scholarly journals Contributions of the N- and C-terminal domains of IGF binding protein-6 to IGF binding

2004 ◽  
Vol 33 (2) ◽  
pp. 377-386 ◽  
Author(s):  
Stephen J Headey ◽  
Kerri S Leeding ◽  
Raymond S Norton ◽  
Leon A Bach
Keyword(s):  
Binding Affinity ◽  
Full Length ◽  
Binding Studies ◽  
Dissociation Kinetics ◽  
Igf Binding Proteins ◽  
Inhibition Of Proliferation ◽  
High Affinity ◽  
Binding Preference ◽  
Igf I ◽  
Igf Binding

Insulin-like growth factors IGF-I and IGF -II are important mediators of growth. A family of six high affinity IGF binding proteins (IGFBPs) modulate IGF action. IGFBPs have three domains, of which the N- and C-domains are involved in high affinity IGF binding. IGFBP-6 is unique in its 20–100-fold IGF-II binding specificity over IGF-I. The aim of this study was to determine the contributions of the N- and C-domains of IGFBP-6 to its IGF binding properties. We confirmed that differential dissociation kinetics are responsible for the IGF-II binding preference of IGFBP-6. The N-domain has rapid association kinetics, similar to full-length IGFBP-6, but both IGF-I and -II dissociate rapidly from this domain, thereby reducing its binding affinity for IGF-II ~50-fold. However, the N-domain binds IGF-I and -II with similar affinities and it has a similar IGF-I binding affinity to full-length IGFBP-6. This suggests that the C-domain confers the IGF-II binding preference of IGFBP-6; indeed, IGF-I bound inconsistently with very low affinity to the C-domain. Coincubation studies showed that isolated N- and C-domains of IGFBP-6 do not strongly cooperate to enhance IGF binding. The results of the binding studies are supported by the effects of the IGFBP-6 domains on IGF-induced colon cancer cell proliferation; the N-domain inhibited IGF-II induced proliferation with ~20-fold lower potency than IGFBP-6 and it was equipotent in inhibiting IGF-I- and IGF-II-induced proliferation. Coincubation of C-domain had no additional effect on N-domain-induced inhibition of proliferation. In conclusion, both the N- and C-domains of IGFBP-6 are involved in IGF binding, the C-domain is responsible for the IGF-II binding preference of IGFBP-6 and intact IGFBP-6 is necessary for high affinity IGF binding.

scholarly journals Transport of IGF-I across epithelial cell monolayers

1999 ◽  
Vol 162 (3) ◽  
pp. 361-369 ◽  
Author(s):  
SE Bastian ◽  
PE Walton ◽  
FJ Ballard ◽  
DA Belford
Keyword(s):  
Epithelial Cell ◽  
Cell Lines ◽  
Igf Binding Proteins ◽  
Cell Monolayers ◽  
High Affinity ◽  
Igf Receptors ◽  
Igf I ◽  
Mdbk Cells ◽  
Igf Binding ◽  
Epithelial Cell Monolayers

Epithelial cells line the lumens of organs including the gastrointestinal tract, kidney tubules and respiratory airways, where they regulate the transport of electrolytes and the movement of macromolecules. The current study aimed to investigate the transport of IGF-I across epithelial cell barriers. Epithelial cell lines derived from gut (IEC-6), kidney (MDBK) and lung (Mv1Lu) were shown to possess high-affinity, functional receptors for IGF-I and formed tight junctions in monolayer culture. To investigate the transport of IGF-I, the three cell lines were grown on microporous filters in a bi-chamber system. In comparison with filters without cells, IEC-6 and Mv1Lu epithelial cell monolayers restricted the passage of (125)I-IGF-I and [(3)H]inulin, whereas the MDBK cells virtually occluded any passage of these molecules. Transport of (125)I-IGF-I across the epithelial cell monolayers was significantly less than that of [(3)H]inulin, suggesting that the binding of (125)I-IGF-I to high-affinity IGF receptors or IGF-binding proteins retarded its transport. Moreover, (125)I-IGF-I transport was not inhibited by the presence of excess unlabelled IGF-I. Our findings provide evidence for the restricted diffusion of intact, free IGF-I across gut, kidney and lung epithelial cell monolayers via a paracellular or low-affinity transcellular pathway.

