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Almon RR, Dubois DC, Jin JY, Jusko WJ. Temporal profiling of the transcriptional basis for the development of corticosteroid-induced insulin resistance in rat muscle. J Endocrinol 2005; 184:219-32. [PMID: 15642798 PMCID: PMC2574435 DOI: 10.1677/joe.1.05953] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Elevated systemic levels of glucocorticoids are causally related to peripheral insulin resistance. The pharmacological use of synthetic glucocorticoids (corticosteroids) often results in insulin resistance/type II diabetes. Skeletal muscle is responsible for close to 80% of the insulin-induced systemic disposal of glucose and is a major target for glucocorticoid-induced insulin resistance. We used Affymetrix gene chips to profile the dynamic changes in mRNA expression in rat skeletal muscle in response to a single bolus dose of the synthetic glucocorticoid methyl-prednisolone. Temporal expression profiles (analyzed on individual chips) were obtained from tissues of 48 drug-treated animals encompassing 16 time points over 72 h following drug administration along with four vehicle-treated controls. Data mining identified 653 regulated probe sets out of 8799 present on the chip. Of these 653 probe sets we identified 29, which represented 22 gene transcripts, that were associated with the development of insulin resistance. These 29 probe sets were regulated in three fundamental temporal patterns. 16 probe sets coding for 12 different genes had a profile of enhanced expression. 10 probe sets coding for eight different genes showed decreased expression and three probe sets coding for two genes showed biphasic temporal signatures. These transcripts were grouped into four general functional categories: signal transduction, transcription regulation, carbohydrate/fat metabolism, and regulation of blood flow to the muscle. The results demonstrate the polygenic nature of transcriptional changes associated with insulin resistance that can provide a temporal scaffolding for translational and post-translational data as they become available.
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Affiliation(s)
- Richard R Almon
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14260, USA.
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52
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Qiu W, Avramoglu RK, Dubé N, Chong TM, Naples M, Au C, Sidiropoulos KG, Lewis GF, Cohn JS, Tremblay ML, Adeli K. Hepatic PTP-1B expression regulates the assembly and secretion of apolipoprotein B-containing lipoproteins: evidence from protein tyrosine phosphatase-1B overexpression, knockout, and RNAi studies. Diabetes 2004; 53:3057-66. [PMID: 15561934 DOI: 10.2337/diabetes.53.12.3057] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Protein tyrosine phosphatase-1B (PTP-1B) plays an important role in regulation of insulin signal transduction, and modulation of PTP-1B expression seems to have a profound effect on insulin sensitivity and diet-induced weight gain. The molecular link between PTP-1B expression and metabolic dyslipidemia, a major complication of insulin resistance, was investigated in the present study using PTP-1B knockout mice as well as overexpression and suppression of PTP-1B. Chronic fructose feeding resulted in a significant increase in plasma VLDL in wild-type mice but not in PTP-1B knockout mice. Lipoprotein profile analysis of plasma from PTP-1B knockout mice revealed a significant reduction in apolipoprotein B (apoB100) lipoproteins, associated with reduced hepatic apoB100 secretion from isolated primary hepatocytes. In addition, treatment of cultured hepatoma cells with PTP-1B siRNA reduced PTP-1B mass by an average of 41% and was associated with a 53% decrease in secretion of metabolically labeled apoB100. Conversely, adenoviral-mediated overexpression of PTP-1B in HepG2 cells downregulated the phosphorylation of insulin receptor and insulin receptor substrate-1 and caused increases in cellular and secreted apoB100 as a result of increased intracellular apoB100 stability. Collectively, these findings suggest that PTP-1B expression level is a key determinant of hepatic lipoprotein secretion, and its overexpression in the liver can be sufficient to induce VLDL overproduction and the transition to a metabolic dyslipidemic state.
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Affiliation(s)
- Wei Qiu
- Department of Laboratory Medicine and Pathobiology, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
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53
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Ugi S, Imamura T, Maegawa H, Egawa K, Yoshizaki T, Shi K, Obata T, Ebina Y, Kashiwagi A, Olefsky JM. Protein phosphatase 2A negatively regulates insulin's metabolic signaling pathway by inhibiting Akt (protein kinase B) activity in 3T3-L1 adipocytes. Mol Cell Biol 2004; 24:8778-89. [PMID: 15367694 PMCID: PMC516764 DOI: 10.1128/mcb.24.19.8778-8789.2004] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Protein phosphatase 2A (PP2A) is a multimeric serine/threonine phosphatase which has multiple functions, including inhibition of the mitogen-activated protein (MAP) kinase pathway. Simian virus 40 small t antigen specifically inhibits PP2A function by binding to the PP2A regulatory subunit, interfering with the ability of PP2A to associate with its cellular substrates. We have reported that the expression of small t antigen inhibits PP2A association with Shc, leading to augmentation of insulin and epidermal growth factor-induced Shc phosphorylation with enhanced activation of the Ras/MAP kinase pathway. However, the potential involvement of PP2A in insulin's metabolic signaling pathway is presently unknown. To assess this, we overexpressed small t antigen in 3T3-L1 adipocytes by adenovirus-mediated gene transfer and found that the phosphorylation of Akt and its downstream target, glycogen synthase kinase 3beta, were enhanced both in the absence and in the presence of insulin. Furthermore, protein kinase C lambda (PKC lambda) activity was also augmented in small-t-antigen-expressing 3T3-L1 adipocytes. Consistent with this result, both basal and insulin-stimulated glucose uptake were enhanced in these cells. In support of this result, when inhibitory anti-PP2A antibody was microinjected into 3T3-L1 adipocytes, we found a twofold increase in GLUT4 translocation in the absence of insulin. The small-t-antigen-induced increase in Akt and PKC lambda activities was not inhibited by wortmannin, while the ability of small t antigen to enhance glucose transport was inhibited by dominant negative Akt (DN-Akt) expression and Akt small interfering RNA (siRNA) but not by DN-PKC lambda expression or PKC lambda siRNA. We conclude that PP2A is a negative regulator of insulin's metabolic signaling pathway by promoting dephosphorylation and inactivation of Akt and PKC lambda and that most of the effects of PP2A to inhibit glucose transport are mediated through Akt.
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Affiliation(s)
- Satoshi Ugi
- Division of Endocrinology and Metabolism, Department of Medicine, Shiga University of Medical Science, Otsu, Japan
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54
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Zabolotny JM, Haj FG, Kim YB, Kim HJ, Shulman GI, Kim JK, Neel BG, Kahn BB. Transgenic overexpression of protein-tyrosine phosphatase 1B in muscle causes insulin resistance, but overexpression with leukocyte antigen-related phosphatase does not additively impair insulin action. J Biol Chem 2004; 279:24844-51. [PMID: 15031294 DOI: 10.1074/jbc.m310688200] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies implicate protein-tyrosine phosphatase 1B (PTP1B) and leukocyte antigen-related phosphatase (LAR) as negative regulators of insulin signaling. The expression and/or activity of PTP1B and LAR are increased in muscle of insulin-resistant rodents and humans. Overexpression of LAR selectively in muscle of transgenic mice causes whole body insulin resistance. To determine whether overexpression of PTP1B also causes insulin resistance, we generated transgenic mice overexpressing human PTP1B selectively in muscle at levels similar to those observed in insulin-resistant humans. Insulin-stimulated insulin receptor (IR) tyrosyl phosphorylation and phosphatidylinositol 3'-kinase activity were impaired by 35% and 40-60% in muscle of PTP1B-overexpressing mice compared with controls. Insulin stimulation of protein kinase C (PKC)lambda/zeta activity, which is required for glucose transport, was impaired in muscle of PTP1B-overexpressing mice compared with controls, showing that PTP1B overexpression impairs activation of these PKC isoforms. Furthermore, hyperinsulinemic-euglycemic clamp studies revealed that whole body glucose disposal and muscle glucose uptake were decreased by 40-50% in PTP1B-overexpressing mice. Overexpression of PTP1B or LAR alone in muscle caused similar impairments in insulin action; however, compound overexpression achieved by crossing PTP1B- and LAR-overexpressing mice was not additive. Antibodies against specific IR phosphotyrosines indicated overlapping sites of action of PTP1B and LAR. Thus, overexpression of PTP1B in vivo impairs insulin sensitivity, suggesting that overexpression of PTP1B in muscle of obese humans and rodents may contribute to their insulin resistance. Lack of additive impairment of insulin signaling by PTP1B and LAR suggests that these PTPs have overlapping actions in causing insulin resistance in vivo.
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Affiliation(s)
- Janice M Zabolotny
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, Massachusetts 02215, USA
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55
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Cooney GJ, Lyons RJ, Crew AJ, Jensen TE, Molero JC, Mitchell CJ, Biden TJ, Ormandy CJ, James DE, Daly RJ. Improved glucose homeostasis and enhanced insulin signalling in Grb14-deficient mice. EMBO J 2004; 23:582-93. [PMID: 14749734 PMCID: PMC1271812 DOI: 10.1038/sj.emboj.7600082] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2003] [Accepted: 12/23/2003] [Indexed: 01/10/2023] Open
Abstract
Gene targeting was used to characterize the physiological role of growth factor receptor-bound (Grb)14, an adapter-type signalling protein that associates with the insulin receptor (IR). Adult male Grb14(-/-) mice displayed improved glucose tolerance, lower circulating insulin levels, and increased incorporation of glucose into glycogen in the liver and skeletal muscle. In ex vivo studies, insulin-induced 2-deoxyglucose uptake was enhanced in soleus muscle, but not in epididymal adipose tissue. These metabolic effects correlated with tissue-specific alterations in insulin signalling. In the liver, despite lower IR autophosphorylation, enhanced insulin-induced tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and activation of protein kinase B (PKB) was observed. In skeletal muscle, IR tyrosine phosphorylation was normal, but signalling via IRS-1 and PKB was increased. Finally, no effect of Grb14 ablation was observed on insulin signalling in white adipose tissue. These findings demonstrate that Grb14 functions in vivo as a tissue-specific modulator of insulin action, most likely via repression of IR-mediated IRS-1 tyrosine phosphorylation, and highlight this protein as a potential target for therapeutic intervention.
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Affiliation(s)
- Gregory J Cooney
- Diabetes and Obesity, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | - Ruth J Lyons
- Cancer Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | - A Jayne Crew
- Cancer Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | - Thomas E Jensen
- Diabetes and Obesity, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | - Juan Carlos Molero
- Diabetes and Obesity, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | | | - Trevor J Biden
- Diabetes and Obesity, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | - Christopher J Ormandy
- Cancer Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | - David E James
- Diabetes and Obesity, Garvan Institute of Medical Research, Sydney, NSW, Australia
| | - Roger J Daly
- Cancer Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia
- Cancer Research Program, Garvan Institute of Medical Research, 384 Victoria St, Sydney, NSW 2010, Australia. Tel: 61 2 92 95 8333; Fax: 61 2 92 95 8321; E-mail:
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56
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Théberge JF, Mehdi MZ, Pandey SK, Srivastava AK. Prolongation of insulin-induced activation of mitogen-activated protein kinases ERK 1/2 and phosphatidylinositol 3-kinase by vanadyl sulfate, a protein tyrosine phosphatase inhibitor. Arch Biochem Biophys 2003; 420:9-17. [PMID: 14622970 DOI: 10.1016/j.abb.2003.09.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Vanadium salts such as vanadyl sulfate (VS), potent inhibitors of protein tyrosine phosphatases, have been shown to mimic, augment, and prolong insulin's action. However, the molecular mechanism of responses to these salts is not clear. In the present studies, we examined if VS-induced effects on insulin action are associated with enhancement or augmentation in the activation state of key components of the insulin signaling pathway. Treatment of insulin receptor-overexpressing cells with insulin or VS resulted in a time-dependent transient increase in phosphorylation and activation of extracellular signal-regulated kinases 1 and 2 (ERK 1/2) that peaked at about 5 min, then declined rapidly to about baseline within 30 min. However, when the cells were treated with VS before stimulation with insulin, sustained ERK 1/2 phosphorylation and activation were observed well beyond 60 min. VS treatment also prolonged the insulin-stimulated activation of phosphatidylinositol 3-kinase (PI3-K), which was associated with sustained interaction between insulin receptor substrate-1 (IRS-1) and the p(85 alpha) subunit of phosphatidylinositol 3-kinase (PI3-K) in response to insulin. These data indicate that prolongation of insulin-stimulated ERK 1/2 and PI3-K activation by VS is due to a more stable complex formation of IRS-1 with the p(85 alpha) subunit which may, in turn, be responsible for its ability to enhance and extend the biological effects of insulin.
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Affiliation(s)
- Jean-François Théberge
- Research Centre, Centre hospitalier de l'Université de Montréal-Hôtel-Dieu, and Department of Medicine, Universitéde Montréal, 3850 rue Saint-Urbain, Montreal, Que., H2W1T8, Canada
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57
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Rahman SM, Dobrzyn A, Dobrzyn P, Lee SH, Miyazaki M, Ntambi JM. Stearoyl-CoA desaturase 1 deficiency elevates insulin-signaling components and down-regulates protein-tyrosine phosphatase 1B in muscle. Proc Natl Acad Sci U S A 2003; 100:11110-5. [PMID: 12960377 PMCID: PMC196935 DOI: 10.1073/pnas.1934571100] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2003] [Indexed: 11/18/2022] Open
Abstract
We have shown previously that mice with a targeted disruption in the stearoyl-CoA desaturase 1 gene (SCD1-/-) have increased insulin sensitivity compared with control mice. Here we show that the SCD1-/- mice have increased insulin signaling in muscle. The basal tyrosine phosphorylation of the insulin receptor and insulin receptor substrates 1 and 2 are elevated. The tyrosine phosphorylation of insulin-like growth factor-1 receptor was similar between SCD1+/+ and SCD1-/- mice. The association of insulin receptor substrates 1 and 2 with alphap85 subunit of phosphatidylinositol 3-kinase as well as the phosphorylation of Akt-Ser-473 and Akt-Thr-308 are also elevated in the SCD1-/- mice. Interestingly, the mRNA levels, protein mass, and activity of the protein-tyrosine phosphatase-1B implicated in the attenuation of the insulin signal are reduced in the SCD1-/- mice, whereas the levels of the leukocyte antigen-related protein phosphatase are similar between two groups of mice. The content of glucose transporter 4 in the plasma membrane and basal as well as insulin-mediated glucose uptake are increased in the SCD1-/- mice. In addition, the muscle glycogen content and the activities of glycogen synthase and phosphorylase are increased in the SCD1-/- mice. We hypothesize that loss of SCD1 function induces increased insulin signaling at least in part by a reduction in the expression of protein-tyrosine phosphatase 1B. SCD1 could be a therapeutic target in the treatment of diabetes.
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58
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Abella A, Marti L, Camps M, Claret M, Fernández-Alvarez J, Gomis R, Gumà A, Viguerie N, Carpéné C, Palacín M, Testar X, Zorzano A. Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 activity exerts an antidiabetic action in Goto-Kakizaki rats. Diabetes 2003; 52:1004-13. [PMID: 12663473 DOI: 10.2337/diabetes.52.4.1004] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In this study we have explored whether the bifunctional protein semicarbazide-sensitive amine oxidase (SSAO)/vascular adhesion protein-1 (VAP-1) represents a novel target for type 2 diabetes. To this end, Goto-Kakizaki (GK) diabetic rats were treated with the SSAO substrate benzylamine and with low ineffective doses of vanadate previously shown to have antidiabetic effects in streptozotocin-induced diabetic rats. The administration of benzylamine in combination with vanadate in type 2 diabetic rats acutely stimulated glucose tolerance, and the chronic treatment normalized hyperglycemia, stimulated glucose transport in adipocytes, and reversed muscle insulin resistance. Acute in vivo administration of benzylamine and vanadate stimulated skeletal muscle glucose transport, an effect that was also observed in incubated muscle preparations coincubated with adipose tissue explants or with human recombinant SSAO. Acute administration of benzylamine/vanadate also ameliorated insulin secretion in diabetic GK rats, and this effect was also observed in incubated pancreatic islets. In keeping with these observations, we also demonstrate that pancreatic islets express SSAO/VAP-1. As far as mechanisms of action, we have found that benzylamine/vanadate causes enhanced tyrosine phosphorylation of proteins and reduced protein tyrosine phosphatase activity in adipocytes. In addition, incubation of human recombinant SSAO, benzylamine, and vanadate generates peroxovanadium compounds in vitro. Based on these data, we propose that benzylamine/vanadate administration generates peroxovanadium locally in pancreatic islets, which stimulates insulin secretion and also produces peroxovanadium in adipose tissue, activating glucose metabolism in adipocytes and in neighboring muscle. This opens the possibility of using the SSAO/VAP-1 activity as a local generator of protein tyrosine phosphatase inhibitors in antidiabetic therapy.
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Affiliation(s)
- Anna Abella
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain
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59
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Zhang ZY, Lee SY. PTP1B inhibitors as potential therapeutics in the treatment of type 2 diabetes and obesity. Expert Opin Investig Drugs 2003; 12:223-33. [PMID: 12556216 DOI: 10.1517/13543784.12.2.223] [Citation(s) in RCA: 197] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Coordinated tyrosine phosphorylation is essential for signalling pathways regulated by insulin and leptin. Type 2 diabetes and obesity are characterised by resistance to hormones insulin and leptin, possibly due to attenuated or diminished signalling from the receptors. Pharmacological agents capable of inhibiting the negative regulator(s) of the signalling pathways are expected to potentiate the action of insulin and leptin and therefore be beneficial for the treatment of Type 2 diabetes and obesity. A large body of data from cellular, biochemical, mouse and human genetic and chemical inhibitor studies have identified protein tyrosine phosphatase 1B (PTP1B) as a major negative regulator of both insulin and leptin signalling. In addition, evidence suggests that insulin and leptin action can be enhanced by the inhibition of PTP1B. Consequently, PTP1B has emerged as an attractive novel target for the treatment of both Type 2 diabetes and obesity. The link between PTP1B and diabetes and obesity has led to an avalanche of research dedicated to finding inhibitors of this phosphatase. With the combined use of structure and medicinal chemistry, several groups have demonstrated that it is feasible to obtain small-molecule PTP1B inhibitors with the requisite potency and selectivity. The challenge for the future will be to transform potent and selective small molecule PTP1B inhibitors into orally available drugs with desirable physicochemical properties and in vivo efficacies.
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Affiliation(s)
- Zhong-Yin Zhang
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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60
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Clampit JE, Meuth JL, Smith HT, Reilly RM, Jirousek MR, Trevillyan JM, Rondinone CM. Reduction of protein-tyrosine phosphatase-1B increases insulin signaling in FAO hepatoma cells. Biochem Biophys Res Commun 2003; 300:261-7. [PMID: 12504077 DOI: 10.1016/s0006-291x(02)02839-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Protein-tyrosine phosphatase-1B (PTP1B) has been implicated as a negative regulator of insulin signaling. PTP1B dephosphorylates the insulin receptor and insulin receptor substrates (IRS-1/2), inhibiting the insulin-signaling pathway. PTP1B has been reported to be elevated in diabetes and insulin-resistant states. Conversely, PTP1B null mice have increased insulin sensitivity. To further investigate the effect of PTP1B reduction on insulin signaling, FAO rat hepatoma cells were transfected, by electroporation, with a specific PTP1B antisense oligonucleotide (ASO), or a control oligonucleotide. The PTP1B ASO caused a 50-70% reduction in PTP1B protein expression as measured by Western blot analysis. Upon insulin stimulation, an increase in the phosphorylation of the insulin receptor and insulin receptor substrates was observed, without any change in protein expression levels. Reduction of PTP1B expression in FAO cells also caused an increase in insulin-stimulated phosphorylation of PKB and GSK3, without any change in protein expression. These results demonstrate that reduction of PTP1B can modulate key insulin signaling events downstream of the insulin receptor.
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Affiliation(s)
- Jill E Clampit
- Insulin Signaling, Metabolic Diseases Research, Global Pharmaceutical Research Division, Abbott Laboratories, Department 47R, Building AP10, 100 Abbott Park Road, Abbott Park, IL 60064-6009, USA
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61
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62
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Seiichi T, Shinji S, Toshiro H, Haruhiko Y, Hideaki H, Kosei O, Masaharu N, Hajime I. Effects of troglitazone on skeletal muscle and liver protein tyrosine phosphatase activity in insulin-resistant otsuka long-evans tokushima fatty rats. Curr Ther Res Clin Exp 2002. [DOI: 10.1016/s0011-393x(02)80062-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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63
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Carpentier A, Taghibiglou C, Leung N, Szeto L, Van Iderstine SC, Uffelman KD, Buckingham R, Adeli K, Lewis GF. Ameliorated hepatic insulin resistance is associated with normalization of microsomal triglyceride transfer protein expression and reduction in very low density lipoprotein assembly and secretion in the fructose-fed hamster. J Biol Chem 2002; 277:28795-802. [PMID: 12048212 DOI: 10.1074/jbc.m204568200] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To determine whether reduction of insulin resistance could ameliorate fructose-induced very low density lipoprotein (VLDL) oversecretion and to explore the mechanism of this effect, fructose-fed hamsters received placebo or rosiglitazone for 3 weeks. Rosiglitazone treatment led to normalization of the blunted insulin-mediated suppression of the glucose production rate and to a approximately 2-fold increase in whole body insulin-mediated glucose disappearance rate (p < 0.001). Rosiglitazone ameliorated the defect in hepatocyte insulin-stimulated tyrosine phosphorylation of the insulin receptor, IRS-1, and IRS-2 and the reduced protein mass of IRS-1 and IRS-2 induced by fructose feeding. Protein-tyrosine phosphatase 1B levels were increased with fructose feeding and were markedly reduced by rosiglitazone. Rosiglitazone treatment led to a approximately 50% reduction of VLDL secretion rates (p < 0.05) in vivo and ex vivo. VLDL clearance assessed directly in vivo was not significantly different in the FR (fructose-fed + rosiglitazone-treated) versus F (fructose-fed + placebo-treated) hamsters, although there was a trend toward a lower clearance with rosiglitazone. Enhanced stability of nascent apolipoprotein B (apoB) in fructose-fed hepatocytes was evident, and rosiglitazone treatment resulted in a significant reduction in apoB stability. The increase in intracellular mass of microsomal triglyceride transfer protein seen with fructose feeding was reduced by treatment with rosiglitazone. In conclusion, improvement of hepatic insulin signaling with rosiglitazone, a peroxisome proliferator-activated receptor gamma agonist, is associated with reduced hepatic VLDL assembly and secretion due to reduced intracellular apoB stability.
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Affiliation(s)
- Andre Carpentier
- Department of Medicine, Division of Endocrinology and Metabolism, University Health Network, Hospital for Sick Children, University of Toronto, Toronto, Ontario M5G 2C4, Canada
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64
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Rondinone CM, Trevillyan JM, Clampit J, Gum RJ, Berg C, Kroeger P, Frost L, Zinker BA, Reilly R, Ulrich R, Butler M, Monia BP, Jirousek MR, Waring JF. Protein tyrosine phosphatase 1B reduction regulates adiposity and expression of genes involved in lipogenesis. Diabetes 2002; 51:2405-11. [PMID: 12145151 DOI: 10.2337/diabetes.51.8.2405] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Protein tyrosine phosphatase 1B (PTP1B) has been implicated as a negative regulator of insulin action. Overexpression of PTP1B protein has been observed in insulin-resistant states associated with obesity. Mice lacking a functional PTP1B gene exhibit increased insulin sensitivity and are resistant to weight gain. To investigate the role of PTP1B in adipose tissue from obese animals, hyperglycemic obese (ob/ob) mice were treated with PTP1B antisense oligonucleotide (ISIS-113715). A significant reduction in adiposity correlated with a decrease of PTP1B protein levels in fat. Antisense treatment also influenced the triglyceride content in adipocytes, correlating with a downregulation of genes encoding proteins involved in lipogenesis, such as sterol regulatory element-binding protein 1 and their downstream targets spot14 and fatty acid synthase, as well as other adipogenic genes, lipoprotein lipase, and peroxisome proliferator-activated receptor gamma. In addition, an increase in insulin receptor substrate-2 protein and a differential regulation of the phosphatidylinositol 3-kinase regulatory subunit (p85alpha) isoforms expression were found in fat from antisense-treated animals, although increased insulin sensitivity measured by protein kinase B phosphorylation was not observed. These results demonstrate that PTP1B antisense treatment can modulate fat storage and lipogenesis in adipose tissue and might implicate PTP1B in the enlargement of adipocyte energy stores and development of obesity.
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Affiliation(s)
- Cristina M Rondinone
- Metabolic Diseases Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, Illinois 60064, USA.
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65
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Tagami S, Honda T, Yoshimura H, Homma H, Ohno K, Ide H, Sakaue S, Kawakami Y. Troglitazone ameliorates abnormal activity of protein tyrosine phosphatase in adipose tissues of Otsuka Long-Evans Tokushima Fatty rats. TOHOKU J EXP MED 2002; 197:169-81. [PMID: 12365558 DOI: 10.1620/tjem.197.169] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Protein tyrosine phosphatases (PTPases) play an essential role in the regulation of steady-state phosphorylation of the insulin receptor and other proteins in the insulin signaling pathway. To determine the role of PTPases in adipose tissue in the development into an insulin-resistant state, we examined PTPase activities and protein levels of three major candidate PTPases in adipose tissues of 26-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Particulate PTPase activities in visceral and epididymal adipose tissues of OLETF rats were increased compared to those in Long-Evans Tokushima Otsuka (LETO) rats, non-insulin-resistant controls. Cytosolic PTPase activities in these tissues were conversely decreased in OLETF rats. In subcutaneous adipose tissues, those changes were not observed. Western blot analysis showed that the amounts of leukocyte antigen-related PTPase (LAR), PTPase 1B (PTP1B), and src homology 2-containing PTPase (SH-PTP2) were increased in particulate fractions of visceral and epididymal fat of OLETF rats. On the other hand, those in the cytosolic fractions were slightly decreased. Troglitazone was administered to OLETF rats to examine the effect of the drug on the changes in PTPase activity and distribution. Troglitazone treatment restored those alterations in PTPase activity in the particulate fraction and the amounts of LAR, PTP1B and SH-PTP2 in both fractions of visceral and epididymal adipose tissues of OLETF rats. Although it remains unknown whether such effects of troglitazone are mediated by peroxisome proliferator-activated receptor y, these data provide useful information for understanding the significance of PTPase in insulin-resistant rats and the molecular mechanism of troglitazone action.
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Affiliation(s)
- Seiichi Tagami
- First Department of Medicine, Hokkaido University School of Medicine, Sapporo, Japan
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66
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Hiroki A, Hatakeyama H, Kawakami M, Watanabe T, Takei I, Umezawa K. Antidiabetic effect of a nitrosamine-free dephostatin analogue, methoxime-3,4-dephostatin, in db/db mice. Biomed Pharmacother 2002; 56:179-85. [PMID: 12109810 DOI: 10.1016/s0753-3322(02)00176-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Et-3,4-dephostatin, a protein-tyrosine phosphatase (PTPase) inhibitor, potentiates insulin-dependent signal transduction and shows an antidiabetic effect in mice. However, it contains a nitrosamine moiety that is often mutagenic and carcinogenic. Therefore, we previously designed and synthesized methoxime-3,4-dephostatin as a nitrosamine-free analogue of dephostatin. In the present paper, we studied in situ and in vivo antidiabetic effects of this PTPase inhibitor. Methoxime-3,4-dephostatin induced 2-deoxyglucose transport by mouse 3T3-L1 adipocytes and rat L6 myocytes without insulin. It also inhibited glucagon-induced glucose release from primary culture rat hepatocytes. When hepatocytes were prepared from starved rats, methoxime-3,4-dephostatin did not inhibit the release of glucose, indicating that the chemical may act on glycogenolysis. Oral administration of methoxime-3,4-dephostatin for 3-7 days inhibited the increase in the blood glucose level in type-2 diabetes model db/db mice. It also decreased food and water intakes of mice, but showed no liver or blood toxicity.
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Affiliation(s)
- A Hiroki
- Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Yokohama, Japan
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67
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Ukkola O, Santaniemi M. Protein tyrosine phosphatase 1B: a new target for the treatment of obesity and associated co-morbidities. J Intern Med 2002; 251:467-75. [PMID: 12028501 DOI: 10.1046/j.1365-2796.2002.00992.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Impaired insulin action is important in the pathophysiology of multiple metabolic abnormalities such as obesity and type 2 diabetes. Protein tyrosine phosphatase 1B (PTP1B) is considered a negative regulator of insulin signalling. This is best evidenced by studies on knockout mice showing that lack of PTP1B is associated with increased insulin sensitivity as well as resistance to obesity and in vitro studies whilst studies in animals and humans have given contradictory results. However, several studies support the notion that insulin signalling can be enhanced by the inhibition of PTP1B providing an attractive target for therapy against type 2 diabetes and obesity. In addition, recent genetic studies support the association between PTP1B with insulin resistance. The development of PTP1B inhibitors has already begun although it has become clear that is not easy to find both a selective, safe and effective PTP1B inhibitor. The objective of this paper is to review the current evidence of PTP1B in the pathophysiology of obesity, type 2 diabetes and cancer as well as in the treatment of these disorders.
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Affiliation(s)
- O Ukkola
- Department of Internal Medicine and Biocenter Oulu, University of Oulu, Oulu, Finland.
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68
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Mohammad A, Wang J, McNeill JH. Bis(maltolato)oxovanadium(IV) inhibits the activity of PTP1B in Zucker rat skeletal muscle in vivo. Mol Cell Biochem 2002; 229:125-8. [PMID: 11936837 DOI: 10.1023/a:1017984930836] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The insulin signalling pathway consists of a series of phosphorylation and dephosphorylation steps inside the target cell. Phosphotyrosine phosphatase 1B (PTP1B) dephosphorylates phosphotyrosine (pTyr) residues present on the insulin receptor (IR). In this study we examined the effect of bis(maltolato)oxovanadium(IV) (BMOV) on PTP1B and its possible role in the amelioration of insulin resistance. Fourteen to sixteen week old fatty Zucker rats (F), an animal model of insulin resistance, were treated with BMOV in drinking water for 3 weeks (FT) along with age matched lean littermate controls. The fatty rats responded to vanadium with a significant decrease in plasma insulin, (F = 5.1+/-0.8 FT = 3.3+/-0.7 ng/ml). During insulin resistance the activity of PTP1B has been shown to increase, thus diminishing insulin signalling in the target tissues. Hence, PTP1B is an important target for anti-diabetic drug research. In our investigation we found that the PTP1B activity was increased to 200% in the skeletal muscle of untreated Zucker fatty rats compared to lean littermates. Three weeks of BMOV treatment reduced the activity of PTP1B by 25% in fatty treated rats, in vivo, compared to untreated fatty rats. There was no significant change in the activity of PTP1B in the lean treated rats. There was also no difference in the gene expression of PTP1B in the skeletal muscle of different groups of rats. Vanadium compounds also inhibited PTP1B in vitro. These results indicate that PTP1B may be a potential target for the action of BMOV at least in the Zucker fatty rat model.
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Affiliation(s)
- Askar Mohammad
- Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, The University of British Columbia, Vancouver, Canada
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69
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Wang J, Cheung AT, Kolls JK, Starks WW, Martinez-Hernandez A, Dietzen D, Bryer-Ash M. Effects of adenovirus-mediated liver-selective overexpression of protein tyrosine phosphatase-1b on insulin sensitivity in vivo. Diabetes Obes Metab 2001; 3:367-80. [PMID: 11703427 DOI: 10.1046/j.1463-1326.2001.00173.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AIM Protein tyrosine phosphatase-1B (PTP-1B) is an intracellular PTP known to dephosphorylate and inactivate upstream tyrosine phosphoproteins in the insulin signalling cascade. We and others reported increased abundance of catalytically impaired PTP-1B in tissue lysates from obese human subjects with and without type 2 diabetes, while genetic knockout of PTP-1B improves insulin sensitivity and prevents nutritionally mediated insulin resistance and obesity. The aim of the present work was to further elucidate the role of PTP-1B in glucose metabolism in vivo. METHODS We used adenoviral constructs incorporating cDNAs for either wild-type (W/T) or a catalytically inactive C(215)S (C/S) mutant PTP-1B to achieve liver-selective PTP-1B overexpression in young Sprague-Dawley rats using tail vein injection, based on the high degree of hepatotropism of adenovirus 5 (Ad5). An Ad5-lacZ construct encoding beta-galactosidase was used as a control for viral effects alone. A hyperinsulinaemic euglycaemic clamp was used to study whole body glucose disposal and endogenous glucose production rates. RESULTS Control studies in HIRcB cells confirmed catalytic activity and inactivity of W/T and C/S respectively. Mean PTP-1B abundance was 2.24 +/- 0.02- and 2.33 +/- 0.04-fold of saline-treated control in liver lysates of W/T and C/S rats respectively. Liver selective overexpression was confirmed by analysis of tissue lysates from liver, fat and muscle tissues. Ad5 treatment did not result in a statistically or clinically significant liver injury, as determined by serum alanine aminotransferase and histological examination. Seven days post injection, no significant difference in rate of weight gain, fasting blood glucose or insulin levels were seen in any group. Similarly, under steady-state glucose clamp conditions, glucose disposal rate (R(d)), endogenous glucose production rate (EGP) and serum insulin levels were similar in all groups. CONCLUSION We conclude that moderate medium-term overabundance, to a degree resembling that seen in insulin-resistant states, of PTP-1B in liver tissue does not alter insulin action on glucose metabolism and that the major site of action of PTP-1B is presumably at insulin-responsive target tissue or tissues other than the liver.
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Affiliation(s)
- J Wang
- University of Tennessee, Memphis, TN, USA
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70
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Tao J, Malbon CC, Wang HY. Insulin stimulates tyrosine phosphorylation and inactivation of protein-tyrosine phosphatase 1B in vivo. J Biol Chem 2001; 276:29520-5. [PMID: 11395511 DOI: 10.1074/jbc.m103721200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Protein-tyrosine phosphatase (PTP) 1B has been implicated in negative regulation of insulin action, although little is known of the ability of insulin to regulate PTP1B itself. The ability of insulin to regulate phosphorylation and activation of PTP1B was probed in vivo. Challenge with insulin in vivo provoked a transient, sharp increase in the phosphotyrosine content of PTP1B in fat and skeletal muscle that peaked within 15 min. Insulin stimulated a decline of 60--70% in PTP1B activity. In mouse adipocytes, the inhibition of PTP1B activity and increased tyrosine phosphorylation of the enzyme were blocked by the insulin receptor tyrosine kinase inhibitor AG1024. Phosphoserine content of PTP1B declined in response to insulin stimulation. Elevation of intracellular cyclic AMP provokes a sharp increase in PTP1B activity and leads to increased phosphorylation of serine residues and decreased tyrosine phosphorylation. Suppression of cyclic AMP levels or inhibition of protein kinase A leads to a sharp decline in PTP1B activity, a decrease in phosphoserine content, and an increase in PTP1B phosphotyrosine content. PTP1B appears to be a critical point for insulin and catecholamine counter-regulation.
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Affiliation(s)
- J Tao
- Department of Molecular Pharmacology, University Medical Center, SUNY/Stony Brook, Stony Brook, New York 11794-8651, USA
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71
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Zabolotny JM, Kim YB, Peroni OD, Kim JK, Pani MA, Boss O, Klaman LD, Kamatkar S, Shulman GI, Kahn BB, Neel BG. Overexpression of the LAR (leukocyte antigen-related) protein-tyrosine phosphatase in muscle causes insulin resistance. Proc Natl Acad Sci U S A 2001; 98:5187-92. [PMID: 11309481 PMCID: PMC33185 DOI: 10.1073/pnas.071050398] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Previous reports indicate that the expression and/or activity of the protein-tyrosine phosphatase (PTP) LAR are increased in insulin-responsive tissues of obese, insulin-resistant humans and rodents, but it is not known whether these alterations contribute to the pathogenesis of insulin resistance. To address this question, we generated transgenic mice that overexpress human LAR, specifically in muscle, to levels comparable to those reported in insulin-resistant humans. In LAR-transgenic mice, fasting plasma insulin was increased 2.5-fold compared with wild-type controls, whereas fasting glucose was normal. Whole-body glucose disposal and glucose uptake into muscle in vivo were reduced by 39-50%. Insulin injection resulted in normal tyrosyl phosphorylation of the insulin receptor and insulin receptor substrate 1 (IRS-1) in muscle of transgenic mice. However, phosphorylation of IRS-2 was reduced by 62%, PI3' kinase activity associated with phosphotyrosine, IRS-1, or IRS-2 was reduced by 34-57%, and association of p85alpha with both IRS proteins was reduced by 39-52%. Thus, overexpression of LAR in muscle causes whole-body insulin resistance, most likely due to dephosphorylation of specific regulatory phosphotyrosines on IRS proteins. Our data suggest that increased expression and/or activity of LAR or related PTPs in insulin target tissues of obese humans may contribute to the pathogenesis of insulin resistance.
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Affiliation(s)
- J M Zabolotny
- Division of Endocrinology and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, 99 Brookline Avenue, Boston, MA 02215, USA
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72
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He J, Watkins S, Kelley DE. Skeletal muscle lipid content and oxidative enzyme activity in relation to muscle fiber type in type 2 diabetes and obesity. Diabetes 2001; 50:817-23. [PMID: 11289047 DOI: 10.2337/diabetes.50.4.817] [Citation(s) in RCA: 366] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In obesity and type 2 diabetes, skeletal muscle has been observed to have a reduced oxidative enzyme activity, increased glycolytic activity, and increased lipid content. These metabolic characteristics are related to insulin resistance of skeletal muscle and are factors potentially related to muscle fiber type. The current study was undertaken to examine the interactions of muscle fiber type in relation to oxidative enzyme activity, glycolytic enzyme activity, and muscle lipid content in obese and type 2 diabetic subjects compared with lean healthy volunteers. The method of single-fiber analysis was used on vastus lateralis muscle obtained by percutaneous biopsy from 22 lean, 20 obese, and 20 type 2 diabetic subjects (ages 35+/-1, 42+/-2, and 52+/-2 years, respectively), with values for BMI that were similar in obese and diabetic subjects (23.7+/-0.7, 33.2+/-0.8, and 31.8+/-0.8 kg/m2, respectively). Oxidative enzyme activity followed the order of type I > type IIa > type IIb, but within each fiber type, skeletal muscle from obese and type 2 diabetic subjects had lower oxidative enzyme activity than muscle from lean subjects (P < 0.01). Muscle lipid content followed a similar pattern in relation to fiber type, and within each fiber type, muscle from obese and type 2 diabetic subjects had greater lipid content (P < 0.01). In summary, based on single-fiber analysis, skeletal muscle in obese and type 2 diabetic subjects mani-fests disturbances of oxidative enzyme activity and increased lipid content that are independent of the effect of fiber type.
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Affiliation(s)
- J He
- Department of Medicine, University of Pittsburgh School of Medicine, Pennsylvania, USA
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73
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Egawa K, Maegawa H, Shimizu S, Morino K, Nishio Y, Bryer-Ash M, Cheung AT, Kolls JK, Kikkawa R, Kashiwagi A. Protein-tyrosine phosphatase-1B negatively regulates insulin signaling in l6 myocytes and Fao hepatoma cells. J Biol Chem 2001; 276:10207-11. [PMID: 11136729 DOI: 10.1074/jbc.m009489200] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin signaling is regulated by tyrosine phosphorylation of the signaling molecules, such as the insulin receptor and insulin receptor substrates (IRSs). Therefore, the balance between protein-tyrosine kinases and protein-tyrosine phosphatase activities is thought to be important in the modulation of insulin signaling in insulin-resistant states. We thus employed the adenovirus-mediated gene transfer technique, and we analyzed the effect of overexpression of a wild-type protein-tyrosine phosphatase-1B (PTP1B) on insulin signaling in both L6 myocytes and Fao cells. In both cells, PTP1B overexpression blocked insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1 by more than 70% and resulted in a significant inhibition of the association between IRS-1 and the p85 subunit of phosphatidylinositol 3-kinase and Akt phosphorylation as well as mitogen-activated protein kinase phosphorylation. Moreover, insulin-stimulated glycogen synthesis was also inhibited by PTP1B overexpression in both cells. These effects were specific for insulin signaling, because platelet-derived growth factor (PDGF)-stimulated PDGF receptor tyrosine phosphorylation and Akt phosphorylation were not inhibited by PTP1B overexpression. The present findings demonstrate that PTP1B negatively regulates insulin signaling in L6 and Fao cells, suggesting that PTP1B plays an important role in insulin resistance in muscle and liver.
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Affiliation(s)
- K Egawa
- Third Department of Medicine, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan
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74
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Abstract
A role for protein tyrosine phosphatases in the negative regulation of insulin signaling and a putative involvement in the insulin resistance associated with type 2 diabetes have been postulated since their discovery. The recent demonstration that mice lacking the protein tyrosine phosphatase-1B (PTP-1B) have enhanced insulin sensitivity validates this. Furthermore, when fed a high fat diet, these mice maintained insulin sensitivity and were resistant to obesity, suggesting that inhibition of PTP-1B activity could be a novel way of treating type 2 diabetes and obesity. This commentary reviews our current knowledge of PTP-1B in insulin signaling and its role in diabetes and discusses the development of potent and selective PTP-1B inhibitors.
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Affiliation(s)
- B P Kennedy
- Department of Biochemistry and Molecular Biology, Merck Frosst Center for Therapeutic Research, Pointe Claire-Dorval, H9R 4P8, Quebec, Canada.
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75
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Klaman LD, Boss O, Peroni OD, Kim JK, Martino JL, Zabolotny JM, Moghal N, Lubkin M, Kim YB, Sharpe AH, Stricker-Krongrad A, Shulman GI, Neel BG, Kahn BB. Increased energy expenditure, decreased adiposity, and tissue-specific insulin sensitivity in protein-tyrosine phosphatase 1B-deficient mice. Mol Cell Biol 2000; 20:5479-89. [PMID: 10891488 PMCID: PMC85999 DOI: 10.1128/mcb.20.15.5479-5489.2000] [Citation(s) in RCA: 969] [Impact Index Per Article: 40.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2000] [Accepted: 04/24/2000] [Indexed: 12/16/2022] Open
Abstract
Protein-tyrosine phosphatase 1B (PTP-1B) is a major protein-tyrosine phosphatase that has been implicated in the regulation of insulin action, as well as in other signal transduction pathways. To investigate the role of PTP-1B in vivo, we generated homozygotic PTP-1B-null mice by targeted gene disruption. PTP-1B-deficient mice have remarkably low adiposity and are protected from diet-induced obesity. Decreased adiposity is due to a marked reduction in fat cell mass without a decrease in adipocyte number. Leanness in PTP-1B-deficient mice is accompanied by increased basal metabolic rate and total energy expenditure, without marked alteration of uncoupling protein mRNA expression. In addition, insulin-stimulated whole-body glucose disposal is enhanced significantly in PTP-1B-deficient animals, as shown by hyperinsulinemic-euglycemic clamp studies. Remarkably, increased insulin sensitivity in PTP-1B-deficient mice is tissue specific, as insulin-stimulated glucose uptake is elevated in skeletal muscle, whereas adipose tissue is unaffected. Our results identify PTP-1B as a major regulator of energy balance, insulin sensitivity, and body fat stores in vivo.
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Affiliation(s)
- L D Klaman
- Cancer Biology Program, Division of Hematology-Oncology, Boston, Massachusetts 02215, USA
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76
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Abstract
Protein-tyrosine kinases (PTKs) and their associated signaling pathways are crucial for the regulation of numerous cell functions including growth, mitogenesis, motility, cell-cell interactions, metabolism, gene transcription, and the immune response. Since tyrosine phosphorylation is reversible and dynamic in vivo, the phosphorylation states of proteins are governed by the opposing actions of PTKs and protein-tyrosine phosphatases (PTPs). In this light, both PTKs and PTPs play equally important roles in signal transduction in eukaryotic cells, and comprehension of mechanisms behind the reversible pTyr-dependent modulation of protein function and cell physiology must necessarily encompass the characterization of PTPs as well as PTKs. In spite of the large number of PTPs identified to date and the emerging role played by PTPs in disease, a detailed understanding of the role played by PTPs in signaling pathways has been hampered by the absence of PTP-specific agents. Such PTP-specific inhibitors could potentially serve as useful tools in determining the physiological significance of protein tyrosine phosphorylation in complex cellular signal transduction pathways and may constitute valuable therapeutics in the treatment of several human diseases. The goal of this review is therefore to summarize current understandings of PTP structure and mechanism of catalysis and the relationship of these to PTP inhibitor development. The review is organized such that enzyme structure is covered first, followed by mechanisms of catalysis then PTP inhibitor development. In discussing PTP inhibitor development, nonspecific inhibitors and those obtained by screening methods are initially presented with the focus then shifting to inhibitors that utilize a more structure-based rationale.
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Affiliation(s)
- T R Burke
- Laboratory of Medicinal Chemistry, National Institutes of Health, Bethesda, MD 20892, USA
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77
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Venable CL, Frevert EU, Kim YB, Fischer BM, Kamatkar S, Neel BG, Kahn BB. Overexpression of protein-tyrosine phosphatase-1B in adipocytes inhibits insulin-stimulated phosphoinositide 3-kinase activity without altering glucose transport or Akt/Protein kinase B activation. J Biol Chem 2000; 275:18318-26. [PMID: 10751417 DOI: 10.1074/jbc.m908392199] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies suggested that protein-tyrosine phosphatase 1B (PTP1B) antagonizes insulin action by catalyzing dephosphorylation of the insulin receptor (IR) and/or other key proteins in the insulin signaling pathway. In adipose tissue and muscle of obese humans and rodents, PTP1B expression is increased, which led to the hypothesis that PTP1B plays a role in the pathogenesis of insulin resistance. Consistent with this, mice in which the PTP1B gene was disrupted exhibit increased insulin sensitivity. To test whether increased expression of PTP1B in an insulin-sensitive cell type could contribute to insulin resistance, we overexpressed wild-type PTP1B in 3T3L1 adipocytes using adenovirus-mediated gene delivery. PTP1B expression was increased approximately 3-5-fold above endogenous levels at 16 h, approximately 14-fold at 40 h, and approximately 20-fold at 72 h post-transduction. Total protein-tyrosine phosphatase activity was increased by 50% at 16 h, 3-4-fold at 40 h, and 5-6-fold at 72 h post-transduction. Compared with control cells, cells expressing high levels of PTP1B showed a 50-60% decrease in maximally insulin-stimulated tyrosyl phosphorylation of IR and insulin receptor substrate-1 (IRS-1) and phosphoinositide 3-kinase (PI3K) activity associated with IRS-1 or with phosphotyrosine. Akt phosphorylation and activity were unchanged. Phosphorylation of p42 and p44 MAP kinase (MAPK) was reduced approximately 32%. Overexpression of PTP1B had no effect on basal, submaximally or maximally (100 nm) insulin-stimulated glucose transport or on the EC(50) for transport. Our results suggest that: 1) insulin stimulation of glucose transport in adipocytes requires </=45% of maximal tyrosyl phosphorylation of IR or IRS-1 and <50% of maximal activation of PI3K, 2) a novel PI3K-independent pathway may play a role in insulin-induced glucose transport in adipocytes, and 3) overexpression of PTP1B alone in adipocytes does not impair glucose transport.
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Affiliation(s)
- C L Venable
- Diabetes Unit, Division of Endocrinology and Cancer Biology Program, Division of Hematology-Oncology, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, Massachusetts 02215, USA
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78
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Carvalho E, Rondinone C, Smith U. Insulin resistance in fat cells from obese Zucker rats--evidence for an impaired activation and translocation of protein kinase B and glucose transporter 4. Mol Cell Biochem 2000; 206:7-16. [PMID: 10839189 DOI: 10.1023/a:1007009723616] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The effect of insulin on glucose transport, glucose transporter 4 (Glut4) translocation, and intracellular signaling were measured in fat cells from lean and obese Zucker rats of different ages. Insulin-stimulated glucose transport was markedly reduced in adipocytes from old and obese animals. The protein content of Glut4 and insulin receptor substrates (IRS) 1 and 2 were also reduced while other proteins, including the p85 subunit of PI3-kinase, Shc and the MAP kinases (ERK1 and 2) were essentially unchanged. There was a marked impairment in the insulin stimulated tyrosine phosphorylation of IRS-1 and 2 as well as activation of PI3-kinase and PKB in cells from old and obese animals. Furthermore, insulin-stimulated translocation of both Glut4 and PKB to the plasma membrane was virtually abolished. The phosphotyrosine phosphatase inhibitor, vanadate, increased the insulin-stimulated upstream signaling including PI3-kinase and PKB activities as well as rate of glucose transport. Thus, the insulin resistance in cells from old and obese Zucker rats can be accounted for by an impaired translocation process, due to signaling defects leading to a reduced activation of PI3-kinase and PKB, as well as an attenuated Glut4 protein content.
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Affiliation(s)
- E Carvalho
- Department of Internal Medicine, University of Göteborg, Sahlgrenska University Hospital, Sweden
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79
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Nawano M, Oku A, Ueta K, Umebayashi I, Ishirahara T, Arakawa K, Saito A, Anai M, Kikuchi M, Asano T. Hyperglycemia contributes insulin resistance in hepatic and adipose tissue but not skeletal muscle of ZDF rats. Am J Physiol Endocrinol Metab 2000; 278:E535-43. [PMID: 10710509 DOI: 10.1152/ajpendo.2000.278.3.e535] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To determine the contribution of hyperglycemia to the insulin resistance in various insulin-sensitive tissues of Zucker diabetic fatty (ZDF) rats, T-1095, an oral sodium-dependent glucose transporter (SGLT) inhibitor, was administered by being mixed into food. Long-term treatment with T-1095 lowered both fed and fasting blood glucose levels to near normal ranges. A hyperinsulinemic euglycemic clamp study that was performed after 4 wk of T-1095 treatment demonstrated partial recovery of the reduced glucose infusion rate (GIR) in the T-1095-treated group. In the livers of T-1095-treated ZDF rats, hepatic glucose production rate (HGP) and glucose utilization rate (GUR) showed marked recovery, with almost complete normalization of reduced glucokinase/glucose-6-phosphatase (G-6-Pase) activities ratio. In adipose tissues, decreased GUR was also shown to be significantly improved with a normalization of insulin-induced GLUT-4 translocation. In contrast, in skeletal muscles, the reduced GUR was not significantly improved in response to amelioration of hyperglycemia by T-1095 treatment. These results suggest that the contribution of hyperglycemia to insulin resistance in ZDF rats is very high in the liver and considerably elevated in adipose tissues, although it is very low in skeletal muscle.
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Affiliation(s)
- M Nawano
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Tokyo 113-0033, Japan
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80
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Abstract
Type 2 or non-insulin-dependent diabetes mellitus (NIDDM) is reaching epidemic proportions in industrialized countries. Obesity is a major factor in this disease, since about 75% of obese individuals will develop type 2 diabetes. There is an urgent need to develop new therapies for these diseases. Recently, the protein tyrosine phosphatase PTP-1B has been shown to be a negative regulator of the insulin signaling pathway, suggesting that inhibitors of this enzyme may be beneficial in the treatment of type 2 diabetes. Mice lacking PTP-1B are resistant to both diabetes and obesity.
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Affiliation(s)
- B P Kennedy
- Department of Biochemistry and Molecular Biology, Merck Frosst Center for Therapeutic Research, Pointe Claire-Dorval, Quebec, Canada
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81
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Shafrir E, Ziv E, Mosthaf L. Nutritionally induced insulin resistance and receptor defect leading to beta-cell failure in animal models. Ann N Y Acad Sci 1999; 892:223-46. [PMID: 10842665 DOI: 10.1111/j.1749-6632.1999.tb07798.x] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Animals with genetically or nutritionally induced insulin resistance and Type 2 diabetes comprise two groups: those with resilient beta-cells, e.g., ob/ob mice or fa/fa rats, capable of longstanding compensatory insulin hypersecretion and those with labile beta-cells in which the secretion pressure leads to beta-cell degranulation and apoptosis, e.g., db/db mice and Psammomys gerbils (sand rats). Psammomys features low insulin receptor density; on a relatively high energy diet it becomes hyperinsulinemic and hyperglycemic. In hyperinsulinemic clamp the hepatic glucose production is only partially suppressed by insulin, even in the normoglycemic state. The capacity of insulin to activate muscle and liver receptor tyrosine kinase is nearly abolished. GLUT4 content and mRNA are markedly reduced. Hyperinsulinemia was also demonstrated to inhibit insulin signaling and glucose transport in several other species. Among the factors affecting the insulin signaling pathway, phosphorylation of serine/threonine appears to be the prominent cause of receptor malfunction as inferred from the finding of overexpression of PKC epsilon isoforms in the muscle and liver of Psammomys. The insulin resistance syndrome progressing in animals with labile beta-cells to overt diabetes and beta-cell failure is a "thrifty gene" characteristic. This is probably also true for human populations emerging from food scarcity into nutritional affluence, inappropriate for their metabolic capacity. Thus, the nutritionally induced hyperinsulinemia, associated with PKC epsilon activation may be looked upon from the molecular point of view as "PKC epsilon overexpression syndrome."
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Affiliation(s)
- E Shafrir
- Department of Biochemistry, Hadassah University Hospital, Jerusalem, Israel.
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82
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Cheung A, Kusari J, Jansen D, Bandyopadhyay D, Kusari A, Bryer-Ash M. Marked impairment of protein tyrosine phosphatase 1B activity in adipose tissue of obese subjects with and without type 2 diabetes mellitus. THE JOURNAL OF LABORATORY AND CLINICAL MEDICINE 1999; 134:115-23. [PMID: 10444024 DOI: 10.1016/s0022-2143(99)90115-4] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Protein tyrosine phosphatases (PTPs) are required for the dephosphorylation of the insulin receptor (IR) and its initial cellular substrates, and it has recently been reported that PTP-1B may play a role in the pathogenesis of insulin resistance in obesity and type 2 diabetes mellitus (DM). We therefore determined the amount and activity of PTP-1B in abdominal adipose tissue obtained from lean nondiabetic subjects (lean control (LC)), obese nondiabetic subjects (obese control (OC)), and subjects with both type 2 DM (DM2) and obesity (obese diabetic (OD)). PTP-1B protein levels were 3-fold higher in OC than in LC (1444 +/- 195 U vs 500 +/- 146 U (mean +/- SEM), P < .015), while OD exhibited a 5.5-fold increase (2728 +/- 286 U, P < .01). PTP activity was assayed by measuring the dephosphorylating activity toward a phosphorus 32-labeled synthetic dodecapeptide. In contrast to the increased PTP-1B protein levels, PTP-1B activity per unit of PTP-1B protein was markedly reduced, by 71% and 88% in OC and OD, respectively. Non-PTP-1B tyrosine phosphatase activity was comparable in all three groups. Similar results were obtained when PTP-1B activity was measured against intact human IR. A significant correlation was found between body mass index (BMI) and PTP-1B level (r = 0.672, P < .02), whereas BMI and PTP-1B activity per unit of PTP-1B showed a strong inverse correlation (r = -0.801, P < .002). These data suggest that the insulin resistance of obesity and DM2 is characterized by the increased expression of a catalytically impaired PTP-1B in adipose tissue and that impaired PTP-1B activity may be pathogenic for insulin resistance in these conditions.
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Affiliation(s)
- A Cheung
- Department of Medicine, University of Tennessee College of Medicine, Memphis, USA
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83
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Kole HK, Kole S, Mallory BP, Li PM, Goldstein BJ, Bernier M. Inhibition of the transmembrane protein tyrosine phosphatase lar by 3S-peptide-I enhances insulin receptor phosphorylation in intact cells. J Basic Clin Physiol Pharmacol 1999; 9:111-26. [PMID: 10212829 DOI: 10.1515/jbcpp.1998.9.2-4.111] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
3S-peptide-I, a tris-sulfotyrosyl dodecapeptide that corresponds to the major autophosphorylation domain within the insulin receptor beta-subunit, selectively enhances insulin signal transduction by specifically inhibiting dephosphorylation of the insulin receptor catalyzed by protein tyrosine phosphatases (PTPases). Because of the potential role of the transmembrane PTPase LAR in the regulation of insulin signaling, we assessed the effect of 3S-peptide-I on recombinant LAR PTPase activity and in McA-RH7777 rat hepatoma cells overexpressing full-length LAR protein (McA4B/LAR). 3S-peptide-I significantly reduced insulin receptor dephosphorylation by recombinant LAR (p < 0.001) while blocking dephosphorylation of the insulin receptor by approximately 72% in semi-permeabilized McA4B/LAR cells (p < 0.001). Increased LAR expression resulted in 40% reduction in ligand-mediated phosphorylation of the insulin receptor compared with null vector control (p < 0.001). However, treatment of intact McA4B/LAR cells with a fatty acid derivative of 3S-peptide-I (50 microM) led to an enhancement of insulin-stimulated receptor phosphorylation by 89% (p < 0.001). As a result, control and McA4B/LAR cells showed comparable steady-state levels of insulin receptor phosphorylation in the presence of insulin. These findings provide evidence that 3S-peptide-I may improve insulin responsiveness in intact cells by inhibiting LAR, an enzyme whose activity has been implicated in the pathogenesis of insulin resistance.
