PP1 inhibits SCF-induced internalization of c-Kit. MO7e cells were preincubated without PP1 (◍) or with PP1 (○) for 30 minutes at 37°C, then SCF (200 ng/mL) was added. Aliquots of cells were removed at time 0, 3, 15, and 60 minutes after the addition of SCF, fixed in 0.5% paraformaldehyde, labeled with the anti–c-Kit MoAb 104D2, followed by PE-conjugated goat antimouse IgG, and analyzed by flow cytometry. The MO7e cells incubated in the absence of PP1 exhibited a PE mean fluorescence intensity at time 0 identical to that of the MO7e cells incubated in the presence of PP1. One additional experiment gave similar results.