title: Insulin-like growth factor-binding protein-3 activates a phosphotyrosine phosphatase. Effects on the insulin-like growth factor signaling pathway.
abstract: The proliferative action of insulin-like growth factors (IGF-I and -II) is mediated via the type I IGF receptor (IGF-IR) and is modulated by their association with high affinity binding proteins, IGFBP-1 to -6. We recently found that, in addition to its ability to bind IGFs, IGFBP-3 also inhibits IGF-IR activation independently of IGF binding and without interacting directly with IGF-IR. Here, we show that IGFBP-3 is capable of blocking the signal triggered by IGFs. Breast carcinoma-derived cells (MCF-7) were stimulated by des(1-3)IGF-I or [Gln(3),Ala(4),Tyr(15),Leu(16)]IGF-I, two IGF analogues with intact affinity for IGF-IR, but with weak or virtually no affinity for IGFBPs, then incubated with IGFBP-3. The activated IGF-IR was desensitized through reversal of its autophosphorylation, following which both phosphatidylinositol 3-kinase and p42(MAPK) activities were depressed. Direct measurement of phosphotyrosine phosphatase activity and reconstitution experiments using tyrosine-phosphorylated insulin receptor substrate-1 (IRS-1) indicated that IGFBP-3 activated a phosphotyrosine phosphatase (PTPase). This action appeared to be peculiar to IGFBP-3 among the IGFBPs, since neither IGFBP-1 nor IGFBP-5 (structurally the closest to IGFBP-3), had any such effect. Several cell lines derived from normal or tumor cells responsive to IGF-I were used to show that IGFBP-3-stimulated PTPase is cell type-specific. Although the precise nature of the phosphatase remains to be determined, the results of this study demonstrate that IGFBP-3 stimulates a phosphotyrosine phosphatase activity that down-regulates the IGF-I signaling pathway, suggesting a major role for IGFBP-3 in regulating cell proliferation.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale, Unité 515, Assistance Publique-Hôpitaux de Paris, Université Paris VI, Hôpital Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75571 Paris CEDEX 12, France. ricort@st-antoine.inserm.fr
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Ricort
authors.forename: Michel
authors.initials: M
authors.lastname: Binoux
mesh_terms: D017209:Apoptosis; D002455:Cell Division; D002712:Chlorides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; D010750:Phosphoproteins; D017967:Zinc Compounds; D019000:Phosphotyrosine; D014443:Tyrosine; C016837:zinc chloride; D019869:Phosphatidylinositol 3-Kinases; D019950:Mitogen-Activated Protein Kinase 1; D017027:Protein Tyrosine Phosphatases