title: Granzyme B-induced apoptosis requires both direct caspase activation and relief of caspase inhibition.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Ing Swie
authors.initials: IS
authors.lastname: Goping
authors.forename: Michele
authors.initials: M
authors.lastname: Barry
authors.forename: Peter
authors.initials: P
authors.lastname: Liston
authors.forename: Tracy
authors.initials: T
authors.lastname: Sawchuk
authors.forename: Gabriela
authors.initials: G
authors.lastname: Constantinescu
authors.forename: Karolina M
authors.initials: KM
authors.lastname: Michalak
authors.forename: Irene
authors.initials: I
authors.lastname: Shostak
authors.forename: Darren L
authors.initials: DL
authors.lastname: Roberts
authors.forename: Allison M
authors.initials: AM
authors.lastname: Hunter
authors.forename: Robert
authors.initials: R
authors.lastname: Korneluk
authors.forename: R Chris
authors.initials: RC
authors.lastname: Bleackley
mesh_terms: 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
chemical_list: 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