Effects of Microtubule-Associated Protein (MAP) Expression on Methylmercury-Induced Microtubule Disassembly

Abstract

The sensitivity of microtubules (MTs) to methylmercury- (MeHg) induced disassembly was compared in undifferentiated, MAP1A- and MAP2C-transfected, and neuronally differentiated P19 Embyronal Carcinoma (EC) cells. The extent of MT disassembly was examined qualitatively by immunofluorescence microscopy and Western blotting and quantitatively by dot blotting of polymer and soluble proteins extracts. Immunofluorescence microscopy showed that MeHg disassembled MTs in a time- and dose-dependent manner and that MTs in both MAP2C-transfected and neuronally differentiated cells, but not those in MAP1A-transfected cells, were significantly more resistant to MeHg-induced MT depolymerization than those in undifferentiated cells. These results suggest that MAP2C has a greater ability to stabilize MTs against MeHg-induced disassembly than MAP1A. Surprisingly, however, when the extent of MT disassembly was assessed by Western blotting and by quantitative dot blotting, no change was observed in the amounts of tubulin, MAP2, or MAP1A, in the polymer and soluble fractions in MeHg-treated samples, compared to the control cells that were not treated. These data show that, although MeHg treatment resulted in the disassembly of MTs, they were not depolymerized as detergent-soluble subunits, but rather appeared to form insoluble tubulin–MAP oligomers or aggregates.