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Affiliation(s)
- H K Kole
- Diabetes Section, Laboratory of Clinical Investigation, NIA, NIH, Baltimore, MD 21224
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84
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Shafrir E, Ziv E. Cellular mechanism of nutritionally induced insulin resistance: the desert rodent Psammomys obesus and other animals in which insulin resistance leads to detrimental outcome. J Basic Clin Physiol Pharmacol 1999; 9:347-85. [PMID: 10212843 DOI: 10.1515/jbcpp.1998.9.2-4.347] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Animal species with genetic or nutritionally induced insulin resistance, diabetes and obesity (diabesity) may be divided into two broad groups: those with resilient pancreatic beta-cells, e.g. ob/ob mice and fa/fa rats, capable of long-lasting compensatory insulin over-secretion, and those with labile beta-cells in which the secretion pressure leads to irreversible beta-cell degranulation, e.g. db/db mice, Macaca mulatta primates, ZDF diabetic rats. Prominent in this group is the Israeli desert gerbil Psammomys obesus (sand rat), which features low insulin receptor density in liver and muscle. On a diet of relatively high energy, the capacity of insulin to activate the receptor tyrosine kinase (TK) is reduced, in the face of hyperinsulinemia. With the following hyperglycemia, the rising insulin resistance imposes a vicious cycle of insulinemia and glycemia, accentuating the TK activation failure and the beta-cell failure. Among various factors affecting the insulin signaling pathway, multisite phosphorylation, including serine and threonine on the receptor beta-subunit, due to overexpression of certain protein kinase C isoforms, seems to be responsible for the inhibition of the critical step of TK phosphorylation activity. The compromised TK activation is reversible by diet restriction which restores to normal the glycemia and insulinemia. The beta-cell response to long-lasting stimulation and the receptor malfunction in diabesity have implications for a similar etiology in human insulin resistance syndrome and type 2 diabetes, particularly in populations emerging from a food scarce environment into nutritional affluence, inappropriate to the human metabolic capacity. It is suggested that the "thrifty gene" is characterized by a low threshold for insulin secretion and low capacity for insulin clearance. Thus, nutritionally-induced hyperinsulinemia is potentiated and becomes the primary phenotypic expression of the thrifty gene, linked to the insulin receptor signaling pathway malfunction.
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Affiliation(s)
- E Shafrir
- Diabetes Research Unit, Hadassah University Hospital, Jerusalem, Israel
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85
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Goldstein BJ, Li PM, Ding W, Ahmad F, Zhang WR. Regulation of insulin action by protein tyrosine phosphatases. VITAMINS AND HORMONES 1998; 54:67-96. [PMID: 9529974 DOI: 10.1016/s0083-6729(08)60922-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- B J Goldstein
- Dorrance H. Hamilton Research Laboratories, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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86
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Xu B, Berkich DA, Crist GH, LaNoue KF. A1 adenosine receptor antagonism improves glucose tolerance in Zucker rats. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:E271-9. [PMID: 9486158 DOI: 10.1152/ajpendo.1998.274.2.e271] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The A1 adenosine receptor (A1ar) antagonist 1,3-dipropyl-8-(p-acrylic)-phenylxanthine (BW-1433) was administered to lean and obese Zucker rats to probe the influence of endogenously activated A1ars on whole body energy metabolism. The drug induced a transient increase in lipolysis as indicated by a rise in serum glycerol in obese rats. The disappearance of the response by day 7 of chronic studies was accompanied by an increase in A1ar numbers. Glucose tolerance tests were administered to rats treated with BW-1433. Peak serum insulin levels and areas under glucose curves (AUGs) were 34 and 41% lower in treated obese animals than in controls, respectively, and 19 and 39% lower in lean animals. With chronic administration (6 wk), AUGs decreased 47 and 33% in obese and lean animals, respectively. There was no effect of BW-1433 in either lean or obese rats on weight gain or percent body fat. Thus the major sustained influence of whole body A1ar antagonism in both lean and obese animals was an increase in whole body glucose tolerance at lower levels of insulin.
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Affiliation(s)
- B Xu
- Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey 17033-0850, USA
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87
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Schaapveld R, Wieringa B, Hendriks W. Receptor-like protein tyrosine phosphatases: alike and yet so different. Mol Biol Rep 1997; 24:247-62. [PMID: 9403867 DOI: 10.1023/a:1006870016238] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Reversible phosphorylation on tyrosine residues is an extremely rapid and powerful posttranslational modification that is used in signalling pathways for the regulation of cell growth and differentiation. Over the past several years an impressive number of receptor-like protein tyrosine phosphatase (RPTPase) family members have been identified by molecular cloning, and undoubtedly many more will follow. This review provides an overview of the molecular data that are available for the currently identified RPTPases and discusses their possible biological implications.
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Affiliation(s)
- R Schaapveld
- Department of Cell Biology & Histology, Institute of Cellular Signalling, University of Nijmegen, The Netherlands
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88
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Klimes I, Seböková E. Hypertension and the insulin resistance syndrome of rats. Are they related? Ann N Y Acad Sci 1997; 827:13-34. [PMID: 9329739 DOI: 10.1111/j.1749-6632.1997.tb51819.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- I Klimes
- Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovak Republic
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89
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Abstract
Numerous endocrine alterations are associated with obesity (Table 1). The majority of the alterations are secondary to obesity and must be considered simply associated and potentially in the pathogenesis of the complications of obesity. The discovery of new endocrine peptides such as leptin that signal body fat content will increase our understanding of the regulation of body fat content. As a result, therapies will most certainly be developed that are directly targeted at the alterations in endocrine function.
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Affiliation(s)
- S R Smith
- Inpatient Metabolic Unit, Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, USA
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90
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Worm D, Vinten J, Staehr P, Henriksen JE, Handberg A, Beck-Nielsen H. Altered basal and insulin-stimulated phosphotyrosine phosphatase (PTPase) activity in skeletal muscle from NIDDM patients compared with control subjects. Diabetologia 1996; 39:1208-14. [PMID: 8897009 DOI: 10.1007/bf02658508] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
To measure possible changes in basal and insulin-stimulated phosphotyrosine phosphatase (PTPase) activity in skeletal muscle from insulin-resistant individuals, soluble and particulate muscle fractions were prepared from biopsies taken before and after a 3-h hyperinsulinaemic euglycaemic clamp in eight non-insulin-dependent diabetic (NIDDM) patients and nine control subjects. We used a sensitive sandwich-immunofluorescence assay and the human insulin receptor as the substrate. PTPase activity was expressed as percentage of dephosphorylation of phosphotyrosyl-residues in immobilized insulin receptors per 2 h incubation time per 83 micrograms and 19 micrograms muscle fraction protein (soluble and particulate fraction, respectively). In the diabetic soluble muscle fractions, the basal PTPase activity was decreased compared with that of control subjects (11.5 +/- 5.5 vs 27.5 +/- 3.3, p < 0.04, mean +/- SEM). In the particulate muscle fractions from the control subjects, PTPase activity was increased after 3 h hyperinsulinaemia (20.0 +/- 3.2 vs 30.2 +/- 3.6, p < 0.03) and in the corresponding soluble fractions PTPase activity seemed decreased (27.5 +/- 3.3 vs 19.9 +/- 5.9, NS). No effect of insulin on PTPase activity was found in NIDDM patients (25.1 +/- 4.1 vs 27.2 +/- 5.2, 11.5 +/- 5.5 vs 15.1 +/- 4.5 [particulate and soluble fractions], NS). In conclusion, we found that the basal PTPase activity in soluble muscle fractions was decreased in NIDDM patients; furthermore, insulin stimulation was unable to increase PTPase activities in the particulate fractions, as opposed to the effect of insulin in control subjects.
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Affiliation(s)
- D Worm
- Diabetes Research Centre, Odense University Hospital, Denmark
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