Minireview: nuclear insulin and insulin-like growth factor-1 receptors: a novel paradigm in signal transduction

Emerging therapies in the medical management of thyroid eye disease

Introduction

Thyroid eye disease (TED) is an immune-mediated disorder associated with a heterogenous array of manifestations that may unfavorably impact vision and quality of life. As understanding of this entity's complex pathogenesis has evolved, so have therapies with novel molecular targets offering promise for improved patient outcomes.

Results

Emerging immunologic therapies for the management of thyroid eye disease have diverse mechanisms of actions and routes of administration. Different conventional and biological immunosuppressive agents have been studied as mediators of the autoimmune and autoinflammatory pathways in thyroid eye disease. Teprotumumab - an anti-IGF-1R monoclonal antibody that has recently emerged as a first-line therapy for active, moderate-to-severe TED - has demonstrated statistically significant improvements in proptosis, diplopia, clinical activity score, and quality of life compared to placebo. Currently under investigation are several other agents, with varying administration modalities, that aim to inhibit IGF-1R: VRDN-001 (intravenous), VRDN-002 or VRDN-003 (subcutaneous), lonigutamab (subcutaneous), and linsitinib (oral). Tocilizumab, a monoclonal antibody of interleukin 6, has played a role in the management of multiple autoimmune and inflammatory conditions and may offer promise in TED. Another incipient biologic target for TED management is the neonatal Fc receptor, inhibition of which has potential to decrease recycling of immunoglobulin and antibody levels; agents addressing this target including monoclonal antibodies as well as antibody fragments. Finally, hypolipidemic agents may play a role as mediators of TED-associated inflammation.

Conclusion

Among the agents under investigation that aim to decrease ocular morbidity associated with TED are agents that IGF-1R, interleukin 6, and the neonatal Fc receptor. The management of TED continues to expand with novel immunologic approaches for disease therapy.

The IGF1 Signaling Pathway: From Basic Concepts to Therapeutic Opportunities

Insulin-like growth factor 1 (IGF1) is a peptide growth factor with important functions in multiple aspects of growth, development and metabolism. The biological actions of IGF1 are mediated by the IGF1 receptor (IGF1R), a cell-surface protein that is evolutionarily related to the insulin receptor (InsR). The effects of IGF1 are moderated by a group of binding proteins (IGFBPs) that bind and transport the ligand in the circulation and extracellular fluids. In mechanistic terms, IGF1R function is linked to the MAPK and PI3K signaling pathways. Furthermore, IGF1R has been shown to migrate to cell nucleus, where it functions as a transcriptional activator. The co-localization of IGF1R and MAPK in the nucleus is of major interest as it suggests novel mechanistic paradigms for the IGF1R-MAPK network. Given its potent anti-apoptotic and pro-survival roles, and in view of its almost universal pattern of expression in most types of cancer, IGF1R has emerged as a promising molecular target in oncology. The present review article provides a concise overview of key scientific developments in the research area of IGF and highlights a number of more recent findings, including its nuclear migration and its interaction with oncogenes and tumor suppressors.

Cortisol controls endoplasmic reticulum stress and hypoxia dependent regulation of insulin receptor and related genes expression in HEK293 cells

Objective. Glucocorticoids are important stress-responsive regulators of insulin-dependent metabolic processes realized through specific changes in genome function. The aim of this study was to investigate the impact of cortisol on insulin receptor and related genes expression in HEK293 cells upon induction the endoplasmic reticulum (ER) stress by tunicamycin and hypoxia. Methods. The human embryonic kidney cell line HEK293 was used. Cells were exposed to cortisol (10 µM) as well as inducers of hypoxia (dimethyloxalylglycine, DMOG; 0.5 mM) and ER stress (tunicamycin; 0.2 µg/ml) for 4 h. The RNA from these cells was extracted and reverse transcribed. The expression level of INSR, IRS2, and INSIG2 and some ER stress responsive genes encoding XBP1n, non-spliced variant, XBP1s, alternatively spliced variant of XBP1, and DNAJB9 proteins, was measured by quantitative polymerase chain reaction and normalized to ACTB. Results. We showed that exposure of HEK293 cells to cortisol elicited up-regulation in the expression of INSR and DNAJB9 genes and down-regulation of XBP1s, XBP1n, IRS2, and INSIG2 mRNA levels. At the same time, induction of hypoxia by DMOG led to an up-regulation of the expression level of most studied mRNAs: XBP1s and XBP1n, IRS2 and INSIG2, but did not change significantly INSR and DNAJB9 gene expression. We also showed that combined impact of cortisol and hypoxia introduced the up-regulation of INSR and suppressed XBP1n mRNA expression levels. Furthermore, the exposure of HEK293 cells to tunicamycin affected the expression of IRS2 gene and increased the level of XBP1n mRNA. At the same time, the combined treatment of these cells with cortisol and inductor of ER stress had much stronger impact on the expression of all the tested genes: strongly increased the mRNA level of ER stress dependent factors XBP1s and DNAJB9 as well as INSR and INSIG2, but down-regulated IRS2 and XBP1n. Conclusion. Taken together, the present study indicates that cortisol may interact with ER stress and hypoxia in the regulation of ER stress dependent XBP1 and DNAJB9 mRNA expression as well as INSR and its signaling and that this corticosteroid hormone modified the impact of hypoxia and especially tunicamycin on the expression of most studied genes in HEK293 cells. These data demonstrate molecular mechanisms of glucocorticoids interaction with ER stress and insulin signaling at the cellular level.

Overview of the regulation of the class IA PI3K/AKT pathway by SUMO

The phosphatidylinositol-3-kinase (PI3K)/AKT pathway is a major regulator of metabolism, migration, survival, proliferation, and antiviral immunity. Both an overactivation and an inhibition of the PI3K/AKT pathway are related to different pathologies. Activation of this signaling pathway is tightly controlled through a multistep process and its deregulation can be associated with aberrant post-translational modifications including SUMOylation. Here, we review the complex modulation of the PI3K/AKT pathway by SUMOylation and we discuss its putative incvolvement in human disease.

Hallmarks of cancer: The insulin-like growth factors perspective

The identification of a series of attributes or hallmarks that are shared by virtually all cancer cells constitutes a true milestone in cancer research. The conceptualization of a catalogue of common genetic, molecular, biochemical and cellular events under a unifying Hallmarks of Cancer idea had a major impact in oncology. Furthermore, the fact that different types of cancer, ranging from pediatric tumors and leukemias to adult epithelial cancers, share a large number of fundamental traits reflects the universal nature of the biological events involved in oncogenesis. The dissection of a complex disease like cancer into a finite directory of hallmarks is of major basic and translational relevance. The role of insulin-like growth factor-1 (IGF1) as a progression/survival factor required for normal cell cycle transition has been firmly established. Similarly well characterized are the biochemical and cellular activities of IGF1 and IGF2 in the chain of events leading from a phenotypically normal cell to a diseased one harboring neoplastic traits, including growth factor independence, loss of cell-cell contact inhibition, chromosomal abnormalities, accumulation of mutations, activation of oncogenes, etc. The purpose of the present review is to provide an in-depth evaluation of the biology of IGF1 at the light of paradigms that emerge from analysis of cancer hallmarks. Given the fact that the IGF1 axis emerged in recent years as a promising therapeutic target, we believe that a careful exploration of this signaling system might be of critical importance on our ability to design and optimize cancer therapies.

Biglycan Interacts with Type I Insulin-like Receptor (IGF-IR) Signaling Pathway to Regulate Osteosarcoma Cell Growth and Response to Chemotherapy

Simple Summary

Osteosarcoma (OS) is an aggressive, primary bone cancer. OS cells produce altered osteoid whose components participate in signaling correlated to the development of this cancer. Biglycan (BGN), a proteoglycan, is correlated to aggressive OS type and resistance to chemotherapy. A constitutive signaling of insulin-like growth factor receptor I (IGF-IR) signaling in sarcoma progression was established. We showed that biglycan binds IGF-IR resulting in prolonged IGF-IR activation, nuclear translocation, and growth response of the poorly-differentiated MG63 cells correlated to increased aggressiveness markers expression and enhanced chemoresistance. This mechanism is not valid in moderately and well-differentiated, biglycan non-expressing U-2OS and Saos-2 OS cells.

Abstract

Osteosarcoma (OS) is a mesenchymally derived, aggressive bone cancer. OS cells produce an aberrant nonmineralized or partly mineralized extracellular matrix (ECM) whose components participate in signaling pathways connected to specific pathogenic phenotypes of this bone cancer. The expression of biglycan (BGN), a secreted small leucine-rich proteoglycan (SLRP), is correlated to aggressive OS phenotype and resistance to chemotherapy. A constitutive signaling of IGF-IR signaling input in sarcoma progression has been established. Here, we show that biglycan activates the IGF-IR signaling pathway to promote MG63 biglycan-secreting OS cell growth by forming a complex with the receptor. Computational models of IGF-IR and biglycan docking suggest that biglycan binds IGF-IR dimer via its concave surface. Our binding free energy calculations indicate the formation of a stable complex. Biglycan binding results in prolonged IGF-IR activation leading to protracted IGF-IR-dependent cell growth response of the poorly-differentiated MG63 cells. Moreover, biglycan facilitates the internalization (p ≤ 0.01, p ≤ 0.001) and sumoylation-enhanced nuclear translocation of IGF-IR (p ≤ 0.05) and its DNA binding in MG63 cells (p ≤ 0.001). The tyrosine kinase activity of the receptor mediates this mechanism. Furthermore, biglycan downregulates the expression of the tumor-suppressor gene, PTEN (p ≤ 0.01), and increases the expression of endothelial–mesenchymal transition (EMT) and aggressiveness markers vimentin (p ≤ 0.01) and fibronectin (p ≤ 0.01) in MG63 cells. Interestingly, this mechanism is not valid in moderately and well-differentiated, biglycan non-expressing U-2OS and Saos-2 OS cells. Furthermore, biglycan exhibits protective effects against the chemotherapeutic drug, doxorubicin, in MG63 OS cells (p ≤ 0.01). In conclusion, these data indicate a potential direct and adjunct therapeutical role of biglycan in osteosarcoma.

The safety and efficacy of metformin in fragile X syndrome: An open-label study

Fragile X syndrome (FXS) is a rare genetic disorder characterized by a deficit of the fragile X mental retardation protein (FMRP), encoded by the fragile X mental retardation gene (FMR1) on the X chromosome. It has been hypothesized that the absence of FRMP leads to higher levels of Insulin-like Growth Factor 1 (IGF-1) in the brain, possibly contributing to the intellectual impairment characteristic of the disorder. Preclinical studies have shown that metformin downregulates the insulin/IGF-1 signaling pathway, corrects dendritic defects, and improves repetitive behavior in Fmr1 knockout mice. Here, we conducted an open-label study to evaluate: (1) the safety of metformin in normoglycemic individuals with FXS; and (2) the efficacy of metformin to improve aberrant behavior, attention, and to modulate cortical functioning. Fifteen patients with FXS, aged from 17 to 44, received 500 mg of metformin twice/daily over a 9-week treatment period. The primary outcome measures were: (1) the incidence of adverse events (AE); (2) the decrease in IGF-1 levels; and (3) the global score of the Aberrant Behavior Checklist-Community, Fragile X. The secondary outcomes were: (1) the Test of Attentional Performance for children (KiTAP); and (2) the Transcranial Magnetic Stimulation (TMS) parameters measuring cortical excitability. The metformin treatment was well tolerated, with no significant related AE. The TMS data showed an increase in corticospinal inhibition mediated by GABA_A and GABA_B mechanisms. This study demonstrates the safety of metformin in normoglycemic patients with FXS, and suggests the potential of this medication in modifying GABA-mediated inhibition, a hallmark of FXS pathophysiology. Implications for future clinical trials are discussed.

IGFBP-3 Mediates Metabolic Homeostasis During Hyperosmolar Stress in the Corneal Epithelium

Purpose

The insulin-like growth factor binding protein-3 (IGFBP-3) is a multifunctional secretory protein with well-known roles in cell growth and survival. Data in our laboratory suggest that IGFBP-3 may be functioning as a stress response protein in the corneal epithelium. The purpose of this study is to determine the role of IGFBP-3 in mediating the corneal epithelial cell stress response to hyperosmolarity, a well-known pathophysiological event in the development of dry eye disease.

Methods

Telomerase-immortalized human corneal epithelial (hTCEpi) cells were used in this study. Cells were cultured in serum-free media with (growth) or without (basal) supplements. Hyperosmolarity was achieved by increasing salt concentrations to 450 and 500 mOsM. Metabolic and mitochondrial changes were assessed using Seahorse metabolic flux analysis and assays for mitochondrial calcium, polarization and mtDNA. Levels of IGFBP-3 and inflammatory mediators were quantified using ELISA. Cytotoxicity was evaluated using a lactate dehydrogenase assay. In select experiments, cells were cotreated with 500 ng/mL recombinant human (rh)IGFBP-3.

Results

Hyperosmolar stress altered metabolic activity, shifting cells towards a respiratory phenotype. Hyperosmolar stress further altered mitochondrial calcium levels, depolarized mitochondria, decreased levels of ATP, mtDNA, and expression of IGFBP-3. In contrast, hyperosmolar stress increased production of the proinflammatory cytokines IL-6 and IL-8. Supplementation with rhIGFBP-3 abrogated metabolic and mitochondrial changes with only marginal effects on IL-8.

Conclusions

These findings indicate that IGFBP-3 is a critical protein involved in hyperosmolar stress responses in the corneal epithelium. These data further support a new role for IGFBP-3 in the control of cellular metabolism.

Activation of Insulin Signaling by Botanical Products

Type 2 diabetes (T2D) is a worldwide health problem, ranked as one of the leading causes for severe morbidity and premature mortality in modern society. Management of blood glucose is of major importance in order to limit the severe outcomes of the disease. However, despite the impressive success in the development of new antidiabetic drugs, almost no progress has been achieved with regard to the development of novel insulin-sensitizing agents. As insulin resistance is the most eminent factor in the patho-etiology of T2D, it is not surprising that an alarming number of patients still fail to meet glycemic goals. Owing to its wealth of chemical structures, the plant kingdom is considered as an inventory of compounds exerting various bioactivities, which might be used as a basis for the development of novel medications for various pathologies. Antidiabetic activity is found in over 400 plant species, and is attributable to varying mechanisms of action. Nevertheless, relatively limited evidence exists regarding phytochemicals directly activating insulin signaling, which is the focus of this review. Here, we will list plants and phytochemicals that have been found to improve insulin sensitivity by activation of the insulin signaling cascade, and will describe the active constituents and their mechanism of action.

The Role of Nuclear Insulin and IGF1 Receptors in Metabolism and Cancer

Insulin (InsR) and insulin-like growth factor-1 (IGF1R) receptors mediate the metabolic and growth-promoting actions of insulin and IGF1/IGF2, respectively. Evidence accumulated in recent years indicates that, in addition to their typical cell-surface localization pattern and ligand-activated mechanism of action, InsR and IGF1R are present in the cell nucleus of both normal and transformed cells. Nuclear translocation seems to involve interaction with a small, ubiquitin-like modifier protein (SUMO-1), although this modification is not always a prerequisite. Nuclear InsR and IGF1R exhibit a number of biological activities that classically fit within the definition of transcription factors. These nuclear activities include, among others, sequence-specific DNA binding and transcriptional control. Of particular interest, nuclear IGF1R was capable of binding and stimulating its cognate gene promoter. The physiological relevance of this autoregulatory mechanism needs to be further investigated. In addition to its nuclear localization, studies have identified IGF1R in the Golgi apparatus, and this particular distribution correlated with a migratory phenotype. In summary, the newly described roles of InsR and IGF1R as gene regulators, in concert with their atypical pattern of subcellular distribution, add a further layer of complexity to traditional models of cell signaling. Furthermore, and in view of the emerging role of IGF1R as a potential therapeutic target, a better understanding of the mechanisms responsible for nuclear IGF1R transport and identification of IGF1R interactors might help optimize target directed therapies in oncology.

