Treatment with PP1 blocks capping of c-Kit. MO7e cells were preincubated without PP1 (A,B) or with PP1 (C,D) as described in Fig 1, then labeled with the 104D2 antibody. Before exposure to SCF (A,C), or after a 3-minute exposure to SCF (200 ng/mL; B,D), the cells were fixed and labeled with goat antimouse IgG-FITC plus propidium iodide, and photographed at a magnification of 60×.