Binding affinities of insulin-like growth factor-I (IGF-I) fusion proteins to IGF binding protein 1 and IGF-I receptor are not correlated with mitogenic activity.
In this report, comparisons between molecular affinities and cellular proliferation activities have been made for insulin-like growth factor-I (IGF-I) and two IGF-I fusion proteins in order to evaluate fusion proteins as tools for receptor binding studies. Binding affinities and growth promoting effects of the N-terminal fusion Z-IGF-I and the C-terminal fusion IGF-I-Z, and native recombinant human IGF-I, were analyzed. Binding kinetic properties of the three IGF-I variants were analyzed using BIAcore kinetic interaction analysis testing for binding to both human IGF binding protein 1 (IGFBP-1) and a soluble form of the human IGF type I receptor extracellular domains (sIGF-IR). The growth promoting effects on SaOS-2 human osteosarcoma cells of the different fusion proteins were analyzed. A comparison of receptor binding affinities and growth promoting effects shows that the fusion protein receptor affinity does not correlate with proliferative potential. The IGF-I-Z fusion, with the lowest receptor affinity, shows similar proliferative potential to native IGF-I. However, the Z-IGF-I fusion protein, with twice the receptor affinity of IGF-I-Z, displays only about 70% of the IGF-I-Z growth promoting activity. Both IGF-I fusion proteins possess similar affinity to IGFBP-1. These results indicate that determinants other than the receptor affinity could be involved in the regulation of IGF-I proliferative action. This study demonstrates that ligand fusion proteins may be useful to study mechanisms of ligand induced receptor activation.
Jansson
M
M
Royal Institute of Technology, Department of Biochemistry and Biotechnology, Stockholm, Sweden.
Dixelius
J
J
Uhlen
M
M
Nilsson
B O
BO
D001665:Binding Sites; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002942:Circular Dichroism; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D007668:Kidney; D007700:Kinetics; D011487:Protein Conformation; D017526:Receptor, IGF Type 1 / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology
D018970:Insulin-Like Growth Factor Binding Protein 1; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1