The Role of IGF/IGF-1R Signaling in Hepatocellular Carcinomas: Stemness-Related Properties and Drug Resistance

Insulin-like Growth Factor (IGF)/IGF-1 Receptor (IGF-1R) signaling is known to regulate stem cell pluripotency and differentiation to trigger cell proliferation, organ development, and tissue regeneration during embryonic development. Unbalanced IGF/IGF-1R signaling can promote cancer cell proliferation and activate cancer reprogramming in tumor tissues, especially in the liver. Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death, with a high incidence and mortality rate in Asia. Most patients with advanced HCC develop tyrosine kinase inhibitor (TKI)-refractoriness after receiving TKI treatment. Dysregulation of IGF/IGF-1R signaling in HCC may activate expression of cancer stemness that leads to TKI refractoriness and tumor recurrence. In this review, we summarize the evidence for dysregulated IGF/IGF-1R signaling especially in hepatitis B virus (HBV)-associated HCC. The regulation of cancer stemness expression and drug resistance will be highlighted. Current clinical treatments and potential therapies targeting IGF/IGF-1R signaling for the treatment of HCC will be discussed.

Tumor suppressor p53 regulates insulin receptor (INSR) gene expression via direct binding to the INSR promoter

A significant volume of clinical and epidemiological data provides support to the concept that insulin and the insulin receptor (INSR) have an important role in breast cancer. Tumor suppressor p53 is the most frequently mutated molecule in human cancer. The present study was aimed at evaluating the hypothesis that p53 governs the expression and activation of the INSR gene in breast cancer cells. In addition, the study was designed to investigate the mechanism of action of p53 in the context of INSR gene regulation. The availability of MCF7 breast cancer-derived cell lines with specific disruption of either the insulin-like growth factor-1 receptor (IGF1R) or INSR allowed us to address the impact of the IGF1R and INSR pathways on p53 expression. Data indicate that the INSR gene constitutes a target for p53 action. Wild-type p53 stimulated INSR promoter activity in control cells while disruption of endogenous IGF1R or INSR led to inhibition of promoter activity by p53. Mutant p53 strongly stimulated INSR promoter. Furthermore, p53 directly binds to the INSR promoter in cells with a disrupted IGF1R. Combined, our results identified complex functional and physical interactions between p53 and the INSR pathway. The implications of the p53-INSR interplay in breast cancer needs to be further investigated.

Role of Tumor and Stroma-Derived IGF/IGFBPs in Pancreatic Cancer

Pancreatic cancer (PC) is the utmost stroma-rich cancer, which is accompanied by fibrotic reactions that stimulate interactions between tumor cells and stroma to promote tumor progression. Considerable research evidence denotes that insulin-like growth factor (IGF)/IGF binding proteins (IGFBP) signaling axis facilitate tumor growth, metastasis, drug resistance, and thereby facilitate PC into an advanced stage. The six members of IGFBPs were initially considered as passive carriers of free IGFs; however, current evidence revealed their functions beyond the endocrine role in IGF transport. Though numerous efforts have been made in blocking IGF/IGFBPs, the targeted therapies remain unsuccessful due to the complexity of tumor-stromal interactions in the pancreas. In this review, we explore the emerging evidence of the various roles of the tumor as well as stroma derived IGF/IGFBPs and highlight as a novel therapeutic target against PC progression.

New Insights from IGF-IR Stimulating Activity Analyses: Pathological Considerations

Insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II) play a crucial factor in the growth, differentiation and survival of cells in health and disease. IGF-I and IGF-II primarily activate the IGF-I receptor (IGF-IR), which is present on the cell surface. Activation of the IGF-IR stimulates multiple pathways which finally results in multiple biological effects in a variety of tissues and cells. In addition, activation of the IGF-IR has been found to be essential for the growth of cancers. The conventional view in the past was that the IGF-IR was exclusively a tyrosine kinase receptor and that phosphorylation of tyrosine residues, after binding of IGF-I to the IGF-IR, started a cascade of post-receptor events. Recent research has shown that this view was too simplistic. It has been found that the IGF-IR also has kinase-independent functions and may even emit signals in the unoccupied state through some yet-to-be-defined non-canonical pathways. The IGF-IR may further form hybrids with the insulin receptors but also with receptor tyrosine kinases (RTKs) outside the insulin-IGF system. In addition, the IGF-IR has extensive cross-talk with many other receptor tyrosine kinases and their downstream effectors. Moreover, there is now emerging evidence that the IGF-IR utilizes parts of the G-protein coupled receptor (GPCR) pathways: the IGF-IR can be considered as a functional RTK/GPCR hybrid, which integrates the kinase signaling with some IGF-IR mediated canonical GPCR characteristics. Like the classical GPCRs the IGF-IR can also show homologous and heterologous desensitization. Recently, it has been found that after activation by a ligand, the IGF-IR may be translocated into the nucleus and function as a transcriptional cofactor. Thus, in recent years, it has become clear that the IGF-IR signaling pathways are much more complex than first thought. Therefore a big challenge for the (near) future will be how all the new knowledge about IGF-IR signaling can be translated into the clinical practice and improve diagnosis and treatment of diseases.

Different intracellular signalling sensitivity and cell behaviour of porcine insulin with aging

Insulin has many important biological functions. Insulin interacts with the insulin receptor (IR) to play its physiological role and execute its functions. Here, we isolated porcine hepatocytes from young and aged pigs, which endogenously express the IR, as a model to study the intracellular signalling properties and cellular behaviour of insulin with aging. Firstly, we analysed the intracellular signal transduction that is triggered by insulin in porcine hepatocytes that were isolated from young and aged pigs and found that insulin can strongly activate insulin receptor subunit (IRS), protein kinase B (AKT), and GSK in a time- and dose-dependent manner in hepatocytes from young pigs. On the contrary, the signalling response to insulin in hepatocytes from aged pigs was significantly reduced compared to that of the young pig. Secondly, the different subcellular locations of insulin/insulin receptor (IR) may result in different biological activities, although nuclear-localized insulin/IR still could exhibit important functions and roles. We found that insulin can translocate into cell nuclei in the hepatocytes of the young pigs; however, insulin/insulin receptor fails to transports into the cell nucleus in hepatocytes from aged pigs, although insulin/insulin receptor could internalize into cell cytoplasm. In summary, in the current study, we explored and compared for the first time insulin's behaviour and signalling properties in the cells of young pig hepatocytes and aged pig hepatocytes. Furthermore, we found that the insulin signalling response in hepatocytes was significantly reduced with age; more importantly, we found that the cell behaviour of insulin was changed significantly in the hepatocytes from aged pigs compared to young pigs, and it is noteworthy that insulin/IR cannot translocate into the cell nuclei in the hepatocytes from the aged pig. This may be a potential new reason contributing to insulin resistance with aging, suggesting that we need to study the reason for insulin resistance from a new point of view.

The IGF/Insulin-IGFBP Axis in Corneal Development, Wound Healing, and Disease

The insulin-like growth factor (IGF) family plays key roles in growth and development. In the cornea, IGF family members have been implicated in proliferation, differentiation, and migration, critical events that maintain a smooth refracting surface that is essential for vision. The IGF family is composed of multiple ligands, receptors, and ligand binding proteins. Expression of IGF type 1 receptor (IGF-1R), IGF type 2 receptor (IGF-2R), and insulin receptor (INSR) in the cornea has been well characterized, including the presence of the IGF-1R and INSR hybrid (Hybrid-R) in the corneal epithelium. Recent data also indicates that each of these receptors display unique intracellular localization. Thus, in addition to canonical ligand binding at the plasma membrane and the initiation of downstream signaling cascades, IGF-1R, INSR, and Hybrid-R also function to regulate mitochondrial stability and nuclear gene expression. IGF-1 and IGF-2, two of three principal ligands, are polypeptide growth factors that function in all cellular layers of the cornea. Unlike IGF-1 and IGF-2, the hormone insulin plays a unique role in the cornea, different from many other tissues in the body. In the corneal epithelium, insulin is not required for glucose uptake, due to constitutive activation of the glucose transporter, GLUT1. However, insulin is needed for the regulation of metabolism, circadian rhythm, autophagy, proliferation, and migration after wounding. There is conflicting evidence regarding expression of the six IGF-binding proteins (IGFBPs), which function primarily to sequester IGF ligands. Within the cornea, IGFBP-2 and IGFBP-3 have identified roles in tissue homeostasis. While IGFBP-3 regulates growth control and intracellular receptor localization in the corneal epithelium, both IGFBP-2 and IGFBP-3 function in corneal fibroblast differentiation and myofibroblast proliferation, key events in stromal wound healing. IGFBP-2 has also been linked to cellular overgrowth in pterygium. There is a clear role for IGF family members in regulating tissue homeostasis in the cornea. This review summarizes what is known regarding the function of IGF and related proteins in corneal development, during wound healing, and in the pathophysiology of disease. Finally, we highlight key areas of research that are in need of future study.

