Insulin-Like Growth Factor-I E-Peptide Activity Is Dependent on the IGF-I Receptor
Figure 4
E-peptides augment IGF-IR activation and cell surface localization.
A. P6 cells overexpressing IGF-IR were treated with synthetic E-peptides with and without recombinant IGF-I for 15 minutes, and cell lysates were utilized for KIRA assays. Level of absorbance indicates the extent of IGF-IR phosphorylation. Bars represent means ± s.e.m. of N = 6 wells. B. OD 450 from A were compared to No Peptide for each IGF-I concentration, and the % change is graphed. C. P6 cells were treated as in A for a localization assay for times indicated, and biotin labeled before lysis. The optimal concentrations of E-peptides and IGF-I from the A were used (E-peptides 100 nM, IGF-I 10 nM). Surface IGF-IR was normalized to Total IGF-IR and compared to NoTx at t0 to get % IGF-IR on cell surface. Bars represent means ± s.e.m. of N = 6 wells. Samples were compared to no peptide (A and B,*), NoTx (C,*) or IGF-I (C,†) via 2-way ANOVA followed by a Bonferroni post-test. * or †, p<0.05; ***, p<0.001.
