PI-3 kinase inhibition affects both PKB and Erk activation upon SF stimulation. Serum-starved HPCs were incubated 30 minutes with 20 μM LY294002 (lane 3), 10 μM PD98059 (lane 4), or 10 μM PP1 (lane 5), as indicated (+) prior to 5 minutes of stimulation with 50 ng/mL SF (lanes 2-5, panels A-D). Cell lysates (20 μg per lane) were subjected to SDS-PAGE and then immunoblotted with antiphospho-specific Erk and PKB (A), anti-Erk (B), antiphospho-specific Y-719 c-Kit (C), and anti–c-Kit (D) antibodies. Dose-dependent inhibition of PKB and Erk by LY294002 (E). Cell lysates (20 μg protein per lane) were subjected to SDS-PAGE and then immunoblotted with antiphospho-specific Erk and PKB (E) and anti-Erk (F). In panels E-F, serum-starved cells were incubated 30 minutes with 0.1 μM (lane 3), 1 μM (lane 4), 5 μM (lane 5), 10 μM (lane 6), and 20 μM (lane 7) LY294002, as indicated prior to 5 minutes of stimulation with 50 ng/mL SF (lanes 2-7).