1
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Hendriks WJAJ, van Cruchten RTP, Pulido R. Hereditable variants of classical protein tyrosine phosphatase genes: Will they prove innocent or guilty? Front Cell Dev Biol 2023; 10:1051311. [PMID: 36755664 PMCID: PMC9900141 DOI: 10.3389/fcell.2022.1051311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Accepted: 12/28/2022] [Indexed: 01/24/2023] Open
Abstract
Protein tyrosine phosphatases, together with protein tyrosine kinases, control many molecular signaling steps that control life at cellular and organismal levels. Impairing alterations in the genes encoding the involved proteins is expected to profoundly affect the quality of life-if compatible with life at all. Here, we review the current knowledge on the effects of germline variants that have been reported for genes encoding a subset of the protein tyrosine phosphatase superfamily; that of the thirty seven classical members. The conclusion must be that the newest genome research tools produced an avalanche of data that suggest 'guilt by association' for individual genes to specific disorders. Future research should face the challenge to investigate these accusations thoroughly and convincingly, to reach a mature genotype-phenotype map for this intriguing protein family.
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Affiliation(s)
- Wiljan J. A. J. Hendriks
- Department of Cell Biology, Radboud University Medical Centre, Nijmegen, The Netherlands,*Correspondence: Wiljan J. A. J. Hendriks,
| | | | - Rafael Pulido
- Biomarkers in Cancer Unit, Biocruces Bizkaia Health Research Institute, Barakaldo, Spain,Ikerbasque, Basque Foundation for Science, Bilbao, Spain
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2
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Reiterer V, Pawłowski K, Desrochers G, Pause A, Sharpe HJ, Farhan H. The dead phosphatases society: a review of the emerging roles of pseudophosphatases. FEBS J 2020; 287:4198-4220. [PMID: 32484316 DOI: 10.1111/febs.15431] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 05/12/2020] [Accepted: 05/27/2020] [Indexed: 12/11/2022]
Abstract
Phosphatases are a diverse family of enzymes, comprising at least 10 distinct protein folds. Like most other enzyme families, many have sequence variations that predict an impairment or loss of catalytic activity classifying them as pseudophosphatases. Research on pseudoenzymes is an emerging area of interest, with new biological functions repurposed from catalytically active relatives. Here, we provide an overview of the pseudophosphatases identified to date in all major phosphatase families. We will highlight the degeneration of the various catalytic sequence motifs and discuss the challenges associated with the experimental determination of catalytic inactivity. We will also summarize the role of pseudophosphatases in various diseases and discuss the major challenges and future directions in this field.
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Affiliation(s)
| | | | - Guillaume Desrochers
- Department of Biochemistry, McGill University, Montréal, QC, Canada.,Goodman Cancer Research Centre, McGill University, Montréal, QC, Canada
| | - Arnim Pause
- Department of Biochemistry, McGill University, Montréal, QC, Canada.,Goodman Cancer Research Centre, McGill University, Montréal, QC, Canada
| | | | - Hesso Farhan
- Institute of Basic Medical Sciences, University of Oslo, Norway
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3
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Acevedo-Calado MJ, Pietropaolo SL, Morran MP, Schnell S, Vonberg AD, Verge CF, Gianani R, Becker DJ, Huang S, Greenbaum CJ, Yu L, Davidson HW, Michels AW, Rich SS, Pietropaolo M. Autoantibodies Directed Toward a Novel IA-2 Variant Protein Enhance Prediction of Type 1 Diabetes. Diabetes 2019; 68:1819-1829. [PMID: 31167877 PMCID: PMC6702638 DOI: 10.2337/db18-1351] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2018] [Accepted: 05/30/2019] [Indexed: 02/06/2023]
Abstract
We identified autoantibodies (AAb) reacting with a variant IA-2 molecule (IA-2var) that has three amino acid substitutions (Cys27, Gly608, and Pro671) within the full-length molecule. We examined IA-2var AAb in first-degree relatives of type 1 diabetes (T1D) probands from the TrialNet Pathway to Prevention Study. The presence of IA-2var-specific AAb in relatives was associated with accelerated progression to T1D in those positive for AAb to GAD65 and/or insulin but negative in the standard test for IA-2 AAb. Furthermore, relatives with single islet AAb (by traditional assays) and carrying both IA-2var AAb and the high-risk HLA-DRB1*04-DQB1*03:02 haplotype progress rapidly to onset of T1D. Molecular modeling of IA-2var predicts that the genomic variation that alters the three amino acids induces changes in the three-dimensional structure of the molecule, which may lead to epitope unmasking in the IA-2 extracellular domain. Our observations suggest that the presence of AAb to IA-2var would identify high-risk subjects who would benefit from participation in prevention trials who have one islet antibody by traditional testing and otherwise would be misclassified as "low risk" relatives.
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Affiliation(s)
- Maria J. Acevedo-Calado
- Diabetes Research Center, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
| | - Susan L. Pietropaolo
- Diabetes Research Center, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
| | - Michael P. Morran
- Department of Surgery, College of Medicine, University of Toledo, Toledo, OH
| | - Santiago Schnell
- Department of Molecular & Integrative Physiology and Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI
| | - Andrew D. Vonberg
- Diabetes Research Center, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
| | - Charles F. Verge
- School of Women’s and Children’s Health, University of New South Wales, Sydney, New South Wales, Australia
| | - Roberto Gianani
- Diabetes Research Center, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
| | - Dorothy J. Becker
- Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, PA
| | - Shuai Huang
- Department of Industrial & Systems Engineering, University of Washington, Seattle, WA
| | | | - Liping Yu
- Barbara Davis Center for Childhood Diabetes, University of Colorado Denver, Aurora, CO
| | - Howard W. Davidson
- Barbara Davis Center for Childhood Diabetes, University of Colorado Denver, Aurora, CO
| | - Aaron W. Michels
- Barbara Davis Center for Childhood Diabetes, University of Colorado Denver, Aurora, CO
| | - Stephen S. Rich
- Center for Public Health Genomics, Department of Public Health Sciences, University of Virginia, Charlottesville, VA
| | - Massimo Pietropaolo
- Diabetes Research Center, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
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4
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Mulukutla SN, Acevedo-Calado M, Hampe CS, Pietropaolo M, Balasubramanyam A. Autoantibodies to the IA-2 Extracellular Domain Refine the Definition of "A+" Subtypes of Ketosis-Prone Diabetes. Diabetes Care 2018; 41:2637-2640. [PMID: 30327357 PMCID: PMC6245211 DOI: 10.2337/dc18-0613] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 09/10/2018] [Indexed: 02/03/2023]
Abstract
OBJECTIVE Autoantibodies directed against tyrosine phosphatase IA-2 antibody (IA-2 Ab) are diagnostic for autoimmune type 1 diabetes. Conventional assays target the intracellular domain of IA-2. Among patients with ketosis-prone diabetes (KPD), characterized by presentation with diabetic ketoacidosis (DKA), >60% of adults lack three classic islet autoantibodies-IA-2, GAD65, and ZnT8 Abs-associated with type 1 diabetes. We aimed to determine whether apparently autoantibody-negative ("A-") KPD patients possess occult IA-2 Ab directed against full-length IA-2 (IA-2FL) or its extracellular domain (IA-2EC). RESEARCH DESIGN AND METHODS We developed an assay that targets IA-2FL and IA-2EC and used it to analyze 288 subjects with A- KPD. RESULTS Ten A- KPD patients were positive for IA-2EC Ab (3.5%), and three were also positive for IA-2FL Ab (1.0%), similar to frequencies in type 1 and type 2 diabetes. CONCLUSIONS Measurement of IA-2FL Ab and IA-2EC Ab improves the accuracy of the Aβ classification of KPD patients.
