Cephalostatin 1 selectively triggers the release of Smac/DIABLO and subsequent apoptosis that is characterized by an increased density of the mitochondrial matrix

• Published in: Cancer research (Chicago, Ill.) Vol. 63; no. 24; pp. 8869 - 8876
• Main Authors: DIRSCH, Verena M, MÜLLER, Irina M, EICHHORST, Sören T, PETTIT, George R, KAMANO, Yoshiaki, INOUE, Masuo, XU, Jun-Ping, ICHIHARA, Yoshitatsu, WANNER, Gerhard, VOLLMAR, Angelika M
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 15.12.2003
• Subjects: Antineoplastic agents; Apoptosis - drug effects; Apoptosis - physiology; Apoptotic Protease-Activating Factor 1; bcl-X Protein; Biological and medical sciences; Carrier Proteins - physiology; Carrier Proteins - secretion; Caspase 8; Caspase 9; Caspases - metabolism; Cell Membrane Permeability - drug effects; Humans; Intracellular Membranes - drug effects; Intracellular Membranes - metabolism; Intracellular Signaling Peptides and Proteins; Jurkat Cells; Leukemia, T-Cell - drug therapy; Leukemia, T-Cell - enzymology; Leukemia, T-Cell - pathology; Medical sciences; Mitochondria - drug effects; Mitochondria - metabolism; Mitochondrial Proteins - physiology; Mitochondrial Proteins - secretion; Pharmacology. Drug treatments; Phenazines - pharmacology; Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - biosynthesis; Spiro Compounds - pharmacology; Steroids; Tumors; X-Linked Inhibitor of Apoptosis Protein; Mitochondria; Second mitochondria derived activator of caspase; Cell death; Density; Apoptosis
• ISSN: 0008-5472; 1538-7445

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.