The nuclear translocation of insulin-like growth factor receptor and its significance in cancer cell survival

The nuclear translocation of insulin-like growth factor receptor type 1 (IGF-1R) has been documented in a variety of previous studies. The exact mechanism of this translocation, however, is still poorly understood. Furthermore, the functional role of IGF-1R in the nucleus shows promise of transcriptional control. This function is particularly important in cancer cells. Understanding this role may also give insights into cancer biology and treatment methods. Processes including SUMOylation and clathrin-mediated endocytosis are necessary for IGF-1R nuclear translocation to occur. The antiapoptotic qualities of IGF-1R likely contribute to its function in cancer cells. This review aims to synthesize the work on IGF-1R in order to propose a mechanism of translocation. Using this mechanism, new therapeutic targets can be proposed that hinder the role of IGF-1R in cancer metastasis.

Roles of the insulin signaling pathway in insect development and organ growth

Organismal development is a complex process as it requires coordination of many aspects to grow into fit individuals, such as the control of body size and organ growth. Therefore, the mechanisms of precise control of growth are essential for ensuring the growth of organisms at a correct body size and proper organ proportions during development. The control of the growth rate and the duration of growth (or the cessation of growth) are required in size control. The insulin signaling pathway and the elements involved are essential in the control of growth. On the other hand, the ecdysteroid molting hormone determines the duration of growth. The secretion of these hormones is controlled by environmental factors such as nutrition. Moreover, the target of rapamycin (TOR) pathway is considered as a nutrient sensing pathway. Important cross-talks have been shown to exist among these pathways. In this review, we outline the control of body and organ growth by the insulin/TOR signaling pathway, and also the interaction between nutrition via insulin/TOR signaling and ecdysteroids at the coordination of organismal development and organ growth in insects, mainly focusing on the well-studied fruit fly Drosophila melanogaster.

Differential Effects of Insulin and IGF1 Receptors on ERK and AKT Subcellular Distribution in Breast Cancer Cells

Insulin and insulin-like growth factor-1 (IGF1) have important roles in breast cancer development. The recent identification of nuclear insulin (INSR) and IGF1 (IGF1R) receptors provides a novel paradigm in the area of signal transduction. The fact that INSR and IGF1R can function as transcription factors, capable of binding DNA and controlling transcription, adds a new layer of biological complexity by conferring upon cell-surface receptors the ability to regulate genomic events. The present study was designed to assess the hypothesis that insulin and IGF1 pathways elicit differential effects on subcellular distribution and activation of ERK1/2 and AKT. To this end, MCF7 breast cancer-derived cell lines with specific INSR or IGF1R disruption were employed. In addition, small interfering RNA technology was used to specifically down-regulate INSR or IGF1R expression in T47D breast cancer cells. DNA affinity chromatography assays were conducted to address the specific binding of ERK1/2 and AKT to the IGF1R promoter region. We demonstrate that both INSR and IGF1R exhibit a nuclear localization in breast cancer-derived cells. In addition, the insulin and IGF1 pathways have different effects on the subcellular distribution (and, particularly, the nuclear presence) of ERK1/2 and AKT molecules. Both cytoplasmic mediators are capable of binding and transactivating the IGF1R promoter. In conclusion, our data are consistent with the notion that, in addition to their classical roles as targets for insulin-like molecules, both ERK1/2 and AKT are involved in transcriptional control of the IGF1R gene. This previously unrecognized regulatory loop may provide mechanistic advantages to breast cancer cells. Given the potential role of INSR and IGF1R as therapeutic targets in oncology, it will be of clinical relevance to address the future use of nuclear receptors and their downstream cytoplasmic mediators as biomarkers for INSR/IGF1R targeted therapy.

The Insulin/IGF System in Mammalian Sexual Development and Reproduction

Persistent research over the past few decades has clearly established that the insulin-like family of growth factors, which is composed of insulin and insulin-like growth factors 1 (IGF1) and 2 (IGF2), plays essential roles in sexual development and reproduction of both males and females. Within the male and female reproductive organs, ligands of the family act in an autocrine/paracrine manner, in order to guide different aspects of gonadogenesis, sex determination, sex-specific development or reproductive performance. Although our knowledge has greatly improved over the last years, there are still several facets that remain to be deciphered. In this review, we first briefly outline the principles of sexual development and insulin/IGF signaling, and then present our current knowledge, both in rodents and humans, about the involvement of insulin/IGFs in sexual development and reproductive functions. We conclude by highlighting some interesting remarks and delineating certain unanswered questions that need to be addressed in future studies.

Insulin/IGF signaling and discoidin domain receptors: An emerging functional connection

The insulin/insulin-like growth factor system (IIGFs) plays a fundamental role in the regulation of prenatal and postnatal growth, metabolism and homeostasis. As a consequence, dysregulation of this axis is associated with growth disturbance, type 2 diabetes, chronic inflammation and tumor progression. A functional crosstalk between IIGFs and discoidin domain receptors (DDRs) has been recently discovered. DDRs are non-integrin collagen receptors that canonically undergo slow and long-lasting autophosphorylation after binding to fibrillar collagen. While both DDR1 and DDR2 functionally interact with IIGFs, the crosstalk with DDR1 is so far better characterized. Notably, the IIGFs-DDR1 crosstalk presents a feed-forward mechanism, which does not require collagen binding, thus identifying novel non-canonical action of DDR1. Further studies are needed to fully explore the role of this IIGFs-DDRs functional loop as potential target in the treatment of inflammatory and neoplastic disorders.

Identification of nucleolar protein NOM1 as a novel nuclear IGF1R-interacting protein

The insulin-like growth factor-1 receptor (IGF1R) mediates the biological actions of both IGF1 and IGF2. In recent years, evidence has accumulated showing that, in addition to its classical cell-surface distribution, IGF1R translocates to cell nucleus via an apparently SUMO-1-dependent mechanism. While the role of IGF1R in nucleus has not yet been settled, available information suggests that the nuclear receptor displays activities usually linked to transcription factors, including DNA binding and transcription regulation. To gain insight into the biological pathways associated with nuclear IGF1R action we conducted a mass spectrometry-based proteomic analysis aimed at identifying interactors of IGF1R in nucleus of both benign and malignant breast cells. The nucleolar NOM1 molecule belongs to a family of proteins that contain the middle domain of eukaryotic initiation factor 4G (MIF4G) and/or interaction module (MA3), and functions in translation, cell growth and proliferation. Using a combination of co-immunoprecipitation and silencing assays we provide evidence of a complex, bi-directional interplay between nuclear IGF1R and nucleolar protein NOM1. Inhibition of nuclear IGF1R translocation by dansylcadaverine reduced NOM1 levels in nuclei of MCF7 cells. On the other hand, IGF1R overexpression enhanced NOM1 levels in the nuclear fraction. Of interest, NOM1 silencing led to a major increase in IGF1R biosynthesis. In summary, results are consistent with a physiologically-relevant interplay between the nuclear IGF1 signaling pathway and nucleolar protein NOM1.

Insulin-like Growth Factor-I Receptor and Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a complex disease process presumed to emerge from autoimmunity occurring in the thyroid gland, most frequently in Graves disease (GD). It is disfiguring and potentially blinding, culminating in orbital tissue remodeling and disruption of function of structures adjacent to the eye. There are currently no medical therapies proven capable of altering the clinical outcome of TAO in randomized, placebo-controlled multicenter trials. The orbital fibroblast represents the central target for immune reactivity. Recent identification of fibroblasts that putatively originate in the bone marrow as monocyte progenitors provides a plausible explanation for why antigens, the expressions of which were once considered restricted to the thyroid, are detected in the TAO orbit. These cells, known as fibrocytes, express relatively high levels of functional TSH receptor (TSHR) through which they can be activated by TSH and the GD-specific pathogenic antibodies that underpin thyroid overactivity. Fibrocytes also express insulin-like growth factor I receptor (IGF-IR) with which TSHR forms a physical and functional signaling complex. Notably, inhibition of IGF-IR activity results in the attenuation of signaling initiated at either receptor. Some studies suggest that IGF-IR-activating antibodies are generated in GD, whereas others refute this concept. These observations served as the rationale for implementing a recently completed therapeutic trial of teprotumumab, a monoclonal inhibitory antibody targeting IGF-IR in TAO. Results of that trial in active, moderate to severe disease revealed dramatic and rapid reductions in disease activity and severity. The targeting of IGF-IR with specific biologic agents may represent a paradigm shift in the therapy of TAO.

