Isolation of a biologically active fragment from the carboxy terminus of the fetal rat binding protein for insulin-like growth factors

Insulin-like growth factors (IGFs) I and II are considered to be autocrine regulators of bone cell function. Recently, we demonstrated that IGF-I induces IGF-binding protein-5 (IGFBP-5) expression in cultures of osteoblast-enriched cells from 22-day fetal rat calvariae (Ob cells). In the present study, we postulated that IGFs play an autocrine role in the maintenance of IGFBP-5 basal expression in Ob cells. IGFBP-2 and -3, at concentrations that bind endogenous IGFs, decreased IGFBP-5 mRNA levels, as determined by Northern blot analysis, and protein levels, as determined by Western immunoblots of extracellular matrix extracts of Ob cells. IGFBP-2 and -3 in excess inhibited IGFBP-5 heterogeneous nuclear RNA levels, as determined by RT-PCR, and did not alter the half-life of IGFBP-5 mRNA in transcriptionally arrested Ob cells. In conclusion, blocking endogenous IGFs in Ob cells represses IGFBP-5 expression, suggesting that IGFs are autocrine inducers of IGFBP-5 synthesis in osteoblasts.

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Isolation of complexes formed between insulin-like growth factor-binding protein-3 and transferrin from the human serum

Journal of the Serbian Chemical Society ◽

10.2298/jsc110831211m ◽

2012 ◽

Vol 77 (5) ◽

pp. 607-617 ◽

Cited By ~ 4

Author(s):

Goran Miljus ◽

Miomir Petrovic ◽

Olgica Nedic

Keyword(s):

Growth Factors ◽

Binding Protein ◽

Biologically Active ◽

Molecular Forms ◽

Igf Binding Proteins ◽

Igf Binding ◽

The Relationship ◽

Igfbp 3 ◽

Insulin Like Growth Factors

Insulin-like growth factors (IGFs) play an important role in the regulation of cell growth, differentiation and metabolism. The amount of free, biologically active IGFs is regulated by the IGF-binding proteins (IGFBPs). IGFBP-3 is the most abundant binding protein and it is known to interact with other circulating proteins, including transferrin (Tf). In order to elucidate the possible role of IGF/IGFBP-3 in the iron metabolism, it is necessary to isolate IGFBP-3/Tf complexes. Several affinity-based techniques were employed. Results have shown that only double immunoprecipitation method with anti-Tf and anti-IGFBP-3 antibodies selectively separated complexes from other molecular forms, such as monomers, oligomers or fragments of IGFBP-3 and Tf. Isolated complexes can now be used to investigate the relationship between IGF/IGFBP-3 and iron, both in structural and metabolic t?rms.

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Nucleotide Sequence and Expression of a cDNA Clone Encoding a Fetal Rat Binding Protein for Insulin-like Growth Factors

Journal of Biological Chemistry ◽

10.1016/s0021-9258(18)83711-5 ◽

1989 ◽

Vol 264 (9) ◽

pp. 5148-5154 ◽

Cited By ~ 5

Author(s):

A L Brown ◽

L Chiariotti ◽

C C Orlowski ◽

T Mehlman ◽

W H Burgess ◽

...

Keyword(s):

Growth Factors ◽

Nucleotide Sequence ◽

Cdna Clone ◽

Binding Protein ◽

Fetal Rat ◽

Insulin Like Growth Factors

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Preferential association of the insulin-like growth factors I and II with metabolically inactive and active carrier-bound complexes in serum

Biochemical Journal ◽

10.1042/bj2410745 ◽

1987 ◽

Vol 241 (3) ◽

pp. 745-750 ◽

Cited By ~ 17

Author(s):

H J Cornell ◽

G Enberg ◽

A C Herington

Keyword(s):

