Caspase-independent commitment phase to apoptosis in activated blood T lymphocytes: reversibility at low apoptotic insult

Abstract

Little is known about the mechanisms of programmed death triggered in T lymphocytes by stimuli that can bypass caspase activation. Anti-CD2 monoclonal antibody and staurosporine are such apoptosis inducers because they operate in the presence of broad-spectrum caspase inhibitors BOC-D.fmk and Z-VAD.fmk. A system was devised, based on the isolation according to density of activated blood T cells progressively engaged in the apoptotic process. This allowed definition of a sequence of caspase-dependent and caspase-independent apoptogenic events that are triggered by anti-CD2 and staurosporine. Thus, a commitment phase to apoptosis was defined that is entirely caspase independent and that is characterized by cell volume loss, partial chromatin condensation, and release into the cytosol and the nucleus of mitochondrial “apoptosis-inducing factor ” (AIF). Committed cells were viable, displayed a high mitochondrial inner transmembrane potential (▵Ψm), and lacked large-scale and oligonucleosomal DNA fragmentation. Mitochondrial release of AIF was selective because cytochrome c was retained in mitochondria of the very same cells. Mitochondrial release of cytochrome c occurred later, at the onset of the execution phase of apoptosis, concurrently with ▵Ψm collapse, poly (ADP-ribose) polymerase cleavage, and DNA fragmentation. The apoptogenic events of this commitment phase are reversible if the strength of the stimulus is low and of short duration.

Effect of proteasome inhibitors on proliferation and apoptosis of human cutaneous melanoma-derived cell lines

“…Recent publications have proposed that apoptosis would follow a general scheme where cytochrome c release from mitochondria would stimulate the activation of caspases, which then triggers AIF release from mitochondria 45 . Our data are in agreement with other studies that have described the release of AIF in the absence of detectable caspase activation 20,46 …”

Vibrio parahaemolyticusthermostable direct hemolysin can induce an apoptotic cell death in Rat-1 cells from inside and ouside of the cells

“…It is possible that ZVAD‐FMK might not be sufficient to inhibit apoptotic signalling from mitochondria in TDH‐exposed Rat‐1 cells. Alternatively, recent evidence from an increasing number of experimental systems using ZVAD‐FMK supports the notion that apoptosis can also proceed in a caspase‐independent manner [26,27]. This pathway is another possibility of TDH action leading to apoptosis.…”

Hypoxia induces caspase‐9 and caspase‐3 activation without neuronal death in gerbil brains

“…These data suggest that in hypoxic conditions, unlike ischemic insult, apoptotic processes are aborted despite a high neuronal level of caspase‐3 cleaved product as shown by immunostaining experiments. Some recent in vitro studies reported that apoptogenic events such as the cytochrome c release, the initial collapse of mitochondrial inner transmembrane potential, as well as the mitochondrial release of apoptosis‐inducing factor were reversible depending on the strength of the stimulus (Dumont et al ., 2000). In primary rat hippocampal neurons, membrane phosphatidylserine exposure, a marker of apoptosis, was shown to be reversible in the initial 6‐h period following NO toxic injury (Lin et al ., 2000).…”