Proteolytic fragments of insulin-like growth factor binding protein-3: N-terminal sequences and relationships between structure and biological activity.
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.
Lalou
C
C
Unité de recherches sur la régulation de la croissance, Inserm U. 142, hôpital Saint-Antoine, Paris, France.
Sawamura
S
S
Segovia
B
B
Ogawa
Y
Y
Binoux
M
M
D000595:Amino Acid Sequence; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D005341:Fibrinolysin / Q000378:metabolism*; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D013329:Structure-Activity Relationship
D018972:Insulin-Like Growth Factor Binding Protein 3; D010446:Peptide Fragments; D005341:Fibrinolysin