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© The Rockefeller University Press, 0021-9525/2001//999 $5.00
The Journal of Cell Biology, Volume 153, Number 5, , 2001 999-1010

Cathepsin B Acts as a Dominant Execution Protease in Tumor Cell Apoptosis Induced by Tumor Necrosis Factor

^a Apoptosis Laboratory, Danish Cancer Society, Copenhagen, Denmark
^b Department of Molecular Toxicology, University of Konstanz, Konstanz, Germany
^c Institute of Molecular Pathology, University of Copenhagen, Copenhagen, Denmark
^d Department of Pathology, Harvard Medical School, Boston, Massachusetts
^e H. Lundbeck A/S, Valby, Denmark
Apoptosis Laboratory, Danish Cancer Society, Strandboulevarden 49, DK-2100 Copenhagen, Denmark.45-3525772145-35257318

mhj{at}biobase.dk

Death receptors can trigger cell demise dependent or independent of caspases. In WEHI-S fibrosarcoma cells, tumor necrosis factor (TNF) induced an increase in cytosolic cathepsin B activity followed by death with apoptotic features. Surprisingly, this process was enhanced by low, but effectively inhibiting, concentrations of pan-caspase inhibitors. Contrary to caspase inhibitors, a panel of pharmacological cathepsin B inhibitors, the endogenous cathepsin inhibitor cystatin A as well as antisense-mediated depletion of cathepsin B rescued WEHI-S cells from apoptosis triggered by TNF or TNF-related apoptosis-inducing ligand. Thus, cathepsin B can take over the role of the dominant execution protease in death receptor-induced apoptosis. The conservation of this alternative execution pathway was further examined in other tumor cell lines. Here, cathepsin B acted as an essential downstream mediator of TNF-triggered and caspase-initiated apoptosis cascade, whereas apoptosis of primary cells was only minimally dependent on cathepsin B. These data imply that cathepsin B, which is commonly overexpressed in human primary tumors, may have two opposing roles in malignancy, reducing it by its proapoptotic features and enhancing it by its known facilitation of invasion.

Key Words: apoptosis • cancer • caspase independent • cathepsins • tumor necrosis factor

© 2001 The Rockefeller University Press

M. Leist and M. Jäättelä share senior authorship.

Abbreviations used in this paper: AFC, 7-amino-trifluoromethylcoumarin; ALLN, N-Acetyl-leu-Leu-Nle-CHO; anti-CD95, agonistic antibody against CD95; Boc-D-fmk, Boc-Asp-CH₂F; DEVD-CHO, acetyl-Asp-Glu-Val-Asp-aldehyde; IETD-CHO, acetyl-Ile-Glu-Thr-Asp-aldehyde; lactacystine, clasto-lactacystin-β-lactone; LDH, lactate dehydrogenase; MEF, murine embryonic fibroblast; MTT, 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide; NF-B, nuclear factor B; PS, phosphatidylserine; rhTNF, recombinant human TNF; rmTNF, recombinant murine TNF; TLCK, N--Tosyl-L-Lys-chloromethyl ketone; TNF, tumor necrosis factor; TNF-R, TNF receptor; TPCK, tosyl-L-Phe-chloromethyl ketone; TRAIL, TNF-related apoptosis-inducing ligand; zFA-fmk, z-Phe-Ala-CH₂F; zFK-mbmk, z-Phe-Lys-2,4,6-trimethylbenzoyloxymethylketone; zVAD-fmk, z-Val-Ala-DL-Asp-CH₂F; zVDVAD-fmk, z-Val-Asp(OMe)-Val-Ala-Asp(OMe)-CH₂F.

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