Caspase-dependent and -independent pathways for cadmium-induced apoptosis in cultured kidney proximal tubule cells.
The nephrotoxic metal cadmium at micromolar concentrations induces apoptosis of rat kidney proximal tubule (PT) cells within 3-6 h of exposure. The underlying cell death pathways remain poorly defined. Using Hoechst 33342/ethidium bromide nuclear staining and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell death assays, 10-50 microM cadmium induced apoptosis of immortalized rat kidney cells derived from the S1-segment of PT at 6 and 24 h, but necrosis at 24 h only. Cadmium (10-50 microM) also caused mitochondrial cytochrome c (cyt. c)- and apoptosis-inducing factor release at 24 h, but not at 6 h, as measured by immunofluorescence imaging and immunoblotting. Caspases-9 and -3 were activated only by 10 microM cadmium for 24 h, and accordingly apoptosis was significantly reduced by the respective inhibitors (z-LEHD-fmk, z-DEVD-fmk; 10 microg/ml) at 24 h, but not at 6 h, without affecting necrosis. At 6 h, 10 microM cadmium increased the activity of the calcium-activated protease calpain, but not at 24 h, and calpain inhibitors (ALLN, PD 150606; 10-30 microM) blocked apoptosis by 10 microM cadmium at 3-6 h. However, PD-150606 also attenuated caspase-3 activity and apoptosis at 24 h, suggesting calpain-dependent caspase activation. Thus cadmium-induced apoptosis of PT cells involves a complex and sensitive interplay of signaling cascades involving mitochondrial proapoptotic factors, calpains and caspases, whose activation is also determined by cadmium concentration and the duration of cadmium exposure.
Lee
Wing-Kee
WK
Department of Physiology and Pathophysiology, Faculty of Medicine, University of Witten/Herdecke, Witten, Germany.
Abouhamed
Marouan
M
Thévenod
Frank
F
D000179:Acrylates / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002104:Cadmium / Q000633:toxicity*; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D051381:Rats
D000179:Acrylates; C100442:PD 150606; D002104:Cadmium; D045304:Cytochromes c; D020169:Caspases