Major secretory protein of human decidualized endometrium in pregnancy is an insulin-like growth factor-binding protein

ABSTRACT Pregnancy-associated endometrial α1-globulin (α1-PEG) is quantitatively the major secretory protein product, synthesized and secreted in vitro, of the human decidualized endometrium during pregnancy. This protein has been purified from cytosolic extracts of this tissue and has now been characterized as a 32 kDa somatomedin/insulin-like growth factor (IGF)-binding protein. Immunoreactive α1-PEG isolated from amniotic fluid exhibited identical physiochemical properties and IGF-I-binding characteristics. In cytosolic extracts of pregnancy endometrium, in incubation medium of this tissue and in amniotic fluid, the 32 kDa protein represented the major α1-PEG immunoreactive protein and major IGF-I-binding component. Purified α1-PEG and incubation medium of pregnancy endometrium competed for IGF-I with placental membrane IGF receptors in vitro. The implications of the endometrial source of IGF-I-binding protein are dicussed with reference to the origin of the amniotic fluid and serum small Mr IGF-binding protein and to the suggested paracrine effect upon trophoblast proliferation. J. Endocr. (1988) 118, 317–328

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Characterization of insulin-like growth factor-binding protein in ovine amniotic fluid

Journal of Endocrinology ◽

10.1677/joe.0.1270325 ◽

1990 ◽

Vol 127 (2) ◽

pp. 325-333 ◽

Cited By ~ 1

Author(s):

J.-F. Wang ◽

L. J. Fraher ◽

D. J. Hill

Keyword(s):

Growth Factor ◽

Amniotic Fluid ◽

Binding Protein ◽

Binding Activity ◽

Scatchard Analysis ◽

Insulin Like Growth Factor ◽

Fetal Plasma ◽

Igf I ◽

Igf Binding ◽

Igf Binding Protein

ABSTRACT We have characterized an insulin-like growth factor (IGF)-binding protein present in ovine amniotic fluid. Using an activated charcoal-binding assay, whole amniotic fluid specifically bound approximately 20–30% of 125I-labelled human (h) IGF-II added, while the binding of 125I-labelled hIGF-I was minimal. Radioimmunoassay for IGF-I or -II in ovine biological fluids showed that values in amniotic fluid were 9- to 13-fold less than in fetal plasma, while gel filtration of amniotic fluid on Sephadex G-50 eluted with 1 mol acetic acid/l revealed no additional binding activity which had been complexed to IGFs at neutral pH. Together, these observations suggest that the binding activity in amniotic fluid is largely unsaturated. Competition studies for the displacement of 125I-labelled IGF-II binding to amniotic fluid by increasing amounts of unlabelled IGF-I or -II, using the charcoal assay, showed that IGF-II was 30-fold more potent than IGF-I. Scatchard analysis revealed a single class of binding site for IGF-II, with a binding affinity of 0·68 ±0·18 litres/nmol (mean ± s.d., n = 3). Ligand blot analysis of amniotic fluid by separation on 8% SDS-PAGE, transfer to nitrocellulose membranes, incubation with 125I-labelled IGF-II and autoradiography revealed a single band of IGF-binding protein with approximate molecular size of 38 kDa. Additional IGF-binding species of 20, 28, 48 and > 180 kDa were present in ovine fetal plasma. Separation of amniotic fluid on Concanavalin A–Sepharose revealed that it had little carbohydrate content. These results show that ovine amniotic fluid contains an unsaturated, non-glycosylated IGF-binding protein with high affinity for IGF-II. These characteristics differ from those of the IGF-binding proteins purified from human amniotic fluid. Journal of Endocrinology (1990) 127, 325–333

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Recognition of insulin-like-growth-factor-binding proteins in serum and amniotic fluid by an antiserum against a low-molecular-mass insulin-like-growth-factor-inhibitor/binding protein

Biochemical Journal ◽

10.1042/bj2670615 ◽

1990 ◽

Vol 267 (3) ◽

pp. 615-620 ◽

Cited By ~ 5

Author(s):

G T Ooi ◽

A C Herington

Keyword(s):

Growth Factor ◽

Amniotic Fluid ◽

Binding Proteins ◽

Binding Protein ◽

Insulin Like Growth Factor ◽

Inhibitor Protein ◽

Igf I ◽

Igf Binding ◽

Igf Binding Protein ◽

Ir Bands

An antiserum (R8) raised against a purified specific low-Mr (16,000-18,000) insulin-like-growth-factor (IGF)-inhibitor/binding protein, which is immunologically related to the native growth hormone (GH)-dependent Mr-150,000 IGF-binding protein in serum, has been used to probe a possible additional relationship to the predominant non-GH-dependent IGF-binding protein (Mr approximately 30,000) of human amniotic fluid. Amniotic-fluid fractions and an IGF-inhibitory fraction of serum were analysed by covalent cross-linking, ligand-blotting and immunoblotting techniques. Western blotting of the serum fraction using the R8 antiserum gave five immunoreactive (ir) bands, of which at least three (Mr 38,000, 34,000 and 23,000) possessed IGF-binding activity, as indicated by ligand (125I-IGF-I) blotting. Western blotting of two differently prepared amniotic-fluid fractions, which both showed potent IGF-inhibitory bioactivity, gave several (Mr range 14,500-73,000) ir bands, of which two (Mr 28,000 and 17,000) were most prominent. Ligand-blotting analysis gave a single intensely labelled band at Mr 28,000, consistent with the major presence of the Mr-28,000-30,000 amniotic-fluid IGF-binding protein. Covalent cross-linking of the amniotic-fluid fractions to 125I-IGF-I gave three specifically cross-linked complexes (Mr 36,000, 32,000 and 23,000), which, assuming a 1:1 binding stoichiometry with IGF (Mr 7500), represent binding proteins of Mr 28,500, 24,500 and 15,500 respectively. The Mr-15,500 binding protein, very similar to the Mr-17,000 ir band, in all likelihood represents the IGF-inhibitor protein. Our results indicate that inhibitor-sized binding proteins and IGF-inhibitor bioactivity are present in human amniotic fluid, and that the IGF-inhibitor protein (Mr 16,000) and amniotic-fluid IGF-binding protein (Mr 28,000) are immunologically related. Since the IGF-inhibitor protein is also immunologically and structurally related to the native, GH-dependent, Mr-150,000 binding protein in serum, our data suggest a heretofore-unrecognized immunological similarity between the Mr-150,000 binding protein and the amniotic-fluid binding protein and its serum analogue, the Mr approximately 30,000, non-GH-dependent, binding protein.

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