Apoptosis signaling triggered by the marine alkaloid ascididemin is routed via caspase-2 and JNK to mitochondria.
The marine alkaloid ascididemin (ASC) was shown to exert cytotoxicity even against multidrug-resistant cancer cells. Here, we address the signaling pathways utilized by ASC to trigger apoptosis in Jurkat leukemia T cells. We show that ASC (0.5-20 microM) induces a mitochondrial pathway that requires the activation of the initiator caspase-2 upstream of mitochondria. ASC-triggered apoptosis occurred independent of CD95, but required mitochondrial dysfunction. The activation of caspase-2 was shown to precede the processing of caspase-8, -9 and -3. The specific caspase-2 inhibitor zVDVADfmk abrogated ASC-induced DNA fragmentation almost completely. Overexpression of Bcl-x(L) blocked caspase-8 but not caspase-2 processing. Conversely, caspase-2 inhibition strongly reduced caspase-9 activation. As a possible link between caspase-2 and mitochondrial dysfunction, Bid was found to be cleaved by ASC. In addition, JNK was activated by ASC upstream of mitochondria via reactive oxygen species. The specific JNK inhibitor SP600125 partially inhibited caspase-2 and -9 processing as well as cytochrome c release and DNA fragmentation indicating that JNK contributes to, but is not necessary for ASC-mediated apoptosis. Thus, ASC triggers a pathway in which early activation of caspase-2 provides a possible link between its DNA-damaging activity and the induction of mitochondrial dysfunction. The activation of JNK contributes to this signaling upstream of mitochondria.
Dirsch
Verena M
VM
Department of Pharmacy, Center of Drug Research, University of Munich, Butenandtstrasse 5-13, D-81377 Munich, Germany.
Kirschke
Stephanie O
SO
Estermeier
Michael
M
Steffan
Bert
B
Vollmar
Angelika M
AM
D000470:Alkaloids / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival; D045304:Cytochromes c / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005434:Flow Cytometry; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D019169:Jurkat Cells; D048670:MAP Kinase Kinase 4; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D010618:Phenanthrolines / Q000494:pharmacology*; D011804:Quinolines / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000032:analysis; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
D000470:Alkaloids; D010618:Phenanthrolines; D011804:Quinolines; D017382:Reactive Oxygen Species; C412046:ascididemin; D045304:Cytochromes c; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D020169:Caspases