Figure 4.

Effect of the ERK1/2 inhibitor PD98059 on metal-induced BrdU incorporation (panel A, cell proliferation) and secondary thyrospheres’ formation (panel B). (A) Histograms represent the mean value ± SEM of three separate experiments. For each metal and their mixture values are expressed as percent of CTRL (untreated thyrospheres). After thyrospheres’ exposure to metals for 3 days in the absence or the presence of PD98059 (20 µM) BrdU incorporation was significantly iblunted in all cases by the inhibition of the ERK1/2 pathway. *p < 0.05; **p < 0.01 and ***p < 0.001 vs. CTRL. (B) Inhibition of the ERK1/2 pathway reduces secondary thyrospheres’ formation. Cells from dissociated thyrospheres were plated at a density of 3,000 cells in nonadherent 96-wel plates and exposed to metals in the absence or the presence of PD98059 (20 µM) for 8 days. Spheres were counted in 4 wells for each condition. The results are expressed as mean value ± SEM of three separate experiments. *p < 0.05; **p < 0.01 and ***p < 0.001 comparing thyrospheres’ number in the presence of PD98059 to the number measured under the same condition in control thyrospheres. ns, non significant; °p < 0.05; °°p < 0.01 and °°°p < 0.001 comparing thyrospheres’ number in the absence or the presence of PD98059.