Fig. 1. Src kinase inhibitor PP1 inhibits [3H]thymidine incorporation by IGF-I. Proliferating 3T3-L1 cells were treated with or without 10 µM PP1 in the presence of 10 nM IGF-I (solid bars) or no hormone (open bars) for 24 h. [3H]thymidine (1 µCi/well) was added for the last 4 h. Cells were lysed in 0.33 M NaOH, an aliquot was removed for protein concentration determination, and DNA was precipitated with cold TCA. n = 6 wells (samples) per condition. This experiment was repeated once with identical results.