P53-independent early and late apoptosis is mediated by ceramide after exposure of tumor cells to photon or carbon ion irradiation

Gersende Alphonse,Claire Rodriguez-Lafrasse,Gisela Taucher-Scholz,Priscillia Battiston-Montagne,Dominique Ardail,Claudia Fournier,Mira Maalouf,Robert Rousson,Michaël Beuve

doi:10.1186/1471-2407-13-151

Abstract

BackgroundTo determine whether ceramide is responsible for the induction of p53-independent early or late apoptosis in response to high- and low-Linear-Energy-Transfer (LET) irradiation.MethodsFour cell lines displaying different radiosensitivities and p53-protein status were irradiated with photons or 33.4 or 184 keV/μm carbon ions. The kinetics of ceramide production was quantified by fluorescent microscopy or High-Performance-Liquid-Chromatogaphy and the sequence of events leading to apoptosis by flow cytometry.ResultsRegardless of the p53-status, both low and high-LET irradiation induced an early ceramide production in radiosensitive cells and late in the radioresistant. This production strongly correlated with the level of early apoptosis in radiosensitive cells and delayed apoptosis in the radioresistant ones, regardless of radiation quality, tumor type, radiosensitivity, or p53-status. Inhibition of caspase activity or ceramide production showed that, for both types of radiation, ceramide is essential for the initiation of early apoptosis in radiosensitive cells and late apoptosis following mitotic catastrophe in radioresistant cells.ConclusionsCeramide is a determining factor in the onset of early and late apoptosis after low and high-LET irradiation and is the mediator of the p53-independent-apoptotic pathway. We propose that ceramide is the molecular bridge between mitotic catastrophe and the commitment phase of delayed apoptosis in response to irradiation.

Highlights

To determine whether ceramide is responsible for the induction of p53-independent early or late apoptosis in response to high- and low-Linear-Energy-Transfer (LET) irradiation
The involvement of ceramide in the response to photon exposure is well characterized in early apoptosis, its involvement in late apoptosis, or last step of mitotic catastrophe as well as its role in the triggering of cell death after exposure to different radiation qualities such as carbon ion irradiation needs to be strongly clarified
Involvement of ceramide production in the response to low- and high-LET radiation The kinetics of intracellular ceramide production was assessed after exposure of the four HNSCC or glioblastoma cells, displaying different radiosensitivity and p53status [11,15] (Table 1), to 10Gy irradiation with photons or with 2 high LET carbon ions (33.4 or 184 keV/μm)

Summary

Introduction

To determine whether ceramide is responsible for the induction of p53-independent early or late apoptosis in response to high- and low-Linear-Energy-Transfer (LET) irradiation. Ionizing-radiation can act directly on free-nucleus membrane preparations, generating ceramide. These data suggest that the membrane represents an alternative target to DNA in radiation-induced-cell-response [2]. Apoptosis can occur before the first mitosis (early apoptosis) or as the last step of mitotic catastrophe [7] (late apoptosis). The involvement of ceramide in the response to photon exposure is well characterized in early apoptosis, its involvement in late apoptosis, or last step of mitotic catastrophe as well as its role in the triggering of cell death after exposure to different radiation qualities such as carbon ion irradiation needs to be strongly clarified

Objectives

Methods

Results

Conclusion