Identification of Transcription Factor-Binding Sites in the Mouse FOXO1 Promoter

One critical determinant of levels of gene expression is binding of transcription factors to cognate DNA sequences in promoter and enhancer regions of target genes. Transcription factors are DNA-binding proteins to which transcriptional co-regulators are bound, ultimately resulting in histone modifications that change chromatin structure to regulate transcription. Examples of transcription factors include hormone-activated transcription factors such as the glucocorticoid receptor, transcription factors regulated by cell surface receptors such as FOXO1 and Smad2/Smad3, and many others. Promoter regions typically contain multiple, diverse transcription factor-binding sites. Binding sites for cell-type-specific transcription factors involved in cell fate determination such as Runx2, MyoD, or myogenin are frequently observed. Promoter regions are located within ~2 kb upstream of the transcriptional start site, whereas enhancers may be located at some distance from promoter sequences and exert long-range effects. Here, we will discuss classical and emerging technologies by which one can understand the role of binding of specific transcription factors in regulation of transcription of FOXO genes.

Role of IGF-1R in ameliorating apoptosis of GNE deficient cells

Sialic acids (SAs) are nine carbon acidic amino sugars, found at the outermost termini of glycoconjugates performing various physiological and pathological functions. SA synthesis is regulated by UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE) that catalyzes rate limiting steps. Mutations in GNE result in rare genetic disorders, GNE myopathy and Sialuria. Recent studies indicate an alternate role of GNE in cell apoptosis and adhesion, besides SA biosynthesis. In the present study, using a HEK cell-based model for GNE myopathy, the role of Insulin-like Growth Factor Receptor (IGF-1R) as cell survival receptor protein was studied to counter the apoptotic effect of non-functional GNE. In the absence of functional GNE, IGF-1R was hyposialylated and transduced a downstream signal upon IGF-1 (IGF-1R ligand) treatment. IGF-1 induced activation of IGF-1R led to AKT (Protein Kinase B) phosphorylation that may phosphorylate BAD (BCL2 Associated Death Promoter) and its dissociation from BCL2 to prevent apoptosis. However, reduced ERK (Extracellular signal-regulated kinases) phosphorylation in GNE deficient cells after IGF-1 treatment suggests downregulation of the ERK pathway. A balance between the ERK and AKT pathways may determine the cell fate towards survival or apoptosis. Our study suggests that IGF-1R activation may rescue apoptotic cell death of GNE deficient cell lines and has potential as therapeutic target.

Hsa-let-7c controls the committed differentiation of IGF-1-treated mesenchymal stem cells derived from dental pulps by targeting IGF-1R via the MAPK pathways

The putative tumor suppressor microRNA let-7c is extensively associated with the biological properties of cancer cells. However, the potential involvement of let-7c in the differentiation of mesenchymal stem cells has not been fully explored. In this study, we investigated the influence of hsa-let-7c (let-7c) on the proliferation and differentiation of human dental pulp-derived mesenchymal stem cells (DPMSCs) treated with insulin-like growth factor 1 (IGF-1) via flow cytometry, CCK-8 assays, alizarin red staining, real-time RT-PCR, and western blotting. In general, the proliferative capabilities and cell viability of DPMSCs were not significantly affected by the overexpression or deletion of let-7c. However, overexpression of let-7c significantly inhibited the expression of IGF-1 receptor (IGF-1R) and downregulated the osteo/odontogenic differentiation of DPMSCs, as indicated by decreased levels of several osteo/odontogenic markers (osteocalcin, osterix, runt-related transcription factor 2, dentin sialophosphoprotein, dentin sialoprotein, alkaline phosphatase, type 1 collagen, and dentin matrix protein 1) in IGF-1-treated DPMSCs. Inversely, deletion of let-7c resulted in increased IGF-1R levels and enhanced osteo/odontogenic differentiation. Furthermore, the ERK, JNK, and P38 MAPK pathways were significantly inhibited following the overexpression of let-7c in DPMSCs. Deletion of let-7c promoted the activation of the JNK and P38 MAPK pathways. Our cumulative findings indicate that Let-7c can inhibit the osteo/odontogenic differentiation of IGF-1-treated DPMSCs by targeting IGF-1R via the JNK/P38 MAPK signaling pathways.

Identification of a unique loss-of-function mutation in IGF1R and a crosstalk between IGF1R and Wnt/β-catenin signaling pathways

IGF1R is a ubiquitous receptor tyrosine kinase that plays critical roles in cell proliferation, growth and survival. Clinical studies have demonstrated upregulation of IGF1R mediated signaling in a number of malignancies including colon, breast, and lung cancers. Overexpression of the IGF1R in these malignancies is associated with a poor prognosis and overall survival. IGF1R specific kinase inhibitors have failed in multiple clinical trials partly because of the complex nature of IGF1R signaling. Thus identifying new binding partners and allosteric sites on IGF1R are emerging areas of research. More recently, IGF1R has been shown to translocate into the nucleus and perform many functions. In this study, we generated a library of IGF1R deletion and point mutants to examine IGF1R subcellular localization and activation of downstream signaling pathways. We show that the nuclear localization of IGF1R is primarily defined by its cytoplasmic domain. We identified a cross-talk between IGF1R and Wnt/β-catenin signaling pathways and showed, for the first time, that IGF1R is associated with upregulation of TCF-mediated β-catenin transcriptional activity. Using loss-of-function mutants, deletion analysis and IGF1R specific inhibitor(s), we show that cytoplasmic and nuclear activities are two independent functions of IGF1R. Furthermore, we identified a unique loss-of-function mutation in IGF1R. This unique loss-of-function mutant retains only nuclear functions and sits in a pocket, outside ATP and substrate binding region, that is suited for designing allosteric inhibitors of IGF1R.

Insulin mediates de novo nuclear accumulation of the IGF-1/insulin Hybrid Receptor in corneal epithelial cells

Insulin and insulin-like growth factor-1 (IGF-1) are present in human tears and likely play an important role in mediating ocular surface homeostasis. We previously characterized the IGF-1/insulin hybrid receptor (Hybrid–R) in corneal epithelial cells and found that it was activated by IGF-1 and not insulin; and reported the novel finding that it localized to the corneal epithelial cell nucleus. Since the corneal epithelium is an insulin insensitive tissue and does not require insulin for glucose uptake, this study investigated the function of insulin in corneal epithelial cells. We show that stress induced by growth factor deprivation triggers transcriptional upregulation and de novo nuclear accumulation of Hybrid-R through the homodimeric insulin receptor (INSR). This occurs independent of PI3K/Akt signaling. Nuclear accumulation of Hybrid-R was associated with partial cell cycle arrest and a corresponding reduction in mitochondrial respiration. Treatment with insulin, and not IGF-1, attenuated IGF-1R and INSR transcription and restored cell cycle and metabolic homeostasis. Together, these findings support that insulin mediates receptor homeostasis in corneal epithelial cells, favoring an IGF-1 mediated pathway. This may have important implications in diabetic corneal disease and wound healing.

Type 1 IGF Receptor Localization in Paediatric Gliomas: Significant Association with WHO Grading and Clinical Outcome

Nuclear localization of insulin-like growth factor receptor type 1 (IGF-1R) has been described as adverse prognostic factor in some cancers. We studied the expression and localization of IGF-1R in paediatric patients with gliomas, as well as its association with World Health Organization (WHO) grading and survival. We conducted a single cohort, prospective study of paediatric patients with gliomas. Samples were taken at the time of the initial surgery; IGF-1R expression and localization were characterized by immunohistochemistry (IHC), subcellular fractionation and western blotting. Tumours (47/53) showed positive staining for IGF-1R by IHC. IGF-1R nuclear labelling was observed in 10/47 cases. IGF-1R staining was mostly non-nuclear in low-grade tumours, while IGF-1R nuclear labelling was predominant in high-grade gliomas (p = 0.0001). Survival was significantly longer in patients with gliomas having non-nuclear IGF-1R localization than in patients with nuclear IGF-1R tumours (p = 0.016). In gliomas, IGF-1R nuclear localization was significantly associated with both high-grade tumours and increased risk of death. Based on a prospective design, we provide evidence of a potential usefulness of intracellular localization of IGF-1R as prognostic factor in paediatric patients with gliomas.

