Structural biology of insulin and IGF1 receptors: implications for drug design

Insulin growth factor binding proteins as therapeutic targets in type 2 diabetes

INTRODUCTION

The signaling pathways of the insulin-like growth factors (IGFs) have been implicated in the aetiology of type 2 diabetes (T2D) and a number of therapeutic modalities aiming at the IGF-axis have been considered. Administration of IGF-I has been reported to improve insulin sensitivity in healthy subjects and patients with T2D. In recent years, the IGF binding proteins (IGFBPs) have also been associated with metabolic disorders, prompting the idea that IGFBPs play important roles in the pathogenesis of T2D. Thus, by virtue of their role in the regulation of IGF effects, the IGFBPs have emerged as potential biomarkers and therapeutic targets in metabolic syndromes and T2D.

AREAS COVERED

The article provides an overview on recent findings in clinical and experimental IGFBP-research and addresses the studies that have investigated the potentials of the IGFBPs as therapeutic targets in T2D.

EXPERT OPINION

There is plenty of therapeutic promise within the IGF system, but further understanding of the IGFs in T2D is necessary to avoid off-target effects. Strong evidence supports the use of IGFBPs as therapeutic targets in the treatment of T2D, and it is not difficult to foresee the use of IGFBPs as part of a combination therapy alongside other anti-diabetic drugs.

Reducing IRS-1 Activation Cause Mutation of Tyrosine Kinase Domain hINSR Gene on Type-2 Diabetes Mellitus Patients

The purpose of this study is to examine the effect of mutation on tyrosine kinase hINSR gene of DM Type 2 patients reduce the IRS- 1 activation by in silico analysis. Blood DNA of DM Type 2 patients from Saeful Anwar Hospital Malang were amplified and sequenced by specific primers of tyrosine kinase domain of hINSR gene. These gene sequences were converted to protein sequence by BLAST and the IRS-1 protein sequence is retrieved from NCBI database. Both of the protein sequence was aligned by using Bio edit version 5.0.6. The model of three dimension protein was predicted by SWISS MODEL webserver, and visualized the structure alteration by using Pymol 0.99rc6 and Hex 5.0, and then superimpose of the hINSR and IRS-1 interaction were examined by docking using Hex 5.0. The results showed that one substitution and one deletion of 8-3F patient exon-22 hINSR gene tyrosine kinase domain cause loss of four helixes and three coils structures on tyrosine kinase hINSR protein. Six-deletions and six-substitutions on same gene domain of DMK9 patient changed the two helixes became coil structure. The binding energy of hINSR tyrosine kinase with IRS-1 of normal is E= -494.67 kJ/mol, DMK9 patient is E= -458.4 kJ/mol, and 8-3F patient is E=-544.20 kJ/mol. The DMK9 patient prognosis has better physiological condition than 8-3F patient. Interaction between 8-3F of hINSR tyrosine kinase domain mutation and PTB domain IRS-1 is more spontaneous than DMK9, but both of them were reduced on IRS-1 activation respectively.

Novel roles for insulin receptor (IR) in adipocytes and skeletal muscle cells via new and unexpected substrates

The insulin signaling pathway regulates whole-body glucose homeostasis by transducing extracellular signals from the insulin receptor (IR) to downstream intracellular targets, thus coordinating a multitude of biological functions. Dysregulation of IR or its signal transduction is associated with insulin resistance, which may culminate in type 2 diabetes. Following initial stimulation of IR, insulin signaling diverges into different pathways, activating multiple substrates that have roles in various metabolic and cellular processes. The integration of multiple pathways arising from IR activation continues to expand as new IR substrates are identified and characterized. Accordingly, our review will focus on roles for IR substrates as they pertain to three primary areas: metabolism/glucose uptake, mitogenesis/growth, and aging/longevity. While IR functions in a seemingly pleiotropic manner in many cell types, through these three main roles in fat and skeletal muscle cells, IR multi-tasks to regulate whole-body glucose homeostasis to impact healthspan and lifespan.

Insulin-like growth factor-1 secreted by brain microvascular endothelial cells attenuates neuron injury upon ischemia

Insulin-like growth factor (IGF)-1 is essential for the development of the nervous system, and is present in many cell types. Relatively little is known about IGF-1 expression in brain microvascular endothelial cells (BMECs). For in vivo studies, we examined the expression of IGF-1 and insulin-like growth factor-binding protein (IGFBP)-2 after focal cerebral ischemia for 12 h, 24 h, 3 days and 7 days, utilizing a permanent middle cerebral artery occlusion (MCAO) model in rats. For in vitro studies, we examined the levels of IGF-1 and IGFBP-2 in the culture medium or primary culture of BMECs injured by oxygen-glucose deprivation (OGD). Then, we elucidated the protective effects of IGF-1 on cortical neurons injured by OGD and the possible mechanism. In addition, we investigated the effect of BMEC-conditioned medium on IGF-1 receptor expression in neurons. The results showed that IGF-1 expression increased in serum and brain tissue, whereas IGFBP-2 expression decreased in brain tissue of MCAO-injured rats. In primary culture of BMECs, the expression levels of IGF-1 and IGFBP-2 were significantly higher under OGD conditions in culture. IGF-1 administration improved neuron viability upon normoxia or OGD, and upregulated p-Akt expression. This effect was reversed by LY294002, a specific inhibitor of the phosphoinositide 3-kinase-Akt signaling pathway. Furthermore, conditioned medium from OGD-treated BMECs substantially suppressed neuron viability and the expression of IGF-1 receptor simultaneously. These data demonstrate that therapeutic strategies that prioritize the early recovery of the IGF-1 system in BMECs might be promising in ischemic injury.

Is dynamic autocrine insulin signaling possible? A mathematical model predicts picomolar concentrations of extracellular monomeric insulin within human pancreatic islets

Insulin signaling is essential for -cell survival and proliferation in vivo. Insulin also has potent mitogenic and anti-apoptotic actions on cultured -cells, with maximum effect in the high picomolar range and diminishing effect at high nanomolar doses. In order to understand whether these effects of insulin are constitutive or can be subjected to physiological modulation, it is essential to estimate the extracellular concentration of monomeric insulin within an intact islet. Unfortunately, the in vivo concentration of insulin monomers within the islet cannot be measured directly with current technology. Here, we present the first mathematical model designed to estimate the levels of monomeric insulin within the islet extracellular space. Insulin is released as insoluble crystals that exhibit a delayed dissociation into hexamers, dimers, and eventually monomers, which only then can act as signaling ligands. The rates at which different forms of insulin dissolve in vivo have been estimated from studies of peripheral insulin injection sites. We used this and other information to formulate a mathematical model to estimate the local insulin concentration within a single islet as a function of glucose. Model parameters were estimated from existing literature. Components of the model were validated using experimental data, if available. Model analysis predicted that the majority of monomeric insulin in the islet is that which has been returned from the periphery, and the concentration of intra-islet monomeric insulin varies from 50–300 pM when glucose is in the physiological range. Thus, our results suggest that the local concentration of monomeric insulin within the islet is in the picomolar ‘sweet spot’ range of insulin doses that activate the insulin receptor and have the most potent effects on -cells in vitro. Together with experimental data, these estimations support the concept that autocrine/paracrine insulin signalling within the islet is dynamic, rather than constitutive and saturated.

Diabetes mellitus due to the toxic misfolding of proinsulin variants

Dominant mutations in the human insulin gene can lead to pancreatic β-cell dysfunction and diabetes mellitus due to toxic folding of a mutant proinsulin. Analogous to a classical mouse model (the Akita mouse), this monogenic syndrome highlights the susceptibility of human β-cells to endoreticular stress due to protein misfolding and aberrant aggregation. The clinical mutations directly or indirectly perturb native disulfide pairing. Whereas the majority of mutations introduce or remove a cysteine (leading in either case to an unpaired residue), non-cysteine-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the evolution of insulin has been constrained not only by its structure and function, but also by the susceptibility of its single-chain precursor to impaired foldability.

Structural analysis and aggregation propensity of reduced and nonreduced glycated insulin adducts

The milieu within pancreatic β cells represents a favorable environment for glycation of insulin. Therefore, in this study, insulin samples were individually subjected to glycation under reducing and nonreducing conditions. As monitored by ortho-phthalaldehyde and fluorescamine assays, the reduced glycated insulin adduct demonstrates extensively higher level of glycation than the nonreduced glycated counterpart. Also, gel electrophoresis experiments suggest a significant impact of glycation under a reducing system on the level of insulin oligomerization. Furthermore, reduced and nonreduced glycated insulin adducts respectively exhibit full and partial resistance against dithiothreitol-induced aggregation. The results of thioflavin T and Congo red assays suggest the existence of a significant quantity of amyloid-like entities in the sample of reduced glycated insulin adduct. Both fluorescence and far-ultraviolet circular dichroism studies respectively suggest that the extents of unfolding and secondary structural alteration were closely correlated to the level of insulin glycation. Moreover, the surface tension of two glycated insulin adducts was inversely correlated to their glycation extents and to the quantity of exposed hydrophobic patches. Overall, the glucose-modified insulin molecules under reducing and nonreducing systems display different structural features having significant consequences on aggregation behaviors and surface tension properties. The particular structural constraints of glycated insulin may reduce the binding interaction of this hormone to its receptor which is important for both insulin function and clearance.

Targeting the insulin-like growth factor-1 receptor in human cancer

The insulin-like growth factor (IGF) signaling system plays a crucial role in human cancer and the IGF-1 receptor (IGF-1R) is an attractive drug target against which a variety of novel anti-tumor agents are being developed. Deregulation of the IGF signaling pathway frequently occurs in human cancer and involves the establishment of autocrine loops comprising IGF-1 or IGF-2 and/or IGF-1R over-expression. Epidemiologic studies have documented a link between elevated IGF levels and the development of solid tumors, such as breast, colon, and prostate cancer. Anti-cancer strategies targeting the IGF signaling system involve two main approaches, namely neutralizing antibodies and small molecule inhibitors of the IGF-1R kinase activity. There are numerous reports describing anti-tumor activity of these agents in pre-clinical models of major human cancers. In addition, multiple clinical trials have started to evaluate the safety and efficacy of selected IGF-1R inhibitors, in combination with standard chemotherapeutic regimens or other targeted agents in cancer patients. In this mini review, I will discuss the role of the IGF signaling system in human cancer and the main strategies which have been so far evaluated to target the IGF-1R.

Hepatic gene expression analysis of 2-aminoanthracene exposed Fisher-344 rats reveal patterns indicative of liver carcinoma and type 2 diabetes

The goal of the present study was to examine hepatic differential gene expression patterns in Fisher-344 rats in response to dietary 2-aminoanthracene (2AA) ingestion for 14 and 28 days. Twenty four post-weaning 3-4 week old F-344 male rats were exposed to 0 mgkg(-1)-diet (control), 50 mgkg(-1)-diet (low dose), 75 mgkg(-1)-diet (medium dose) and 100 mgkg(-1)-diet (high dose) 2AA for 14 and 28 days. This was followed by analysis of the liver for global gene expression changes. In both time points, the numbers of genes affected seem to correlate with the dose of 2AA. Sixteen mRNAs were differentially expressed in all treatment groups for the short-term exposure group. Similarly, 51 genes were commonly expressed in all 28-day exposure group. Almost all the genes seem to have higher expression relative to the controls. In contrast, cytochrome P450 family 4, subfamily a, polypeptide 8 (Cyp4a8), and monocyte to macrophage differentiation-associated (Mmd2) were down-regulated relative to controls. Differentially expressed mRNAs were further analyzed for associations via DAVID. GO categories show the effect of 2AA to be linked with genes responsible for carbohydrate utilization and transport, lipid metabolic processes, stress responses such as inflammation and apoptosis processes, immune system response, DNA damage response, cancer processes and circadian rhythm. The data from the current study identified altered hepatic gene expression profiles that may be associated with carcinoma, autoimmune response, and/or type 2 diabetes. Possible biomarkers due to 2AA toxicity in the liver for future study include Abcb1a, Nhej1, Adam8, Cdkn1a, Mgmt, and Nrcam.

The pro-forms of insulin-like growth factor I (IGF-I) are predominant in skeletal muscle and alter IGF-I receptor activation

IGF-I is a key regulator of muscle development and growth. The pre-pro-peptide produced by the Igf1gene undergoes several posttranslational processing steps to result in a secreted mature protein, which is thought to be the obligate ligand for the IGF-I receptor (IGF-IR). The goals of this study were to determine what forms of IGF-I exist in skeletal muscle, and whether the mature IGF-I protein was the only form able to activate the IGF-IR. We measured the proportion of IGF-I species in murine skeletal muscle and found that the predominant forms were nonglycosylated pro-IGF-I and glycosylated pro-IGF-I, which retained the C-terminal E peptide extension, instead of mature IGF-I. These forms were validated using samples subjected to viral expression of IGF-I combined with furin and glycosidase digestion. To determine whether the larger molecular weight IGF-I forms were also ligands for the IGF-IR, we generated each specific form through transient transfection of 3T3 cells and used the enriched media to perform kinase receptor activation assays. Compared with mature IGF-I, nonglycosylated pro-IGF-I had similar ability to activate the IGF-IR, whereas glycosylation of pro-IGF-I significantly reduced receptor activation. Thus, it is important to understand not only the quantity, but also the proportion of IGF-I forms produced, to evaluate the true biological activity of this growth factor.

All-atom structural models of insulin binding to the insulin receptor in the presence of a tandem hormone-binding element

Insulin regulates blood glucose levels in higher organisms by binding to and activating insulin receptor (IR), a constitutively homodimeric glycoprotein of the receptor tyrosine kinase (RTK) superfamily. Therapeutic efforts in treating diabetes have been significantly impeded by the absence of structural information on the activated form of the insulin/IR complex. Mutagenesis and photo-crosslinking experiments and structural information on insulin and apo-IR strongly suggest that the dual-chain insulin molecule, unlike the related single-chain insulin-like growth factors, binds to IR in a very different conformation than what is displayed in storage forms of the hormone. In particular, hydrophobic residues buried in the core of the folded insulin molecule engage the receptor. There is also the possibility of plasticity in the receptor structure based on these data, which may in part be due to rearrangement of the so-called CT-peptide, a tandem hormone-binding element of IR. These possibilities provide opportunity for large-scale molecular modeling to contribute to our understanding of this system. Using various atomistic simulation approaches, we have constructed all-atom structural models of hormone/receptor complexes in the presence of CT in its crystallographic position and a thermodynamically favorable displaced position. In the "displaced-CT" complex, many more insulin-receptor contacts suggested by experiments are satisfied, and our simulations also suggest that R-insulin potentially represents the receptor-bound form of hormone. The results presented in this work have further implications for the design of receptor-specific agonists/antagonists.

Type 1 insulin-like growth factor receptor targeted therapies in pediatric cancer

Data from over 20 years ago demonstrated potential use for insulin-like growth factor (IGF) signaling modulators, specifically with IGF-1R antagonists, in a variety of pediatric and adolescent cancers, particularly in sarcomas. However, in spite of promising preclinical data, IGF-1R inhibitors have not had the success as single agents that was originally hoped for in clinical trials. Several potential mechanisms exist by which tumors are resistant to IGF-1R inhibitors. Notably, these resistance mechanisms are currently best understood in Ewing sarcoma and alveolar rhabdomyosarcoma. Various treatment schema have been proposed as a potential way to overcome this resistance. The use of IGF-1R inhibitors, mechanisms of resistance, and current ongoing clinical studies using IGF-1R inhibitors in pediatric cancers are reviewed here.

Epitope-specific mechanisms of IGF1R inhibition by ganitumab

Background

Therapeutic antibodies targeting the IGF1R have shown diverse efficacy and safety signals in oncology clinical trials. The success of these agents as future human therapeutics depends on understanding the specific mechanisms by which these antibodies target IGF1R signaling.

Methodology/Principal Findings

A panel of well-characterized assays was used to investigate the mechanisms by which ganitumab, a fully human anti-IGF1R antibody undergoing clinical testing, inhibits IGF1R activity. Epitope mapping using IGF1R subdomains localized the ganitumab binding site to the L2 domain. Binding of ganitumab inhibited the high-affinity interaction of IGF-1 and IGF-2 required to activate IGF1R in cells engineered for IGF1R hypersensitivity and in human cancer cell lines, resulting in complete blockade of ligand-induced cellular proliferation. Inhibition of IGF1R activity by ganitumab did not depend on endosomal sequestration, since efficient ligand blockade was obtained without evidence of receptor internalization and degradation. Clinically relevant concentrations of ganitumab also inhibited the activation of hybrid receptors by IGF-1 and IGF-2. Ganitumab was not an agonist of homodimeric IGF1R or hybrid receptors in MCF-7 and COLO 205 cells, but low-level IGF1R activation was detected in cells engineered for IGF1R hypersensitivity. This activation seems biologically irrelevant since ganitumab completely inhibited ligand-driven proliferation. The in vivo efficacy profile of ganitumab was equivalent or better than CR and FnIII-1 domain-specific antibodies, alone or in combination with irinotecan. CR domain-specific antibodies only blocked IGF-1 binding to IGF1R but were more potent than ganitumab at inducing homodimer and hybrid receptor downregulation in vitro, however this difference was less obvious in vivo. No inhibition of hybrid receptors was observed with the FnIII-1 domain antibodies, which were relatively strong homodimer and hybrid agonists.

Conclusions/Significance

The safety and efficacy profile of ganitumab and other anti-IGF1R antibodies may be explained by the distinct molecular mechanisms by which they inhibit receptor signaling.

The metabolic and mitogenic properties of basal insulin analogues

CONTEXT

Retrospective, observational studies have reported an association between diabetes treatment with insulin and a higher incidence of cancer.

OBJECTIVE

Overview the literature for in vitro and in vivo studies of the metabolic and mitogenic properties of basal insulin analogues and assess the implications for clinical use.

METHODS

Relevant studies were identified through PubMed and congress abstract database searches; data on metabolic and mitogenic signalling in relation to insulin treatment of diabetes are included in this review.

RESULTS

The balance of evidence shows that although some analogues have demonstrated mitogenic potency in some in vitro studies in cancer cell lines, these findings do not translate to the in vivo setting in animals or to the clinical setting in humans.

CONCLUSIONS

The current consensus is that there is no clinical or in vivo evidence to indicate that any commercially available insulin analogue has carcinogenic effects. Large-scale, prospective clinical and observational studies will further establish any potential link.

The IGF-1 receptor and regulation of nitric oxide bioavailability and insulin signalling in the endothelium

The insulin-like growth factor-1 receptor (IGF-1R), like the insulin receptor (IR), plays a significant role in determining bioavailability of the critical signalling molecule nitric oxide (NO) and hence, modulates endothelial cell function, particularly in response to stimulation with insulin. In particular, the ability of the IGF-1R to form hybrid receptors with the IR appears to be highly significant in determining the sensitivity of the endothelial cell to insulin. This review will examine the structure of the IGF-1R and how this, with particular reference to the ability of the IGF-1R and the IR to form hybrid receptors, may have an effect both on endothelial cell function and the development of cardiovascular disease.

Steady-state of an enzymatic reaction is dependent on the density of reactant

The post-translational modification of proteins is controlled by the relative activities of two opposing enzymes. For example, the extent of phosphorylation of tyrosine residues reflects the balance of a kinase and a phosphatase enzyme. The present article uses as a model system a self-assembled monolayer that presents a peptide that can be phosphorylated by Abl kinase and subsequently dephosphorylated by Lambda phosphatase. Treatment of monolayers with a reaction mixture containing both enzymes reveals that the steady-state level of peptide phosphorylation is dependent on the density of the peptide. Using identical reaction mixtures, surfaces that presented the substrate at high density led to a phosphorylated peptide at steady-state, whereas surfaces that presented the substrate at low density led to unphosphorylated peptide at steady-state. This dependence owes to an autocatalytic phosphorylation reaction that operates at high densities of substrate. This work provides an example of an interfacial reaction that has properties that have no analogue in the corresponding solution phase reaction. It also provides a model system that is relevant to understanding mechanisms that regulate signaling at the cellular membrane.

BRET Biosensor Analysis of Receptor Tyrosine Kinase Functionality

Bioluminescence resonance energy transfer (BRET) is an improved version of earlier resonance energy transfer technologies used for the analysis of biomolecular protein interaction. BRET analysis can be applied to many transmembrane receptor classes, however the majority of the early published literature on BRET has focused on G protein-coupled receptor (GPCR) research. In contrast, there is limited scientific literature using BRET to investigate receptor tyrosine kinase (RTK) activity. This limited investigation is surprising as RTKs often employ dimerization as a key factor in their activation, as well as being important therapeutic targets in medicine, especially in the cases of cancer, diabetes, neurodegenerative, and respiratory conditions. In this review, we consider an array of studies pertinent to RTKs and other non-GPCR receptor protein-protein signaling interactions; more specifically we discuss receptor-protein interactions involved in the transmission of signaling communication. We have provided an overview of functional BRET studies associated with the RTK superfamily involving: neurotrophic receptors [e.g., tropomyosin-related kinase (Trk) and p75 neurotrophin receptor (p75NTR)]; insulinotropic receptors [e.g., insulin receptor (IR) and insulin-like growth factor receptor (IGFR)] and growth factor receptors [e.g., ErbB receptors including the EGFR, the fibroblast growth factor receptor (FGFR), the vascular endothelial growth factor receptor (VEGFR) and the c-kit and platelet-derived growth factor receptor (PDGFR)]. In addition, we review BRET-mediated studies of other tyrosine kinase-associated receptors including cytokine receptors, i.e., leptin receptor (OB-R) and the growth hormone receptor (GHR). It is clear even from the relatively sparse experimental RTK BRET evidence that there is tremendous potential for this technological application for the functional investigation of RTK biology.

Evidence for the Possible Biological Significance of the igf-1 Gene Alternative Splicing in Prostate Cancer

Insulin-like growth factor-I (IGF-I) has been implicated in the pathogenesis of prostate cancer (PCa), since it plays a key role in cell proliferation, differentiation, and apoptosis. The IGF-I actions are mediated mainly via its binding to the type I IGF receptor (IGF-IR), however IGF-I signaling via insulin receptor (IR) and hybrid IGF-I/IR is also evident. Different IGF-I mRNA splice variants, namely IGF-IEa, IGF-IEb, and IGF-IEc, are expressed in human cells and tissues. These transcripts encode several IGF-I precursor proteins which contain the same bioactive product (mature IGF-I), however, they differ by the length of their signal peptides on the amino-terminal end and the structure of the extension peptides (E-peptides) on the carboxy-terminal end. There is an increasing interest in the possible different role of the IGF-I transcripts and their respective non-(mature)IGF-I products in the regulation of distinct biological activities. Moreover, there is strong evidence of a differential expression profile of the IGF-I splice variants in normal versus PCa tissues and PCa cells, implying that the expression pattern of the various IGF-I transcripts and their respective protein products may possess different functions in cancer biology. Herein, the evidence that the IGF-IEc transcript regulates PCa growth via Ec peptide specific and IGF-IR/IR-independent signaling is discussed.

Agonism and antagonism at the insulin receptor

Insulin can trigger metabolic as well as mitogenic effects, the latter being pharmaceutically undesirable. An understanding of the structure/function relationships between insulin receptor (IR) binding and mitogenic/metabolic signalling would greatly facilitate the preclinical development of new insulin analogues. The occurrence of ligand agonism and antagonism is well described for G protein-coupled receptors (GPCRs) and other receptors but in general, with the exception of antibodies, not for receptor tyrosine kinases (RTKs). In the case of the IR, no natural ligand or insulin analogue has been shown to exhibit antagonistic properties, with the exception of a crosslinked insulin dimer (B29-B’29). However, synthetic monomeric or dimeric peptides targeting sites 1 or 2 of the IR were shown to be either agonists or antagonists. We found here that the S961 peptide, previously described to be an IR antagonist, exhibited partial agonistic effects in the 1–10 nM range, showing altogether a bell-shaped dose-response curve. Intriguingly, the agonistic effects of S961 were seen only on mitogenic endpoints (³H-thymidine incorporation), and not on metabolic endpoints (¹⁴C-glucose incorporation in adipocytes and muscle cells). The agonistic effects of S961 were observed in 3 independent cell lines, with complete concordance between mitogenicity (³H-thymidine incorporation) and phosphorylation of the IR and Akt. Together with the B29-B’29 crosslinked dimer, S961 is a rare example of a mixed agonist/antagonist for the human IR. A plausible mechanistic explanation based on the bivalent crosslinking model of IR activation is proposed.

