HSP27 inhibits cytochrome c-dependent activation of procaspase-9.
We have previously shown that the small heat shock protein HSP27 inhibited apoptotic pathways triggered by a variety of stimuli in mammalian cells. The present study demonstrates that HSP27 overexpression decreases U937 human leukemic cell sensitivity to etoposide-induced cytotoxicity by preventing apoptosis. As observed for Bcl-2, HSP27 overexpression delays poly(ADP-ribose)polymerase cleavage and procaspase-3 activation. In contrast with Bcl-2, HSP27 overexpression does not prevent etoposide-induced cytochrome c release from the mitochondria. In a cell-free system, addition of cytochrome c and dATP to cytosolic extracts from untreated cells induces the proteolytic activation of procaspase-3 in both control and bcl-2-transfected U937 cells but fails to activate procaspase-3 in HSP27-overexpressing cells. Immunodepletion of HSP27 from cytosolic extracts increases cytochrome c/dATP-mediated activation of procaspase-3. Overexpression of HSP27 also prevents procaspase-9 activation. In the cell-free system, immunodepletion of HSP27 increases LEDH-AFC peptide cleavage activity triggered by cytochrome c/dATP treatment. We conclude that HSP27 inhibits etoposide-induced apoptosis by preventing cytochrome c and dATP-triggered activity of caspase-9, downstream of cytochrome c release.
Garrido
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C
INSERM U517, Groupe Biologie et Thérapie des Cancers (JE 515), Faculty of Medicine and Pharmacy, 21033 Dijon, France. cgarrido@u-bourgogne.fr
Bruey
J M
JM
Fromentin
A
A
Hammann
A
A
Arrigo
A P
AP
Solary
E
E
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3; D053453:Caspase 9; D061945:Caspase Inhibitors; D003574:Cytochrome c Group / Q000502:physiology*; D003838:Deoxyadenine Nucleotides / Q000502:physiology; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors*; D005047:Etoposide / Q000494:pharmacology*; D006360:Heat-Shock Proteins / Q000502:physiology*; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D020298:U937 Cells
D000972:Antineoplastic Agents, Phytogenic; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D003838:Deoxyadenine Nucleotides; D004792:Enzyme Precursors; D006360:Heat-Shock Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D005047:Etoposide; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; C026600:2'-deoxyadenosine triphosphate