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1.
Protein-tyrosine phosphatases (PTPases) play a key role in maintaining the steady-state tyrosine phosphorylation of the insulin receptor (IR) and its substrate proteins such as insulin receptor substrate 1 (IRS-1). However, the PTPase(s) that inactivate IR and IRS-1 under physiological conditions remain unidentified. Here, we analyze the subcellular distribution in rat adipocytes of several PTPases thought to be involved in the counterregulation of insulin signaling. We found that the transmembrane enzymes, protein-tyrosine phosphatase (PTP)-alpha and leukocyte common antigen-related (LAR), were detected predominantly in the plasma membrane and to a lesser extent in the heavy microsomes, a distribution similar to that of insulin receptor. PTP-1B and IRS-1 were present in light microsomes and cytosol, whereas SHPTP2/Syp was exclusively cytosolic. Insulin induced a redistribution of PTP-alpha from the plasma membrane to the heavy microsomes in a parallel fashion with the receptor. The distribution of PTP-1B in the light microsomes from resting adipocytes was similar to that of IRS-1 as determined by sucrose velocity gradient fractionation. Analysis of the catalytic activity of partially purified rat adipocyte PTP-alpha and LAR and recombinant PTP-1B showed that all three PTPases dephosphorylate IR. When a mix of IR/IRS-1 was used as a substrate, PTP-1B was particularly effective in dephosphorylating IRS-1. Considering that IR and IRS-1 can be dephosphorylated in internal membrane compartments from rat adipocytes (Kublaoui, B., Lee, J., and Pilch, P.F. (1995) J. Biol. Chem. 270, 59-65) and that PTP-alpha and PTP-1B are the respective PTPases in these fractions, we conclude that these PTPases are responsible for the counterregulation of insulin signaling there, whereas both LAR and PTP-alpha may act upon cell surface insulin receptors. 相似文献
2.
The SPOT technique as a tool for studying protein tyrosine phosphatase substrate specificities
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Espanel X Huguenin-Reggiani M Hooft van Huijsduijnen R 《Protein science : a publication of the Protein Society》2002,11(10):2326-2334
The activity of protein tyrosine phosphatases (PTPs) is restricted by their substrate specificities. The analysis of PTP specificity was greatly helped by the discovery that "substrate-trapping" PTP mutants, such as PTP-1B D181A, stably and specifically bind their substrates. We have set up a PTP substrate specificity assay based on the SPOT technique, which involves the microsynthesis of (phospho)peptides on membranes. To validate this approach, substrate trapping PTP-1B was tested on its cognate ligand, the autophosphorylated insulin receptor (IR). On SPOT membranes, IR peptides with phosphotyrosine 1163 were efficiently bound by PTP1B D181A, and dephosphorylated by PTP-1B. Phosphotyrosine 1163 was preferred over the neighboring 1158 and 1162 phosphotyrosines. PTP-1B also recognized IR-like motifs in Trk autophosphorylation domains, and STAT 5 phosphopeptides. Using a gridded 20-by-20 SPOT library, we show that peptides with the YZM motif (Z: phosphotyrosine) are the strongest ligands for PTP-1B D181A, but not the optimal substrates for dephosphorylation by wild-type PTP1B. In addition we show that PTP-1B and PTP-beta dephosphorylation efficiency is strongly modulated by the introduction of phospho-serine or phospho-threonine in their cognate phospho-tyrosine substrates. Altogether our data illustrate that the SPOT technique is a highly efficient tool for the study of PTP substrate specificity. 相似文献
3.
Wälchli S Curchod ML Gobert RP Arkinstall S Hooft van Huijsduijnen R 《The Journal of biological chemistry》2000,275(13):9792-9796
Many pharmacologically important receptors, including all cytokine receptors, signal via tyrosine (auto)phosphorylation, followed by resetting to their original state through the action of protein tyrosine phosphatases (PTPs). Establishing the specificity of PTPs for receptor substrates is critical both for understanding how signaling is regulated and for the development of specific PTP inhibitors that act as ligand mimetics. We have set up a systematic approach for finding PTPs that are specific for a receptor and have validated this approach with the insulin receptor kinase. We have tested nearly all known human PTPs (45) in a membrane binding assay, using "substrate-trapping" PTP mutants. These results, combined with secondary dephosphorylation tests, confirm and extend earlier findings that PTP-1b and T-cell PTP are physiological enzymes for the insulin receptor kinase. We demonstrate that this approach can rapidly reduce the number of PTPs that have a particular receptor or other phosphoprotein as their substrate. 相似文献
4.
5.
McCain DF Wu L Nickel P Kassack MU Kreimeyer A Gagliardi A Collins DC Zhang ZY 《The Journal of biological chemistry》2004,279(15):14713-14725
Protein-tyrosine phosphatases (PTPs) are important signaling enzymes that have emerged within the last decade as a new class of drug targets. It has previously been shown that suramin is a potent, reversible, and competitive inhibitor of PTP1B and Yersinia PTP (YopH). We therefore screened 45 suramin analogs against a panel of seven PTPs, including PTP1B, YopH, CD45, Cdc25A, VHR, PTPalpha, and LAR, to identify compounds with improved potency and specificity. Of the 45 compounds, we found 11 to have inhibitory potency comparable or significantly improved relative to suramin. We also found suramin to be a potent inhibitor (IC(50) = 1.5 microm) of Cdc25A, a phosphatase that mediates cell cycle progression and a potential target for cancer therapy. In addition we also found three other compounds, NF201, NF336, and NF339, to be potent (IC(50) < 5 microm) and specific (at least 20-30-fold specificity with respect to the other human PTPs tested) inhibitors of Cdc25A. Significantly, we found two potent and specific inhibitors, NF250 and NF290, for YopH, the phosphatase that is an essential virulence factor for bubonic plague. Two of the compounds tested, NF504 and NF506, had significantly improved potency as PTP inhibitors for all phosphatases tested except for LAR and PTPalpha. Surprisingly, we found that a significant number of these compounds activated the receptor-like phosphatases, PTPalpha and LAR. In further characterizing this activation phenomenon, we reveal a novel role for the membrane-distal cytoplasmic PTP domain (D2) of PTPalpha: the direct intramolecular regulation of the activity of the membrane-proximal cytoplasmic PTP domain (D1). Binding of certain of these compounds to PTPalpha disrupts D1-D2 basal state contacts and allows new contacts to occur between D1 and D2, which activates D1 by as much as 12-14-fold when these contacts are optimized. 相似文献
6.
Chang Y Zhuang D Zhang C Hassid A 《American journal of physiology. Heart and circulatory physiology》2004,287(5):H2201-H2208
Migration and proliferation of vascular smooth muscle cells are key events in injury-induced neointima formation. Several growth factors and ANG II are thought to be involved in neointima formation. A recent report indicated that vascular injury is associated with increased mRNA levels of protein tyrosine phosphatase (PTP)-1B (PTP-1B). In the present study, we tested the following hypotheses: 1) rat carotid artery injury induces the expression of PTP-1B, Src homology-2 domain phosphatase (SHP-2), and PTP-proline, glutamate, serine, and threonine sequence (PEST) protein; and 2) polypeptide growth factors as well as ANG II increase the levels of tyrosine phosphatases in cultured rat aortic smooth muscle cells. We found that vascular injury induced by balloon catheter increases the protein levels of aforementioned phosphatases and that these effects occur in a PTP specific, as well as temporally and regionally specific, manner. Moreover, treatment of cultured primary rat aortic smooth muscle cells with PDGF or bFGF, but not with IGF1, EGF, or ANG II, increases PTP-1B, SHP-2, and PTP-PEST protein levels. These results suggest that increased PDGF and bFGF levels, occurring after vascular injury, may induce expression of several PTPs. 相似文献
7.
Protein tyrosine phosphatase (PTP) in-gel assays were used to explore association of PTPs with the platelet-derived growth factor beta-receptor (PDGFbetaR). Five PTP activity bands of approximately 120, approximately 70, approximately 60, approximately 53, and approximately 45 kDa could be detected in PDGFbetaR immunoprecipitates and were identified by immunodepletion experiments as PTP-PEST, SHP-2, an active fragment of SHP-2, PTP-1B, and T-cell PTP, respectively. The PTP pattern that was obtained was similar in PDGFbetaR immunoprecipitates from HEK 293 cells overexpressing the human PDGFbetaR and from murine fibroblasts. Association of PTP-1B with the PDGFbetaR was stabilized by pretreatment of the cells with hydrogen peroxide. The epidermal growth factor receptor (EGFR) immunoprecipitated from fibroblasts, and c-Kit isolated from CHRF myeloid cells, were associated with partially overlapping but quantitatively different patterns of PTPs. PTP-PEST was the predominant PTP in EGFR immunoprecipitates, and SHP-1 appeared in c-Kit immunoprecipitates. We propose that the differential association of PTPs with different RTKs is related to their respective contributions to regulation of RTK signaling. 相似文献
8.
Pasquali C Curchod ML Wälchli S Espanel X Guerrier M Arigoni F Strous G Hooft van Huijsduijnen R 《Molecular endocrinology (Baltimore, Md.)》2003,17(11):2228-2239
Protein tyrosine phosphatases (PTPs) play key roles in switching off tyrosine phosphorylation cascades, such as initiated by cytokine receptors. We have used substrate-trapping mutants of a large set of PTPs to identify members of the PTP family that have substrate specificity for the phosphorylated human GH receptor (GHR) intracellular domain. Among 31 PTPs tested, T cell (TC)-PTP, PTP-beta, PTP1B, stomach cancer-associated PTP 1 (SAP-1), Pyst-2, Meg-2, and PTP-H1 showed specificity for phosphorylated GHR that had been produced by coexpression with a kinase in bacteria. We then used GH-induced, phosphorylated GH receptor, purified from overexpressing mammalian cells, in a Far Western-based approach to test whether these seven PTPs were also capable of recognizing ligand-induced, physiologically phosphorylated GHR. In this assay, only TC-PTP, PTP1B, PTP-H1, and SAP-1 interacted with the mature form of the phosphorylated GHR. In parallel, we show that these PTPs recognize very different subsets of the seven GHR tyrosines that are potentially phosphorylated. Finally, mRNA tissue distribution of these PTPs by RT-PCR analysis and coexpression of the wild-type PTPs to test their ability to dephosphorylate ligand-activated GHR suggest PTP-H1 and PTP1B as potential candidates involved in GHR signaling. 相似文献
9.
Karpen HE Bukowski JT Hughes T Gratton JP Sessa WC Gailani MR 《The Journal of biological chemistry》2001,276(22):19503-19511
The Hedgehog signaling pathway is involved in early embryonic patterning as well as in cancer; however, little is known about the subcellular localization of the Hedgehog receptor complex of Patched and Smoothened. Since Hh has been found in lipid rafts in Drosophila, we hypothesized that Patched and Smoothened might also be found in these cholesterol-rich microdomains. In this study, we demonstrate that both Smoothened and Patched are in caveolin-1-enriched/raft microdomains. Immunoprecipitation studies show that Patched specifically interacts with caveolin-1, whereas Smoothened does not. Fractionation studies show that Patched and caveolin-1 can be co-isolated from buoyant density fractions that represent caveolae/raft microdomains and that Patched and caveolin-1 co-localize by confocal microscopy. Glutathione S-transferase fusion protein experiments show that the interaction between Patched and caveolin-1 involves the caveolin-1 scaffolding domain and a Patched consensus binding site. Immunocytochemistry data and fractionation studies also show that Patched seems to be required for transport of Smoothened to the membrane. Depletion of plasmalemmal cholesterol influences the distribution of the Hh receptor complex in the caveolin-enriched/raft microdomains. These data suggest that caveolin-1 may be integral for sequestering the Hh receptor complex in these caveolin-enriched microdomains, which act as a scaffold for the interactions with the Hh protein. 相似文献
10.
