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J. Exp. Med., Volume 189, Number 1, January 4, 1999 131-144

Mitochondria-dependent and -independent Regulation of Granzyme B-induced Apoptosis

By Glen MacDonald,* Lianfa Shi,* Christine Vande Velde,* Judy Lieberman,Dagger and Arnold H. Greenberg*

From the * Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba, Canada R3E OV9; and the Dagger  Center for Blood Research, Harvard Medical School, Boston, Massachusetts 02115

Granzyme B (GraB) is required for the efficient activation of apoptosis by cytotoxic T lymphocytes and natural killer cells. We find that GraB and perforin induce severe mitochondrial perturbation as evidenced by the release of cytochrome c into the cytosol and suppression of transmembrane potential (Delta psi ). The earliest mitochondrial event was the release of cytochrome c, which occurred at the same time as caspase 3 processing and consistently before the activation of apoptosis. Granzyme K/perforin or perforin treatment, both of which kill target cells efficiently but are poor activators of apoptosis in short-term assays, did not induce rapid cytochrome c release. However, they suppressed Delta psi and increased reactive oxygen species generation, indicating that mitochondrial dysfunction is also associated with this nonapoptotic cell death.

Pretreatment with peptide caspase inhibitors zVAD-FMK or YVAD-CHO prevented GraB apoptosis and cytochrome c release, whereas DEVD-CHO blocked apoptosis but did not prevent cytochrome c release, indicating that caspases act both up- and downstream of mitochondria. Of additional interest, Delta psi suppression mediated by GraK or GraB and perforin was not affected by zVAD-FMK and thus was caspase independent. Overexpression of Bcl-2 and Bcl-XL suppressed caspase activation, mitochondrial cytochrome c release, Delta psi suppression, and apoptosis and cell death induced by GraB, GraK, or perforin.

In an in vitro cell free system, GraB activates nuclear apoptosis in S-100 cytosol at high doses, however the addition of mitochondria amplified GraB activity over 15-fold. GraB- induced caspase 3 processing to p17 in S-100 cytosol was increased only threefold in the presence of mitochondria, suggesting that another caspase(s) participates in the mitochondrial amplification of GraB apoptosis. We conclude that GraB-induced apoptosis is highly amplified by mitochondria in a caspase-dependent manner but that GraB can also initiate caspase 3 processing and apoptosis in the absence of mitochondria.

Key words: granzyme Bapoptosismitochondriacytochrome ccaspase


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