Effects of insulin-like growth factor-1 on B-cell precursor acute lymphoblastic leukemia

Insulin-like growth factor-1 (IGF-1) is known to be a major growth factor with effects on various cell types, including hematopoietic cells, as well as neoplasms, and is regulated by IGF-binding proteins (IGFBPs). In this study, we investigated the effects of IGF-1 on B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells. When the expression of IGF-1R in clinical samples of BCP-ALL was examined, five of thirty-two cases showed IGF-1R expression, whereas IGF-1R was expressed in most BCP-ALL cell lines. We observed that IGF-1 enhanced the proliferation of BCP-ALL cell lines that can be partially inhibited by IGFBP-1, -3, and -4, but not other IGFBPs. IGF-1 also partially inhibited dexamethasone-induced apoptosis, but not apoptosis mediated by VP-16 and irradiation. Interestingly, the proliferative effect of IGF-1 was partially blocked by inhibitors of MAPK and AKT, whereas the inhibition of dexamethasone-induced apoptosis was completely blocked by both inhibitors. Our data indicate that IGF-1 is involved in cell proliferation and apoptosis regulation in BCP-ALL cells. Since some BCP-ALL cases express IGF-1R, it appears to be a plausible target for prognostic evaluation and may represent a new therapeutic strategy.

Gender-specific care of diabetes

Diabetic men have benefited in the last 30 years from a significant improvement in total and cardiovascular mortality, whereas diabetic women have had no improvement at all. Moreover, recent research focused on the role of sex hormones in glucose homeostasis, and might account for different pathophysiologic mechanisms in the development of diabetes-related complications. Thus, care of diabetic women is a challenge that requires particular attention. The available data regarding gender-specific care of diabetes mellitus are uneven, rich in some domains but very poor in others. The large prospective trials performed in the last 20 years have assumed that the natural history of diabetes mellitus in men and women, as well as the efficiency of glucose-lowering therapies and management of hyperglycemic-related complications, could be attributable without distinction to men and women. We propose in this paper to analyze the published medical literature according to the specific management of diabetes mellitus in women, and to try to distinguish some particular features. We found important distinctions between diabetic men and women regarding the patterns of abnormalities of glucose regulation, epidemiology, development of diabetes-related complications, ischemic heart disease, morbidity and mortality, impact of cardiovascular risk factors, development of the metabolic syndrome, depression and osteoporosis, as well as the impact of lifestyle modifications or primary and secondary preventions on cardiovascular risk factors, and finally medical therapeutics. Moreover, special considerations were given to some particular aspects of the medical life in diabetic women, such as the features of gestational diabetes mellitus and the management of pregnancy in pregestational diabetic women, use of contraception, hormone-replacement therapy and polycystic ovary syndrome.

The insulin-like growth factor mutation database (IGFmdb)

Insulin-like growth factors (IGF-I and IGF-II), and insulin are evolutionarily conserved hormonal regulators of eukaryotic growth and development. Through interactions with their cognate receptors, all three molecules can influence cellular growth, proliferation, differentiation, migration, and survival, as well as metabolic processes. As such, perturbations in signaling by IGFs and insulin are a well-documented cause of altered growth, development and survival during both embryonic and post-natal life. A key approach in understanding how IGFs and insulin elicit their biological effects has been through identifying structural features of the ligands that influence their receptor interactions. Over the years, the study of many hundreds of specifically engineered IGF and insulin analogues has provided a wealth of knowledge about how specific residues of these ligands contribute to ligand:receptor interactions. Some analogues have even provided the basis for designing therapeutic agents for the treatment of IGF and insulin-related diseases. As the list of IGF and insulin analogues continues to grow we find that, while many have been produced and studied, it would be of considerable value to have a central repository from which information about specific analogues and their receptor binding data were readily available in an easily searchable and comparable format. To address this, we have created the "Insulin-like growth factor mutation database" (IGFmdb). The IGFmdb is a web-based curated database of annotated ligand analogues and their receptor binding affinities that can be accessed via http://www.adelaide.edu.au/igfmutation. Currently the IGFmdb contains receptor-binding data for 67 IGF-II analogues that were publicly accessible prior to 2012, as well as 67 IGF-I analogues, including all of those produced and characterised in our laboratory. A small number of these are IGF species homologues. There are also 32 insulin analogues within IGFmdb that were reported within the included IGF analogue studies, representing only a small fraction of existing insulin mutants. Future developments of the IGFmdb will incorporate receptor-binding data for all publicly accessible IGF-I analogues and the data will be expanded to include IGF-binding protein (IGFBP) binding affinities.

Novel role of the IGF-1 receptor in endothelial function and repair: studies in endothelium-targeted IGF-1 receptor transgenic mice

We recently demonstrated that reducing IGF-1 receptor (IGF-1R) numbers in the endothelium enhances nitric oxide (NO) bioavailability and endothelial cell insulin sensitivity. In the present report, we aimed to examine the effect of increasing IGF-1R on endothelial cell function and repair. To examine the effect of increasing IGF-1R in the endothelium, we generated mice overexpressing human IGF-1R in the endothelium (human IGF-1R endothelium-overexpressing mice [hIGFREO]) under direction of the Tie2 promoter enhancer. hIGFREO aorta had reduced basal NO bioavailability (percent constriction to N(G)-monomethyl-l-arginine [mean (SEM) wild type 106% (30%); hIGFREO 48% (10%)]; P < 0.05). Endothelial cells from hIGFREO had reduced insulin-stimulated endothelial NO synthase activation (mean [SEM] wild type 170% [25%], hIGFREO 58% [3%]; P = 0.04) and insulin-stimulated NO release (mean [SEM] wild type 4,500 AU [1,000], hIGFREO 1,500 AU [700]; P < 0.05). hIGFREO mice had enhanced endothelium regeneration after denuding arterial injury (mean [SEM] percent recovered area, wild type 57% [2%], hIGFREO 47% [5%]; P < 0.05) and enhanced endothelial cell migration in vitro. The IGF-1R, although reducing NO bioavailability, enhances in situ endothelium regeneration. Manipulating IGF-1R in the endothelium may be a useful strategy to treat disorders of vascular growth and repair.

A regulatory circuit of miR-148a/152 and DNMT1 in modulating cell transformation and tumor angiogenesis through IGF-IR and IRS1

Dysregulation of microRNAs is a common feature in human cancers, including breast cancer (BC). Here we describe the epigenetic regulation of miR-148a and miR-152 and their impact on BC cells. Due to the hypermethylation of CpG island, the expression levels of both miR-148a and miR-152 (miR-148a/152) are decreased in BC tissues and cells. DNMT1, the DNA methyltransferase 1 for the maintenance methylation, is aberrantly up-regulated in BC and its overexpression is responsible for hypermethylation of miR-148a and miR-152 promoters. Intriguingly, we found that DNMT1 expression, which is one of the targets of miR-148a/152, is inversely correlated with the expression levels of miR-148a/152 in BC tissues. Those results lead us to propose a negative feedback regulatory loop between miR-148a/152 and DNMT1 in BC. More importantly, we demonstrate that IGF-IR and IRS1, often overexpressed in BC, are two novel targets of miR-148a/152. Overexpression of miR-148a or miR-152 significantly inhibits BC cell proliferation, colony formation, and tumor angiogenesis via targeting IGF-IR and IRS1 and suppressing their downstream AKT and MAPK/ERK signaling pathways. Our results suggest a novel miR-148a/152-DNMT1 regulatory circuit and reveal that miR-148a and miR-152 act as tumor suppressors by targeting IGF-IR and IRS1, and that restoration of miR-148a/152 expression may provide a strategy for therapeutic application to treat BC patients.

Novel nuclear localization and potential function of insulin-like growth factor-1 receptor/insulin receptor hybrid in corneal epithelial cells

Background

Type I insulin-like growth factor receptor (IGF-1R) and insulin receptor (INSR) are highly homologous molecules, which can heterodimerize to form an IGF-1R/INSR hybrid (Hybrid-R). The presence and biological significance of the Hybrid-R in human corneal epithelium has not yet been established. In addition, while nuclear localization of IGF-1R was recently reported in cancer cells and human corneal epithelial cells, the function and profile of nuclear IGF-1R is unknown. In this study, we characterized the nuclear localization and function of the Hybrid-R and the role of IGF-1/IGF-1R and Hybrid-R signaling in the human corneal epithelium.

