Granzyme B mimics apical caspases. Description of a unified pathway for trans-activation of executioner caspase-3 and -7.
Granzyme B (GrB) is predicted to trigger apoptosis by activating preferred caspases, but the zymogens that are directly processed by the granzyme and the requirements for these interactions remain unclarified. We examined this dilemma by comparing the kinetics and pattern of GrB-mediated activation of the executioner caspase-7 in vitro and in vivo. GrB rapidly activates procaspase-7 in vitro by cleaving between the large and small subunits leaving the propeptide intact. During GrB-mediated apoptosis, the caspase-7 propeptide is removed and cleavage occurs between the subunits. Strikingly, caspase-7 is unprocessed in caspase-3-deficient MCF-7 cells exposed to GrB but is rapidly activated when the cells are solubilized. Transfection with caspase-3 restores the removal of the caspase-7 propeptide and the capacity of GrB to subsequently activate the caspase. The data suggest that GrB activates caspase-3, which then removes the propeptide of caspase-7 allowing activation by GrB. Thus GrB initiates the death pathway by processing the accessible caspase-3, and the caspase-7 propeptide regulates trans-activation of the zymogen by granzyme. As a consequence, two proteases, caspase-3 and GrB, are required to activate procaspase-7.
Yang
X
X
Evanston Northwestern Healthcare Research Institute, Evanston, Illinois 60201, USA.
Stennicke
H R
HR
Wang
B
B
Green
D R
DR
Jänicke
R U
RU
Srinivasan
A
A
Seth
P
P
Salvesen
G S
GS
Froelich
C J
CJ
D017209:Apoptosis; D001943:Breast Neoplasms; D053455:Caspase 10; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000235:genetics* / Q000378:metabolism; D004792:Enzyme Precursors / Q000235:genetics; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D053804:Granzymes; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008954:Models, Biological; D011499:Protein Processing, Post-Translational; D012697:Serine Endopeptidases / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D004792:Enzyme Precursors; D046911:Macromolecular Substances; C509213:GZMB protein, human; D053804:Granzymes; D012697:Serine Endopeptidases; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053455:Caspase 10; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; C506438:CASP10 protein, human