Modulates Insulin Signaling Research Articles

Factor XIII-A transglutaminase deficient mice show signs of metabolically healthy obesity on high fat diet

F13A1 gene, which encodes for Factor XIII-A blood clotting factor and a transglutaminase enzyme, was recently identified as a potential causative gene for obesity in humans. In our previous in vitro work, we showed that FXIII-A regulates preadipocyte differentiation and modulates insulin signaling via promoting plasma fibronectin assembly into the extracellular matrix. To understand the role of FXIII-A in whole body energy metabolism, here we have characterized the metabolic phenotype of F13a1−/− mice. F13a1−/− and F13a1+/+ type mice were fed chow or obesogenic, high fat diet for 20 weeks. Weight gain, total fat mass and fat pad mass, glucose handling, insulin sensitivity, energy expenditure and, morphological and biochemical analysis of adipose tissue was performed. We show that mice lacking FXIII-A gain weight on obesogenic diet, similarly as wild type mice, but exhibit a number of features of metabolically healthy obesity such as protection from developing diet-induced insulin resistance and hyperinsulinemia. Mice also show normal fasting glucose levels, larger adipocytes, decreased extracellular matrix accumulation and inflammation of adipose tissue, as well as decreased circulating triglycerides. This study reveals that FXIII-A transglutaminase can regulate whole body insulin sensitivity and may have a role in the development of diet-induced metabolic disturbances.

Lentivirus-mediated shRNA interference of ghrelin receptor blocks proliferation in the colorectal cancer cells.

Ghrelin, an orexigenic peptide, acts via the growth hormone secretagogue receptor (GHSR) to stimulate the release of growth hormone. Moreover, it has a range of biological actions, including the stimulation of food intake, modulation of insulin signaling and cardiovascular effects. Recently, it has been demonstrated that ghrelin has a proliferative and antiapoptotic effects in cancers, suggesting a potential role in promoting tumor growth. However, it remains unknown whether GHSR contributes to colorectal cancer proliferation. In this study, the therapeutic effect of lentivirus‐mediated short hairpin RNA (shRNA) targeting ghrelin receptor 1a (GHSR1a) was analyzed in colorectal cancer cell line SW480 both in vitro and in vivo. Our study demonstrated that ghrelin and GHSR1a are significantly upregulated in cancerous colorectal tissue samples and cell lines. In vitro, human colorectal cancer cell line SW480 with downregulation of GHSR1a by shRNA showed significant inhibition of cell viability compared with blank control (BC) or scrambled control (SC) regardless of the application of exogenous ghrelin. Furthermore, GHSR1a silencing by target specific shRNA was shown capable of increasing PTEN, inhibiting AKT phosphorylation and promoting the release of p53 in SW480 cells. In addition, the effects of GHSR1a knockdown were further explored in vivo using colorectal tumor xenograft mouse model. The tumor weights were decreased markedly in GHSR1α knockdown SW480 mouse xenograft tumors compared with blank control or negative control tumors. Our results suggested that the expression of GHSR1a is significantly correlated with the growth of colorectal cancer cells, and the GHSR1a knockdown approach may be a potential therapy for the treatment of colorectal cancer.

Metabolism: MAD interactions with insulin receptor.

Proteins of the mitotic checkpoint regulate insulin receptor internalization through clathrin-mediated endocytosis, thereby modulating insulin signalling and systemic glucose metabolism.

Protein Scaffolds Control Localized Protein Kinase Cζ Activity

Atypical protein kinase C (aPKC) isozymes modulate insulin signaling and cell polarity, but how their activity is controlled in cells is not well understood. These enzymes are constitutively phosphorylated, insensitive to second messengers, and have relatively low activity. Here we show that protein scaffolds not only localize but also differentially control the catalytic activity of the aPKC PKCζ, thus promoting activity toward localized substrates and restricting activity toward global substrates. Using cellular substrate readouts and scaffolded activity reporters in live cell imaging, we show that PKCζ has highly localized and differentially controlled activity on the scaffolds p62 and Par6. Both scaffolds tether aPKC in an active conformation as assessed through pharmacological inhibition of basal activity, monitored using a genetically encoded reporter for PKC activity. However, binding to Par6 is of higher affinity and is more effective in locking PKCζ in an active conformation. FRET-based translocation assays reveal that insulin promotes the association of both p62 and aPKC with the insulin-regulated scaffold IRS-1. Using the aPKC substrate MARK2 as another readout for activity, we show that overexpression of IRS-1 reduces the phosphorylation of MARK2 and enhances its plasma membrane localization, indicating sequestration of aPKC by IRS-1 away from MARK2. These results are consistent with scaffolds serving as allosteric activators of aPKCs, tethering them in an active conformation near specific substrates. Thus, signaling of these intrinsically low activity kinases is kept at a minimum in the absence of scaffolding interactions, which position the enzymes for stoichiometric phosphorylation of substrates co-localized on the same protein scaffold.

Zinc stimulates glucose consumption by modulating the insulin signaling pathway in L6 myotubes: essential roles of Akt–GLUT4, GSK3β and mTOR–S6K1

The present study was performed to evaluate the insulin-like effects of zinc in normal L6 myotubes as well as its ability to alleviate insulin resistance. Glucose consumption was measured in both normal and insulin-resistant L6 myotubes. Western blotting and immunofluorescence revealed that zinc exhibited insulin-like glucose transporting effects by activating key markers that are involved in the insulin signaling cascade (including Akt, GLUT4 and GSK3β), and downregulating members of the insulin signaling feedback cascade such as mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase (S6K1). In normal L6 myotubes, zinc enhanced glucose consumption via a mechanism that might involve the activation of Akt phosphorylation, glucose transporter 4 (GLUT4) translocation and GSK3β phosphorylation. In contrast, zinc exerted insulin-mimetic effects in insulin-resistant L6 myotubes by upregulating Akt phosphorylation, GLUT4 translocation and GSK3β phosphorylation, and downregulating the expression of mTOR and S6K1. In conclusion, zinc might enhance glucose consumption by modulating insulin signaling pathways including Akt–GLUT4, GSK3β, mTOR and S6K1.

Valproic acid reduces insulin-resistance, fat deposition and FOXO1-mediated gluconeogenesis in type-2 diabetic rat.

Recent evidences highlighted the role of histone deacetylases (HDACs) in insulin-resistance, gluconeogenesis and islet function. HDACs can modulate the expression of various genes, which directly or indirectly affect glucose metabolism. This study was aimed to evaluate the role of valproic acid (VPA) on fat deposition, insulin-resistance and gluconeogenesis in type-2 diabetic rat. Diabetes was developed in Sprague-Dawley rats by the combination of high-fat diet and low dose streptozotocin. VPA at the doses of 150 and 300mg/kg/day and metformin (positive control) 150mg/kg twice daily for 10 weeks were administered by oral gavage. Insulin-resistance, dyslipidemia and glycemia were evaluated by biochemical estimations, while fat accumulation and structural alteration were assessed by histopathology. Protein expression and insulin signaling were evaluated by western blot and immunohistochemistry. VPA treatment significantly reduced the plasma glucose, HbA1c, insulin-resistance, fat deposition in brown adipose tissue, white adipose tissue and liver, which are comparable to metformin treatment. Further, VPA inhibited the gluconeogenesis and glucagon expression as well as restored the histopathological alterations in pancreas and liver. Our findings provide new insights on the anti-diabetic role of VPA in type-2 diabetes mellitus by the modulation of insulin signaling and forkhead box protein O1 (FOXO1)-mediated gluconeogenesis. Since VPA is a well established clinical drug, the detailed molecular mechanisms of the present findings can be further investigated for possible clinical use.

An insulin signaling feedback loop regulates pancreas progenitor cell differentiation during islet development and regeneration

As one of the key nutrient sensors, insulin signaling plays an important role in integrating environmental energy cues with organism growth. In adult organisms, relative insufficiency of insulin signaling induces compensatory expansion of insulin-secreting pancreatic beta (β) cells. However, little is known about how insulin signaling feedback might influence neogenesis of β cells during embryonic development. Using genetic approaches and a unique cell transplantation system in developing zebrafish, we have uncovered a novel role for insulin signaling in the negative regulation of pancreatic progenitor cell differentiation. Blocking insulin signaling in the pancreatic progenitors hastened the expression of the essential β cell genes insulin and pdx1, and promoted β cell fate at the expense of alpha cell fate. In addition, loss of insulin signaling promoted β cell regeneration and destabilization of alpha cell character. These data indicate that insulin signaling constitutes a tunable mechanism for β cell compensatory plasticity during early development. Moreover, using a novel blastomere-to-larva transplantation strategy, we found that loss of insulin signaling in endoderm-committed blastomeres drove their differentiation into β cells. Furthermore, the extent of this differentiation was dependent on the function of the β cell mass in the host. Altogether, our results indicate that modulation of insulin signaling will be crucial for the development of β cell restoration therapies for diabetics; further clarification of the mechanisms of insulin signaling in β cell progenitors will reveal therapeutic targets for both in vivo and in vitro β cell generation.

Genome-wide microRNA screening reveals that the evolutionary conserved miR-9a regulates body growth by targeting sNPFR1/NPYR.

MicroRNAs (miRNAs) regulate many physiological processes including body growth. Insulin/IGF signalling is the primary regulator of animal body growth, but the extent to which miRNAs act in insulin-producing cells (IPCs) is unclear. Here we generate a UAS-miRNA library of Drosophila stocks and perform a genetic screen to identify miRNAs whose overexpression in the IPCs inhibits body growth in Drosophila. Through this screen, we identify miR-9a as an evolutionarily conserved regulator of insulin signalling and body growth. IPC-specific miR-9a overexpression reduces insulin signalling and body size. Of the predicted targets of miR-9a, we find that loss of miR-9a enhances the level of sNPFR1. We show via an in vitro binding assay that miR-9a binds to sNPFR1 mRNA in insect cells and to the mammalian orthologue NPY2R in rat insulinoma cells. These findings indicate that the conserved miR-9a regulates body growth by controlling sNPFR1/NPYR-mediated modulation of insulin signalling.

Abstract 524: Role of Transmembrane Protein 55B in Insulin Signaling and Hepatic Lipid Metabolism

Hepatic steatosis is the leading cause of liver disease in the United States and is associated with increased risk of cardiovascular disease. Insulin resistance appears to be a major determinant of hepatic steatosis, as improper hepatic insulin signaling stimulates lipogenesis and dysregulates lipoprotein secretion, resulting in fat accumulation in the liver. Insulin signal transduction is dependent on phosphatidylinositol-4,5-biphosphate (PIP 2 ) conversion to phosphatidylinositol-3,4,5-biphosphate (PIP 3 ), which results in activation of AKT. Transmembrane protein 55B ( TMEM55B ), a gene we recently identified as a novel regulator of cellular cholesterol metabolism, encodes a phosphatidylinositol phosphatase that converts PIP 2 to phosphatidylinositol-5-phosphate (PI5P). PI5P has also been shown to activate AKT; however, the physiological effects of this pathway are less well understood. In the first in vivo model of Tmem55b modulation, we found that hepatic Tmem55b knockdown in Western diet-fed C57BL/6 mice caused increased body weight, hepatic steatosis, hyperinsulinemia and elevated plasma cholesterol compared to controls. In addition, hepatic expression of insulin-regulated lipogenic genes, including Srebp1c and Dgat2, was increased, suggesting that Tmem55b knockdown promotes lipogenesis. In addition, two genes involved in VLDL secretion, ApoC3 and Mtp , were upregulated. Notably, we observed a significant inverse correlation between TMEM55B expression, quantified in 480 human lymphoblastoid cell lines, with plasma triglyceride, VLDL and APOC3 levels in the cell line donors. These relationships were significantly stronger in individuals with elevated plasma glucose (>110 mg/dL), suggesting that the relationship between TMEM55B and these measures may be enhanced in the insulin resistant state. Based on these findings, we hypothesize that TMEM55B modulates insulin signaling and affects hepatic lipid accumulation, potentially through stimulation of lipogenesis. With the ever-rising incidence of type 2 diabetes, elucidation of a novel pathway by which insulin resistance leads to hepatic steatosis may inform the development of therapeutics used for the prevention or treatment of this disease.

Cocoa-rich diet ameliorates hepatic insulin resistance by modulating insulin signaling and glucose homeostasis in Zucker diabetic fatty rats

Insulin resistance is the primary characteristic of type 2 diabetes and results from insulin signaling defects. Cocoa has been shown to exert anti-diabetic effects by lowering glucose levels. However, the molecular mechanisms responsible for this preventive activity and whether cocoa exerts potential beneficial effects on the insulin signaling pathway in the liver remain largely unknown. Thus, in this study, the potential anti-diabetic properties of cocoa on glucose homeostasis and insulin signaling were evaluated in type 2 diabetic Zucker diabetic fatty (ZDF) rats. Male ZDF rats were fed a control or cocoa-rich diet (10%), and Zucker lean animals received the control diet. ZDF rats supplemented with cocoa (ZDF-Co) showed a significant decrease in body weight gain, glucose and insulin levels, as well as an improved glucose tolerance and insulin resistance. Cocoa-rich diet further ameliorated the hepatic insulin resistance by abolishing the increased serine-phosphorylated levels of the insulin receptor substrate 1 and preventing the inactivation of the glycogen synthase kinase 3/glycogen synthase pathway in the liver of cocoa-fed ZDF rats. The anti-hyperglycemic effect of cocoa appeared to be at least mediated through the decreased levels of hepatic phosphoenolpyruvate carboxykinase and increased values of glucokinase and glucose transporter 2 in the liver of ZDF-Co rats. Moreover, cocoa-rich diet suppressed c-Jun N-terminal kinase and p38 activation caused by insulin resistance. These findings suggest that cocoa has the potential to alleviate both hyperglycemia and hepatic insulin resistance in type 2 diabetic ZDF rats.

Silymarin extends lifespan and reduces proteotoxicity in C. elegans Alzheimer's model.

Aging is a process of progressive decline in physiological functions resulting in increased vulnerability to diseases and death. Aging results in increased rates of age related disorders like neurodegenerative diseases, cardiovascular diseases, diabetes, cancer, arthritis etc. Modulation of insulin signaling, protein aggregation, stress, free radical damage and inflammation are the major causes for deleterious changes resulting in aging. Many studies are being undertaken to find novel compounds which can improve a typical human life span and aid in healthy aging. We investigated the potential of one such compound silymarin for its anti-aging effect. Silymarin is a flavanone derivative extracted from the seeds of the milk thistle Silybum marianum. It is widely used for the treatment of liver diseases in clinical practice. We tested the anti-aging efficacy of silymarin using the Caenorhabditis elegans model system. Our results demonstrate that C. elegans treated with 25μM and 50μM silymarin concentration resulted in an increase in mean lifespan by 10.1% and 24.8% respectively compared to untreated control. Besides increased lifespan, silymarin treated aged animals showed better locomotion rate, higher response to stimuli and improved tolerance to stress compared to untreated control. We also checked the potential of silymarin to slow the progression of neurodegenerative disorder like Alzheimer's disease (AD) by using CL4176 C. elegans model for AD. C. elegans CL4176 transgenic animal induces expression of amyloid beta-protein (Aβ1-42) in muscle tissues when subjected to temperature of 23°C and above resulting in worm paralysis. CL4176 animals treated with silymarin showed delayed paralysis via enhancing resistance to oxidative stress. These results suggested that silymarin is a potential hormetin for preventing aging and age-related diseases.

Endogenous interleukin 18 suppresses hyperglycemia and hyperinsulinemia during the acute phase of endotoxemia in mice.

Hyperglycemia associated with insulin resistance is common among critically ill patients. Interleukin (IL)-18 has been linked with hyperglycemia and insulin resistance in chronic disease, but the relation between IL-18 and insulin resistance during critical illness was unexplored. This study investigated whether IL-18 modulates hyperglycemia and insulin resistance during acute inflammation. We injected lipopolysaccharide (LPS) 40 mg/kg into wild-type (WT) and IL-18 knockout (KO) mice to induce endotoxemia and examined insulin resistance and insulin-dependent signaling pathways during the acute phase. During the first hour after LPS treatment, IL-18 KO mice showed higher blood glucose and insulin and less insulin receptor substrate-1 and less phosphorylated Akt in the liver compared with WT mice. Interleukin-18 KO mice exhibited better survival after LPS treatment. The findings suggest that endogenous IL-18 may attenuate hyperglycemia and modulate insulin signaling in liver. Accordingly, IL-18 may modulate glucose tolerance during acute inflammation.

Control of homeostatic and pathogenic balance in adipose tissue by ganglioside GM3.

Ganglioside GM3 (Siaα2-3Galβ1-4Glcβ1-1Cer) has been known to participate in insulin signaling by regulating the association of the insulin receptor in caveolae microdomains (lipid rafts), which is essential for the execution of the complete insulin metabolic signaling in adipocytes. Macrophage-secreted factors including proinflammatory cytokines, tumor necrosis factor-α and interleukin-1β, in adipose tissues have been known to limit the local adipogenesis and induce insulin resistance; however, the interplay between adipocytes and macrophages upon regulation of GM3 expression is not clear. GM3 was virtually absent in primary adipocytes differentiated from macrophage-depleted mesenteric stromal vesicular cells, which accompanies enhancement of insulin signaling and adipogenesis. We found that the expression of GM3 is governed by soluble factors including steady-state levels of proinflammatory cytokines secreted from resident macrophages. The direct involvement of GM3 in insulin signaling is demonstrated by the fact that embryonic fibroblasts obtained from GM3 synthase (GM3S)-deficient mice have increased insulin signaling, when compared with wild-type embryonic fibroblasts, which in turn leads to enhanced adipogeneis. In addition, GM3 expression in primary adipocytes is increased under proinflammatory conditions as well as in adipose tissue of diet-induced obese mice. Moreover, GM3S-deficient mice fed high-fat diets become obese but are resistant to the development of insulin resistance and chronic low-grade inflammatory states. Thus, GM3 functions as a physiological regulatory factor of the balance between homeostatic and pathological states in adipocytes by modulating insulin signaling in lipid rafts.

Essential Role of Protein-tyrosine Phosphatase 1B in the Modulation of Insulin Signaling by Acetaminophen in Hepatocytes

Many drugs are associated with the development of glucose intolerance or deterioration in glycemic control in patients with pre-existing diabetes. We have evaluated the cross-talk between signaling pathways activated by acetaminophen (APAP) and insulin signaling in hepatocytes with or without expression of the protein-tyrosine phosphatase 1B (PTP1B) and in wild-type and PTP1B-deficient mice chronically treated with APAP. Human primary hepatocytes, Huh7 hepatoma cells with silenced PTP1B, mouse hepatocytes from wild-type and PTP1B-deficient mice, and a mouse model of chronic APAP treatment were used to examine the mechanisms involving PTP1B in the effects of APAP on glucose homeostasis and hepatic insulin signaling. In APAP-treated human hepatocytes at concentrations that did not induce death, phosphorylation of JNK and PTP1B expression and enzymatic activity were increased. APAP pretreatment inhibited activation of the early steps of insulin signaling and decreased Akt phosphorylation. The effects of APAP in insulin signaling were prevented by suramin, a PTP1B inhibitor, or rosiglitazone that decreased PTP1B levels. Likewise, PTP1B deficiency in human or mouse hepatocytes protected against APAP-mediated impairment in insulin signaling. These signaling pathways were modulated in mice with chronic APAP treatment, resulting in protection against APAP-mediated hepatic insulin resistance and alterations in islet alpha/beta cell ratio in PTP1B(-/-) mice. Our results demonstrate negative cross-talk between signaling pathways triggered by APAP and insulin signaling in hepatocytes, which is in part mediated by PTP1B. Moreover, our in vivo data suggest that chronic use of APAP may be associated with insulin resistance in the liver.

TNFa and Serum Galectin-3 in Patients with Heart Failure with Preserved Left Ventricular Ejection Fraction, Insulin Resistance and Type 2 Diabetes Mellitus

Background: Proinflammatory cytokines may modulate insulin signaling and contribute to systemic insulin resistance (IR). Galectin-3 (Gal-3) is a marker of myocardial fibrosis. Purpose: To investigate the relation between serum Gal-3 levels (sGal3), THF-alpha(TNFa), Nt-proBNP, HOMA index and insulin in patients with heart failure with preserved left ventricular ejection fraction (HFpEF), IR and type 2 diabetes mellitus (T2DM). Methods: Seventy four patients (40 males and 34 females; mean age 62.2768.7 years) with HFpEF with and without concomitant T2DM were examined. The sGal3, Nt-proBNP, TNF-alpha and insulin were measured in serum by ELISA, according to manufacturer’s instructions. HOmeostasis Model Assessment (HOMA) index was calculated as a measure of IR at fasting state (IR5fasting glucose fasting insulin/ 22.5), after what patients were divided into three groups: 30 patients with HFpEF and IR, 31 patients with HFpEF and T2DM and 11 patients with HFpEF and without T2DM and IR. Spearman’s correlation analysis and Kruskal-Wallis test were used. All statistical tests were 2-tailed, and p!0.05 was considered statistically significant. Results: IR was diagnosed in 31 (43.6%) patients without a history of diabetes. In the group with HFpEF and IR the level of sGal3, TNF-alpha and insulin were significantly higher compared to the HFpEF patients with T2DM and HFpEF patients without IR and T2DM (p!0.05, p!0.05 and p!0.0001 respectively) (Table 1). Therewith analyses detected that increasing of sGal3 levels associated with increasing TNFa levels (r50.610; p ! 0.001), insulin levels (r 5 0.33; p !0.01) and HOMA index (r 5 0.29; p !0.05). In addition, our data showed that the strength of relation of sGal3 and TNFa levels increased from HFpEF patients with IR (r 5 0.520) to HFpEF patients with T2DM (r 5 0.709) (p !0.05). Multiple linear regression analysis suggested a significant dependence between sGal3 and TNFa (HFpEF patients with IR and without T2DM group: r 5 0.23, p ! 0.01, HFpEF patients with T2DM group: r 5 0.76, p ! 0.0001), but the dependences between TNF and Nt-proBNP (r 5 0.37, p ! 0.01), and between sGal3 and Nt-proBNP (r 5 0.82, p ! 0.0001) was significant only in patients with IR and without T2DM. Conclusions: Our results clearly show that sGal3, TNF-alpha and insulin are significantly increased in HFpEF patients with IR and without T2DM. Our findings show the association between sGal3 levels and TNFa levels in the presence of impaired glucose tolerance in HFpEF patients. This dependence increases with the progression of IR.

P283 SORTILIN DEFICIENCY IMPROVES HEPATIC AND ADIPOSE TISSUE INSULIN RESISTANCE AND INFLAMMATION IN DIET-INDUCED OBESITY

Background and Aims: Sortilin is a trafficking molecule directing newly synthesized molecules from the trans-Golgi network to secretory pathways, endosomes, lysosomes or cell surface. Several of the molecules trafficked by sortilin, such as acidic sphingomyelinase (ASM) and sphingolipid activating proteins (SAPs), regulate the synthesis of ceramide, a major modulator of insulin signaling. We hypothesized that in sortilin mice, reduced hepatic ASM may improve insulin sensitivity and reduce steatosis in a diet-induced obesity (DIO) model. Methods: DIO and insulin resistance were induced by feeding high fat diet for 10 weeks to WT and sortilin mice. Results: Sortilin mice had significantly reduced body weight and visceral fat, despite similar food intake. Sortilin mice had better insulin tolerance test and displayed increased insulin signaling in both liver and adipose tissue as demonstrated by increased Akt phosphorylation. In accordance with the proposed role of sortilin in ASM trafficking, ASM activity in both liver and adipose tissue of sortilin mice was significantly reduced. Sortilin mice had almost no steatosis and a three-fold reduction in total hepatic triglyceride levels compared to WT mice. In addition, expression of proinflammatory cytokines was reduce in both livers and adipose tissue of sortilin. Looking at ceramide synthesis enzymes, we observed a significant reduction in ceramide synthase 6, which synthesizes long chain ceramides, in both liver and adipose tissue of sortilin. Conclusions: Sortilin deficiency induces a beneficial metabolic phenotype in DIO, with respect to both liver and adipose tissue, which may be mediated in part by reduced ASM activity and reduced ceramide levels.

Effects of Honey and Its Mechanisms of Action on the Development and Progression of Cancer

Honey is a natural product known for its varied biological or pharmacological activities—ranging from anti-inflammatory, antioxidant, antibacterial, antihypertensive to hypoglycemic effects. This review article focuses on the role of honey in modulating the development and progression of tumors or cancers. It reviews available evidence (some of which is very recent) with regards to the antimetastatic, antiproliferative and anticancer effects of honey in various forms of cancer. These effects of honey have been thoroughly investigated in certain cancers such as breast, liver and colorectal cancer cell lines. In contrast, limited but promising data are available for other forms of cancers including prostate, bladder, endometrial, kidney, skin, cervical, oral and bone cancer cells. The article also underscores the various possible mechanisms by which honey may inhibit growth and proliferation of tumors or cancers. These include regulation of cell cycle, activation of mitochondrial pathway, induction of mitochondrial outer membrane permeabilization, induction of apoptosis, modulation of oxidative stress, amelioration of inflammation, modulation of insulin signaling and inhibition of angiogenesis. Honey is highly cytotoxic against tumor or cancer cells while it is non-cytotoxic to normal cells. The data indicate that honey can inhibit carcinogenesis by modulating the molecular processes of initiation, promotion, and progression stages. Thus, it may serve as a potential and promising anticancer agent which warrants further experimental and clinical studies.

Acute and long-term effects of arsenite in HepG2 cells: modulation of insulin signaling

Epidemiological studies have indicated a relationship between the prevalence of diabetes and exposure to arsenic. Mechanisms by which arsenic may cause this diabetogenic effect are largely unknown. The phosphoinositide 3'-kinase (PI3K)/Akt signaling pathway plays an important role in insulin signaling by controlling glucose metabolism, in part through regulating the activity of FoxO transcription factors. The present study aimed at investigating the effect of short and long-term exposure to arsenite on insulin signaling in HepG2 human hepatoma cells, the role of PI3K/Akt signaling therein and the modulation of target genes controlled by insulin. Exposure of cells to arsenite for 24h rendered cells less responsive toward stimulation of Akt by insulin. At the same time, short-term exposure to arsenite induced a concentration-dependent increase in phosphorylation of Akt at Ser-473, followed by phosphorylation of FoxO proteins at sites known to be phosphorylated by Akt. Phosphorylation of FoxOs was prevented by wortmannin, pointing to the involvement of PI3K. Arsenite exposure resulted in attenuation of FoxO DNA binding and in nuclear exclusion of FoxO1a-EGFP. A 24-h exposure of HepG2 cells to submicromolar concentrations of arsenite resulted in downregulation of glucose 6-phosphatase (G6Pase) and selenoprotein P (SelP) mRNA levels. Curiously, arsenite had a dual effect on SelP protein levels, inducing a small increase in the nanomolar and a distinct decrease in the micromolar concentration range. Interestingly, arsenite-induced long-term effects on G6Pase and SelP mRNA or SelP protein levels were not blocked by the PI3K inhibitor, wortmannin. In conclusion, arsenite perturbs cellular signaling pathways involved in fuel metabolism: it impairs cellular responsiveness toward insulin, while at the same time stimulating insulin-like signaling to attenuate the expression of genes involved in glucose metabolism and the release of the hepatokine SelP, which is known to modulate peripheral insulin sensitivity.

PID1 (NYGGF4), a New Growth-Inhibitory Gene in Embryonal Brain Tumors and Gliomas

We present here the first report of PID1 (Phosphotyrosine Interaction Domain containing 1; NYGGF4) in cancer. PID1 was identified in 2006 as a gene that modulates insulin signaling and mitochondrial function in adipocytes and muscle cells. Using four independent medulloblastoma datasets, we show that mean PID1 mRNA levels were lower in unfavorable medulloblastomas (groups 3 and 4, and anaplastic histology) compared with favorable medulloblastomas (SHH and WNT groups, and desmoplastic/nodular histology) and with fetal cerebellum. In two large independent glioma datasets, PID1 mRNA was lower in glioblastomas (GBM), the most malignant gliomas, compared with other astrocytomas, oligodendrogliomas and nontumor brains. Neural and proneural GBM subtypes had higher PID1 mRNA compared with classical and mesenchymal GBM. Importantly, overall survival and radiation-free progression-free survival were longer in medulloblastoma patients whose tumors had higher PID1 mRNA (univariate and multivariate analyses). Higher PID1 mRNA also correlated with longer overall survival in patients with glioma and GBM. In cell culture, overexpression of PID1 inhibited colony formation in medulloblastoma, atypical teratoid rhabdoid tumor (ATRT), and GBM cell lines. Increasing PID1 also increased cell death and apoptosis, inhibited proliferation, induced mitochondrial depolaization, and decreased serum-mediated phosphorylation of AKT and ERK in medulloblastoma, ATRT, and/or GBM cell lines, whereas siRNA to PID1 diminished mitochondrial depolarization. These data are the first to link PID1 to cancer and suggest that PID1 may have a tumor inhibitory function in these pediatric and adult brain tumors.

TheDrosophilainsulin-degrading enzyme restricts growth by modulating the PI3K pathway in a cell-autonomous manner

Mammalian insulin-degrading enzyme (IDE) cleaves insulin, among other peptidic substrates, but its function in insulin signaling is elusive. We use the Drosophila system to define the function of IDE in the regulation of growth and metabolism. We find that either loss or gain of function of Drosophila IDE (dIDE) can restrict growth in a cell-autonomous manner by affecting both cell size and cell number. dIDE can modulate Drosophila insulin-like peptide 2 levels, thereby restricting activation of the phosphatidylinositol-3-phosphate kinase pathway and promoting activation of Drosophila forkhead box, subgroup O transcription factor. Larvae reared in high sucrose exhibit delayed developmental timing due to insulin resistance. We find that dIDE loss of function exacerbates this phenotype and that mutants display increased levels of circulating sugar, along with augmented expression of a lipid biosynthesis marker. We propose that dIDE is a modulator of insulin signaling and that its loss of function favors insulin resistance, a hallmark of diabetes mellitus type II.