Methodology/Principle Findings

IGF-1-mediated signaling and cell growth were examined in a human telomerized corneal epithelial (hTCEpi) cell line using co-immunoprecipitation, immunoblotting and cell proliferation assays. The presence of Hybrid-R in hTCEpi and primary cultured human corneal epithelial cells was confirmed by immunofluorescence and reciprocal immunoprecipitation of whole cell lysates. We found that IGF-1 stimulated Akt and promoted cell growth through IGF-1R activation, which was independent of the Hybrid-R. The presence of Hybrid-R, but not IGF-1R/IGF-1R, was detected in nuclear extracts. Knockdown of INSR by small interfering RNA resulted in depletion of the INSR/INSR and preferential formation of Hybrid-R. Chromatin-immunoprecipitation sequencing assay with anti-IGF-1R or anti-INSR was subsequently performed to identify potential genomic targets responsible for critical homeostatic regulatory pathways.

Conclusion/Significance

In contrast to previous reports on nuclear localized IGF-1R, this is the first report identifying the nuclear localization of Hybrid-R in an epithelial cell line. The identification of a nuclear Hybrid-R and novel genomic targets suggests that IGF-1R traffics to the nucleus as an IGF-1R/INSR heterotetrameric complex to regulate corneal epithelial homeostatic pathways. The development of novel therapeutic strategies designed to target the IGF-1/IGF-1R pathway must take into account the modulatory roles IGF-1R/INSR play in the epithelial cell nucleus.

Quantification of the GH/IGF-axis components: lessons from human studies

Originally, the circulating bioactivity of IGF-I was estimated by bioassays measuring the ability of serum to stimulate uptake of labeled sulfate or thymidine in cultures of costal cartilage or by the ability of serum to stimulate the uptake of glucose in fat tissue cultures. However, because of their laborious and unspecific nature, the original bioassays were quickly abandoned with the development of the first RIA for IGF-I in 1977. Consequently, for the past three decades the endogenous IGF-I bioactivity has been almost exclusively estimated by the use of immunoassays. Beyond any doubt, the immunoassays have provided an extensive insight into IGF-I physiology and pathophysiology. However, immunoassays ignore the presence of the IGFBPs, which are important regulators of IGF-I action in vivo. In addition, immunoassays do not consider the presence of IGF-II, which also interacts with the IGF-I receptor (IGF-IR). This aroused our interest to reintroduce the bioassay; therefore, we established a cell-based kinase receptor activation (KIRA) assay based on cells transfected with the human IGF-IR. The output signal of the KIRA assay is IGF-IR phosphorylation, and, as such, it is highly specific. Further, because detection of phosphorylated IGF-IRs is based on modern immunoassay techniques, the overall performance of the assay is close to that of a traditional IGF-I immunoassay. The first part of this review comprises a short description of the bioassay, and a more in-depth presentation of the data that have been obtained so far. It will be demonstrated that the bioassay is indeed able to yield novel information on the IGF system, most likely because it is able to integrate the different components of the IGF system into one signal: IGF-IR activation. As IGF-I, circulating GH is bound to larger proteins, the far most important GH-binding protein (GHBP) is identical to the extracellular domain of the GH receptor (GHR). Because of its origin, GHBP binds GH with the same affinity as GHR and, consequently, GHBP may affect GH bioactivity as well as pharmacokinetics. To improve our knowledge on the complex interaction between GH and GHBP in vivo, we found it of interest to develop a method for determination of free GH. To this end, we developed an ultrafiltration assay that enabled isolation of free GH in undiluted serum during approached in vivo-like conditions. The last part of this review presents our current data on free GH and its interaction with GHBP.

Novel missense mutation in the IGF-I receptor L2 domain results in intrauterine and postnatal growth retardation

BACKGROUND

IGFs play key roles in intrauterine and postnatal growth through the IGF-I receptor (IGF-IR). We identified a family bearing a new heterozygous missense mutation at the L2 domain of IGF-IR (R431L).

METHOD

We analysed the nucleotide sequences of the IGF1R gene of the family. We prepared R(-) cells (fibroblasts with targeted disruption of the IGF-IR gene) expressing wild-type or R431L IGF-IR and performed functional analyses by evaluating IGF-I binding, IGF-I-stimulated DNA synthesis, tyrosine phosphorylation of IGF-IR and its substrates, and internalization by measuring [(125) I]IGF-I internalization. We also performed confocal microscopy analysis.

RESULTS

We identified a family bearing a new heterozygous missense mutation at the L2 domain of IGF-IR (R431L) through an 8-year-old girl and her mother, both born with intrauterine growth retardation. In experiments conducted using cells homozygously transfected with the IGF-IR R431L mutation; (i) IGF-I binding was not affected; (ii) DNA synthesis induced by IGF-I was decreased; (iii) IGF-IR internalization stimulated by IGF-I was decreased and (iv) IGF-I-stimulated tyrosine phosphorylation was reduced IGF-IR by low concentrations of IGF-I and on insulin receptor substrate (IRS)-1 and IRS-2.

CONCLUSION

A missense mutation (R431L) leads to the inhibition of cell proliferation, attenuation of IGF signalling and decrease in internalization of IGF-IR. The results of this study suggest a novel link between a mutation at the IGF-IR L2 domain and intrauterine and postnatal growth retardation.

Insulin-like growth factor type 1 receptor (IGF-1R) exclusive nuclear staining: a predictive biomarker for IGF-1R monoclonal antibody (Ab) therapy in sarcomas

AIMS

A minority of patients with advanced sarcoma achieve prolonged progression free survival (PFS) with insulin growth factor type 1 receptor (IGF-1R) monoclonal antibody (Ab) therapy. A biomarker identifying those patients beforehand would be useful to select patients for the development of these agents.

METHODS

This single centre series includes patients with unresectable or metastatic soft tissue sarcomas (STS), Ewing sarcoma (ES) and osteosarcoma treated with IGF-1R Ab (R1507, IMC-A12, SCH 717454 and CP-751.871) in the Centre Léon Bérard. Tumour samples were analysed by immunohistochemistry for expression of IGF-1R, insulin-like growth factor binding protein type 3 (IGFBP-3), Ki67, epidermal growth factor receptor (HER1) and human epidermal growth factor receptor 2 (HER2). Predictive factors for PFS and overall survival (OS) were investigated.

RESULTS

All tumour samples had a positive IGF-1R immunostaining on 60% to 100% of tumour cells. IGFBP-3 immunostaining was observed in 12 (75%) samples with 5% to 100% of positive cells. IGF-1R immunostaining was nuclear (n=9, 56%), cytoplasmic (n=4, 25%), or nuclear +cytoplasmic (n=3, 19%). Neither IGFBP-3 expression, nor Ki67 was correlated to PFS. HER2 and HER1 staining were positive in 0 and 2 samples respectively (both primary resistant to IGF-1R Ab therapy). Exclusive intra-nuclear immunoreactivity for IGF-1R was significantly associated with a better PFS (p=0.01) and OS (p=0.007).

CONCLUSION

Exclusive nuclear localisation of IGF-1R is an easily testable biomarker associated with a better PFS and OS for patients treated with IGF-1R Ab therapy. Nuclear localisation of IGF-1R in tumour cells might be a hallmark of pathway activation.

Role of insulin-like growth factor-1 (IGF-1) pathway in the pathogenesis of Graves' orbitopathy

The etiology of Graves' orbitopathy (GO) remains enigmatic and thus controversy surrounds its pathogenesis. The role of the thyroid stimulating hormone receptor (TSHR) and activating antibodies directed against it in the hyperthyroidism of Graves' disease (GD) is firmly established. Less well elucidated is what part the TSHR pathway might play in the development of GO. Also uncertain is the participation of other cell surface receptors in the disease. Elevated levels of insulin-like growth factor-1 receptor (IGF-1R) have been found in orbital fibroblasts as well as B and T cells from patients with GD. These abnormal patterns of IGF-1R display are also found in rheumatoid arthritis and carry functional consequences. In addition, activating IgGs capable of displacing IGF-1 from IGF-1R have also been detected in patients with these diseases. IGF-1R forms a complex with TSHR which is necessary for at least some of the non-canonical signaling observed following TSHR activation. Functional TSHR and IGF-1R have also been found on fibrocytes, CD34⁺ bone marrow-derived cells from the monocyte lineage. Levels of TSHR on fibrocytes greatly exceed those found on orbital fibroblasts. When ligated by TSH or M22, a TSHR-activating monoclonal antibody, fibrocytes produce extremely high levels of several cytokines and chemokines. Moreover, fibrocytes infiltrate both the orbit and thyroid in GD. In sum, based on current evidence, IGF-1R and TSHR can be thought of as "partners in crime". Involvement of the former probably transcends disease boundaries, while TSHR may not.