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Affiliation(s)
- Surya N Mulukutla
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
| | - Maria Acevedo-Calado
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
| | - Christiane S Hampe
- Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, University of Washington, Seattle, WA
| | - Massimo Pietropaolo
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
| | - Ashok Balasubramanyam
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX
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5
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Hendriks W, Bourgonje A, Leenders W, Pulido R. Proteinaceous Regulators and Inhibitors of Protein Tyrosine Phosphatases. Molecules 2018; 23:molecules23020395. [PMID: 29439552 PMCID: PMC6016963 DOI: 10.3390/molecules23020395] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Revised: 02/09/2018] [Accepted: 02/09/2018] [Indexed: 12/18/2022] Open
Abstract
Proper control of the phosphotyrosine content in signal transduction proteins is essential for normal cell behavior and is lost in many pathologies. Attempts to normalize aberrant tyrosine phosphorylation levels in disease states currently involve either the application of small compounds that inhibit tyrosine kinases (TKs) or the addition of growth factors or their mimetics to boost receptor-type TK activity. Therapies that target the TK enzymatic counterparts, the multi-enzyme family of protein tyrosine phosphatases (PTPs), are still lacking despite their undisputed involvement in human diseases. Efforts to pharmacologically modulate PTP activity have been frustrated by the conserved structure of the PTP catalytic core, providing a daunting problem with respect to target specificity. Over the years, however, many different protein interaction-based regulatory mechanisms that control PTP activity have been uncovered, providing alternative possibilities to control PTPs individually. Here, we review these regulatory principles, discuss existing biologics and proteinaceous compounds that affect PTP activity, and mention future opportunities to drug PTPs via these regulatory concepts.
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Affiliation(s)
- Wiljan Hendriks
- Department of Cell Biology, Radboud University Medical Center, Geert Grooteplein 26, 6525 GA Nijmegen, The Netherlands.
| | - Annika Bourgonje
- Department of Cell Biology, Radboud University Medical Center, Geert Grooteplein 26, 6525 GA Nijmegen, The Netherlands.
| | - William Leenders
- Department of Biochemistry, Radboud University Medical Center, Geert Grooteplein 26, 6525 GA Nijmegen, The Netherlands.
| | - Rafael Pulido
- Biomarkers in Cancer Unit, Biocruces Health Research Institute, 48903 Barakaldo, Spain.
- IKERBASQUE, Basque Foundation for Science, Bilbao, Spain.
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6
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Palma A, Tinti M, Paoluzi S, Santonico E, Brandt BW, Hooft van Huijsduijnen R, Masch A, Heringa J, Schutkowski M, Castagnoli L, Cesareni G. Both Intrinsic Substrate Preference and Network Context Contribute to Substrate Selection of Classical Tyrosine Phosphatases. J Biol Chem 2017; 292:4942-4952. [PMID: 28159843 DOI: 10.1074/jbc.m116.757518] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Revised: 01/31/2017] [Indexed: 01/19/2023] Open
Abstract
Reversible tyrosine phosphorylation is a widespread post-translational modification mechanism underlying cell physiology. Thus, understanding the mechanisms responsible for substrate selection by kinases and phosphatases is central to our ability to model signal transduction at a system level. Classical protein-tyrosine phosphatases can exhibit substrate specificity in vivo by combining intrinsic enzymatic specificity with the network of protein-protein interactions, which positions the enzymes in close proximity to their substrates. Here we use a high throughput approach, based on high density phosphopeptide chips, to determine the in vitro substrate preference of 16 members of the protein-tyrosine phosphatase family. This approach helped identify one residue in the substrate binding pocket of the phosphatase domain that confers specificity for phosphopeptides in a specific sequence context. We also present a Bayesian model that combines intrinsic enzymatic specificity and interaction information in the context of the human protein interaction network to infer new phosphatase substrates at the proteome level.
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Affiliation(s)
- Anita Palma
- From the Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy
| | - Michele Tinti
- From the Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy
| | - Serena Paoluzi
- From the Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy
| | - Elena Santonico
- From the Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy
| | - Bernd Willem Brandt
- the Centre for Integrative Bioinformatics, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands, and
| | | | - Antonia Masch
- the Institut für Biochemie & Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, 06108 Halle, Germany
| | - Jaap Heringa
- the Centre for Integrative Bioinformatics, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands, and
| | - Mike Schutkowski
- the Institut für Biochemie & Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, 06108 Halle, Germany
| | - Luisa Castagnoli
- From the Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy
| | - Gianni Cesareni
- From the Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy,
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7
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Biochemical, biophysical, and functional properties of ICA512/IA-2 RESP18 homology domain. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2016; 1864:511-22. [DOI: 10.1016/j.bbapap.2016.01.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Revised: 01/04/2016] [Accepted: 01/29/2016] [Indexed: 02/04/2023]
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8
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Cai T, Notkins AL. Pathophysiologic changes in IA-2/IA-2β null mice are secondary to alterations in the secretion of hormones and neurotransmitters. Acta Diabetol 2016; 53:7-12. [PMID: 25861885 PMCID: PMC5243143 DOI: 10.1007/s00592-015-0750-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 03/26/2015] [Indexed: 12/13/2022]
Abstract
IA-2 and IA-2β are transmembrane proteins of dense-core vesicles (DCV). The deletion of these proteins results in a reduction in the number of DCV and the secretion of hormones and neurotransmitters. As a result, this leads to a variety of pathophysiologic changes. The purpose of this review is to describe these changes, which are characterized by glucose intolerance, female infertility, behavior and learning abnormalities and alterations in the diurnal circadian rhythms of blood pressure, heart rate, spontaneous physical activity and body temperature. These findings show that the deletion of IA-2 and IA-2β results in multiple pathophysiologic changes and represents a unique in vivo model for studying the effect of hormone and neurotransmitter reduction on known and still unrecognized targets.
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Affiliation(s)
- Tao Cai
- Experimental Medicine Section, Laboratory of Sensory Biology, National Institute of Dental and Craniofacial Research (NIDCR), National Institutes of Health (NIH), B30/Rm106, Bethesda, MD, 20892, USA
| | - Abner L Notkins
- Experimental Medicine Section, Laboratory of Sensory Biology, National Institute of Dental and Craniofacial Research (NIDCR), National Institutes of Health (NIH), B30/Rm106, Bethesda, MD, 20892, USA.
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9
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Stability of proICA512/IA-2 and its targeting to insulin secretory granules require β4-sheet-mediated dimerization of its ectodomain in the endoplasmic reticulum. Mol Cell Biol 2015; 35:914-27. [PMID: 25561468 DOI: 10.1128/mcb.00994-14] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The type 1 diabetes autoantigen ICA512/IA-2/RPTPN is a receptor protein tyrosine phosphatase of the insulin secretory granules (SGs) which regulates the size of granule stores, possibly via cleavage/signaling of its cytosolic tail. The role of its extracellular region remains unknown. Structural studies indicated that β2- or β4-strands in the mature ectodomain (ME ICA512) form dimers in vitro. Here we show that ME ICA512 prompts proICA512 dimerization in the endoplasmic reticulum. Perturbation of ME ICA512 β2-strand N-glycosylation upon S508A replacement allows for proICA512 dimerization, O-glycosylation, targeting to granules, and conversion, which are instead precluded upon G553D replacement in the ME ICA512 β4-strand. S508A/G553D and N506A/G553D double mutants dimerize but remain in the endoplasmic reticulum. Removal of the N-terminal fragment (ICA512-NTF) preceding ME ICA512 allows an ICA512-ΔNTF G553D mutant to exit the endoplasmic reticulum, and ICA512-ΔNTF is constitutively delivered to the cell surface. The signal for SG sorting is located within the NTF RESP18 homology domain (RESP18-HD), whereas soluble NTF is retained in the endoplasmic reticulum. Hence, we propose that the ME ICA512 β2-strand fosters proICA512 dimerization until NTF prevents N506 glycosylation. Removal of this constraint allows for proICA512 β4-strand-induced dimerization, exit from the endoplasmic reticulum, O-glycosylation, and RESP18-HD-mediated targeting to granules.
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10
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X-ray structure of the mature ectodomain of phogrin. ACTA ACUST UNITED AC 2014; 16:1-9. [PMID: 25421040 DOI: 10.1007/s10969-014-9191-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Accepted: 11/19/2014] [Indexed: 10/24/2022]
Abstract
Phogrin/IA-2β and ICA512/IA-2 are two paralogs receptor-type protein-tyrosine phosphatases (RPTP) that localize in secretory granules of various neuroendocrine cells. In pancreatic islet β-cells, they participate in the regulation of insulin secretion, ensuring proper granulogenesis, and β-cell proliferation. The role of their cytoplasmic tail has been partially unveiled, while that of their luminal region remains unclear. To advance the understanding of its structure-function relationship, the X-ray structure of the mature ectodomain of phogrin (ME phogrin) at pH 7.4 and 4.6 has been solved at 1.95- and 2.01-Å resolution, respectively. Similarly to the ME of ICA512, ME phogrin adopts a ferredoxin-like fold: a sheet of four antiparallel β-strands packed against two α-helices. Sequence conservation among vertebrates, plants and insects suggests that the structural similarity extends to all the receptor family. Crystallized ME phogrin is monomeric, in agreement with solution studies but in striking contrast with the behavior of homodimeric ME ICA512. The structural details that may cause the quaternary structure differences are analyzed. The results provide a basis for building models of the overall orientation and oligomerization state of the receptor in biological membranes.
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11
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Kharitidi D, Manteghi S, Pause A. Pseudophosphatases: methods of analysis and physiological functions. Methods 2013; 65:207-18. [PMID: 24064037 DOI: 10.1016/j.ymeth.2013.09.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 08/20/2013] [Accepted: 09/11/2013] [Indexed: 01/27/2023] Open
Abstract
Protein tyrosine phosphatases (PTPs) are key enzymes in the regulation of cellular homeostasis and signaling pathways. Strikingly, not all PTPs bear enzymatic activity. A considerable fraction of PTPs are enzymatically inactive and are known as pseudophosphatases. Despite the lack of activity they execute pivotal roles in development, cell biology and human disease. The present review is focused on the methods used to identify pseudophosphatases, their targets, and physiological roles. We present a strategy for detailed enzymatic analysis of inactive PTPs, regulation of inactive PTP domains and identification of binding partners. Furthermore, we provide a detailed overview of human pseudophosphatases and discuss their regulation of cellular processes and functions in human pathologies.
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Affiliation(s)
- Dmitri Kharitidi
- Department of Biochemistry and Goodman Cancer Research Centre, McGill University, 3655, Promenade Sir William Osler, Montreal, QC H3G 1Y6, Canada.
| | - Sanaz Manteghi
- Department of Biochemistry and Goodman Cancer Research Centre, McGill University, 3655, Promenade Sir William Osler, Montreal, QC H3G 1Y6, Canada.
| | - Arnim Pause
- Department of Biochemistry and Goodman Cancer Research Centre, McGill University, 3655, Promenade Sir William Osler, Montreal, QC H3G 1Y6, Canada.
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Karisch R, Fernandez M, Taylor P, Virtanen C, St-Germain JR, Jin LL, Harris IS, Mori J, Mak TW, Senis YA, Östman A, Moran MF, Neel BG. Global proteomic assessment of the classical protein-tyrosine phosphatome and "Redoxome". Cell 2011; 146:826-40. [PMID: 21884940 DOI: 10.1016/j.cell.2011.07.020] [Citation(s) in RCA: 133] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2010] [Revised: 05/06/2011] [Accepted: 07/01/2011] [Indexed: 12/30/2022]
Abstract
Protein-tyrosine phosphatases (PTPs), along with protein-tyrosine kinases, play key roles in cellular signaling. All Class I PTPs contain an essential active site cysteinyl residue, which executes a nucleophilic attack on substrate phosphotyrosyl residues. The high reactivity of the catalytic cysteine also predisposes PTPs to oxidation by reactive oxygen species, such as H(2)O(2). Reversible PTP oxidation is emerging as an important cellular regulatory mechanism and might contribute to diseases such as cancer. We exploited these unique features of PTP enzymology to develop proteomic methods, broadly applicable to cell and tissue samples, that enable the comprehensive identification and quantification of expressed classical PTPs (PTPome) and the oxidized subset of the PTPome (oxPTPome). We find that mouse and human cells and tissues, including cancer cells, display distinctive PTPomes and oxPTPomes, revealing additional levels of complexity in the regulation of protein-tyrosine phosphorylation in normal and malignant cells.
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Affiliation(s)
- Robert Karisch
- Department of Medical Biophysics, University of Toronto, Toronto M5G 2M9, ON, Canada.
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13
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Primo ME, Jakoncic J, Noguera ME, Risso VA, Sosa L, Sica MP, Solimena M, Poskus E, Ermácora MR. Protein-protein interactions in crystals of the human receptor-type protein tyrosine phosphatase ICA512 ectodomain. PLoS One 2011; 6:e24191. [PMID: 21935384 PMCID: PMC3174154 DOI: 10.1371/journal.pone.0024191] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 08/02/2011] [Indexed: 11/19/2022] Open
Abstract
ICA512 (or IA-2) is a transmembrane protein-tyrosine phosphatase located in secretory granules of neuroendocrine cells. Initially, it was identified as one of the main antigens of autoimmune diabetes. Later, it was found that during insulin secretion, the cytoplasmic domain of ICA512 is cleaved and relocated to the nucleus, where it stimulates the transcription of the insulin gene. The role of the other parts of the receptor in insulin secretion is yet to be unveiled. The structures of the intracellular pseudocatalytic and mature extracellular domains are known, but the transmembrane domain and several intracellular and extracellular parts of the receptor are poorly characterized. Moreover the overall structure of the receptor remains to be established. We started to address this issue studying by X-ray crystallography the structure of the mature ectodomain of ICA512 (ME ICA512) and variants thereof. The variants and crystallization conditions were chosen with the purpose of exploring putative association interfaces, metal binding sites and all other structural details that might help, in subsequent works, to build a model of the entire receptor. Several structural features were clarified and three main different association modes of ME ICA512 were identified. The results provide essential pieces of information for the design of new experiments aimed to assess the structure in vivo.
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Affiliation(s)
- María E. Primo
- Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), Ciudad Autónoma de Buenos Aires, Argentina
- Cátedra de Inmunología de la Facultad de Farmacia y Bioquímica, Idehu, and División Endocrinología del Hospital de Clínicas J. de San Martín, Universidad de Buenos Aires—Conicet, Ciudad Autónoma de Buenos Aires, Argentina
| | - Jean Jakoncic
- Photon Science Directorate, Brookhaven National Laboratory, Upton, New York, United States of America
| | - Martín E. Noguera
- Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), Ciudad Autónoma de Buenos Aires, Argentina
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Bernal, Buenos Aires, Argentina
| | - Valeria A. Risso
- Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), Ciudad Autónoma de Buenos Aires, Argentina
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Bernal, Buenos Aires, Argentina
| | - Laura Sosa
- Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), Ciudad Autónoma de Buenos Aires, Argentina
- Cátedra de Inmunología de la Facultad de Farmacia y Bioquímica, Idehu, and División Endocrinología del Hospital de Clínicas J. de San Martín, Universidad de Buenos Aires—Conicet, Ciudad Autónoma de Buenos Aires, Argentina
| | - Mauricio P. Sica
- Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), Ciudad Autónoma de Buenos Aires, Argentina
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Bernal, Buenos Aires, Argentina
| | - Michele Solimena
- Paul Langerhans Institute Dresden, Molecular Diabetology, Universitätsklinikum “Carl Gustav Carus”, University of Technology Dresden, Dresden, Germany
- Max Planck Institute of Molecular Cell Biology and Genetics Dresden, Dresden, Germany
| | - Edgardo Poskus
- Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), Ciudad Autónoma de Buenos Aires, Argentina
- Cátedra de Inmunología de la Facultad de Farmacia y Bioquímica, Idehu, and División Endocrinología del Hospital de Clínicas J. de San Martín, Universidad de Buenos Aires—Conicet, Ciudad Autónoma de Buenos Aires, Argentina
| | - Mario R. Ermácora
- Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), Ciudad Autónoma de Buenos Aires, Argentina
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Bernal, Buenos Aires, Argentina
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14
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Romá-Mateo C, Sacristán-Reviriego A, Beresford NJ, Caparrós-Martín JA, Culiáñez-Macià FA, Martín H, Molina M, Tabernero L, Pulido R. Phylogenetic and genetic linkage between novel atypical dual-specificity phosphatases from non-metazoan organisms. Mol Genet Genomics 2011; 285:341-54. [DOI: 10.1007/s00438-011-0611-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Accepted: 02/27/2011] [Indexed: 11/29/2022]
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15
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Saito N, Takeuchi T, Kawano A, Hosaka M, Hou N, Torii S. Luminal interaction of phogrin with carboxypeptidase E for effective targeting to secretory granules. Traffic 2011; 12:499-506. [PMID: 21210912 DOI: 10.1111/j.1600-0854.2011.01159.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phogrin, a receptor tyrosine phosphatase-like protein, is localized to dense-core secretory granules (SGs) in various neuroendocrine cells. A previous report showed that the N-terminal luminal domain mediates targeting of this protein to SGs in AtT-20 cells. Here, we show that the luminal domain specifically interacts with carboxypeptidase E (CPE), one of the key proteins involved in peptide hormone sorting, in a weakly acidic condition. The luminal domain consists of pro-sequence domain (pro) and subsequent N-side mature domain and the pro domain was preferentially required for phogrin interaction with CPE and for its targeting to SGs. Small interfering RNA-directed reduction of the CPE protein level resulted in an improper accumulation of phogrin at the trans-Golgi network in AtT-20 cells. This finding indicates that CPE is involved in the sorting process of phogrin to SGs. However, SG localization of CPE was hindered by overexpression of the phogrin mutants that lack the transport motif of binding to clathrin adaptor complexes. Phogrin-depleted AtT-20 cells also exhibited reduced CPE targeting and increased CPE degradation. Our results suggest that the luminal interaction between phogrin and CPE contributes to their targeting to SGs in a cooperative manner in neuroendocrine cells.
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Affiliation(s)
- Naoya Saito
- Laboratory of Secretion Biology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
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16
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Suckale J, Solimena M. The insulin secretory granule as a signaling hub. Trends Endocrinol Metab 2010; 21:599-609. [PMID: 20609596 DOI: 10.1016/j.tem.2010.06.003] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Revised: 06/01/2010] [Accepted: 06/03/2010] [Indexed: 02/06/2023]
Abstract
The insulin granule was previously thought of as merely a container, but accumulating evidence suggests that it also acts as a signaling node. Regulatory pathways intersect at but also originate from the insulin granule membrane. Examples include the small G-proteins Rab3a and Rab27a, which influence granule movement, and the transmembrane proteins (tyrosine phosphatase receptors type N) PTPRN and PTPRN2, which upregulate β-cell transcription and proliferation. In addition, many cosecreted compounds possess regulatory functions, often related to energy metabolism. For instance, ATP and γ-amino butyric acid (GABA) modulate insulin and glucagon secretion, respectively; C-peptide protects β-cells and kidney cells; and amylin reduces gastric emptying and food intake via the brain. In this paper, we review the current knowledge of the insulin granule proteome and discuss its regulatory functions.
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Affiliation(s)
- Jakob Suckale
- Molecular Diabetology, Paul Langerhans Institute Dresden, School of Medicine and University Clinic Carl Gustav Carus, Dresden University of Technology, Dresden 01307, Germany
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17
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Nishimura T, Harashima SI, Yafang H, Notkins AL. IA-2 modulates dopamine secretion in PC12 cells. Mol Cell Endocrinol 2010; 315:81-6. [PMID: 19799965 PMCID: PMC3495171 DOI: 10.1016/j.mce.2009.09.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2009] [Revised: 09/16/2009] [Accepted: 09/22/2009] [Indexed: 11/28/2022]
Abstract
The secretion of the hormone insulin from beta cells is modulated by the expression of the dense core vesicle transmembrane protein IA-2. Since IA-2 is found in neuroendocrine cells throughout the body, the present experiments were initiated to determine whether the expression of IA-2 also modulates the secretion of neurotransmitters. Using the dopamine-secreting pheochromocytoma cell line PC12, we found that the overexpressions of IA-2 increased the cellular content and secretion of dopamine, whereas the knockdown of IA-2 by siRNA decreased the cellular content and secretion of dopamine. Neither the overexpression nor knockdown of IA-2 influenced the uptake of [H(3)]dopamine by PC12 cells, but did influence the amount of [H(3)]dopamine secreted. Overexpression of IA-2 also increased the level of the dense core vesicle-associated proteins Rab3A, IA-2beta and secretogranin II, whereas the knockdown of IA-2 decreased the level of these proteins. We conclude that the expression of IA-2 profoundly influences the function of dense core vesicles and has a broad modulating effect on the cellular content and secretion of both hormones and neurotransmitters.
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Affiliation(s)
- Takuya Nishimura
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
| | - Shin-ichi Harashima
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Hu Yafang
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
- Center for Cancer and Immunology Research, Children’s National Medical Center, Washington, DC, USA
| | - Abner Louis Notkins
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
- Corresponding author at: National Institutes of Health, Building 30, Room 106, 30 Convent Drive, MSC4322, Bethesda, MD 20892-4322, USA. Tel.: +1 301 496 4535; fax: +1 301 402 4163. (A.L. Notkins)
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18
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Balasu MC, Spiridon LN, Miron S, Craescu CT, Scheidig AJ, Petrescu AJ, Szedlacsek SE. Interface analysis of the complex between ERK2 and PTP-SL. PLoS One 2009; 4:e5432. [PMID: 19424502 PMCID: PMC2675061 DOI: 10.1371/journal.pone.0005432] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2009] [Accepted: 03/27/2009] [Indexed: 01/13/2023] Open
Abstract
The activity of ERK2, an essential component of MAP-kinase pathway, is under the strict control of various effector proteins. Despite numerous efforts, no crystal structure of ERK2 complexed with such partners has been obtained so far. PTP-SL is a major regulator of ERK2 activity. To investigate the ERK2–PTP-SL complex we used a combined method based on cross-linking, MALDI-TOF analysis, isothermal titration calorimetry, molecular modeling and docking. Hence, new insights into the stoichiometry, thermodynamics and interacting regions of the complex are obtained and a structural model of ERK2-PTP-SL complex in a state consistent with PTP-SL phosphatase activity is developed incorporating all the experimental constraints available at hand to date. According to this model, part of the N-terminal region of PTP-SL has propensity for intrinsic disorder and becomes structured within the complex with ERK2. The proposed model accounts for the structural basis of several experimental findings such as the complex-dissociating effect of ATP, or PTP-SL blocking effect on the ERK2 export to the nucleus. A general observation emerging from this model is that regions involved in substrate binding in PTP-SL and ERK2, respectively are interacting within the interface of the complex.
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Affiliation(s)
- Mihaela C. Balasu
- Department of Enzymology, Institute of Biochemistry, Bucharest, Romania
- Department of Organic Chemistry , University POLITEHNICA, Bucharest, Romania
| | - Laurentiu N. Spiridon
- Department of Bioinformatics and Structural Biochemistry, Institute of Biochemistry, Bucharest, Romania
| | - Simona Miron
- Institut Curie Centre de Recherche, Orsay, France
- INSERM U759, Orsay, France
| | | | - Axel J. Scheidig
- Zoologisches Institut, Strukturbiologie/ZBM, Christian-Albrechts-Universität Kiel, Kiel, Germany
| | - Andrei-Jose Petrescu
- Department of Bioinformatics and Structural Biochemistry, Institute of Biochemistry, Bucharest, Romania
| | - Stefan E. Szedlacsek
- Department of Enzymology, Institute of Biochemistry, Bucharest, Romania
- * E-mail:
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19
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Torii S, Saito N, Kawano A, Hou N, Ueki K, Kulkarni RN, Takeuchi T. Gene silencing of phogrin unveils its essential role in glucose-responsive pancreatic beta-cell growth. Diabetes 2009; 58:682-92. [PMID: 19073770 PMCID: PMC2646067 DOI: 10.2337/db08-0970] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVE Phogrin and IA-2, autoantigens in insulin-dependent diabetes, have been shown to be involved in insulin secretion in pancreatic beta-cells; however, implications at a molecular level are confusing from experiment to experiment. We analyzed biological functions of phogrin in beta-cells by an RNA interference technique. RESEARCH DESIGN AND METHODS Adenovirus-mediated expression of short hairpin RNA specific for phogrin (shPhogrin) was conducted using cultured beta-cell lines and mouse islets. Both glucose-stimulated insulin secretion and cell proliferation rate were determined in the phogrin-knockdown cells. Furthermore, protein expression was profiled in these cells. To see the binding partner of phogrin in beta-cells, coimmunoprecipitation analysis was carried out. RESULTS Adenoviral expression of shPhogrin efficiently decreased its endogenous expression in pancreatic beta-cells. Silencing of phogrin in beta-cells abrogated the glucose-mediated mitogenic effect, which was accompanied by a reduction in the level of insulin receptor substrate 2 (IRS2) protein, without any changes in insulin secretion. Phogrin formed a complex with insulin receptor at the plasma membrane, and their interaction was promoted by high-glucose stimulation that in turn led to stabilization of IRS2 protein. Corroboratively, phogrin knockdown had no additional effect on the proliferation of beta-cell line derived from the insulin receptor-knockout mouse. CONCLUSIONS Phogrin is involved in beta-cell growth via regulating stability of IRS2 protein by the molecular interaction with insulin receptor. We propose that phogrin and IA-2 function as an essential regulator of autocrine insulin action in pancreatic beta-cells.
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Affiliation(s)
- Seiji Torii
- Secretion Biology Lab, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma, Japan
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20
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Barr AJ, Ugochukwu E, Lee WH, King ON, Filippakopoulos P, Alfano I, Savitsky P, Burgess-Brown NA, Müller S, Knapp S. Large-scale structural analysis of the classical human protein tyrosine phosphatome. Cell 2009; 136:352-63. [PMID: 19167335 PMCID: PMC2638020 DOI: 10.1016/j.cell.2008.11.038] [Citation(s) in RCA: 358] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Revised: 09/15/2008] [Accepted: 11/20/2008] [Indexed: 02/05/2023]
Abstract
Protein tyrosine phosphatases (PTPs) play a critical role in regulating cellular functions by selectively dephosphorylating their substrates. Here we present 22 human PTP crystal structures that, together with prior structural knowledge, enable a comprehensive analysis of the classical PTP family. Despite their largely conserved fold, surface properties of PTPs are strikingly diverse. A potential secondary substrate-binding pocket is frequently found in phosphatases, and this has implications for both substrate recognition and development of selective inhibitors. Structural comparison identified four diverse catalytic loop (WPD) conformations and suggested a mechanism for loop closure. Enzymatic assays revealed vast differences in PTP catalytic activity and identified PTPD1, PTPD2, and HDPTP as catalytically inert protein phosphatases. We propose a “head-to-toe” dimerization model for RPTPγ/ζ that is distinct from the “inhibitory wedge” model and that provides a molecular basis for inhibitory regulation. This phosphatome resource gives an expanded insight into intrafamily PTP diversity, catalytic activity, substrate recognition, and autoregulatory self-association.
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Affiliation(s)
- Alastair J. Barr
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
- Corresponding author
| | - Emilie Ugochukwu
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Wen Hwa Lee
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Oliver N.F. King
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Panagis Filippakopoulos
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Ivan Alfano
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Pavel Savitsky
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Nicola A. Burgess-Brown
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Susanne Müller
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
| | - Stefan Knapp
- University of Oxford, Structural Genomics Consortium, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK
- University of Oxford, Department of Clinical Pharmacology, Old Road Campus, Roosevelt Drive, Oxford OX3 7DQ, UK
- Corresponding author
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21
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Torii S. Expression and function of IA-2 family proteins, unique neuroendocrine-specific protein-tyrosine phosphatases. Endocr J 2009; 56:639-48. [PMID: 19550073 DOI: 10.1507/endocrj.k09e-157] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
IA-2 (also known as islet cell antigen ICA-512) and IA-2 beta (also known as phogrin, phosphatase homologue in granules of insulinoma) are major autoantigens in insulin-dependent diabetes mellitus (IDDM). Autoantibodies against both proteins are expressed years before clinical onset, and they become predictive markers for high-risk subjects. However, the role of these genes in the IDDM pathogenesis has been reported fairly negative by recent studies. IA-2 and IA-2 beta are type I transmembrane proteins that possess one inactive protein-tyrosine phosphatase (PTP) domain in the cytoplasmic region, and act as one of the constituents of regulated secretory pathways in various neuroendocrine cell types including pancreatic beta-cells. Existence of IA-2 homologues in different species suggests a fundamental role in neuroendocrine function. Studies of knockout animals have shown their involvement in maintaining hormone content, however, their specific steps in the secretory pathway IA-2 functions as well as their molecular mechanisms in the hormone content regulation are still unknown. More recent studies have suggested a novel function showing that they contribute to pancreatic beta-cell growth. This review attempts to show the possible biological functions of IA-2 family, focusing on their expression and localization in the neuroendocrine cells.
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Affiliation(s)
- Seiji Torii
- Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
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22
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Trajkovski M, Mziaut H, Schubert S, Kalaidzidis Y, Altkrüger A, Solimena M. Regulation of insulin granule turnover in pancreatic beta-cells by cleaved ICA512. J Biol Chem 2008; 283:33719-29. [PMID: 18824546 DOI: 10.1074/jbc.m804928200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Insulin maintains homeostasis of glucose by promoting its uptake into cells from the blood. Hyperglycemia triggers secretion of insulin from pancreatic beta-cells. This process is mediated by secretory granule exocytosis. However, how beta-cells keep granule stores relatively constant is still unknown. ICA512 is an intrinsic granule membrane protein, whose cytosolic domain binds beta2-syntrophin, an F-actin-associated protein, and is cleaved upon granule exocytosis. The resulting cleaved cytosolic fragment, ICA512-CCF, reaches the nucleus and up-regulates the transcription of granule genes, including insulin and ICA512. Here, we show that ICA512-CCF also dimerizes with intact ICA512 on granules, thereby displacing it from beta2-syntrophin. This leads to increased granule mobility and insulin release. Based on these findings, we propose a model whereby the generation of ICA512-CCF first amplifies insulin secretion. The ensuing reduction of granule stores would then increase the probability of newly generated ICA512-CCF to reach the nucleus and enhance granule biogenesis, thus allowing beta-cells to constantly adjust production of granules to their storage size and consumption. Pharmacological modulation of these feedback loops may alleviate deficient insulin release in diabetes.
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Affiliation(s)
- Mirko Trajkovski
- Laboratory of Experimental Diabetology, School of Medicine, Dresden University of Technology, Dresden 01307, Germany
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23
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Hendriks WJAJ, Elson A, Harroch S, Stoker AW. Protein tyrosine phosphatases: functional inferences from mouse models and human diseases. FEBS J 2008; 275:816-30. [DOI: 10.1111/j.1742-4658.2008.06249.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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24
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Primo ME, Klinke S, Sica MP, Goldbaum FA, Jakoncic J, Poskus E, Ermácora MR. Structure of the Mature Ectodomain of the Human Receptor-type Protein-tyrosine Phosphatase IA-2. J Biol Chem 2008; 283:4674-81. [DOI: 10.1074/jbc.m708144200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
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25
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Almo SC, Bonanno JB, Sauder JM, Emtage S, Dilorenzo TP, Malashkevich V, Wasserman SR, Swaminathan S, Eswaramoorthy S, Agarwal R, Kumaran D, Madegowda M, Ragumani S, Patskovsky Y, Alvarado J, Ramagopal UA, Faber-Barata J, Chance MR, Sali A, Fiser A, Zhang ZY, Lawrence DS, Burley SK. Structural genomics of protein phosphatases. ACTA ACUST UNITED AC 2007; 8:121-40. [PMID: 18058037 DOI: 10.1007/s10969-007-9036-1] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Accepted: 11/06/2007] [Indexed: 12/11/2022]
Abstract
The New York SGX Research Center for Structural Genomics (NYSGXRC) of the NIGMS Protein Structure Initiative (PSI) has applied its high-throughput X-ray crystallographic structure determination platform to systematic studies of all human protein phosphatases and protein phosphatases from biomedically-relevant pathogens. To date, the NYSGXRC has determined structures of 21 distinct protein phosphatases: 14 from human, 2 from mouse, 2 from the pathogen Toxoplasma gondii, 1 from Trypanosoma brucei, the parasite responsible for African sleeping sickness, and 2 from the principal mosquito vector of malaria in Africa, Anopheles gambiae. These structures provide insights into both normal and pathophysiologic processes, including transcriptional regulation, regulation of major signaling pathways, neural development, and type 1 diabetes. In conjunction with the contributions of other international structural genomics consortia, these efforts promise to provide an unprecedented database and materials repository for structure-guided experimental and computational discovery of inhibitors for all classes of protein phosphatases.
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Affiliation(s)
- Steven C Almo
- Albert Einstein College of Medicine, Bronx, NY, USA.
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26
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Noordman YE, Augustus ED, Schepens JTG, Chirivi RGS, Ríos P, Pulido R, Hendriks WJAJ. Multimerisation of receptor-type protein tyrosine phosphatases PTPBR7 and PTP-SL attenuates enzymatic activity. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1783:275-86. [PMID: 18068678 DOI: 10.1016/j.bbamcr.2007.10.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2007] [Revised: 10/22/2007] [Accepted: 10/30/2007] [Indexed: 11/16/2022]
Abstract
Dimerisation of receptor-type protein tyrosine phosphatases (RPTPs) represents an appealing mechanism to regulate their enzymatic activity. Studies thus far mostly concern the dimerisation behaviour of RPTPs possessing two tandemly oriented catalytic PTP domains. Mouse gene Ptprr encodes four different protein isoforms (i.e. PTPBR7, PTP-SL and PTPPBSgamma-42/37) that contain a single PTP domain. Using selective membrane permeabilisation we here demonstrate that PTP-SL, like PTPBR7, is a single membrane-spanning RPTP. Furthermore, these two receptor-type PTPs constitutively formed homo- and hetero-meric complexes as witnessed in chemical cross-linking and co-immunoprecipitation experiments, in sharp contrast to the cytosolic PTPPBSgamma-42 and PTPPBSgamma-37 PTPRR isoforms. This multimerisation occurs independently of the PTP domain and requires the transmembrane domain and/or the proximal hydrophobic region. Using overexpression of a PTPBR7 mutant that essentially lacks the intracellular PTP domain-containing segment, a monomer-mimicking state was forced upon full-length PTPBR7 immunoprecipitates. This resulted in a significant increase in the enzymatic activity of the PTPRR PTP domain, which strengthens the notion that multimerisation represents a general mechanism to tone down RPTP catalytic activity.
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Affiliation(s)
- Yvet E Noordman
- Department of Cell Biology, Radboud University Nijmegen Medical Centre, Geert Grooteplein 28, 6525 GA Nijmegen, The Netherlands
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27
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Kim SJ, Jeong DG, Jeong SK, Yoon TS, Ryu SE. Crystal structure of the major diabetes autoantigen insulinoma-associated protein 2 reveals distinctive immune epitopes. Diabetes 2007; 56:41-8. [PMID: 17192463 DOI: 10.2337/db06-0237] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Insulinoma-associated protein-2 (IA-2) is a major autoantigen in type 1 diabetes that occurs through autoimmune-mediated beta-cell destruction. We present here the crystal structure of the protein tyrosine phosphatase (PTP)-like domain of human IA-2. The structure reveals a canonical PTP domain with the closed WPD loop over the active site pocket, explaining the lack of enzyme activity in the native protein. The structural interpretation of previous mutagenesis studies indicates that the B-cell epitopes are concentrated on two distinctive regions on peripheral loops of the central beta-sheet surrounding T-cell epitopes within the sheet. The detailed structural information on immune epitopes provides a framework for the future development of immune intervention strategies against diabetes.
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Affiliation(s)
- Seung Jun Kim
- Systemic Proteomics Research Center, Korea Research Institute of Bioscience and Biotechnology, 52 Euh-eun-dong, Yuseong-gu, Daejeon 305-333, Korea
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28
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Kubosaki A, Nakamura S, Clark A, Morris JF, Notkins AL. Disruption of the transmembrane dense core vesicle proteins IA-2 and IA-2beta causes female infertility. Endocrinology 2006; 147:811-5. [PMID: 16269463 DOI: 10.1210/en.2005-0638] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Female infertility is a worldwide problem affecting 10-15% of the population. The cause of the infertility in many cases is not known. In the present report, we demonstrate that alterations in two transmembrane structural proteins, IA-2 and IA-2beta, located in dense core secretory vesicles (DCV) of many endocrine and neuroendocrine cells, can result in female infertility. IA-2 and IA-2beta are best known as major autoantigens in type 1 diabetes, but their normal function has remained an enigma. Recently we showed in mice that deletion of IA-2 and/or IA-2beta results in impaired insulin secretion and glucose intolerance. We now report that double knockout (DKO), but not single knockout, female mice are essentially infertile. Vaginal smears showed a totally abnormal estrous cycle, and examination of the ovaries revealed normal-appearing oocytes but the absence of corpora lutea. The LH surge that is required for ovulation occurred in wild-type mice but not in DKO mice. Additional studies showed that the LH level in the pituitary of DKO female mice was decreased compared with wild-type mice. Treatment of DKO females with gonadotropins restored corpora lutea formation. In contrast to DKO female mice, DKO male mice were fertile and LH levels in the serum and pituitary were within the normal range. From these studies we conclude that the DCV proteins, IA-2 and IA-2beta, play an important role in LH secretion and that alterations in structural proteins of DCV can result in female infertility.
