Fig. 7. Inhibition of MAPK activation fails to block SCF-mediated growth. In A, H526 cells were pretreated with 40 µM PD 98059 or DMSO vehicle for 30 min and then left either unstimulated (NS) or stimulated with SCF (100 ng/ml) for 5 min. MAPK activation was assessed by Western blotting. In B, H526 cells in serum-free medium containing SCF were incubated in increasing concentrations of PD 98059 and growth over 72 h was measured using the MTT method. Despite efficiently inhibiting MAPK activation, the MEK inhibitor had no effect on growth. Error bars, the SD from the mean of eight replicate wells; results are representative of three replicate experiments.