Similar but different: ligand-induced activation of the insulin and epidermal growth factor receptor families

The insulin and epidermal growth factor receptor families are among the most intensively studied proteins in biology. They are closely related members of the receptor tyrosine kinase superfamily and deregulated signaling by members of either receptor family has been implicated in the progression of a variety of cancers. These receptors have thus emerged as validated therapeutic targets for the development of anti-tumour agents. Recent studies have revealed detail of the ligand-binding sites in the insulin receptor family, as well as detail of conformational change upon ligand binding in the epidermal growth factor receptor family. Taken together, these findings and further data relating to kinase activation highlight the fact that while the receptor families share common structural elements, the structural detail of their functioning is remarkably different.

Nuclear targeting of IGF-1 receptor in orbital fibroblasts from Graves' disease: apparent role of ADAM17

Insulin-like growth factor-1 receptor (IGF-1R) comprises two subunits, including a ligand binding domain on extra- cellular IGF-1Rα and a tyrosine phosphorylation site located on IGF-1Rβ. IGF-1R is over-expressed by orbital fibroblasts in the autoimmune syndrome, Graves' disease (GD). When activated by IGF-1 or GD-derived IgG (GD-IgG), these fibroblasts produce RANTES and IL-16, while those from healthy donors do not. We now report that IGF-1 and GD-IgG provoke IGF-1R accumulation in the cell nucleus of GD fibroblasts where it co-localizes with chromatin. Nuclear IGF-1R is detected with anti-IGF-1Rα-specific mAb and migrates to approximately 110 kDa, consistent with its identity as an IGF-1R fragment. Nuclear IGF-1R migrating as a 200 kDa protein and consistent with an intact receptor was undetectable when probed with either anti-IGF-1Rα or anti-IGF-1Rβ mAbs. Nuclear redistribution of IGF-1R is absent in control orbital fibroblasts. In GD fibroblasts, it can be abolished by an IGF-1R-blocking mAb, 1H7 and by physiological concentrations of glucocorticoids. When cell-surface IGF-1R is cross-linked with ¹²⁵I IGF-1, ¹²⁵I-IGF-1/IGF-1R complexes accumulate in the nuclei of GD fibroblasts. This requires active ADAM17, a membrane associated metalloproteinase, and the phosphorylation of IGF-1R. In contrast, virally encoded IGF-1Rα/GFP fusion protein localizes equivalently in nuclei in both control and GD fibroblasts. This result suggests that generation of IGF-1R fragments may limit the accumulation of nuclear IGF-1R. We thus identify a heretofore-unrecognized behavior of IGF-1R that appears limited to GD-derived fibroblasts. Nuclear IGF-1R may play a role in disease pathogenesis.

Molecular docking studies of banana flower flavonoids as insulin receptor tyrosine kinase activators as a cure for diabetes mellitus

Diabetes mellitus is a metabolic disorder caused due to insulin deficiency. Banana flower is a rich source of flavonoids that exhibit anti diabetic activity. Insulin receptor is a tetramer that belongs to a family of receptor tyrosine kinases. It contains two alpha subunits that form the extracellular domain and two beta subunits that constitute the intracellular tyrosine kinase domain. Insulin binds to the extracellular region of the receptor and causes conformational changes that lead to the activation of the tyrosine kinase. This leads to autophosphorylation, a step that is crucial in insulin signaling pathway. Hence, compounds that augment insulin receptor tyrosine kinase activity would be useful in the treatment of diabetes mellitus. The 3D structure of IR tyrosine kinase was obtained from PDB database. The list of flavonoids found in banana flower was obtained from USDA database. The structures of the flavonoids were obtained from NCBI Pubchem. Docking analysis of the flavonoids was performed using Autodock 4.0 and Autodock Vina. The results indicate that few of the flavonoids may be potential activators of IR tyrosine kinase.

Heterodimerization of glycosylated insulin-like growth factor-1 receptors and insulin receptors in cancer cells sensitive to anti-IGF1R antibody

BACKGROUND

Identification of predictive biomarkers is essential for the successful development of targeted therapy. Insulin-like growth factor 1 receptor (IGF1R) has been examined as a potential therapeutic target for various cancers. However, recent clinical trials showed that anti-IGF1R antibody and chemotherapy are not effective for treating lung cancer.

METHODOLOGY/PRINCIPAL FINDINGS

In order to define biomarkers for predicting successful IGF1R targeted therapy, we evaluated the anti-proliferation effect of figitumumab (CP-751,871), a humanized anti-IGF1R antibody, against nine gastric and eight hepatocellular cancer cell lines. Out of 17 cancer cell lines, figitumumab effectively inhibited the growth of three cell lines (SNU719, HepG2, and SNU368), decreased p-AKT and p-STAT3 levels, and induced G 1 arrest in a dose-dependent manner. Interestingly, these cells showed co-overexpression and altered mobility of the IGF1R and insulin receptor (IR). Immunoprecipitaion (IP) assays and ELISA confirmed the presence of IGF1R/IR heterodimeric receptors in figitumumab-sensitive cells. Treatment with figitumumab led to the dissociation of IGF1-dependent heterodimeric receptors and inhibited tumor growth with decreased levels of heterodimeric receptors in a mouse xenograft model. We next found that both IGF1R and IR were N-linked glyosylated in figitumumab-sensitive cells. In particular, mass spectrometry showed that IGF1R had N-linked glycans at N913 in three figitumumab-sensitive cell lines. We observed that an absence of N-linked glycosylation at N913 led to a lack of membranous localization of IGF1R and figitumumab insensitivity.

CONCLUSION AND SIGNIFICANCE

The data suggest that the level of N-linked glycosylated IGF1R/IR heterodimeric receptor is highly associated with sensitivity to anti-IGF1R antibody in cancer cells.

Molecular basis of signaling specificity of insulin and IGF receptors: neglected corners and recent advances

Insulin and insulin-like growth factor (IGF) receptors utilize common phosphoinositide 3-kinase/Akt and Ras/extracellular signal-regulated kinase signaling pathways to mediate a broad spectrum of "metabolic" and "mitogenic" responses. Specificity of insulin and IGF action in vivo must in part reflect expression of receptors and responsive pathways in different tissues but it is widely assumed that it is also determined by the ligand binding and signaling mechanisms of the receptors. This review focuses on receptor-proximal events in insulin/IGF signaling and examines their contribution to specificity of downstream responses. Insulin and IGF receptors may differ subtly in the efficiency with which they recruit their major substrates (IRS-1 and IRS-2 and Shc) and this could influence effectiveness of signaling to "metabolic" and "mitogenic" responses. Other substrates (Grb2-associated binder, downstream of kinases, SH2Bs, Crk), scaffolds (RACK1, β-arrestins, cytohesins), and pathways (non-receptor tyrosine kinases, phosphoinositide kinases, reactive oxygen species) have been less widely studied. Some of these components appear to be specifically involved in "metabolic" or "mitogenic" signaling but it has not been shown that this reflects receptor-preferential interaction. Very few receptor-specific interactions have been characterized, and their roles in signaling are unclear. Signaling specificity might also be imparted by differences in intracellular trafficking or feedback regulation of receptors, but few studies have directly addressed this possibility. Although published data are not wholly conclusive, no evidence has yet emerged for signaling mechanisms that are specifically engaged by insulin receptors but not IGF receptors or vice versa, and there is only limited evidence for differential activation of signaling mechanisms that are common to both receptors. Cellular context, rather than intrinsic receptor activity, therefore appears to be the major determinant of whether responses to insulin and IGFs are perceived as "metabolic" or "mitogenic."

Insight into the molecular basis for the kinetic differences between the two insulin receptor isoforms

More than 20 years after the description of the two IR (insulin receptor) isoforms, designated IR-A (lacking exon 11) and IR-B (with exon 11), nearly every functional aspect of the alternative splicing both in vitro and in vivo remains controversial. In particular, there is no consensus on the precise ligand-binding properties of the isoforms. Increased affinity and dissociation kinetics have been reported for IR-A in comparison with IR-B, but the opposite results have also been reported. These are not trivial issues considering the reported possible increased mitogenic potency of IR-A, and the reported link between slower dissociation and increased mitogenesis. We have re-examined the ligand-binding properties of the two isoforms using a novel rigorous mathematical analysis based on the concept of a harmonic oscillator. We found that insulin has 1.5-fold higher apparent affinity towards IR-A and a 2-fold higher overall dissociation rate. Analysis based on the model showed increased association (3-fold) and dissociation (2-fold) rate constants for binding site 1 of IR in comparison with IR-B. We also provide a structural interpretation of these findings on the basis of the structure of the IR ectodomain and the proximity of the sequence encoded by exon 11 to the C-terminal peptide that is a critical trans-component of site 1.

