Comparison studies of IGFBP-5 binding to osteoblasts and osteoblast-derived extracellular matrix.
Recent studies have identified a specific membrane protein in osteoblast-like cells which binds intact and carboxy-truncated IGFBP-5 with high affinity. The purpose of the present study was to evaluate the IGFBP-5 binding properties of osteoblast-derived extracellular matrix (ECM), with special interest in determining whether ECM proteoglycans were necessary for IGFBP-5 binding. Neonatal mouse osteoblasts and the ECM of these cells both bound intact [125I]IGFBP-5 and [125I] IGFBP-5(1-169), though the ECM bound both forms with lower affinity when compared to their cellular binding. Treatment of the ECM with heparinase or chondroitinase, to remove glycosaminoglycan (GAG) side-chains of proteoglycans, resulted in 20-34% enhanced binding of intact [125I]IGFBP-5 and a 92-100% enhancement of [125I]IGFBP-5(1-169) binding. Similar enzymatic treatment of osteoblast monolayers had no effect on the binding of either form of [125I]IGFBP-5. These results indicate that GAGs within ECM secreted by neonatal mouse osteoblasts do not mediate the binding of IGFBP-5. This study also shows that intact and carboxy-truncated IGFBP-5 preferentially bind to the osteoblast surface, but that removal of GAGs from osteoblast-derived ECM can increase IGFBP-5 localization to this pericellular space, particularly the carboxy-truncated form of IGFBP-5.
Andress
D L
DL
Department of Medicine, VA Medical Center, Seattle, WA 98108, USA.
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D005109:Extracellular Matrix / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*
D018975:Insulin-Like Growth Factor Binding Protein 5; D008565:Membrane Proteins; D006493:Heparin