Changes induced by non-enzymatic glycosylation of IGF-binding protein-3: effects on its binding properties and on its modulatory effect on IGF-I mitogenic action.
The aim of this study was to demonstrate the feasibility of in vitro non-enzymatic glycosylation of IGF-binding protein-3 (IGFBP-3) and whether this process affects its binding properties and its modulatory effect on IGF-I mitogenic activity. Swiss 3T3 fibroblasts were cultured and the IGFBP-3 released into the medium (CM) glycated with either labelled or unlabelled glucose. Parallel glycation studies were performed using standard human IGFBP-3. Both species of IGFBP-3 became effectively glycated in a dose-dependent manner. Glycated IGFBP-3 bound larger amounts of 125I-labelled IGF-I than its non-glycated form. According to Scatchard analysis this effect might be due to an increase in the number of binding sites of the IGFBP-3 molecule rather than to changes in its affinity constants, which remain unchanged. Preincubation of fibroblasts with CM containing IGFBP-3 for 16 h before the addition of IGF-I enhanced the stimulatory effect of the hormone on thymidine incorporation into cell DNA. This potentiation was blunted when in vitro glycated instead of non-glycated IGFBP-3 was employed. These results provide further evidence of the in vitro glycation of IGFBP-3 and demonstrate that this process affects both its binding properties and its enhancing effect on IGF-I mitogenic activity. These changes may explain, at least partially, the development of many alterations observed in poorly controlled diabetic patients.
Cortizo
A M
AM
CENEXA-Centro de Endocrinología Experimental y Aplicada (UNLP-CONICET), Facultad de Ciencias Médicas, La Plata, Argentina.
Gagliardino
J J
JJ
D016475:3T3 Cells / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D006031:Glycosylation; D006131:Growth Inhibitors / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D051379:Mice; D011485:Protein Binding; D011869:Radioligand Assay; D013002:Somatomedins / Q000378:metabolism*
D002352:Carrier Proteins; D006131:Growth Inhibitors; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I