Type I and type II insulin-like growth factor receptors and their function in human Ewing's sarcoma cells

Summary

Binding studies using recombinant human¹²⁵I-labelled insulin-like growth factor I ([¹²⁵I]IGF-I) revealed IGF-I receptors in three Ewing's sarcoma cell lines withK _d ranging from 74×10⁻¹² M to 100×10⁻¹² M andB _max=36–63 fmol/mg cell protein. [¹²⁵I]IGF-I binding was displaced by IGF-I, IGF-II and insulin with IC₅₀ values of 1.5 nM, 6.3 nM and 0.7 μM respectively. Recombinant human [¹²⁵I]IGF-II radioligand-binding assays in the cell lines disclosed specific binding sites for IGF-II withK _d=(110–175)×10⁻¹² M andB _max varying from 21 fmol/mg to 72 fmol/mg cell protein. Neither IGF-I nor insulin displaced [¹²⁵I]IGF-II binding. IGF-I was found to increase basal glucose transport by maximally 1.5 times with EC₅₀=0.9 nM IGF-I. The efficacy and potency of IGF-II on glucose uptake were comparable to those of IGF-I whereas insulin was ineffective. IGF-I and IGF-II also provoked stimulation of glycogen synthesis in Ewing's sarcoma cells. The maximal glycogenic response was reached at 0.01 μM IGF-I and 0.1 μM IGF-II, the EC₅₀ value being approximately 1 nM IGF-I and 2 nM IGF-II. Insulin did not significantly influence glycogen formation. IGF-I and IGF-II but not insulin increased DNA synthesis in Ewing's sarcoma cells. The maximal mitogenic response was obtained with 10 nM IGF-I or IGF-II with an EC₅₀ value of about 0.7 nM for both peptides. α-IR-3, a monoclonal antibody specific for the IGF type I receptor, effectively blocked IGF-I- and IGF-II-mediated metabolic responses. In conclusion, the data show that IGF-I and IGF-II induce rapid and longterm biological responses in Ewing's sarcoma cells exclusively through interaction with IGF type I receptors.