Obesity, Thrombotic Risk, and Inflammation in Cancer

Neoplasms exhibits a high incidence and mortality rates due to their complex and commonly overlapping clinical, biochemical, and morphologic profiles influenced by acquired or inherited molecular abnormalities, cell of origin, and level of differentiation. Obesity appears related to ~20% of cancers including endometrial, esophageal, colorectal, postmenopausal breast, prostate, and renal. Several factors other than obesity, i.e., insulin, insulin-like growth factor, sexual hormones, and adipokines may play a potential role in neoplasia. Cancer-associated hypercoagulable and thrombotic states are influenced by abnormalities in the vascular wall and susceptibility to invasion, interference in blood flow and increase in circulating tissue factor and thrombin, activation of cell growth factors, the presence of a central catheter, chemotherapies, neoplasm type, and surgery. In cancer, thromboembolic complications are the second most frequent cause of death with pulmonary thromboembolism in ~50% of cases postmortem. Thrombosis worsens prognosis as demonstrated with a survival rate as low as 12% per year vs 36% in nonthrombic patients. Deep vein thrombosis is the most frequent thromboembolic complication in cancer. It is usually detected at diagnosis and within the first 3 months of chemotherapy. The underlining mechanisms of this association should be further studied to identify patients at higher risk and develop adequate prevention, diagnostic, and treatment measures. The D-dimer test can be successfully used to assess the fibrinolytic phase of coagulation and as such is routinely used in suspected cases of deep vein thrombosis and pulmonary thromboembolism. In addition, significant advances have been made in understanding the composition and functional capabilities of the gut microbiota in the inflammatory process, obesity, and its roles in cancer; however, the intricate balance that exists within the microbiota may not only affect the host directly, it can also disrupt the entire microbial community.

CONCLUSIONS

Cancer is a prothrombotic and inflammatory state in which the activation of coagulation is related to tumor growth, angiogenesis, and metastasis. It is important to identify the relationship between body mass index with these processes and clarify their importance in cancer prognosis. Future research should answer the question if manipulation of resident microbial communities could potentially improve prognosis and treatment outcome.

Insulin-like growth factor receptor and sphingosine kinase are prognostic and therapeutic targets in breast cancer

Background

Targeting the type 1 insulin-like growth factor receptor (IGF1R) in breast cancer remains an ongoing clinical challenge. Oncogenic IGF1R-signaling occurs via activation of PI3K/AKT/MAPK downstream mediators which regulate cell proliferation and protein synthesis. To further understand IGF1R signaling we have investigated the involvement of the oncogenic IGF1R-related sphingosine kinase (SphK) pathway.

Methods

The prognostic (overall survival, OS) and therapeutic (anti-endocrine therapy) co-contribution of IGF1R and SphK1 were investigated using breast cancer patient samples (n = 236) for immunohistochemistry to measure total and phosphorylated IGF1R and SphK1. Kaplan-Meier and correlation analyses were performed to determine the contribution of high versus low IGF1R and/or SphK1 expression to OS in patients treated with anti-endocrine therapy. Cell viability and colony formation in vitro studies were completed using estrogen receptor (ER) positive and negative breast cancer cell-lines to determine the benefit of IGF1R inhibitor (OSI-906) and SphK inhibitor (SKI-II) co-therapy. Repeated measures and 1-way ANOVA were performed to compare drug treatments groups and the Chou-Talalay combination index (CI) was calculated to estimate drug synergism in vitro (CI < 1).

Results

High IGF1R and SphK1 protein co-expression in tumor tissue was associated with improved OS specifically in ER-positive disease and stratified for anti-endocrine therapy. A significant synergistic inhibition of cell viability and/or colony formation following OSI-906 and SKI-II co-treatment in vitro was evident (p < 0.05, CI < 1).

Conclusion

We conclude that high IGF1R and SphK1 co-expression act together as prognostic indicators and are potentially, dual therapeutic targets for the development of a more effective IGF1R-directed combination breast cancer therapy.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3809-0) contains supplementary material, which is available to authorized users.

Insulin Receptor Isoforms in Physiology and Disease: An Updated View

The insulin receptor (IR) gene undergoes differential splicing that generates two IR isoforms, IR-A and IR-B. The physiological roles of IR isoforms are incompletely understood and appear to be determined by their different binding affinities for insulin-like growth factors (IGFs), particularly for IGF-2. Predominant roles of IR-A in prenatal growth and development and of IR-B in metabolic regulation are well established. However, emerging evidence indicates that the differential expression of IR isoforms may also help explain the diversification of insulin and IGF signaling and actions in various organs and tissues by involving not only different ligand-binding affinities but also different membrane partitioning and trafficking and possibly different abilities to interact with a variety of molecular partners. Of note, dysregulation of the IR-A/IR-B ratio is associated with insulin resistance, aging, and increased proliferative activity of normal and neoplastic tissues and appears to sustain detrimental effects. This review discusses novel information that has generated remarkable progress in our understanding of the physiology of IR isoforms and their role in disease. We also focus on novel IR ligands and modulators that should now be considered as an important strategy for better and safer treatment of diabetes and cancer and possibly other IR-related diseases.

Insulin-Like Growth Factor (IGF) Pathway Targeting in Cancer: Role of the IGF Axis and Opportunities for Future Combination Studies

Despite a strong preclinical rationale for targeting the insulin-like growth factor (IGF) axis in cancer, clinical studies of IGF-1 receptor (IGF-1R)-targeted monotherapies have been largely disappointing, and any potential success has been limited by the lack of validated predictive biomarkers for patient enrichment. A large body of preclinical evidence suggests that the key role of the IGF axis in cancer is in driving treatment resistance, via general proliferative/survival mechanisms, interactions with other mitogenic signaling networks, and class-specific mechanisms such as DNA damage repair. Consequently, combining IGF-targeted agents with standard cytotoxic agents, other targeted agents, endocrine therapies, or immunotherapies represents an attractive therapeutic approach. Anti-IGF-1R monoclonal antibodies (mAbs) do not inhibit IGF ligand 2 (IGF-2) activation of the insulin receptor isoform-A (INSR-A), which may limit their anti-proliferative activity. In addition, due to their lack of specificity, IGF-1R tyrosine kinase inhibitors are associated with hyperglycemia as a result of interference with signaling through the classical metabolic INSR-B isoform; this may preclude their use at clinically effective doses. Conversely, IGF-1/IGF-2 ligand-neutralizing mAbs inhibit proliferative/anti-apoptotic signaling via IGF-1R and INSR-A, without compromising the metabolic function of INSR-B. Therefore, combination regimens that include these agents may be more efficacious and tolerable versus IGF-1R-targeted combinations. Herein, we review the preclinical and clinical experience with IGF-targeted therapies to-date, and discuss the rationale for future combination approaches as a means to overcome treatment resistance.

The RhoGAP Myo9b Promotes Bone Growth by Mediating Osteoblastic Responsiveness to IGF-1

The Ras homolog A (RhoA) subfamily of Rho guanosine triphosphatases (GTPases) regulates actin-based cellular functions in bone such as differentiation, migration, and mechanotransduction. Polymorphisms or genetic ablation of RHOA and some of its regulatory guanine exchange factors (GEFs) have been linked to poor bone health in humans and mice, but the effects of RhoA-specific GTPase-activating proteins (GAPs) on bone quality have not yet been identified. Therefore, we examined the consequences of RhoGAP Myo9b gene knockout on bone growth, phenotype, and cellular activity. Male and female mice lacking both alleles demonstrated growth retardation and decreased bone formation rates during early puberty. These mice had smaller, weaker bones by 4 weeks of age, but only female KOs had altered cellular numbers, with fewer osteoblasts and more osteoclasts. By 12 weeks of age, bone quality in KOs worsened. In contrast, 4-week-old heterozygotes demonstrated bone defects that resolved by 12 weeks of age. Throughout, Myo9b ablation affected females more than males. Osteoclast activity appeared unaffected. In primary osteogenic cells, Myo9b was distributed in stress fibers and focal adhesions, and its absence resulted in poor spreading and eventual detachment from culture dishes. Similarly, MC3T3-E1 preosteoblasts with transiently suppressed Myo9b levels spread poorly and contained decreased numbers of focal adhesions. These cells also demonstrated reduced ability to undergo IGF-1-induced spreading or chemotaxis toward IGF-1, though responses to PDGF and BMP-2 were unaffected. IGF-1 receptor (IGF1R) activation was normal in cells with diminished Myo9b levels, but the activated receptor was redistributed from stress fibers and focal adhesions into nuclei, potentially affecting receptor accessibility and gene expression. These results demonstrate that Myo9b regulates a subset of RhoA-activated processes necessary for IGF-1 responsiveness in osteogenic cells, and is critical for normal bone formation in growing mice. © 2017 American Society for Bone and Mineral Research.

