Granzyme B-mediated apoptosis proceeds predominantly through a Bcl-2-inhibitable mitochondrial pathway.
Cytotoxic T lymphocytes kill virus-infected and tumor cell targets through the concerted action of proteins contained in cytolytic granules, primarily granzyme B and perforin. Granzyme B, a serine proteinase with substrate specificity similar to the caspase family of apoptotic cysteine proteinases, is capable of cleaving and activating a number of death proteins in target cells. Despite the ability to engage the death pathway at multiple entry points, the preferred mechanism for rapid induction of apoptosis by granzyme B has yet to be clearly established. Here we use time lapse confocal microscopy to demonstrate that mitochondrial cytochrome c release is the primary mode of granzyme B-induced apoptosis and that Bcl-2 is a potent inhibitor of this pivotal event. Caspase activation is not required for cytochrome c release, an activity that correlates with cleavage and activation of Bid, which we have found to be cleaved more readily by granzyme B than either caspase-3 or caspase-8. Bcl-2 blocks the rapid destruction of targets by granzyme B by blocking mitochondrial involvement in the process.
Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
M J
MJ
Pinkoski
N J
NJ
Waterhouse
J A
JA
Heibein
B B
BB
Wolf
T
T
Kuwana
J C
JC
Goldstein
D D
DD
Newmeyer
R C
RC
Bleackley
D R
DR
Green
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000187:drug effects*; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation; D053804:Granzymes; D006801:Humans; D006868:Hydrolysis; D019169:Jurkat Cells; D007700:Kinetics; D008928:Mitochondria / Q000502:physiology*; D008969:Molecular Sequence Data; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D012697:Serine Endopeptidases / Q000494:pharmacology*
D003574:Cytochrome c Group; D019253:Proto-Oncogene Proteins c-bcl-2; C509213:GZMB protein, human; D053804:Granzymes; D012697:Serine Endopeptidases