Cytoplasmic Tyrosine Phosphatase Research Articles

Cancer-associated point mutations within the extracellular domain of PTPRD affect protein stability and HSPG interaction.

PTPRD, a well-established tumor suppressor gene, encodes the protein tyrosine phosphatase-type D. This protein consists of three immunoglobulin-like (Ig) domains, four to eight fibronectin type 3 (FN) domains, a single transmembrane segment, and two cytoplasmic tandem tyrosine phosphatase domains. PTPRD is known to harbor various cancer-associated point mutations. While it is assumed that PTPRD regulates cellular functions as a tumor suppressor through the tyrosine phosphatase activity in the intracellular region, the function of its extracellular domain (ECD) in cancer is not well understood. In this study, we systematically examined the impact of 92 cancer-associated point mutations within the ECD. We found that 69.6% (64 out of 92) of these mutations suppressed total protein expression and/or plasma membrane localization. Notably, almost all mutations (20 out of 21) within the region between the last FN domain and transmembrane segment affected protein expression and/or localization, highlighting the importance of this region for protein stability. We further found that some mutations within the Ig domains adjacent to the glycosaminoglycan-binding pocket enhanced PTPRD's binding ability to heparan sulfate proteoglycans (HSPGs). This interaction is proposed to suppress phosphatase activity. Our findings therefore suggest that HSPG-mediated attenuation of phosphatase activity may be involved in tumorigenic processes through PTPRD dysregulation.

Mechanisms of action for different checkpoint inhibitors.

Mechanisms of action for different checkpoint inhibitors.

Abstract 2808: Simultaneous inhibition of SHP2 phosphatase at two allosteric sites

Abstract SHP2 is a cytoplasmic non-receptor tyrosine phosphatase involved in the propagation of extracellular signaling through receptor tyrosine kinases. Aberrant SHP2 activity has been identified as a driver in multiple cancers and SHP2 has also been implicated in the PD-1/PD-L1-mediated exhaustion of effector T-cells, leading to immune system evasion of tumors. Recently, we reported the identification of SHP099, an allosteric inhibitor of SHP2 with in in vivo efficacy against multiple RTK-driven tumor xenograft models. Here we report the use of alternate screening paradigms to identify a novel allosteric inhibitor which binds to a previously uncharacterized pocket on SHP2. Like SHP099, the second allosteric inhibitor stabilizes a closed conformation of SHP2, which blocks access to the phosphatase active site. Structure based drug design led to improvements in potency, and combination studies in biochemical, biophysical and cellular assays confirm dual occupation of SHP099 and the second allosteric molecule, resulting in improved potency. This work highlights a rare opportunity for dual occupation of inhibitors for a single target and provides additional tools for the exploration of SHP2 biology. Citation Format: Michelle Fodor, Edmund Price, Ping Wang, Hengyu Lu, Andreea Argintaru, Zhouliang Chen, Meir Glick, Huai-Xiang Hao, Mitsunori Kato, Robert Koenig, Jonathan R. LaRochelle, Gang Liu, Eric McNeill, Dyuti Majumdar, Gisele Nishiguchi, Lawrence Perez, Greg Paris, Christopher Quinn, Timothy Ramsey, Martin Sendzik, Michael Shultz, Sarah Williams, Travis Stams, Stephen C. Blacklow, Matthew J. LaMarche, Michael G. Acker. Simultaneous inhibition of SHP2 phosphatase at two allosteric sites [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2808.

Shp2 deletion in hepatocytes suppresses hepatocarcinogenesis driven by oncogenic β-Catenin, PIK3CA and MET

