Alterations in cytoskeletal organization and homeostasis of cellular thiols in cadmium-resistant cells.
To understand further the mechanisms of cadmium toxicity, cytoskeletal organization and homeostasis of cellular thiols were examined in cadmium-resistant cells isolated from Swiss mouse 3T3 cells by incubation in graded concentrations of CdCl2 (Cd2+) in the culture medium. Cd(2+)-resistant cells displayed profound alterations in their cytoskeletal organization characterized by the appearance of many elongated, tadpole-shaped cells with a high density of microtubules (MT) and microfilaments (MF), with the former being mainly distributed along the long axis of the cell. Exposure of Cd(2+)-resistant cells to 50 microM Cd2+ for 16 hr did not cause apparent cytoskeletal perturbations, whereas treatment of parental cells with 5 microM Cd2+ for the same duration produced a severe loss of MT and smeared patches of MF. Thus, the cytoskeleton of Cd(2+)-resistant cells is markedly more preserved and protected against Cd2+ damage than that of their parental counterparts. Cd(2+)-resistant cells contained a higher basal level of protein sulfhydryls (PSH) in both the cytoskeletal and cytosolic fractions than the parental cells. Exposure to 50 microM Cd2+ further increased cellular PSH contents, reaching 192 and 215% of the basal levels for the cytoskeletal and cytosolic fractions, respectively. Although 5 microM Cd2+ exposure also elevated the amounts of PSH in parental cells, the "absolute" values were still below the corresponding basal levels in Cd(2+)-resistant cells. Furthermore, Cd(2+)-resistant cells also exhibited enhanced basal levels of metallothionein and cellular glutathione (GSH), amounting to 19- and 2.1-fold of the parental basal levels, respectively. Thus, the Cd(2+)-resistant cells produced larger quantities of both protein and nonprotein thiol-containing elements than the parental cells. Interestingly, exposure of Cd(2+)-resistant cells to 50 microM Cd2+ also further increased metallothionein and cellular GSH to 178 and 138% of the basal levels, respectively. Based on the affinity of Cd2+ for sulfhydryls as a mechanism of Cd2+ toxicity, we propose that the coordinately increased levels of metallothionein, GSH, and PSH in Cd(2+)-resistant cells would provide a mechanistic basis for the homeostasis of cellular thiols which may collectively contribute to the cytoskeletal preservation by protecting the cytoskeleton from Cd2+ insult.
Li
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Department of Biochemistry, Boston University School of Medicine, Massachusetts 02118.
Kagan
H M
HM
Chou
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D016475:3T3 Cells; D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D003599:Cytoskeleton / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D003600:Cytosol / Q000378:metabolism; D004351:Drug Resistance; D005978:Glutathione / Q000096:biosynthesis; D006706:Homeostasis / Q000502:physiology; D008668:Metallothionein / Q000096:biosynthesis; D051379:Mice; D008856:Microscopy, Fluorescence; D013438:Sulfhydryl Compounds / Q000378:metabolism*
D013438:Sulfhydryl Compounds; D002104:Cadmium; D008668:Metallothionein; D005978:Glutathione