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Affiliation(s)
- Atsutaka Kubosaki
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892, USA
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29
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Doi A, Shono T, Nishi M, Furuta H, Sasaki H, Nanjo K. IA-2beta, but not IA-2, is induced by ghrelin and inhibits glucose-stimulated insulin secretion. Proc Natl Acad Sci U S A 2006; 103:885-90. [PMID: 16418280 PMCID: PMC1347964 DOI: 10.1073/pnas.0502470102] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Ghrelin is a newly discovered peptide and an endogenous ligand for growth hormone (GH) secretagogue (GHS) receptor. It has been shown to possess various central and peripheral effects, including GH secretion, food intake, and gastric and cardiac effects. Ghrelin and the GHS receptor are expressed also in pancreatic islets. We have identified several ghrelin-induced genes by PCR-select subtraction methods, among which is a beta-cell autoantigen for type 1 diabetes, IA-2beta. Administration of ghrelin increased IA-2beta mRNA in mouse brain, pancreas, and insulinoma cell lines (MIN6 and betaTC3). However, the expression of IA-2, another structurally related beta-cell autoantigen, was not induced by ghrelin. Administration of ghrelin or overexpression of IA-2beta, but not overexpression of IA-2, inhibited glucose-stimulated insulin secretion in MIN6 insulinoma cells and, moreover, inhibition of IA-2beta expression by the RNA interference technique ameliorated ghrelin's inhibitory effects on glucose-stimulated insulin secretion. These findings strongly suggest that inhibitory effects of ghrelin on glucose-stimulated insulin secretion are at least partly due to increased expression of IA-2beta induced by ghrelin. Our data demonstrate the link among ghrelin, IA-2beta, and glucose-stimulated insulin secretion.
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Affiliation(s)
- Asako Doi
- The First Department of Medicine, Wakayama Medical University, 811-1 Kimiidera, Wakayama 641-8509, Japan
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30
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Hu YF, Zhang HL, Cai T, Harashima S, Notkins AL. The IA-2 interactome. Diabetologia 2005; 48:2576-81. [PMID: 16273344 DOI: 10.1007/s00125-005-0037-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2005] [Accepted: 08/02/2005] [Indexed: 11/25/2022]
Abstract
AIMS/HYPOTHESIS Islet antigen-2 (IA-2), a major autoantigen in type 1 diabetes, is an enzymatically inactive member of the transmembrane protein tyrosine phosphatase (PTP) family. IA-2 is located in dense-core secretory vesicles and is involved in the regulation of insulin secretion. The present experiments were initiated to identify those proteins that interact with IA-2 (i.e. the IA-2 interactome) as a first step towards elucidating the mechanism(s) by which IA-2 influences insulin secretion and serves as an autoantigen. MATERIALS AND METHODS To determine the proteins with which IA-2 interacts, a yeast two-hybrid system was used to screen a human foetal library, and deletion mutants were used to determine the binding sites. Positive interactions were confirmed by immunoprecipitation pull-down experiments using cell lysate from transfected mammalian cell lines. RESULTS Six new interacting proteins were identified by this approach: mitogen-activated protein kinase-activating death domain (MADD), the MADD isoform IG20, PTPrho, PTPsigma, sorting nexin 19 (SNX19) and cyclophilin A. Using a series of IA-2 deletion mutants, we identified the regions on the IA-2 molecule to which five of the interacting proteins bound. Amino acids 744-979 of IA-2 were required for the maximum binding of MADD, IG20 and SNX19, whereas amino acids 602-907 of IA-2 were required for the maximum binding of PTPrho and PTPsigma. Pull-down experiments with cell lysate from transfected mammalian cells confirmed the binding of the interacting proteins to IA-2. CONCLUSIONS/INTERPRETATION The IA-2 interactome based on, pull-down experiments, currently consists of 12 proteins. The identification of these interacting proteins provides clues as to how IA-2 exerts its biological functions.
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Affiliation(s)
- Y F Hu
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institutes of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
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Kubosaki A, Nakamura S, Notkins AL. Dense core vesicle proteins IA-2 and IA-2beta: metabolic alterations in double knockout mice. Diabetes 2005; 54 Suppl 2:S46-51. [PMID: 16306340 DOI: 10.2337/diabetes.54.suppl_2.s46] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
IA-2 and IA-2beta are members of the transmembrane protein tyrosine phosphatase family located in dense core vesicles of neuroendocrine cells, including the beta-cells of pancreatic islets. In the present study, by mating C57BL/6Nci IA-2(+/-) with IA-2beta(+/-) mice, we generated double knockout mice (IA-2(-/-)/IA-2beta(-/-)) to study the effect of the combined deletion of these two proteins on insulin secretion and blood glucose levels. The double knockout mice appeared healthy at birth and showed normal growth and development. Histological examination and immunostaining for insulin, glucagon, somatostatin, and pancreatic polypeptide revealed no difference between the double knockout and wild-type mice. Nonfasting blood glucose and insulin levels also were within the normal range. However, compared with the wild-type mice, the double knockout mice showed glucose intolerance and an absent first-phase insulin release curve. No evidence of insulin resistance was observed nor were there alterations in fasting blood glucose, insulin, or leptin levels in the double knockout mice maintained on a high-fat diet compared with the wild-type mice maintained on the same diet. In addition, to determine whether the combined deletion of IA-2 and IA-2beta played any role in the development of diabetes in NOD mice, we generated double knockout mice on the NOD/LtJ background. The incidence of diabetes in these mice was not significantly different than that in the wild-type mice. Taken together, our experiments show that the dense core vesicle proteins IA-2 and IA-2beta, alone or in combination, are involved in insulin secretion, but neither alone nor in combination are they required for the development of diabetes in NOD mice.
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Affiliation(s)
- Atsutaka Kubosaki
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Building 30/Room 106, 30 Convent Dr., MSC 4322, Bethesda, Maryland 20892-4322, USA
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Wasmeier C, Burgos PV, Trudeau T, Davidson HW, Hutton JC. An extended tyrosine-targeting motif for endocytosis and recycling of the dense-core vesicle membrane protein phogrin. Traffic 2005; 6:474-87. [PMID: 15882444 DOI: 10.1111/j.1600-0854.2005.00292.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Integral membrane proteins of neuroendocine dense-core vesicles (DCV) appear to undergo multiple rounds of exocytosis; however, their trafficking and site of incorporation into nascent DCVs is unclear. Previous studies with phogrin (IA-2beta) identified sorting signals in the luminal domain that is cleaved post-translationally; we now describe an independent DCV targeting motif in the cytosolic domain that may function at the level of endocytosis and recycling. Pulse-chase radiolabeling and cell surface biotinylation experiments in the pituitary corticotroph cell line AtT20 showed that the mature 60/65 kDa form that resides in the DCV is generated by limited proteolysis in a post-trans Golgi network compartment with similar kinetics to the formation of the principal cargo, ACTH. Phogrin is exposed on the cell surface in response to stimuli and progressively internalized to a perinuclear compartment that overlaps with recycling endosomes marked by transferrin. Chimeric molecules of phogrin transmembrane and cytosolic sequences with the interleukin-2 receptor alpha chain (Tac) were sorted to DCVs through the action of an extended tyrosine-based motif Y(654)QELCRQRMA located in a 27aa sequence adjacent to the membrane-spanning domain. A 36aa domain terminating in this sequence conferred DCV localization to Tac in the absence of any other cytosolic or luminal phogrin components. The endocytosis and DCV targeting of phogrin Y(654) > A mutants correlated with the impaired binding of the phogrin cytosolic tail to the micro-subunit of the AP2 adaptor complex in vitro.
