Cytoskeletal injury induced by hexavalent chromate

To understand the mechanisms of toxicity of hexavalent chromate (K(2)CrO(4), Cr(6+)), the effects of this metal ion on the organization of microtubules (MTs) and microfilaments (MFs), DNA synthesis, cytoskeletal protein synthesis, cytoskeletal protein sulphhydryls (-SH groups), and cellular glutathione (GSH) levels in 3T3 cells were examined. Exposure of cells to Cr(6+) for 16 hr resulted in a dose-dependent inhibition of DNA synthesis with 50% inhibition occurring at 16.6 mum. Treatment of cells with 3.13 mum-Cr(6+) for 16 hr resulted in a slight cell retraction and, in some cells, MT bundling, without much effect on the morphology of dense MFs. At 25 mum, Cr(6+) caused disruption of the cell sheet, depolymerization of MTs, particularly those in the peripheral areas, and redistribution of MFs, which assumed a smearing morphology. Exposure to 100 mum-Cr(6+) induced severe thinning of MTs and loss of MFs. Although doses of 3.13 mum-Cr(6+) or less slightly enhanced the level of cytoskeletal protein synthesis (e.g. 38% increase at 3.13 mum-Cr(6+)), Cr(6+) at 6.25 mum or more produced a dose-dependent inhibition of cytoskeletal protein synthesis (50% inhibition at 11.25 mum). Exposure of cells to Cr(6+) for 16 hr resulted in a dose- and time-dependent increase of cellular GSH level. Furthermore, the elevated cellular GSH induced by Cr(6+) was diminished by treatment with buthionine sulphoximine (BSO), a potent inhibitor of GSH biosynthesis. In addition, depletion of GSH by BSO increased cell sensitivity to Cr(6+) insult and aggravated Cr(6+)-induced cytoskeletal perturbation. However, Cr(6+) treatment of cells did not significantly affect the amount of cytoskeletal protein sulphhydryls. These results suggest that cytoskeletal injury may be an important part of the mechanism for Cr(6+) toxicity. The cytoskeletal damage may result directly from the inhibition of cytoskeletal protein synthesis rather than from the interaction between Cr(6+) and cytoskeletal protein sulphhydryls.