Growth Factors ◽

Formic Acid ◽

Binding Protein ◽

Gel Permeation Chromatography ◽

Exchange Chromatography ◽

Biologically Active ◽

Igf I ◽

Direct Contrast ◽

First Time ◽

Insulin Like Growth Factors

Ion-exchange chromatography of serum on DEAE-Sephadex A-50 using a stepwise NaCl gradient showed that complexes enriched with insulin-like growth factors I and II (IGF-I and IGF-II) could be preferentially eluted. A fraction eluted with 0.075 M-NaCl preferentially contained immunoreactive IGF-I with peak levels appearing in fractions of Mr approx. 110,000. The IGF-I-binding protein complex itself had low bioactivity as measured in a non-suppressible insulin-like (NSILA) bioassay. On conversion to free IGF-I by gel-permeation chromatography on Sephadex G-75 in 1% formic acid, however, the IGF-I did express its intrinsic NSILA bioactivity. In contrast, an IGF-II-enriched complex was eluted from the DEAE-Sephadex with 0.15 M-NaCl. Practically all of the recovered NSILA of the original serum was present in this fraction, in the Mr range 70,000-300,000 with a peak of 150,000. Chromatography on Sephadex G-75 in 1% formic acid separated this high-Mr NSILA into low-Mr (less than 15000) IGF-II and high-Mr acid-stable NSILA-P. The high-Mr IGF-II complex bound to concanavalin A-Sepharose, suggesting that it was a glycoprotein. The results confirm previous reports that a large portion of the NSILA of whole serum can be accounted for by a biologically active acid-dissociable complex. These data show for the first time that this active complex consists of an IGF-II-preferring binding protein. In direct contrast, the IGF-I-preferring complex does not express NSILA bioactivity until the IGF-I is liberated through acidification. The presence of a metabolically active IGF-II complex in serum raises questions as to its possible biological role in the adult.

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Influence of insulin-like growth factor-binding protein-2 on plasma clearance and transfer of insulin-like growth factors-I and -II from plasma into mammary-derived lymph and milk of goats

Journal of Endocrinology ◽

10.1677/joe.0.1500121 ◽

1996 ◽

Vol 150 (1) ◽

pp. 121-127 ◽

Cited By ~ 6

Author(s):

C G Prosser ◽

J Schwander

Keyword(s):

Growth Factors ◽

Growth Factor ◽

Plasma Clearance ◽

Binding Protein ◽

Plasma Concentrations ◽

Insulin Like Growth Factor ◽

Factor Binding ◽

Lactating Goats ◽

Igf I ◽

Insulin Like Growth Factors

Abstract Plasma clearance of insulin-like growth factors-I and -II (IGF-I and -II) and insulin-like growth factor-binding protein-2 (IGFBP-2) from lactating goats (n=4) was determined following a single intravenous injection of the corresponding 125I-labelled human protein. Transfer of these proteins out of the vascular space was monitored by their subsequent appearance in mammary-derived lymph and milk. Clearance of 125I-IGFBP-2 from circulation was 0·37 ± 0·06 ml/min/kg, which is markedly greater than that of 125I-IGF-I or -II (0·11 ± and 0·12 ± 0·01 ml/min/kg respectively). This was also reflected in longer elimination half-lives for IGF-I (353 ± 6 min) and -II (254 ± 8 min) compared with IGFBP-2 (110 ± 9 min). Three hours after injection of the 125I-labelled protein, the plasma:lymph ratio of trichloroacetic acid-precipitable radioactivity was 1·54 ±0·04, 3·3 ±0·6 and 4·1 ±0·4 for IGFBP-2, IGF-I and -II respectively. The form of 125I-IGFBP-2 in lymph was not different from that of plasma. Elevation of plasma concentrations of IGFBP-2 by its intravenous infusion significantly decreased plasma half-life of both IGF-I and -II (251 ± 8 and 198 ±7 min respectively). Although the amount and rate of transfer of IGF into mammary-derived lymph was decreased slightly by IGFBP-2, concentrations eventually obtained were not different from control. However, secretion of IGFs into milk was significantly reduced by IGFBP-2, particularly in the case of IGF-I. These results are consistent with the ability of all three compounds to cross the vascular endothelium intact and of IGFBP-2 to decrease the uptake of IGF by mammary epithelium and subsequent secretion into milk. IGFBP-2 may well have acted to target plasma IGF towards non-mammary tissues, thus explaining the more rapid plasma clearance of IGFs in the presence of elevated IGFBP-2. Journal of Endocrinology (1996) 150, 121–127

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