Regulation of CD95 (Fas) Expression and Fas-Mediated Apoptotic Signaling in HLE B-3 Cells by 4-Hydroxynonenal

Abstract

The Fas (apo/CD95) receptor which belongs to the TNF-alpha family is a transmembrane protein involved in the signaling for apoptosis through the extrinsic pathway. During this study, we have examined a correlation between intracellular levels of 4-HNE and expression of Fas in human lens epithelial (HLE B-3) cells. Our results show that in HLE B-3 cells, Fas is induced by 4-HNE in a concentration- and time-dependent manner, and it is accompanied by the activation of JNK, caspase 3, and the onset of apoptosis. Fas induction and activation of JNK are also observed in various tissues of mGsta4 null mice which have elevated levels of 4-HNE. Conversely, when 4-HNE is depleted in HLE B-3 cells by a transient transfection with hGSTA4, Fas expression is suppressed. However, upon the cessation of hGSTA4 expression in these transiently transfected cells, Fas and 4-HNE return to their basal levels. Fas-deficient transformed HLE B-3 cells stably transfected with hGSTA4 show remarkable resistance to apoptosis. Also, the wild-type HLE B-3 cells in which Fas is partially depleted by siRNA acquire resistance to 4-HNE-induced apoptosis, suggesting an at least partial role of Fas in 4-HNE-induced apoptosis in HLE B-3 cells. We also demonstrate that during 4-HNE-induced apoptosis of HLE B-3 cells, Daxx is induced and it binds to Fas. Together, these results show an important role of 4-HNE in regulation of the expression and functions of Fas.

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

“…Since HNE concentrations in cells are increased in stressed cells and that it is a common denominator in the mechanisms of apoptosis caused by the diverse forms of oxidative stress including UV [7,9], it is likely to affect the expression and/or activation of p53. If so, HNE-mediated activation of p53 may be one of the mechanisms responsible for HNE-induced apoptosis reported in many cell types [7][8][9][12][13][14][15][16][46][47][48]61]. Our recent studies are in accordance with this prediction.…”

“…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].…”

“…The enzymes such as glutathione S-transferases, aldehyde dehydrogenases, and aldose reductases and transporters such as RalBP1 and MRP1 that catalyze the efflux of its metabolites regulate its intracellular concentrations [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. GSTs catalyze the conjugation of HNE to glutathione (GSH) which is the major pathway for disposition of HNE.…”

“…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.…”