4-Hydroxynonenal Self-Limits Fas-Mediated DISC-Independent Apoptosis by Promoting Export of Daxx from the Nucleus to the Cytosol and Its Binding to Fas

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Abstract
Previously, we have shown that 4-hydroxynonenal (4-HNE) induces Fas-mediated apoptosis in HLE B-3 cells through a pathway which is independent of FasL, FADD, procaspase 8, and DISC (Li, J., et al. (2006) Biochemistry45, 12253−12264). The involvement of Daxx has also been suggested in this pathway, but its role is not clear. Here, we report that Daxx plays an important regulatory role during 4-HNE-induced, Fas-mediated apoptosis in Jurkat cells. 4-HNE induces Fas-dependent apoptosis in procaspase 8-deficient Jurkat cells via the activation of ASK1, JNK, and caspase 3, and the apoptosis can be inhibited by masking Fas with the antagonistic anti-Fas antibodies. We demonstrate that 4-HNE exposure to Jurkat cells leads to the induction of both Fas and Daxx. 4-HNE binds to both Fas and Daxx and promotes the export of Daxx from the nucleus to the cytosol, where it binds to Fas and inhibits apoptosis. Depletion of Daxx results in an increase in the activation of ASK1, JNK, and caspase 3 along with exacerbation of 4-HNE-induced apoptosis, suggesting that Daxx inhibits apoptosis by binding to Fas. 4-HNE-induced translocation of Daxx is also accompanied by the activation of the transcription factor HSF1. The results of these studies are consistent with a model in which, by interacting with Fas, 4-HNE promotes proapoptotic signaling via ASK1, JNK, and caspase 3. In parallel, 4-HNE induces Daxx and promotes its export from the nucleus to the cytosol, where it interacts with Fas to self-limit the extent of apoptosis by inhibiting the downstream proapoptotic signaling. Cytoplasmic translocation of Daxx also results in up-regulation of HSF1-associated stress-responsive genes.