Studies on the mechanisms of Ni2(+)-induced cell injury: I. Effects of Ni2+ on microtubules.
Cytoskeletal perturbations have been associated with exposures to a variety of toxic agents as well as a number of human pathological conditions. We have observed dramatic alterations in the organization of microtubules (MT), a major component of the cytoskeleton, in 3T3 cells exposed to Ni2+. Severe perinuclear bundling and aggregation of MT occurred in both a time- and dose-dependent fashion, and this MT damage was reversible upon removal of Ni2+ from the culture media. To understand the mechanism of the Ni2(+)-induced MT change, we investigated the effect of Ni2+ (0.01 to 3.0 mM) on in vitro tubulin polymerization. Ni2+ at lower concentrations (0.01 to 1.0 mM) had little or no significant effect on the kinetics of MT polymerization. In contrast, in the presence of 1.5 to 2.0 mM Ni2+, a significant promoting effect on both the rate and the final extent of polymerization was observed. However, at Ni2+ concentrations higher than 2.0 mM, such stimulatory effect on the rate and the final extent of tubulin polymerization declined. Furthermore, the promoting effects of Ni2+ on MT polymerization were accompanied by a significant decrease in the lag period. Electron microscopic examination of samples of the polymerization product showed that MT, polymerized in the presence of 2.0 mM Ni2+, appeared more numerous and shorter (1.10 +/- 1.02 microns) than those of control (3.81 +/- 2.29 microns; p less than 0.005). This was probably a direct result of an increase in the number of initiation centers in the presence of Ni2+ as a consequence of the decreased critical concentration (7%, p less than 0.05) necessary for polymerization to occur. Our results suggest that Ni2+ may exert its toxic effect on MT in cultured cells by altering the normal kinetics of MT polymerization.
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Department of Pathology, Boston University School of Medicine, Massachusetts 02118.
Chou
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D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D003080:Cold Temperature; D003599:Cytoskeleton / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008854:Microscopy, Electron; D008868:Microtubule Proteins / Q000378:metabolism; D008870:Microtubules / Q000187:drug effects* / Q000648:ultrastructure; D009532:Nickel / Q000633:toxicity*; D013997:Time Factors; D014404:Tubulin / Q000378:metabolism
D008868:Microtubule Proteins; D014404:Tubulin; D009532:Nickel; D002118:Calcium