c-Myc protein stability was unaltered by GM-CSF and IL-3. Determination of the half-life of the c-Myc protein in MO7e (left panels) and F36P (right panels) cells incubated with or without GM-CSF and IL-3. Pulse-labeling and immunoprecipitation were performed as described in “Materials and methods.” Cells were labeled with radioisotope for 30 minutes at 37°C and were then incubated for the indicated periods with or without 10 ng/mL (MO7e) or 1 ng/mL (F36P) GM-CSF and IL-3 at 37°C. Immunoprecipitates were subjected to SDS-PAGE, and the amount of radiolabel incorporated into each band was determined using a Phosphor Imager. (A) Representative gels of pulse-labeling immunoprecipitations. (B) Phosphor Imager analysis of the gels shown in panel A. □ indicates cells incubated without HGFs; ▪, cells incubated with GM-CSF; •, cells incubated with IL-3. These show the representative results that were performed on a minimum of 3 independent experiments.