Diversity and complexity of ceramide generation after exposure of jurkat leukemia cells to irradiation.

PURPOSE

To define which intracellular pools of sphingomyelin and ceramide are involved in the triggering of apoptosis of Jurkat leukemia cells in response to gamma-ray exposure.

METHODS AND MATERIALS

We examined the kinetics of ceramide generation at the whole-cell level and in different subcellular compartments (plasma membrane rafts, mitochondria, and endoplasmic reticulum) after irradiation with photons. Ceramide was measured by high-performance liquid chromatography or after pulse labeling experiments, and the presence of sphingomyelinase within mitochondria was assessed by electron microscopy.

RESULTS

Irradiation of Jurkat leukemia cells resulted in the sequential triggering of sphingomyelin hydrolysis, followed by de novo synthesis that led to a late ceramide response (from 24 h) correlated with the triggering of apoptosis. At the subcellular level, pulse-label experiments, using [(3)H]-palmitate as a precursor, strengthened the involvement of the radiation-induced sphingomyelin breakdown and revealed a very early peak (15 min) of ceramide in plasma membrane rafts. A second peak in mitochondria was measured 4 h after irradiation, resulting from an increase of the sphingomyelin content relating to the targeting of acid sphingomyelinase toward this organelle.

CONCLUSION

These data confirm that ceramide is a major determinant in the triggering of radiation-induced apoptosis and highlight the complexity of the sequential compartment-specific ceramide-mediated response of Jurkat leukemia cells to gamma-rays.