K Takakura J S Beckman L A MacMillan-Crow J P Crow 《Archives of biochemistry and biophysics》1999,369(2):197-207
Protein tyrosine phosphatases (PTPs) contain an essential thiol in the active site which may be susceptible to attack by nitric oxide-derived biological oxidants. We assessed the effects of peroxynitrite, nitric oxide, and S-nitrosoglutathione on the activity of three human tyrosine phosphatases in vitro. The receptor-like T-cell tyrosine phosphatase (CD45), the non-receptor-like tyrosine phosphatase PTP1B, and leukocyte-antigen-related (LAR) phosphatase were all irreversibly inactivated by peroxynitrite in less than 1 s with IC(50) values of =0.9 microM. PTP inactivation was also seen with equivalent concentrations of peroxynitrite generated by SIN-1, indicating that bolus peroxynitrite and cogeneration of superoxide and nitric oxide were equipotent. Rate constants for peroxynitrite-mediated PTP inactivation were determined by competition with cysteine and were among the fastest rates yet seen for reaction of peroxynitrite with any biological molecules. The bimolecular reaction rates for CD45, LAR, and PTP1B were 2.0 x 10(8), 2.3 x 10(7), and 2.2 x 10(7) M(-1) s(-1), respectively. Inactivation by peroxynitrite was essentially irreversible as incubation with dithiothreitol (DTT) restored less than 10% of the original phosphatase activity. Prolonged treatment with 0.4 mM DETA NONOate, which generated a steady-state concentration of 2 microM nitric oxide, was only slightly inhibitory. S-Nitrosoglutathione (1.0 mM) inhibited PTPs by approximately 50% after 30 min and the inhibition was completely reversed by DTT. Nitrotyrosine immunoblots of peroxynitrite-treated PTP1B revealed that peroxynitrite completely inactivated PTP1B prior to the appearance of protein tyrosine nitration. Peroxynitrite anion is structurally similar to phosphate anion both in terms of molecular diameter and charge. Thus, the extreme vulnerability of these PTPs to peroxynitrite-mediated inactivation is consistent with attraction of peroxynitrite anion to the active site and subsequent oxidation of the essential thiolate. These findings suggest that any PTP possessing the CXXXXXR active-site sequence could potentially be inactivated by peroxynitrite in vivo resulting in a net increase in tyrosine phosphorylation and profound effects on phosphotyrosine-dependent signaling cascades. 相似文献
11.
Roles of superoxide radical anion in signal transduction mediated by reversible regulation of protein-tyrosine phosphatase 1B 总被引:12,自引:0,他引:12
Barrett WC DeGnore JP Keng YF Zhang ZY Yim MB Chock PB 《The Journal of biological chemistry》1999,274(49):34543-34546
Growth factors induce intracellular production of reactive oxygen species in non-phagocytic cells and elevation of their phosphorylated protein tyrosine level. The latter can be achieved by activating protein-tyrosine kinases and/or inactivating protein-tyrosine phosphatases (PTPs). A highly abundant PTP, PTP-1B, is known to be inactivated by oxidation of its catalytic site Cys-215. We show that O-(2) is kinetically more efficient and chemically more specific oxidant than H(2)O(2) for inactivating PTP-1B. The second-order rate constant for the O-(2)- and H(2)O(2)-mediated inactivation is 334 +/- 45 M(-1) s(-1) and 42.8 +/- 3.8 M(-1) s(-1), respectively. PTP-1B oxidized by H(2)O(2) exhibits significantly more oxidized methionine residues and shows a lower degree of reversibility. The initial oxidative product, the Cys-215 sulfenic derivative, can easily be oxidized further to its irreversible sulfinic and sulfonic derivatives. This step is prevented by glutathionylation of the sulfenic derivative to form a S-glutathionylated PTP-1B, which can be reactivated by dithiothreitol or thioltransferase. Thus, a signal transduction mechanism mediated by the O-(2) and the participation of glutathione is proposed for the regulation of PTP-1B. This mechanism is supported by the in vivo demonstration that glutathionylated PTP-1B at Cys-215 is formed in A431 cells when they were treated with epidermal growth factor. 相似文献
12.
Protein tyrosine phosphatases (PTPs) play a central role in cellular signaling processes, resulting in an increased interest in modulating the activities of PTPs. We therefore decided to undertake a detailed enzyme kinetic evaluation of various transmembrane and cytosolic PTPs (PTPalpha, PTPbeta, PTPepsilon, CD45, LAR, PTP1B and SHP-1), using pNPP as substrate. Most noticeable is the increase in the turnover number for PTPbeta with increasing pH and the weak pH-dependence of the turnover number of CD45. The kinetic data for PTPalpha-D1 and PTPalpha-D1D2 suggest that D2 affects the catalysis of pNPP. PTPepsilon and the closely homologous PTPalpha behave differently. The K(m) data were lower for PTPepsilon than those for PTPalpha, while the inverse was observed for the catalytic efficiencies. 相似文献
13.
2-(oxalylamino)-benzoic acid is a general, competitive inhibitor of protein-tyrosine phosphatases 总被引:2,自引:0,他引:2
Andersen HS Iversen LF Jeppesen CB Branner S Norris K Rasmussen HB Møller KB Møller NP 《The Journal of biological chemistry》2000,275(10):7101-7108
Protein-tyrosine phosphatases (PTPs) are critically involved in regulation of signal transduction processes. Members of this class of enzymes are considered attractive therapeutic targets in several disease states, e.g. diabetes, cancer, and inflammation. However, most reported PTP inhibitors have been phosphorus-containing compounds, tight binding inhibitors, and/or inhibitors that covalently modify the enzymes. We therefore embarked on identifying a general, reversible, competitive PTP inhibitor that could be used as a common scaffold for lead optimization for specific PTPs. We here report the identification of 2-(oxalylamino)-benzoic acid (OBA) as a classical competitive inhibitor of several PTPs. X-ray crystallography of PTP1B complexed with OBA and related non-phosphate low molecular weight derivatives reveals that the binding mode of these molecules to a large extent mimics that of the natural substrate including hydrogen bonding to the PTP signature motif. In addition, binding of OBA to the active site of PTP1B creates a unique arrangement involving Asp(181), Lys(120), and Tyr(46). PTP inhibitors are essential tools in elucidating the biological function of specific PTPs and they may eventually be developed into selective drug candidates. The unique enzyme kinetic features and the low molecular weight of OBA makes it an ideal starting point for further optimization. 相似文献
14.
Xie Y Massa SM Ensslen-Craig SE Major DL Yang T Tisi MA Derevyanny VD Runge WO Mehta BP Moore LA Brady-Kalnay SM Longo FM 《The Journal of biological chemistry》2006,281(24):16482-16492
Inhibition of protein-tyrosine phosphatases (PTPs) counterbalancing protein-tyrosine kinases (PTKs) offers a strategy for augmenting PTK actions. Conservation of PTP catalytic sites limits development of specific PTP inhibitors. A number of receptor PTPs, including the leukocyte common antigen-related (LAR) receptor and PTPmu, contain a wedge-shaped helix-loop-helix located near the first catalytic domain. Helix-loop-helix domains in other proteins demonstrate homophilic binding and inhibit function; therefore, we tested the hypothesis that LAR wedge domain peptides would exhibit homophilic binding, bind to LAR, and inhibit LAR function. Fluorescent beads coated with LAR or PTPmu wedge peptides demonstrated PTP-specific homophilic binding, and LAR wedge peptide-coated beads precipitated LAR protein. Administration of LAR wedge Tat peptide to PC12 cells resulted in increased proliferation, decreased cell death, increased neurite outgrowth, and augmented Trk PTK-mediated responses to nerve growth factor (NGF), a phenotype matching that found in PC12 cells with reduced LAR levels. PTPmu wedge Tat peptide had no effect on PC12 cells but blocked the PTPmu-dependent phenotype of neurite outgrowth of retinal ganglion neurons on a PTPmu substrate, whereas LAR wedge peptide had no effect. The survival- and neurite-promoting effect of the LAR wedge peptide was blocked by the Trk inhibitor K252a, and reciprocal co-immunoprecipitation demonstrated LAR/TrkA association. The addition of LAR wedge peptide inhibited LAR co-immunoprecipitation with TrkA, augmented NGF-induced activation of TrkA, ERK, and AKT, and in the absence of exogenous NGF, induced activation of TrkA, ERK, and AKT. PTP wedge domain peptides provide a unique PTP inhibition strategy and offer a novel approach for augmenting PTK function. 相似文献
15.
Calpain-catalyzed cleavage and subcellular relocation of protein phosphotyrosine phosphatase 1B (PTP-1B) in human platelets. 总被引:10,自引:0,他引:10
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The non-transmembrane phosphotyrosine phosphatase 1B (PTP-1B) is an abundant enzyme, normally localized to the cytosolic face of the endoplasmic reticulum via a C-terminal targeting sequence. We have found that agonist-induced platelet activation results in proteolytic cleavage of PTP-1B at a site upstream from this targeting sequence, causing subcellular relocation of its catalytic domain from membranes to the cytosol. PTP-1B cleavage is catalyzed by the calcium-dependent neutral protease calpain and is a general feature of platelet agonist-induced aggregation. Moreover, PTP-1B cleavage correlates with the transition from reversible to irreversible platelet aggregation in platelet-rich plasma. Engagement of gpIIb-IIIa is necessary for inducing PTP-1B cleavage, suggesting that integrins regulate tyrosine phosphatases as well as tyrosine kinases. PTP-1B cleavage is accompanied by a 2-fold stimulation of its enzymatic activity, as measured by immune complex phosphatase assay, and correlates with discrete changes in the pattern of tyrosyl phosphorylation. Cleavage and subcellular relocation of PTP-1B represents a novel mechanism for altering tyrosyl phosphorylation that may have important physiological implications in cell types other than platelets. 相似文献
16.
García-Ruiz I Solís-Muñoz P Gómez-Izquierdo E Muñoz-Yagüe MT Valverde AM Solís-Herruzo JA 《The Journal of biological chemistry》2012,287(23):19564-19573
Insulin resistance is a risk factor for non-response to interferon/ribavirin therapy in patients with chronic hepatitis C. The aim of this study was to determine the role played by protein-tyrosine phosphatases (PTPs) in the absence of interferon-α (IFNα) response associated with insulin resistance. We induced insulin resistance by silencing IRS-2 or by treating HepG2 cells with tumor necrosis factor-α (TNFα) and analyzed insulin response by evaluating Akt phosphorylation and IFNα response by measuring Stat-1 tyrosine phosphorylation and 2',5'-oligoadenylate synthase and myxovirus resistance gene expression. The response to IFNα was also measured in insulin-resistant obese mice (high fat diet and ob/ob mice) untreated and treated with metformin. Silencing IRS-2 mRNA induces insulin resistance and inhibits IFNα response. Likewise, TNFα suppresses insulin and IFNα response. Treatment of cells with pervanadate and knocking down PTP-1B restores insulin and IFNα response. Both silencing IRS-2 and TNFα treatment increase PTP and PTP-1B activity. Metformin inhibits PTP and improves IFNα response in insulin-resistant cells. Insulin-resistant ob/ob mice have increased PTP-1B gene expression and activity in the liver and do not respond to IFNα administration. Treatment with metformin improves this response. In HepG2 cells, insulin resistance provokes IFNα resistance, which is associated with an increased PTP-1B activity in the liver. Inhibition of PTP-1B activity with pervanadate and metformin or knocking down PTP-1B reestablishes IFNα response. Likewise, metformin decreases PTP-1B activity and improves response to IFNα in insulin-resistant obese mice. The use of PTP-1B inhibitors may improve the response to IFNα/ribavirin therapy. 相似文献
17.
Zabolotny JM Haj FG Kim YB Kim HJ Shulman GI Kim JK Neel BG Kahn BB 《The Journal of biological chemistry》2004,279(23):24844-24851
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. 相似文献
18.
PTP1B is a cytosolic protein tyrosine phosphatase that is a regulator of the kinase activity of the insulin receptor; the two protein tyrosine phosphatases LAR and CD45 are receptor type phosphatases crucially important to cell function. LAR also is involved in regulation of the insulin receptor while CD45 is critical for T-cell activation. Although LAR and CD45 are both transmembrane phosphatases, these enzymes manifest their phosphatase activity through a catalytic cytosolic domain. We have utilized X-ray coordinates of related phosphatases (RPTPalpha and RPTmu) and comparative protein modeling to obtain molecular models of the D1 catalytic domains of CD45 and LAR. The models were tested using established protocols and found to be comparable to low resolution X-ray structures. The structure obtained for LAR was compared with the recently reported X-ray structure. Both the CD45-D1 and LAR-D1 structures were then compared to and contrasted with PTP1B. The active site of pockets of the three enzymes were found to be very uniform in structure and charge distribution. Also, the gross surface topology around the active site was found to be somewhat similar for the 3 phosphatases. However, there were significant differences in surface topology, and, more importantly, large changes in surface charge distribution. The differences between the surface features of these enzymes provide an explanation for the selectivity of inhibition by a number of peptides. 相似文献
19.
Asante-Appiah E Kennedy BP 《American journal of physiology. Endocrinology and metabolism》2003,284(4):E663-E670
Type 2 diabetes is increasing at an alarming rate worldwide, and there has been a considerable effort in several laboratories to identify suitable targets for the design of drugs against the disease. To this end, the protein tyrosine phosphatases that attenuate insulin signaling by dephosphorylating the insulin receptor (IR) have been actively pursued. This is because inhibiting the phosphatases would be expected to prolong insulin signaling and thereby facilitate glucose uptake and, presumably, result in a lowering of blood glucose. Targeting the IR protein tyrosine phosphatase, therefore, has the potential to be a significant disease-modifying strategy. Several protein tyrosine phosphatases (PTPs) have been implicated in the dephosphorylation of the IR. These phosphatases include PTPalpha, LAR, CD45, PTPepsilon, SHP2, and PTP1B. In most cases, there is evidence for and against the involvement of the phosphatases in insulin signaling. The most convincing data, however, support a critical role for PTP1B in insulin action. PTP1B knockout mice are not only insulin sensitive but also maintain euglycemia (in the fed state), with one-half the level of insulin observed in wild-type littermates. Interestingly, these mice are also resistant to diet-induced obesity when fed a high-fat diet. The insulin-sensitive phenotype of the PTP1B knockout mouse is reproduced when the phosphatase is also knocked down with an antisense oligonucleotide in obese mice. Thus PTP1B appears to be a very attractive candidate for the design of drugs for type 2 diabetes and obesity. 相似文献
20.
Identification of phosphocaveolin-1 as a novel protein tyrosine phosphatase 1B substrate 总被引:1,自引:0,他引:1
Lee H Xie L Luo Y Lee SY Lawrence DS Wang XB Sotgia F Lisanti MP Zhang ZY 《Biochemistry》2006,45(1):234-240
Protein tyrosine phosphatase 1B (PTP1B) is implicated in a number of signaling pathways including those mediated by insulin, epidermal growth factor (EGF), and the Src family kinases. The scaffolding protein caveolin-1 is also a participant in these pathways and is specifically phosphorylated on tyrosine 14, when these pathways are activated. Here, we provide evidence that PTP1B can efficiently catalyze the removal of the phosphoryl group from phosphocaveolin-1. Overexpression of PTP1B decreases tyrosine 14 phosphorylation in caveolin-1, while expression of the substrate-trapping mutant PTP1B/D181A causes the accumulation of phosphocaveolin-1 and prevents its dephosphorylation by endogenous PTPs. We further demonstrate that PTP1B physically associates with caveolin-1. Finally, we show that inhibition of PTP1B activity with a potent and specific small molecule PTP1B inhibitor blocks the PTP1B-catalyzed caveolin-1 dephosphorylation both in vitro and in vivo. Taken together, the results strongly suggest that caveolin-1 is a specific substrate for PTP1B. Identification of caveolin-1 as a PTP1B substrate represents an important new step in further understanding the signaling pathways regulated by PTP1B. 相似文献