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Affiliation(s)
- Christina Wasmeier
- Barbara Davis Center for Childhood Diabetes, University of Colorado at Denver and Health Sciences Center, 4200 East 9th Avenue, Box B140, Denver, CO 80262, USA
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Harashima SI, Clark A, Christie MR, Notkins AL. The dense core transmembrane vesicle protein IA-2 is a regulator of vesicle number and insulin secretion. Proc Natl Acad Sci U S A 2005; 102:8704-9. [PMID: 15939893 PMCID: PMC1150807 DOI: 10.1073/pnas.0408887102] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
IA-2 is an enzymatically inactive member of the transmembrane protein tyrosine phosphate family located in dense core secretory vesicles and a major autoantigen in type 1 diabetes. Recent studies showed that targeted disruption of the IA-2 gene in mice resulted in impairment of insulin secretion and glucose intolerance. Insulin homeostasis, however, is a complex process involving a cascade of regulatory factors, and IA-2 is widely expressed in neuroendocrine cells throughout the body. Consequently, it is uncertain whether the impairment of insulin secretion in IA-2 knockout mice is a direct result of the knockout of IA-2 in beta cells or to counter regulatory alterations resulting from IA-2 knockout in other neuroendocrine cells. To define the function of IA-2, we studied the secretion of insulin in a single cell type, MIN-6, by overexpressing and knocking down IA-2. Our experiments showed that overexpression of IA-2 resulted in a 6-fold increase in glucose- or K+-induced insulin secretion and a approximately 3-fold increase in the number of secretory vesicles and the insulin content of cells. In contrast, knockdown of endogenous IA-2 by short interfering RNA resulted in nearly a complete loss of glucose-induced insulin secretion and a 50% decrease in basal insulin release. The half-life of insulin in cells overexpressing IA-2 was nearly twice as great as that in mock-transfected cells, suggesting that IA-2 was stabilizing the insulin-containing vesicles. From these results we conclude that in beta cells, IA-2 is an important regulator of dense core vesicle number and glucose-induced and basal insulin secretion.
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Affiliation(s)
- Shin-ichi Harashima
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
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Wansink DG, Peters W, Schaafsma I, Sutmuller RPM, Oerlemans F, Adema GJ, Wieringa B, van der Zee CEEM, Hendriks W. Mild impairment of motor nerve repair in mice lacking PTP-BL tyrosine phosphatase activity. Physiol Genomics 2004; 19:50-60. [PMID: 15226483 DOI: 10.1152/physiolgenomics.00079.2004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mouse PTP-BL is a large, nontransmembrane protein tyrosine phosphatase of unclear physiological function that consists of a KIND domain, a FERM domain, five PDZ domains, and a COOH-terminal catalytic PTP domain. PTP-BL and its human ortholog PTP-BAS have been proposed to play a role in the regulation of microfilament dynamics, cytokinesis, apoptosis, and neurite outgrowth. To investigate the biological function of PTP-BL enzyme activity, we have generated mice that lack the PTP-BL PTP moiety. These PTP-BLΔP/ΔPmice are viable and fertile and do not present overt morphological alterations. Although PTP-BL is expressed in most hematopoietic cell lineages, no alterations of thymocyte development in PTP-BLΔP/ΔPmice could be detected. Sciatic nerve lesioning revealed that sensory nerve recovery is unaltered in these mice. In contrast, a very mild but significant impairment of motor nerve repair was observed. Our findings exclude an essential role for PTP-BL as a phosphotyrosine phosphatase and rather are in line with a role as scaffolding or anchoring molecule.
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Affiliation(s)
- Derick G Wansink
- Department of Cell Biology, Nijmegen Center for Molecular Life Sciences, University Medical Center Nijmegen, 6525 GA Nijmegen, The Netherlands
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Kubosaki A, Gross S, Miura J, Saeki K, Zhu M, Nakamura S, Hendriks W, Notkins AL. Targeted disruption of the IA-2beta gene causes glucose intolerance and impairs insulin secretion but does not prevent the development of diabetes in NOD mice. Diabetes 2004; 53:1684-91. [PMID: 15220191 DOI: 10.2337/diabetes.53.7.1684] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Insulinoma-associated protein (IA)-2beta, also known as phogrin, is an enzymatically inactive member of the transmembrane protein tyrosine phosphatase family and is located in dense-core secretory vesicles. In patients with type 1 diabetes, autoantibodies to IA-2beta appear years before the development of clinical disease. The genomic structure and function of IA-2beta, however, is not known. In the present study, we determined the genomic structure of IA-2beta and found that both human and mouse IA-2beta consist of 23 exons and span approximately 1,000 and 800 kb, respectively. With this information, we prepared a targeting construct and inactivated the mouse IA-2beta gene as demonstrated by lack of IA-2beta mRNA and protein expression. The IA-2beta(-/-) mice, in contrast to wild-type controls, showed mild glucose intolerance and impaired glucose-stimulated insulin secretion. Knockout of the IA-2beta gene in NOD mice, the most widely studied animal model for human type 1 diabetes, failed to prevent the development of cyclophosphamide-induced diabetes. We conclude that IA-2beta is involved in insulin secretion, but despite its importance as a major autoantigen in human type 1 diabetes, it is not required for the development of diabetes in NOD mice.
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Affiliation(s)
- Atsutaka Kubosaki
- Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892-4322, USA
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Toledano-Katchalski H, Tiran Z, Sines T, Shani G, Granot-Attas S, den Hertog J, Elson A. Dimerization in vivo and inhibition of the nonreceptor form of protein tyrosine phosphatase epsilon. Mol Cell Biol 2003; 23:5460-71. [PMID: 12861030 PMCID: PMC165729 DOI: 10.1128/mcb.23.15.5460-5471.2003] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
cyt-PTP epsilon is a naturally occurring nonreceptor form of the receptor-type protein tyrosine phosphatase (PTP) epsilon. As such, cyt-PTP epsilon enables analysis of phosphatase regulation in the absence of extracellular domains, which participate in dimerization and inactivation of the receptor-type phosphatases receptor-type protein tyrosine phosphatase alpha (RPTPalpha) and CD45. Using immunoprecipitation and gel filtration, we show that cyt-PTP epsilon forms dimers and higher-order associations in vivo, the first such demonstration among nonreceptor phosphatases. Although cyt-PTP epsilon readily dimerizes in the absence of exogenous stabilization, dimerization is increased by oxidative stress. Epidermal growth factor receptor stimulation can affect cyt-PTP epsilon dimerization and tyrosine phosphorylation in either direction, suggesting that cell surface receptors can relay extracellular signals to cyt-PTP epsilon, which lacks extracellular domains of its own. The inactive, membrane-distal (D2) phosphatase domain of cyt-PTP epsilon is a major contributor to intermolecular binding and strongly interacts in a homotypic manner; the presence of D2 and the interactions that it mediates inhibit cyt-PTP epsilon activity. Intermolecular binding is inhibited by the extreme C and N termini of D2. cyt-PTP epsilon lacking these regions constitutively dimerizes, and its activities in vitro towards para-nitrophenylphosphate and in vivo towards the Kv2.1 potassium channel are markedly reduced. We conclude that physiological signals can regulate dimerization and phosphorylation of cyt-PTP epsilon in the absence of direct interaction between the PTP and extracellular molecules. Furthermore, dimerization can be mediated by the D2 domain and does not strictly require the presence of PTP extracellular domains.
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