FIGURE 4.

Inhibition of cell proliferation and phospho-ERK expression by an ERK activation inhibitor (PD98059) in the SH-SY5Y cells. A, cells were cultured in medium without fetal bovine serum for 24 h and then with 10% fetal bovine serum in the presence of various concentrations of PD98059 for 2 days. Cell numbers were then measured and normalized by those at the beginning of the fetal bovine serum stimulation. B–D, cells treated as described for panel A were harvested for Western blotting of phospho-ERK (pERK), total ERK (tERK), phospho-SMAD2/3 (pSMAD2/3), total SMAD2/3 (tSMAD2/3), and phospho-SMAD1/5/8 (pSMAD1/5/8). The ERK and SMAD Western blot results were normalized by those of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The results from cells incubated with PD98059 were then normalized by those from control cells. Results are mean ± S.D. (n = 3–4). *, p < 0.05 compared with the corresponding results without PD98059.