Ceramide-induced cell death is independent of the Fas/Fas ligand pathway and is prevented by Nur77 overexpression in A20 B cells

Abstract

The role of ceramide in triggering apoptosis is still a matter of debate. While in some experimental systems, ceramide was shown to mediate Fas-induced cell death, in other instances it was claimed to induce the expression of Fas ligand (FasL), killing cells in a caspase-dependent fashion. We found that, in mature A20 B cells, ceramide-induced apoptosis is independent of the caspase pathway, since we observed no ICE-like, CPP32-like and Mch2 activities and no PARP proteolysis. Moreover, we were unable to protect these cells from ceramide-induced apoptosis using caspase inhibitors, while they blocked Fas-induced apoptosis and no FasL induction could be detected following ceramide treatment. These results suggest that ceramide does not induce apoptosis through the Fas/FasL pathway. We also found that overexpression of Nur77, a zinc-finger transcription factor described to upregulate FasL, antagonizes ceramide-induced apoptosis, but not Fas-induced apoptosis. This further supports the hypothesis that Fas and ceramide death pathways are independent in A20 cells. Ceramide-induced cell death was associated with increased c-myc, p53, Bax and p27kip1 levels; in contrast, cells transfected with Nur77 (A20Nur77), resistant to ceramide-induced apoptosis, showed a marked downregulation of p53 after ceramide treatment, with neither Bax nor p27kip1 induction. In conclusion, our results suggest that, in the A20 B cell line, Fas and ceramide trigger two distinct pathways and that Nur77 overexpression confers protection against ceramide-mediated apoptosis which correlates with inhibition of p53, Bax and p27kip1 induction. Cell Death and Differentiation (2000) 7, 262 ± 271.

p53 and Nur77/TR3 – transcription factors that directly target mitochondria for cell death induction

“…Interestingly, Nur77 family members are found as NF-kB-responsive genes in macrophage (Pei et al, 2005a), controlling expression of cyclin D2 (Pei et al, 2005b). Overexpression of Nur77 also blocks cell death induced by ceramide in A20 B cell line (Bras et al, 2000) and protect fibroblasts from undergoing tumor necrosis factor-induced cell death (Suzuki et al, 2003). Induction of Nur77 by hepatitis B virus X protein may play a role in viral carcinogenesis (Lee et al, 2001).…”

Inhibition of apoptosis by Nur77 through NF-κB activity modulation

“…17,18 On the other hand, Nur77 expression can prevent ceramide-induced apoptosis in B cells and tumour necrosis factor-induced cell death in macrophages. 19,20 Nur77 can therefore contribute to cell death or survival depending on the cell type and the nature of proapoptotic signal received.…”

Mitochondrially targeted ceramide LCL-30 inhibits colorectal cancer in mice

“…Several inductors of cell death, for example, TNFa (Obeid et al, 1993), anthracyclines (Bose et al, 1995), or irradiation (El-Assaad et al, 2003) involve ceramide signalling. Administration of exogenous ceramide also causes cell death in various cancer cell lines (Oh et al, 1998;Bras et al, 2000). It is noteworthy that, many cancer cells have a specific 'sphingolipidphenotype', including lower endogenous ceramide levels (Itoh et al, 2003) and a higher sensitivity to the effects of exogenous ceramide (Selzner et al, 2001).…”