Two CD95 (APO-1/Fas) signaling pathways.
We have identified two cell types, each using almost exclusively one of two different CD95 (APO-1/Fas) signaling pathways. In type I cells, caspase-8 was activated within seconds and caspase-3 within 30 min of receptor engagement, whereas in type II cells cleavage of both caspases was delayed for approximately 60 min. However, both type I and type II cells showed similar kinetics of CD95-mediated apoptosis and loss of mitochondrial transmembrane potential (DeltaPsim). Upon CD95 triggering, all mitochondrial apoptogenic activities were blocked by Bcl-2 or Bcl-xL overexpression in both cell types. However, in type II but not type I cells, overexpression of Bcl-2 or Bcl-xL blocked caspase-8 and caspase-3 activation as well as apoptosis. In type I cells, induction of apoptosis was accompanied by activation of large amounts of caspase-8 by the death-inducing signaling complex (DISC), whereas in type II cells DISC formation was strongly reduced and activation of caspase-8 and caspase-3 occurred following the loss of DeltaPsim. Overexpression of caspase-3 in the caspase-3-negative cell line MCF7-Fas, normally resistant to CD95-mediated apoptosis by overexpression of Bcl-xL, converted these cells into true type I cells in which apoptosis was no longer inhibited by Bcl-xL. In summary, in the presence of caspase-3 the amount of active caspase-8 generated at the DISC determines whether a mitochondria-independent apoptosis pathway is used (type I cells) or not (type II cells).
Scaffidi
C
C
Tumor Immunology Program, German Cancer Research Center, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
Fulda
S
S
Srinivasan
A
A
Friesen
C
C
Li
F
F
Tomaselli
K J
KJ
Debatin
K M
KM
Krammer
P H
PH
Peter
M E
ME
D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000502:physiology; D001402:B-Lymphocytes / Q000201:enzymology / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation; D053200:Fas-Associated Death Domain Protein; D015870:Gene Expression; D006801:Humans; D008564:Membrane Potentials; D008928:Mitochondria / Q000502:physiology; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013601:T-Lymphocytes / Q000201:enzymology / Q000502:physiology*; D051020:bcl-X Protein; D019014:fas Receptor / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; C494811:BCL2L1 protein, human; D002352:Carrier Proteins; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D019014:fas Receptor; 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; D003546:Cysteine Endopeptidases