scholarly journals Characterisation of insulin-like growth factor-binding protein-3 binding to a novel receptor on human platelet membranes

2001 ◽  
Vol 168 (2) ◽  
pp. 307-315 ◽  
Author(s):  
VL Taylor ◽  
EM Spencer
Keyword(s):  
Growth Factor ◽  
Binding Sites ◽  
Human Platelet ◽  
Affinity Binding ◽  
Insulin Like Growth Factor ◽  
High Affinity Binding ◽  
High Affinity ◽  
Platelet Membranes ◽  
Igf I ◽  
Igfbp 3

Insulin-like growth factor-binding protein-3 (IGFBP-3) is an important regulator of insulin-like growth factor (IGF) bioavailability and IGF-independent growth responses. IGFBP-3 is stored within the alpha granules of platelets, permitting its rapid and concentrated delivery at sites of platelet lysis. Previous studies have demonstrated a lack of mRNA for IGFBP-3 in platelets and in the megakaryocytes from which platelets are formed, indicating that IGFBP-3 is endocytosed from the extracellular milieu. In this study, the binding of IGFBP-3 to platelet membranes was characterised to determine whether specific cell-surface IGFBP-3 receptors exist that might account for IGFBP-3 uptake into the alpha granules by megakaryocytes. IGFBP-3 binding to platelets was saturable, requiring at least 4.6 nM (125)I-labelled IGFBP-3 to occupy all binding sites present on 100 microg of platelet membranes. Non-linear regression analysis revealed the presence of a single class of high-affinity binding sites for IGFBP-3 on platelets, with a K(d) between 2.6x10(-10) and 8.0x10(-10) M and 1.51-4.89x10(11) binding sites/mg of platelet membrane. Kinetic analysis of (125)I-IGFBP-3 binding to platelet membranes demonstrated a forward rate (k(on)) of 8.1x 10(8) per M per min. The reverse rate constant (k(off)) was calculated to be 1.6x10(-1) per min (t(1/2)=4.2 min) and confirmed experimentally to be 3.3x10(-1) per min (t(1/2)=2.1 min). Binding of (125)I-IGFBP-3 to platelet membranes was inhibited in a dose-dependent manner by recombinant Escherichia coli IGFBP-3. In contrast, rat IGFBP-4 was not able to compete with (125)I-IGFBP-3 for platelet binding sites. Additionally, concentrations of IGF-I ranging from a 15-fold to a 40 000-fold molar excess caused a consistent 20% reduction in (125)I-IGFBP-3 binding. The mechanism of this slight reduction is unknown, but suggests that IGF-I does not compete directly with IGFBP-3 for receptor binding sites. However, it does not preclude the possibility that IGF-I may be endocytosed into the alpha granules as part of an IGF-I-IGFBP-3 complex. These results demonstrate the presence of high-affinity binding sites for IGFBP-3 on human platelet membranes. The nature and kinetics of the binding reaction are characteristic of a receptor-ligand interaction. This receptor may be involved in the endocytosis of circulating IGFBP-3 by megakaryocytes for packaging within the alpha granules of platelets. It is unknown if it is present in other tissues.

scholarly journals The C Region of Human Insulin-like Growth Factor (IGF) I Is Required for High Affinity Binding to the Type 1 IGF Receptor

1989 ◽  
Vol 264 (19) ◽  
pp. 11004-11008 ◽  
Author(s):  
M L Bayne ◽  
J Applebaum ◽  
D Underwood ◽  
G G Chicchi ◽  
B G Green ◽  
...  
Keyword(s):  
Growth Factor ◽  
Human Insulin ◽  
Affinity Binding ◽  
Insulin Like Growth Factor ◽  
High Affinity Binding ◽  
High Affinity ◽  
Igf I ◽  
Igf Receptor

High-affinity growth hormone binding protein, insulin-like growth factor I and insulin-like growth factor binding protein 3 in adults with growth hormone deficiency

1996 ◽  
Vol 135 (1) ◽  
pp. 82-86 ◽  
Author(s):  
Corné A Roelen ◽  
Hans P Koppeschaar ◽  
Wouter R de Vries ◽  
Pierre M Zelissen ◽  
Yvonne E Snel ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Growth Factor ◽  
Gh Deficiency ◽  
Binding Protein ◽  
Insulin Like Growth Factor ◽  
High Affinity ◽  
Growth Hormone Binding Protein ◽  
Igf I ◽  
Hormone Binding Protein ◽  
Igfbp 3

Roelen CA, Koppeschaar HP, de Vries WR, Zelissen PM, Snel YE, Doerga ME, Thijssen JH, Blankenstein RA. High-affinity growth hormone binding protein, insulin-like growth factor I and insulin-like growth factor binding protein 3 in adults with growth hormone deficiency. Eur J Endocrinol 1996;135:82–6. ISSN 0804–4643 The high-affinity growth hormone binding protein (GHBP) circulates in human blood and represents the extracellular domain of the growth hormone (GH) receptor. The effects of GH deficiency on GHBP in adults are not clear. The aim of this study was to evaluate serum GHBP levels in adults with GH deficiency and to assess whether GHBP measurement may contribute to the diagnosis of adult GH deficiency, based on a two-step model. We measured insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP-3) and GHBP levels in serum samples of 36 patients with adult-onset GH deficiency. The GHBP levels were measured by FPLC size-exclusion chromatography; IGF-I and IGFBP-3 levels were measured by RIA. Serum GHBP levels were elevated above the upper limit of the 95% confidence interval in 26 patients, whereas IGF-I and IGFBP-3 levels were low in 10 patients and in 16 patients, respectively. The combination of low serum IGF-I and low IGFBP-3 levels was found in 10 patients. In nine patients, serum IGF-I levels were low, with elevated GHBP levels. Low serum IGF-I, low IGFBP-3 and elevated GHBP levels were found in five patients. Only four out of 36 patients had serum IGF-I, IGFBP-3 and GHBP levels that were within the 95% confidence interval of the control values. We conclude that adults with acquired GH deficiency have elevated GHBP levels in comparison to healthy subjects. We suggest that measurement of GHBP levels might contribute to the diagnosis of adult GH deficiency, though further research is required to study the additional value of GHBP measurements. HPF Koppeschaar, Department of Endocrinology, University Hospital Utrecht, HPL00.407, PO Box 85500, 3508 GA Utrecht, The Netherlands

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