Insulin Receptor Substrate 2 Promoter Research Articles

Activation of Wnt/β-catenin signaling restores insulin sensitivity in insulin resistant neurons through transcriptional regulation of IRS-1.

Aberrant expression and phosphorylation of insulin receptor substrate 1 (IRS-1) contribute to brain insulin resistance. However, the underlying mechanism remains elusive. The insulin signaling and Wnt/β-catenin signaling are two critical pathways for normal cellular function, which interact in both peripheral tissues and the brain and may contribute to insulin resistance. In this study, we aimed to investigate the regulation of IRS-1 and its downstream insulin signaling by Wnt/β-catenin signaling in primary neurons. We found that the Wnt agonist Wnt3a enhances the insulin signaling in neurons at the basal state via up-regulation of IRS-1. Moreover, Wnt3a up-regulates IRS-1 expression and effectively ameliorates insulin resistance in rat primary neurons induced by chronic high insulin exposure. The insulin-mediated glucose uptake is also stimulated by Wnt3a at both basal and insulin resistant states. We observed that Wnt activation up-regulates IRS-1 gene transcription and the subsequent protein expression in SH-SY5Y cells and rat primary neurons via different means of Wnt/β-catenin signaling activation, including S33Y β-catenin over-expression, CHIR99021 and Wnt3a treatment. We further clarified the molecular mechanism of IRS-1 transcriptional activation by Wnt/β-catenin signaling. The Wnt transcription factor TCF4 binds to the -529bp to -516bp of the human IRS-1 promoter fragment and activates IRS-1 transcription. Overall, these data suggested that Wnt/β-catenin signaling positively regulates IRS-1 and insulin signaling and protects against insulin resistance in neurons.

TAZ enhances mammary cell proliferation in 3D culture through transcriptional regulation of IRS1

WW domain-containing transcriptional regulator 1 (TAZ) is a transcriptional co-activator and effector of the Hippo signaling pathway. In certain breast cancer subtypes, Hippo signaling is dysregulated leading to activation of TAZ and altered expression of TAZ transcriptional targets. Over the past decade, we and others have found that TAZ transcriptionally regulates genes that affect multiple aspects of breast cancer cell behaviour. However, while cancer cell-intrinsic oncogenic functions of TAZ have emerged, less is known about whether TAZ might also contribute to tumourigenesis by sensitizing tumour cells to factors present in the tumour microenvironment or in systemic circulation. Here, we show that TAZ directly regulates the expression of insulin receptor substrate 1 (IRS1) in breast cancer cells. TAZ or IRS1 overexpression induces a similar proliferative transformation phenotype in MCF10A mammary epithelial cells. TAZ enhances IRS1 mRNA, protein levels and downstream signaling in MCF10A. Mechanistically, TAZ interacts with the IRS1 promoter through the TEAD family of transcription factors and enhances its activity. Critically, TAZ-induced IRS1 upregulation contributes to the proliferation of TAZ-overexpressing MCF10A in 3-dimensional (3D) Matrigel culture. Therefore, we offer compelling evidence that TAZ regulates signaling through the insulin pathway in breast cancer cells. These findings highlight an additional mechanism by which TAZ may promote breast cancer tumourigenesis and progression by modulating cancer cell responses to exogenously produced factors.

Data in support of FSH induction of IRS-2 in human granulosa cells: Mapping the transcription factor binding sites in human IRS-2 promoter.

Insulin receptor substrate-2 (IRS-2) plays critical role in the regulation of various metabolic processes by insulin and IGF-1. The defects in its expression and/or function are linked to diseases like polycystic ovary syndrome (PCOS), insulin resistance and cancer. To predict the transcription factors (TFs) responsible for the regulation of human IRS-2 gene expression, the transcription factor binding sites (TFBS) and the corresponding TFs were investigated by analysis of IRS-2 promoter sequence using MatInspector Genomatix software (Cartharius et al., 2005 [1]). The ibid data is part of author׳s publication (Anjali et al., 2015 [2]) that explains Follicle stimulating hormone (FSH) mediated IRS-2 promoter activation in human granulosa cells and its importance in the pathophysiology of PCOS. Further analysis was carried out for binary interactions of TF regulatory genes in IRS-2 network using Cytoscape software tool and R-code. In this manuscript, we describe the methodology used for the identification of TFBSs in human IRS-2 promoter region and provide details on experimental procedures, analysis method, validation of data and also the raw files. The purpose of this article is to provide the data on all TFBSs in the promoter region of human IRS-2 gene as it has the potential for prediction of the regulation of IRS-2 gene in normal or diseased cells from patients with metabolic disorders and cancer.

Effects of transcription factor sterol regulatory element binding protein-1c in palmitate acid-induced L6 cells insulin resistance and its mechanism

Sterol regulatory element binding protein-1c (SREBP-1c) is a master regulator of fatty acid synthase and controls lipogenesis. And insulin receptor substrate-1 (IRS-1) is a key insulin signaling mediator in skeletal muscle. The present study was conducted to explore the mechanism of SREBP-1c in the regulation of IRS-1 in skeletal muscle cells and elucidate the role of SREBP-1c in high fat-induced skeletal muscle insulin resistance. L6 cells differentiated into myotubes in differentiation medium with 2%FBS. An in vitro insulin resistant model in L6 myotubes was established by 500 µmol/L of palmitate acid (PA). SREBP-1c, p-IRS-1(Tyr608/612), IRS-1, p-AKT (Ser473) and AKT were detected by Western blot after incubating L6 myobutes with 500 µmol/L of PA for 0.5, 1, 3, 6, 12, 18 or 24 h.SREBP-1c, FAS and molecules related to insulin signaling pathway were detected by Western blot when L6 myotubes over-expressed SREBP-1c or after a treatment of liver X receptor (LXR) agonist (TO901317, 5 µmol/L). The regulatory effects of transcription factor SREBP-1c on promoter region of IRS-1 were assessed by dual-luciferase reporter assay. SREBP-1c protein expression increased significantly after 1-hour exposure to PA. The protein levels of p-IRS-1(Tyr608/612),IRS-1 and p-AKt (Ser473) decreased significantly after a 6-hour incubation of PA. However AKT protein levels were unaffected. The protein expressions of SREBP-1c and FAS were up-regulated by LXR agonist treatment versus controls. By contrast, LXR agonist treatment led to decreased expressions of IRS-1, p-IRS-1(Tyr608/612) and p-AKt (Ser473)/AKT proteins versus controls. The expressions of related proteins were similar to the observations made with LXR agonist intervention. The results of dual-luciferase reporter assay indicated that IRS-1 promoter activity was repressed significantly by SREBP-1c over-expression or TO901317 treatment whereas the dominant negative form of SREBP-1c (a mutant of Tyr320Ala lacking the ability of binding DNA) had no effect. SREBP-1c may suppress IRS-1 expression and the subsequent insulin signaling pathway. And it plays a key role in PA-induced insulin resistance of skeletal muscle.

Retinoid X receptor α overexpression alleviates mitochondrial dysfunction-induced insulin resistance through transcriptional regulation of insulin receptor substrate 1.

Mitochondrial dysfunction is associated with insulin resistance and diabetes. We previously showed that retinoid X receptor α (RXRα) played an important role in transcriptional regulation of oxidative phosphorylation (OXPHOS) genes in cells with mitochondrial dysfunction caused by mitochondrial DNA mutation. In this study, we investigated whether mitochondrial dysfunction induced by incubation with OXPHOS inhibitors affects insulin receptor substrate 1 (IRS1) mRNA and protein levels and whether RXRα activation or overexpression can restore IRS1 expression. Both IRS1 and RXRα protein levels were significantly reduced when C2C12 myotubes were treated with the OXPHOS complex inhibitors, rotenone and antimycin A. The addition of RXRα agonists, 9-cis retinoic acid (9cRA) and LG1506, increased IRS1 transcription and protein levels and restored mitochondrial function, which ultimately improved insulin signaling. RXRα overexpression also increased IRS1 transcription and mitochondrial function. Because RXRα overexpression, knock-down, or activation by LG1506 regulated IRS1 transcription mostly independently of mitochondrial function, it is likely that RXRα directly regulates IRS1 transcription. Consistent with the hypothesis, we showed that RXRα bound to the IRS1 promoter as a heterodimer with peroxisome proliferator-activated receptor δ (PPARδ). These results suggest that RXRα overexpression or activation alleviates insulin resistance by increasing IRS1 expression.

FoxO Feedback Control of Basal IRS-2 Expression in Pancreatic β-Cells Is Distinct From That in Hepatocytes

OBJECTIVEAppropriate regulation of insulin receptor substrate 2 (IRS-2) expression in pancreatic β-cells is essential to adequately compensate for insulin resistance. In liver, basal IRS-2 expression is controlled via a temporal negative feedback of sterol regulatory element–binding protein 1 (SREBP-1) to antagonize transcription factors forkhead box class O (FoxO)1/FoxO3a at an insulin response element (IRE) on the IRS-2 promoter. The purpose of the study was to examine if a similar mechanism controlled IRS-2 expression in β-cells.RESEARCH DESIGN AND METHODSIRS-2 mRNA and protein expression, as well as IRS-2 gene promoter activity, were examined in isolated rat islets. Specific transcription factor association with the IRE on the IRS-2 promoter was examined by chromatin immunoprecipitation (ChIP) assay, and their nuclear translocation was examined by immunofluorescence. A direct in vivo effect of insulin on control of IRS-2 expression in liver and pancreatic islets was also investigated.RESULTSIn IRS-2 promoter-reporter assays conducted in isolated islets, removal of the IRE decreased basal IRS-2 promoter activity in β-cells up to 80%. Activation of IRS signaling in isolated rat islets by insulin/IGF-I (used as an experimental in vitro tool) or downstream constitutive activation of protein kinase B (PKB) significantly decreased IRS-2 expression. In contrast, inhibition of phosphatidylinositol 3-kinase (PI3K) or PKB significantly increased IRS-2 levels in β-cells. ChIP assays indicated that transcription factors FoxO1 and FoxO3a associated with the IRE on the IRS-2 promoter in β-cells in a PI3K/PKB–dependent manner, whereas others, such as SREBP-1, the transcription factor binding to immunoglobulin heavy chain enhancer 3′, and the aryl hydrocarbon receptor nuclear translocator (ARNT), did not. However, only FoxO3a, not FoxO1, was capable of driving IRS-2 promoter activity via the IRE in β-cells. In vivo studies showed insulin was able to suppress IRS-2 expression via activation of SREBP-1 in the liver, but this mechanism was not apparent in pancreatic islets from the same animal.CONCLUSIONSThe molecular mechanism for feedback control of IRS signaling to decrease IRS-2 expression in liver and β-cells is quite distinct, with a predominant role played by FoxO3a in β-cells.

Abstract 3291: Upregulation of Insulin Receptor Substrate-2 (IRS-2) expression by hypoxia

Abstract Insulin Receptor Substrate-2 (IRS-2) belongs to the IRS family of cytoplasmic adaptor proteins that mediate signaling from cell surface receptors, including growth factor, cytokine and integrin receptors. Many of these receptors have been implicated in cancer. Although the IRS proteins are highly homologous in structure and have some complementary functions, growing evidence supports that the IRS proteins have unique roles in cancer. IRS-1 has been shown to promote tumor cell proliferation, while IRS-2 has been positively associated with tumor cell motility and invasion. Previously, our lab demonstrated that Polyoma Middle T-derived Irs-2−/− mouse mammary tumors are significantly less metastatic, and Irs-1−/− tumors significantly more metastatic, than their wild-type counterparts. In recent studies, we observed that IRS-2 expression increases in response to hypoxia in both metastatic mouse mammary tumor cells and poorly differentiated ER-negative metastatic human breast carcinoma cells. In contrast, IRS-1 expression does not increase in response to hypoxia, supporting the notion of their non-overlapping functions. Hypoxia promotes the adaptation and resistance of cancer cells to chemo- and radiation therapy, and also promotes tumor cell survival, invasion and metastasis by selecting for aggressive tumor cells that can survive under stressful low oxygen conditions. We have also shown that IRS-2 upregulation in response to hypoxia promotes tumor cell viability and invasion, selecting for tumor cells with increased metastatic potential. To understand how IRS-2 is regulated by hypoxia, we identified a minimal 200 bp region of the IRS-2 promoter located 700 bp upstream from the translation start site that is hypoxia-responsive. Mutation of an E-box binding site within this region that has been previously implicated in regulating IRS-2 in response to hormone stimulation inhibits hypoxic upregulation of IRS-2. We are currently investigating the factors that bind to this E-box to regulate IRS-2 expression. In addition, we have established that HIF is required for IRS-2 upregulation in hypoxic environments, and we are investigating if HIF acts in a direct or indirect manner to regulate IRS-2 expression. Identifying the mechanism by which IRS-2 expression is regulated by hypoxia is essential for developing novel methods to inhibit IRS-2 expression to suppress metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3291.

Transcription factor AP-2β: A negative regulator of IRS-1 gene expression

Down-regulation of insulin receptor substrate-1 (IRS-1) expression could modify the ability of IRS-1 to fulfill its functions. It has been proposed that the phosphorylation of IRS-1 on serine residues could promote its degradation. However, few studies have investigated the transcriptional regulation of IRS-1 in the pathogenesis of insulin resistance. Genotyping for genome-wide single nucleotide polymorphisms revealed that the transcription factor activating enhancer-binding protein-2β (AP-2β) is a novel candidate gene for conferring susceptibility to obesity and type 2 diabetes. AP-2β is expressed in adipose tissue and its expression is increased during the maturation of adipocytes. Overexpression of AP-2β leads to adipocyte hypertrophy, directly inhibits adiponectin expression, and enhanced the expression of inflammatory adipokines such as IL-6 and MCP-1. In this study, we found that overexpression of AP-2β in 3T3-L1 adipocytes impaired the promoter activity of IRS-1, and subsequently decreased mRNA and protein expression. Electrophoretic mobility shift assays showed that AP-2β bound specifically to the IRS-1 promoter region. Furthermore, site-directed mutagenesis of the AP-2 binding site located at −362 to −351, relative to the transcription start site, markedly decreased AP-2-induced suppression of IRS-1 promoter activity, whereas other putative AP-2 binding sites did not. Our results clearly showed that AP-2β directly decreased IRS-1 expression by binding to its promoter. Based on these findings, we speculate that the AP-2β transcriptional factor is a unique regulator of IRS-1 and a candidate gene for insulin resistance.

Neuronal insulin receptor substrate 2 (IRS2) expression is regulated by ZBP89 and SP1 binding to the IRS2 promoter

Since neuronal insulin receptor substrate 2 (IRS2)-mediated signals coordinate key processes in rodent physiology such as food intake, fertility, longevity, and aging-related behavior, we analyzed the mechanisms of neuronal IRS2 expression in neuroblastoma (SHSY5Y) and hypothalamic (GT1-7) cell lines. Using dual luciferase reporter assays and IRS2 promoter deletion constructs, we identified a regulatory cassette within the IRS2 promoter between -779 and -679 bp from the translational start which is responsible for approximately 50% of neuronal IRS2 promoter activity. Chromatin immunoprecipitation assays and electromobility shift assay revealed four overlapping ZBP89/specificity protein 1 (SP1) binding sites which alternatively bind to ZBP89 (ZNF148 as listed in the HUGO Database) or SP1. Activation of this cassette is inhibited by phosphoinositide-3-kinase (PI3K) via increased ZBP89 binding to the promoter. Serum starvation caused increased SP1 binding at one specific SP1 site and decreased binding to another, proving a regulatory interaction between the different binding sites within this promoter cassette to tightly control IRS2 expression. Mutants containing all the possible combinations of one, two, three, or all the four SP1 binding sites of the IRS2 promoter revealed that SP1 binding to one particular site is most important for promoter activation. Stable downregulation of ZBP89 using siRNA substantially increased IRS2 mRNA and protein expression. Thus, alternative binding of ZBP89 or SP1 to the described region in the IRS2 promoter regulates neuronal IRS2 expression in a PI3K-dependent manner.

Expression and localisation of insulin receptor substrate 2 in normal intestine and colorectal tumours. Regulation by intestine-specific transcription factor CDX2

Background and aims:Self-renewal and differentiation of intestinal epithelium is a tightly regulated process, whose perturbations are implicated in human colorectal tumourigenesis. The insulin/insulin-like growth factor (IGF) signalling pathway may play...

The Repression of IRS2 Gene by ATF3, a Stress-Inducible Gene, Contributes to Pancreatic β-Cell Apoptosis

beta-Cell failure is an essential component of all types of diabetes, and the insulin receptor substrate 2 (IRS2) branch of signaling plays a key role in beta-cell survival and function. We tested the hypothesis that activating transcription factor 3 (ATF3), a stress-inducible proapoptotic gene, downregulates the expression of IRS2 in beta-cells. We used both the gain- and loss-of-function approaches to test the effects of ATF3 on IRS2 gene expression. We also analyzed the binding of ATF3 to the IRS2 promoter by chromatin immunoprecipitation assay and the transcription of the IRS2 gene by polymerase II occupancy assay. Furthermore, we tested the ability of IRS2 to alleviate the proapoptotic effects of ATF3 in cultured beta-cells and in transgenic mice using the rat insulin promoter to drive the transgenes. Expression of ATF3 is sufficient to reduce IRS2 gene expression; in contrast, knockdown or knockout of ATF3 reduces the ability of stress signals to downregulate IRS2 expression. ATF3 binds to the IRS2 promoter in vivo, and the binding of ATF3 correlates with decreased IRS2 gene transcription. Functionally, expression of IRS2 protects beta-cells from ATF3-induced apoptosis. IRS2 is a target gene of ATF3, and its repression by ATF3 contributes, at least partly, to the apoptosis induced by ATF3. Because ATF3 is a stress-inducible gene, our work provides a direct link to explain how environmental stress factors can modulate IRS2 gene transcription.

Evidence that the mouse insulin receptor substrate-1 belongs to the gene family on which the promoter is activated by estrogen receptor α through its interaction with Sp1

In the present study, the molecular mechanism underlying the up-regulatory effect of estradiol (E2) on mouse insulin receptor substrate-1 (IRS-1) promoter was investigated in CHO cells on which the same promoter had first been functionally characterized. The mouse IRS-1 promoter bears four consensus half Estrogen Responsive Elements (ERE) sequences and thirteen AP-1- and ten Sp1-binding elements. We performed molecular dissection of this promoter gene providing 3' different deleted constructs, containing the same AP-1 rich region with a progressively increased number of ERE half sites located downstream. None of these constructs was responsive to E2, while a downstream region (nt -1420 to -160) rich in GC elements was induced by E2. However, the latter region lost its intrinsic E2 responsiveness when the whole IRS-1 promoter was mutated for deletion in all four ERE half sites. Deletion analysis of the ERE half sites demonstrated that only ERE located at the position -1500 to -1495, close to the GC-rich region, was able to maintain the induced activatory effect of E2 on the IRS-1 gene. Electrophoretic mobility shift and chromatin immunoprecipitation assays identified the region containing the half ERE/Sp1 (nt -1500 to -1477) as the one conferring E2 responsiveness to the whole promoter. This effect occurs through the functional interaction between E2/ERalpha and Sp1.

SREBPs suppress IRS-2-mediated insulin signalling in the liver.

Insulin receptor substrate 2 (IRS-2) is the main mediator of insulin signalling in the liver, controlling insulin sensitivity. Sterol regulatory element binding proteins (SREBPs) have been established as transcriptional regulators of lipid synthesis. Here, we show that SREBPs directly repress transcription of IRS-2 and inhibit hepatic insulin signalling. The IRS-2 promoter is activated by forkhead proteins through an insulin response element (IRE). Nuclear SREBPs effectively replace and interfere in the binding of these transactivators, resulting in inhibition of the downstream PI(3)K/Akt pathway, followed by decreased glycogen synthesis. These data suggest a molecular mechanism for the physiological switching from glycogen synthesis to lipogenesis and hepatic insulin resistance that is associated with hepatosteatosis.

Identification of a single nucleotide polymorphism showing no insulin-mediated suppression of the promoter activity in the human insulin receptor substrate 2 gene.

To understand the transcriptional regulation and to investigate the pathological influence upon Type II (non-insulin-dependent) diabetes mellitus of insulin receptor substrate 2 ( IRS2), the 5' flanking region of the human IRS2 gene was cloned and screened in Japanese diabetic patients. Luciferase reporter assay and electrophoretic mobility shift assay (EMSA) were combined in HepG2, Fao, RINm5F, and HeLa cells to characterise the human IRS2 promoter region. Single nucleotide polymorphisms (SNPs) were identified in Japanese Type II diabetic patients by sequencing and were genotyped. The proximal 2399 bp of the 5' flanking region of the human IRS2 gene was cloned. A core promoter region was extended between nucleotide positions -834 and -557 (relative to the translation initiation site). The region [(-758)AGGGGGAGGG(-749)] that appears important in the positive regulation of IRS2transcription was identified by EMSA with (32)P-labelled double-stranded oligonucleotides encompassing regions protected from DNase I digestion by nuclear extract of HepG2 cells. Two SNPs (-765 C/ T and -2062 T/ C), identified by screening Japanese Type II diabetic patients, were not associated with Type II diabetes. IRS2-driven reporter activity in the plasmid containing thymine at -765 was not suppressed by insulin when measured in Fao cells. The 5' flanking sequence of the human IRS2 was investigated and two SNPs were identified. The SNP at -765 was suggested to be involved in the insulin-mediated regulation of the transcriptional activity of IRS2.

Cell-specific regulation of IRS-1 gene expression: role of E box and C/EBP binding site in HepG2 cells and CHO cells.

Insulin receptor substrate 1 (IRS-1) is one of the major substrates of insulin receptor tyrosine kinase and mediates multiple insulin signals downstream. We have previously shown that the levels of IRS-1 mRNA varied in different tissues. To elucidate the molecular mechanisms of the tissue specific regulation of IRS-1, we have studied the cis-acting elements and transacting factors in CHO and HepG2 cells. Using the chloramphenicol acetyltransferase (CAT) assay with the various deletion mutants of the IRS-1 promoter-CAT fusion plasmids, several regions responsible for positive or negative regulation in each cell line were identified. A region from -1645 to -1585 bp, which regulated expression negatively in CHO cells and positively in HepG2 cells, was further analyzed. Within this region a fragment from -1645 to -1605 bp upregulated the IRS-1 promoter only in HepG2 cells, whereas a fragment from -1605 to -1585 bp downregulated only in CHO cells. In the gel mobility shift assay, several nuclear proteins that bind to these fragments were detected, and among them, two nuclear proteins that bind to a potential E box (nucleotide [nt] -1635 to -1630) and two nuclear proteins that bind to a potential C/EBP binding site (nt -1599 to -1591) were identified in HepG2 and CHO cells, respectively. CAT assays using promoters mutated at the E box or at the C/EBP binding site revealed that these sequences were responsible for cell-specific regulation of the IRS-1 gene. We therefore concluded that the two nuclear proteins that bind to the E box regulate IRS-1 gene expression positively in HepG2 cells and the two nuclear proteins that bind to the C/EBP binding site regulate it negatively in CHO cells.