Cadmium-induced apoptosis in rat kidney epithelial cells involves decrease in nuclear factor-kappa B activity.
Renal epithelial cells undergo apoptosis upon exposure to cadmium (Cd). Transcription factors, such as nuclear factor-kappa B (NF-kappaB), mediate the expression of a number of genes involved in apoptosis. The present study was designed to examine the involvement of this transcription factor in Cd-induced apoptosis. Rat kidney proximal tubular epithelial cells, NRK-52E, were incubated with up to 20 microM CdCl2 in serum-free medium for 5 h followed by incubation in serum-containing medium (without Cd) for an additional 12 h. The cells accumulated 582 +/- 19 ng Cd/mg protein after 5-h exposure to 20 microM Cd. As a result of Cd exposure, the DNA-binding activity of the p65 subunit of NF-kappaB was decreased in a concentration- and time-dependent manner. The activity of tumor necrosis factor-alpha-induced inhibitor of kappa B (IkappaB) kinase alpha was also inhibited by Cd. In addition, the phosphorylation of IkappaB-alpha and NF-kappaB p65, as well as the levels of NF-kappaB target gene products, cIAP-1 and cIAP-2, were reduced. Pretreatment of the cells with the antioxidant U83836E or butylated hydroxytoluene preserved the DNA-binding activity and blocked the Cd-induced decease in IkappaB-alpha phosphorylation. Cd exposure caused the activation of caspase-3, -7, and -9 and DNA fragmentation. By flow cytometry, 14.6 and 30.5% apoptosis was detected at 6 and 12 h after stopping the Cd exposure. Overexpression of NF-kappaB p65 by transient transfection protected the cells from the Cd-induced apoptosis. Conversely, attenuation of NF-kappaB activity by pretreatment with SN50, an NF-kappaB nuclear translocation inhibitor, potentiated apoptosis. These results suggest that Cd-induced apoptosis involves suppression of NF-kappaB activity which may be mediated by oxidative stress.
Department of Biomedical and Pharmaceutical Sciences and Center for Molecular Toxicology, College of Pharmacy, University of Rhode Island, Kingston, Rhode Island 02881, USA.
Jianxun
J
Xie
Zahir A
ZA
Shaikh
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D002104:Cadmium / Q000633:toxicity*; D002460:Cell Line; D024202:Electrophoretic Mobility Shift Assay; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005434:Flow Cytometry; D007668:Kidney / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D009841:Oligonucleotides; D010766:Phosphorylation; D051381:Rats
D016328:NF-kappa B; D009841:Oligonucleotides; D002104:Cadmium