Ordering of ceramide formation, caspase activation, and mitochondrial changes during CD95- and DNA damage-induced apoptosis.
To evaluate the role of ceramide (Cer) in apoptosis signaling, we examined Cer formation induced by CD95, etoposide, or gamma-radiation (IR) in relation to caspase activation and mitochondrial changes in Jurkat T cells. The Cer response to all three stimuli was mapped in between caspases sensitive to benzoyloxycarbonyl-VAD-fluoromethylketone (zVAD-fmk) and acetyl-DEVD-aldehyde (DEVD-CHO). Cer production was independent of nuclear fragmentation but associated with the occurrence of other aspects of the apoptotic morphology. Caspase-8 inhibition abrogated Cer formation and apoptosis induced by CD95 but did not affect the response to etoposide or IR, placing CD95-induced Cer formation downstream from caspase-8 and excluding a role for caspase-8 in the DNA damage pathways. CD95 signaling to the mitochondria required caspase-8, whereas cytochrome c release in response to DNA damage was caspase-independent. These results indicate that the caspases required for the Cer response to etoposide and IR reside at or downstream from the mitochondria. Bcl-2 overexpression abrogated the Cer response to etoposide and IR and reduced CD95-induced Cer accumulation. We conclude that the Cer response to DNA damage fully depends on mitochondrion-dependent caspases, whereas the response to CD95 partially relies on these caspases. Our data imply that Cer is not instrumental in the activation of inducer caspases or signaling to the mitochondria. Rather, Cer formation is associated with the execution phase of apoptosis.
Tepper
A D
AD
Division of Cellular Biochemistry, Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.
de Vries
E
E
van Blitterswijk
W J
WJ
Borst
J
J
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002518:Ceramides / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D004249:DNA Damage / Q000235:genetics* / Q000528:radiation effects; D053938:DNA Fragmentation / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D005720:Gamma Rays; D006801:Humans; D019169:Jurkat Cells; D007700:Kinetics; D048629:Micronuclei, Chromosome-Defective; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D019014:fas Receptor / Q000276:immunology
D000590:Amino Acid Chloromethyl Ketones; D002518:Ceramides; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D019253:Proto-Oncogene Proteins c-bcl-2; C108637:aspartyl-glutamyl-valyl-aspartal; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D005047:Etoposide; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases