Identification of novel high molecular weight insulin-like growth factor-binding protein-3 association proteins in human serum.
The insulin-like growth factor (IGF)-binding proteins (IGFBPs) carry IGFs in serum and regulate their activity and bioavailability. The main IGFBP in serum, IGFBP-3, is known to form a 150-kDa complex with IGFs and the acid-labile subunit (ALS). We investigated the binding of IGFBP-3 to additional association proteins in human serum (IGFBP-3 APs). Ligand blots, column chromatography, and affinity cross-linking experiments revealed the specific binding of IGFBP-3 to at least three novel serum proteins. These techniques demonstrated the presence of proteins with molecular masses of 70, 100, and 150 kDa that bind IGFBP-3 with high affinity. Serum ALS migrated separately (at 88 kDa) from the novel IGFBP-3 APs (as evident by Western immunoblot), and bound IGFBP-3 weakly (by reverse ligand blots). We also demonstrated that large amounts of one of the IGFBP-3 APs and small amounts of ALS were coimmunoprecipitated with IGFBP-3 from human serum. Similar to ALS, these IGFBP-3 APs are acid labile and lose their IGFBP-3 binding capacity after exposure to low pH. We conclude that there are several serum proteins in addition to ALS and IGFs that bind IGFBP-3 with high affinity. These IGFBP-3 APs may serve as an additional reservoir of IGFBP-3 or modulate its functions.
Division of Endocrinology and Diabetes, The Children's Hospital of Philadelphia, University of Pennsylvania 19104, USA.
P F
PF
Collett-Solberg
S E
SE
Nunn
T B
TB
Gibson
P
P
Cohen
D001345:Autoradiography; D001798:Blood Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D015153:Blotting, Western; D002845:Chromatography; D003432:Cross-Linking Reagents; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007163:Immunosorbent Techniques; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007457:Iodine Radioisotopes; D008297:Male; D008970:Molecular Weight; D011247:Pregnancy; D011994:Recombinant Proteins / Q000378:metabolism
D001798:Blood Proteins; D003432:Cross-Linking Reagents; D018972:Insulin-Like Growth Factor Binding Protein 3; D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I