Fig. 2. Src kinase inhibitor PP1 inhibits MAPK activation by IGF-I. Proliferating 3T3-L1 cells were treated with 10 µM PP1 for 30 min prior to stimulation with 10 nM IGF-I (solid bars) for 5 min or no stimulation (open bars). Proteins in cell lysates were separated by SDS-PAGE and analyzed by Western blotting using phospho-MAPK antibodies (top panel) followed by ERK1/2 MAPK antibodies (not shown). Below the blot, densitometry of the phospho-MAPK bands, corrected for total MAPK content. This experiment was repeated two more times with the same results.