Insulin-like growth factor-1 signaling in cardiac aging

Cardiovascular disease (CVD) is the leading cause of death in most developed countries. Aging is associated with enhanced risk of CVD. Insulin-like growth factor-1 (IGF-1) binds to its cognate receptor, IGF-1 receptor (IGF-1R), and exerts pleiotropic effects on cell growth, differentiation, development, and tissue repair. Importantly, IGF-1/IGF-1R signaling is implicated in cardiac aging and longevity. Cardiac aging is an intrinsic process that results in cardiac dysfunction, accompanied by molecular and cellular changes. In this review, we summarize the current state of knowledge regarding the link between the IGF-1/IGF-1R system and cardiac aging. The biological effects of IGF-1R and insulin receptor will be discussed and compared. Furthermore, we describe data regarding how deletion of IGF-1R in cardiomyocytes of aged knockout mice may delay the development of senescence-associated myocardial pathologies. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Identification of BRCA1 As a Potential Biomarker for Insulin-Like Growth Factor-1 Receptor Targeted Therapy in Breast Cancer

The insulin-like growth factor-1 receptor (IGF1R) emerged in recent years as a promising therapeutic target in oncology. Identification of potential biomarkers capable of predicting response to IGF1R-targeted therapy is of cardinal importance. Tumor suppressor BRCA1 has important roles in multiple pathways, including gene transcription, DNA damage repair, and control of apoptosis. Early studies have identified the IGF1R gene as a downstream target for inhibitory regulation by wild-type, but not mutant, BRCA1. The aim of the present study was to evaluate the hypothesis that the mutational status of BRCA1 may influence the ability of IGF1R-directed therapies to efficiently inhibit the IGF1R axis. Using breast cancer-derived cell lines expressing a wild-type or a mutant BRCA1, we demonstrate that the capacity of MK-0646, a monoclonal antibody antagonist to the human IGF1R, to inhibit insulin-like growth factor-1-stimulated IGF1R and downstream mediators' phosphorylation was impaired in mutant BRCA1-expressing cell lines. In addition, the antibody was able to reduce proliferation of wild-type BRCA1-expressing cells but had a reduced inhibitory effect in mutant BRCA1-expressing cells. In summary, our data indicate that the mutational status of BRCA1 must be taken into account when selecting patients for IGF1R targeting protocols.

The Role of Insulin Receptor Isoforms in Diabetes and Its Metabolic and Vascular Complications

The insulin receptor (IR) presents by alternative splicing two isoforms: IRA and IRB. The differential physiological and pathological role of both isoforms is not completely known, and it is determinant the different binding affinity for insulin-like growth factor. IRB is more abundant in adult tissues and it exerts mainly the metabolic actions of insulin, whereas IRA is mainly expressed in fetal and prenatal period and exerts mitogenic actions. However, the change in the expression profile of both IR isoforms and its dysregulation are associated with the development of different pathologies, such as cancer, insulin resistance, diabetes, obesity, and atherosclerosis. In some of them, there is a significant increase of IRA/IRB ratio conferring a proliferative and migratory advantage to different cell types and favouring IGF-II actions with a sustained detriment in the metabolic effects of insulin. This review discussed specifically the role of IR isoforms as well as IGF-IR in diabetes and its associated complications as obesity and atherosclerosis. Future research with new IR modulators might be considered as possible targets to improve the treatment of diabetes and its associated complications.

Expression of two insulin receptor subtypes, insra and insrb, in zebrafish (Danio rerio) ovary and involvement of insulin action in ovarian function

Present study reports differential expression of the two insulin receptor (IR) subtypes in zebrafish ovary at various stages of follicular growth and potential involvement of IR in insulin-induced oocyte maturation. The results showed that mRNA expression for IR subtypes, insra and insrb, exhibited higher levels in mid-vitellogenic (MV) and full-grown (FG) rather than pre-vitellogenic (PV) oocytes. Interestingly, compared to the levels in denuded oocytes, mRNAs for both insra and insrb were expressed at much higher level in the follicle layer harvested from FG oocytes. Immunoprecipitation using IRβ antibody could detect a protein band of desired size (∼95kDa) in FG oocyte lysates. Further, IRβ immunoreactivity was detected in ovarian tissue sections, especially at the follicle layer and oocyte membrane of MV and FG, but not PV stage oocytes. While hCG (10IU/ml) stimulation was without effect, priming with insulin (5μM) could promote oocyte maturation of MV oocytes in a manner sensitive to de novo protein and steroid biosynthesis. Compared to hCG, in insulin pre-incubated MV oocytes, stimulation with maturation inducing steroid (MIS), 17α,20β-dihydroxy-4-pregnen-3-one (DHP) elicited higher maturational response. Potential involvement of insulin-mediated action on acquisition of maturational competence and regulation of oocyte maturation was further manifested through up regulation of 20β-hydroxysteroid dehydrogenase (20β-hsd), MIS receptor (mPRα), insulin-like growth factor 3 (igf3) and IGF1 receptor (igf1rb), but not cyp19a expression in MV oocytes. Moreover, priming with anti-IRβ attenuated insulin action on meiotic G2-M1 transition indicating the specificity of insulin action and physiological relevance of IR in zebrafish ovary.

Insulin-like growth factor-1 signaling in renal cell carcinoma

Renal cell carcinoma (RCC) incidence is highest in highly developed countries and it is the seventh most common neoplasm diagnosed. RCC management include nephrectomy and targeted therapies. Type 1 insulin-like growth factor (IGF-1) pathway plays an important role in cell proliferation and apoptosis resistance. IGF-1 and insulin share overlapping downstream signaling pathways in normal and cancer cells. IGF-1 receptor (IGF1R) stimulation may promote malignant transformation promoting cell proliferation, dedifferentiation and inhibiting apoptosis. Clear cell renal cell carcinoma (ccRCC) patients with IGF1R overexpression have 70 % increased risk of death compared to patients who had tumors without IGF1R expression. IGF1R signaling deregulation may results in p53, WT, BRCA1, VHL loss of function. RCC cells with high expression of IGF1R are more resistant to chemotherapy than cells with low expression. Silencing of IGF1R increase the chemosensitivity of ccRCC cells and the effect is greater in VHL mutated cells. Understanding the role of IGF-1 signaling pathway in RCC may result in development of new targeted therapeutic interventions. First preclinical attempts with anti-IGF-1R monoclonal antibodies or fragment antigen-binding (Fab) fragments alone or in combination with an mTOR inhibitor were shown to inhibit in vitro growth and reduced the number of colonies formed by of RCC cells.

Hydrophilic trans-Cyclooctenylated Noncanonical Amino Acids for Fast Intracellular Protein Labeling

Introduction of bioorthogonal functionalities (e.g., trans-cyclooctene-TCO) into a protein of interest by site-specific genetic encoding of non-canonical amino acids (ncAAs) creates uniquely targetable platforms for fluorescent labeling schemes in combination with tetrazine-functionalized dyes. However, fluorescent labeling of an intracellular protein is usually compromised by high background, arising from the hydrophobicity of ncAAs; this is typically compensated for by hours-long washout to remove excess ncAAs from the cellular interior. To overcome these problems, we designed, synthesized, and tested new, hydrophilic TCO-ncAAs. One derivative, DOTCO-lysine was genetically incorporated into proteins with good yield. The increased hydrophilicity shortened the excess ncAA washout time from hours to minutes, thus permitting rapid labeling and subsequent fluorescence microscopy.

