Endotoxin reduces CD95-induced neutrophil apoptosis by cIAP-2-mediated caspase-3 degradation.

摘要

BACKGROUND: Reduced apoptosis of neutrophil granulocytes (PMN) contributes to pathogenesis of systemic inflammatory response syndrome, sepsis, and multiple organ dysfunction syndrome. The intracellular inhibitor of apoptosis proteins has been shown to inhibit activated caspase-3. We investigated the turnover dynamics of cIAP-2 mRNA and caspase-3 protein in a neutrophil ex vivo model of sepsis. STUDY DESIGN: PMN (1 x 10(6)/mL) from 7 healthy volunteers were preincubated with endotoxin (lipopolysaccharide [LPS], 1 microg/mL) for 5 hours, followed by an additional hour with or without the proteasome inhibitor (30 microM), before incubation with or without agonistic CD95 antibody (100 ng/mL) for another 16 hours. Apoptosis was quantified by Annexin-V and propidium iodide staining by flow cytometry (using a fluorescence-activated cell sorter). Caspase-3 activity was determined by DEVD-afc-cleavage assay. Expression of ubiquitinated caspase-3 and cIAP-2 protein was detected by Western blot analysis and cIAP-2 mRNA by reverse transcriptase-polymerase chain reaction. RESULTS: Within 2 hours LPS induced cIAP-2 mRNA and protein. In addition, LPS increased ubiquitination of activated caspase-3. LPS significantly (p < 0.05) reduced spontaneous (66.1 +/- 2.3% to 24.8 +/- 4.8%) and CD95-induced (90.8 +/- 0.9% to 64.3 +/- 4.2%) apoptosis and caspase-3 activation. Inhibition of the proteasome completely abolished the antiapoptotic effect of LPS on spontaneous (52.6 +/- 2.4%) and CD95-induced (88.7 +/- 2.6%) apoptosis and degradation of caspase-3. CONCLUSIONS: Induction of cIAP-2 by endotoxins and accelerated degradation of activated caspase-3 by the proteasome might be responsible for reduced apoptosis in PMN during sepsis.