Proteolytic fragments of insulin-like growth factor binding protein-3: N-terminal sequences and relationships between structure and biological activity

C R Acad Sci III. 1997 Aug;320(8):621-8. doi: 10.1016/s0764-4469(97)85695-8.

Abstract

Insulin-like growth factors (IGF-I and IGF-II) in biological fluids bind to high-affinity binding proteins (IGFBP-1 to -6), which transport them and regulate their activities. Limited proteolysis of certain IGFBPs plays a major role in this regulation. IGFBP-3 is proteolysed in vivo and in several cell lines by serine proteases, including plasmin. In earlier studies we reproduced this proteolysis in vitro using recombinant human non-glycosylated IGFBP-3. Two major fragments were obtained, the larger retaining weak affinity for IGF-I and weakly inhibiting IGF I mitogenic effects. The smaller fragment, though lacking affinity for IGFs, is a potent growth inhibitor. These proteolytic fragments were isolated by HPLC and their N-terminal amino acids sequenced. Both major fragments contain the N-terminal region of the intact protein, the larger form corresponding to residues 1-160, and the smaller form, to residues 1-95. Kinetics experiments using the MG-63 osteoblast-like cell line showed that the larger peptide is generated before the smaller peptide, the latter probably being a product of secondary proteolysis of the former. Our data suggest that proteolysis of IGFBP-3 is intimately linked to its biological function. We propose a model for its action at cellular level.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Blotting, Western
  • Cell Division / drug effects
  • Chromatography, High Pressure Liquid
  • Fibrinolysin / metabolism*
  • Humans
  • Insulin-Like Growth Factor Binding Protein 3 / chemistry*
  • Insulin-Like Growth Factor Binding Protein 3 / isolation & purification
  • Insulin-Like Growth Factor Binding Protein 3 / metabolism
  • Insulin-Like Growth Factor Binding Protein 3 / pharmacology
  • Molecular Sequence Data
  • Osteoblasts / metabolism*
  • Peptide Fragments / chemistry*
  • Peptide Fragments / isolation & purification
  • Peptide Fragments / metabolism
  • Peptide Fragments / pharmacology
  • Structure-Activity Relationship

Substances

  • Insulin-Like Growth Factor Binding Protein 3
  • Peptide Fragments
  • Fibrinolysin