Shp2 is an SH2-tyrosine phosphatase acting downstream of receptor tyrosine kinases (RTKs). Most recent data demonstrated a liver tumor-suppressing role for Shp2, as ablating Shp2 in hepatocytes aggravated hepatocellular carcinoma (HCC) induced by chemical carcinogens or Pten loss. We further investigated the effect of Shp2 deficiency on liver tumorigenesis driven by classical oncoproteins c-Met (receptor for HGF), β-catenin and PIK3CA. We performed hydrodynamic tail vein injection of two pairs of plasmids expressing c-Met and ΔN90-β-catenin (MET/CAT), or c-Met and PIK3CAH1047R (MET/PIK), into WT and Shp2hep-/- mice. We compared liver tumor loads and investigated the pathogenesis and molecular mechanisms involved using multidisciplinary approaches. Despite the induction of oxidative and metabolic stresses, Shp2 deletion in hepatocytes suppressed hepatocarcinogenesis driven by overexpression of oncoproteins MET/CAT or MET/PIK. Shp2 loss inhibited proliferative signaling from c-Met, Wnt/β-catenin, Ras/Erk and PI3K/Akt pathways, but triggered cell senescence following exogenous expression of the oncogenes. Shp2, acting downstream of RTKs, is positively required for hepatocyte-intrinsic tumorigenic signaling from these oncoproteins, even if Shp2 deficiency induces a tumor-promoting hepatic microenvironment. These data suggest a new and more effective therapeutic strategy for HCCs driven by oncogenic RTKs and other upstream molecules, by inhibiting Shp2 and also suppressing any tumor-enhancing stromal factors produced because of Shp2 inhibition. Primary liver cancer is a malignant disease with poor prognosis, largely because there are limited systemic therapies available. We show here that a cytoplasmic tyrosine phosphatase Shp2 is required for liver tumorigenesis. This tumorigenesis is driven by two oncoproteins that are implicated in human liver cancer. This, together with our previous studies, uncovers the complexity of liver tumorigenesis, by elucidating the pro- and anti-tumor effects of Shp2 in mouse models. This data can be used to guide new therapies.

Functional variation of SHP-2 promoter is associated with preterm birth and delayed myelination and motor development in preterm infants

Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP-2) is a cytoplasmic tyrosine phosphatase that is highly expressed in hematopoietic cells and in the CNS and exerts opposite effects on signal transduction by exerting a neuroprotective or proapoptotic effect. Several mutations of SHP-2 have been found in children with myeloproliferative disorders or malignant leukemia, and some of these can affect brain development. In the present study, we aimed to identify and functionally characterize genetic variations in SHP-2 in 72 preterm and 58 full-term infants and to evaluate the effect of the variations on neurodevelopment in preterm infants. Twelve genetic variations were identified. Among them, two variations in the SHP-2 promoter, g.-317C > T and g.-273G > A, were found to significantly increase promoter activity, and the frequency of g.-273G > A was higher in preterm infants than in full-term infants. Two transcription factors, NF-κB and GABPα, were found to be involved in the transcriptional regulation of SHP-2 by the two above-mentioned variations. In particular, we found that g.-273G > A was significantly associated with delayed myelination and poor motor development in preterm infants. Our results suggest that a functional promoter variation in SHP-2 is associated with spontaneous preterm birth itself as well as white matter myelination and neurodevelopment.

Shp1 function in myeloid cells.

The motheaten mouse was first described in 1975 as a model of systemic inflammation and autoimmunity, as a result of immune system dysregulation. The phenotype was later ascribed to mutations in the cytoplasmic tyrosine phosphatase Shp1. This phosphatase is expressed widely throughout the hematopoietic system and has been shown to impact a multitude of cell signaling pathways. The determination of which cell types contribute to the different aspects of the phenotype caused by global Shp1 loss or mutation and which pathways within these cell types are regulated by Shp1 is important to further our understanding of immune system regulation. In this review, we focus on the role of Shp1 in myeloid cells and how its dysregulation affects immune function, which can impact human disease.

Cd47-Sirpα interaction and IL-10 constrain inflammation-induced macrophage phagocytosis of healthy self-cells

