Structural and functional evidence for the interaction of insulin-like growth factors (IGFs) and IGF binding proteins with vitronectin.
Previous studies demonstrated that IGF-II binds directly to vitronectin (VN), whereas IGF-I binds poorly. However, binding of VN to integrins has been demonstrated to be essential for a range of IGF-I-stimulated biological effects, including IGF binding protein (IGFBP)-5 production, IGF type-1 receptor autophosphorylation, and cell migration. Thus, we hypothesized that a link between IGF-I and VN must occur and may be mediated through IGFBPs. This was tested using competitive binding assays with VN and (125)iodine-labeled IGFs in the absence and presence of IGFBPs. IGFBP-4, IGFBP-5, and nonglycosylated IGFBP-3 were shown to significantly enhance binding of IGF-I to VN, whereas IGFBP-2 and glycosylated IGFBP-3 had a smaller effect. Furthermore, binding studies with analogs indicate that glycosylation status and the heparin-binding domain of IGFBP-3 are important in this interaction. To examine the functional significance of IGFs binding to VN, cell migration in MCF7 cells was measured and found to be enhanced when VN was prebound to IGF-I in the presence of IGFBP-5. The effect required IGF:IGFBP:VN complex formation; this was demonstrated by use of a non-IGFBP-binding IGF-I analog. Together, these data indicate the importance of IGFBPs in modulating IGF-I binding to VN and that this binding has functional consequences in cells.
Kricker
Jennifer A
JA
Tissue BioRegeneration and Integration Program, School of Life Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia. j.kricker@qut.edu.au
Towne
Chris L
CL
Firth
Sue M
SM
Herington
Adrian C
AC
Upton
Zee
Z
D001667:Binding, Competitive; D001943:Breast Neoplasms; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D004347:Drug Interactions; D006031:Glycosylation; D006801:Humans; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000378:metabolism / Q000494:pharmacology; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism / Q000494:pharmacology; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000378:metabolism / Q000494:pharmacology; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism / Q000494:pharmacology; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism* / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D007457:Iodine Radioisotopes; D014407:Tumor Cells, Cultured; D019096:Vitronectin / Q000378:metabolism*
D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018974:Insulin-Like Growth Factor Binding Protein 4; D018975:Insulin-Like Growth Factor Binding Protein 5; D018969:Insulin-Like Growth Factor Binding Proteins; D007457:Iodine Radioisotopes; D019096:Vitronectin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II