Influence of polymorphisms in IRS1, IRS2, MC3R, and MC4R on metabolic and inflammatory status and food intake in Brazilian adults: An exploratory pilot study

Polymorphisms in genes of leptin-melanocortin and insulin pathways have been associated with obesity and type 2 diabetes. We hypothesized that polymorphisms in IRS1, IRS2, MC3R, and MC4R influence metabolic and inflammatory markers and food intake composition in Brazilian subjects. This exploratory pilot study included 358 adult subjects. Clinical, anthropometric, and laboratory data were obtained through interview and access to medical records. The variants IRS1 rs2943634 A˃C, IRS2 rs1865434 C>T, MC3R rs3746619 C>A, and MC4R rs17782313 T>C were analyzed by real-time polymerase chain reaction. Food intake composition was assessed in a group of subjects with obesity (n = 84) before and after a short-term nutritional counseling program (9 weeks). MC4R rs17782313 was associated with increased risk of obesity (P = .034). Multivariate linear regression analysis adjusted by covariates indicated associations of IRS2 rs1865434 with reduced low-density lipoprotein cholesterol and resistin, MC3R rs3746619 with high glycated hemoglobin, and IRS1 rs2943634 and MC4R rs17782313 with increased high-sensitivity C-reactive protein (P < .05). Energy intake and carbohydrate and total fat intakes were reduced after the diet-oriented program (P < .05). Multivariate linear regression analysis showed associations of IRS2 rs1865434 with high basal fiber intake, IRS1 rs2943634 with low postprogram carbohydrate intake, and MC4R rs17782313 with low postprogram total fat and saturated fatty acid intakes (P < .05). Although significant associations did not survive correction for multiple comparisons using the Benjamini-Hochberg method in this exploratory study, polymorphisms in IRS1, IRS2, MC3R, and MC4R influence metabolic and inflammatory status in Brazilian adults. IRS1 and MC4R variants may influence carbohydrate, total fat, and saturated fatty acid intakes in response to a diet-oriented program in subjects with obesity.

Research progress on drugs for diabetes based on insulin receptor/insulin receptor substrate

The number of people with diabetes worldwide is increasing annually, resulting in a serious economic burden. Insulin resistance is a major pathology in the early onset of diabetes mellitus, and therefore, related drug studies have attracted research attention. The insulin receptor/insulin receptor substrate (INSR/IRS) serves as the primary conduit in the insulin signal transduction cascade, and dysregulation of this pathway can lead to insulin resistance. Currently, there exist a plethora of hypoglycemic drugs in the market; however, drugs that specifically target INSR/IRS are comparatively limited. The literature was collected by direct access to the PubMed database, and was searched using the terms "diabetes mellitus; insulin resistance; insulin receptor; insulin receptor substrate; diabetes drug" as the main keywords for literature over the last decade. This article provides a comprehensive analysis of the structure and function of INSR and IRS proteins, as well as the drugs used for the treatment of diabetes. Additionally, it serves as a valuable reference for the advancement of novel therapeutic agents for diabetes management.

Phosphorylation of insulin receptor substrates (IRS-1 and IRS-2) is attenuated following cecal ligation and puncture in mice

BACKGROUND

Sepsis is characterized as an insulin resistant state. However, the effects of sepsis on insulin's signal transduction pathway are unknown. The molecular activity driving insulin signaling is controlled by tyrosine phosphorylation of the insulin receptor β-subunit (IRβ) and of insulin receptor substrate molecules (IRS) -1 and IRS-2.

HYPOTHESIS

Cecal ligation and puncture (CLP) attenuates IRβ, IRS-1 and IRS-2 phosphorylation.

METHODS

IACUC-approved studies conformed to ARRIVE guidelines. CLP was performed on C57BL/6 mice; separate cohorts received intraperitoneal insulin at baseline (T0) or at 23 or 47 h. post-CLP, 1 h before mice were euthanized. We measured levels of (1) glucose and insulin in serum, (2) IRβ, IRS-1 and IRS-2 in skeletal muscle and liver homogenate and (3) phospho-Irβ (pIRβ) in liver and skeletal muscle, phospho-IRS-1 (pIRS-1) in skeletal muscle and pIRS-2 in liver. Statistical significance was determined using ANOVA with Sidak's post-hoc correction.

RESULTS

CLP did not affect the concentrations of IRβ, IRS-1or IRS-2 in muscle or liver homogenate or of IRS-1 in liver. Muscle IRS-1 concentration at 48 h. post-CLP was higher than at T0. Post-CLP pIRS-1 levels in muscle and pIRβ and pIRS-2 levels in liver were indistinguishable from T0 levels. At 48 h. post-CLP pIRβ levels in muscle were higher than at T0. Following insulin administration, the relative abundance of pIRβ in muscle and liver at T0 and at both post-CLP time points was significantly higher than abundance in untreated controls. In T0 controls, the relative abundance of pIRS-1 in muscle and of pIRS-2 in liver following insulin administration was higher than in untreated mice. However, at both post-CLP time points, the relative abundance of pIRS-1 in muscle and of pIRS-2 in liver following insulin administration was not distinguishable from the abundance in untreated mice at the same time point. Serum glucose concentration was significantly lower than T0 at 24 h., but not 48 h., post-CLP. Glucose concentration was lower following insulin administration to T0 mice but not in post-CLP animals. Serum insulin levels were significantly higher than baseline at both post-CLP time points.

CONCLUSIONS

CLP impaired insulin-induced tyrosine phosphorylation of both IRS-1 in muscle and IRS-2 in liver. These findings suggest that the molecular mechanism underlying CLP-induced insulin resistance involves impaired IRS-1/IRS-2 phosphorylation.

Hepatic follistatin increases basal metabolic rate and attenuates diet-induced obesity during hepatic insulin resistance

OBJECTIVE

Body weight change and obesity follow the variance of excess energy input balanced against tightly controlled EE (energy expenditure). Since insulin resistance can reduce energy storage, we investigated whether genetic disruption of hepatic insulin signaling reduced adipose mass with increased EE.

METHODS

Insulin signaling was disrupted by genetic inactivation of Irs1 (Insulin receptor substrate 1) and Irs2 in hepatocytes of LDKO mice (Irs1L/L·Irs2L/L·CreAlb), creating a state of complete hepatic insulin resistance. We inactivated FoxO1 or the FoxO1-regulated hepatokine Fst (Follistatin) in the liver of LDKO mice by intercrossing LDKO mice with FoxO1L/L or FstL/L mice. We used DEXA (dual-energy X-ray absorptiometry) to assess total lean mass, fat mass and fat percentage, and metabolic cages to measure EE (energy expenditure) and estimate basal metabolic rate (BMR). High-fat diet was used to induce obesity.

RESULTS

Hepatic disruption of Irs1 and Irs2 (LDKO mice) attenuated HFD (high-fat diet)-induced obesity and increased whole-body EE in a FoxO1-dependent manner. Hepatic disruption of the FoxO1-regulated hepatokine Fst normalized EE in LDKO mice and restored adipose mass during HFD consumption; moreover, hepatic Fst disruption alone increased fat mass accumulation, whereas hepatic overexpression of Fst reduced HFD-induced obesity. Excess circulating Fst in overexpressing mice neutralized Mstn (Myostatin), activating mTORC1-promoted pathways of nutrient uptake and EE in skeletal muscle. Similar to Fst overexpression, direct activation of muscle mTORC1 also reduced adipose mass.

CONCLUSIONS

Thus, complete hepatic insulin resistance in LDKO mice fed a HFD revealed Fst-mediated communication between the liver and muscle, which might go unnoticed during ordinary hepatic insulin resistance as a mechanism to increase muscle EE and constrain obesity.

The pivotal role of JAK/STAT and IRS/PI3K signaling pathways in neurodegenerative diseases: Mechanistic approaches to polyphenols and alkaloids

BACKGROUND

Neurodegenerative diseases (NDDs) are characterized by progressive neuronal dysfunctionality which results in disability and human life-threatening events. In recent decades, NDDs are on the rise. Besides, conventional drugs have not shown potential effectiveness to attenuate the complications of NDDs. So, exploring novel therapeutic agents is an urgent need to combat such disorders. Accordingly, growing evidence indicates that polyphenols and alkaloids are promising natural candidates, possessing several beneficial pharmacological effects against diseases. Considering the complex pathophysiological mechanisms behind NDDs, Janus kinase (JAK), insulin receptor substrate (IRS), phosphoinositide 3-kinase (PI3K), and signal transducer and activator of transcription (STAT) seem to play critical roles during neurodegeneration/neuroregeneration. In this line, modulation of the JAK/STAT and IRS/PI3K signaling pathways and their interconnected mediators by polyphenols/alkaloids could play pivotal roles in combating NDDs, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), stroke, aging, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), depression and other neurological disorders.

PURPOSE

Thus, the present study aimed to investigate the neuroprotective roles of polyphenols/alkaloids as multi-target natural products against NDDs which are critically passing through the modulation of the JAK/STAT and IRS/PI3K signaling pathways.

STUDY DESIGN AND METHODS

A systematic and comprehensive review was performed to highlight the modulatory roles of polyphenols and alkaloids on the JAK/STAT and IRS/PI3K signaling pathways in NDDs, according to the PRISMA guideline, using scholarly electronic databases, including Scopus, PubMed, ScienceDirect, and associated reference lists.

RESULTS

In the present study 141 articles were included from a total of 1267 results. The results showed that phenolic compounds such as curcumin, epigallocatechin-3-gallate, and quercetin, and alkaloids such as berberine could be introduced as new strategies in combating NDDs through JAK/STAT and IRS/PI3K signaling pathways. This is the first systematic review that reveals the correlation between the JAK/STAT and IRS/PI3K axis which is targeted by phytochemicals in NDDs. Hence, this review highlighted promising insights into the neuroprotective potential of polyphenols and alkaloids through the JAK/STAT and IRS/PI3K signaling pathway and interconnected mediators toward neuroprotection.

CONCLUSION

Amongst natural products, phenolic compounds and alkaloids are multi-targeting agents with the most antioxidants and anti-inflammatory effects possessing the potential of combating NDDs with high efficacy and lower toxicity. However, additional reports are needed to prove the efficacy and possible side effects of natural products.

Far-western Blotting Detection of the Binding of Insulin Receptor Substrate to the Insulin Receptor

Far-western blotting, derived from the western blot, has been used to detect interactions between proteins in vitro, such as receptor-ligand interactions. The insulin signaling pathway plays a critical role in the regulation of both metabolism and cell growth. The binding of the insulin receptor substrate (IRS) to the insulin receptor is essential for the propagation of downstream signaling after the activation of the insulin receptor by insulin. Here, we describe a step-by-step far-western blotting protocol for determining the binding of IRS to the insulin receptor.

Analysis of Insulin Resistance in Nonalcoholic Steatohepatitis

Insulin resistance is a major phenotype observed in nonalcoholic steatohepatitis (NASH), the advanced stage of nonalcoholic fatty liver disease (NAFLD). Insulin resistance in NASH is characterized by reductions in whole body, hepatic, and adipose tissue insulin sensitivity. The mechanisms underlying hepatic insulin resistance is primarily associated with hepatic glucose production (HGP) rate. Hepatic insulin resistance can also be a consequence or a driving factor of hepatic lipid accumulation by increasing free fatty acid synthesis, delivery, and catabolism. The common method to assess hepatic insulin resistance is to measure hepatic glucose production (HGP) using isotope tracer distribution technique. However, non-radioactive approaches have been developed to assess hepatic insulin resistance in the context of NASH. In this chapter, we describe the methods to evaluate hepatic insulin resistance in animal models of NASH by examining insulin sensitivity and glucose tolerance as well as the key molecules in hepatic insulin signaling pathways.

Differential involvement of insulin receptor substrate (IRS)-1 and IRS-2 in brain insulin signaling is associated with the effects on amyloid pathology in a mouse model of Alzheimer's disease

Insulin signaling has been implicated in the metabolism as well as aging and longevity. Type 2 diabetes mellitus and its core pathology, insulin resistance, has also been implicated in the development of Alzheimer's disease (AD) and amyloid-β deposition in humans. By contrast, genetic ablation of the insulin/IGF-1 signaling (IIS) pathway components, e.g. insulin receptor substrate (IRS)-2, has been documented to suppress amyloid-β accumulation in the brains of transgenic mice overexpressing AD mutant β-amyloid precursor protein (APP). Therefore, the brain IIS may be a key modifiable molecular target in the pathophysiology of AD. IRS-1 and IRS-2 are critical nodes in IIS as substrates for insulin receptor and IGF-1 receptor, although the functional differences between IRS-1 and IRS-2 in the adult brain are yet to be explored. To examine their relative contribution to the brain IIS activity and AD pathomechanism, we generated APP transgenic mice lacking either IRS-1 or IRS-2. IRS-1 deficiency had little effects on the brain IIS pathway associated with compensatory activation of IRS-2, whereas IRS-2 deficiency was not fully compensated by activation of IRS-1, and the downstream activation of Akt also was significantly compromised. Pathological analyses of the cortical tissues showed that the biochemical levels of soluble and insoluble amyloid-β, the amyloid-β histopathology, and tau phosphorylation were not affected by the absence of IRS-1, in contrast to the marked alteration in IRS-2 deleted mice. These results suggest the predominance of IRS-2 in the brain IIS, and support the hypothesis that reduced IIS exerts anti-amyloid effects in the brain.

Adenosine monophosphate activated protein kinase (AMPK) is essential for the memory improving effect of adiponectin

Adiponectin (APN) plays a major role in the regulation of insulin sensitivity and glucose homeostasis. Insulin and APN have a positive effect on memory. In this study, we examined whether the inhibition of AMPK could block the memory improving effect of APN or affect the IRS1 expression. Animal model of AD was developed by intracerebroventricular (icv) injection of 3 mg/kg streptozotocin (STZ), in 12 weeks old Wistar rats, on days 1 and 3 after cannulation. Dorsomorphin (DM) and APN (600 nM) were injected 30 and 20 min before the acquisition phase, respectively. DM was applied in 3 different doses (0.2, 2 and 20 μM). All behavioral tests were performed on days 15 and 16; the Preference Index (PI) was calculated for novel object recognition (NOR) test, while the step through latency (STL) and total time in dark compartment (TDC) were recorded and analyzed for the passive avoidance task. Relative expression of insulin receptor substrate-1 (IRS-1) protein in the hippocampus was measured by western blotting. In early retrieval test, STZ + APN treatment increased STL (P < 0.0001) and decreased TDC (P < 0.05) in comparison to STZ group, while STZ + APN + DM (2μM) caused a decrease in STL (P < 0.05) and increase in TDC (0.2μM and 2μM DM; P < 0.05). Icv injection of DM (0.2μM and 2μM) before APN decreased the PI significantly (P < 0.05) in comparison to STZ + APN group. APN treatment raised the IRS-1 expression and DM reversed this increment, significantly (P < 0.0001). It is concluded that the memory improving effect of APN is mediated, at least in part, by the AMPK pathway. APN is also able to boost insulin signaling by overexpression of IRS-1 in the hippocampus.

Ethno-pharmacological insulin signaling induction of aqueous extract of Syzygium paniculatum fruits in a high-fat diet induced hepatic insulin resistance

ETHNOPHARMACOLOGICAL RELEVANCE

The ethnopharmacological significance of the fruits of Syzygium paniculatum Gaertn (Magenta Cherry) is widely recognized in the Indian traditional medicine system to treat various disorders, such as diabetes, hyperlipidaemia, hypertension, and cardiovascular problems.

AIM OF THE STUDY

This research work investigated the supplementation of the aqueous extract of S. paniculatum fruit (AESPF) on liver function; the molecular effects on the expression of the protein of insulin receptor (IR) and insulin receptor substrate 1 (IRS-1) in high-fat diet-induced hepatic insulin resistance in the rat model.

MATERIALS AND METHODS

High-fat diet was used to induce obesity in albino Wistar for 120 days. Biochemical, enzymatic, and histopathological analysis, as well as analysis of hepatic insulin resistance proteins and expression of IRS-1, were performed.

RESULTS

The supplementation of AESPF with a dose of 100 mg/kg bw significantly reduced bodyweight, blood sugar, insulin, lipid profiles, and liver enzymes. Hepatic insulin resistance was improved with a reduced level of IR and IRS-1 to protein levels. HFD alters the sensitivity of hepatocytes to insulin due to the down-regulation of insulin receptor proteins.

CONCLUSIONS

The fruits of S. paniculatum possess biological activities to alleviate all risky effects by regulating hepatic lipogenesis activity that can be used in the progress of medication for HFD-induced hepatic insulin resistance and metabolic disorders.

The IRS/PI3K/Akt signaling pathway mediates olanzapine-induced hepatic insulin resistance in male rats

AIMS

Chronic treatment with antipsychotics, especially most of atypical ones, leads to development of metabolic abnormalities. Olanzapine is an atypical antipsychotic widely used in the treatment of schizophrenia and bipolar disorder. The mechanisms underlying olanzapine-induced metabolic adverse effects in the liver, however, remain unclear. This study was designed to investigate olanzapine-induced insulin-desensitivity in the liver.

MAIN METHODS

Male rats were treated with olanzapine (5 mg/kg, by a gavage method, once daily for consecutive 8 weeks. Blood and liver variables were determined enzymatically or histologically. Gene/protein expression was analyzed by real-time PCR and Western blot.

KEY FINDINGS

Olanzapine treatment significantly increased fasting plasma insulin concentration, the index of the homeostasis model assessment of insulin resistance (HOMA-IR), and hepatic triglyceride and fatty droplet accumulation in rats. Hepatic gene/protein expression profile revealed that olanzapine activated mRNA and protein expression of sterol regulatory element-binding protein-1c, and mRNA levels of its downstream lipogenic enzymes, acetyl-CoA carboxylase-1, fatty acid synthase and stearoyl-CoA desaturase-1. More importantly, phosphorylated protein level of both Ser³⁰⁷ in insulin receptor substrate (IRS)-1 and Ser⁷³¹ in IRS-2 was increased. Furthermore, phosphorylation of Tyr⁶⁰⁷ in phosphoinositide 3-kinase (PI3K) p85α, Ser⁴⁷³ in Akt and Ser²⁴⁴⁸ in mammalian target of rapamycin was also enhanced.

SIGNIFICANCE

Our results suggest that the IRS/PI3K/Akt signaling pathway mediates olanzapine-induced hepatic insulin resistance in male rats. Our findings may provide better understanding of the antipsychotic-induced metabolic adverse effects.

RNA interference against the putative insulin receptor substrate gene chico affects metamorphosis in Leptinotarsa decemlineata

It is noted that insect insulin/insulin-like growth factor/target of rapamycin signaling is critical for the regulation of metamorphosis in holometabolous insects. However, the molecular mechanism remains undetermined. Our previous findings reveal that RNA interference (RNAi)-mediated knockdown of an insulin gene (LdILP2) in Leptinotarsa decemlineata disturbs both 20-hydroxyecdysone (20E) and juvenile hormone (JH) signaling, and impairs pupation. In the present paper, we further observed that the expression of the insulin receptor substrate gene chico (Ldchico) and the phosphoinositide-3-kinase gene pi3k (Ldpi3k92E) was repressed in LdILP2 depleted larvae. Moreover, RNAi of Ldchico or Ldpi3k92E decreased food consumption, affected absorption and metabolism of amino acids and sugars, and reduced expression of several 20E (LdEcR, LdHR3 and LdE75) and JH (LdJHAMT, LdKr-h1 and LdHairy) signaling genes. As a result, larval development was postponed and larval growth was inhibited. Intriguingly, knockdown of Ldchico, rather than Ldpi3k92E, impaired larval-pupal and pupal-adult ecdysis, and specifically repressed transcription of another 20E signaling gene LdUSP. Ingestion of 20E rescued the expression of LdEcR, LdHR3 and LdE75, whereas 20E feeding restored neither the decreased LdUSP mRNA level, nor the reduced pupation and adult emergence rates in Ldchico RNAi larvae. Therefore, Chico is critical for the regulation of larval-pupal-adult transition by a PI3K-independent pathway, perhaps through activation of USP in L. decemlineata.

A low-protein diet eliminates the circadian rhythm of serum insulin and hepatic lipid metabolism in mice

Insulin is a key molecule that synchronizes peripheral clocks, such as that in the liver. Although we previously reported that mice fed a low-protein diet showed altered expression of lipid-related genes in the liver and induction of hepatic steatosis, it is unknown whether a low-protein diet impairs insulin secretion and modifies the hepatic circadian rhythm. Therefore, we investigated the effects of the intake of a low-protein diet on the circadian rhythm of insulin secretion and hepatic lipid metabolism in mice. Under 12-h light/12-h dark cycle, mice fed a low-protein diet for 7 days displayed enhanced food intake at the end of the light phase, although central and peripheral PER2 expression rhythm was maintained. Serum insulin levels in mice fed a low-protein diet remained low during the day, and the insulin secretion in OGTT was also markedly lower than in normal mice. In mice fed low-protein diet, hepatic TG accumulation was observed during the nighttime, with relatively high levels of ACC1 mRNA and total ACC proteins. Although there were no differences in the activity rhythm of hepatic mTOR between mice fed a normal or low-protein diet, hepatic IRS-2 expression in mice fed a low-protein diet remained low during the day, with no increase at the beginning of the light period. These results suggested that the low-protein diet eliminated the circadian rhythm of serum insulin and hepatic lipid metabolism in mice, providing insights into our understanding of the mechanisms of hepatic disorders of lipid metabolism.

Distinct signalling properties of insulin receptor substrate (IRS)-1 and IRS-2 in mediating insulin/IGF-1 action

Insulin/IGF-1 action is driven by a complex and highly integrated signalling network. Loss-of-function studies indicate that the major insulin/IGF-1 receptor substrate (IRS) proteins, IRS-1 and IRS-2, mediate different biological functions in vitro and in vivo, suggesting specific signalling properties despite their high degree of homology. To identify mechanisms contributing to the differential signalling properties of IRS-1 and IRS-2 in the mediation of insulin/IGF-1 action, we performed comprehensive mass spectrometry (MS)-based phosphoproteomic profiling of brown preadipocytes from wild type, IRS-1^-/- and IRS-2^-/- mice in the basal and IGF-1-stimulated states. We applied stable isotope labeling by amino acids in cell culture (SILAC) for the accurate quantitation of changes in protein phosphorylation. We found ~10% of the 6262 unique phosphorylation sites detected to be regulated by IGF-1. These regulated sites included previously reported substrates of the insulin/IGF-1 signalling pathway, as well as novel substrates including Nuclear Factor I X and Semaphorin-4B. In silico prediction suggests the protein kinase B (PKB), protein kinase C (PKC), and cyclin-dependent kinase (CDK) as the main mediators of these phosphorylation events. Importantly, we found preferential phosphorylation patterns depending on the presence of either IRS-1 or IRS-2, which was associated with specific sets of kinases involved in signal transduction downstream of these substrates such as PDHK1, MAPK3, and PKD1 for IRS-1, and PIN1 and PKC beta for IRS-2. Overall, by generating a comprehensive phosphoproteomic profile from brown preadipocyte cells in response to IGF-1 stimulation, we reveal both common and distinct insulin/IGF-1 signalling events mediated by specific IRS proteins.

El papel de los ácidos grasos libres en la resistencia a la insulina

Free fatty acids are essential nutritional components and recent studies identified them as signaling molecules in various physiological processes. It has now been shown that high levels of free fatty acids, particularly saturated fatty acids, may be associated with insulin resistance in obese patients with type 2 diabetes mellitus. Insulin resistance is important in clinical since it is related to various diseases including type 2 diabetes mellitus, dyslipidemia, and abnormalities at cardiovascular level. Recent studies have proposed different molecular mechanisms by which these lipids may alter the signaling pathway of insulin. The purpose of this review is to highlight recent advances in the study of the effect of free fatty acids as modulators of insulin response.

Divergent Roles of IRS (Insulin Receptor Substrate) 1 and 2 in Liver and Skeletal Muscle

IRS1 and IRS2 are the most important representatives of the IRS protein family and critical nodes in insulin/IGF1-signaling. Although they are quite similar in their structural and functional features they show tissue-specific differences. In this review, we outline the functions of IRS1 and IRS2 in skeletal muscle and liver with regard to their importance for metabolism, growth and differentiation. Mechanisms contributing to IRS1 and IRS2 dysregulation in disease states as well as consequences thereof are discussed. IRS1 plays the dominant role in skeletal muscle. It is crucial for normal growth and differentiation of myofibers, insulin-dependent glucose uptake and glycogen synthesis. The presence of IRS2 in skeletal muscle is negligible for insulin-induced glucose uptake and the general role of IRS2 in muscle is still not fully understood. In liver IRS1 and IRS2 are important to mediate insulindependent regulation of glucose and lipid metabolism and complement each other in the diurnal regulation thereof. IRS1 in the liver is more important for signaling in the late refeeding period, whereas IRS2 signaling is mostly dominating in the period directly after food intake and during fasting. Importantly, the expression level of IRS1 and IRS2 is different within the liver lobule, which could be an explanation for the phenomenon of selective insulin resistance. Dysregulated muscular or hepatic abundance and/or phosphorylation status of IRS1 and IRS2 are important factors in the pathogenesis of insulin resistance, type 2 diabetes and muscle wasting.

Evolution of the vertebrate insulin receptor substrate (Irs) gene family

BACKGROUND

Insulin receptor substrate (Irs) proteins are essential for insulin signaling as they allow downstream effectors to dock with, and be activated by, the insulin receptor. A family of four Irs proteins have been identified in mice, however the gene for one of these, IRS3, has been pseudogenized in humans. While it is known that the Irs gene family originated in vertebrates, it is not known when it originated and which members are most closely related to each other. A better understanding of the evolution of Irs genes and proteins should provide insight into the regulation of metabolism by insulin.

RESULTS

Multiple genes for Irs proteins were identified in a wide variety of vertebrate species. Phylogenetic and genomic neighborhood analyses indicate that this gene family originated very early in vertebrae evolution. Most Irs genes were duplicated and retained in fish after the fish-specific genome duplication. Irs genes have been lost of various lineages, including Irs3 in primates and birds and Irs1 in most fish. Irs3 and Irs4 experienced an episode of more rapid protein sequence evolution on the ancestral mammalian lineage. Comparisons of the conservation of the proteins sequences among Irs paralogs show that domains involved in binding to the plasma membrane and insulin receptors are most strongly conserved, while divergence has occurred in sequences involved in interacting with downstream effector proteins.

CONCLUSIONS

The Irs gene family originated very early in vertebrate evolution, likely through genome duplications, and in parallel with duplications of other components of the insulin signaling pathway, including insulin and the insulin receptor. While the N-terminal sequences of these proteins are conserved among the paralogs, changes in the C-terminal sequences likely allowed changes in biological function.

IGF-1R signalling contributes to IL-6 production and T cell dependent inflammation in rheumatoid arthritis

BACKGROUND

Signalling through insulin-like growth factor 1 receptor (IGF-1R) is essential for cell survival, but may turn pathogenic in uncontrolled tissue growth in tumours. In rheumatoid arthritis (RA), the IGF-1R signalling is activated and supports expansion of the inflamed synovia.

AIM

In the present study, we assess if disruption of IGF-1R signalling resolves arthritis.

MATERIAL AND METHODS

Clinical associations of IGF-1R expression in leukocytes of the peripheral blood were studied in 84 RA patients. Consequences of the IGF-1R signalling inhibition for arthritis were studied in mBSA immunised Balb/c mice treated with NT157 compound promoting degradation of insulin receptor substrates.

RESULTS

In RA patients, high expression of IGF-1R in leukocytes was associated with systemic inflammation as verified by higher expression of NF-kB, serum levels of IL6 and erythrocyte sedimentation rate, and higher pain perception. Additionally, phosphorylated IGF-1R and STAT3 enriched T cells infiltrate in RA synovia. Treatment with NT157 inhibited the phosphorylation of IGF-1R and STAT3 in synovia, and alleviated arthritis and joint damage in mice. It also reduced expression of IGF-1R and despaired ERK and Akt signalling in spleen T cells. This limited IL-6 production, changed RoRgt/FoxP3 balance and IL17 levels.

CONCLUSION

IGF-1R signalling contributes to T cell dependent inflammation in arthritis. Inhibition of IGF-1R on the level of insulin receptor substrates alleviates arthritis by restricting IL6-dependent formation of Th17 cells and may open for new treatment strategies in RA.

IRS1 and IRS2: molecular characterization, tissue expression and transcriptional regulation by insulin in yellow catfish Pelteobagrus fulvidraco

The insulin receptor substrate (IRS) proteins, in particular, IRS1 and IRS2, are the key downstream players of insulin signaling pathway and the regulation of lipid metabolism. In the present study, two genes of IRS (IRS1 and IRS2) were isolated and characterized from yellow catfish Pelteobagrus fulvidraco. Their molecular characterizations, tissue expressions, and transcriptional levels by insulin both in vivo and in vitro were determined. The validated complementary DNAs encoding for IRS1 and IRS2 were 3693 and 3177 bp in length, encoding proteins of 1230 and 1058 amino acid residues, respectively. Similarly to mammals, amino acid sequence alignment revealed that IRSs contained an N-terminal pleckstrin homology (PH) domain, a phosphotyrosine-binding (PTB) domain, and several C-terminal multiple sites of tyrosine phosphorylation. Both IRS1 and IRS2 were widely expressed across the ten tissues (liver, white muscle, spleen, brain, gill, mesenteric fat, anterior intestine, heart, mid-kidney, and ovary), but at the variable levels. Insulin injection at 1 μg/g in vivo significantly stimulated the messenger RNA (mRNA) expression of IRS2, but not IRS1 mRNA expression levels in the liver of yellow catfish after 48 h. In hepatocytes of yellow catfish, insulin incubation significantly stimulated the IRS1 (at a 1000 nM insulin group) and IRS2 (at both 100 and 1000 nM insulin groups) mRNA expressions, which indicated that IRS2 was more sensitive than IRS1 to insulin stimulation in the liver of yellow catfish, and IRS2 played a more important role in mediating insulin's effects on the liver metabolism. The present study serves to increase our understanding into the function of IRS in fish.

IRS proteins and diabetic complications

IRS proteins are cellular adaptor molecules that mediate many of the key metabolic actions of insulin. When tyrosine is phosphorylated by the activated insulin receptor, IRS proteins recruit downstream effectors, such as phosphoinositide 3-kinase and mitogen-activated protein kinase, in order to elicit cellular responses such as glucose uptake, lipid metabolism and cell proliferation. There are two main IRS proteins in humans (IRS1 and IRS2), both of which are widely expressed. Given their central role in the insulin signalling pathway, it is not surprising that male mice lacking Irs1 or Irs2 present with elevated blood glucose or type 2 diabetes, respectively. For reasons yet to be identified, female Irs2 (-/-) mice do not develop type 2 diabetes. A number of organs are affected by complications of diabetes; macrovascular complications include stroke and coronary artery disease, while nephropathy, neuropathy and retinopathy fall into the category of microvascular complications. Given the serious consequences of these complications on patient morbidity and mortality, it is essential to identify the molecular pathogenesis underlying diabetic complications, with a view to improving therapeutic intervention and patient outcomes. A number of recently published papers have converged on the hypothesis that the loss of insulin signalling and IRS proteins is instrumental to the development and/or progression of diabetic complications. This review will summarise some highlights from the published work in which this hypothesis is discussed.

High fructose-mediated attenuation of insulin receptor signaling does not affect PDGF-induced proliferative signaling in vascular smooth muscle cells

Insulin resistance is associated with accelerated atherosclerosis. Although high fructose is known to induce insulin resistance, it remains unclear as to how fructose regulates insulin receptor signaling and proliferative phenotype in vascular smooth muscle cells (VSMCs), which play a major role in atherosclerosis. Using human aortic VSMCs, we investigated the effects of high fructose treatment on insulin receptor substrate-1 (IRS-1) serine phosphorylation, insulin versus platelet-derived growth factor (PDGF)-induced phosphorylation of Akt, S6 ribosomal protein, and extracellular signal-regulated kinase (ERK), and cell cycle proteins. In comparison with PDGF (a potent mitogen), neither fructose nor insulin enhanced VSMC proliferation and cyclin D1 expression. d-[¹⁴C(U)]fructose uptake studies revealed a progressive increase in fructose uptake in a time-dependent manner. Concentration-dependent studies with high fructose (5-25mM) showed marked increases in IRS-1 serine phosphorylation, a key adapter protein in insulin receptor signaling. Accordingly, high fructose treatment led to significant diminutions in insulin-induced phosphorylation of downstream signaling components including Akt and S6. In addition, high fructose significantly diminished insulin-induced ERK phosphorylation. Nevertheless, high fructose did not affect PDGF-induced key proliferative signaling events including phosphorylation of Akt, S6, and ERK and expression of cyclin D1 protein. Together, high fructose dysregulates IRS-1 phosphorylation state and proximal insulin receptor signaling in VSMCs, but does not affect PDGF-induced proliferative signaling. These findings suggest that systemic insulin resistance rather than VSMC-specific dysregulation of insulin receptor signaling by high fructose may play a major role in enhancing atherosclerosis and neointimal hyperplasia.

Expression and correlation of sex hormone-binding globulin and insulin signal transduction and glucose transporter proteins in gestational diabetes mellitus placental tissue

OBJECTIVE

The aim of the present study was to investigate the probable pathogenesis of gestational diabetes mellitus (GDM) by analyzing the correlation between sex hormone-binding globulin (SHBG) secreted by the placenta during pregnancy and insulin signaling components and glucose transporter proteins (GLUTs) in the placental tissue.

DESIGN AND METHODS

Placental tissue was collected from full-term and non-obese [body mass index <25kg/m(2)] pregnant women; 10 diagnosed with GDM and 10 with normal pregnancy. We used real-time polymerase chain reaction (PCR), immunohistochemistry and western blotting to detect expression of protein and mRNA of SHBG and insulin signaling components and GLUTs in placental tissue.

RESULTS

In the placental tissue of non-obese women, there was a decrease in expression of SHBG protein and mRNA, with a concurrent decrease in expression of GLUT-4 protein and mRNA in women with GDM compared with normal controls. There was a decrease in GLUT-3 and insulin receptor substrate (IRS)-1 protein expression and lower IRS-2 mRNA expression was also observed in GDM placental tissue. Linear correlation analyses showed a positive correlation between SHBG and IRS-2 mRNA (P=0.038, R(2)=0.2178, y=0.249x+1.4208); positive correlation between SHBG and phosphatidylinositol 3-kinase (PI3K) p85α mRNA (P=0.035, R(2)=0.224, y=0.3506x+0.7433); positive correlation between SHBG and GLUT-4 mRNA (P=0.000, R(2)=0.5174, y=1.3822+1.7811x); positive correlation between IRS-2 and GLUT-4 mRNA (P=0.002, R(2)=0.4064, y=-0.8272+2.9592x); negative correlation between IRS-1 and PI3K p85α mRNA (P=0.005, R(2)=0.366, y=2.4492-0.1929x); negative correlation between IRS-1 and GLUT-3 mRNA (P=0.027, R(2)=0.243, y=0.9254-0.0714x); and positive correlation between IRS-2 and GLUT-1 mRNA (P=0.004, R(2)=0.3794, y=0.0225+0.6298x).

CONCLUSION

The results confirm that defective receptors for insulin signal transduction and GLUT proteins are present in GDM placental tissue. Decreasing expression of SHBG may participate in regulation of insulin signaling, leading to a concomitant decrease in expression of relevant insulin signaling components in placental tissue, implying insulin resistance and eventual development of GDM.

LncRNA NONRATT021972 siRNA rescued decreased heart rate variability in diabetic rats in superior cervical ganglia

Diabetic cardiac autonomic neuropathy (DCAN) is a serious and common complication in diabetes mellitus (DM). Long noncoding RNAs (lncRNAs), an important class of regulatory molecules in diverse biological processes, have attracted considerable interest in DCAN. Our previous study has indicated a lncRNA, NONRATT021972 (NONCODE ID), was enhanced in sympathetic neuronal-like PC12 cells in the setting of high glucose (HG) and high FFAs (HF); its silence was found to significantly alleviate HGHF-induced tumor necrosis factor-α (TNF-α) release in PC12 cells. Here we further explore the effects of NONRATT021972 small interference RNA (siRNA) on heart rate variability (HRV) mediated by superior cervical ganglia (SCG) in diabetic rats and the possible mechanism underlying. We found an increment of NONRATT021972 in SCG of DM rats. Treatment of NONRATT021972 siRNA in DM rats decreased the elevated expression of TNF-α, blocked serine phosphorylation of insulin receptor substrate (IRS) 1 and increased the down-regulated expression of IRS1 in SCG. Meanwhile, NONRATT021972 siRNA rescued decreased HRV in DM rats. Therefore, inhibition of NONRATT021972 may serve as a novel therapeutic strategy for preventing the development of DCAN.

Exercise and dietary change ameliorate high fat diet induced obesity and insulin resistance via mTOR signaling pathway

[Purpose]

The purpose of this study was to investigate the effect of exercise and dietary change on obesity and insulin resistance and mTOR signaling protein levels in skeletal muscles of obese rats.

[Methods]

Sixty male Sprague-Dawley rats were divided into CO (Normal diet) and HF (High Fat diet) groups in order to induce obesity for 15 weeks. The rats were then subdivided into CO, COT (CO + Training), HF, HFT (HF + Training), HFND (Dietary change), and HFNDT (HFND + Training) groups (10 rats / group). The training groups underwent moderate-intensity treadmill exercise for 8 weeks, after which soleus muscles were excised and analyzed. Data was statistically analyzed by independent t-test and One-way ANOVA tests with a 0.05 significance level.

[Results]

Fasting blood glucose, plasma insulin, and HOMA-IR in the HF group were significantly higher, as compared with other groups (p <.05). Protein levels of insulin receptor subunit-1 (IRS-1), IRS-2, and p-Akt were significantly higher in the HFT, HFND, and HFNDT groups, as compared with HF group. In addition, the protein levels of the mammalian target of rapamycin complex 1 (mTORC1) and ribosomal S6 protein kinase 1 were significantly decreased by exercise and dietary change (p <.05). However, mTORC2 and phosphoinositide 3-kinase were significantly increased (p <.05).

[Conclusion]

In summary, despite the negative impact of continuous high fat intake, regular exercise and dietary change showed a positive effect on insulin resistance and mTOR signaling protein levels.

Impact of insulin-like growth factor 2, insulin-like growth factor receptor 2, insulin receptor substrate 2 genes polymorphisms on susceptibility and clinicopathological features of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the major causes of cancer-related death worldwide. Insulin-like growth factor-2 (IGF-2) is an important autocrine and paracrine growth factor which may induce cell proliferation and inhibit cell apoptosis leading to the transformation of normal cells into malignant cells. This study aimed to evaluate the possible roles of IGF-2, insulin-like growth factor-2 receptor (IGF-2R), and insulin receptor substrate (IRS)-2 genes polymorphisms in susceptibility and clinicopathological features of HCC in Egyptian population.

MATERIALS AND METHODS

Four hundred and twenty-six HCC patients and 334 controls were enrolled in the study. Polymorphisms of IGF-2+3580, IGF-2+3123, IGF-2R 1619, and IRS-2 1057 gene were detected using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). Serum IGF-2 were determined using ELISA.

RESULTS

Serum IGF-2 levels were significantly lower in HCC patients than in healthy controls. IGF-2+3580 AA genotype, IGF-2+3123 GG genotype or G allele, IRS-2 1057 DD genotype and D allele were significantly associated with HCC risk. The combination of IGF-2+3580 AA homozygosity and IGF-2R 1619 GG homozygosity presented a significant protective effect against HCC (OR=0.16,95% CI=0. 08-0.34, P=0. 005). Serum IGF-2 concentrations were significantly increased in HCC patients with the IGF-2+3580 AA genotype. We also observed that increased alpha-fetoprotein (AFP), Child-Pugh grade, tumor size, and number of malignant lesions were accompanied by a significant increase of serum IGF-2 mean values of in HCC patients.

CONCLUSION

IGF-2, IGF-2R, and IRS-2 genes polymorphisms and their combinations are associated with risk of HCC.

Aspp2 negatively regulates body growth but not developmental timing by modulating IRS signaling in zebrafish embryos

The growth and developmental rate of developing embryos and fetus are tightly controlled and coordinated to maintain proper body shape and size. The insulin receptor substrate (IRS) proteins, key intracellular transducers of insulin and insulin-like growth factor signaling, play essential roles in the regulation of growth and development. A short isoform of apoptosis-stimulating protein of p53 2 (ASPP2) was recently identified as a binding partner of IRS-1 and IRS-2 in mammalian cells in vitro. However, it is unclear whether ASPP2 plays any role in vertebrate embryonic growth and development. Here, we show that zebrafish Aspp2a and Aspp2b negatively regulate embryonic growth without affecting developmental rate. Human ASPP2 had similar effects on body growth in zebrafish embryos. Aspp2a and 2b inhibit Akt signaling. This inhibition was reversed by coinjection of myr-Akt1, a constitutively active form of Akt1. Zebrafish Aspp2a and Aspp2b physically bound with Irs-1, and the growth inhibitory effects of ASPP2/Aspp2 depend on the presence of their ankyrin repeats and SH3 domains. These findings uncover a novel role of Aspp2 in regulating vertebrate embryonic growth.

Distinctive microRNA signature associated of neoplasms with the Wnt/β-catenin signaling pathway

As the crucial biological regulators, microRNAs that act by suppressing their target genes are involved in a variety of pathophysiological processes. It is generally accepted that microRNAs are often dysregulated in many types of neoplasm and other human diseases. In neoplasm, microRNAs may function as oncogenes or tumor suppressors. As constitutive activation of the Wnt signaling pathway is a common feature of neoplasm and contributes to its development, progression and metastasis in various cancers, numerous studies have revealed that microRNA-mediated gene regulation are interconnected with the Wnt/β-catenin signaling pathway, forming a Wnt/β-catenin-microRNA regulatory network, which is critical to successful targeting of the Wnt/β-catenin pathway for oncotherapy. In this review, we aim to accumulate recent advances on microRNAs that work in tandem with Wnt/β-catenin signaling in tumorigenesis, with particular focus on how microRNAs affect Wnt/β-catenin activity as well as how microRNAs are regulated through the Wnt/β-catenin pathway.

Distinctive microRNA signature associated of neoplasms with the Wnt/β-catenin signaling pathway

As the crucial biological regulators, microRNAs that act by suppressing their target genes are involved in a variety of pathophysiological processes. It is generally accepted that microRNAs are often dysregulated in many types of neoplasm and other human diseases. In neoplasm, microRNAs may function as oncogenes or tumor suppressors. As constitutive activation of the Wnt signaling pathway is a common feature of neoplasm and contributes to its development, progression and metastasis in various cancers, numerous studies have revealed that microRNA-mediated gene regulation are interconnected with the Wnt/β-catenin signaling pathway, forming a Wnt/β-catenin-microRNA regulatory network, which is critical to successful targeting of the Wnt/β-catenin pathway for oncotherapy. In this review, we aim to accumulate recent advances on microRNAs that work in tandem with Wnt/β-catenin signaling in tumorigenesis, with particular focus on how microRNAs affect Wnt/β-catenin activity as well as how microRNAs are regulated through the Wnt/β-catenin pathway.

Recent advances in understanding the anti-diabetic actions of dietary flavonoids

Flavonoids are polyphenolic compounds that are abundant in fruits and vegetables, and increasing evidence demonstrates a positive relationship between consumption of flavonoid-rich foods and disease prevention. Epidemiological, in vitro and animal studies support the beneficial effects of dietary flavonoids on glucose and lipid homeostasis. It is encouraging that the beneficial effects of some flavonoids are at physiological concentrations and comparable to clinically-used anti-diabetic drugs; however, clinical research in this field and studies on the anti-diabetic effects of flavonoid metabolites are limited. Flavonoids act on various molecular targets and regulate different signaling pathways in pancreatic β-cells, hepatocytes, adipocytes and skeletal myofibers. Flavonoids may exert beneficial effects in diabetes by (i) enhancing insulin secretion and reducing apoptosis and promoting proliferation of pancreatic β-cells; (ii) improving hyperglycemia through regulation of glucose metabolism in hepatocytes; (iii) reducing insulin resistance, inflammation and oxidative stress in muscle and fat and (iv) increasing glucose uptake in skeletal muscle and white adipose tissue. This review highlights recent findings on the anti-diabetic effects of dietary flavonoids, including flavan-3-ols, flavanones, flavonols, anthocyanidins, flavones and isoflavones, with particular emphasis on the studies that investigated the cellular and molecular mechanisms involved in the beneficial effects of the compounds.

Insulin receptor substrate-1 (IRS-1) forms a ribonucleoprotein complex associated with polysomes

Insulin receptor substrates (IRSs) are known to play important roles in mediating intracellular insulin-like growth factors (IGFs)/insulin signaling. In this study, we identified components of messenger ribonucleoprotein (mRNP) as IRS-1-associated proteins. IRS-1 complex formation analysis revealed that IRS-1 is incorporated into the complexes of molecular mass more than 1000 kDa, which were disrupted by treatment with RNase. Furthermore, oligo(dT) beads precipitated IRS-1 from cell lysates, showing that the IRS-1 complexes contained messenger RNA. Taken together with the data that IRS-1 was fractionated into the polysome-containing high-density fractions, we concluded that IRS-1 forms the novel complexes with mRNPs.

Cellular and molecular players in adipose tissue inflammation in the development of obesity-induced insulin resistance

There is increasing evidence showing that inflammation is an important pathogenic mediator of the development of obesity-induced insulin resistance. It is now generally accepted that tissue-resident immune cells play a major role in the regulation of this obesity-induced inflammation. The roles that adipose tissue (AT)-resident immune cells play have been particularly extensively studied. AT contains most types of immune cells and obesity increases their numbers and activation levels, particularly in AT macrophages (ATMs). Other pro-inflammatory cells found in AT include neutrophils, Th1 CD4 T cells, CD8 T cells, B cells, DCs, and mast cells. However, AT also contains anti-inflammatory cells that counter the pro-inflammatory immune cells that are responsible for the obesity-induced inflammation in this tissue. These anti-inflammatory cells include regulatory CD4 T cells (Tregs), Th2 CD4 T cells, and eosinophils. Hence, AT inflammation is shaped by the regulation of pro- and anti-inflammatory immune cell homeostasis, and obesity skews this balance towards a more pro-inflammatory status. Recent genetic studies revealed several molecules that participate in the development of obesity-induced inflammation and insulin resistance. In this review, the cellular and molecular players that participate in the regulation of obesity-induced inflammation and insulin resistance are discussed, with particular attention being placed on the roles of the cellular players in these pathogeneses. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Opioid μ-receptors as new target for insulin resistance

Type-2 diabetes is one of the fastest growing public health problems worldwide resulting from both environmental and genetic factors. Activation of μ-opioid receptor (MOR) could result in reversal of the impairment of insulin-stimulated glucose disposal in genetically obese Zucker rats via exercise training. This improvement of insulin resistance was associated with an elevation of circulating β-endorphin to ameliorate the post-receptor insulin signaling cascade, including downstream effectors of the phosphatidylinositol 3-kinase (PI3-kinase) signaling pathway. In insulin resistant rats, Loperamide treatment effected on the insulin receptor substrate (IRS)-1/PI3-kinase/Akt signaling cascade and subsequent insulin-stimulated glucose transport trafficking on skeletal muscle, which were all suppressed by MOR antagonism. In addition, induction of insulin resistance by the intake of high fructose is more rapid in MOR knockout mice than in wild-type mice. Improvements in insulin sensitivity through the peripheral MOR activation overcoming defects related to the post-receptor in IRS-1-associated PI3-kinase step have been defined. Opioid receptor activation, especially of the μ-subtype, may provide merits in the amelioration of defective insulin action. Atypical zeta (ζ) isoform of protein kinase C serves as a factor that integrates with peripheral MOR pathway and insulin signals for glucose utilization. The developments call new insights into the chemical compounds and/or herbal products that might enhance opioid peptide secretion and/or stimulate MOR in peripheral insulin-sensitive tissues to serve as potential agents or adjuvants for helping the glucose metabolism. In the present review, we update these topics and discuss the concept of targeting peripheral MOR pathway for the treatment of insulin resistance.

IRS1 is highly expressed in localized breast tumors and regulates the sensitivity of breast cancer cells to chemotherapy, while IRS2 is highly expressed in invasive breast tumors

Insulin receptor substrate (IRS) proteins have been shown to play an important role in breast cancer by differentially regulating cancer cell survival, proliferation, and motility. Furthermore, the IL-4-induced tyrosine phosphorylation of the transcription factor STAT6 was shown to protect breast cancer cells from apoptosis. Here, we analyzed human breast cancer tissues for the expression of IRS1, IRS2, STAT6, and tyrosine phosphorylated STAT6 (pSTAT6). We found that IRS1 and pSTAT6 were both highly expressed in ductal carcinoma in situ (DCIS). On the other hand, IRS2 expression was low in DCIS, but increased significantly in relation to tumor invasiveness. We utilized cell lines with disparate IRS1 expression, MDA-MB-231, MCF7, and MCF7 cells with depleted IRS1 due to shRNA lentiviral infection, to examine the role of IRS1 and IRS2 in the responsiveness of breast cancer cells to chemotherapy. We report that high IRS1 sensitized MCF7 cells to specific chemotherapeutic agents. These results suggest that high IRS1 with low IRS2 expression may predict the effectiveness of specific types of chemotherapy in breast cancer.

Reactivation of the insulin-like growth factor-II signaling pathway in human hepatocellular carcinoma

Constitutive activation of the insulin-like growth factor (IGF)-signaling axis is frequently observed in human hepatocellular carcinoma (HCC). Especially the overexpression of the fetal growth factor IGF-II, IGF-Ireceptor (IGF-IR), and cytoplasmic downstream effectors such as insulin-receptor substrates (IRS) contribute to proliferation, anti-apoptosis, and invasive behavior. This review focuses on the relevant alterations in this signaling pathway and independent in vivo models that support the central role IGF-II signaling during HCC development and progression. Since this pathway has become the center of interest as a target for potential anti-cancer therapy in many types of malignancies, various experimental strategies have been developed, including neutralizing antibodies and selective receptor kinase inhibitors, with respect to the specific and efficient reduction of oncogenic IGF-II/IGF-IR-signaling.