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-converting Enzyme Related Proteases/Caspases Are
Involved in TRAIL-induced Apoptosis of Myeloma and Leukemia Cells
Tumor Immunology and * Molecular Immunology Program/Division of Immunogenetics, German Cancer Research Center,
Heidelberg, Germany
The Fas/APO-1/CD95 ligand (CD95L) and
the recently cloned TRAIL ligand belong to the TNFfamily and share the ability to induce apoptosis in sensitive target cells. Little information is available on the
degree of functional redundancy between these two
ligands in terms of target selectivity and intracellular
signalling pathway(s). To address these issues, we have
expressed and characterized recombinant mouse
TRAIL. Specific detection with newly developed rabbit
anti-TRAIL antibodies showed that the functional
TRAIL molecule released into the supernatant of recombinant baculovirus-infected Sf9 cells is very similar
to that associated with the membrane fraction of Sf9
cells. CD95L resistant myeloma cells were found to be
sensitive to TRAIL, displaying apoptotic features similar to those of the CD95L- and TRAIL-sensitive T leukemia cells Jurkat. To assess if IL-1 These results indicate that TRAIL seems to complement the activity of the CD95 system as it allows cells,
otherwise resistant, to undergo apoptosis triggered by
specific extracellular ligands. Conversely, however, induction of apoptosis in sensitive cells by TRAIL involves IRPs/caspases in a fashion similar to CD95L. Thus, differential sensitivity to CD95L and TRAIL
seems to map to the proximal signaling events associated with receptor triggering.
-converting enzyme (ICE) and/or ICE-related proteases (IRPs)
(caspases) are involved in TRAIL-induced apoptosis of
both cell types, peptide inhibition experiments were
performed. The irreversible IRP/caspase-inhibitor AcYVAD-cmk and the reversible IRP/caspase-inhibitor
Ac-DEVD-CHO blocked the morphological changes, disorganization of plasma membrane phospholipids,
DNA fragmentation, and loss of cell viability associated
with TRAIL-induced apoptosis. In addition, cells undergoing TRAIL-mediated apoptosis displayed cleavage of poly(ADP)-ribose polymerase (PARP) that was
completely blocked by Ac-DEVD-CHO.
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