Cephalostatin 1 selectively triggers the release of Smac/DIABLO and subsequent apoptosis that is characterized by an increased density of the mitochondrial matrix.
Cephalostatin 1 is a bis-steroidal marine natural product with a unique cytotoxicity profile in the in vitro screen system of the National Cancer Institute, suggesting that it may affect novel molecular target(s). Here we show that cephalostatin 1 induces a novel pathway of receptor-independent apoptosis that selectively uses Smac/DIABLO (second mitochondria-derived activator of caspases/direct inhibitor of apoptosis-binding protein with a low isoelectric point) as a mitochondrial signaling molecule. At nanomolar concentrations, cephalostatin 1 triggers dose- and time-dependent DNA fragmentation in leukemia Jurkat T cells. Apoptosis was found to be dependent on caspase activity because the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone blocks cephalostatin 1-mediated DNA fragmentation. The CD95 death receptor as well as other caspase-8-requiring death receptors were not involved because Jurkat T cells lacking the CD95 receptor or caspase-8 and control cells responded equally to cephalostatin 1. Although cephalostatin 1 affects mitochondria by dissipating the mitochondrial membrane potential, neither cytochrome c nor apoptosis-inducing factor is released, as shown by Western blot analysis. Interestingly, cephalostatin 1 selectively triggers the mitochondrial release of the inhibitor of apoptosis antagonist Smac/DIABLO. Overexpression of the antiapoptotic protein Bcl-x(L) delayed both Smac/DIABLO release and onset of apoptosis, suggesting that Smac/DIABLO is required for cephalostatin 1-induced apoptosis. This new mitochondrial pathway is accompanied by marked structural changes of mitochondria as shown by transmission electron microscopy.
Dirsch
Verena M
VM
Department of Pharmacy, Center of Drug Research, University of Munich, Munich, Germany. Verena.Dirsch@cup.uni-muenchen.de
Müller
Irina M
IM
Eichhorst
Sören T
ST
Pettit
George R
GR
Kamano
Yoshiaki
Y
Inoue
Masuo
M
Xu
Jun-Ping
JP
Ichihara
Yoshitatsu
Y
Wanner
Gerhard
G
Vollmar
Angelika M
AM
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D053477:Apoptotic Protease-Activating Factor 1; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D015458:Leukemia, T-Cell / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism / Q000502:physiology*; D010619:Phenazines / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D013141:Spiro Compounds / Q000494:pharmacology*; D013256:Steroids; D051636:X-Linked Inhibitor of Apoptosis Protein; D051020:bcl-X Protein
C506592:APAF1 protein, human; D051017:Apoptosis Regulatory Proteins; D053477:Apoptotic Protease-Activating Factor 1; C494811:BCL2L1 protein, human; D002352:Carrier Proteins; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D010619:Phenazines; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D013141:Spiro Compounds; D013256:Steroids; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D051020:bcl-X Protein; C454806:cephalostatin I; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases