Structure of the human insulin receptor gene and characterization of its promoter

Insulin receptor isoform B is required for efficient proinsulin processing in pancreatic β cells

The insulin receptor (INSR, IR) has two isoforms, IRA and IRB, through alternative splicing. However, their distinct functions in vivo remain unclear. Here we generated β cell-specific IRB knockout (KO) mice (βIRBKO). The KO mice displayed worsened hyperinsulinemia and hyperproinsulinemia in diet-induced obesity due to impaired proinsulin processing in β cells. Mechanistically, loss of IRB suppresses eukaryotic translation initiation factor 4G1 (eIF4G1) by stabilizing the transcriptional receptor sterol-regulatory element binding protein 1 (SREBP1). Moreover, excessive autocrine proinsulin in βIRBKO mice enhances the activity of extracellular signal-regulated kinase (ERK) through the remaining IRA to further stabilize nuclear SREBP1, forming a feedback loop. Collectively, our study paves the way to dissecting the isoform-specific function of IR in vivo and highlights the important roles of IRB in insulin processing and protecting β cells from lipotoxicity in obesity.

Insulin Receptor Isoforms and Insulin Growth Factor-like Receptors: Implications in Cell Signaling, Carcinogenesis, and Chemoresistance

This comprehensive review thoroughly explores the intricate involvement of insulin receptor (IR) isoforms and insulin-like growth factor receptors (IGFRs) in the context of the insulin and insulin-like growth factor (IGF) signaling (IIS) pathway. This elaborate system encompasses ligands, receptors, and binding proteins, giving rise to a wide array of functions, including aspects such as carcinogenesis and chemoresistance. Detailed genetic analysis of IR and IGFR structures highlights their distinct isoforms, which arise from alternative splicing and exhibit diverse affinities for ligands. Notably, the overexpression of the IR-A isoform is linked to cancer stemness, tumor development, and resistance to targeted therapies. Similarly, elevated IGFR expression accelerates tumor progression and fosters chemoresistance. The review underscores the intricate interplay between IRs and IGFRs, contributing to resistance against anti-IGFR drugs. Consequently, the dual targeting of both receptors could present a more effective strategy for surmounting chemoresistance. To conclude, this review brings to light the pivotal roles played by IRs and IGFRs in cellular signaling, carcinogenesis, and therapy resistance. By precisely modulating these receptors and their complex signaling pathways, the potential emerges for developing enhanced anti-cancer interventions, ultimately leading to improved patient outcomes.

Hot Spots for the Use of Intranasal Insulin: Cerebral Ischemia, Brain Injury, Diabetes Mellitus, Endocrine Disorders and Postoperative Delirium

A decrease in the activity of the insulin signaling system of the brain, due to both central insulin resistance and insulin deficiency, leads to neurodegeneration and impaired regulation of appetite, metabolism, endocrine functions. This is due to the neuroprotective properties of brain insulin and its leading role in maintaining glucose homeostasis in the brain, as well as in the regulation of the brain signaling network responsible for the functioning of the nervous, endocrine, and other systems. One of the approaches to restore the activity of the insulin system of the brain is the use of intranasally administered insulin (INI). Currently, INI is being considered as a promising drug to treat Alzheimer's disease and mild cognitive impairment. The clinical application of INI is being developed for the treatment of other neurodegenerative diseases and improve cognitive abilities in stress, overwork, and depression. At the same time, much attention has recently been paid to the prospects of using INI for the treatment of cerebral ischemia, traumatic brain injuries, and postoperative delirium (after anesthesia), as well as diabetes mellitus and its complications, including dysfunctions in the gonadal and thyroid axes. This review is devoted to the prospects and current trends in the use of INI for the treatment of these diseases, which, although differing in etiology and pathogenesis, are characterized by impaired insulin signaling in the brain.

Interaction of a viral insulin-like peptide with the IGF-1 receptor produces a natural antagonist

Lymphocystis disease virus-1 (LCDV-1) and several other Iridoviridae encode viral insulin/IGF-1 like peptides (VILPs) with high homology to human insulin and IGFs. Here we show that while single-chain (sc) and double-chain (dc) LCDV1-VILPs have very low affinity for the insulin receptor, scLCDV1-VILP has high affinity for IGF1R where it can antagonize human IGF-1 signaling, without altering insulin signaling. Consequently, scLCDV1-VILP inhibits IGF-1 induced cell proliferation and growth hormone/IGF-1 induced growth of mice in vivo. Cryo-electron microscopy reveals that scLCDV1-VILP engages IGF1R in a unique manner, inducing changes in IGF1R conformation that led to separation, rather than juxtaposition, of the transmembrane segments and hence inactivation of the receptor. Thus, scLCDV1-VILP is a natural peptide with specific antagonist properties on IGF1R signaling and may provide a new tool to guide development of hormonal analogues to treat cancers or metabolic disorders sensitive to IGF-1 without affecting glucose metabolism.

[The insulin receptor discovery is 50 years old - A review of achieved progress]

The isolation of insulin from the pancreas and its purification to a degree permitting its safe administration to type 1 diabetic patients were accomplished 100 years ago at the University of Toronto by Banting, Best, Collip and McLeod and constitute undeniably one of the major medical therapeutic revolutions, recognized by the attribution of the 1923 Nobel Prize in Physiology or Medicine to Banting and McLeod. The clinical spin off was immediate as well as the internationalization of insulin's commercial production. The outcomes regarding basic research were much slower, in particular regarding the molecular mechanisms of insulin action on its target cells. It took almost a half-century before the determination of the tri-dimensional structure of insulin in 1969 and the characterization of its cell receptor in 1970-1971. The demonstration that the insulin receptor is in fact an enzyme named tyrosine kinase came in the years 1982-1985, and the crystal structure of the intracellular kinase domain 10 years later. The crystal structure of the first intracellular kinase substrate (IRS-1) in 1991 paved the way for the elucidation of the intracellular signalling pathways but it took 15 more years to obtain the complete crystal structure of the extracellular receptor domain (without insulin) in 2006. Since then, the determination of the structure of the whole insulin-receptor complex in both the inactive and activated states has made considerable progress, not least due to recent improvement in the resolution power of cryo-electron microscopy. I will here review the steps in the development of the concept of hormone receptor, and of our knowledge of the structure and molecular mechanism of activation of the insulin receptor.

Influence of Insulin Receptor Single Nucleotide Polymorphisms on Glycaemic Control and Formation of Anti-Insulin Antibodies in Diabetes Mellitus

Single nucleotide polymorphisms (SNPs) in insulin and insulin receptor genes may influence the interaction between the two molecules, as may anti-insulin antibodies (IAs), commonly found in patients with type 1 diabetes mellitus (T1D) or type 2 diabetes mellitus (T2D) treated with exogenous insulin. We examined the impact of two SNPs in the human insulin gene (INS), rs3842752 and rs689, and two in the insulin receptor gene (INSR) rs2245649 and rs2229429, on disease susceptibility, glycaemic control, and IAs formation in 100 T1D patients and 101 T2D patients treated with insulin. 79 individuals without diabetes were typed as healthy controls. The minor alleles of rs3842752 and rs689 in INS protected against T1D (OR: 0.50, p = 0.01 and OR: 0.44; p = 0.002, respectively). The minor alleles of both rs2245649 and rs2229429 in INSR were risk factors for poor glycaemic control (HbA1c ≥ 80 mmol/mol) in T1D (OR: 5.35, p = 0.009 and OR: 3.10, p = 0.01, respectively). Surprisingly, the minor alleles of rs2245649 and rs2229429 in INSR associated strongly with the absence of IAs in T1D (OR = 0.28, p = 0.008 and OR = 0.30, p = 0.002, respectively). In conclusion, the minor alleles of the investigated INS SNPs protect against T1D, and the minor alleles of the investigated INSR SNPs are associated with poor glycaemic control and the absence of IAs in T1D.

Free fatty acid receptor 1: a ray of hope in the therapy of type 2 diabetes mellitus

Free fatty acid receptor 1 (FFAR1) is a G-protein coupled receptor with prominent expression on pancreatic beta cells, bones, intestinal cells as well as the nerve cells. This receptor mediates a multitude of functions in the body including release of incretins, secretion of insulin as well as sensation of pain. Since FFAR1 causes secretion of insulin and regulates glucose metabolism, efforts were made to unfold its structure followed by discovering agonists for the receptor and the utilization of these agonists in the therapy of type 2 diabetes mellitus. Development of such functional FFAR1 agonists is a necessity because the currently available therapy for type 2 diabetes mellitus has numerous drawbacks, of which, the major one is hypoglycemia. Since the most prominent effect of the FFAR1 agonists is on glucose concentration in the body, so the major research is focused on treating type 2 diabetes mellitus, though the agonists could benefit other metabolic disorders and neurological disorders as well. The agonists developed so far had one major limitation, i.e., hepatotoxicity. Although, the only agonist that could reach phase 3 clinical trials was TAK-875 developed by Takeda Pharmaceuticals but it was also withdrawn due to toxic effects on the liver. Thus, there are numerous agonists for the varied binding sites of the receptor but no drug available yet. There does seem to be a ray of hope in the drugs that target FFAR1 but a lot more efforts towards drug discovery would result in the successful management of type 2 diabetes mellitus.

Insulin Resistance and Cancer: In Search for a Causal Link

Insulin resistance (IR) is a condition which refers to individuals whose cells and tissues become insensitive to the peptide hormone, insulin. Over the recent years, a wealth of data has made it clear that a synergistic relationship exists between IR, type 2 diabetes mellitus, and cancer. Although the underlying mechanism(s) for this association remain unclear, it is well established that hyperinsulinemia, a hallmark of IR, may play a role in tumorigenesis. On the other hand, IR is strongly associated with visceral adiposity dysfunction and systemic inflammation, two conditions which favor the establishment of a pro-tumorigenic environment. Similarly, epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNA, in IR states, have been often associated with tumorigenesis in numerous types of human cancer. In addition to these observations, it is also broadly accepted that gut microbiota may play an intriguing role in the development of IR-related diseases, including type 2 diabetes and cancer, whereas potential chemopreventive properties have been attributed to some of the most commonly used antidiabetic medications. Herein we provide a concise overview of the most recent literature in this field and discuss how different but interrelated molecular pathways may impact on tumor development.

Insulin Receptor Isoforms Differently Regulate Cell Proliferation and Apoptosis in the Ligand-Occupied and Unoccupied State

The insulin receptor (IR) presents two isoforms (IR-A and IR-B) that differ for the α-subunit C-terminal. Both isoforms are expressed in all human cells albeit in different proportions, yet their functional properties-when bound or unbound to insulin-are not well characterized. From a cell model deprived of the Insulin-like Growth Factor 1 Receptor (IGF1-R) we therefore generated cells exhibiting no IR (R-shIR cells), or only human IR-A (R-shIR-A), or exclusively human IR-B (R-shIR-B) and we studied the specific effect of the two isoforms on cell proliferation and cell apoptosis. In the absence of insulin both IR-A and IR-B similarly inhibited proliferation but IR-B was 2–3 fold more effective than IR-A in reducing resistance to etoposide-induced DNA damage. In the presence of insulin, IR-A and IR-B promoted proliferation with the former significantly more effective than the latter at increasing insulin concentrations. Moreover, only insulin-bound IR-A, but not IR-B, protected cells from etoposide-induced cytotoxicity. In conclusion, IR isoforms have different effects on cell proliferation and survival. When unoccupied, IR-A, which is predominantly expressed in undifferentiated and neoplastic cells, is less effective than IR-B in protecting cells from DNA damage. In the presence of insulin, particularly when present at high levels, IR-A provides a selective growth advantage.

Rbfox2 mediates exon 11 inclusion in insulin receptor pre-mRNA splicing in hepatoma cells

Insulin receptor (IR) pre-mRNA undergoes alternative splicing that produces two isoforms, IR-A and IR-B. The ratio of IR-A to IR-B varies among tissues, which strongly suggests that IR mRNA alternative splicing is regulated in a tissue-specific manner. However, the precise molecular mechanism for IR alternative splicing remains to be elucidated, especially in liver. In this study, we have analyzed IR alternative splicing mechanism by preparing a mini-gene splicing reporter with rat genomic DNA. The splicing reporter that contains exon 11 and its flanking intronic sequences could reproduce alternative splicing pattern in rat hepatoma H4IIE cells. Introducing several deletions in introns of the reporter revealed that intron 11 contains the region near exon 11 essential to promote exon 11 inclusion. This region contains an UGCAUG sequence, a specific binding site for the Rbfox splicing regulator, and mutation in this sequence results in exon 11 skipping. Furthermore, RbFox2 knockdown in H4IIE cells enhanced exon 11 skipping of endogenous IR pre-mRNA. Lastly mutations in the SRSF3 binding site of exon11 together with the Rbfox2 binding site completely abolished exon 11 inclusion with a mini-gene reporter pre-mRNA. Our results indicate that RbFox2 and SRSF3 proteins mediate exon 11 inclusion in rat hepatoma cells.

Defining the underlying defect in insulin action in type 2 diabetes

Insulin resistance is one of the earliest defects in the pathogenesis of type 2 diabetes. Over the past 50 years, elucidation of the insulin signalling network has provided important mechanistic insights into the abnormalities of glucose, lipid and protein metabolism that underlie insulin resistance. In classical target tissues (liver, muscle and adipose tissue), insulin binding to its receptor initiates a broad signalling cascade mediated by changes in phosphorylation, gene expression and vesicular trafficking that result in increased nutrient utilisation and storage, and suppression of catabolic processes. Insulin receptors are also expressed in non-classical targets, such as the brain and endothelial cells, where it helps regulate appetite, energy expenditure, reproductive hormones, mood/behaviour and vascular function. Recent progress in cell biology and unbiased molecular profiling by mass spectrometry and DNA/RNA-sequencing has provided a unique opportunity to dissect the determinants of insulin resistance in type 2 diabetes and the metabolic syndrome; best studied are extrinsic factors, such as circulating lipids, amino acids and other metabolites and exosomal microRNAs. More challenging has been defining the cell-intrinsic factors programmed by genetics and epigenetics that underlie insulin resistance. In this regard, studies using human induced pluripotent stem cells and tissues point to cell-autonomous alterations in signalling super-networks, involving changes in phosphorylation and gene expression both inside and outside the canonical insulin signalling pathway. Understanding how these multi-layered molecular networks modulate insulin action and metabolism in different tissues will open new avenues for therapy and prevention of type 2 diabetes and its associated pathologies.

Heterozygous Insulin Receptor (INSR) Mutation Associated with Neonatal Hyperinsulinemic Hypoglycaemia and Familial Diabetes Mellitus: Case Series

Mutations in the insulin receptor (INSR) gene are associated with insulin resistance and hyperglycaemia. Various autosomal dominant heterozygous INSR mutations leading to hyperinsulinemic hypoglycaemia (HH) have been described in adults and children (more than 3 years of age) but not in the neonatal period. Family 1: A small for gestational age (SGA) child born to a mother with gestational diabetes presented with persistent hypoglycaemia, was diagnosed with HH and responded well to diazoxide treatment. Diazoxide was gradually weaned and discontinued by 8 months of age. Later, the younger sibling had a similar course of illness. On genetic analysis a heterozygous INSR missense variant p.(Met1180Lys) was found in the siblings, mother and grandfather but not in the father. Family 2: A twin preterm and SGA baby presented with persistent hypoglycaemia, which was confirmed as HH. He responded to diazoxide, which was subsequently discontinued by 10 weeks of life. Genetic analysis revealed a novel heterozygous INSR missense variant p.(Arg1119Gln) in the affected twin and the mother. Family 3: An SGA child presented with diazoxide responsive HH. Diazoxide was gradually weaned and discontinued by 9 weeks of age. Genetic analysis revealed a novel heterozygous INSR p.(Arg1191Gln) variant in the proband and her father. We report, for the first time, an association of INSR mutation with neonatal HH responsive to diazoxide therapy that resolved subsequently. Our case series emphasizes the need for genetic analysis and long-term follow up of these patients.

Insulin Therapy in Pregnancy Hypertensive Diseases and its Effect on the Offspring and Mother Later in Life

Pregnancy hypertensive disorders such as Preeclampsia (PE) are strongly correlated with insulin resistance, a condition in which the metabolic handling of D-glucose is deficient. In addition, the impact of preeclampsia is enhanced by other insulin-resistant disorders, including polycystic ovary syndrome and obesity. For this reason, there is a clear association between maternal insulin resistance, polycystic ovary syndrome, obesity and the development of PE. However, whether PE is a consequence or the cause of these disorders is still unclear. Insulin therapy is usually recommended to pregnant women with diabetes mellitus when dietary and lifestyle measures have failed. The advantage of insulin therapy for Gestational Diabetes Mellitus (GDM) patients with hypertension is still controversial; surprisingly, there are no studies in which insulin therapy has been used in patients with hypertension in pregnancy without or with an established GDM. This review is focused on the use of insulin therapy in hypertensive disorders in the pregnancy and its effect on offspring and mother later in life. PubMed and relevant medical databases have been screened for literature covering research in the field especially in the last 5-10 years.

Insulin: The Friend and the Foe in the Development of Type 2 Diabetes Mellitus

Insulin, a hormone produced by pancreatic β-cells, has a primary function of maintaining glucose homeostasis. Deficiencies in β-cell insulin secretion result in the development of type 1 and type 2 diabetes, metabolic disorders characterized by high levels of blood glucose. Type 2 diabetes mellitus (T2DM) is characterized by the presence of peripheral insulin resistance in tissues such as skeletal muscle, adipose tissue and liver and develops when β-cells fail to compensate for the peripheral insulin resistance. Insulin resistance triggers a rise in insulin demand and leads to β-cell compensation by increasing both β-cell mass and insulin secretion and leads to the development of hyperinsulinemia. In a vicious cycle, hyperinsulinemia exacerbates the metabolic dysregulations that lead to β-cell failure and the development of T2DM. Insulin and IGF-1 signaling pathways play critical roles in maintaining the differentiated phenotype of β-cells. The autocrine actions of secreted insulin on β-cells is still controversial; work by us and others has shown positive and negative actions by insulin on β-cells. We discuss findings that support the concept of an autocrine action of secreted insulin on β-cells. The hypothesis of whether, during the development of T2DM, secreted insulin initially acts as a friend and contributes to β-cell compensation and then, at a later stage, becomes a foe and contributes to β-cell decompensation will be discussed.

circINSR Promotes Proliferation and Reduces Apoptosis of Embryonic Myoblasts by Sponging miR-34a

As a diverse and abundant class of endogenous RNAs, circular RNAs (circRNAs) participate in processes including cell proliferation and apoptosis. Nevertheless, few researchers have investigated the function of circRNAs in bovine muscle development. Based on existing sequencing data, we identified circINSR. The localization of circINSR in bovine myoblasts was investigated by fluorescence in situ hybridization. Molecular and biochemical assays were used to confirm the role of circINSR in myoblast proliferation and the cell cycle. Mitochondrial membrane potential and annexin V-PE/7-AAD staining assays were performed to assess cell apoptosis. Additionally, interactions between circINSR, miR-34a, and target mRNAs were examined using bioinformatics, a luciferase assay, and RNA immunoprecipitation. We found that circINSR was highly expressed in embryonic muscle tissue. Overexpression of circINSR significantly promoted proliferation and reduced apoptosis of embryonic myoblasts. Our data suggested that circINSR may act as a sponge of miR-34a and could function through de-repression of target genes in muscle cells. This study proposes that circINSR may function as a regulator of embryonic muscle development. circINSR regulates cells proliferation and apoptosis through miR-34a-modulated Bcl-2 and CyclinE2 expression.

Transcriptional Regulation of INSR, the Insulin Receptor Gene

The insulin receptor gene encodes an evolutionarily conserved signaling protein with a wide spectrum of functions in metazoan development. The insulin signaling pathway plays key roles in processes such as metabolic regulation, growth control, and neuronal function. Misregulation of the pathway features in diabetes, cancer, and neurodegenerative diseases, making it an important target for clinical interventions. While much attention has been focused on differential pathway activation through ligand availability, sensitization of overall signaling may also be mediated by differential expression of the insulin receptor itself. Although first characterized as a “housekeeping” gene with stable expression, comparative studies have shown that expression levels of the human INSR mRNA differ by tissue and in response to environmental signals. Our recent analysis of the transcriptional controls affecting expression of the Drosophila insulin receptor gene indicates that a remarkable amount of DNA is dedicated to encoding sophisticated feedback and feed forward signals. The human INSR gene is likely to contain a similar level of transcriptional complexity; here, we summarize over three decades of molecular biology and genetic research that points to a still incompletely understood regulatory control system. Further elucidation of transcriptional controls of INSR will provide the basis for understanding human genetic variation that underlies population-level physiological differences and disease.

Insulin receptors in the kidneys in health and disease

Insulin is an important hormone that affects various metabolic processes, including kidney function. Impairment in insulin’s action leads to insulin resistance in the target tissue. Besides defects in post-receptor insulin signaling, impairment at the receptor level could significantly affect insulin sensitivity of the target tissue. The kidney is a known target of insulin; however, whether the kidney develops “insulin resistance” is debatable. Regulation of the insulin receptor (IR) expression and its function is very well studied in major metabolic tissues like liver, skeletal muscles, and adipose tissue. The physiological relevance of IRs in the kidney has recently begun to be clarified. The credit goes to studies that showed a wide distribution of IR throughout the nephron segments and their reduced expression in the insulin resistance state. Moreover, altered renal and systemic metabolism observed in mice with targeted deletion of the IR from various epithelial cells of the kidney has strengthened this proposition. In this review, we recapitulate the crucial findings from literature that have expanded our knowledge regarding the significance of the renal IR in normal- and insulin-resistance states.

Role of insulin, adenosine, and adipokine receptors in the foetoplacental vascular dysfunction in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is a disease of pregnancy associated with maternal and foetal hyperglycaemia and altered foetoplacental vascular function. Human foetoplacental microvascular and macrovascular endothelium from GDM pregnancy show increased maximal l-arginine transport capacity via the human cationic amino acid transporter 1 (hCAT-1) isoform and nitric oxide (NO) synthesis by the endothelial NO synthase (eNOS). These alterations are paralleled by lower maximal transport activity of the endogenous nucleoside adenosine via the human equilibrative nucleoside transporter 1 (hENT1) and activation of adenosine receptors. A causal relationship has been described for adenosine-activation of A_2A adenosine receptors, hCAT-1, and eNOS activity (i.e. the Adenosine/l-Arginine/Nitric Oxide, ALANO, signalling pathway). Insulin restores these alterations in GDM via activation of insulin receptor A (IR-A) form in the macrovascular but IR-A and IR-B forms in the microcirculation of the human placenta. Adipokines are secreted from adipocytes influencing the foetoplacental metabolic and vascular function. Various adipokines are dysregulated in GDM, with adiponectin and leptin playing major roles. Abnormal plasma concentration of these adipokines and the activation or their receptors are involved in the pathophysiology of GDM. However, involvement of adipokines, adenosine, and insulin receptors and membrane transporters in the aetiology of this disease of pregnancy is unknown. This review focuses on the pathophysiology of insulin and adenosine receptors and l-arginine and adenosine membranes transporters giving an overview of the key adipokines leptin and adiponectin in the foetoplacental vasculature in GDM. This article is part of a Special Issue entitled: Membrane Transporters and Receptors in Pregnancy Metabolic Complications edited by Luis Sobrevia.

DDR1 regulates thyroid cancer cell differentiation via IGF-2/IR-A autocrine signaling loop

Patients with thyroid cancers refractory to radioiodine (RAI) treatment show a limited response to various therapeutic options and a low survival rate. The recent use of multikinase inhibitors has also met limited success. An alternative approach relies on drugs that induce cell differentiation, as the ensuing increased expression of the cotransporter for sodium and iodine (NIS) may partially restore sensitivity to radioiodine. The inhibition of the ERK1/2 pathway has shown some efficacy in this context. Aggressive thyroid tumors overexpress the isoform-A of the insulin receptor (IR-A) and its ligand IGF-2; this IGF-2/IR-A loop is associated with de-differentiation and stem-like phenotype, resembling RAI-refractory tumors. Importantly, IR-A has been shown to be positively modulated by the non-integrin collagen receptor DDR1 in human breast cancer. Using undifferentiated human thyroid cancer cells, we now evaluated the effects of DDR1 on IGF-2/IR-A loop and on markers of cell differentiation and stemness. DDR1 silencing or downregulation caused significant reduction of IR-A and IGF-2 expression, and concomitant increased levels of differentiation markers (NIS, Tg, TSH, TPO). Conversely, markers of epithelial-to-mesenchymal transition (Vimentin, Snail-2, Zeb1, Zeb2 and N-Cadherin) and stemness (OCT-4, SOX-2, ABCG2 and Nanog) decreased. These effects were collagen independent. In contrast, overexpression of either DDR1 or its kinase-inactive variant K618A DDR1-induced changes suggestive of less differentiated and stem-like phenotype. Collagen stimulation was uneffective. In conclusion, in poorly differentiated thyroid cancer, DDR1 silencing or downregulation blocks the IGF-2/IR-A autocrine loop and induces cellular differentiation. These results may open novel therapeutic approaches for thyroid cancer.

Vanadate inhibits transcription of the rat insulin receptor gene via a proximal sequence of the 5'flanking region

Vanadate, a protein tyrosine phosphatase inhibitor which elicits insulin-like effects, has previously been shown to inhibit expression of the insulin receptor gene at the transcriptional level in rat hepatoma cells. In an attempt to identify the DNA sequence and transcription factors potentially involved in this effect, a fragment of the proximal 5'flanking region of the IR gene (-1143/-252 upstream the ATG codon) has been cloned and functionally characterized. RNase protection allowed the identification of several transcription start sites in the conserved region of the gene, among which two major sites at -455 and -396. Upon fusion to the luciferase gene and transient transfection into hepatoma cells, the -1143/-252 fragment showed promoter activity. This was unaffected by deletion of the -1143/-761 sequence, but markedly decreased (90%) by additional deletion of the -760/-465 sequence. Treatment of hepatoma cells with vanadate led to a dose-dependent decrease in promoter activity of the 1143/-252, -760/-252 and -464/-252 constructs (change relative to untreated cells, 40, 55 and 23% at 125 μM, and 70, 85 and 62% at 250 μM, respectively). These data suggest that although the entire DNA sequence upstream the transcription start sites is probably involved in vanadate-induced inhibition, the short sequence downstream of position -464 and is sufficient for inhibition. Potential targets of vanadate are the transcription factors FoxO1 and HMGA1, two downstream targets of the insulin signaling pathway which have been shown to mediate the inhibitory effect of insulin on IR gene expression.

Structure of the insulin receptor-insulin complex by single-particle cryo-EM analysis

The insulin receptor (IR) is a dimeric protein that plays a crucial role in controlling glucose homeostasis, regulating lipid, protein and carbohydrate metabolism, and modulating brain neurotransmitter levels^1,2. IR dysfunctions have been associated with many diseases, including diabetes, cancer, and Alzheimer’s^1,3,4. The primary sequence has been known since the 1980s⁵, and is composed of an extracellular portion (ectodomain, ECD), a single transmembrane helix and an intracellular tyrosine kinase domain. Insulin binding to the dimeric ECD triggers kinase domain auto-phosphorylation and subsequent activation of downstream signaling molecules. Biochemical and mutagenesis data have identified two putative insulin binding sites (S1 and S2)⁶. While insulin bound to an ECD fragment containing S1 and the apo ectodomain have been characterized structurally^7,8, details of insulin binding to the full receptor and the signal propagation mechanism are still not understood. Here we report single particle cryoEM reconstructions for the 1:2 (4.3 Å) and 1:1 (7.4 Å) IR ECD dimer:Insulin complexes. The symmetric 4.3 Å structure shows two insulin molecules per dimer, each bound between the Leucine-rich sub domain L1 of one monomer and the first fibronectin-like domain (FnIII-1) of the other monomer, and making extensive interactions with the α subunit C-terminal helix (α-CT helix). The 7.4 Å structure has only one similarly bound insulin per receptor dimer. The structures confirm the S1 binding interactions and define the full S2 binding site. These insulin receptor states suggest that recruitment of the α-CT helix upon binding of the first insulin changes the relative sub domain orientations and triggers downstream signal propagation.

