Protein tyrosine phosphatases in signal transduction.
Neel B G,Tonks N K
Current opinion in cell biology
Protein-tyrosyl phosphorylation, regulated by protein tyrosine kinases and protein tyrosine phosphatases (PTPs), is a key cellular control mechanism. Until recently, little was known about PTPs. However, the past two years have witnessed an explosion of information about PTP structure, regulation and function. Crystal structures of several PTPs have provided insights into enzymatic mechanisms and regulation and suggested the design of 'substrate-trapping' mutants. Candidate homophilic and heterophilic ligands for transmembrane PTPs have been identified, and roles for transmembrane PTPs in regulating cell-cell interactions have been suggested. Finally, progress has been made in understanding signaling by Src homology 2 domain containing PTPs and PTPs controlling yeast osmoregulatory pathways.
Signal transduction drug discovery: targets, mechanisms and structure-based design.
Dalgarno D C,Metcalf C A,Shakespeare W C,Sawyer T K
Current opinion in drug discovery & development
Signal transduction targets include catalytic and/or non-catalytic domains, which are critical to various aspects of cell growth, differentiation, metabolism and function, mitogenesis, motility and gene transcription. Specific examples of molecular targets include the catalytic domains of protein tyrosine kinases (PTKs) and of protein tyrosine phosphatases (PTPases), as well as related protein-protein interaction motifs (eg, SH2, PTB and SH3 domains). From the relationship of tyrosine phosphorylation to intracellular pathway regulation by PTKs and PTPases, the dynamic and reversible binding interactions of SH2 and PTB domain-containing proteins with their cognate phosphotyrosine (pTyr)-containing proteins, provide an additional dimension to the modulation of signal transduction pathways which exist as a result of pTyr formation, degradation and molecular recognition events. This review focuses on our current understanding of key relative to recent reports which have provided further insight into their three-dimensional structure and mechanism. This review also highlights recent progress in the design and optimization of molecular mechanism-based signal transduction inhibitors.
The extended human PTPome: a growing tyrosine phosphatase family.
Alonso Andrés,Pulido Rafael
The FEBS journal
Tyr phosphatases are, by definition, enzymes that dephosphorylate phospho-Tyr (pTyr) from proteins. This activity is found in several structurally diverse protein families, including the protein Tyr phosphatase (PTP), arsenate reductase, rhodanese, haloacid dehalogenase (HAD) and His phosphatase (HP) families. Most of these families include members with substrate specificity for non-pTyr substrates, such as phospho-Ser/phospho-Thr, phosphoinositides, phosphorylated carbohydrates, mRNAs, or inorganic moieties. A Cys is essential for catalysis in PTPs, rhodanese and arsenate reductase enzymes, whereas this work is performed by an Asp in HAD phosphatases and by a His in HPs, via a catalytic mechanism shared by all of the different families. The category that contains most Tyr phosphatases is the PTP family, which, although it received its name from this activity, includes Ser, Thr, inositide, carbohydrate and RNA phosphatases, as well as some inactive pseudophosphatase proteins. Here, we propose an extended collection of human Tyr phosphatases, which we call the extended human PTPome. The addition of new members (SACs, paladin, INPP4s, TMEM55s, SSU72, and acid phosphatases) to the currently categorized PTP group of enzymes means that the extended human PTPome contains up to 125 proteins, of which ~ 40 are selective for pTyr. We set criteria to ascribe proteins to the extended PTPome, and summarize the more important features of the new PTPome members in the context of their phosphatase activity and their relationship with human disease.
Molecular mechanism of ERK dephosphorylation by striatal-enriched protein tyrosine phosphatase.
Li Rong,Xie Di-Dong,Dong Jun-Hong,Li Hui,Li Kang-Shuai,Su Jing,Chen Lai-Zhong,Xu Yun-Fei,Wang Hong-Mei,Gong Zheng,Cui Guo-Ying,Yu Xiao,Wang Kai,Yao Wei,Xin Tao,Li Min-Yong,Xiao Kun-Hong,An Xiao-Fei,Huo Yuqing,Xu Zhi-Gang,Sun Jin-Peng,Pang Qi
Journal of neurochemistry
Striatal-enriched tyrosine phosphatase (STEP) is an important regulator of neuronal synaptic plasticity, and its abnormal level or activity contributes to cognitive disorders. One crucial downstream effector and direct substrate of STEP is extracellular signal-regulated protein kinase (ERK), which has important functions in spine stabilisation and action potential transmission. The inhibition of STEP activity toward phospho-ERK has the potential to treat neuronal diseases, but the detailed mechanism underlying the dephosphorylation of phospho-ERK by STEP is not known. Therefore, we examined STEP activity toward para-nitrophenyl phosphate, phospho-tyrosine-containing peptides, and the full-length phospho-ERK protein using STEP mutants with different structural features. STEP was found to be a highly efficient ERK tyrosine phosphatase that required both its N-terminal regulatory region and key residues in its active site. Specifically, both kinase interaction motif (KIM) and kinase-specific sequence of STEP were required for ERK interaction. In addition to the N-terminal kinase-specific sequence region, S245, hydrophobic residues L249/L251, and basic residues R242/R243 located in the KIM region were important in controlling STEP activity toward phospho-ERK. Further kinetic experiments revealed subtle structural differences between STEP and HePTP that affected the interactions of their KIMs with ERK. Moreover, STEP recognised specific positions of a phospho-ERK peptide sequence through its active site, and the contact of STEP F311 with phospho-ERK V205 and T207 were crucial interactions. Taken together, our results not only provide the information for interactions between ERK and STEP, but will also help in the development of specific strategies to target STEP-ERK recognition, which could serve as a potential therapy for neurological disorders. Regulation of phospho-ERK by STEP underlies important neuronal activities. A detailed enzymologic characterisation and cellular studies of STEP revealed that specific residues in KIM and active site mediated ERK recognition. Structural differences between the KIM-ERK interfaces and the active site among different ERK phosphatases could be targeted to develop specific STEP inhibitor, which has therapeutic potential for neurological disorders. PKA, protein kinase A & NGF, nerve growth factor.
Protein tyrosine phosphatases: structure, function, and implication in human disease.
Tautz Lutz,Critton David A,Grotegut Stefan
Methods in molecular biology (Clifton, N.J.)
Protein tyrosine phosphorylation is a key regulatory mechanism in eukaryotic cell physiology. Aberrant expression or function of protein tyrosine kinases and protein tyrosine phosphatases can lead to serious human diseases, including cancer, diabetes, as well as cardiovascular, infectious, autoimmune, and neuropsychiatric disorders. Here, we give an overview of the protein tyrosine phosphatase superfamily with its over 100 members in humans. We review their structure, function, and implications in human diseases, and discuss their potential as novel drug targets, as well as current challenges and possible solutions to developing therapeutics based on these enzymes.
inhibits protein-tyrosine phosphatase 1B and protects pancreatic beta cell via its insulin mimetic effect.
Sharma Bhesh Raj,Kim Hyun Jung,Rhyu Dong Young
Food science and biotechnology
The aim of this study was to determine whether extract (CLE) can protect pancreatic beta cells and enhance insulin signaling in adipocytes. We measured the protein tyrosine phosphatase (PTP)-1B inhibitory effect of CLE using an in-vitro enzyme assay. Proteins involved in the pancreatic beta-cell death and insulin signaling were measured by western blotting. Oil-red O staining was used to measure the insulin mimetic effect of CLE. CLE strongly inhibited the PTP1B enzyme. In rat insulinoma (RIN)-m5F cells, CLE decreased the activation of extracellular regulated kinase (ERK)-1/2, P38 mitogen activated protein kinase (P38), c-Jun NH2-terminal kinase (JNK), and nuclear factor kappa-light-chain-enhancer of the activated B cells (NF-κB). Furthermore, CLE showed insulin-mimetic effect and enhanced the activation of insulin-signaling molecules including IRS, AKT, PI3K, and GSK-3β in 3T3-L1 adipocytes. Our results suggested that CLE-inhibited PTP1B, protected the pancreatic beta cells, and enhanced insulin sensitization in the adipocytes.
Regulation of platelet-activating factor-induced interleukin-8 expression by protein tyrosine phosphatase 1B.
Hamel-Côté Geneviève,Lapointe Fanny,Gendron Daniel,Rola-Pleszczynski Marek,Stankova Jana
Cell communication and signaling : CCS
BACKGROUND:Platelet-activating factor (PAF) is a potent lipid mediator whose involvement in the onset and progression of atherosclerosis is mediated by, among others, the modulation of cytokine expression patterns. The presence of multiple potential protein-tyrosine phosphatase (PTP) 1B substrates in PAF receptor signaling pathways brought us to investigate its involvement in PAF-induced cytokine expression in monocyte-derived dendritic cells (Mo-DCs) and to study the pathways involved in this modulation. METHODS:We used in-vitro-matured human dendritic cells and the HEK-293 cell line in our studies. PTP1B inhibition was though siRNAs and a selective inhibitor. Cytokine expression was studied with RT-PCR, luciferase assays and ELISA. Phosphorylation status of kinases and transcription factors was studied with western blotting. RESULTS:Here, we report that PTP1B was involved in the modulation of cytokine expression in PAF-stimulated Mo-DCs. A study of the down-regulation of PAF-induced IL-8 expression, by PTP1B, showed modulation of PAF-induced transactivation of the IL-8 promoter which was dependent on the presence of the C/EBPß -binding site. Results also suggested that PTP1B decreased PAF-induced IL-8 production by a glycogen synthase kinase (GSK)-3-dependent pathway via activation of the Src family kinases (SFK). These kinases activated an unidentified pathway at early stimulation times and the PI3K/Akt signaling pathway in a later phase. This change in GSK-3 activity decreased the C/EBPß phosphorylation levels of the threonine 235, a residue whose phosphorylation is known to increase C/EBPß transactivation potential, and consequently modified IL-8 expression. CONCLUSION:The negative regulation of GSK-3 activity by PTP1B and the consequent decrease in phosphorylation of the C/EBPß transactivation domain could be an important negative feedback loop by which cells control their cytokine production after PAF stimulation.
New and Unexpected Biological Functions for the Src-Homology 2 Domain-Containing Phosphatase SHP-2 in the Gastrointestinal Tract.
Coulombe Geneviève,Rivard Nathalie
Cellular and molecular gastroenterology and hepatology
SHP-2 is a tyrosine phosphatase expressed in most embryonic and adult tissues. SHP-2 regulates many cellular functions including growth, differentiation, migration, and survival. Genetic and biochemical evidence show that SHP-2 is required for rat sarcoma viral oncogene/extracellular signal-regulated kinases mitogen-activated protein kinase pathway activation by most tyrosine kinase receptors, as well as by G-protein-coupled and cytokine receptors. In addition, SHP-2 can regulate the Janus kinase/signal transducers and activators of transcription, nuclear factor-κB, phosphatidyl-inositol 3-kinase/Akt, RhoA, Hippo, and Wnt/β-catenin signaling pathways. Emerging evidence has shown that SHP-2 dysfunction represents a key factor in the pathogenesis of gastrointestinal diseases, in particular in chronic inflammation and cancer. Variations within the gene locus encoding SHP-2 have been associated with increased susceptibility to develop ulcerative colitis and gastric atrophy. Furthermore, mice with conditional deletion of SHP-2 in intestinal epithelial cells rapidly develop severe colitis. Similarly, hepatocyte-specific deletion of SHP-2 induces hepatic inflammation, resulting in regenerative hyperplasia and development of tumors in aged mice. However, the SHP-2 gene initially was suggested to be a proto-oncogene because activating mutations of this gene were found in pediatric leukemias and certain forms of liver and colon cancers. Moreover, SHP-2 expression is up-regulated in gastric and hepatocellular cancers. Notably, SHP-2 functions downstream of cytotoxin-associated antigen A (CagA), the major virulence factor of , and is associated with increased risks of gastric cancer. Further compounding this complexity, most recent findings suggest that SHP-2 also coordinates carbohydrate, lipid, and bile acid synthesis in the liver and pancreas. This review aims to summarize current knowledge and recent data regarding the biological functions of SHP-2 in the gastrointestinal tract.
Impaired caudal fin-fold regeneration in zebrafish deficient for the tumor suppressor Pten.
Hale Alexander James,Kiai Ali,Sikkens Jelte,den Hertog Jeroen
Regeneration (Oxford, England)
Zebrafish are able to completely regrow their caudal fin-folds after amputation. Following injury, wound healing occurs, followed by the formation of a blastema, which produces cells to replace the lost tissue in the final phase of regenerative outgrowth. Here we show that, surprisingly, the phosphatase and tumor suppressor Pten, an antagonist of phosphoinositide-3-kinase (PI3K) signaling, is required for zebrafish caudal fin-fold regeneration. We found that homozygous knock-out mutant ( ) zebrafish embryos, lacking functional Pten, did not regenerate their caudal fin-folds. AKT phosphorylation was enhanced, which is consistent with the function of Pten. Reexpression of Pten, but not catalytically inactive mutant Pten-C124S, rescued regeneration, as did pharmacological inhibition of PI3K. Blastema formation, determined by in situ hybridization for the blastema marker , appeared normal upon caudal fin-fold amputation of zebrafish embryos. Whole-mount immunohistochemistry using specific markers indicated that proliferation was arrested in embryos lacking functional Pten, and that apoptosis was enhanced. Together, these results suggest a critical role for Pten by limiting PI3K signaling during the regenerative outgrowth phase of zebrafish caudal fin-fold regeneration.
Therapeutic Targeting of Oncogenic Tyrosine Phosphatases.
Frankson Rochelle,Yu Zhi-Hong,Bai Yunpeng,Li Qinglin,Zhang Ruo-Yu,Zhang Zhong-Yin
Protein tyrosine phosphatases (PTP) are exciting and novel targets for cancer drug discovery that work in concert with protein tyrosine kinases (PTK) in controlling cellular homeostasis. Given the activating role that some PTKs play in initiating growth factor-mediated cellular processes, PTPs are usually perceived as the negative regulators of these events and therefore tumor suppressive in nature. However, mounting evidence indicate that PTPs do not always antagonize the activity of PTKs in regulating tyrosine phosphorylation, but can also play dominant roles in the initiation and progression of signaling cascades that regulate cell functions. It follows, therefore, that PTP malfunction can actively contribute to a host of human disorders, in particular, cancer, metabolic syndromes, and autoimmune diseases. The Src homology domain containing phosphatase 2 (SHP2) and the three-membered family of phosphatases of regenerating liver (PRL) are infamously oncogenic members of the PTP superfamily. Both are established regulators of major cancer pathways such as Ras/ERK1/2, Src, JAK/STAT, JNK, NF-κB, and PTEN/PI3K/AKT. Furthermore, upregulation, mutation, or other dysregulation of these PTPs has been positively correlated with cancer initiation and progression. This review will provide topical coverage of target validation and drug discovery efforts made in targeting these oncogenic PTPs as compelling candidates for cancer therapy. .
MEG2 is regulated by miR-181a-5p and functions as a tumour suppressor gene to suppress the proliferation and migration of gastric cancer cells.
Liu Zhijian,Sun Feng,Hong Yeting,Liu Yanqing,Fen Min,Yin Kai,Ge Xiaolong,Wang Feng,Chen Xi,Guan Wenxian
BACKGROUND:Protein-tyrosine phosphatase MEG2 (MEG2) is a classic tyrosine-specific protein tyrosine phosphatase (PTP). It has been reported that MEG2 participates in the carcinogenesis of the breast and liver. However, functions of MEG2 in gastric cancer remain poorly understood. METHODS:We examined the expression of MEG2 protein by western blotting and that of miR-181a-5p by qRT-PCR. We used bioinformatic analyses to search for miRNAs that potentially target MEG2. We performed a luciferase reporter assay to investigate the interaction between miR-181a-5p and MEG2. In addition, we assessed the effects of MEG2 and miR-181a-5p on gastric cancer cells in vitro and in vivo. RESULTS:We found that MEG2 is downregulated in human gastric cancer and that miR-181a-5p is predicted to be a potential regulator of MEG2. We also observed that expression of MEG2 is reversely correlated with that of miR-181a-5p in gastric cancer. Moreover, we observed that MEG2 regulation by miR-181a-5p significantly suppresses the proliferation and migration of gastric cancer cells in vitro and decelerates tumour growth in vivo. CONCLUSIONS:Our results revealed that MEG2 is a tumour suppressor gene and negatively regulated by miR-181a-5p in gastric cancer.
Ferulate, an Active Component of Wheat Germ, Ameliorates Oxidative Stress-Induced PTK/PTP Imbalance and PP2A Inactivation.
Koh Eun Mi,Lee Eun Kyeong,Song Chi Hun,Song Jeongah,Chung Hae Young,Chae Chang Hoon,Jung Kyung Jin
Ferulate is a phenolic compound abundant in wheat germ and bran and has been investigated for its beneficial activities. The aim of the present study is to evaluate the efficacy of ferulate against the oxidative stress-induced imbalance of protein tyrosine kinases (PTKs), protein tyrosine phosphatases (PTPs), and serine/threonine protein phosphatase 2A (PP2A), in connection with our previous finding that oxidative stress-induced imbalance of PTKs and PTPs is linked with proinflammatory nuclear factor-kappa B (NF-κB) activation. To test the effects of ferulate on this process, we utilized two oxidative stress-induced inflammatory models. First, YPEN-1 cells were pretreated with ferulate for 1 hr prior to the administration of 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (AAPH). Second, 20-month-old Sprague-Dawley rats were fed ferulate for 10 days. After ferulate treatment, the activities of PTKs, PTPs, and PP2A were measured because these proteins either directly or indirectly promote NF-κB activation. Our results revealed that in YPEN-1 cells, ferulate effectively suppressed AAPH-induced increases in reactive oxygen species (ROS) and NF-κB activity, as well as AAPH-induced PTK activation. Furthermore, ferulate also inhibited AAPH-induced PTP and PP2A inactivation. In the aged kidney model, ferulate suppressed aging-induced activation of PTKs and ameliorated aging-induced inactivation of PTPs and PP2A. Thus, herein we demonstrated that ferulate could modulate PTK/PTP balance against oxidative stress-induced inactivation of PTPs and PP2A, which is closely linked with NF-κB activation. Based on these results, the ability of ferulate to modulate oxidative stress-related inflammatory processes is established, which suggests that this compound could act as a novel therapeutic agent.
Dual-specificity phosphatase 18 modulates the SUMOylation and aggregation of Ataxin-1.
Ryu Joohyun,Lee Do Hee
Biochemical and biophysical research communications
We previously reported that SUMOylation promotes the aggregation of ataxin-1 and JNK is involved in the process. Here we show that dual-specificity phosphatase 18 (DUSP18), a member of protein tyrosine phosphatases, exerts the opposite effects on ataxin-1. DUSP18 associated with ataxin-1 and suppressed JNK activated by ataxin-1. Interestingly DUSP18, but not the other DUSPs interacting with ataxin-1, caused the mobility shift of ataxin-1. De-phosphorylation by DUSP18 was initially suspected as a cause for such an effect; however, the phosphorylation of ataxin-1 was unchanged. Instead DUSP18 inhibited SUMOylation and reduced ataxin-1 aggregation. The catalytic mutant of DUSP18 failed to reduce the SUMOylation and aggregation of ataxin-1 indicating that the phosphatase activity is indispensable for the effects. Moreover, DUSP18 disrupted the co-localization of ataxin-1 with the PML component Sp100. These results together implicate that JNK and DUSP18 reciprocally modulate the SUMOylation, which plays a regulatory role in the aggregation of ataxin-1.
Analysis of PTP1B sumoylation.
Saha Sayanti,Chernoff Jonathan
Methods (San Diego, Calif.)
Signaling enzymes are typically regulated by a variety of post-translational modifications. One such enzyme, protein tyrosine phosphatase (PTP) 1B, which plays an important role in metabolic and growth signaling, has recently been shown to be inhibited by posttranslational modifications by ubiquitin-related proteins of the SUMO family. We have adapted several approaches to analyzing the sites and effects of sumoylation of PTP1B in cells and in vitro. The principal outline of the assays should be applicable to other enzymes as well.
"PEST control": regulation of molecular barcodes by tyrosine phosphatases.
Doody Karen M,Bottini Nunzio
The emerging concept of "molecular barcodes" refers to the dynamic combination of post-translational modifications, often of different nature (e.g., phosphorylation and ubiquitination) that gives rise to multiple forms of a protein which can relay distinct signals throughout a cell. In a recent Cell Research paper by Wang et al., the authors report that a PEST domain-containing tyrosine phosphatase, PTPN18, is able to regulate both phosphorylation and ubiquitination of the HER2 oncogene, barcoding HER2 for increased proteasomal degradation rather than for intracellular trafficking.
Protein tyrosine phosphatases in cancer: friends and foes!
Labbé David P,Hardy Serge,Tremblay Michel L
Progress in molecular biology and translational science
Tyrosine phosphorylation of proteins serves as an exquisite switch in controlling several key oncogenic signaling pathways involved in cell proliferation, apoptosis, migration, and invasion. Since protein tyrosine phosphatases (PTPs) counteract protein kinases by removing phosphate moieties on target proteins, one may intuitively think that PTPs would act as tumor suppressors. Indeed, one of the most described PTPs, namely, the phosphatase and tensin homolog (PTEN), is a tumor suppressor. However, a growing body of evidence suggests that PTPs can also function as potent oncoproteins. In this chapter, we provide a broad historical overview of the PTPs, their mechanism of action, and posttranslational modifications. Then, we focus on the dual properties of classical PTPs (receptor and nonreceptor) and dual-specificity phosphatases in cancer and summarize the current knowledge of the signaling pathways regulated by key PTPs in human cancer. In conclusion, we present our perspective on the potential of these PTPs to serve as therapeutic targets in cancer.
Phosphotyrosine phosphatase R3 receptors: Origin, evolution and structural diversification.
Chicote Javier U,DeSalle Rob,García-España Antonio
Subtype R3 phosphotyrosine phosphatase receptors (R3 RPTPs) are single-spanning membrane proteins characterized by a unique modular composition of extracellular fibronectin repeats and a single cytoplasmatic protein tyrosine phosphatase (PTP) domain. Vertebrate R3 RPTPs consist of five members: PTPRB, PTPRJ, PTPRH and PTPRO, which dephosphorylate tyrosine residues, and PTPRQ, which dephosphorylates phophoinositides. R3 RPTPs are considered novel therapeutic targets in several pathologies such as ear diseases, nephrotic syndromes and cancer. R3 RPTP vertebrate receptors, as well as their known invertebrate counterparts from animal models: PTP52F, PTP10D and PTP4e from the fruitfly Drosophila melanogaster and F44G4.8/DEP-1 from the nematode Caenorhabditis elegans, participate in the regulation of cellular activities including cell growth and differentiation. Despite sharing structural and functional properties, the evolutionary relationships between vertebrate and invertebrate R3 RPTPs are not fully understood. Here we gathered R3 RPTPs from organisms covering a broad evolutionary distance, annotated their structure and analyzed their phylogenetic relationships. We show that R3 RPTPs (i) have probably originated in the common ancestor of animals (metazoans), (ii) are variants of a single ancestral gene in protostomes (arthropods, annelids and nematodes); (iii) a likely duplication of this ancestral gene in invertebrate deuterostomes (echinodermes, hemichordates and tunicates) generated the precursors of PTPRQ and PTPRB genes, and (iv) R3 RPTP groups are monophyletic in vertebrates and have specific conserved structural characteristics. These findings could have implications for the interpretation of past studies and provide a framework for future studies and functional analysis of this important family of proteins.
Cell signaling by protein tyrosine phosphorylation.
Fischer E H
Advances in enzyme regulation
The above data, and others not described herein, indicate the following: First, that phosphatases are not scavenger enzymes, simply there to remove the phosphate groups introduced by the kinases. They cannot be viewed simply as providing an 'off' switch in an 'on/off' kinase/phosphatase system. Kinases and phosphatases do not carry out one-way and opposing reactions. The same enzyme, depending on where it localizes within the cell, or the molecule with which it might interact, can serve either as a positive or negative determinant in defining cell behavior. In many instances, it can act synergistically with the kinases to enhance the phosphorylation reaction. Second, the factors that determine whether a phosphatase would enhance or oppose a kinase reaction would seem to depend less on its state of activity than on its subcellular localization. This would suggest that if one wanted to call upon it to control transformation, one should try to tamper with its localization segments or whatever binding proteins it might be attached to--rather than with its catalytic domains. Displacement of these enzymes from where they are meant to bind would seem a more promising approach than trying to modulate their catalytic activity. Finally, their architectural features are so basically different from those of the kinases, with receptor tyrosine phosphatases displaying all the structural characteristics of cell adhesion molecules, that they must also have a mission of their own in cell development, survival and death, quite apart from that of the kinases.
PTP1b Inhibition, A Promising Approach for the Treatment of Diabetes Type II.
Eleftheriou Phaedra,Geronikaki Athina,Petrou Anthi
Current topics in medicinal chemistry
BACKGROUND:Diabetes Mellitus (DM), is a metabolic disorder characterized by high blood glucose levels. The main types of diabetes mellitus are Diabetes mellitus type I, Diabetes mellitus type II, gestational diabetes and Diabetes of other etiology. Diabetes type II, the Non Insulin Dependent Type (NIDDM) is the most common type, characterized by the impairment in activation of the intracellular mechanism leading to the insertion and usage of glucose after interaction of insulin with its receptor, known as insulin resistance. Although, a number of drugs have been developed for the treatment of diabetes type II, their ability to reduce blood glucose levels is limited, while several side effects are also observed. Furthermore, none of the market drugs targets the enhancement of the action of the intracellular part of insulin receptor or recuperation of the glucose transport mechanism in GLUT4 dependent cells. The Protein Tyrosine Phosphatase (PTP1b) is the main enzyme involved in insulin receptor desensitization and has become a drug target for the treatment of Diabetes type II. Several PTP1b inhibitors have already been found, interacting with the binding site of the enzyme, surrounding the catalytic amino acid Cys215 and the neighboring area or with the allosteric site of the enzyme, placed at a distance of 20 Å from the active site, around Phe280. However, the research continues for finding more potent inhibitors with increased cell permeability and specificity. OBJECTIVE:The aim of this review is to show the attempts made in developing of Protein Tyrosine Phosphatase (PTP1b) inhibitors with high potency, selectivity and bioavailability and to sum up the indications for favorable structural characteristics of effective PTP1b inhibitors. METHODS:The methods used include a literature survey and the use of Protein Structure Databanks such as PuBMed Structure and RCSB and the tools they provide. CONCLUSION:The research for finding PTP1b inhibitors started with the design of molecules mimicking the Tyrosine substrate of the enzyme. The study revealed that an aromatic ring connected to a polar group, which preferably enables hydrogen bond formation, is the minimum requirement for small inhibitors binding to the active site surrounding Cys215. Molecules bearing two hydrogen bond donor/acceptor (Hb d/a) groups at a distance of 8.5-11.5 Å may form more stable complexes, interacting simultaneously with a secondary area A2. Longer molecules with two Hb d/a groups at a distance of 17 Å or 19 Å may enable additional interactions with secondary sites (B and C) that confer stability as well as specificity. An aromatic ring linked to polar or Hb d/a moieties is also required for allosteric inhibitors. A lower distance between Hb d/a moieties, around 7.5 Å may favor allosteric interaction. Permanent inhibition of the enzyme by oxidation of the catalytic Cys215 has also been referred. Moreover, covalent modification of Cys121, placed near but not inside the catalytic pocket has been associated with permanent inhibition of the enzyme.
Protein-tyrosine phosphatases: biological function, structural characteristics, and mechanism of catalysis.
Zhang Z Y
Critical reviews in biochemistry and molecular biology
The protein-tyrosine phosphatases (PTPases) superfamily consists of tyrosine-specific phosphatases, dual specificity phosphatases, and the low-molecular-weight phosphatases. They are modulators of signal transduction pathways that regulate numerous cell functions. Malfunction of PTPases have been linked to a number of oncogenic and metabolic disease states, and PTPases are also employed by microbes and viruses for pathogenicity. There is little sequence similarity among the three subfamilies of phosphatases. Yet, three-dimensional structural data show that they share similar conserved structural elements, namely, the phosphate-binding loop encompassing the PTPase signature motif (H/V)C(X)5R(S/T) and an essential general acid/base Asp residue on a surface loop. Biochemical experiments demonstrate that phosphatases in the PTPase superfamily utilize a common mechanism for catalysis going through a covalent thiophosphate intermediate that involves the nucleophilic Cys residue in the PTPase signature motif. The transition states for phosphoenzyme intermediate formation and hydrolysis are dissociative in nature and are similar to those of the solution phosphate monoester reactions. One strategy used by these phosphatases for transition state stabilization is to neutralize the developing negative charge in the leaving group. A conformational change that is restricted to the movement of a flexible loop occurs during the catalytic cycle of the PTPases. However, the relationship between loop dynamics and enzyme catalysis remains to be established. The nature and identity of the rate-limiting step in the PTPase catalyzed reaction requires further investigation and may be dependent on the specific experimental conditions such as temperature, pH, buffer, and substrate used. In-depth kinetic and structural analysis of a representative number of phosphatases from each group of the PTPase superfamily will most likely continue to yield insightful mechanistic information that may be applicable to the rest of the family members.
Structure and catalytic mechanism of human protein tyrosine phosphatome.
Kim Seung Jun,Ryu Seong Eon
Together with protein tyrosine kinases (PTKs), protein tyrosine phosphatases (PTPs) serve as hallmarks in cellular signal transduction by controlling the reversible phosphorylation of their substrates. The human genome is estimated to encode more than 100 PTPs, which can be divided into eleven sub-groups according to their structural and functional characteristics. All the crystal structures of catalytic domains of sub-groups have been elucidated, enabling us to understand their precise catalytic mechanism and to compare their structures across all sub-groups. In this review, I describe the structure and mechanism of catalytic domains of PTPs in the structural context.
Probing the phosphopeptide specificities of protein tyrosine phosphatases, SH2 and PTB domains with combinatorial library methods.
Vetter Stefan W,Zhang Zhong-Yin
Current protein & peptide science
Protein tyrosine phosphatases, SH2 and PTB domains are crucial elements for cellular signal transduction and regulation. Much effort has been directed towards elucidating their specificity in the past decade using a variety of approaches. Combinatorial library methods have contributed significantly to the understanding of substrate and ligand specificity of phosphoprotein recognizing domains. This review gives a brief overview of the structural characteristics of protein tyrosine phosphatases, SH2 and PTB domains and their binding to phosphopeptides. The chemical synthesis of peptides containing phosphotyrosine or phosphotyrosine mimics and the various formats of synthesis and deconvolution of combinatorial libraries are explained in detail. Examples are given as how different combinatorial libraries have been used to study the interaction of phosphopeptides with SH2 domains and phosphatases. The intrinsic advantages and difficulties of library synthesis, screening and deconvolution are pointed out. Finally, some experimental results on the substrate specificity of protein tyrosine phosphatase 1B and the SH2 domain of the adaptor protein Grb-2 are summarized and discussed.
Catalytic efficiency and some structural properties of cold-active protein-tyrosine-phosphatase.
Tsuruta Hiroki,Aizono Yasuo
Journal of biochemistry
A procedure was established for expression and purification of abundant recombinant cold-active protein-tyrosine-phosphatase (RCPTPase), which showed identical enzymatic characteristics to the native enzyme (NCPTPase). The purified RCPTPase showed high catalytic activity at low temperature and maximal activity at 30 degrees C. RCPTPase has a thermodynamic characteristic in that its activation enthalpy was determined to be low, 4.3 kcal/mol, at temperatures below 19.3 degrees C, where the Arrhenius relationship exhibited an inflection point, in comparison with 20.3 kcal/mol above 19.3 degrees C. Also, the thermostability, DeltaG(water), of the catalytic site in the RCPTPase molecule was increased with a decrease in temperature. It was considered that cold-active protein-tyrosine-phosphatase could maintain its catalytic site in a stable conformation for eliciting high catalytic activity with low activation enthalpy at low temperature.
Receptor-type protein tyrosine phosphatase κ directly dephosphorylates CD133 and regulates downstream AKT activation.
Shimozato O,Waraya M,Nakashima K,Souda H,Takiguchi N,Yamamoto H,Takenobu H,Uehara H,Ikeda E,Matsushita S,Kubo N,Nakagawara A,Ozaki T,Kamijo T
Although CD133 has been considered to be a molecular marker for cancer stem cells, its functional roles in tumorigenesis remain unclear. We here examined the molecular basis behind CD133-mediated signaling. Knockdown of CD133 resulted in the retardation of xenograft tumor growth of colon cancer-derived HT-29 and LoVo cells accompanied by hypophosphorylation of AKT, which diminished β-catenin/T-cell factor-mediated CD44 expression. As tyrosine residues of CD133 at positions 828 and 852 were phosphorylated in HT-29 and SW480 cells, we further addressed the significance of this phosphorylation in the tumorigenesis of SW480 cells expressing mutant CD133, with substitution of these tyrosine residues by glutamate (CD133-EE) or phenylalanine (CD133-FF). Forced expression of CD133-EE promoted much more aggressive xenograft tumor growth relative to wild-type CD133-expressing cells accompanied by hyperphosphorylation of AKT; however, CD133-FF expression had negligible effects on AKT phosphorylation and xenograft tumor formation. Intriguingly, the tyrosine phosphorylation status of CD133 was closely linked to the growth of SW480-derived spheroids. Using yeast two-hybrid screening, we finally identified receptor-type protein tyrosine phosphatase κ (PTPRK) as a binding partner of CD133. In vitro studies demonstrated that PTPRK associates with the carboxyl-terminal region of CD133 through its intracellular phosphatase domains and also catalyzes dephosphorylation of CD133 at tyrosine-828/tyrosine-852. Silencing of PTPRK elevated the tyrosine phosphorylation of CD133, whereas forced expression of PTPRK reduced its phosphorylation level markedly and abrogated CD133-mediated AKT phosphorylation. Endogenous CD133 expression was also closely associated with higher AKT phosphorylation in primary colon cancer cells, and ectopic expression of CD133 enhanced AKT phosphorylation. Furthermore, lower PTPRK expression significantly correlated with the poor prognosis of colon cancer patients with high expression of CD133. Thus, our present findings strongly indicate that the tyrosine phosphorylation of CD133, which is dephosphorylated by PTPRK, regulates AKT signaling and has a critical role in colon cancer progression.
Protein-tyrosine phosphatase H1 increases breast cancer sensitivity to antiestrogens by dephosphorylating estrogen receptor at Tyr537.
Suresh Padmanaban S,Ma Shao,Migliaccio Antimo,Chen Guan
Molecular cancer therapeutics
Estrogen receptor α (ERα or ER) is the only target of breast cancer therapy using antiestrogens. However, about 50% of ER-expressing breast cancer is intrinsically refractory to the antihormone therapy and strategies to improve the therapeutic response are urgently needed. Dynamic ER phosphorylation and dephosphorylation play an important role in ER activity and antihormone response. Although more than 10 kinases participate in phosphorylating ER protein, phosphatases involved remain mostly unidentified. Here, we tested the hypothesis that the protein-tyrosine phosphatase H1 (PTPH1) may regulate ER tyrosine phosphorylation and thereby impact breast cancer antihormone sensitivity. Our results showed that PTPH1 dephosphorylates ER at Tyr537 in vitro and in breast cancer cells. Moreover, PTPH1 stimulates ER nuclear accumulation and increases breast cancer sensitivity to tamoxifen (TAM) and/or fulvestrant in cell culture and in a xenograft model. Further analysis revealed that PTPH1 depends on its catalytic activity to stimulate ER nuclear accumulation and to enhance breast cancer antihormone sensitivity. These studies thus identified PTPH1 as a novel ER phosphatase and further demonstrate a therapeutic potential of enhancing breast cancer sensitivity to antiestrogens through dephosphorylating ER by PTPH1.
CD148 tyrosine phosphatase promotes cadherin cell adhesion.
Takahashi Keiko,Matafonov Anton,Sumarriva Katherine,Ito Hideyuki,Lauhan Colette,Zemel Dana,Tsuboi Nobuo,Chen Jin,Reynolds Albert,Takahashi Takamune
CD148 is a transmembrane tyrosine phosphatase that is expressed at cell junctions. Recent studies have shown that CD148 associates with the cadherin/catenin complex and p120 catenin (p120) may serve as a substrate. However, the role of CD148 in cadherin cell-cell adhesion remains unknown. Therefore, here we addressed this issue using a series of stable cells and cell-based assays. Wild-type (WT) and catalytically inactive (CS) CD148 were introduced to A431D (lacking classical cadherins), A431D/E-cadherin WT (expressing wild-type E-cadherin), and A431D/E-cadherin 764AAA (expressing p120-uncoupled E-cadherin mutant) cells. The effects of CD148 in cadherin adhesion were assessed by Ca2+ switch and cell aggregation assays. Phosphorylation of E-cadherin/catenin complex and Rho family GTPase activities were also examined. Although CD148 introduction did not alter the expression levels and complex formation of E-cadherin, p120, and β-catenin, CD148 WT, but not CS, promoted cadherin contacts and strengthened cell-cell adhesion in A431D/E-cadherin WT cells. This effect was accompanied by an increase in Rac1, but not RhoA and Cdc42, activity and largely diminished by Rac1 inhibition. Further, we demonstrate that CD148 reduces the tyrosine phosphorylation of p120 and β-catenin; causes the dephosphorylation of Y529 suppressive tyrosine residue in Src, a well-known CD148 site, increasing Src activity and enhancing the phosphorylation of Y228 (a Src kinase site) in p120, in E-cadherin contacts. Consistent with these findings, CD148 dephosphorylated both p120 and β-catenin in vitro. The shRNA-mediated CD148 knockdown in A431 cells showed opposite effects. CD148 showed no effects in A431D and A431D/E-cadherin 764AAA cells. In aggregate, these findings provide the first evidence that CD148 promotes E-cadherin adhesion by regulating Rac1 activity concomitant with modulation of p120, β-catenin, and Src tyrosine phosphorylation. This effect requires E-cadherin and p120 association.
β1,6 GlcNAc branches-modified protein tyrosine phosphatase alpha enhances its stability and promotes focal adhesion formation in MCF-7 cells.
Xiao Jin,Gao Yan,Yang Fuming,Wang Can,Xu Yaolin,Chang Ruiqi,Zha Xiliang,Wang Liying
Biochemical and biophysical research communications
Receptor-like protein tyrosine phosphatase alpha (RPTPα or PTPα), a type I transmembrane glycoprotein with complex N-glycans, executes multifunction roles on cell behaviors. However, its effect on tumorigenesis and metastasis remains controversial. In this study, PTPα is identified as a novel substrate of N-Acetylglucosaminyltransferase V (GnT-V). Immunofluorescence results showed that addition of β1,6 GlcNAc branches on PTPα enhanced PTPα's cytomembrane assemble in GnT-V-MCF-7 compared with Mock-MCF-7 (MCF7 cells transfected with the vector pcDNA3). Then we found the alleviating degradation of PTPα was observed in GnT-V-MCF-7 while PTPα in Mock-MCF-7 was prone to quick degradation. Increased cell-surface retention subsequently enhanced PTPα's catalytic activity on the dephosphorylation of Src kinase at Tyr529 and promoted focal adhesion formation and mature. Therefore, our findings could provide an insight into the molecular mechanism of how GnT-V promoted cell migration, suggesting that PTPα could be one of factors regulating promote migration of breast cancer cell.
Protein tyrosine phosphatase UBASH3B is overexpressed in triple-negative breast cancer and promotes invasion and metastasis.
Lee Shuet Theng,Feng Min,Wei Yong,Li Zhimei,Qiao Yuanyuan,Guan Peiyong,Jiang Xia,Wong Chew Hooi,Huynh Kelly,Wang Jinhua,Li Juntao,Karuturi K Murthy,Tan Ern Yu,Hoon Dave S B,Kang Yibin,Yu Qiang
Proceedings of the National Academy of Sciences of the United States of America
Efforts to improve the clinical outcome of highly aggressive triple-negative breast cancer (TNBC) have been hindered by the lack of effective targeted therapies. Thus, it is important to identify the specific gene targets/pathways driving the invasive phenotype to develop more effective therapeutics. Here we show that ubiquitin-associated and SH3 domain-containing B (UBASH3B), a protein tyrosine phosphatase, is overexpressed in TNBC, where it supports malignant growth, invasion, and metastasis largely through modulating epidermal growth factor receptor (EGFR). We also show that UBASH3B is a functional target of anti-invasive microRNA200a (miR200a) that is down-regulated in TNBC. Importantly, the oncogenic potential of UBASH3B is dependent on its tyrosine phosphatase activity, which targets CBL ubiquitin ligase for dephosphorylation and inactivation, leading to EGFR up-regulation. Thus, UBASH3B may function as a crucial node in bridging multiple invasion-promoting pathways, thereby providing a potential therapeutic target for TNBC.
Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities.
Hendriks Wiljan J A J,Pulido Rafael
Biochimica et biophysica acta
Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.
Redundant Regulation of Cdk1 Tyrosine Dephosphorylation in Saccharomyces cerevisiae.
Kennedy Erin K,Dysart Michael,Lianga Noel,Williams Elizabeth C,Pilon Sophie,Doré Carole,Deneault Jean-Sebastien,Rudner Adam D
Cdk1 activity drives both mitotic entry and the metaphase-to-anaphase transition in all eukaryotes. The kinase Wee1 and the phosphatase Cdc25 regulate the mitotic activity of Cdk1 by the reversible phosphorylation of a conserved tyrosine residue. Mutation of cdc25 in Schizosaccharomyces pombe blocks Cdk1 dephosphorylation and causes cell cycle arrest. In contrast, deletion of MIH1, the cdc25 homolog in Saccharomyces cerevisiae, is viable. Although Cdk1-Y19 phosphorylation is elevated during mitosis in mih1∆ cells, Cdk1 is dephosphorylated as cells progress into G1, suggesting that additional phosphatases regulate Cdk1 dephosphorylation. Here we show that the phosphatase Ptp1 also regulates Cdk1 dephosphorylation in vivo and can directly dephosphorylate Cdk1 in vitro. Using a novel in vivo phosphatase assay, we also show that PP2A bound to Rts1, the budding yeast B56-regulatory subunit, regulates dephosphorylation of Cdk1 independently of a function regulating Swe1, Mih1, or Ptp1, suggesting that PP2A(Rts1) either directly dephosphorylates Cdk1-Y19 or regulates an unidentified phosphatase.
Protein-tyrosine Phosphatase and Kinase Specificity in Regulation of SRC and Breast Tumor Kinase.
Fan Gaofeng,Aleem Saadat,Yang Ming,Miller W Todd,Tonks Nicholas K
The Journal of biological chemistry
Despite significant evidence to the contrary, the view that phosphatases are "nonspecific" still pervades the field. Systems biology approaches to defining how signal transduction pathways are integrated at the level of whole organisms also often downplay the contribution of phosphatases, defining them as "erasers" that serve merely to restore the system to its basal state. Here, we present a study that counteracts the idea of "nonspecific phosphatases." We have characterized two structurally similar and functionally related kinases, BRK and SRC, which are regulated by combinations of activating autophosphorylation and inhibitory C-terminal sites of tyrosine phosphorylation. We demonstrated specificity at the level of the kinases in that SRMS phosphorylated the C terminus of BRK, but not SRC; in contrast, CSK is the kinase responsible for C-terminal phosphorylation of SRC, but not BRK. For the phosphatases, we observed that RNAi-mediated suppression of PTP1B resulted in opposing effects on the activity of BRK and SRC and have defined the mechanisms underlying this specificity. PTP1B inhibited BRK by directly dephosphorylating the Tyr-342 autophosphorylation site. In contrast, PTP1B potentiated SRC activity, but not by dephosphorylating SRC itself directly; instead, PTP1B regulated the interaction between CBP/PAG and CSK. SRC associated with, and phosphorylated, the transmembrane protein CBP/PAG at Tyr-317, resulting in CSK recruitment. We identified PAG as a substrate of PTP1B, and dephosphorylation abolished recruitment of the inhibitory kinase CSK. Overall, these findings illustrate how the combinatorial effects of PTKs and PTPs may be integrated to regulate signaling, with both classes of enzymes displaying exquisite specificity.
Effects of protein tyrosine phosphatase-PEST are reversed by Akt in T cells.
Arimura Yutaka,Shimizu Kazuhiko,Koyanagi Madoka,Yagi Junji
T cell activation is regulated by a balance between phosphorylation and dephosphorylation that is under the control of kinases and phosphatases. Here, we examined the role of a non-receptor-type protein tyrosine phosphatase, PTP-PEST, using retrovirus-mediated gene transduction into murine T cells. Based on observations of vector markers (GFP or Thy1.1), exogenous PTP-PEST-positive CD4(+) T cells appeared within 2 days after gene transduction; the percentage of PTP-PEST-positive cells tended to decrease during a resting period in the presence of IL-2 over the next 2 days. These vector markers also showed much lower expression intensities, compared with control cells, suggesting a correlation between the percent reduction and the low marker expression intensity. A catalytically inactive PTP-PEST mutant also showed the same tendency, and stepwise deletion mutants gradually lost their ability to induce the above phenomenon. On the other hand, these PTP-PEST-transduced cells did not have an apoptotic phenotype. No difference in the total cell numbers was found in the wells of a culture plate containing VEC- and PTP-PEST-transduced T cells. Moreover, serine/threonine kinase Akt, but not the anti-apoptotic molecules Bcl-2 and Bcl-XL, reversed the phenotype induced by PTP-PEST. We discuss the novel mechanism by which Akt interferes with PTP-PEST.
PTPs emerge as PIPs: protein tyrosine phosphatases with lipid-phosphatase activities in human disease.
Pulido Rafael,Stoker Andrew W,Hendriks Wiljan J A J
Human molecular genetics
Protein tyrosine phosphatases (PTPs) constitute a family of key homeostatic regulators, with wide implications on physiology and disease. Recent findings have unveiled that the biological activity of PTPs goes beyond the dephosphorylation of phospho-proteins to shut down protein tyrosine kinase-driven signaling cascades. Substrates dephosphorylated by clinically relevant PTPs extend to phospholipids and phosphorylated carbohydrates as well. In addition, non-catalytic functions are also used by PTPs to regulate essential cellular functions. Consequently, PTPs have emerged as novel potential therapeutic targets for human diseases, including cancer predispositions, myopathies and neuropathies. In this review, we highlight recent advances on the multifaceted role of lipid-phosphatase PTPs in human pathology, with an emphasis on hereditary diseases. The involved PTP regulatory networks and PTP modulatory strategies with potential therapeutic application are discussed.
Protein tyrosine phosphatase receptor type γ is a JAK phosphatase and negatively regulates leukocyte integrin activation.
Mirenda Michela,Toffali Lara,Montresor Alessio,Scardoni Giovanni,Sorio Claudio,Laudanna Carlo
Journal of immunology (Baltimore, Md. : 1950)
Regulation of signal transduction networks depends on protein kinase and phosphatase activities. Protein tyrosine kinases of the JAK family have been shown to regulate integrin affinity modulation by chemokines and mediated homing to secondary lymphoid organs of human T lymphocytes. However, the role of protein tyrosine phosphatases in leukocyte recruitment is still elusive. In this study, we address this issue by focusing on protein tyrosine phosphatase receptor type γ (PTPRG), a tyrosine phosphatase highly expressed in human primary monocytes. We developed a novel methodology to study the signaling role of receptor type tyrosine phosphatases and found that activated PTPRG blocks chemoattractant-induced β2 integrin activation. Specifically, triggering of LFA-1 to high-affinity state is prevented by PTPRG activation. High-throughput phosphoproteomics and computational analyses show that PTPRG activation affects the phosphorylation state of at least 31 signaling proteins. Deeper examination shows that JAKs are critically involved in integrin-mediated monocyte adhesion and that PTPRG activation leads to JAK2 dephosphorylation on the critical 1007-1008 phosphotyrosine residues, implying JAK2 inhibition and thus explaining the antiadhesive role of PTPRG. Overall, the data validate a new approach to study receptor tyrosine phosphatases and show that, by targeting JAKs, PTPRG downmodulates the rapid activation of integrin affinity in human monocytes, thus emerging as a potential novel critical regulator of leukocyte trafficking.
A Human Tyrosine Phosphatase Interactome Mapped by Proteomic Profiling.
Kumar Parveen,Munnangi Prathyusha,Chowdary Kvs Rammohan,Shah Varun J,Shinde Swapnil R,Kolli Nanci R,Halehalli Rachita R,Nagarajaram Hampapathalu A,Maddika Subbareddy
Journal of proteome research
Tyrosine phosphatases play a critical role in many cellular processes and pathogenesis, yet comprehensive analysis of their functional interacting proteins in the cell is limited. By utilizing a proteomic approach, here we present an interaction network of 81 human tyrosine phosphatases built on 1884 high-confidence interactions of which 85% are unreported. Our analysis has linked several phosphatases with new cellular processes and unveiled protein interactions genetically linked to various human diseases including cancer. We validated the functional importance of an identified interaction network by characterizing a distinct novel interaction between PTPN5 and Mob1a. PTPN5 dephosphorylates Mob1a at Y26 residue. Further, we identify that PTPN5 is required for proper midbody abscission during cytokinesis through regulation of Mob1a dephosphorylation. In conclusion, our study provides a valuable resource of tyrosine phosphatase interactions, which can be further utilized to dissect novel cellular functions of these enzymes.
Protein Tyrosine Phosphatases as Potential Regulators of STAT3 Signaling.
Kim Mihwa,Morales Liza D,Jang Ik-Soon,Cho Yong-Yeon,Kim Dae Joon
International journal of molecular sciences
The signal transducer and activator of transcription 3 (STAT3) protein is a major transcription factor involved in many cellular processes, such as cell growth and proliferation, differentiation, migration, and cell death or cell apoptosis. It is activated in response to a variety of extracellular stimuli including cytokines and growth factors. The aberrant activation of STAT3 contributes to several human diseases, particularly cancer. Consequently, STAT3-mediated signaling continues to be extensively studied in order to identify potential targets for the development of new and more effective clinical therapeutics. STAT3 activation can be regulated, either positively or negatively, by different posttranslational mechanisms including serine or tyrosine phosphorylation/dephosphorylation, acetylation, or demethylation. One of the major mechanisms that negatively regulates STAT3 activation is dephosphorylation of the tyrosine residue essential for its activation by protein tyrosine phosphatases (PTPs). There are seven PTPs that have been shown to dephosphorylate STAT3 and, thereby, regulate STAT3 signaling: PTP receptor-type D (PTPRD), PTP receptor-type T (PTPRT), PTP receptor-type K (PTPRK), Src homology region 2 (SH-2) domain-containing phosphatase 1(SHP1), SH-2 domain-containing phosphatase 2 (SHP2), MEG2/PTP non-receptor type 9 (PTPN9), and T-cell PTP (TC-PTP)/PTP non-receptor type 2 (PTPN2). These regulators have great potential as targets for the development of more effective therapies against human disease, including cancer.
Stepping out of the shadows: Oncogenic and tumor-promoting protein tyrosine phosphatases.
The international journal of biochemistry & cell biology
Protein tyrosine phosphorylation is critical for proper function of cells and organisms. Phosphorylation is regulated by the concerted but generically opposing activities of tyrosine kinases (PTKs) and tyrosine phosphatases (PTPs), which ensure its proper regulation, reversibility, and ability to respond to changing physiological situations. Historically, PTKs have been associated mainly with oncogenic and pro-tumorigenic activities, leading to the generalization that protein dephosphorylation is anti-oncogenic and hence that PTPs are tumor-suppressors. In many cases PTPs do suppress tumorigenesis. However, a growing body of evidence indicates that PTPs act as dominant oncogenes and drive cell transformation in a number of contexts, while in others PTPs support transformation that is driven by other oncogenes. This review summarizes the known transforming and tumor-promoting activities of the classical, tyrosine specific PTPs and highlights their potential as drug targets for cancer therapy.
The Extended Family of Protein Tyrosine Phosphatases.
Alonso Andrés,Nunes-Xavier Caroline E,Bayón Yolanda,Pulido Rafael
Methods in molecular biology (Clifton, N.J.)
In higher eukaryotes, the Tyr phosphorylation status of cellular proteins results from the coordinated action of Protein Tyrosine Kinases (PTKs) and Protein Tyrosine Phosphatases (PTPs). PTPs have emerged as highly regulated enzymes with diverse substrate specificity, and proteins with Tyr-dephosphorylation or Tyr-dephosphorylation-like properties can be clustered as the PTPome. This includes proteins from the PTP superfamily, which display a Cys-based catalytic mechanism, as well as enzymes from other gene families (Asp-based phosphatases, His-based phosphatases) that have converged in protein Tyr-dephosphorylation-related functions by using non-Cys-based catalytic mechanisms. Within the Cys-based members of the PTPome, classical PTPs dephosphorylate specific phosphoTyr (pTyr) residues from protein substrates, whereas VH1-like dual-specificity PTPs dephosphorylate pTyr, pSer, and pThr residues, as well as nonproteinaceous substrates, including phosphoinositides and phosphorylated carbohydrates. In addition, several PTPs have impaired catalytic activity as a result of amino acid substitutions at their active sites, but retain regulatory functions related with pTyr signaling. As a result of their relevant biological activity, many PTPs are linked to human disease, including cancer, neurodevelopmental, and metabolic diseases, making these proteins important drug targets and molecular markers in the clinic. Here, a brief overview on the biochemistry and physiology of the different groups of proteins that belong to the mammalian PTPome is presented.