Fig. 6. The Grb2-SH2 blocking peptide inhibits EGF-induced but not HGF-induced DNA synthesis. The Grb2-SH2 blocking peptide or its control phenylalanine-containing counterpart was introduced at the indicated concentrations by in situ electroporation into NIH-3T3 (A) or A549 (B) cells growing on fully conductive slides (Fig. 1 B) and growth-arrested by serum starvation. Five min after electroporation, cells were stimulated with 100 ng/ml EGF (A), 40 ng/ml HGF (B), or 10% fetal bovine serum (FBS), respectively, as indicated. Twelve h later, cells were labeled with [3H]thymidine for 2 h, and TCA precipitable radioactivity was determined. In A, the two lanes at the far right represent cells labeled at 40–42 h after electroporation and EGF stimulation. phe, control peptide containing phenylalanine at the position of the EGFR-Tyr1068. Pmp, Grb2-SH2 binding peptide containing Pmp at the position of Tyr1068. The results represent the mean ± SE cpm from three experiments.