FIG. 6.

Cell-permeable fusion peptides of the Grb10 Pro-rich region interfere with IGF-I- and insulin-mediated, but not PDGF-BB-mediated, DNA synthesis. Mouse NIH 3T3 fibroblasts were starved in 0.5% serum-containing medium for 24 h, incubated with 0, 1, 5, 10, or 20 μg of the Grb10 fusion peptide (RQIKIWFQNRRMKWKK-TASLPAIPNPFPELTG) per ml or with 0, 1, 3, or 10 μg of a control peptide (RQIKIWFQNRRMKWKK) per ml (in parentheses), and stimulated with 25 ng of PDGF-BB, 100 ng of IGF-I, 100 ng of insulin, or 100 ng of EGF per ml or left untreated for 18 h; 0.5 μCi of [methyl-³H]thymidine was then added for 5 h, and acid (10% TCA)-precipitated radioactivity was quantified by scintillation spectroscopy. The data presented are based on three independent experiments. Error bars indicate the variation between duplicate measurements of the representative experiment shown. DNA synthesis in the absence of growth factor has been defined as zero.