Rapid clearance of adoptively transferred Cd47-null (Cd47(-/-)) cells in congeneic WT mice suggests a critical self-recognition mechanism, in which CD47 is the ubiquitous marker of self, and its interaction with macrophage signal regulatory protein α (SIRPα) triggers inhibitory signaling through SIRPα cytoplasmic immunoreceptor tyrosine-based inhibition motifs and tyrosine phosphatase SHP-1/2. However, instead of displaying self-destruction phenotypes, Cd47(-/-) mice manifest no, or only mild, macrophage phagocytosis toward self-cells except under the nonobese diabetic background. Studying our recently established Sirpα-KO (Sirpα(-/-)) mice, as well as Cd47(-/-) mice, we reveal additional activation and inhibitory mechanisms besides the CD47-SIRPα axis dominantly controlling macrophage behavior. Sirpα(-/-) mice and Cd47(-/-) mice, although being normally healthy, develop severe anemia and splenomegaly under chronic colitis, peritonitis, cytokine treatments, and CFA-/LPS-induced inflammation, owing to splenic macrophages phagocytizing self-red blood cells. Ex vivo phagocytosis assays confirmed general inactivity of macrophages from Sirpα(-/-) or Cd47(-/-) mice toward healthy self-cells, whereas they aggressively attack toward bacteria, zymosan, apoptotic, and immune complex-bound cells; however, treating these macrophages with IL-17, LPS, IL-6, IL-1β, and TNFα, but not IFNγ, dramatically initiates potent phagocytosis toward self-cells, for which only the Cd47-Sirpα interaction restrains. Even for macrophages from WT mice, phagocytosis toward Cd47(-/-) cells does not occur without phagocytic activation. Mechanistic studies suggest a PKC-Syk-mediated signaling pathway, to which IL-10 conversely inhibits, is required for activating macrophage self-targeting, followed by phagocytosis independent of calreticulin Moreover, we identified spleen red pulp to be one specific tissue that provides stimuli constantly activating macrophage phagocytosis albeit lacking in Cd47(-/-) or Sirpα(-/-) mice.

Controlling macrophage phagocytosis towards healthy self cells: Two layers of activating and inhibitory mechanisms

Abstract Rapid clearance of adoptively transferred CD47-null cells in mice suggests a critical self-recognition mechanism, in which CD47 is the ubiquitous marker of ‘self’, and its interaction with macrophage SIRPα triggers inhibitory signaling through SIRPα cytoplasmic ITIMs and tyrosine phosphatase SHP-1/2. However, instead of displaying self-destruction phenotype, the mice deficient of CD47 manifest no enhanced macrophage phagocytosis towards self, a phenomenon suggesting that additional mechanisms besides CD47-SIRPα command macrophage behavior. Studying our recently established SIRPα-knockout (SIRPα−/−) mice, as well as CD47−/− mice, we reveal that macrophage phagocytosis toward self is not only inhibited by CD47-SIRPα signaling but also requires an activation mechanism induced by unique inflammatory stimuli. SIRPα−/− mice and CD47−/− mice, though being healthy under normal condition, develop severe anemia and splenomegaly owing to splenic macrophages aggressively phagocytizing self RBC under chronic colitis, peritonitis, inflammatory cytokine treatments, or CFA and LPS-induced inflammation. Ex vivo phagocytosis assays demonstrate that macrophages from SIRPα−/− or CD47−/− mice, and even peritoneal macrophages from WT mice, are generally incompetent to attack self cells albeit their aggressiveness towards bacteria, fungi, apoptotic cells and immune complexes. However, treating all macrophages with IL-17, LPS, IL-6, IL-1β and TNFα, but not IFNg, dramatically initiates potent phagocytosis towards self cells providing an absence of the SIRPα-CD47 restraint. In addition, we identify that WT spleen red pulp is one specific environment that stimulates macrophage phagocytosis and that is lacking in deficient mice.

Abstract 3697: Development of a focused non-hydrolyzable phosphopeptide library based on a high affinity SHP2 substrate

Abstract The Src homology-2 domain containing protein tyrosine phosphatase-2 (SHP2), a widely expressed cytoplasmic tyrosine phosphatase with two src-homology 2 (SH2) domains, has received much attention in the signal transduction field. SHP2 is a transducer of growth factor, cytokine, integrin, and hormone signaling pathways that regulate processes such as cell proliferation, differentiation, adhesion, migration, and apoptosis and plays a pivotal role in growth factor and cytokine signaling. Gain-of-function SHP2 mutations are associated with several types of leukemias, and solid tumors; this makes SHP2 is an attractive target for cancer therapy Several small molecules have been developed for inhibition of this important phosphatase, which serve as chemical tools to probe the role of SHP2 in disease and lead compounds for optimization. Nevertheless it is challenging to improve these lead compounds with better potency, selectivity and cell permeability. To gain structural insights for development of potent and selective SHP2 inhibitors, we synthesized a non-hydrolyzable phosphotyrosine peptide mimetic based on reported SHP2 substrate peptide sequence (10-mer). The non-hydrolyzable phosphopeptide, containing the phosphotyrosyl surrogate difluoromethylphosphonate, was synthesized using solid phase peptide synthesis methods from the known building block N-FMOCF2Pmp and we improved the coupling reaction conditions to generate a peptide library of difluoromethylphosphonate to understand the SHP2 affinity. We will present the synthesis of the peptide library, analysis of SHP2 phosphatase inhibition, and the binding mode (X-ray crystal structure) of the phosphopeptide mimic to SHP2. Citation Format: Harshani R. Lawrence, Yunting Luo, Steven Gunawan, Andreas Becker, Yuan Ren, Ernst Schonbrunn, Jie Wu, Nicholas J. Lawrence. Development of a focused non-hydrolyzable phosphopeptide library based on a high affinity SHP2 substrate. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3697. doi:10.1158/1538-7445.AM2015-3697