Fine details of IGF-1R activation, inhibition, and asymmetry determined by associated hydrogen /deuterium-exchange and peptide mass mapping

The structural features of the asymmetric activated states of the insulin receptor family are still poorly understood. We investigated hydrogen/deuterium (H/D)-exchange within the extracellular domain of the type-I insulin-like growth factor receptor (IGF-1R) in the absence and presence of IGF-1 (active state) and in the presence of antibody inhibitors (inactive state). Near complete coverage of the 210 kDa receptor sequence was obtained by mass mapping of proteolytically derived peptides at all H/D-exchange time points. The data provide details regarding solvent exposure and dynamics across the extracellular region as well as conformational changes induced by activation or inactivation. Multiple peptides, distant in structure, individually demonstrated two distinct H/D-exchange rates, suggesting that each of these peptides exists in two separate environments in IGF-1R. The dual-exchange behavior of these peptides was enhanced on ligand binding and eliminated on inhibitor binding, clearly associating these regions with active state asymmetry and enabling them to serve as reporters of receptor activity.

New insights into the signaling system and function of insulin in fish

Fish have provided essential information about the structure, biosynthesis, evolution, and function of insulin (INS) as well as about the structure, evolution, and mechanism of action of insulin receptors (IR). INS, insulin-like growth factor (IGF)-1, and IGF-2 share a common ancestor; INS and a single IGF occur in Agnathans, whereas INS and distinct IGF-1 and IGF-2s appear in Chondrichthyes. Some but not all teleost fish possess multiple INS genes, but it is not clear if they arose from a common gene duplication event or from multiple separate gene duplications. INS is produced by the endocrine pancreas of fish as well as by several other tissues, including brain, pituitary, gastrointestinal tract, and adipose tissue. INS regulates various aspects of feeding, growth, development, and intermediary metabolism in fish. The actions of INS are mediated through the insulin receptor (IR), a member of the receptor tyrosine kinase family. IRs are widely distributed in peripheral tissues of fish, and multiple IR subtypes that derive from distinct mRNAs have been described. The IRs of fish link to several cellular effector systems, including the ERK and IRS-PI3k-Akt pathways. The diverse effects of INS can be modulated by altering the production and release of INS as well as by adjusting the production/surface expression of IR. The diverse actions of INS in fish as well as the diverse nature of the neural, hormonal, and environmental factors known to affect the INS signaling system reflects the various life history patterns that have evolved to enable fish to occupy a wide range of aquatic habitats.

The insulin-like growth factor-1 receptor is a negative regulator of nitric oxide bioavailability and insulin sensitivity in the endothelium

OBJECTIVE

In mice, haploinsufficiency of the IGF-1 receptor (IGF-1R(+/-)), at a whole-body level, increases resistance to inflammation and oxidative stress, but the underlying mechanisms are unclear. We hypothesized that by forming insulin-resistant heterodimers composed of one IGF-1Rαβ and one insulin receptor (IR), IRαβ complex in endothelial cells (ECs), IGF-1R reduces free IR, which reduces EC insulin sensitivity and generation of the antioxidant/anti-inflammatory signaling radical nitric oxide (NO).

RESEARCH DESIGN AND METHODS

Using a number of complementary gene-modified mice with reduced IGF-1R at a whole-body level and specifically in EC, and complementary studies in EC in vitro, we examined the effect of changing IGF-1R/IR stoichiometry on EC insulin sensitivity and NO bioavailability.

RESULTS

IGF-1R(+/-) mice had enhanced insulin-mediated glucose lowering. Aortas from these mice were hypocontractile to phenylephrine (PE) and had increased basal NO generation and augmented insulin-mediated NO release from EC. To dissect EC from whole-body effects we generated mice with EC-specific knockdown of IGF-1R. Aortas from these mice were also hypocontractile to PE and had increased basal NO generation. Whole-body and EC deletion of IGF-1R reduced hybrid receptor formation. By reducing IGF-1R in IR-haploinsufficient mice we reduced hybrid formation, restored insulin-mediated vasorelaxation in aorta, and insulin stimulated NO release in EC. Complementary studies in human umbilical vein EC in which IGF-1R was reduced using siRNA confirmed that reducing IGF-1R has favorable effects on NO bioavailability and EC insulin sensitivity.

CONCLUSIONS

These data demonstrate that IGF-1R is a critical negative regulator of insulin sensitivity and NO bioavailability in the endothelium.

The role of insulin-like growth factor-I in the physiopathology of hearing

Insulin-like growth factor-I (IGF-I) belongs to the family of polypeptides of insulin, which play a central role in embryonic development and adult nervous system homeostasis by endocrine, autocrine, and paracrine mechanisms. IGF-I is fundamental for the regulation of cochlear development, growth, and differentiation, and its mutations are associated with hearing loss in mice and men. Low levels of IGF-I have been shown to correlate with different human syndromes showing hearing loss and with presbyacusis. Animal models are fundamental to understand the genetic, epigenetic, and environmental factors that contribute to human hearing loss. In the mouse, IGF-I serum levels decrease with aging and there is a concomitant hearing loss and retinal degeneration. In the Igf1(-/-) null mouse, hearing loss is due to neuronal loss, poor innervation of the sensory hair cells, and age-related stria vascularis alterations. In the inner ear, IGF-I actions are mediated by intracellular signaling networks, RAF, AKT, and p38 MAPK protein kinases modulate the expression and activity of transcription factors, as AP1, MEF2, FoxM1, and FoxP3, leading to the regulation of cell cycle and metabolism. Therapy with rhIGF-I has been approved in humans for the treatment of poor linear growth and certain neurodegenerative diseases. This review will discuss these findings and their implications in new IGF-I-based treatments for the protection or repair of hearing loss.

Targeting the insulin-like growth factor signaling pathway: figitumumab and other novel anticancer strategies

INTRODUCTION

There are clear preclinical data that support the involvement of the insulin-like growth factor (IGF) signaling pathway in oncogenesis and cancer progression. Such evidence has led to the design and conduct of drug development programs targeting the IGF-I receptor (IGF-IR) over the past 10 years.

AREAS COVERED

This review details the structure and function of different members of the IGF system and related pathways, describes the rationale for targeting IGF-IR in cancer and updates the current advances in drug development. The preclinical development of figitumumab, the furthest developed mAb against IGF-IR, is examined as well as the reported data from Phase I - III clinical trials. Future prospects for this target and pathway are also discussed.

EXPERT OPINION

While there have been both successes and failures in the development of novel targeted therapeutics targeting the IGF pathway, the evaluation of such agents should continue, with greater emphasis placed on combinatorial strategies and the development of predictive biomarkers that enhance antitumor responses through appropriate patient selection.

Insulin-like growth factor 2 enhances insulinogenic differentiation of human eyelid adipose stem cells via the insulin receptor

OBJECTIVES

Previously, we have isolated stem cells (HEAC) from human eyelid adipose tissue and functionally differentiated them into insulin-secreting cells. In the present study, we examined whether insulin family members might influence insulinogenic differentiation of HEAC.

MATERIALS AND METHODS

Following culture in differentiation media containing insulin family member or not, cells were examined for gene expression, protein expression and, particularly, insulin and C-peptide secretion, in response to high glucose challenge. Using antibodies against the specific receptor, target receptor mediating effect of the insulin family member was investigated.

RESULTS

Insulin treatment during culture had little effect on either insulin or C-peptide secretion from HEAC, against high glucose challenge after culture. However, insulin-like growth factor (IGF) 1 treatment decreased both secretions, and interestingly, IGF2 greatly increased the secretions. HEAC treated with IGF2 had strong expression of Pdx1, Isl1, Pax6 and PC1/3 genes, and distinct staining after insulin and C-peptide antibodies, and dithizone. IGF2-enhanced insulinogenic differentiation was totally blocked by antibody against insulin receptor (IR), but not by anti-IGF1 receptor (IGF1R). Differentiated HEAC expressed both IR and IGF1R genes, whereas they expressed neither IGF2 nor IGF2R genes.

CONCLUSIONS

From these results, it is suggested that IGF1 might inhibit insulinogenic differentiation of HEAC, whereas IGF2 enhances differentiation, and that enhancement of IGF2 appeared to be mediated via IR.

