title: Caspase-8/FLICE functions as an executioner caspase in anticancer drug-induced apoptosis.
abstract: Caspase-8 plays an essential role in apoptosis triggered by death receptors. Through the cleavage of Bid, a proapoptotic Bcl-2 member, it further activates the mitochondrial cytochrome c/Apaf-1 pathway. Because caspase-8 can be processed also by anticancer drugs independently of death receptors, we investigated its exact role and order in the caspase cascade. We show that in Jurkat cells either deficient for caspase-8 or overexpressing its inhibitor c-FLIP apoptosis mediated by CD95, but not by anticancer drugs was inhibited. In the absence of active caspase-8, anticancer drugs still induced the processing of caspase-9, -3 and Bid, indicating that Bid cleavage does not require caspase-8. Overexpression of Bcl-x(L) prevented the processing of caspase-8 as well as caspase-9, -6 and Bid in response to drugs, but was less effective in CD95-induced apoptosis. Similar responses were observed by overexpression of a dominant-negative caspase-9 mutant. To further determine the order of caspase-8 activation, we employed MCF7 cells lacking caspase-3. In contrast to caspase-9 that was cleaved in these cells, anticancer drugs induced caspase-8 activation only in caspase-3 transfected MCF7 cells. Thus, our data indicate that, unlike its proximal role in receptor signaling, in the mitochondrial pathway caspase-8 rather functions as an amplifying executioner caspase.
authors.affiliation: Department of Immunology and Cell Biology, University of Münster, Germany.
authors.forename: I H
authors.initials: IH
authors.lastname: Engels
authors.forename: A
authors.initials: A
authors.lastname: Stepczynska
authors.forename: C
authors.initials: C
authors.lastname: Stroh
authors.forename: K
authors.initials: K
authors.lastname: Lauber
authors.forename: C
authors.initials: C
authors.lastname: Berg
authors.forename: R
authors.initials: R
authors.lastname: Schwenzer
authors.forename: H
authors.initials: H
authors.lastname: Wajant
authors.forename: R U
authors.initials: RU
authors.lastname: Jänicke
authors.forename: A G
authors.initials: AG
authors.lastname: Porter
authors.forename: C
authors.initials: C
authors.lastname: Belka
authors.forename: M
authors.initials: M
authors.lastname: Gregor
authors.forename: K
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: S
authors.initials: S
authors.lastname: Wesselborg
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology / Q000473:pathology; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein; D001943:Breast Neoplasms / Q000201:enzymology / Q000473:pathology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells / Q000187:drug effects / Q000201:enzymology; D008928:Mitochondria / Q000502:physiology*; D016685:Mitomycin / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology; D051020:bcl-X Protein; D019014:fas Receptor / Q000502:physiology
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000970:Antineoplastic Agents; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D016685:Mitomycin; D005047:Etoposide; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases