Insulin receptor substrate 1, but not IRS2, plays a dominant role in regulating pancreatic alpha cell function in mice.

Dysregulated glucagon secretion deteriorates glycemic control in type 1 and type 2 diabetes. Although insulin is known to regulate glucagon secretion via its cognate receptor (insulin receptor, INSR) in pancreatic alpha cells, the role of downstream proteins and signaling pathways underlying insulin's activities are not fully defined. Using in vivo (knockout) and in vitro (knockdown) studies targeting insulin receptor substrate (IRS) proteins, we compared the relative roles of IRS1 and IRS2 in regulating alpha cell function. Alpha cell-specific IRS1-knockout mice exhibited glucose intolerance and inappropriate glucagon suppression during glucose tolerance tests. In contrast, alpha cell-specific IRS2-knockout animals manifested normal glucose tolerance and suppression of glucagon secretion after glucose administration. Alpha cell lines with stable IRS1 knockdown could not repress glucagon mRNA expression and exhibited a reduction in phosphorylation of AKT Ser/Thr kinase (AKT, at Ser-473 and Thr-308). AlphaIRS1KD cells also displayed suppressed global protein translation, including reduced glucagon expression, impaired cytoplasmic Ca2+ response, and mitochondrial dysfunction. This was supported by the identification of novel IRS1-specific downstream target genes, Trpc3 and Cartpt, that are associated with glucagon regulation in alpha cells. These results provide evidence that IRS1, rather than IRS2, is a dominant regulator of pancreatic alpha cell function.

Insulin resistance disrupts epithelial repair and niche-progenitor Fgf signaling during chronic liver injury.

Insulin provides important information to tissues about feeding behavior and energy status. Defective insulin signaling is associated with ageing, tissue dysfunction, and impaired wound healing. In the liver, insulin resistance leads to chronic damage and fibrosis, but it is unclear how tissue-repair mechanisms integrate insulin signals to coordinate an appropriate injury response or how they are affected by insulin resistance. In this study, we demonstrate that insulin resistance impairs local cellular crosstalk between the fibrotic stroma and bipotent adult liver progenitor cells (LPCs), whose paracrine interactions promote epithelial repair and tissue remodeling. Using insulin-resistant mice deficient for insulin receptor substrate 2 (Irs2), we highlight dramatic impairment of proregenerative fibroblast growth factor 7 (Fgf7) signaling between stromal niche cells and LPCs during chronic injury. We provide a detailed account of the role played by IRS2 in promoting Fgf7 ligand and receptor (Fgfr2-IIIb) expression by the two cell compartments, and we describe an insulin/IRS2-dependent feed-forward loop capable of sustaining hepatic re-epithelialization by driving FGFR2-IIIb expression. Finally, we shed light on the regulation of IRS2 and FGF7 within the fibrotic stroma and show-using a human coculture system-that IRS2 silencing shifts the equilibrium away from paracrine epithelial repair in favor of fibrogenesis. Hence, we offer a compelling insight into the contribution of insulin resistance to the pathogenesis of chronic liver disease and propose IRS2 as a positive regulator of communication between cell types and the transition between phases of stromal to epithelial repair.

Insulin receptor substrate-1 inhibits high-fat diet-induced obesity by browning of white adipose tissue through miR-503.

Genetic variation of insulin receptor substrate 1 (IRS-1) was found to modulate the insulin resistance of adipose tissues, but the underlying mechanism was not clear. To investigate how the IRS-1 was involved in the browning of white adipose tissue through miRNA, we identified a mutated Irs-1 (Irs-1-/- ) mice model and found that this mice had a reduced subcutaneous WAT (sWAT) and increased brown adipose tissue (BAT) in the interscapular region. So we isolated the bone marrow stromal cells and analyzed differentially expressed miRNAs and adipogenesis-related genes with miRNA arrays and PCR arrays. Irs-1-/- mice showed decreased miR-503 expression, but increased expression of its target, bone morphogenetic protein receptor type 1a (BMPR1a). Overexpression of miR-503 in preadipocytes downregulated BMPR1a and impaired adipogenic activity through the phosphotidylinositol 3-kinase (PI3K/Akt) pathway, while the inhibitor had the opposite effect. In both Irs-1-/- and cold-induced models, sWAT exhibited BAT features, and showed tissue-specific increased BMPR1a expression, PI3K expression, and Akt phosphorylation. Thus, our results showed that IRS-1 regulated brown preadipocyte differentiation and induced browning in sWAT through the miR-503-BMPR1a pathway, which played important roles in high-fat diet-induced obesity.

Ablation of insulin receptor substrates 1 and 2 suppresses Kras-driven lung tumorigenesis.

Non-small-cell lung cancer (NSCLC) is a leading cause of cancer death worldwide, with 25% of cases harboring oncogenic Kirsten rat sarcoma (KRAS). Although KRAS direct binding to and activation of PI3K is required for KRAS-driven lung tumorigenesis, the contribution of insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1R) in the context of mutant KRAS remains controversial. Here, we provide genetic evidence that lung-specific dual ablation of insulin receptor substrates 1/2 (Irs1/Irs2), which mediate insulin and IGF1 signaling, strongly suppresses tumor initiation and dramatically extends the survival of a mouse model of lung cancer with Kras activation and p53 loss. Mice with Irs1/Irs2 loss eventually succumb to tumor burden, with tumor cells displaying suppressed Akt activation and strikingly diminished intracellular levels of essential amino acids. Acute loss of IRS1/IRS2 or inhibition of IR/IGF1R in KRAS-mutant human NSCLC cells decreases the uptake and lowers the intracellular levels of amino acids, while enhancing basal autophagy and sensitivity to autophagy and proteasome inhibitors. These findings demonstrate that insulin/IGF1 signaling is required for KRAS-mutant lung cancer initiation, and identify decreased amino acid levels as a metabolic vulnerability in tumor cells with IR/IGF1R inhibition. Consequently, combinatorial targeting of IR/IGF1R with autophagy or proteasome inhibitors may represent an effective therapeutic strategy in KRAS-mutant NSCLC.

AMPK-mediated activation of Akt protects renal tubular cells from stress-induced apoptosis in vitro and ameliorates ischemic AKI in vivo.

We have reported that preconditioning renal tubular cells (RTCs) with A-769662 [a pharmacological activator of AMP-activated protein kinase (AMPK)] reduces apoptosis of RTCs induced by subsequent stress and ameliorates the severity of ischemic acute kidney injury (AKI) in mice. In the present study, we examined the role of the phosphoinositide 3-kinase (PI3K)/Akt pathway in mediating these effects. Using shRNA, we developed knockdown (KD) RTCs to confirm that any novel effects of A-769662 are mediated specifically by AMPK. We reduced expression of the total ß-domain of AMPK in KD RTCs by >80%. Control RTCs were transfected with "scrambled" shRNA. Preconditioning control RTCs with A-769662 increased both the phosphorylation (activity) of AMPK and survival of these cells when exposed to subsequent stress, but neither effect was observed in KD cells. These data demonstrate that activation of AMPK by A-769662 is profoundly impaired in KD cells. A-769662 activated PI3K and Akt in control but not KD RTCs. These data provide novel evidence that activation of the PI3K/Akt pathway by A-769662 is mediated specifically through activation of AMPK and not by a nonspecific mechanism. We also demonstrate that, in control RTCs, Akt plays a role in mediating the antiapoptotic effects of A-769662. In addition, we provide evidence that AMPK ameliorates the severity of ischemic AKI in mice and that this effect is also partially mediated by Akt. Finally, we provide evidence that AMPK activates PI3K by inhibiting mechanistic target of rapamycin complex 1 and preventing mechanistic target of rapamycin complex 1-mediated inhibition of insulin receptor substrate-1-associated activation of PI3K.

Sequential testicular atrophy involves changes in cellular proliferation and apoptosis associated with variations in aromatase P450 expression levels in Irs-2-deficient mice.

Insulin receptor substrate 2 (Irs-2) is an intracellular protein susceptible to phosphorylation after activation of the insulin receptor. Its suppression affects testis development and its absence induces peripheral resistance to insulin. The aim of this study was to identify changes induced by the deletion of Irs-2 in the testicular structure and by the altered expression of cytochrome P450 aromatase, a protein necessary for the development and maturation of germ cells. Adult knockout (KO) mice (Irs-2-/- , 6 and 12 weeks old) and age-matched wild-type (WT) mice were used in this study. Immunohistochemistry and Western blot analyses were performed to study proliferation (PCNA), apoptosis (active caspase-3) and P450 aromatase expression in testicular histological sections. Deletion of Irs-2 decreased the number of epithelial cells in the seminiferous tubule and rete testis. Aberrant cells were frequently detected in the epithelia of Irs-2-/- mice, accompanied by variations in spermatogonia, which were shown to exhibit small hyperchromatic nuclei as well as polynuclear and anuclear structures. The amount of cell proliferation was significantly lower in Irs-2-/- mice than in WT mice, whereas apoptotic processes were more common in Irs-2-/- mice. Aromatase P450 reactivity was higher in 6-week-old KO mice than in WT mice of the same age and was even higher at 12 weeks. Our results suggest that Irs-2 is a key element in spermatogenesis because silencing Irs-2 induces the sequential development of testicular atrophy. The effects are observed mainly in germ cells present in the seminiferous tubule, which may be due to changes in cytochrome P450 aromatase expression.

[miR-494-3p reduces insulin sensitivity in diabetic cardiomyocytes by down-regulation of insulin receptor substrate 1].

More and more evidence suggests that microRNA is widely involved in the regulation of cardiovascular function. Our preliminary experiment showed that miR-494-3p was increased in heart of diabetic rats, and miR-494-3p was reported to be related to metabolism such as obesity and exercise. Therefore, this study was aimed to explore the role of miR-494-3p in diabetic myocardial insulin sensitivity and the related mechanism. The diabetic rat model was induced by high fat diet (45 kcal% fat, 12 weeks) combined with streptozotocin (STZ, 30 mg/kg), and cardiac tissue RNA was extracted for qPCR. The results showed that the level of miR-494-3p was significantly up-regulated in the myocardium of diabetic rats compared with the control (P < 0.05). The level of miR-494-3p in H9c2 cells cultured in high glucose and high fat medium (HGHF) was significantly increased (P < 0.01) with the increase of sodium palmitate concentration, whereas down-regulation of miR-494-3p in HGHF treated cells led to an increase in insulin-stimulated glucose uptake (P < 0.01) and the ratio of p-Akt/Akt (P < 0.05). Over-expression of miR-494-3p in H9c2 cell line significantly inhibited insulin-stimulated glucose uptake and phosphorylation of Akt (P < 0.01). Bioinformatics combined with Western blotting experiments confirmed insulin receptor substrate 1 (IRS1) as a target molecule of miR-494-3p. These results suggest that miR-494-3p reduces insulin sensitivity in diabetic cardiomyocytes by down-regulating IRS1.

Inhibition of p53 Relieves Insulin Resistance in Fetal Growth Restriction Mice with Catch-Up Growth via Activating IGFBP3/IGF-1/IRS-1/Akt Signaling Pathway.

To investigate insulin resistance of the fetal growth restriction (FGR) mice with catch-up growth (CUG) and the underlying mechanism, in this study, low protein diet was used during pregnancy to establish the FGR mice model, and high fat diet was applied to establish the CUG model of FGR mice. The insulin and Pifithrin-α stimulation was performed via intraperitoneal injection. The physical characters, biochemical parameters, expression of related molecules in each group were detected via ELISA, RT-PCR, WB, etc. The results showed FBG, FINS and HOAM-IR in CUG-FGR group were higher than those in high fat feeding control group (NC+HF), but the content of IGF-1 in blood was lower than that in NC + HF group. Meanwhile, RT-PCR and WB showed that the expression of IGF was negatively correlated with the expression of P53/IGFBP3. Moreover, the expression of P-IRS/p-PI3K/p-Akt decreased with the increasing of HOAM-IR in IGF signaling pathway. When the mice were injected with Pifithrin-α, the phosphorylation level of IGF signaling pathway and insulin resistance index in the CUG-FGR group were increased and decreased, respectively. In conclusion, insulin resistance in CUG-FGR mice is correlated with the IGFBP3/IGF-1/IRS-1/Akt signaling pathway and inhibited p53 could activate this signaling pathway and relieve insulin resistance.

IRS2 and PTEN are key molecules in controlling insulin sensitivity in podocytes.

Insulin signaling to the glomerular podocyte is important for normal kidney function and is implicated in the pathogenesis of diabetic nephropathy (DN). This study determined the role of the insulin receptor substrate 2 (IRS2) in this system. Conditionally immortalized murine podocytes were generated from wild-type (WT) and insulin receptor substrate 2-deficient mice (Irs2(-/-)). Insulin signaling, glucose transport, cellular motility and cytoskeleton rearrangement were then analyzed. Within the glomerulus IRS2 is enriched in the podocyte and is preferentially phosphorylated by insulin in comparison to IRS1. Irs2(-/-) podocytes are significantly insulin resistant in respect to AKT signaling, insulin-stimulated GLUT4-mediated glucose uptake, filamentous actin (F-actin) cytoskeleton remodeling and cell motility. Mechanistically, we discovered that Irs2 deficiency causes insulin resistance through up-regulation of the phosphatase and tensin homolog (PTEN). Importantly, suppressing PTEN in Irs2(-/-) podocytes rescued insulin sensitivity. In conclusion, this study has identified for the first time IRS2 as a critical molecule for sensitizing the podocyte to insulin actions through its ability to modulate PTEN expression. This finding reveals two potential molecular targets in the podocyte for modulating insulin sensitivity and treating DN.

Effect of mulberry leaf (Folium Mori) on insulin resistance via IRS-1/PI3K/Glut-4 signalling pathway in type 2 diabetes mellitus rats.

CONTEXT: Folium Mori, the leaf of Morus alba L. (Moraceae), has been used in traditional Chinese medicine (TCM) for treating diabetes. However, it is unclear which components in the mulberry leaf are effective for the treatment of type 2 diabetes mellitus (T2DM). OBJECTIVE: To investigate the flavonoids and polyphenols in mulberry leaves and their antihyperglycemic and antihyperlipidemic effects in T2DM rats. MATERIALS AND METHODS: Male Sprague-Dawley rats were divided into five groups: normal control (NC), diabetic control (DBC), diabetic group with 0.3 mg/kg b.w./day rosiglitazone (RSG), diabetic group with 7 g/kg b.w./day TCM formula and diabetic group with 2 g/kg b.w./day Folium Mori extract (FME). After 4 weeks, the rats were sacrificed; biochemical parameters, gene and protein expression were measured. RESULTS: The FBG level was significantly lower in the FME group than in the DBC group (p < 0.05). In oral glucose tolerance test, the AUC was significantly lower in the FME group (p < 0.05). The HOMA-IR level was significantly decreased in the FME group (p < 0.05). FME decreased the total cholesterol (TC), triglyceride (TG) and low density lipoprotein (LDL) levels (p < 0.05). FME increased the mRNA and protein expression of IRS-1, PI3K p85α and Glut-4 increased significantly (p < 0.05). Histological analysis revealed amelioration of lipid accumulation following FME treatment. Additionally, immunohistochemical analysis displayed stronger staining of Glut-4 in the FME group compared to the DBC group. DISCUSSION AND CONCLUSION: FME could decrease the body weight, blood glucose, TG, TC and LDL levels, and improve insulin resistance. FME possessed significant antihyperglycemic and antihyperlipidemic activities via the IRS-1/PI3K/Glut-4 signalling pathway.

Tungstate promotes ß-cell survival in Irs2-/- mice.

Pancreatic ß-cells play a central role in type 2 diabetes (T2D) development, which is characterized by the progressive decline of the functional ß-cell mass that is associated mainly with increased ß-cell apoptosis. Thus, understanding how to enhance survival of ß-cells is key for the management of T2D. The insulin receptor substrate-2 (IRS-2) protein is pivotal in mediating the insulin/IGF signaling pathway in ß-cells. In fact, IRS-2 is critically required for ß-cell compensation in conditions of increased insulin demand and for ß-cell survival. Tungstate is a powerful antidiabetic agent that has been shown to promote ß-cell recovery in toxin-induced diabetic rodent models. In this study, we investigated whether tungstate could prevent the onset of diabetes in a scenario of dysregulated insulin/IGF signaling and massive ß-cell death. To this end, we treated mice deficient in IRS2 (Irs2(-/-)), which exhibit severe ß-cell loss, with tungstate for 3 wk. Tungstate normalized glucose tolerance in Irs2(-/-) mice in correlation with increased ß-cell mass, increased ß-cell replication, and a striking threefold reduction in ß-cell apoptosis. Islets from treated Irs2(-/-) exhibited increased phosphorylated Erk1/2. Interestingly, tungstate repressed apoptosis-related genes in Irs2(-/-) islets in vitro, and ERK1/2 blockade abolished some of these effects. Gene expression profiling showed evidence of a broad impact of tungstate on cell death pathways in islets from Irs2(-/-) mice, consistent with reduced apoptotic rates. Our results support the finding that ß-cell death can be arrested in the absence of IRS2 and that therapies aimed at reversing ß-cell mass decline are potential strategies to prevent the progression to T2D.

Hypoglycemic effect of triterpenoid-rich extracts from Euryale ferox shell on normal and streptozotocin-diabetic mice.

The antioxidant effects of the triterpenoid-rich extracts from Euryale ferox shell (ES) have been confirmed in vitro. This study examined whether the triterpenoid-rich extract from ES eases human hyperglycemia and diabetes caused by metabolic disorders. Normal and streptozocin (STZ)-induced diabetic mice were used as controls for the four groups that received the triterpenoid-rich extracts of ES suspended in distilled water orally at doses of 200, 300, 400, 500±2 mg/L. Body weight, blood glucose and pancreatic tissue morphology were observed after 4 weeks. The expression of protein tyrosine phosphatase-1B (PTP1B) and insulin receptor substrate (IRS-1) proteins, which are related to the regulation of glucose metabolism in vivo, were also investigated. Compared with the model group (LD50 900±2 mg/L), it was found that the triterpenoid-rich extracts of ES could regulate glucose metabolism (P<0.01) and cause body weight to return to normal levels (P<0.05). Islet morphology recovered well, the expression of the negative regulation protein PTP1B gene was reduced and insulin receptor IRS-1 protein expression was increased. These data prove that the triterpenoid-rich extracts from ES have a therapeutic effect on diabetes by insulin resistance.

Accelerated atherosclerosis in Apoe-/- mice heterozygous for the insulin receptor and the insulin receptor substrate-1.

OBJECTIVE: Prediabetic states are associated with accelerated atherosclerosis, but the availability of mouse models to study connections between these diseases has been limited. The aim of this study was to test the selective role of impaired insulin receptor/insulin receptor substrate-1 signaling on atherogenesis. METHODS AND RESULTS: To address the effects of impaired insulin signaling associated with hyperinsulinemia on atherosclerosis in the absence of obesity and hyperglycemia, we generated insulin receptor (Insr)/insulin receptor substrate-1 (Insr1) double heterozygous apolipoprotein (Apoe)-knockout mice (Insr(+/-)Irs1(+/-)Apoe(-/-)) mice. Insr(+/-)Irs1(+/-)Apoe(-/-) mice fed a Western diet for 15 weeks showed elevated levels of fasting insulin compared to Insr(+/+)Irs1(+/+)Apoe(-/-) mice. There were no significant differences in glucose, triglyceride, HDL, VLDL, cholesterol levels or free fatty acid in the plasma of Insr(+/-)Irs1(+/-)Apoe(-/-) and Insr(+/+)Irs1(+/+)Apoe(-/-) mice. Atherosclerotic lesions were increased in male (brachiocephalic artery) and female (aortic tree) Insr(+/-)Irs1(+/-)Apoe(-/-) compared to Insr(+/+)Irs1(+/+)Apoe(-/-) mice. Bone marrow transfer experiments demonstrated that nonhematopoietic cells have to be Insr(+/-)Irs1(+/-) to accelerate atherosclerosis. Impaired insulin signaling resulted in decreased levels of vascular phospho-eNOS, attenuated endothelium-dependent vasorelaxation and elevated VCAM-1 expression in aortas of Insr(+/-)Irs1(+/-)Apoe(-/-) mice. In addition, phospho-ERK and vascular smooth muscle cell proliferation were significantly elevated in aortas of Insr(+/-)Irs1(+/-)Apoe(-/-) mice. CONCLUSIONS: These results demonstrate that defective insulin signaling is involved in accelerated atherosclerosis in Insr(+/-)Irs1(+/-)Apoe(-/-) mice by promoting vascular dysfunction and inflammation.

Ceramide inhibitor myriocin restores insulin/insulin growth factor signaling for liver remodeling in experimental alcohol-related steatohepatitis.

BACKGROUND AND AIM: Alcohol-related liver disease (ALD) is mediated in part by insulin resistance. Attendant dysregulation of lipid metabolism increases accumulation of hepatic ceramides that worsen insulin resistance and compromise the structural and functional integrity of the liver. Insulin and insulin growth factor (IGF) stimulate aspartyl-asparaginyl-ß-hydroxylase (AAH), which promotes cell motility needed for structural maintenance and remodeling of the liver. AAH mediates its effects by activating Notch, and in ALD, insulin/IGF signaling, AAH, and Notch are inhibited. METHOD: To test the hypothesis that in ALD, hepatic ceramide load contributes to impairments in insulin, AAH, and Notch signaling, control and chronic ethanol-fed adult Long-Evans rats were treated with myriocin, an inhibitor of serine palmitoyl transferase. Livers were used to assess steatohepatitis, insulin/IGF pathway activation, and expression of AAH-Notch signaling molecules. RESULTS: Chronic ethanol-fed rats had steatohepatitis with increased ceramide levels; impairments in signaling through the insulin receptor, insulin receptor substrate, and Akt; and decreased expression of AAH, Notch, Jagged, Hairy-Enhancer of Split-1, hypoxia-inducible factor 1α, and proliferating cell nuclear antigen. Myriocin abrogated many of these adverse effects of ethanol, particularly hepatic ceramide accumulation, steatohepatitis, and impairments of insulin signaling through Akt, AAH, and Notch. CONCLUSIONS: In ALD, the histopathology and impairments in insulin/IGF responsiveness can be substantially resolved by ceramide inhibitor treatments, even in the context of continued chronic ethanol exposure.

Diet-induced obesity impairs AKT signalling in the retina and causes retinal degeneration.

Retinopathy, a common complication of diabetes, is characterized by an unbalanced production of nitric oxide (NO), a process regulated by nitric oxide synthase (NOS). We hypothesized that retinopathy might stem from changes in the insulin receptor substrate (IRS)/PI3K/AKT pathway and/or expression of NOS isoforms. Thus, we analysed the morphology and apoptosis index in retinas of obese rats in whom insulin resistance had been induced by a high-fat diet (HFD). Immunoblotting analysis revealed that the retinal tissue of HFD rats had lower levels of AKT(1) , eNOS and nNOS protein than those of samples taken from control animals. Furthermore, immunohistochemical analyses indicated higher levels of iNOS and 4-hydroxynonenal and a larger number of apoptotic nuclei in HFD rats. Finally, both the inner and outer retinal layers of HFD rats were thinner than those in their control counterparts. When considered alongside previous results, these patterns suggest two major ways in which HFD might impact animals: direct activity of ingested fatty acids and/or via insulin-resistance-induced changes in intracellular pathways. We discuss these possibilities in further detail and advocate the use of this animal model for further understanding relationships between retinopathy, metabolic syndrome and type 2 diabetes.

miR-370 modulates insulin receptor substrate-1 expression and inhibits the tumor phenotypes of oral carcinoma.

BACKGROUND: MicroRNAs play important roles in carcinogenesis. A preliminary screening study suggested that down-regulation of miR-370 occurs in oral squamous cell carcinoma (OSCC) tissue. Insulin receptor substratre-1 (IRS-1) is the substrate of insulin-like growth factor receptor (IGFR), which modulates AKT/mTOR activation in malignancies. The relationship between miR-370 and IRS-1, and their functional roles in OSCC pathogenesis are unclear. MATERIALS AND METHODS: Primary OSCC specimens were examined for miR-370 expression. Exogenous expression of miR-370 was established using both stable subclones and transient expression, and these were used to gain insights into miR-370's functions in OSCC cells. Knockdown of miR-370 and IRS-1 was also carried out in OSCC cells using a small interference oligonucleotide approach. RESULTS: Squamous cell carcinoma tissues with perineural invasion had lowered miR-370 expression compared with contrasting OSCC. OSCC cells also exhibited lower miR-370 expression than normal oral keratinocytes, and this can be reversed by treatment with 5-aza-2'-deoxycytidine. Exogenous miR-370 expression decreases the migration and anchorage-independent growth of OSCC cells, which implies a suppressor role for miR-370. The enhancement of anchorage-independent growth of OSCC cells through miR-370 inhibiting can be reduced by knockdown of IRS-1 expression. CONCLUSION: This study concludes that miR-370 is able to target IRS-1 for oral tumorigenesis.

[Beyond immunopathogenesis. Insulin resistance and "epidermal dysfunction"]. / Jenseits der Immunpathogenese. Insulinresistenz und "epidermale Dysfunktion".

Insulin is a central player in the regulation of metabolic as well as non-metabolic cells: inefficient signal transduction (insulin resistance) not only represents the cornerstone in the pathogenesis of type 2 diabetes mellitus, but also drives atherosclerosis through inducing endothelial dysfunction. Last but not least epidermal homeostasis depends on insulin. We summarize the effects of insulin on proliferation and differentiation of human keratinocytes as well as the relevance of cytokine-induced insulin resistance for alterations in epidermal homeostasis characteristic for psoriasis. Kinases involved in both insulin- as well as cytokine-receptor signaling represent potential targets for innovative therapeutics. Such small molecules would primarily normalize "epidermal dysfunction", thus complementing the immunomodulatory strategies of today's biologics.

[Advances on relationship between insulin receptor substrate-1 and insulin resistance in liver cirrhosis].

Liver cirrhosis (LC) and insulin resistance (IR) are closely correlated, clinically presenting hyperglycemia, hyperinsulinism, hyperlipidemia and high cytokines levels, however, the underlying mechanism is not completely clear. Recent reports show that insulin receptor substrate-1 (IRS-1) is associated with IR in LC. IRS-1 plays a pivotal role on insulin signal transduction; it changes insulin signaling by up-or down-regulating of protein presentation, post-translational modification and subcellular localization of proteins, particularly in phosphorylation/dephosphorylation of post-translational modification. Furthermore, LC with different etiology may have different mechanism of IRS-1 effect on IR.

Glomerular-specific protein kinase C-ß-induced insulin receptor substrate-1 dysfunction and insulin resistance in rat models of diabetes and obesity.

Insulin resistance has been associated with the progression of chronic kidney disease in both diabetes and obesity. In order to determine the cellular mechanisms contributing to this, we characterized insulin signaling in renal tubules and glomeruli during diabetic and insulin-resistant states using streptozotocin-diabetic and Zucker fatty-insulin-resistant rats. Compared with nondiabetic and Zucker lean rats, the insulin-induced phosphorylation of insulin receptor substrate-1 (IRS1), Akt, endothelial nitric oxide synthase, and glycogen synthase kinase 3α were selectively inhibited in the glomeruli but not in the renal tubules of both respective models. Protein, but not mRNA levels of IRS1, was decreased only in the glomeruli of streptozotocin-diabetic rats likely due to increased ubiquitination. Treatment with the protein kinase C-ß inhibitor, ruboxistaurin, enhanced insulin actions and elevated IRS1 expression. In glomerular endothelial cells, high glucose inhibited the phosphorylation of Akt, endothelial nitric oxide synthase, and glycogen synthase kinase 3α; decreased IRS1 protein expression and increased its association with ubiquitin. Overexpression of IRS1 or the addition of ruboxistaurin reversed the inhibitory effects of high glucose. Thus, loss of insulin's effect on endothelial nitric oxide synthase and glycogen synthase kinase 3α activation may contribute to the glomerulopathy observed in diabetes and obesity.

The insulin receptor substrate-1: a biomarker for cancer?

This review focuses on IRS-1 and the evidence of its role in cell transformation. The literature strongly suggests that IRS-1 should be considered a biomaker for cancers susceptible to IGF-IR targeting. In addition, I would like to propose that IRS-1 may have a more general role in cancer, and could be considered as a protein having the opposite effect of tumor suppressors, a sort of anti-p53 molecule.