ABCB1 Protects Kidney Proximal Tubule Cells Against Cadmium-Induced Apoptosis: Roles of Cadmium and Ceramide Transport

作者：Lee Wing Kee^*; Torchalski Blazej; Kohistani Naschla; Thevenod Frank

来源：Toxicological Sciences, 2011, 121(2): 343-356.

DOI：10.1093/toxsci/kfr071

• P-glycoprotein
• cell death
• multidrug resistance
• sphingolipids
• transition metal

Cadmium (Cd(2+)) damages the kidney proximal tubule (PT) by ceramide-dependent apoptosis and is also a class 1 carcinogen. Multidrug resistance P-glycoprotein (MDR1, ABCB1) confers resistance to Cd(2+) apoptosis, and it has been hypothesized that ABCB1 can directly transport Cd(2+) as a mode of cellular protection. Our aim was to investigate the role of ABCB1 in Cd(2+) transport and ceramide apoptosis. In rat PT or Madin-Darby canine kidney (MDCK) cells overexpressing ABCB1, ABCB1-dependent efflux of rhodamine 123(+) (Rh123(+)) or (109)Cd(2+) were determined, and cell death was assayed with MTT, H-33342 nuclear staining, and monolayer integrity by impedance sensing (Electric cell-substrate impedance sensing [ECIS]). ABCB1 inhibitors (PSC833, UIC-2 antibody) did not affect (109)Cd(2+) efflux in PT cells though Rh123(+) transport was blocked. Furthermore, increased ABCB1 expression did not augment (109)Cd(2+) efflux but attenuated apoptosis by 10-50 mu M Cd(2+) or 5-25 mu M C(6)-ceramide, which was abolished by PSC833 (1 mu M). ECIS measurements of ABCB1-MDCK monolayers exhibited similar effects. Moreover, in ABCB1-MDCK cells, Cd(2+)-induced ceramide formation, determined by a diacylglycerol kinase assay, was abolished and increased extrusion of nitro-2-1,3-benzoxadiazol-4-yl (NBD)-C(6)-ceramide, and NBD-C(6)-glucosylceramide was observed compared with MDCK cells. Whereas pharmacological block of sphingomyelin synthase (0.1mM D609) or sphingosine kinase (1 mu M dimethylsphingosine), which increase the levels of ceramide and its metabolites, augmented Cd(2+)-induced apoptosis, Cd(2+) apoptosis was significantly decreased not only by prevention of de novo ceramide synthesis (0.1 mu M fumonisin B(1)) but also by inhibition of glucosylceramide synthase (2 mu M C(9)DGJ). We therefore conclude that Cd(2+) efflux is not the mechanism behind ABCB1-mediated protection from Cd(2+) apoptosis. Rather, the sphingolipid glucosylceramide may be the proapoptotic substrate extruded by ABCB1.

• 出版日期2011-6