Insulin and insulin-like growth factor-I exhibit a set of non-classical receptor binding properties suggestive of negative co-operativity or site-site interactions between the two receptor halves: ...curvilinear Scatchard plots, acceleration of dissociation of bound labelled ligand at high dilution in the presence of unlabelled ligand. The alpha 2 beta 2 receptor dimer binds only one ligand molecule with high affinity. The dose-response curve for the acceleration of 125I-insulin by unlabelled insulin is bell-shaped, with a disappearance of the negative co-operativity at insulin concentrations over 0.1 mumol/l. This phenomenon had been attributed to insulin dimerization, but new data with non-dimerizing analogues and insulins modified at the hexamer-forming surface indicate the presence of a second binding site on the insulin molecule's hexamer face. This site binds to a second domain on the receptor. A new binding model for insulin and insulin-like growth factor-I is proposed where the bivalent ligand bridges the two receptor alpha subunits alternatively at opposite sites in a symmetrical receptor structure. The implications of the model for negative co-operativity, bell-shaped biological curves, and the divergence between mitogenic and metabolic signalling are discussed in the context of the evolution of the properties of insulin and insulin-like growth factor-I.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Context: Homozygous IGF1 deletions or mutations lead to severe short stature, deafness, microcephaly, and mental retardation. Heterozygosity for an IGF-I defect may modestly decrease height and head ...circumference.
Objective: The objective of the study was to investigate the clinical features of heterozygous carriers of a novel mutation in the IGF1 gene in comparison with noncarriers in a short family and to establish the effect of human GH treatment.
Subjects: Two children, their mother, and their maternal grandfather carried the mutation and were compared with two relatives who were noncarriers.
Results: The two index cases had severe short stature (height sd score −4.1 and −4.6), microcephaly, and low IGF-I levels. Sequencing of IGF1 revealed a heterozygous duplication of four nucleotides, resulting in a frame shift and a premature termination codon. The mother and maternal grandfather had the same IGF1 mutation. Adult height (corrected for shrinking and secular trend) and head circumference sd score of carriers of the paternally transmitted mutation was −2.5 and −1.8, in comparison with −1.6 and 0.3 in noncarriers, respectively. After 2 yr of GH treatment, both index cases exhibited increased growth.
Conclusions: Heterozygosity for this novel IGF1 mutation in children born from a mother with the same mutation, presumably in combination with other genetic factors for short stature, leads to severe short stature, which can be successfully treated with GH.
IGF1 haploinsufficiency can cause reduced height and head circumference, which can be successfully treated with GH.
Type 2 diabetes mellitus -- in which the body produces insufficient amounts of insulin or the insulin that is produced does not function properly to control blood glucose -- is an increasingly common ...disorder. Prospective clinical studies have proven the benefits of tighter glucose control in reducing the frequency and severity of complications of the disease, leading to the advocation of earlier and more aggressive use of insulin therapy. Given the reluctance of patients with type 2 diabetes to inject themselves with insulin, orally active insulin mimetics would be a major therapeutic advance. Here, we discuss recent progress in understanding the structure-function relationships of the insulin and insulin-like growth factor 1 (IGF1) receptors, their mechanism of activation and their implications for the design of insulin-receptor agonists for diabetes therapy and IGF1-receptor antagonists for cancer therapy.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Insulin has traditionally been considered as a hormone essential for metabolic regulation, while the insulin-like growth factors (IGF-I and IGF-II) are postulated to be more specifically involved in ...growth regulation. The conventional wisdom is that they share each other's effects only at high concentrations, due to their weak affinity for the heterologous receptor. We discuss here the evidence that in the proper cellular context, insulin can be mitogenic at physiologic concentrations through its own receptor. We studied the insulin and IGF-I binding characteristics of a new model suitable for analysing insulin receptor mediated mitogenesis; that is, a T-cell lymphoma line that depends on insulin for growth, but is unresponsive to IGFs. The cells showed no specific binding of 125I-IGF-I and furthermore, no IGF-I