Cytoplasmic Tyrosine Phosphatase Shp2 Coordinates Hepatic Regulation of Bile Acid and FGF15/19 Signaling to Repress Bile Acid Synthesis

Bile acid (BA) biosynthesis is tightly controlled by intrahepatic negative feedback signaling elicited by BA binding to farnesoid X receptor (FXR) and also by enterohepatic communication involving ileal BA reabsorption and FGF15/19 secretion. However, how these pathways are coordinated is poorly understood. We show here that nonreceptor tyrosine phosphatase Shp2 is a critical player that couples and regulates the intrahepatic and enterohepatic signals for repression of BA synthesis. Ablating Shp2 in hepatocytes suppressed signal relay from FGFR4, receptor for FGF15/19, and attenuated BA activation of FXR signaling, resulting in elevation of systemic BA levels and chronic hepatobiliary disorders in mice. Acting immediately downstream of FGFR4, Shp2 associates with FRS2α and promotes the receptor activation and signal relay to several pathways. These results elucidate a molecular mechanism for the control of BA homeostasis by Shp2 through the orchestration of multiple signals in hepatocytes.

Kit-Shp2-Kit signaling acts to maintain a functional hematopoietic stem and progenitor cell pool

AbstractThe stem cell factor (SCF)/Kit system has served as a classic model in deciphering molecular signaling events in the hematopoietic compartment, and Kit expression is a most critical marker for hematopoietic stem cells (HSCs) and progenitors. However, it remains to be elucidated how Kit expression is regulated in HSCs. Herein we report that a cytoplasmic tyrosine phosphatase Shp2, acting downstream of Kit and other RTKs, promotes Kit gene expression, constituting a Kit-Shp2-Kit signaling axis. Inducible ablation of PTPN11/Shp2 resulted in severe cytopenia in BM, spleen, and peripheral blood in mice. Shp2 removal suppressed the functional pool of HSCs/progenitors, and Shp2-deficient HSCs failed to reconstitute lethally irradiated recipients because of defects in homing, self-renewal, and survival. We show that Shp2 regulates coordinately multiple signals involving up-regulation of Kit expression via Gata2. Therefore, this study reveals a critical role of Shp2 in maintenance of a functional HSC/progenitor pool in adult mammals, at least in part through a kinase-phosphatase-kinase cascade.

The Protein Tyrosine Phosphatase SHP-1 Modulates the Suppressive Activity of Regulatory T Cells

The importance of regulatory T cells (Tregs) for immune tolerance is well recognized, yet the signaling molecules influencing their suppressive activity are relatively poorly understood. In this article, through in vivo studies and complementary ex vivo studies, we make several important observations. First, we identify the cytoplasmic tyrosine phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP-1) as an endogenous brake and modifier of the suppressive ability of Tregs; consistent with this notion, loss of SHP-1 expression strongly augments the ability of Tregs to suppress inflammation in a mouse model. Second, specific pharmacological inhibition of SHP-1 enzymatic activity via the cancer drug sodium stibogluconate potently augmented Treg suppressor activity both in vivo and ex vivo. Finally, through a quantitative imaging approach, we directly demonstrate that Tregs prevent the activation of conventional T cells and that SHP-1-deficient Tregs are more efficient suppressors. Collectively, our data reveal SHP-1 as a critical modifier of Treg function and a potential therapeutic target for augmenting Treg-mediated suppression in certain disease states.

