Effect of cadmium on cell cycle progression in chinese hamster ovary cells

Chinese hamster ovary K1 (CHO K1) cells are very sensitive to cadmium (Cd) toxicity. They were used to investigate the effect of Cd on cell cycle progression. Cells were cultured with 0.1, 0.4, 1 or 4 muM Cd for various time intervals. There was no difference in growth rate when less than 0.4 muM Cd was given within 24 h. A dose-dependent reduction of cell proliferation was observed when more than 0.4 [muM of Cd was given. The cells were pulse-labeled with 5-bromodeoxyuridine (BrdU), and the labeled cells were cultured in the presence of increasing concentrations of Cd. Cell cycle progression was retarded as a function of Cd concentration. G2/M arrest was observed when the BrdU-Iabeled cells were treated with I muM Cd for 8 h, whereas cells receiving 4 muM Cd stopped at the S phase within 4 h, Cell cycle analysis of cells treated with Cd for 24 h showed that G2/M arrest occurred only when cells received 0.8 to 2 [muM Cd. Despite the occurrence of G2/M arrest in the Cd treatment, only a limited proportion of the cells were blocked in the M phase. However, the increase in M phase cells coincided with an elevation in the cyclin-dependent kinase I activity. To examine whether Cd acts on cells at a specific cell stage, they were synchronized at the G I or G2/M phase then treated with I muM Cd for 12 h. The cells were blocked at the G2/M and G US phase, respectively. This finding indicates that Cd toxicity is global and not cell phase specific. We also investigated the involvement of Cd-induced reactive oxygen species (ROS) with the occurrence of G2/M block and found a lack of correlation between cell cycle arrest and ROS production. We measured the Cd content that caused G2/M arrest from a series of Cd treatments and determined the ranges of cumulative Cd concentrations that could result in cell cycle arrest. (C) 2004 Elsevier Ireland Ltd. All rights reserved.