Insulin/IGF and sex hormone axes in human endometrium and associations with endometrial cancer risk factors

PURPOSE

Experimental and observational data link insulin, insulin-like growth factor (IGF), and estrogens to endometrial tumorigenesis. However, there are limited data regarding insulin/IGF and sex hormone axes protein and gene expression in normal endometrial tissues, and very few studies have examined the impact of endometrial cancer risk factors on endometrial tissue biology.

METHODS

We evaluated endometrial tissues from 77 premenopausal and 30 postmenopausal women who underwent hysterectomy for benign indications and had provided epidemiological data. Endometrial tissue mRNA and protein levels were measured using quantitative real-time PCR and immunohistochemistry, respectively.

RESULTS

In postmenopausal women, we observed higher levels of phosphorylated IGF-I/insulin receptor (pIGF1R/pIR) in diabetic versus non-diabetic women (p value =0.02), while women who reported regular nonsteroidal anti-inflammatory drug use versus no use had higher levels of insulin and progesterone receptors (both p values ≤0.03). We also noted differences in pIGF1R/pIR staining with OC use (postmenopausal women only), and the proportion of estrogen receptor-positive tissues varied by the number of live births and PTEN status (premenopausal only) (p values ≤0.04). Compared to premenopausal proliferative phase women, postmenopausal women exhibited lower mRNA levels of IGF1, but higher IGFBP1 and IGFBP3 expression (all p values ≤0.004), and higher protein levels of the receptors for estrogen, insulin, and IGF-I (all p values ≤0.02). Conversely, pIGF1R/pIR levels were higher in premenopausal proliferative phase versus postmenopausal endometrium (p value =0.01).

CONCLUSIONS

These results highlight links between endometrial cancer risk factors and mechanistic factors that may contribute to early events in the multistage process of endometrial carcinogenesis.

Chapter Seven - When Phosphorylation Encounters Ubiquitination: A Balanced Perspective on IGF-1R Signaling

Cell-surface receptors govern the critical information passage from outside to inside the cell and hence control important cellular decisions such as survival, growth, and differentiation. These receptors, structurally grouped into different families, utilize common intracellular signaling-proteins and pathways, yet promote divergent biological consequences. In rapid processing of extracellular signals to biological outcomes, posttranslational modifications offer a repertoire of protein processing options. Protein ubiquitination was originally identified as a signal for protein degradation through the proteasome system. It is now becoming increasingly recognized that both ubiquitin and ubiquitin-like proteins, all evolved from a common ubiquitin structural superfold, are used extensively by the cell and encompass signal tags for many different cellular fates. In this chapter we examine the current understanding of the ubiquitin regulation surrounding the insulin-like growth factor and insulin signaling systems, major members of the larger family of receptor tyrosine kinases (RTKs) and key regulators of fundamental physiological and pathological states.

Combined treatment with platelet-rich plasma and insulin favours chondrogenic and osteogenic differentiation of human adipose-derived stem cells in three-dimensional collagen scaffolds

Osteochondral lesions due to injury or other pathology commonly result in the development of osteoarthritis and progressive joint destruction. Bioengineered scaffolds are widely studied for regenerative surgery strategies in osteochondral defect management, also combining the use of stem cells, growth factors and hormones. The utility in tissue engineering of human adipose-derived stem cells (ASCs) isolated from adipose tissue has been widely noted. Autologous platelet-rich plasma (PRP) represents an alternative strategy in regenerative medicine for the local release of endogenous growth factors and hormones. Here we compared the effects of three-dimensional (3D) collagen type I scaffold culture and combined treatment with PRP and human recombinant insulin on the chondro-/osteogenic differentiation of ASCs. Histochemical and biomolecular analyses demonstrated that chondro-/osteogenic differentiation was increased in ASC-populated 3D collagen scaffolds compared with two-dimensional (2D) plastic dish culture. Chondro-/osteogenic differentiation was further enhanced in the presence of combined PRP (5% v/v) and insulin (100 nm) treatment. In addition, chondro-/osteogenic differentiation associated with the contraction of ASC-populated 3D collagen scaffold and increased β1/β3-integrin expression. Inhibition studies demonstrated that PRP/insulin-induced chondro-/osteogenic differentiation is independent of insulin-like growth factor 1 receptor (IGF-1R) and mammalian target of rapamycin (mTOR) signalling; IGF-R1/mTOR inhibition even enhanced ASC chondro-/osteogenic differentiation. Our findings underline that 3D collagen scaffold culture in association with platelet-derived growth factors and insulin favour the chondro-/osteogenic differentiation of ASCs, suggesting new translational applications in regenerative medicine for the management of osteochondral defects. Copyright © 2016 John Wiley & Sons, Ltd.

Disrupted TSH Receptor Expression in Female Mouse Lung Fibroblasts Alters Subcellular IGF-1 Receptor Distribution

A relationship between the actions of TSH and IGF-1 was first recognized several decades ago. The close physical and functional associations between their respective receptors (TSHR and IGF-1R) has been described more recently in thyroid epithelium and human orbital fibroblasts as has the noncanonical behavior of IGF-1R. Here we report studies conducted in lung fibroblasts from female wild-type C57/B6 (TSHR(+/+)) mice and their littermates in which TSHR has been knocked out (TSHR(-/-)). Flow cytometric analysis revealed that cell surface IGF-1R levels are substantially lower in TSHR(-/-) fibroblasts compared with TSHR(+/+) fibroblasts. Confocal immunofluorescence microscopy revealed similar divergence with regard to both cytoplasmic and nuclear IGF-1R. Western blot analysis demonstrated both intact IGF-1R and receptor fragments in both cellular compartments. In contrast, IGF-1R mRNA levels were similar in fibroblasts from mice without and with intact TSHR expression. IGF-1 treatment of TSHR(+/+) fibroblasts resulted in reduced nuclear and cytoplasmic staining for IGF-1Rα, whereas it enhanced the nuclear signal in TSHR(-/-) cells. In contrast, IGF-1 enhanced cytoplasmic IGF-1Rβ in TSHR(-/-) fibroblasts while increasing the nuclear signal in TSHR(+/+) cells. These findings indicate the intimate relationship between TSHR and IGF-1R found earlier in human orbital fibroblasts also exists in mouse lung fibroblasts. Furthermore, the presence of TSHR in these fibroblasts influenced not only the levels of IGF-1R protein but also its subcellular distribution and response to IGF-1. They suggest that the mouse might serve as a suitable model for delineating the molecular mechanisms overarching these two receptors.

Insulin and IGF1 signalling pathways in human astrocytes in vitro and in vivo; characterisation, subcellular localisation and modulation of the receptors

Background

The insulin/IGF1 signalling (IIS) pathways are involved in longevity regulation and are dysregulated in neurons in Alzheimer’s disease (AD). We previously showed downregulation in IIS gene expression in astrocytes with AD-neuropathology progression, but IIS in astrocytes remains poorly understood. We therefore examined the IIS pathway in human astrocytes and developed models to reduce IIS at the level of the insulin or the IGF1 receptor (IGF1R).

Results

We determined IIS was present and functional in human astrocytes by immunoblotting and showed astrocytes express the insulin receptor (IR)-B isoform of Ir. Immunocytochemistry and cell fractionation followed by western blotting revealed the phosphorylation status of insulin receptor substrate (IRS1) affects its subcellular localisation. To validate IRS1 expression patterns observed in culture, expression of key pathway components was assessed on post-mortem AD and control tissue using immunohistochemistry. Insulin signalling was impaired in cultured astrocytes by treatment with insulin + fructose and resulted in decreased IR and Akt phosphorylation (pAkt S473). A monoclonal antibody against IGF1R (MAB391) induced degradation of IGF1R receptor with an associated decrease in downstream pAkt S473. Neither treatment affected cell growth or viability as measured by MTT and Cyquant® assays or GFAP immunoreactivity.

Discussion

IIS is functional in astrocytes. IR-B is expressed in astrocytes which differs from the pattern in neurons, and may be important in differential susceptibility of astrocytes and neurons to insulin resistance. The variable presence of IRS1 in the nucleus, dependent on phosphorylation pattern, suggests the function of signalling molecules is not confined to cytoplasmic cascades. Down-regulation of IR and IGF1R, achieved by insulin + fructose and monoclonal antibody treatments, results in decreased downstream signalling, though the lack of effect on viability suggests that astrocytes can compensate for changes in single pathways. Changes in signalling in astrocytes, as well as in neurons, may be important in ageing and neurodegeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-015-0138-6) contains supplementary material, which is available to authorized users.