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Activation of CD95 (APO‐1/Fas) signaling by ceramide mediates cancer therapy‐induced apoptosis

We report here that anticancer drugs such as doxorubicin lead to induction of the CD95 (APO‐1/Fas) system of apoptosis and the cellular stress pathway which includes JNK/SAPKs. Ceramide, which accumulates in response to different types of cellular stress such as chemo‐ and radiotherapy, strongly induced expression of CD95‐L, cleavage of caspases and apoptosis. Antisense CD95‐L as well as dominant‐negative FADD inhibited ceramide‐ and cellular stress‐induced apoptosis. Fibroblasts from type A Niemann–Pick patients (NPA), genetically deficient in ceramide synthesis, failed to up‐regulate CD95‐L expression and to undergo apoptosis after γ‐irradiation or doxorubicin treatment. In contrast, JNK/SAPK activity was still inducible by doxorubicin in the NPA cells, suggesting that activation of JNK/SAPKs alone is not sufficient for induction of the CD95 system and apoptosis. CD95‐L expression and apoptosis in NPA fibroblasts were restorable by exogenously added ceramide. In addition, NPA fibroblasts undergo apoptosis after triggering of CD95 with an agonistic antibody. These data demonstrate that ceramide links cellular stress responses induced by γ‐irradiation or anticancer drugs to the CD95 pathway of apoptosis.