Radiation and anticancer drugs can facilitate mitochondrial bypass by CD95/Fas via c-FLIP downregulation.
In many tumor cell types, ionizing radiation or DNA-damaging anticancer drugs enhance sensitivity to death receptor-mediated apoptosis, which is of clinical interest. APO010, a form of CD95/Fas ligand is currently in a phase I trial in patients with solid tumors. To analyze the potential of combined modality treatment with APO010, we used p53-mutant Jurkat T leukemic cells, in which the mitochondrial pathway was blocked by Bcl-2 overexpression. These cells were strongly sensitized to APO010 by pretreatment with ionizing - or UV radiation, etoposide, histone deacetylase - or proteasome inhibitors. These stimuli alone did not induce apoptosis in J16-Bcl-2 cells. Sensitization could not be explained by the overruling of mitochondrial resistance imposed by Bcl-2, upregulation of CD95 membrane levels or modulation of inhibitor of apoptosis proteins. Rather, the stimuli commonly downregulated c-FLIP(L/S) protein levels, which was causally related to the sensitization: deliberate c-FLIP(L/S) downregulation by RNA interference largely overruled the capacity of the various stimuli to sensitize Jurkat-Bcl-2 cells to apoptotic execution by APO010. In p53-mutant, Bcl-2 overexpressing HCT-15 colon carcinoma cells, c-FLIP downregulation correlated with sensitization to APO010 for some, but not all stimuli. We conclude that c-FLIP downregulation represents a mechanism by which diverse anticancer regimens can facilitate tumor cell execution by CD95/Fas through the direct pathway of caspase activation.
Division of Immunology, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
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Verbrugge
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Maas
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Heijkoop
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Verheij
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Borst
D000970:Antineoplastic Agents / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor / Q000187:drug effects / Q000528:radiation effects; D017321:Clinical Trials, Phase I as Topic; D015536:Down-Regulation; D005047:Etoposide / Q000494:pharmacology; D053222:Fas Ligand Protein / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference
D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053222:Fas Ligand Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D005047:Etoposide; D048031:JNK Mitogen-Activated Protein Kinases