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From the * Centre National de la Recherche Scientifique-UPR420, B.P.8, F-94801 Villejuif, France; According to current understanding, cytoplasmic events including activation of protease cascades and mitochondrial permeability transition (PT) participate in the control of nuclear apoptosis. However, the relationship between protease activation and PT has remained elusive.
When apoptosis is induced by cross-linking of the Fas/APO-1/CD95 receptor, activation of
interleukin-1
The Burnham Institute, La Jolla, California 92037; § Institute for General and Experimental
Pathology of the University of Innsbruck, A-6020 Innsbruck, Austria; and
Division Santé, Domain
Immunologie, ROUSSEL UCLAF, F-93235 Romainville, France
converting enzyme (ICE; caspase 1) or ICE-like enzymes precedes the disruption of the mitochondrial inner transmembrane potential (
m). In contrast, cytosolic CPP32/
Yama/Apopain/caspase 3 activation, plasma membrane phosphatidyl serine exposure, and nuclear apoptosis only occur in cells in which the 
m is fully disrupted. Transfection with the
cowpox protease inhibitor crmA or culture in the presence of the synthetic ICE-specific inhibitor Ac-YVAD.cmk both prevent the 
m collapse and subsequent apoptosis. Cytosols from
anti-Fas-treated human lymphoma cells accumulate an activity that induces PT in isolated mitochondria in vitro and that is neutralized by crmA or Ac-YVAD.cmk. Recombinant purified
ICE suffices to cause isolated mitochondria to undergo PT-like large amplitude swelling and to disrupt their 
m. In addition, ICE-treated mitochondria release an apoptosis-inducing factor
(AIF) that induces apoptotic changes (chromatin condensation and oligonucleosomal DNA
fragmentation) in isolated nuclei in vitro. AIF is a protease (or protease activator) that can be
inhibited by the broad spectrum apoptosis inhibitor Z-VAD.fmk and that causes the proteolytical activation of CPP32. Although Bcl-2 is a highly efficient inhibitor of mitochondrial alterations (large amplitude swelling + 
m collapse + release of AIF) induced by prooxidants or
cytosols from ceramide-treated cells, it has no effect on the ICE-induced mitochondrial PT and AIF release. These data connect a protease activation pathway with the mitochondrial phase of
apoptosis regulation. In addition, they provide a plausible explanation of why Bcl-2 fails to interfere with Fas-triggered apoptosis in most cell types, yet prevents ceramide- and prooxidant-induced apoptosis.
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