scholarly journals Identification and characterization of insulin-like growth factor (IGF)-binding protein expression and secretion by adult human adrenocortical cells: differential regulation by IGFs and adrenocorticotropin

2001 ◽  
Vol 168 (3) ◽  
pp. 465-474 ◽  
Author(s):  
C Fottner ◽  
D Engelhardt ◽  
MW Elmlinger ◽  
MM Weber
Keyword(s):  
Primary Culture ◽  
Conditioned Medium ◽  
Adrenocortical Function ◽  
Adrenocortical Cells ◽  
Igf Binding Proteins ◽  
High Affinity ◽  
Adult Human ◽  
Igf I ◽  
Igf Binding ◽  
Igfbp 3

In previous studies we have shown that IGF-II stimulates basal as well as ACTH-induced cortisol secretion from adult human adrenocortical cells more potently than IGF-I, and that both IGFs predominantly stimulate androgen biosynthesis. The steroidogenic effect of IGF-I and IGF-II is mediated through interaction with the IGF-I receptor, and modified by locally produced IGF-binding proteins (IGFBPs). In the present study, we identified and characterized IGFBP synthesis in normal adult human adrenocortical cells in primary culture, and investigated the effect of ACTH and recombinant human IGF-I and -II on the regulation of IGFBP expression and secretion. Using RT-PCR, we identified the mRNA of all six high-affinity IGFBPs, in both adrenocortical tissue and monolayer cell cultures of adrenocortical cells. Using Western ligand and immunoblotting and two-dimensional Western ligand blotting we confirmed the secretion of IGFBP-1, -2, -3, -4 and -5 by adrenocortical cells in primary culture. The quantification of IGFBPs indicated that IGFBP-3 accounts for almost half the binding activity in conditioned medium of unstimulated cells (47%), followed by IGFBP-4 (20%), IGFBP-5 (15%), IGFBP-2 (12%) and IGFBP-1 (6%). After treatment with ACTH, the abundance of IGFBP-1 was upregulated significantly 2.6-fold, while IGFBP-3 was induced only slightly (1.3-fold). IGFBP-2, -4 and -5 remained unchanged. In contrast, IGF-I and -II (6.5 nM) predominantly induced the abundance of IGFBP-5 (2- and 1.6-fold respectively) and IGFBP-3 (2- and 1.7-fold respectively), while IGFBP-1, -2 and -4 were unaltered. The induction of IGFBP-1 and -5 by ACTH and IGFs, respectively, was paralleled by an increase in the amount of IGFBP-1 and -5 mRNA in these cells. In conclusion, all six high-affinity IGFBPs are expressed in the adult human adrenal gland, and the presence of at least five high-affinity IGFBPs has been demonstrated in conditioned medium of adult human adrenocortical cells. Furthermore, the expression and secretion of IGFBP-1 is upregulated by ACTH, whereas IGFBP-5 is induced by IGF-I and -II. Together with earlier findings, these results suggest that IGFBPs play an important modulatory role in the regulation of the differentiated adrenocortical function.

scholarly journals Structural and Functional Evidence for the Interaction of Insulin-Like Growth Factors (IGFs) and IGF Binding Proteins with Vitronectin

Endocrinology ◽  
2003 ◽  
Vol 144 (7) ◽  
pp. 2807-2815 ◽  
Author(s):  
Jennifer A. Kricker ◽  
Chris L. Towne ◽  
Sue M. Firth ◽  
Adrian C. Herington ◽  
Zee Upton
Keyword(s):  
Cell Migration ◽  
Biological Effects ◽  
Heparin Binding ◽  
Mcf7 Cells ◽  
Binding Studies ◽  
Igf Binding Proteins ◽  
Igf I ◽  
Heparin Binding Domain ◽  
Igf Binding ◽  
Igfbp 3

