Stress-induced apoptosis is not mediated by endolysosomal ceramide.
A major lipid-signaling pathway in mammalian cells implicates the generation of ceramide from the ubiquitous sphingolipid sphingomyelin (SM). Hydrolysis of SM by a sphingomyelinase present in acidic compartments has been reported to mediate, via the production of ceramide, the apoptotic cell death triggered by stress-inducing agents. In the present study, we investigated whether the ceramide formed within or accumulated in lysosomes indeed triggers apoptosis. A series of observations strongly suggests that ceramide involved in stress-induced apoptosis is not endolysosomal: 1) Although short-chain ceramides induced apoptosis, loading cells with natural ceramide through receptor-mediated endocytosis did not result in cell death. 2) Neither TNF-alpha nor anti-CD95 induced the degradation to ceramide of a natural SM that had been first introduced selectively into acidic compartments. 3) Stimulation of SV40-transformed fibroblasts by TNF-alpha or CD40 ligand resulted in apoptosis equally well in cells derived from control individuals and from patients affected with Farber disease, having a genetic defect of acid ceramidase activity leading to lysosomal accumulation of ceramide. Also, induction of apoptosis using anti-CD95 (Fas) or anti-CD40 antibodies, TNF-alpha, daunorubicin, and ionizing radiation was similar in control and Farber disease lymphoid cells. In all cases, apoptosis was preceded by a comparable increase of intracellular ceramide levels. 4) Retroviral-mediated gene transfer and overexpression of acid ceramidase in Farber fibroblasts, which led to complete metabolic correction of the ceramide catabolic defect, did not affect the cell response to TNF-alpha and CD40 ligand.
Ségui
B
B
INSERM U466, Laboratoire de Biochimie, Maladies Métaboliques, Institut Louis Bugnard, C.H.U. Rangueil, 31403 Toulouse, France.
Bezombes
C
C
Uro-Coste
E
E
Medin
J A
JA
Andrieu-Abadie
N
N
Augé
N
N
Brouchet
A
A
Laurent
G
G
Salvayre
R
R
Jaffrézou
J P
JP
Levade
T
T
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D019013:CD40 Antigens / Q000494:pharmacology; D002461:Cell Line, Transformed; D002470:Cell Survival; D002518:Ceramides / Q000502:physiology*; D003630:Daunorubicin / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D016464:Lysosomal Storage Diseases / Q000378:metabolism / Q000473:pathology; D008247:Lysosomes / Q000378:metabolism*; D015398:Signal Transduction; D013109:Sphingomyelins / Q000378:metabolism; D013312:Stress, Physiological / Q000473:pathology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D019014:fas Receptor / Q000494:pharmacology
D019013:CD40 Antigens; D002518:Ceramides; D013109:Sphingomyelins; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D003630:Daunorubicin