Sequential caspase-2 and caspase-8 activation upstream of mitochondria during ceramideand etoposide-induced apoptosis.
Recently, caspase-2 was shown to act upstream of mitochondria in stress-induced apoptosis. Activation of caspase-8, a key event in death receptor-mediated apoptosis, also has been demonstrated in death receptor-independent apoptosis. The regulation of these initiator caspases, which trigger the mitochondrial apoptotic pathway, is unclear. Here we report a potential regulatory role of caspase-2 on caspase-8 during ceramide-induced apoptosis. Our results demonstrate the sequential events of initiator caspase-2 and caspase-8 activation, Bid cleavage and translocation, and mitochondrial damage followed by downstream caspase-9 and -3 activation and cell apoptosis after ceramide induction in T cell lines. The expression of truncated Bid (tBid) and the reduction in mitochondrial transmembrane potential were blocked by caspase-2 or caspase-8, but not caspase-3, knockdown using an RNA interference technique. Ceramide-induced caspase-8 activation, mitochondrial damage, and apoptosis were blocked in caspase-2 short interfering RNA-expressing cells. Therefore, caspase-2 acts upstream of caspase-8 during ceramide-induced mitochondrial apoptosis. Similarly, sequential caspase-2 and caspase-8 activation upstream of mitochondria was also observed in etoposide-induced apoptosis. These data suggest sequential initiator caspase-2 and caspase-8 activation in the mitochondrial apoptotic pathway induced by ceramide or etoposide.
Lin
Chiou-Feng
CF
Department of Microbiology and Immunology, National Cheng Kung University Medical College, Tainan, Taiwan.
Chen
Chia-Ling
CL
Chang
Wen-Tsan
WT
Jan
Ming-Shiou
MS
Hsu
Li-Jin
LJ
Wu
Ren-Huang
RH
Tang
Ming-Jer
MJ
Chang
Wen-Chang
WC
Lin
Yee-Shin
YS
D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism; D053143:Caspase 2; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism*; D002518:Ceramides / Q000378:metabolism*; D016895:Culture Media, Serum-Free / Q000378:metabolism; D004789:Enzyme Activation; D005047:Etoposide / Q000494:pharmacology*; D006801:Humans; D006825:Hybridomas / Q000378:metabolism; D019169:Jurkat Cells; D008564:Membrane Potentials; D051379:Mice; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D013601:T-Lymphocytes / Q000378:metabolism; D013997:Time Factors
D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494815:Bid protein, mouse; D002352:Carrier Proteins; D002518:Ceramides; D016895:Culture Media, Serum-Free; D005047:Etoposide; C505530:CASP8 protein, human; C505526:Casp8 protein, mouse; D053143:Caspase 2; D053181:Caspase 8; D020169:Caspases