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

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, procaspase8-and DISC (Li, J. et al. Biochemistry, 45, 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 procaspase8 deficient Jurkat cells via the activation of ASK1, JNK and caspase3 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 nucleus to cytosol where it binds to Fas and inhibits apoptosis. Depletion of Daxx results in increase in the activation of ASK1, JNK, and caspase3 along with exacerbation of 4-HNE-induced apoptosis suggesting that Daxx inhibits apoptosis by binding to Fas. 4-HNE-induced translocation of the Daxx is also accompanied with the activation of the transcription factor HSF1. Results of these studies are consistent with a model in which by interacting with Fas, 4-HNE promotes pro-apoptotic signaling via ASK1, JNK and caspase3. In parallel, 4-HNE induces Daxx and promotes its export from the nucleus to cytosol where it interacts with Fas to selflimit the extent of apoptosis by inhibiting the downstream pro-apoptotic signaling. Cytoplasmic translocation of Daxx also results in up-regulation of HSF1 associated stress responsive genes.

Self-regulatory role of 4-hydroxynonenal in signaling for stress-induced programmed cell death

“…These studies show that HNE-induced apoptosis in these cells is independent of Fas-L, FADD, procapsase-8, and the components of DISC [16] and suggest that HNE can mimic the effect of the receptor Ligand (Fas-L) and induce Fas-mediated apoptosis through a novel pathway. During stress-induced, Fas-mediated apoptosis, the involvement of a nuclear death-associated protein (Daxx) has also been demonstrated which is translocated to cytoplasm and binds to Fas [87].…”

“…It has been suggested that the binding of Daxx to Fas causes activation of ASK1 and subsequent downstream proapoptotic signals for the execution of apoptosis [87,88]. Our recent studies [15,16] show that during the DISC-independent HNE-induced apoptosis of Jurkat cells, HNE does indeed cause the translocation of Daxx to cytoplasm and promotes its binding to Fas. However, the binding of Daxx to Fas inhibits HNE-triggered apoptosis by blocking the signaling from Fas to ASK1, JNK, and caspase3 that is required for apoptosis.…”

“…Both of these pathways converge on the activation of JNK, caspase3, and eventual programmed death of the cell. Recent studies demonstrate that HNE can induce apoptosis in several different cell lines (e.g., HLE B-3, RPE, and Jurkat cells) through the Fas-mediated extrinsic as well as the p53-mediated intrinsic pathway and that the enzymes that regulate HNE concentration in cells can modulate both of these pathways [15,16].…”

“…Our recent studies showing that HNE induces as well as self-limits Fas-mediated apoptosis and that it induces heat shock proteins (HSPs) [16,25] strongly suggest a novel role of HNE in the mechanisms of defense in stressed cells implying that besides inducing apoptosis, it also plays a protective role under stress conditions. It is possible that because of the diffusiveness of HNE, a proapoptotic signal initiated by HNE could spread beyond the initial site of the insult to adjacent cells or tissues and HNE-triggered export of Daxx to the cytoplasm may serve as protective mechanism that controls and limits a runaway apoptotic process.…”

“…Recent studies suggest that HNE can induce signaling for apoptosis via multiple pathways, which seem to converge on the activation of JNK and caspase3 [15,16]. Furthermore, there is credible evidence that HNE plays an important role in membrane receptor-mediated signaling and that it can directly interact with transcription factors and transcription repressors.…”