Abstract Previous studies demonstrated that IGF-II binds directly to vitronectin (VN), whereas IGF-I binds poorly. However, binding of VN to integrins has been demonstrated to be essential for a range of IGF-I-stimulated biological effects, including IGF binding protein (IGFBP)-5 production, IGF type-1 receptor autophosphorylation, and cell migration. Thus, we hypothesized that a link between IGF-I and VN must occur and may be mediated through IGFBPs. This was tested using competitive binding assays with VN and 125iodine-labeled IGFs in the absence and presence of IGFBPs. IGFBP-4, IGFBP-5, and nonglycosylated IGFBP-3 were shown to significantly enhance binding of IGF-I to VN, whereas IGFBP-2 and glycosylated IGFBP-3 had a smaller effect. Furthermore, binding studies with analogs indicate that glycosylation status and the heparin-binding domain of IGFBP-3 are important in this interaction. To examine the functional significance of IGFs binding to VN, cell migration in MCF7 cells was measured and found to be enhanced when VN was prebound to IGF-I in the presence of IGFBP-5. The effect required IGF:IGFBP:VN complex formation; this was demonstrated by use of a non-IGFBP-binding IGF-I analog. Together, these data indicate the importance of IGFBPs in modulating IGF-I binding to VN and that this binding has functional consequences in cells.

Postprandial changes in plasma growth hormone, insulin, insulin-like growth factor (IGF)-I, and IGF-binding proteins in coho salmon fasted for varying periods

2009 ◽  
Vol 297 (2) ◽  
pp. R352-R361 ◽  
Author(s):  
Munetaka Shimizu ◽  
Kathleen A. Cooper ◽  
Walton W. Dickhoff ◽  
Brian R. Beckman
Keyword(s):  
Growth Hormone ◽  
Growth Factor ◽  
Food Intake ◽  
Binding Proteins ◽  
Coho Salmon ◽  
Fasting Period ◽  
Igf Binding Proteins ◽  
Igf I ◽  
Igf Binding ◽  
Single Meal

We examined postprandial changes in circulating growth hormone (GH), insulin, insulin-like growth factor (IGF)-I, and IGF-binding proteins (IGFBPs) in yearling coho salmon under different feeding regimes. Fish were initially fasted for 1 day, 1 wk, or 3 wk. Fasted fish were then fed, and blood was collected at 4-h intervals over 26 h. After the various periods of fasting, basal levels of insulin were relatively constant, whereas those of IGF-I, IGFBPs and GH changed in proportion to the duration of the fast. A single meal caused a rapid, large increase in the circulating insulin levels, but the degree of the increase was influenced by the fasting period. IGF-I showed a moderate increase 2 h after the meal but only in the regularly fed fish. Plasma levels of 41-kDa IGFBP were increased in all groups within 6 h after the single meal. The fasting period did not influence the response of 41-kDa IGFBP to the meal. IGFBP-1 and GH decreased after the meal to the same extent among groups regardless of the fasting period. The present study shows that insulin and IGF-I respond differently to long (weeks)- and short (hours)-term nutritional changes in salmon; insulin maintains its basal level but changes acutely in response to food intake, whereas IGF-I adjusts its basal levels to the long-term nutritional status and is less responsive to acute nutritional input. IGFBPs maintain their sensitivity to food intake, even after prolonged fasting, suggesting their critical role in the nutritional regulation of salmon growth.

scholarly journals IGFs and IGF-binding proteins in short children with steroid-dependent nephrotic syndrome on chronic glucocorticoids: changes with 1 year exogenous GH

2001 ◽  
pp. 237-243 ◽  
Author(s):  
X Zhou ◽  
KY Loke ◽  
CC Pillai ◽  
HK How ◽  
HK Yap ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Growth Retardation ◽  
Bone Age ◽  
Gh Treatment ◽  
Igf Binding Proteins ◽  
Steroid Dependent ◽  
Igf I ◽  
Igf Binding ◽  
Pre Treatment ◽  
Igfbp 3