The Tyrosine 343 Residue of Nucleophosmin (NPM)-Anaplastic Lymphoma Kinase (ALK) Is Important for Its Interaction with SHP1, a Cytoplasmic Tyrosine Phosphatase with Tumor Suppressor Functions

The cytoplasmic tyrosine phosphatase SHP1 has been shown to inhibit the oncogenic fusion protein nucleophosmin (NPM)-anaplastic lymphoma kinase (ALK), and loss of SHP1 contributes to NPM-ALK-mediated tumorigenesis. In this study, we aimed to further understand how SHP1 interacts and regulates NPM-ALK. We employed an in vitro model in which GP293 cells were transfected with various combinations of NPM-ALK (or mutants) and SHP1 (or mutants) expression vectors. We found that SHP1 co-immunoprecipitated with NPM-ALK, but not the enzymatically inactive NPM-ALK(K210R) mutant, or the mutant in which all three functionally important tyrosine residues (namely, Tyr(338), Tyr(342), and Tyr(343)) in the kinase activation loop (KAL) of ALK were mutated. Interestingly, whereas mutation of Tyr(338) or Tyr(342) did not result in any substantial change in the NPM-ALK/SHP1 binding (assessed by co-immunoprecipitation), mutation of Tyr(343) abrogated this interaction. Furthermore, the NPM-ALK/SHP1 binding was readily detectable when each of the remaining 8 tyrosine residues known to be phosphorylated were mutated. Although the expression of SHP1 effectively reduced the level of tyrosine phosphorylation of NPM-ALK, it did not affect that of the NPM-ALK(Y343F) mutant. In soft agar clonogenic assay, SHP1 expression significantly reduced the tumorigenicity of NPM-ALK but not that of NPM-ALK(Y343F). In conclusion, we identified Tyr(343) of NPM-ALK as the crucial site for mediating the NPM-ALK/SHP1 interaction. Our results also support the notion that the tumor suppressor effects of SHP1 on NPM-ALK are dependent on its ability to bind to this oncogenic protein.

Characterization of the Adhesive Properties of the Type IIb Subfamily Receptor Protein Tyrosine Phosphatases

Receptor protein tyrosine phosphatases (RPTPs) have cell adhesion molecule-like extracellular domains coupled to cytoplasmic tyrosine phosphatase domains. PTPmu is the prototypical member of the type IIb subfamily of RPTPs, which includes PTPrho, PTPkappa, and PCP-2. The authors performed the first comprehensive analysis of the subfamily in one system, examining adhesion and antibody recognition. The authors evaluated if antibodies that they developed to detect PTPmu also recognized other subfamily members. Notably, each antibody recognizes distinct subsets of type IIb RPTPs. PTPmu, PTPrho, and PTPkappa have all been shown to mediate cell-cell aggregation, and prior work with PCP-2 indicated that it can mediate bead aggregation in vitro. This study reveals that PCP-2 is unique among the type IIb RPTPs in that it does not mediate cell-cell aggregation via homophilic binding. The authors conclude from these experiments that PCP-2 is likely to have a distinct biological function other than cell-cell aggregation.

IRS1 and SHP2 Signaling in Myelodysplastic Syndrome and Acute Myeloid Leukemia.