Activation of MAPK signalling results in resistance to saracatinib (AZD0530) in ovarian cancer

SRC tyrosine kinase is frequently overexpressed and activated in late-stage, poor prognosis ovarian tumours, and preclinical studies have supported the use of targeted SRC inhibitors in the treatment of this disease. The SAPPROC trial investigated the addition of the SRC inhibitor saracatinib (AZD0530) to weekly paclitaxel for the treatment of platinum resistant ovarian cancer; however, this drug combination did not provide any benefit to progression free survival (PFS) of women with platinum resistant disease. In this study we aimed to identify mechanisms of resistance to SRC inhibitors in ovarian cancer cells. Using two complementary strategies; a targeted tumour suppressor gene siRNA screen, and a phospho-receptor tyrosine kinase array, we demonstrate that activation of MAPK signalling, via a reduction in NF1 (neurofibromin) expression or overexpression of HER2 and the insulin receptor, can drive resistance to AZD0530. Knockdown of NF1 in two ovarian cancer cell lines resulted in resistance to AZD0530, and was accompanied with activated MEK and ERK signalling. We also show that silencing of HER2 and the insulin receptor can partially resensitize AZD0530 resistant cells, which was associated with decreased phosphorylation of MEK and ERK. Furthermore, we demonstrate a synergistic effect of combining SRC and MEK inhibitors in both AZD0530 sensitive and resistant cells, and that MEK inhibition is sufficient to completely resensitize AZD0530 resistant cells. This work provides a preclinical rationale for the combination of SRC and MEK inhibitors in the treatment of ovarian cancer, and also highlights the need for biomarker driven patient selection for clinical trials.

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.

Structure and dynamics of the insulin receptor: implications for receptor activation and drug discovery

Recently, major progress has been made in uncovering the mechanisms of how insulin engages its receptor and modulates downstream signal transduction. Here, we present in detail the current structural knowledge surrounding the individual components of the complex, binding sites, and dynamics during the activation process. A novel kinase triggering mechanism, the 'bow-arrow model', is proposed based on current knowledge and computational simulations of this system, in which insulin, after its initial interaction with binding site 1, engages with site 2 between the fibronectin type III (FnIII)-1 and -2 domains, which changes the conformation of FnIII-3 and eventually translates into structural changes across the membrane. This model provides a new perspective on the process of insulin binding to its receptor and, thus, could lead to future novel drug discovery efforts.

INSR gene polymorphisms correlate with sensitivity to platinum-based chemotherapy and prognosis in patients with epithelial ovarian cancer

This study aimed to investigate the correlation between INSR gene polymorphisms on platinum-based chemotherapy sensitivity and prognosis in epithelial ovarian cancer (EOC). A total of 339 EOC patients receiving postoperative chemotherapy were recruited for the study. Tag single-nucleotide polymorphism of INSR gene was screened from HapMap combined with available literature. Frequency distribution of genotypes and alleles in INSR gene was sequenced by ABI3100-Avant. Compared with CC+GC genotype, INSR rs2252673 GG genotype and rs3745546 CC genotype showed less platinum-based chemotherapy sensitivity in EOC patients (odds ratio (OR)=0.269, 95% confidence interval (CI)=0.159~0.456; OR=0.445, 95% CI=0.214~0.926, respectively), as well as serous EOC patients (OR=0.083, 95% CI=0.024~0.278; OR=0.235, 95%CI=0.053~1.041, respectively). The clinical characteristics including age, clinical stage, histological grade and residual lesion size were significantly related with chemosensitivity to platinum drugs and mortality in EOC patients. According to Kaplan-Meier curve, compared with CC+GC genotype, rs2252673 GG genotype showed significantly decreased survival rate in EOC patients (P<0.05). Cox regression model indicated that rs2252673, age and clinical stage were independent risk factors for the prognosis in EOC (all P<0.05). These findings indicate that INSR rs2252673 and rs3745546 polymorphisms were associated with sensitivity to platinum-based chemotherapy in EOC patients and rs2252673 polymorphism may be an independent risk factor for EOC prognosis.

Association of Obesity-Related Metabolic Disruptions With Cancer Risk and Outcome

Over the past 40 years, the prevalence of obesity has increased epidemically worldwide, which raises significant concerns regarding public health and the associated economic burden. Obesity is a major risk factor for several conditions including cardiovascular disease and type 2 diabetes, and recent evidence suggests that obesity negatively affects cancer risk and outcome. The relationship between obesity and cancer is complex and involves multiple factors both at the systemic and cellular level. Indeed, disruptions in insulin metabolism, adipokines, inflammation, and sex hormones all contribute to the adverse effects of obesity in cancer development and progression. The focus of this review will be the impact of these systemic obesity-related factors on cancer biology, incidence, and outcome. Potential therapeutic interventions and current clinical trials targeting obesity and its associated factors will also be discussed.

Probing Receptor Specificity by Sampling the Conformational Space of the Insulin-like Growth Factor II C-domain

Insulin and insulin-like growth factors I and II are closely related protein hormones. Their distinct evolution has resulted in different yet overlapping biological functions with insulin becoming a key regulator of metabolism, whereas insulin-like growth factors (IGF)-I/II are major growth factors. Insulin and IGFs cross-bind with different affinities to closely related insulin receptor isoforms A and B (IR-A and IR-B) and insulin-like growth factor type I receptor (IGF-1R). Identification of structural determinants in IGFs and insulin that trigger their specific signaling pathways is of increasing importance in designing receptor-specific analogs with potential therapeutic applications. Here, we developed a straightforward protocol for production of recombinant IGF-II and prepared six IGF-II analogs with IGF-I-like mutations. All modified molecules exhibit significantly reduced affinity toward IR-A, particularly the analogs with a Pro-Gln insertion in the C-domain. Moreover, one of the analogs has enhanced binding affinity for IGF-1R due to a synergistic effect of the Pro-Gln insertion and S29N point mutation. Consequently, this analog has almost a 10-fold higher IGF-1R/IR-A binding specificity in comparison with native IGF-II. The established IGF-II purification protocol allowed for cost-effective isotope labeling required for a detailed NMR structural characterization of IGF-II analogs that revealed a link between the altered binding behavior of selected analogs and conformational rearrangement of their C-domains.

Identification of Host Insulin Binding Sites on Schistosoma japonicum Insulin Receptors

Schistosoma japonicum insulin receptors (SjIRs) have been identified as encouraging vaccine candidates. Interrupting or blocking the binding between host insulin and the schistosome insulin receptors (IRs) may result in reduced glucose uptake leading to starvation and stunting of worms with a reduction in egg output. To further understand how schistosomes are able to exploit host insulin for development and growth, and whether these parasites and their mammalian hosts compete for the same insulin source, we identified insulin binding sites on the SjIRs. Based on sequence analysis and the predicted antigenic structure of the primary sequences of the SjIRs, we designed nine and eleven peptide analogues from SjIR-1 and SjIR-2, respectively. Using the Octet RED system, we identified analogues derived from SjIR-1 (10) and SjIR-2 (20, 21 and 22) with insulin-binding sequences specific for S. japonicum. Nevertheless, the human insulin receptor (HIR) may compete with the SjIRs in binding human insulin in other positions which are important for HIR binding to insulin. However, no binding occurred between insulin and parasite analogues derived from SjIR-1 (2, 7 and 8) and SjIR-2 (14, 16 and 18) at the same locations as HIR sequences which have been shown to have strong insulin binding affinities. Importantly, we found two analogues (1 and 3), derived from SjIR-1, and two analogues (13 and 15) derived from SjIR-2, were responsible for the major insulin binding affinity in S. japonicum. These peptide analogues were shown to have more than 10 times (in KD value) stronger binding capacity for human insulin compared with peptides derived from the HIR in the same sequence positions. Paradoxically, analogues 1, 3, 13 and 15 do not appear to contain major antigenic determinants which resulted in poor antibody responses to native S. japonicum protein. This argues against their future development as peptide-vaccine candidates.

Insulin receptor isoforms: an integrated view focused on gestational diabetes mellitus

The human insulin receptor (IR) exists in two isoforms that differ by the absence (IR-A) or the presence (IR-B) of a 12-amino acid segment encoded by exon 11. Both isoforms are functionally distinct regarding their binding affinities and intracellular signalling. However, the underlying mechanisms related to their cellular functions in several tissues are only partially understood. In this review, we summarize the current knowledge in this field regarding the alternative splicing of IR isoform, tissue-specific distribution and signalling both in physiology and disease, with an emphasis on the human placenta in gestational diabetes mellitus (GDM). Furthermore, we discuss the clinical relevance of IR isoforms highlighted by findings that show altered insulin signalling due to differential IR-A and IR-B expression in human placental endothelium in GDM pregnancies. Future research and clinical studies focused on the role of IR isoform signalling might provide novel therapeutic targets for treating GDM to improve the adverse maternal and neonatal outcomes.

Classic Case Report of Donohue Syndrome (Leprechaunism; OMIM *246200): The Impact of Consanguineous Mating

Donohue syndrome ([DS]; leprechaunism) describes a genetic autosomal recessive disorder that results from the presence of homozygous or compound heterozygous mutations in the insulin receptor gene (INSR; 19p13.3-p13.2).Donohue syndrome is associated with a fatal congenital form of dwarfism with features of intrauterine and postnatal growth retardation, exaggerated hyperglycemia with hyperinsulinism and dysmorphic abnormalities.We present a case of DS owing to the rarity of this syndrome (1 case in every million births). We discuss how the disease presents, its genetic underpinning, and its prevention.The case was encountered in an Arab male born on 1 September, 2014, for consanguineous parents. The delivery was via cesarean section at 37 weeks gestation due to severe intrauterine growth restriction and nonprogress labor term. The patient was admitted to the Neonatal Intensive Care Unit due to infection, and jaundice. Dysmorphic features, abnormalities of the craniofacial region, low birth weight, skin abnormalities, abdominal distension and hypertrichosis were observed. Laboratory examinations showed, hyperinsulinism, increased C-peptide, thrombocytopenia, leucopenia, and anemia.The diagnosis of DS was done based on the combinations of typical dysmorphic characteristics, clinical evaluation, supported by genetic analysis and exaggerated biochemical results. Genetic diagnosis of DS was performed through analysis of DNA via polymerase chain reaction (PCR). A qualitative real-time PCR was used, to monitor the amplification of a targeted DNA molecule during the PCR. Other technique using sequencing of the INSR gene, which permits genetic diagnosis, counseling, and antenatal diagnoses in subsequent pregnancies, were also performed.Treatment of DS is supportive and requires the combined efforts of a multidisciplinary team, which include pediatricians, endocrinologists, dermatologists, and other health care professionals. Currently, treatment with recombinant insulin-like growth factor 1 demonstrates effectiveness, and a combination treatment with insulin-like growth factor binding protein 3 resulted in an increased lifespan.There is a scarcity of genetic information on DS among the Arab population. Consanguinity is one of underlying reasons for the appearance of rare genetic disorders. Inbreeding has long been considered a controversial phenomenon. Genetic counseling and overwhelming the alertness of the negative consequences of consanguinity on public health are warranted.

Genomic organization and expression of insulin receptors in grass carp, Ctenopharyngodon idellus

Insulin receptors have been demonstrated to be involved in embryogenesis, food intake regulation and glucose metabolism in several fish, while more researchis needed for further understanding. In this study, the complete coding sequence (CDS) of insulin receptor a (insra) gene and insulin receptor b (insrb) gene in grass carp were obtained, the CDS were 4068 bp and 4514 bp in length, encoding 1355 aa protein and 1351 aa protein. Both of insra and insrb in grass carp showed high amino acid identities with other fish. Insra and insrb genes were widely expressed in all tested tissues with an overlapping but distinct expressions. The high levels of insra mRNA were distributed in hindgut and heart tissues. The insrb gene showed the highest expression levels in liver and hindgut. We also proved that two forms of grass carp insulin receptors participate in the regulation of blood glucose and might act differently. Phylogenetic analysis confirmed that different isoforms of fish insulin receptors are derived from two distinct genes, which was inconsistent with the generation of mammalian insulin receptors. Synteny analyses of insulin receptor genes showed that genes surrounding the insulin receptor genes were conserved in fish. Arhgef18, PEX11G, humanC19orf45 genes were highly conserved among mammal species. However, no conserved synteny was observed among fish, mammals, avians and amphibians.

Single-Nucleotide Polymorphism on Exon 17 of Insulin Receptor Gene Influences Insulin Resistance in PCOS: A Pilot Study on North Indian Women

Polycystic ovarian syndrome (PCOS), a major cause of infertility, is also strongly associated with insulin resistance. Defects in insulin receptor signaling are considered as one of the major molecular pathogeneses for insulin resistance. To investigate the possible mechanism of this signaling defect at genetic level, single-nucleotide polymorphism (SNP) [His 1085 C/T] at the exon 17 of insulin receptor gene (INSR) was studied in this pilot study. Polymerase chain reaction was performed on leucocytic DNA of women diagnosed with PCOS, selected from the outpatient department of Safdarjung Hospital, New Delhi, using suitable primer to amplify a region on INSR. An equal number of age-matched healthy women were selected as controls. SNP analysis was performed with restriction enzyme length polymorphism technique using Pm II enzyme. Serum insulin level was measured by ELISA kit and HOMA-IR was calculated mathematically. A higher frequency of the CC genotype was observed in PCOS women than in controls. Also, HOMA-IR, a tool for estimating insulin resistance, was significantly high in PCOS women with the CC genotype. C1008T SNP at exon 17 of INSR is associated with insulin resistance in Indian women with PCOS. Presence of CC genotype (C1085T) could be developed as a marker for insulin resistance and metabolic complications in PCOS women.

Obesity and cancer, a case for insulin signaling

Obesity is a worldwide epidemic, with the number of overweight and obese individuals climbing from just over 500 million in 2008 to 1.9 billion in 2014. Type 2 diabetes (T2D), cardiovascular disease and non-alcoholic fatty liver disease have long been associated with the obese state, whereas cancer is quickly emerging as another pathological consequence of this disease. Globally, at least 2.8 million people die each year from being overweight or obese. It is estimated that by 2020 being overweight or obese will surpass the health burden of tobacco consumption. Increase in the body mass index (BMI) in overweight (BMI>25 kg/m²) and obese (BMI>30 kg/m²) individuals is a result of adipose tissue (AT) expansion, which can lead to fat comprising >50% of the body weight in the morbidly obese. Extensive research over the last several years has painted a very complex picture of AT biology. One clear link between AT expansion and etiology of diseases like T2D and cancer is the development of insulin resistance (IR) and hyperinsulinemia. This review focuses on defining the link between obesity, IR and cancer.

Increased insulin-like growth factor-1 in relation to cardiovascular function in polycystic ovary syndrome: friend or foe?

The incidence of cardiovascular disease (CVD) in patients with polycystic ovary syndrome (PCOS) is very high and conventional risk factors only partially explain excessive risk of developing CVD in patients of PCOS. The pathophysiology of PCOS is very unique, and several hormonal and metabolic changes occur. Several observations suggest that serum IGF-1 levels decrease in insulin resistance, which results in IGF-1 deficiency. In patient of PCOS, close relationships have been demonstrated between insulin resistance and serum IGF-1 levels. Hyperinsulinemic insulin resistance results in a general augmentation of steroidogenesis and LH release in PCOS. The action of IGF-1 varies in different tissues possibly via autocrine or paracrine mechanisms. The increase or decrease in IGF-1 in different tissues results in differential outcomes. Several studies suggest that lowered circulating IGF-1 levels play important role in the initiation of the cardiac hypertrophic response which results in the risk of cardiovascular disease. While recent results suggests that individual with elevated IGF-1 is protected against cardiovascular disease. Thus IGF-1 shows versatile pleiotropic actions. This review provides a current perspective on increased level of IGF-1 in PCOS and also adds to the current controversy regarding the roles of IGF-1 in cardiovascular disease.

Nephrin Contributes to Insulin Secretion and Affects Mammalian Target of Rapamycin Signaling Independently of Insulin Receptor

Nephrin belongs to a family of highly conserved proteins with a well characterized function as modulators of cell adhesion and guidance, and nephrin may have a role in metabolic pathways linked to podocyte and pancreatic β-cell survival. However, this role is incompletely characterized. In this study, we developed floxed nephrin mice for pancreatic β-cell-specific deletion of nephrin, which had no effect on islet size and glycemia. Nephrin deficiency, however, resulted in glucose intolerance in vivo and impaired glucose-stimulated insulin release ex vivo Glucose intolerance was also observed in eight patients with nephrin mutations compared with three patients with other genetic forms of nephrotic syndrome or nine healthy controls.In vitro experiments were conducted to investigate if nephrin affects autocrine signaling through insulin receptor A (IRA) and B (IRB), which are both expressed in human podocytes and pancreatic islets. Coimmunoprecipitation of nephrin and IRB but not IRA was observed and required IR phosphorylation. Nephrin per se was sufficient to induce phosphorylation of p70S6K in an phosphatidylinositol 3-kinase-dependent but IR/Src-independent manner, which was not augmented by exogenous insulin. These results suggest a role for nephrin as an independent modulator of podocyte and pancreatic β-cell nutrient sensing in the fasting state and the potential of nephrin as a drug target in diabetes.

The association between polymorphism of INSR and polycystic ovary syndrome: a meta-analysis

Polycystic ovary syndrome (PCOS) is the most common gynecological endocrine disorder. The genetic background is believed to play a crucial role in the pathogenesis of PCOS. In recent years, the role of insulin receptor (INSR) polymorphisms in PCOS predisposition has attracted much attention. We performed a meta-analysis to investigate the association between the single nucleotide polymorphisms (SNPs) of INSR and PCOS. Published literature from Pubmed, Embase, and Cochrane CENTRAL was retrieved up until 7 August 2014. A total of 20 case-control studies including 23,845 controls and 17,460 PCOS cases with an average Newcastle-Ottawa quality assessment scale (NOS) score of 6.75 were analyzed. Ninety-eight SNPs distributed in 23 exons and the flanking regions of INSR were investigated, among which 17 SNPs were found to be associated with PCOS. Three SNPs detected in more than three studies were selected for further analyses. Twelve studies including 1158 controls and 1264 PCOS cases entered the analysis of rs1799817, but no significant association was found for every genotype (p > 0.05). Further subgroup stratification by ethnicity and weight did not lead to discovery of significant correlation (p > 0.05). For rs2059806, four studies including 442 controls and 524 PCOS cases were qualified for meta-analysis, and no significant association with PCOS was found for any genotype (p > 0.05). Four studies including 12,830 controls and 11,683 PCOS cases investigated the correlation between rs2059807 and PCOS, and five of the six cohorts indicated a significant impact. Our current meta-analysis suggests no significant correlation between rs1799817/rs2059806 SNPs and susceptibility of PCOS, while rs2059807 could be a promising candidate SNP that might be involved in the susceptibility of PCOS.

IGF-IR Targeted Therapy: Past, Present and Future

The IGF-I receptor (IGF-IR) has been studied as an anti-cancer target. However, monotherapy trials with IGF-IR targeted antibodies or with IGF-IR specific tyrosine kinase inhibitors have, overall, been very disappointing in the clinical setting. This review discusses potential reasons why IGF-I R targeted therapy fails to inhibit growth of human cancers. It has become clear that intracellular signaling pathways are highly interconnected and complex instead of being linear and simple. One of the most potent candidates for failure of IGF-IR targeted therapy is the insulin receptor isoform A (IR-A). Activation of the IR-A by insulin-like growth factor-II (IGF-II) bypasses the IGF-IR and its inhibition. Another factor may be that anti-cancer treatment may reduce IGF-IR expression. IGF-IR blocking drugs may also induce hyperglycemia and hyperinsulinemia, which may further stimulate cell growth. In addition, circulating IGF-IRs may reduce therapeutic effects of IGF-IR targeted therapy. Nevertheless, it is still possible that the IGF-IR may be a useful adjuvant or secondary target for the treatment of human cancers. Development of functional inhibitors that affect the IGF-IR and IR-A may be necessary to overcome resistance and to make IGF-IR targeted therapy successful. Drugs that modify alternative downstream effects of the IGF-IR, so called "biasing agonists," should also be considered.

Insulin receptor compensates for IGF1R inhibition and directly induces mitogenic activity in prostate cancer cells

Hyperinsulinemia is a major complication associated with the development of insulin resistance. In addition to its normal spectrum of metabolic effects, insulin can act as a growth factor and has the ability to promote mitogenic activity. Thus, hyperinsulinemia is regarded as a potentially important cancer risk factor among diabetic patients. However, the mechanisms of action of insulin in the specific context of prostate cancer (PCa) and, in particular, the specific receptor that mediates its actions have not been elucidated yet. The aims of this study were to investigate whether insulin can directly induce mitogenic activities in PCa-derived cell lines and to examine the mechanisms responsible for these actions. To this end, we used several PCa-derived cell lines, representing early and advanced stages of the disease. Our results indicated that insulin induces cell proliferation in a dose-dependent fashion in the LNCaP, C4-2, and P69 cell lines. We also demonstrated that insulin enabled LNCaP and C4-2 cells to progress through the cell cycle. Immunoprecipitation assays revealed that insulin activated the insulin receptor (INSR), but not the IGF1 receptor (IGF1R). In addition, INSR was able to compensate for and mediate IGF1 mitogenic signals following IGF1R inhibition. In conclusion, insulin exhibits direct mitogenic activities in PCa cells, which are mediated exclusively through the INSR. Further research is needed to fully dissect the molecular mechanisms underlying the biological actions of insulin in PCa.

Insulin in the brain: its pathophysiological implications for States related with central insulin resistance, type 2 diabetes and Alzheimer's disease

Although the brain has been considered an insulin-insensitive organ, recent reports on the location of insulin and its receptors in the brain have introduced new ways of considering this hormone responsible for several functions. The origin of insulin in the brain has been explained from peripheral or central sources, or both. Regardless of whether insulin is of peripheral origin or produced in the brain, this hormone may act through its own receptors present in the brain. The molecular events through which insulin functions in the brain are the same as those operating in the periphery. However, certain insulin actions are different in the central nervous system, such as hormone-induced glucose uptake due to a low insulin-sensitive GLUT-4 activity, and because of the predominant presence of GLUT-1 and GLUT-3. In addition, insulin in the brain contributes to the control of nutrient homeostasis, reproduction, cognition, and memory, as well as to neurotrophic, neuromodulatory, and neuroprotective effects. Alterations of these functional activities may contribute to the manifestation of several clinical entities, such as central insulin resistance, type 2 diabetes mellitus (T2DM), and Alzheimer's disease (AD). A close association between T2DM and AD has been reported, to the extent that AD is twice more frequent in diabetic patients, and some authors have proposed the name "type 3 diabetes" for this association. There are links between AD and T2DM through mitochondrial alterations and oxidative stress, altered energy and glucose metabolism, cholesterol modifications, dysfunctional protein O-GlcNAcylation, formation of amyloid plaques, altered Aβ metabolism, and tau hyperphosphorylation. Advances in the knowledge of preclinical AD and T2DM may be a major stimulus for the development of treatment for preventing the pathogenic events of these disorders, mainly those focused on reducing brain insulin resistance, which is seems to be a common ground for both pathological entities.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Two novel mutations identified in familial cases with Donohue syndrome

Donohue syndrome (DS) is a rare and lethal autosomal recessive disease caused by mutations in the insulin receptor (INSR) gene, manifesting marked insulin resistance, severe growth retardation, hypertrichosis, and characteristic dysmorphic features. We report the clinical, molecular, and biochemical characterization of three new patients with DS, and address genotype–phenotype issues playing a role in the pathophysiology of DS. A female infant born to first-degree cousins Muslim Arab parents and two brothers born to first-degree cousins Druze parents presented classical features of DS with hypertrophic cardiomyopathy and died in infancy. Each patient was found homozygous for one missense mutation within the extracellular domain of the INSR gene. Western blot analysis identified the proreceptor of INSR, but not its mature subunits alpha and beta. Of 95 healthy Muslims, no heterozygous was found and of 52 healthy Druze from the same village, one was heterozygous. This study presents two novel familial mutations in the alpha subunit of the INSR which appear to impair post-translational processing of the INSR, resulting loss of its function. Both mutations cause DS with hypertrophic cardiomyopathy and early death. Identification of the causative mutation enables prevention of this devastating disease.

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.

Concentrations of insulin glargine and its metabolites during long-term insulin therapy in type 2 diabetic patients and comparison of effects of insulin glargine, its metabolites, IGF-I, and human insulin on insulin and igf-I receptor signaling

We investigated 1) the ability of purified glargine (GLA), metabolites 1 (M1) and 2 (M2), IGF-I, and NPH insulin to activate the insulin receptor (IR)-A and IR-B and IGF-I receptor (IGF-IR) in vitro; 2) plasma concentrations of GLA, M1, and M2 during long-term insulin therapy in type 2 diabetic patients; and 3) IR-A and IR-B activation in vitro induced by serum from patients treated with GLA or NPH insulin. A total of 104 patients (age 56.3 ± 0.8 years, BMI 31.4 ± 0.5 kg/m(2), and A1C 9.1 ± 0.1% [mean ± SE]) were randomized to GLA or NPH insulin therapy for 36 weeks. Plasma concentrations of GLA, M1, and M2 were determined by liquid chromatography-tandem mass spectrometry assay. IR-A, IR-B, and IGF-IR autophosphorylation was induced by purified hormones or serum by kinase receptor activation assays. In vitro, M1 induced comparable IR-A, IR-B, and IGF-IR autophosphorylation (activation) as NPH insulin. After 36 weeks, M1 increased from undetectable (<0.2 ng/mL) to 1.5 ng/mL (0.9-2.1), while GLA and M2 remained undetectable. GLA dose correlated with M1 (r = 0.84; P < 0.001). Serum from patients treated with GLA or NPH insulin induced similar IR-A and IR-B activation. These data suggest that M1 rather than GLA mediates GLA effects and that compared with NPH insulin, GLA does not increase IGF-IR signaling during long-term insulin therapy in type 2 diabetes.

Genetic variants associated with insulin signaling and glucose homeostasis in the pathogenesis of insulin resistance in polycystic ovary syndrome: a systematic review

BACKGROUND

Polycystic ovary syndrome must be recognized as a serious issue due to its implication on long term health regardless of an individual's age. PCOS and insulin resistance are interlinked, as approximately 40 % of women with PCOS are insulin resistant. However, the detailed molecular basis for insulin resistance that is coupled with PCOS remains poorly understood.

OBJECTIVE

To review the published evidence that polymorphisms in genes that are involved in insulin secretion and action are associated with an increased risk of PCOS.

METHODS

We reviewed articles published through November 2012 which concerned polymorphisms of genes related to insulin signaling and glucose homeostasis as well as their associations with PCOS. The articles were identified via Medline searches.

CONCLUSIONS

No consistent evidence emerged of a strong association between the risk of PCOS and any known gene that is related to insulin signaling and glucose homeostasis. Moreover, recent genome-wide association studies are inconsistent in identifying the associations between PCOS and insulin metabolism genes. Many of the studies reviewed were limited by heterogeneity in the PCOS diagnosis and by not have having a sufficient number of study participants. Further studies are warranted to determine predisposing risk factors which could modify environmental factors and thus reduce the risk of PCOS. Large genome-wide association studies devoted solely to PCOS will be necessary to identify new candidate genes and proteins that are involved in PCOS risk.