receptor mRNA was detected by RNAse protection assay in the LB cells, in contrast with mouse brain and thymus. The cells bound at saturation about 3000 insulin molecules to receptors that had normal characteristics in terms of affinity, kinetics, pH dependence and negative co-operativity. A series of insulin analogues competed for 125I-insulin binding with relative potencies comparable to those observed in other insulin target cells. The full sequence of the insulin receptor cDNA was determined and found to be identical to the published sequence of the murine insulin receptor cDNA. The LB cell line is therefore an ideal model with which to investigate insulin mitogenic signalling without interference from the IGF-I receptor. Using this model, we have started approaching the molecular basis of insulin-induced mitogenesis, in particular the role of signalling kinetics in choosing between mitogenic and metabolic pathways.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The following report selects and summarises some of the conclusions and recommendations generated throughout a series of workshops and discussions that have lead to the publication of the Science ...Policy Briefing (SPB) Nr. 35, published by the European Science Foundation. (Large parts of the present text are directly based on the ESF SPB. Detailed recommendations with regard to specific application areas are not given here but can be found in the SPB. Issues related to mathematical modelling, including training and the need for an infrastructure supporting modelling are discussed in greater detail in the present text.)The numerous reports and publications about the advances within the rapidly growing field of systems biology have led to a plethora of alternative definitions for key concepts. Here, with 'mathematical modelling' the authors refer to the modelling and simulation of subcellular, cellular and macro-scale phenomena, using primarily methods from dynamical systems theory. The aim of such models is encoding and testing hypotheses about mechanisms underlying the functioning of cells. Typical examples are models for molecular networks, where the behaviour of cells is expressed in terms of quantitative changes in the levels of transcripts and gene products. Bioinformatics provides essential complementary tools, including procedures for pattern recognition, machine learning, statistical modelling (testing for differences, searching for associations and correlations) and secondary data extracted from databases.Dynamical systems theory is the natural language to investigate complex biological systems demonstrating nonlinear spatio-temporal behaviour. However, the generation of experimental data suitable to parameterise, calibrate and validate such models is often time consuming and expensive or not even possible with the technology available today. In our report, we use the term 'computational model' when mathematical models are complemented with information generated from bioinformatics resources. Hence, 'the model' is, in reality, an integrated collection of data and models from various (possibly heterogeneous) sources. The present report focuses on a selection of topics, which were identified as appropriate case studies for medical systems biology, and adopts a particular perspective which the authors consider important. We strongly believe that mathematical modelling represents a natural language with which to integrate data at various levels and, in doing so, to provide insight into complex diseases: 1. Modelling necessitates the statement of explicit hypotheses, a process which often enhances comprehension of the biological system and can uncover critical points where understanding is lacking. 2. Simulations can reveal hidden patterns and/or counter-intuitive mechanisms in complex systems. 3. Theoretical thinking and mathematical modelling constitute powerful tools to integrate and make sense of the biological and clinical information being generated and, more importantly, to generate new hypotheses that can then be tested in the laboratory.Medical Systems Biology projects carried out recently across Europe have revealed a need for action: 4. While the need for mathematical modelling and interdisciplinary collaborations is becoming widely recognised in the biological sciences, with substantial implications for the training and research funding mechanisms within this area, the medical sciences have yet to follow this lead. 5. To achieve major breakthroughs in Medical Systems Biology, existing academic funding schemes for large-scale projects need to be reconsidered. 6. The hesitant stance of the pharmaceutical industry towards major investment in systems biology research has to be addressed. 7. Leading medical journals should be encouraged to promote mathematical modelling.