Abstract 1779Poster Board I-805 IntroductionMyelodysplastic syndrome (MDS) encompasses a heterogeneous group of clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis, refractory cytopenia and a tendency to progress towards acute myeloid leukemia (AML). The occurrence of acute leukemia results from a combination of mutations and changes in protein functions that confer the ability of proliferation, defects in cell differentiation and apoptosis. The deregulation of multiple cellular signaling pathways in MDS and acute leukemia hinders the development of an effective drug for treatment. SHP2 is a cytoplasmic tyrosine phosphatase encoded by the gene PTPN11. The SHP2 signaling pathway is involved in important functions as regulation of proliferation, differentiation and cell migration and has been described as overexpressed and constitutively phosphorylated in acute and chronic leukemic cells. The IGF1/IRS1 signaling pathway has an important role in the development of various cancers such as breast, colon and prostate cancer and multiple myeloma. Increased expression of IRS1 has been described in neoplastic transformation, and reduction of IRS1 expression has been related to the level of differentiation of neoplastic cells and with a poor prognosis in solid tumors. In acute lymphoblastic leukemia (ALL), IRS1 expression was noted to be overexpressed and correlated with prognosis. The expression of SHP2 and IRS1 in MDS has not yet been elucidated, as well the expression of IRS1 in AML. The aim of the present study was to investigate the gene and protein expression of IRS1 and SHP2 in MDS and AML patients, and also PTPN11 exon 3 mutations. Patients and MethodsWe studied 06 healthy donors, 26 patients with MDS (18 low-risk [RA/RARS] and 07 high-risk [RAEB/RAEBt] according to FAB classification), 24 with AML and 5 with ALL. Samples were obtained from bone marrow. Gene expression was evaluated by real time RT-PCR in total cells. Western blot of mononuclear cells was performed for protein expression. PTPN11 mutations were analyzed by PCR with specific primers and sequencing. ResultsReal time RT-PCR demonstrated a reduced expression of IRS1 in MDS cells (0.13 [0.01-1.19], P=0.01) and AML cells (0.10 [0.009-7.14], P=0.02), when compared to normal cells (0.62 [0.10-1.41]). On the other hand, IRS1 expression was significantly increased in LLA samples (2.35[0.73-11.64] P=0.03) when compared to normal cells. Western blot analysis confirmed the gene expression pattern: IRS1 expression and phosphorylation were down-regulated in MDS and AML and upregulated in ALL when compared to normal hematopoietic cells. Regarding PTPN11 expression, no difference was detected in MDS (1.03 [0.07-4.96], P >0.05) and AML cells (0.48 [0.17-2.29], P >0.05) when compared with normal hematopoietic cells (0.56 [0.2-1.0]). Interesting, PTPN11 expression was increased in low risk MDS (1.35 [0.12-4.96], P=0.048) or total MDS (1.03 [0.07-4.96], P =0.039) when compared to AML cells. Western blot analysis confirmed the SHP2 expression pattern. However, SHP2 phosphorylation was marked increased in both MDS and AML compared to normal hematopoietic cells. PTPN11 mutation was not detected in the samples. ConclusionsOur results show that IRS1 expression and phosphorylation is down-regulated in MDS and AML patients compared to normal hematopoietic cells, suggesting that IGF1/IRS1 signaling pathway is differently regulated in normal cells, MDS, AML and ALL. IRS1 overexpression in ALL is in agreement with previous authors and indicates IRS1 as a possible target in ALL, thought not MDS and AML. SHP2 activation is increased in MDS and AML, and was independent from PTPN11 mutation. The increased activation of SHP2 in MDS, not previously described, indicates that this tyrosine phosphatase may play a role in MDS pathophysiology and leukemia transformation.Keywords: IRS1, SHP2, leukemia, myelodysplasia DisclosuresNo relevant conflicts of interest to declare.

Coordinated regulation by Shp2 tyrosine phosphatase of signaling events controlling insulin biosynthesis in pancreatic β-cells

Intracellular signaling by which pancreatic beta-cells synthesize and secrete insulin in control of glucose homeostasis is not fully understood. Here we show that Shp2, a cytoplasmic tyrosine phosphatase possessing 2 SH2 domains, coordinates signaling events required for insulin biosynthesis in beta-cells. Mice with conditional ablation of the Shp2/Ptpn11 gene in the pancreas exhibited defective glucose-stimulated insulin secretion and impaired glucose tolerance. Consistently, siRNA-mediated Shp2-knockdown in rat insulinoma INS-1 832/13 cells resulted in decreased insulin production and secretion despite an increase in cellular ATP. Shp2 modulates the strength of signals flowing through Akt/FoxO1 and Erk pathways, culminating in control of Pdx1 expression and activity on Ins1 and Ins2 promoters, and forced Pdx1 expression rescued insulin production in Shp2-knockdown beta-cells. Therefore, Shp2 acts as a signal coordinator in beta-cells, orchestrating multiple pathways controlling insulin biosynthesis to maintain glucose homeostasis.

SHP-1 and SHP-2 in T cells: two phosphatases functioning at many levels.

