Cadmium Toxicity toward Caspase-Independent Apoptosis through the Mitochondria-Calcium Pathway in mtDNA-Depleted Cells

doi:10.1196/annals.1338.043

^aDepartment of Pathology and Laboratory Medicine, Shin Kong Wu Ho-Su Memorial Hospital, Taipei 111, Taiwan, ROC
^bDepartment of Biochemistry, Taipei Medical University, Taipei 110, Taiwan, ROC
^cGraduate Institute of Medical Science, Taipei Medical University, Taipei 110, Taiwan, ROC
^dDepartment of Biochemistry and Center for Cellular and Molecular Biology, National Yang-Ming University, Taipei 112, Taiwan, ROC

^eY-L.S. and C-J.L. contributed equally to this work.
Address for correspondence: Dr. Chwen-Ming Shih, Department of Biochemistry, School of Medicine, Taipei Medical University, 250 Wu-Hsing Street, Taipei, Taiwan 110, ROC. Voice: +886-2-27361661 ext. 3151; fax: +886-2-86421158. cmshih{at}tmu.edu.tw

Mitochondria are believed to be integrators and coordinatorsof programmed cell death in addition to their respiratory function.Using mitochondrial DNA (mtDNA)-depleted osteosarcoma cells( ${rho}$ ⁰ cells) as a cell model, we investigated the apoptogenic signalingpathway of cadmium (Cd) under a condition of mitochondrial dysfunction.The apoptotic percentage was determined to be around 58.0% aftera 24-h exposure to 25 µM Cd using flow cytometry stainingwith propidium iodine (PI). Pretreatment with Z-VAD-fmk, a broad-spectrumcaspase inhibitor, failed to prevent apoptosis following Cdexposure. Moreover, Cd was unable to activate caspase 3 usingDEVD-AFC as a substrate, indicating that Cd induced a caspase-independentapoptotic pathway in ${rho}$ ⁰ cells. JC-1 staining demonstrated thatmitochondrial membrane depolarization was a prelude to apoptosis.On the other hand, the intracellular calcium concentration increased12.5-fold after a 2-h exposure to Cd. More importantly, theapoptogenic activity of Cd was almost abolished by rutheniumred, a mitochondrial calcium uniporter blocker. This led usto conclude that mtDNA-depleted cells provide an alternativepathway for Cd to conduct caspase-independent apoptosis througha mitochondria-calcium mechanism.

				G. Kroemer, L. Galluzzi, and C. Brenner Mitochondrial Membrane Permeabilization in Cell Death Physiol Rev, January 1, 2007; 87(1): 99 - 163. [Abstract] [Full Text] [PDF]