Alterations in cytoskeletal protein sulfhydryls and cellular glutathione in cultured cells exposed to cadmium and nickel ions

Abstract

To understand the mechanisms of Cd 2+ and Ni 2+ cytotoxicity, we have studied the effects of these two metal ions on the organization of cytoskeletal elements, microtubules (MT) and microfilaments (MF), cytoskeletal protein sulfhydryls and cellular glutathione (GSH) in cultured 3T3 cells. At a metal ion dose that caused 95% inhibition of DNA synthesis, Cd 2+ (10 μM, 16 h exposure) induced MT depolymerization whereas Ni 2+ (2 mM, 20 h exposure) elicited MT aggregation and bundling. Under these conditions, Cd 2+ and Ni 2+ also caused MF aggregation and redistribution. Furthermore, exposure of cells to Cd 2+ resulted in a dose-dependent increase in cytoskeletal protein sulfhydryls and cellular GSH levels. In contrast, treatment of cells with Ni 2+ resulted in a dose-dependent decrease in cytoskeletal protein sulfhydryls as well as cellular GSH content. Time course studies showed that cells exposed to 10 μM Cd 2+ exhibited a biphasic response in regulating their cytoskeletal protein sulfhydryls and cellular GSH, e.g. an initial decrease followed by a steady recovery and overshooting upon prolonged incubation. However, restoration of cytoskeletal protein sulfhydryls occured ∼ 2 h after commencement of cellular GSH recovery in Cd 2+-treated cells. These results suggest that cellular GSH may play an important role in regulating cytoskeletal protein sulfhydryls. On the other hand, decrease of cellular GSH induced by Ni 2+ might facilitate oxidation of cytoskeletal protein sulfhydryls and formationn of disulfide bonds between individual MT polymers which would favor MT aggregation in Ni 2+-exposed cells. in addition, we also demonstrated that elevation of cellular GSH in Cd 2+-treated cells probably resulted from new GSH synthesis.