Glycosaminoglycans inhibit degradation of insulin-like growth factor-binding protein-5

Endocrinology. 1994 Dec;135(6):2358-63. doi: 10.1210/endo.135.6.7527332.

Abstract

Human dermal fibroblasts secrete insulin-like growth factor-binding protein-3 (IGFBP-3), -4, and -5. Fibroblast-conditioned medium contains minimal intact IGFBP-5, and this form of IGFBP is predominantely a 23-kilodalton fragment, suggesting that the IGFBP-5 fragment is derived from intact IGFBP-5 by proteolysis. In this study we investigated the effects of glycosaminoglycans on IGFBP-5 degradation in fibroblast-conditioned medium. The addition of heparin, heparan sulfate, and dermatan sulfate (100 micrograms/ml) to the medium of fibroblast monolayer cultures inhibited IGFBP-5 degradation, as determined by the conversion of intact IGFBP-5 to a 23-kilodalton fragment. In contrast, hyaluronic acid, keratan sulfate, and chondroitin sulfate-A and -C had no effect. Heparin and heparan sulfate inhibited IGFBP-5 degradation at concentrations of 1 or 2.5 micrograms/ml, but 100 micrograms/ml dermatan sulfate were required. Heparin was also inhibitory in vitro, that is when conditioned medium and heparin were incubated without cells. Experiments with modified forms of heparin showed that O-sulfate groups in the 2 or 3 carbon position were required for heparin to be inhibitory. Completely desulfated heparin had no activity, and N-resulfation of desulfated heparin had only a minimal effect. Dextran sulfate, pentosan polysulfate, and fucoidan, which are composed of different saccharide units but contain O-sulfate groups in the 2 or 3 carbon positions, also inhibited IGFBP-5 degradation. These results demonstrate that heparin-like molecules are important regulators of IGFBP-5 degradation. O-Sulfation of the 2 or 3 position of the saccharide ring is required for inhibitory activity. As glycosaminoglycan side-chains are present in proteoglycans that are present in extracellular matrix and on cell surfaces, these side-chains represent a potential mechanism for regulating IGFBP-5 proteolysis in vivo.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Carrier Proteins / antagonists & inhibitors*
  • Carrier Proteins / metabolism
  • Fibroblasts / metabolism
  • Glycosaminoglycans / pharmacology*
  • Heparin / chemistry
  • Heparin / pharmacology
  • Humans
  • Immunoblotting
  • Insulin-Like Growth Factor Binding Protein 5
  • Ligands
  • Peptide Hydrolases / metabolism
  • Precipitin Tests
  • Skin / cytology
  • Skin / metabolism
  • Somatomedins / metabolism
  • Sulfates / metabolism

Substances

  • Carrier Proteins
  • Glycosaminoglycans
  • Insulin-Like Growth Factor Binding Protein 5
  • Ligands
  • Somatomedins
  • Sulfates
  • Heparin
  • Peptide Hydrolases