Phosphorylation of insulin-like growth factor (IGF)-binding protein 1 in cell culture and in vivo: Effects on affinity for IGF-I

Journal Article · Sun Sep 01 00:00:00 EDT 1991 · Proceedings of the National Academy of Sciences of the United States of America; (United States)

DOI:https://doi.org/10.1073/pnas.88.17.7481· OSTI ID:5602006

Jones, J I; D'Ercole, A J; Camacho-Hubner, C; Clemmons, D R ^[1]

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1. Univ. of North Carolina, Chapel Hill (United States)

The insulin-like growth factors (IGF-I and IGF-II) are present in extracellular fluids bound to specific IGF-binding proteins (IGFBPs). The authors and others have reported varying biologic activity of different preparations of IGFBP-1 that appeared to have identical amino acid sequences and molecular sizes. This observation prompted them to determine whether IGFBP-1 undergoes posttranslational modifications. Immunoprecipitation was used to show that Chinese hamster ovary cells and human hepatoma (hepG2) cells secrete {sup 32}P-labeled IGFBP-1 following incubation with ({sup 32}P)orthophosphate. Phospho amino acid analysis of {sup 32}P-labeled IGFBP-1 revealed only phosphoserine residues. A method was developed that could separate nonphosphorylated IGFBP-1 from four or five phosphorylated isoforms. These observations suggest that IGFBP-1 is secreted as a phosphoprotein and is subsequently dephosphorylated in vivo. Binding studies showed that the phosphorylated IGFBP-1 secreted by HepG2 cells has a 6-fold higher affinity for IGF-I than it does after dephosphorylation. They conclude that IGFBP-1 is phosphorylated and that this phosphorylation is a physiologically important posttranslational modification.

• OSTI ID: 5602006
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America; (United States), Vol. 88:17; ISSN 0027-8424
• Country of Publication: United States
• Language: English

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MAMMALS
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MOLECULAR STRUCTURE
NEOPLASMS
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550600* - Medicine