Reactive oxygen species may participate in the mutagenicity and mutational spectrum of cadmium in Chinese hamster ovary-K1 cells.
The molecular nature of mutations induced by Cd was investigated in this study to elucidate the role of Cd in the initiation of carcinogenesis. Exposing Chinese hamster ovary (CHO)-K1 cells to cadmium acetate markedly decreased the colony-forming ability of cells and induced mutation frequency in the hypoxanthine (guanine) phosphoribosyltransferase (hprt) gene. The mutation frequency induced by Cd at LD30-LD20 doses was approximately 20 times that of untreated cells. D-Mannitol, a scavenger of reactive oxygen species (ROS), significantly protects cells against Cd cytotoxicity and mutagenicity. Furthermore, non-cytotoxic doses of 3-amino-1,2,4-triazole, a catalase inhibitor, potentiates Cd cytotoxicity and mutagenicity. The cellular Cd uptake ability was not altered by the combined treatment with either D-mannitol or 3-amino-1,2,4-triazole. The GSH level and the activities of GSH peroxidase, GSSG reductase, and catalase in cells treated with Cd (4 microM, 4 h) decreased to 78%, 47%, 40%, and 22% of the untreated cells, respectively. Those enzymatic activities recovered to normal levels 8 h after removing Cd. Polymerase chain reaction and DNA sequencing analysis of 54 independent Cd mutants revealed Cd-induced base substitutions, splice mutations, and large genomic deletions. All six types of base substitutions were observed; however, base transversions (22/27; 81%) occurred more frequently than transitions (5/27; 19%). The frequencies of mutations occurring at T.A or G.C base pairs were roughly equal. Results in this study strongly suggest that Cd mutagenicity in CHO-K1 cells is ROS-dependent. Moreover, the unique mutational spectrum induced by Cd implies that specific DNA adducts generated through the interaction of Cd-DNA and ROS may play a role in the mutational specificity.
Yang
J L
JL
Department of Life Sciences, National Tsing Hua University, Taiwan, Republic of China. lsyjl@life.nthu.edu.tw
Chao
J I
JI
Lin
J G
JG
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002104:Cadmium / Q000378:metabolism / Q000633:toxicity*; D002374:Catalase / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D005979:Glutathione Peroxidase / Q000378:metabolism; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009153:Mutagens / Q000737:chemistry* / Q000633:toxicity; D016133:Polymerase Chain Reaction; D017382:Reactive Oxygen Species
D009153:Mutagens; D017382:Reactive Oxygen Species; D002104:Cadmium; D002374:Catalase; D005979:Glutathione Peroxidase; D007041:Hypoxanthine Phosphoribosyltransferase