OBJECTIVE: Children with steroid-dependent nephrotic syndrome (SDNS), despite being in remission on glucocorticoids, continue to have growth retardation and short stature. The mechanism is uncertain as both chronic glucocorticosteroids and the nephrotic syndrome may independently affect growth. We investigated the changes in the IGFs and IGF-binding proteins (IGFBPs) in a group of short SDNS children, and studied the changes prospectively with 1 year's treatment with GH. DESIGN AND METHODS: Total and 'free' IGF-I, IGFBP-3 and acid-labile subunit (ALS) were studied in eight SDNS boys (mean age=12.6 years; mean bone age=9.1 years) on long term oral prednisolone (mean dose 0.46 mg/kg per day) before, during, and after, 1 year's treatment with GH (mean dose 0.32 mg/kg per week). Pretreatment comparisons were made with two control groups, one matched for bone age (CBA; mean bone age=9.2 years), and another for chronological age (CCA; mean chronological age=13 years). Subsequently, three monthly measurements of serum and urine IGFBPs were carried out in the GH-treated SDNS patients using Western ligand blot and Western immunoblot. RESULTS: Pre-treatment serum total IGF-I levels and the IGF-I/IGFBP-3 ratio were elevated significantly in SDNS compared with CBA, and were similar to CCA. Serum free IGF-I levels were elevated significantly compared with both control groups, but serum IGFBP-3 did not differ significantly. Urinary IGFBP-2, IGFBP-3 and ALS were detectable in the SDNS children only. With GH treatment, IGF-I and IGFBP-3, but not IGF-II, increased significantly compared with pre-treatment values, and returned to baseline after cessation of GH treatment. Urinary IGFBPs did not change significantly with GH treatment. CONCLUSIONS: There is persistent urinary loss of IGFBP-2, IGFBP-3 and ALS in children with SDNS in remission with growth retardation. However, the significant elevation in serum IGF-I suggests that glucocorticoid-induced resistance to IGF is the main factor responsible for the persistent growth retardation in these children. Exogenous GH was able to overcome this resistance by further increasing serum IGF-I.

scholarly journals Effects of IGF-I bioavailability on bovine preantral follicular development in vitro

Reproduction ◽  
2007 ◽  
Vol 133 (6) ◽  
pp. 1121-1128 ◽  
Author(s):  
Fiona H Thomas ◽  
Bruce K Campbell ◽  
David G Armstrong ◽  
Evelyn E Telfer
Keyword(s):  
Follicular Development ◽  
Follicle Development ◽  
Dependent Manner ◽  
Igf Binding Proteins ◽  
Preantral Follicles ◽  
Follicle Diameter ◽  
Igf I ◽  
Igf Binding ◽  
Development In Vitro

The aim of this study was to determine the effect of regulation of IGF-I bioavailability on preantral follicle development in vitro. Bovine preantral follicles were cultured for 6 days in serum-free medium with increasing doses of Long R3 (LR3) IGF-I (an analog with low affinity for IGF-binding proteins (IGFBPs)), or human recombinant IGF-I (hrIGF-I). Follicle diameter and estradiol production were measured every second day. On day 6, ratios of oocyte/follicle diameter and oocyte morphology were assessed by histological examination, and IGFBP-2 and -3 were detected by immunocytochemistry and in situ hybridization respectively. Both types of IGF-I increased follicle diameter in a dose-dependent manner (P < 0.05) and increased estradiol production over control levels (P < 0.05). However, follicles treated with LR3 IGF-I and the highest concentration of hrIGF-I (1000 ng/ml) had smaller oocyte/follicle ratios, and increased oocyte degeneration, compared with controls or follicles treated with physiological concentrations of hrIGF-I (P < 0.05). IGFBPs were detected in cultured preantral follicles, indicating a requirement for regulation of IGF bioavailability during the early stages of follicular development. Specifically, IGFBP-3 mRNA was found to be expressed in oocytes, and IGFBP-2 immunoreactivity was detected in oocytes and granulosa cells of cultured follicles. In summary, the regulation of IGF-I bioavailability by IGFBPs is necessary for the co-ordination of oocyte and follicle development in vitro.

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