequent expression of the antiapoptotic protein Mcl-1 in neutrophils 56 .…”