Interaction of protein tyrosine phosphatase (PTP) 1B with its substrates is influenced by two distinct binding domains.
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ABSTRACT:
SUBMITTER: Dadke S
PROVIDER: S-EPMC1222582 | biostudies-other | 2002 Jun
REPOSITORIES: biostudies-other
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Project description:The leukocyte antigen related (LAR) family of receptor-like protein tyrosine phosphatases has three members in humans - PTPRF, PTPRD and PTPRS - that have been implicated in diverse processes including embryonic development, inhibition of cell growth and axonal guidance. Mutations in the LAR family are associated with developmental defects such as cleft palate as well as various cancers including breast, neck, lung, colon and brain. Although this family of tyrosine phosphatases is important for many developmental processes, little is known of their substrates. This is partially due to functional redundancy within the LAR family, as deletion of a single gene in the LAR family does not have an appreciable phenotype, but a dual knockout is embryonically lethal in mouse models. To circumvent the inability to knockout multiple members of the LAR family in mouse models, we used a knockout of ptp-3, which is the only known ortholog of the LAR family in Caenorhabditis elegans and allows for the study of the LAR family at the organismal level. Using SILAC-based quantitative phosphoproteomics, we identified 255 putative substrates of ptp-3, which included four of the nine known annotated substrates of the LAR family. A motif analysis of the identified phosphopeptides allowed for the determination of sequences that appear to be preferentially dephosphorylated. Finally, we discovered that kinases were overrepresented in the list of identified putative substrates and tyrosine residues whose phosphorylation is known to increase kinase activity were dephosphorylated by ptp-3. These data are suggestive of ptp-3 as a potential negative regulator of several kinase families, such as the mitogen activated kinases (MAPKs), and multiple tyrosine kinases including FER, MET, and NTRK2.
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Project description:Endothelial dysfunction is a key feature of cardiovascular disorders associated with obesity and diabetes. Several studies identified protein tyrosine phosphatase (PTP)-1B, a member of the PTP superfamily, as a major negative regulator for insulin receptor signaling and a novel molecular player in endothelial dysfunction and cardiovascular disease. Unlike other anti-diabetic approaches, genetic deletion or pharmacological inhibition of PTP1B was found to improve glucose homeostasis and insulin signaling without causing lipid buildup in the liver, which represents an advantage over existing therapies. Furthermore, PTP1B was reported to contribute to cardiovascular disturbances, at various molecular levels, which places this enzyme as a unique single therapeutic target for both diabetes and cardiovascular disorders. Synthesizing selective small molecule inhibitors for PTP1B is faced with multiple challenges linked to its similarity of sequence with other PTPs; however, overcoming these challenges would pave the way for novel approaches to treat diabetes and its concurrent cardiovascular complications. In this review article, we summarized the major roles of PTP1B in cardiovascular disease with special emphasis on endothelial dysfunction and its interplay with insulin resistance. Furthermore, we discussed some of the major challenges hindering the synthesis of selective inhibitors for PTP1B.
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Project description:Obesity is associated with induction of the ER (endoplasmic reticulum)-stress response signalling and insulin resistance. PTP1B (protein tyrosine phosphatase 1B) is a major regulator of adiposity and insulin sensitivity. The aim of the present study was to investigate the role of L-PTP1B (liver-specific PTP1B) in chronically HFD (high-fat diet) and pharmacologically induced (tunicamycin and thapsigargin) ER-stress response signalling in vitro and in vivo. We assessed the effects of ER-stress response induction on hepatic PTP1B expression, and consequences of hepatic-PTP1B deficiency, in cells and mouse liver, on components of ER-stress response signalling. We found that PTP1B protein and mRNA expression levels were up-regulated in response to acute and/or chronic ER stress, in vitro and in vivo. Silencing PTP1B in hepatic cell lines or mouse liver (L-PTP1B(-/-)) protected against induction of pharmacologically induced and/or obesity-induced ER stress. The HFD-induced increase in CHOP (CCAAT/enhancer-binding protein homologous protein) and BIP (binding immunoglobulin protein) mRNA levels were partially inhibited, whereas ATF4 (activated transcription factor 4), GADD34 (growth-arrest and DNA-damage-inducible protein 34), GRP94 (glucose-regulated protein 94), ERDJ4 (ER-localized DnaJ homologue) mRNAs and ATF6 protein cleavage were completely suppressed in L-PTP1B(-/-) mice relative to control littermates. L-PTP1B(-/-) mice also had increased nuclear translocation of spliced XBP-1 (X box-binding protein-1) via increased p85α binding. We demonstrate that the ER-stress response and L-PTP1B expression are interlinked in obesity- and pharmacologically induced ER stress and this may be one of the mechanisms behind improved insulin sensitivity and lower lipid accumulation in L-PTP1B(-/-) mice.
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Project description:The control of tyrosine phosphorylation depends on the fine balance between kinase and phosphatase activities. Protein tyrosine phosphatase 1B (PTP-1B) and T cell protein tyrosine phosphatase (TC-PTP) are 2 closely related phosphatases known to control cytokine signaling. We studied the functional redundancy of PTP-1B and TC-PTP by deleting 1 or both copies of these genes by interbreeding TC-PTP and PTP-1B parental lines. Our results indicate that the double mutant (tcptp(-/-)ptp1b(-/-)) is lethal at day E9.5-10.5 of embryonic development with constitutive phosphorylation of Stat1. Mice heterozygous for TC-PTP on a PTP-1B-deficient background (tcptp(+/-)ptp1b(-/-)) developed signs of inflammation. Macrophages from these animals were highly sensitive to IFN-gamma, as demonstrated by increased Stat1 phosphorylation and nitric oxide production. In addition, splenic T cells demonstrated increased IFN-gamma secretion capacity. Mice with deletions of single copies of TC-PTP and PTP-1B (tcptp(+/-)ptp1b(+/-)) exhibited normal development, confirming that these genes are not interchangeable. Together, these data indicate a nonredundant role for PTP-1B and TC-PTP in the regulation of IFN signaling.
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Project description:The tyrosine kinase Fyn has two regulatory tyrosine residues that when phosphorylated either activate (Tyr(420)) or inhibit (Tyr(531)) Fyn activity. Within the central nervous system, two protein tyrosine phosphatases (PTPs) target these regulatory tyrosines in Fyn. PTP? dephosphorylates Tyr(531) and activates Fyn, while STEP (STriatal-Enriched protein tyrosine Phosphatase) dephosphorylates Tyr(420) and inactivates Fyn. Thus, PTP? and STEP have opposing functions in the regulation of Fyn; however, whether there is cross talk between these two PTPs remains unclear. Here, we used molecular techniques in primary neuronal cultures and in vivo to demonstrate that STEP negatively regulates PTP? by directly dephosphorylating PTP? at its regulatory Tyr(789). Dephosphorylation of Tyr(789) prevents the translocation of PTP? to synaptic membranes, blocking its ability to interact with and activate Fyn. Genetic or pharmacologic reduction in STEP61 activity increased the phosphorylation of PTP? at Tyr(789), as well as increased translocation of PTP? to synaptic membranes. Activation of PTP? and Fyn and trafficking of GluN2B to synaptic membranes are necessary for ethanol (EtOH) intake behaviors in rodents. We tested the functional significance of STEP61 in this signaling pathway by EtOH administration to primary cultures as well as in vivo, and demonstrated that the inactivation of STEP61 by EtOH leads to the activation of PTP?, its translocation to synaptic membranes, and the activation of Fyn. These findings indicate a novel mechanism by which STEP61 regulates PTP? and suggest that STEP and PTP? coordinate the regulation of Fyn. STEP61 , PTP?, Fyn, and NMDA receptor (NMDAR) have been implicated in ethanol intake behaviors in the dorsomedial striatum (DMS) in rodents. Here, we report that PTP? is a novel substrate for STEP61. Upon ethanol exposure, STEP61 is phosphorylated and inactivated by protein kinase A (PKA) signaling in the DMS. As a result of STEP61 inhibition, there is an increase in the phosphorylation of PTP?, which translocates to lipid rafts and activates Fyn and subsequent NMDAR signaling. The results demonstrate a synergistic regulation of Fyn-NMDAR signaling by STEP61 and PTP?, which may contribute to the regulation of ethanol-related behaviors. NMDA, N-methyl-D-aspartate; PTP?, receptor-type protein tyrosine phosphatase alpha; STEP, STriatal-Enriched protein tyrosine Phosphatase.
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Project description:During spinal cord development the proliferation, migration and survival of neural progenitors and precursors is tightly controlled, generating the fine spatial organisation of the cord. In order to understand better the control of these processes, we have examined the function of an orphan receptor protein tyrosine phosphatase (RPTP) PTP?, in the developing chick spinal cord. Widespread expression of PTP? occurs post-embryonic day 3 in the early cord and is consistent with a potential role in either neurogenesis or neuronal maturation. Using gain-of-function and loss-of-function approaches in ovo, we show that PTP? perturbation significantly reduces progenitor proliferation rates and neuronal precursor numbers, resulting in hypoplasia of the neuroepithelium. PTP? gain-of-function causes widespread suppression of Wnt/?-catenin-driven TCF signalling. One potential target of PTP? may therefore be ?-catenin itself, since PTP? can dephosphorylate it in vitro, but alternative targets are also likely. PTP? loss-of-function is not sufficient to alter TCF signalling. Instead, loss-of-function leads to increased apoptosis and defective cell-cell adhesion in progenitors and precursors. Furthermore, motor neuron precursor migration is specifically defective. PTP? therefore regulates neurogenesis during a window of spinal cord development, with molecular targets most likely related to Wnt/?-catenin signalling, cell survival and cell adhesion.
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Project description:A new paradigm in metallobiochemistry describes the activation of inactive metalloenzymes by metal ion removal. Protein tyrosine phosphatases (PTPs) do not seem to require a metal ion for enzymatic activity. However, both metal cations and metal anions modulate their enzymatic activity. One binding site is the phosphate binding site at the catalytic cysteine residue. Oxyanions with structural similarity to phosphate, such as vanadate, inhibit the enzyme with nanomolar to micromolar affinities. In addition, zinc ions (Zn2+) inhibit with picomolar to nanomolar affinities. We mapped the cation binding site close to the anion binding site and established a specific mechanism of inhibition occurring only in the closed conformation of the enzyme when the catalytic cysteine is phosphorylated and the catalytic aspartate moves into the active site. We discuss this dual inhibition by anions and cations here for PTP1B, the most thoroughly investigated protein tyrosine phosphatase. The significance of the inhibition in phosphorylation signaling is becoming apparent only from the functions of PTP1B in the biological context of metal cations as cellular signaling ions. Zinc ion signals complement redox signals but provide a different type of control and longer lasting inhibition on a biological time scale owing to the specificity and affinity of zinc ions for coordination environments. Inhibitor design for PTP1B and other PTPs is a major area of research activity and interest owing to their prominent roles in metabolic regulation in health and disease, in particular cancer and diabetes. Our results explain the apparent dichotomy of both cations (Zn2+) and oxyanions such as vanadate inhibiting PTP1B and having insulin-enhancing ("anti-diabetic") effects and suggest different approaches, namely targeting PTPs in the cell by affecting their physiological modulators and considering a metallodrug approach that builds on the knowledge of the insulin-enhancing effects of both zinc and vanadium compounds.
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Project description:The dynamics of the interaction of the insulin receptor with a substrate-trapping mutant of protein-tyrosine phosphatase 1B (PTP1B) were monitored in living human embryonic kidney cells using bioluminescence resonance energy transfer (BRET). Insulin dose-dependently stimulates this interaction, which could be followed in real time for more than 30 minutes. The effect of insulin on the BRET signal could be detected at early time-points (30 seconds), suggesting that in intact cells the tyrosine-kinase activity of the insulin receptor is tightly controlled by PTP1B. Interestingly, the basal (insulin-independent) interaction of the insulin receptor with PTP1B was much weaker with a soluble form of the tyrosine-phosphatase than with the endoplasmic reticulum (ER)-targeted form. Inhibition of insulin-receptor processing using tunicamycin suggests that the basal interaction occurs during insulin-receptor biosynthesis in the ER. Therefore, localization of PTP1B in this compartment might be important for the regulation of insulin receptors during their biosynthesis.
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Project description:Protein tyrosine phosphatases regulate a myriad of essential subcellular signaling events, yet they remain difficult to study in their native biophysical context. Here we develop a minimally disruptive optical approach to control protein tyrosine phosphatase 1B (PTP1B)-an important regulator of receptor tyrosine kinases and a therapeutic target for the treatment of diabetes, obesity, and cancer-and we use that approach to probe the intracellular function of this enzyme. Our conservative architecture for photocontrol, which consists of a protein-based light switch fused to an allosteric regulatory element, preserves the native structure, activity, and subcellular localization of PTP1B, affords changes in activity that match those elicited by post-translational modifications inside the cell, and permits experimental analyses of the molecular basis of optical modulation. Findings indicate, most strikingly, that small changes in the activity of PTP1B can cause large shifts in the phosphorylation states of its regulatory targets.
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Project description:The HD-PTP protein has been described as a tumor suppressor candidate and based on its amino acid sequence, categorized as a classical non-transmembrane protein tyrosine phosphatase (PTP). To date, no HD-PTP phosphorylated substrate has been identified and controversial results concerning its catalytic activity have been recently reported.Here we report a rigorous enzymatic analysis demonstrating that the HD-PTP protein does not harbor tyrosine phosphatase or lipid phosphatase activity using the highly sensitive DiFMUP substrate and a panel of different phosphatidylinositol phosphates. We found that HD-PTP tyrosine phosphatase inactivity is caused by an evolutionary conserved amino acid divergence of a key residue located in the HD-PTP phosphatase domain since its back mutation is sufficient to restore the HD-PTP tyrosine phosphatase activity. Moreover, in agreement with a tumor suppressor activity, HD-PTP expression leads to colony growth reduction in human cancer cell lines, independently of its catalytic PTP activity status.In summary, we demonstrate that HD-PTP is a catalytically inactive protein tyrosine phosphatase. As such, we identify one residue involved in its inactivation and show that its colony growth reduction activity is independent of its PTP activity status in human cancer cell lines.
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