Mg2+ antagonism on Ni(2+)-induced changes in microtubule assembly and cellular thiol homeostasis.
As an essential metal for cell metabolism, Mg2+ is known to exert antagonism on Ni2+ genotoxic and other effects. This study examined the influence of Mg2+ on Ni(2+)-induced changes in microtubule (MT) assembly in vitro, cytoplasmic MT organization, cellular glutathione (GSH), and cytoskeletal and cytosolic protein sulfhydryls (PSH). As determined by a turbidity assay at 27 degrees C, Ni2+ enhanced the in vitro MT assembly in a Pipes buffer by shortening the initial lag (nucleation phase) and increasing the rate of polymerization with a higher final plateau. However, presence of 1 mM exogenous MgCl2 abolished the Ni2+ enhancing effect. Exposure of 3T3 cells to 2 mM NiCl2 for 20 hr resulted in perinuclear bundling of MTs and decreases in cytoskeletal and cytosolic PSH and cellular GSH levels. However, coincubation of cells with MgCl2 (1.25-20 mM) added to the culture medium markedly diminished the Ni2+ injury to MT organization. Under these conditions the Ni2+ interference with PSH was blocked such that both the cytoskeletal and cytosolic PSH levels returned to the range of control cells without metal treatment. Treatment of cells with Mg2+ (1.25-5 mM) for 20 hr slightly increased, while with higher Mg2+ doses (> 10 mM) decreased, cellular GSH content. Importantly, in Ni(2+)-treated cultures, addition of Mg2+ (1.25-10 mM) elevated GSH levels to > or = 200% of that in cells treated with Ni2+ alone. Furthermore, these Ni2+ and Mg2+ (1.25-10 mM) treated cells actually maintained GSH levels which were essentially unchanged from the basal level of control cells with no metal treatment. Although Mg2+ replacement of Ni2+ bound to MT proteins could be an important mechanism, cellular GSH may also be a critical factor in Mg2+ antagonism on Ni(2+)-enhanced MT assembly in view of the essential role of tubulin PSH in modulating MT assembly and, in turn, the GSH modulation of PSH.
Li
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Department of Microbiology, Boston University School of Medicine, Massachusetts 02118, USA.
Zhao
Y
Y
Chou
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IN
D016475:3T3 Cells / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D003470:Culture Media; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D015636:Magnesium Chloride / Q000494:pharmacology*; D051379:Mice; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000187:drug effects* / Q000473:pathology; D009391:Nephelometry and Turbidimetry; D009532:Nickel / Q000037:antagonists & inhibitors / Q000633:toxicity*; D011108:Polymers; D013438:Sulfhydryl Compounds / Q000378:metabolism*
D003470:Culture Media; D011108:Polymers; D013438:Sulfhydryl Compounds; D015636:Magnesium Chloride; C022838:nickel chloride; D009532:Nickel; D005978:Glutathione