Tyrosine phosphorylation and dephosphorylation of proteins play a critical role for many T-cell functions. The opposing actions of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) determine the level of tyrosine phosphorylation at any time. It is well accepted that PTKs are essential during T-cell signaling; however, the role and importance of PTPs are much less known and appreciated. Both transmembrane and cytoplasmic tyrosine phosphatases have been identified in T cells and shown to regulate T-cell responses. This review focuses on the roles of the two cytoplasmic PTPs, the Src-homology 2 domain (SH2)-containing SHP-1 and SHP-2, in T-cell signaling, development, differentiation, and function.

Deletion of Shp2 Tyrosine Phosphatase in Muscle Leads to Dilated Cardiomyopathy, Insulin Resistance, and Premature Death

The intracellular signaling mechanisms underlying the pathogenesis of cardiac diseases are not fully understood. We report here that selective deletion of Shp2, an SH2-containing cytoplasmic tyrosine phosphatase, in striated muscle results in severe dilated cardiomyopathy in mice, leading to heart failure and premature mortality. Development of cardiomyopathy in this mouse model is coupled with insulin resistance, glucose intolerance, and impaired glucose uptake in striated muscle cells. Shp2 deficiency leads to upregulation of leukemia inhibitory factor-stimulated phosphatidylinositol 3-kinase/Akt, Erk5, and Stat3 pathways in cardiomyocytes. Insulin resistance and impaired glucose uptake in Shp2-deficient mice are at least in part due to impaired protein kinase C-zeta/lambda and AMP-kinase activities in striated muscle. Thus, we have generated a mouse line modeling human patients suffering from cardiomyopathy and insulin resistance. This study reinforces a concept that a compound disease with multiple cardiovascular and metabolic disturbances can be caused by a defect in a single molecule such as Shp2, which modulates multiple signaling pathways initiated by cytokines and hormones.

CD45 Glycosylation controls T‐cell life and death

CD45, an abundant and highly glycosylated cell-surface protein, is a critical regulator of T-cell development. CD45 is differentially glycosylated throughout the life of a T cell, and the glycosylation state of CD45 controls recognition by various binding partners, affects intracellular signaling by the cytoplasmic tyrosine phosphatase domain and modulates the response of the T cell to antigen. Although the importance of CD45 during T-cell development has been established, it is becoming increasingly clear that glycosylation of CD45 is a dynamic process that modifies T-cell survival, activation and immune function. In this review, we address changes that occur in CD45 glycosylation during T-cell development and differentiation, describe carbohydrate-binding proteins that recognize differentially glycosylated forms of CD45, and discuss how differential glycosylation alters the T-cell response to a variety of signals involved in selection, activation and apoptosis.

Positive and negative regulation of FcεRI signaling by SHP‐1

SHP‐1 is a cytoplasmic tyrosine phosphatase and, in mast cells, has been shown to negatively regulate the initial signaling triggered by high affinity receptors for IgE (FcεRI). To clarify the molecular mechanisms of SHP‐1 in mast cells, we generated bone marrow‐derived mast cells (BMMCs) from SHP‐1‐deficient motheaten (me) and control (wt) mice and examined downstream signaling events and final outputs following FcεRI crosslinking. FcεRI‐induced tyrosine phosphorylation of SLP‐76 and LAT was increased in me‐derived BMMCs. The activity of Syk that is responsible for the phosphorylation of SLP‐76 and LAT was comparable in both BMMCs, implying that SLP‐76 and LAT might be substrates of SHP‐1 in mast cells. Lack of SHP‐1 expression resulted in enhanced activation of mitogen activated protein kinases, Erk, JNK, and p38, and transcription of cytokine genes such as TNFα and IL‐6, in good accordance with the previous implication of SHP‐1 as a negative regulator. In contrast, FcεRI‐induced calcium mobilization was severely impaired in me‐derived BMMCs. Whereas wt‐BMMCs showed sprolonged increase in calcium flux upon high intensity stimulation, BMMCs derived from me mice demonstrated decreased and transient responses. In addition, me‐BMMCs exhibited diminished calcium flux at low intensity stimulation. Thapsigargin induced similar level of calcium flux in both BMMCs, indicating that BMMCs lacking SHP‐1 expression are still capable of mobilizing calcium. These studies revealed that SHP‐1 not only regulates FcεRI‐signaling negatively but can act as a positive regulator in mast cells. The experiments to clarify possible molecular mechanisms for the positive regulation of calcium signaling by SHP‐1 are currently under study.