Insulin: a small protein with a long journey

Insulin is a hormone that is essential for regulating energy storage and glucose metabolism in the body. Insulin in liver, muscle, and fat tissues stimulates the cell to take up glucose from blood and store it as glycogen in liver and muscle. Failure of insulin control causes diabetes mellitus (DM). Insulin is the unique medicine to treat some forms of DM. The population of diabetics has dramatically increased over the past two decades, due to high absorption of carbohydrates (or fats and proteins), lack of physical exercise, and development of new diagnostic techniques. At present, the two largest developing countries (India and China) and the largest developed country (United States) represent the top three countries in terms of diabetic population. Insulin is a small protein, but contains almost all structural features typical of proteins: α-helix, β-sheet, β-turn, high order assembly, allosteric T®R-transition, and conformational changes in amyloidal fibrillation. More than ten years' efforts on studying insulin disulfide intermediates by NMR have enabled us to decipher the whole picture of insulin folding coupled to disulfide pairing, especially at the initial stage that forms the nascent peptide. Two structural switches are also known to regulate insulin binding to receptors and progress has been made to identify the residues involved in binding. However, resolving the complex structure of insulin and its receptor remains a challenge in insulin research. Nevertheless, the accumulated knowledge of insulin structure has allowed us to specifically design a new ultra-stable and active single-chain insulin analog (SCI-57), and provides a novel way to design super-stable, fast-acting and cheaper insulin formulations for DM patients. Continuing this long journey of insulin study will benefit basic research in proteins and in pharmaceutical therapy.

Discovery of a novel mode of protein kinase inhibition characterized by the mechanism of inhibition of human mesenchymal-epithelial transition factor (c-Met) protein autophosphorylation by ARQ 197

A number of human malignancies exhibit sustained stimulation, mutation, or gene amplification of the receptor tyrosine kinase human mesenchymal-epithelial transition factor (c-Met). ARQ 197 is a clinically advanced, selective, orally bioavailable, and well tolerated c-Met inhibitor, currently in Phase 3 clinical testing in non-small cell lung cancer patients. Herein, we describe the molecular and structural basis by which ARQ 197 selectively targets c-Met. Through our analysis we reveal a previously undisclosed, novel inhibitory mechanism that utilizes distinct regulatory elements of the c-Met kinase. The structure of ARQ 197 in complex with the c-Met kinase domain shows that the inhibitor binds a conformation that is distinct from published kinase structures. ARQ 197 inhibits c-Met autophosphorylation and is highly selective for the inactive or unphosphorylated form of c-Met. Through our analysis of the interplay between the regulatory and catalytic residues of c-Met, and by comparison between the autoinhibited canonical conformation of c-Met bound by ARQ 197 to previously described kinase domains of type III receptor tyrosine kinases, we believe this to be the basis of a powerful new in silico approach for the design of similar inhibitors for other protein kinases of therapeutic interest.

Differential effects of IGF-I, IGF-II and insulin in human preadipocytes and adipocytes--role of insulin and IGF-I receptors

We compared insulin and IGF effects in adipocytes expressing IR (insulin receptors), and preadipocytes expressing IR and IGF-IR (IGF-I receptors). Treatment of adipocytes with insulin, IGF-II or IGF-I resulted in phosphorylation of IR. Order of potency was insulin>IGF-II>IGF-I. In preadipocytes IR, IGF-IR and insulin/IGF-I hybrid receptors (HR) were detected. Treatment of preadipocytes with IGF-I and IGF-II 10(-8)M resulted in activation of IGF-IR and IR whereas insulin was more potent in activating IR, with no effect on IGF-IR. In adipocytes glucose transport was 100-fold more sensitive to insulin than to IGFs and the maximal effect was higher with insulin. In preadipocytes glucose accumulation and DNA synthesis was equally sensitive to insulin and IGFs but the maximal effect was higher with IGF-I. In conclusion, insulin and IGF-I activate their cognate receptors and IGF-I also HR. IGF-II activates IR, IGF-IR and HR. Insulin and IGF-I are partial agonists to each other's receptors.

Overall mortality in diabetes mellitus: where do we stand today?

Life expectancy for a patient with type 2 diabetes remains substantially shorter than an equivalent individual without diabetes, largely because of a greater risk of cardiovascular disease. Diabetes is also associated with an increased incidence of many types of cancer, suggesting that malignancy may also contribute to higher rates of mortality. Hyperglycemia is one of the key risk factors for diabetes-associated macro- and microvascular disease, and as such, intensive glycemic control is associated with improved outcomes for patients, including a reduction in this risk of death from any cause, when initiated early in the disease course. Recent trials in patients with more advanced disease have failed to demonstrate a mortality benefit with intensive glycemic control, although this may reflect their short observation period. Intensive multifactorial therapy, including lifestyle intervention and control of hyperglycemia, hypertension, lipids, thrombosis, and microalbuminuria, is likely to be the best strategy against diabetes-associated macrovascular mortality. However, analysis of the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial indicates that there may be a subpopulation of patients who are unable to achieve glycemic targets with intensive therapy and that aggressive intensification of treatment in this group may increase mortality risk. It remains to be determined whether the relationship between diabetes and malignancy is causal or whether they share common risk factors. Current recommendations for a healthy lifestyle based on good diet, physical exercise, and weight management in order to control diabetes-related complications are likely to apply in reducing the risk of many forms of cancer and should be advocated for all patients.

Electrophoretic characterization of insulin growth factor (IGF-1) functionalized magnetic nanoparticles

The synthesis of composite nanoparticles consisting of a magnetite core coated with a layer of the hormone insulin growth factor 1 (IGF-1) is described. The adsorption of the hormone in the different formulations is first studied by electrophoretic mobility measurements as a function of pH, ionic strength, and time. Because of the permeable character expected for both citrate and IGF-1 coatings surrounding the magnetite cores, an appropriate analysis of their electrophoretic mobility must be addressed. Recent developments of electrokinetic theories for particles covered by soft surface layers have rendered possible the evaluation of the softness degree from raw electrophoretic mobility data. In the present contribution, the data are quantitatively analyzed based on the theoretical model of the electrokinetics of soft particles. As a result, information is obtained on both the thickness and the charge density of the surrounding layer. It is shown that IGF-1 adsorbs onto the surface of citrate-coated magnetite nanoparticles, and adsorption is confirmed by dot-blot analysis. In addition, it is also demonstrated that the external layer of IGF-1 exerts a shielding effect on the surface charge of citrate-magnetite particles, as suggested by the mobility reduction upon contacting the particles with the hormone. Aging effects are demonstrated, providing an electrokinetic fingerprint of changes in adsorbed protein configuration with time.

A hepatoprotective Lindera obtusiloba extract suppresses growth and attenuates insulin like growth factor-1 receptor signaling and NF-kappaB activity in human liver cancer cell lines

Background

In traditional Chinese and Korean medicine, an aqueous extract derived from wood and bark of the Japanese spice bush Lindera obtusiloba (L.obtusiloba) is applied to treat inflammations and chronic liver diseases including hepatocellular carcinoma. We previously demonstrated anti-fibrotic effects of L.obtusiloba extract in hepatic stellate cells. Thus, we here consequently examine anti-neoplastic effects of L.obtusiloba extract on human hepatocellular carcinoma (HCC) cell lines and the signaling pathways involved.

Methods

Four human HCC cell lines representing diverse stages of differentiation were treated with L.obtusiloba extract, standardized according to its known suppressive effects on proliferation and TGF-β-expression. Beside measurement of proliferation, invasion and apoptosis, effects on signal transduction and NF-κB-activity were determined.

Results

L.obtusiloba extract inhibited proliferation and induced apoptosis in all HCC cell lines and provoked a reduced basal and IGF-1-induced activation of the IGF-1R signaling cascade and a reduced transcriptional NF-κB-activity, particularly in the poorly differentiated SK-Hep1 cells. Pointing to anti-angiogenic effects, L.obtusiloba extract attenuated the basal and IGF-1-induced expression of hypoxia inducible factor-1α, vascular endothelial growth factor, peroxisome proliferator-activated receptor-γ, cyclooxygenase-2 and inducible nitric oxide synthase.

Conclusions

The traditional application of the extract is confirmed by our experimental data. Due to its potential to inhibit critical receptor tyrosine kinases involved in HCC progression via the IGF-1 signaling pathway and NF-κB, the standardized L.obtusiloba extract should be further analysed for its active compounds and explored as (complementary) treatment option for HCC.