Accessible Requires Authentication Published by De Gruyter November 13, 2012

Cysteine cathepsins are not critical for TRAIL- and CD95-induced apoptosis in several human cancer cell lines

Aleš Špes, Barbara Sobotič, Vito Turk and Boris Turk
From the journal Biological Chemistry

Abstract

The potential role of cysteine cathepsins in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L)- and CD95 (Fas/APO-1)-induced apoptosis was investigated using four different cell lines (HeLa, HuH-7, Jurkat, and U-937). All four cell lines exhibited different levels of cathepsins and responded differently to apoptosis triggering, with Jurkat cells being the most sensitive and the only ones that were sensitive to the agonistic anti-APO-1 antibody. Apoptosis was accompanied by caspase activation, loss of the mitochondria and lysosome integrity, and the release of cysteine cathepsins into the cytosol, as judged based on the hydrolysis of the cysteine cathepsin substrate benzyloxycarbonyl-Phe-Arg-7-amino-4-methylcoumarin and by the immunological detection of cathepsin B. The inhibition of caspases by the broad-spectrum inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone prevented apoptosis, including the mitochondrial and lysosomal membrane permeabilization, as well as cathepsin release into the cytosol, consistent with caspases playing a crucial role in the process. Conversely, however, although the broad-spectrum cysteine cathepsin inhibitor (2S,3S)-trans-epoxysuccinyl-leucylamido-3-methyl-butane ethyl ester and the more cathepsin B-selective inhibitor [(2S,3S)-3-propylcarbamoyloxirane-2-carbonyl]-l-isoleucyl-l-proline methyl ester completely blocked cathepsin activity, these inhibitors neither prevented apoptosis and its progression nor the mitochondrial and lysosomal membrane permeabilization associated with this type of cell death. Consequently, cathepsin release into the cytosol was also not prevented. Together, these data indicate that cysteine cathepsins are not required for the TRAIL- and CD95-mediated apoptosis in various human cancer cell lines. This does not, however, rule out that lysosomes and cysteine cathepsins are involved in the amplification, but not in the initiation, of death receptor-mediated apoptosis in certain cell lines or under different stimulation conditions than the ones employed here.


Corresponding author: Boris Turk, J. Stefan Institute, Department of Biochemistry and Molecular and Structural Biology, Jamova 39, SI-1000 Ljubljana, Slovenia

Received: 2012-5-25
Accepted: 2012-7-13
Published Online: 2012-11-13
Published in Print: 2012-12-01

©2012 by Walter de Gruyter Berlin Boston