Cadmium toxicity toward caspase-independent apoptosis through the mitochondria-calcium pathway in mtDNA-depleted cells.
Mitochondria are believed to be integrators and coordinators of programmed cell death in addition to their respiratory function. Using mitochondrial DNA (mtDNA)-depleted osteosarcoma cells (rho0 cells) as a cell model, we investigated the apoptogenic signaling pathway of cadmium (Cd) under a condition of mitochondrial dysfunction. The apoptotic percentage was determined to be around 58.0% after a 24-h exposure to 25 microM Cd using flow cytometry staining with propidium iodine (PI). Pretreatment with Z-VAD-fmk, a broad-spectrum caspase inhibitor, failed to prevent apoptosis following Cd exposure. Moreover, Cd was unable to activate caspase 3 using DEVD-AFC as a substrate, indicating that Cd induced a caspase-independent apoptotic pathway in rho0 cells. JC-1 staining demonstrated that mitochondrial membrane depolarization was a prelude to apoptosis. On the other hand, the intracellular calcium concentration increased 12.5-fold after a 2-h exposure to Cd. More importantly, the apoptogenic activity of Cd was almost abolished by ruthenium red, a mitochondrial calcium uniporter blocker. This led us to conclude that mtDNA-depleted cells provide an alternative pathway for Cd to conduct caspase-independent apoptosis through a mitochondria-calcium mechanism.
Shih
Yung-Luen
YL
Department of Pathology and Laboratory Medicine, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan 110, ROC.
Lin
Chien-Ju
CJ
Hsu
Sheng-Wei
SW
Wang
Sheng-Hao
SH
Chen
Wei-Li
WL
Lee
Mei-Tsu
MT
Wei
Yau-Huei
YH
Shih
Chwen-Ming
CM
D017209:Apoptosis / Q000187:drug effects*; D002104:Cadmium / Q000633:toxicity*; D020013:Calcium Signaling; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D016764:Cell Polarity / Q000187:drug effects; D004272:DNA, Mitochondrial / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017353:Gene Deletion; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000187:drug effects
D061945:Caspase Inhibitors; D004272:DNA, Mitochondrial; D004791:Enzyme Inhibitors; D002104:Cadmium; D020169:Caspases