Abstract Objective While in previous studies heterozygosity for an Insulin-Like Growth Factor 1 ( IGF1 ) defect only modestly decreased height and head circumference, we recently reported on two ...siblings with severe short stature with a maternally transmitted heterozygous duplication of 4 nucleotides, resulting in a frame shift and a premature termination codon in the IGF1 gene. In this paper we describe the structural and functional characteristics of the putative truncated IGF-I protein. Design Two children, their mother and maternal grandfather carried the mutation. In addition, two family members who were not affected were included in the study. Mutant (MT) IGF-I was synthesized in oxidized and reduced form using two methods. Neutral gel filtration studies were carried out with wild-type (WT) and synthetic MT IGF-I. Binding analysis of synthetic MT IGF-I to the IGF1R and insulin receptors were performed with EBNA-293 cells, stably transfected with the IGF-I receptor, and IM9 cells. L6 cells were used to examine the mitogenic potency and the potential antagonizing effect of synthetic MT IGF-I by 3 H-thymidine incorporation assays. Results In the sera of both the carriers and non-carriers the proportion of125 I-IGF-I that was associated with the 150 kDa complex was somewhat less (varying between ~ 37 and ~ 52%) than in normal pooled serum (~ 53 − ~ 63%) and, instead, slightly increased amounts of radioactivity were eluted in the 40−50 kDa fraction (consisting of binary IGF–IGFBP complexes) or remained unbound. Synthetic MT IGF-I did not bind to the IGF-I receptor, nor antagonize the growth-promoting effect of IGF-I. It did bind to IGFBPs, but was barely incorporated into 150 kDa complexes. Because in all cases WT IGF-I immunoreactivity was recovered in one peak, corresponding to the MW of WT IGF-I, i.e. ~ 7.6 kDa, an interaction of circulating truncated mutant peptide with WT IGF-I is very unlikely. Conclusions There is no evidence that the severe short stature associated with heterozygosity for this novel IGF1 mutation in children born from a mother with the same mutation is caused by a dominant negative effect of the truncated protein. We speculate that the growth failure is caused by a combination of partial IGF-I deficiency, placental IGF-I insufficiency, and other genetic factors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We examined the properties of a mutant insulin receptor (IR) with an Arg(252) to Cys (IR(R252C)) substitution in the alpha-subunit originally identified in a patient with extreme insulin resistance ...and acanthosis nigricans.
We studied IR cell biology and signalling pathways in Chinese Hamster Ovary cells overexpressing this IR(R252C).
Our investigation showed an impairment in insulin binding to IR(R252C) related mostly to a reduced affinity of the receptor for insulin and to a reduced rate of IR(R252C) maturation; an inhibition of IR(R252C)-mediated endocytosis resulting in a decreased insulin degradation and insulin-induced receptor down-regulation; a maintenance of IR(R252C) on microvilli even in the presence of insulin; a similar autophosphorylation of mutant IR(R252C) followed by IRS 1/IRS 2 phosphorylation, p85 association with IRS 1 and IRS 2 and Akt phosphorylation similar to those observed in cells expressing wild type IR (IRwt); and finally, a reduced insulin-induced Shc phosphorylation accompanied by decreased ERK1/2 phosphorylation and activity and of thymidine incorporation into DNA in cells expressing IR(R252C) as compared to cells expressing IRwt.
These observations suggest that: parameters other than tyrosine kinase activation participate in or control the first steps of IR internalisation or both; IR-mediated IRS 1/2 phosphorylation can be achieved from the cell surface and microvilli in particular; Shc phosphorylation and its subsequent signalling pathway might require IR internalisation; defective IR endocytosis correlates with an enhancement of some biological responses to insulin and attenuation of others.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
There is compelling evidence from epidemiological studies in humans, as well as in vitro and in vivo experimental observations including transgenic animal models, for a role of the IGF/insulin ...signalling system in cancer tumourigenesis. In this review focused on breast cancer, we review the experimental evidence, discuss the cellular and molecular mechanisms of tumourigenicity by the IGFs and insulin and various possible therapeutic strategies based on the mechanisms discussed.
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