Figure 1.

Reversal of NGF-mediated growth arrest by the MEK-specific inhibitor PD98059. (A) Treatment with PD98059 produces a dose-dependent reversal of the growth arrest induced by NGF treatment. TRK1 cells were grown for 4 days in normal growth medium (▪) or growth medium supplemented with 20 nM NGF added (□). Vehicle [dimethyl sulfoxide (DMSO), 0.2%] or increasing concentrations of PD98059 were included throughout the 4-day incubation as indicated. Cell numbers represent the average of duplicate determinations. Data are representative of two independent experiments. (B) PD98059 blocks NGF stimulation of MAPK activity. Cells were grown in complete growth medium in the presence or absence of 20 nM NGF (as indicated) for 16 hr following addition of vehicle (DMSO, 0.2%) or 40 μM PD98059.