Granzyme B-induced apoptosis requires both direct caspase activation and relief of caspase inhibition.
Cytotoxic lymphocytes employ Granzyme B as a potent initiator of apoptosis to cleave and activate effector caspases. Unexpectedly, cells transfected with Bcl-2 were resistant to granzyme B-induced killing, suggesting that a mitochondrial pathway was critical. Utilizing cells expressing a dominant-negative caspase 9, the current study demonstrated that caspase activation via the apoptosome was not required. Indeed, cleavage of caspase 3 to p20 still occurred in Bcl-2-transfectants but processing to p17 was blocked. This blockade was recapitulated by the Inhibitor-of-Apoptosis-Protein XIAP and relieved by Smac/DIABLO. Thus granzyme B mediates direct cleavage of caspase 3 and also activates mitochondrial disruption, resulting in the release of proapoptotic proteins that suppress caspase inhibition. Engagement of both pathways is critical for granzyme-induced killing.
Goping
Ing Swie
IS
Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
Barry
Michele
M
Liston
Peter
P
Sawchuk
Tracy
T
Constantinescu
Gabriela
G
Michalak
Karolina M
KM
Shostak
Irene
I
Roberts
Darren L
DL
Hunter
Allison M
AM
Korneluk
Robert
R
Bleackley
R Chris
RC
D017209:Apoptosis / Q000276:immunology / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D019254:Genes, bcl-2; D053804:Granzymes; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D024101:Mitochondrial Proteins / Q000378:metabolism; D008954:Models, Biological; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism*; D014162:Transfection; D051636:X-Linked Inhibitor of Apoptosis Protein
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D061945:Caspase Inhibitors; C412403:DIABLO protein, human; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C509213:GZMB protein, human; D053804:Granzymes; D012697:Serine Endopeptidases; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases