PTPH1 is a predominant protein-tyrosine phosphatase capable of interacting with and dephosphorylating the T cell receptor zeta subunit

SHP-1 Regulates CD8+ T Cell Effector Function but Plays a Subtle Role with SHP-2 in T Cell Exhaustion Due to a Stage-Specific Nonredundant Functional Relay

SHP-1 (Src homology region 2 domain-containing phosphatase 1) is a well-known negative regulator of T cells, whereas its close homolog SHP-2 is the long-recognized main signaling mediator of the PD-1 inhibitory pathway. However, recent studies have challenged the requirement of SHP-2 in PD-1 signaling, and follow-up studies further questioned the alternative idea that SHP-1 may replace SHP-2 in its absence. In this study, we systematically investigate the role of SHP-1 alone or jointly with SHP-2 in CD8+ T cells in a series of gene knockout mice. We show that although SHP-1 negatively regulates CD8+ T cell effector function during acute lymphocytic choriomeningitis virus (LCMV) infection, it is dispensable for CD8+ T cell exhaustion during chronic LCMV infection. Moreover, in contrast to the mortality of PD-1 knockout mice upon chronic LCMV infection, mice double deficient for SHP-1 and SHP-2 in CD8+ T cells survived without immunopathology. Importantly, CD8+ T cells lacking both phosphatases still differentiate into exhausted cells and respond to PD-1 blockade. Finally, we found that SHP-1 and SHP-2 suppressed effector CD8+ T cell expansion at the early and late stages, respectively, during chronic LCMV infection.

Protein tyrosine phosphatases as emerging targets for cancer immunotherapy

Contemporary strategies in cancer immunotherapy, despite remarkable success, remain constrained by inherent limitations such as suboptimal patient responses, the emergence of drug resistance, and the manifestation of pronounced adverse effects. Consequently, the need for alternative strategies for immunotherapy becomes clear. Protein tyrosine phosphatases (PTPs) wield a pivotal regulatory influence over an array of essential cellular processes. Substantial research has underscored the potential in targeting PTPs to modulate the immune responses and/or regulate antigen presentation, thereby presenting a novel paradigm for cancer immunotherapy. In this review, we focus on recent advances in genetic and biological validation of several PTPs as emerging targets for immunotherapy. We also highlight recent development of small molecule inhibitors and degraders targeting these PTPs as novel cancer immunotherapeutic agents.

Molecular basis of the interaction of the human tyrosine phosphatase PTPN3 with the hepatitis B virus core protein

Interactions between the hepatitis B virus core protein (HBc) and host cell proteins are poorly understood, although they may be essential for the propagation of the virus and its pathogenicity. HBc has a C-terminal PDZ (PSD-95, Dlg1, ZO-1)-binding motif (PBM) that is responsible for interactions with host PDZ domain-containing proteins. In this work, we focused on the human protein tyrosine phosphatase non-receptor type 3 (PTPN3) and its interaction with HBc. We solved the crystal structure of the PDZ domain of PTPN3 in complex with the PBM of HBc, revealing a network of interactions specific to class I PDZ domains despite the presence of a C-terminal cysteine in this atypical PBM. We further showed that PTPN3 binds the HBc protein within capsids or as a homodimer. We demonstrate that overexpression of PTPN3 significantly affects HBV infection in HepG2 NTCP cells. Finally, we performed proteomics studies on both sides by pull-down assays and screening of a human PDZ domain library. We identified a pool of human PBM-containing proteins that might interact with PTPN3 in cells and that could be in competition with the HBc PBM during infection, and we also identified potential cellular partners of HBc through PDZ-PBM interactions. This study opens up many avenues of future investigations into the pathophysiology of HBV.

Modulation of TCR Signaling by Tyrosine Phosphatases: From Autoimmunity to Immunotherapy

Early TCR signaling is dependent on rapid phosphorylation and dephosphorylation of multiple signaling and adaptor proteins, leading to T cell activation. This process is tightly regulated by an intricate web of interactions between kinases and phosphatases. A number of tyrosine phosphatases have been shown to modulate T cell responses and thus alter T cell fate by negatively regulating early TCR signaling. Mutations in some of these enzymes are associated with enhanced predisposition to autoimmunity in humans, and mouse models deficient in orthologous genes often show T cell hyper-activation. Therefore, phosphatases are emerging as potential targets in situations where it is desirable to enhance T cell responses, such as immune responses to tumors. In this review, we summarize the current knowledge about tyrosine phosphatases that regulate early TCR signaling and discuss their involvement in autoimmunity and their potential as targets for tumor immunotherapy.

A Two-Step Process of Effector Programming Governs CD4+ T Cell Fate Determination Induced by Antigenic Activation in the Steady State

Various processes induce and maintain immune tolerance, but effector T cells still arise under minimal perturbations of homeostasis through unclear mechanisms. We report that, contrary to the model postulating primarily tolerogenic mechanisms initiated under homeostatic conditions, effector programming is an integral part of T cell fate determination induced by antigenic activation in the steady state. This effector programming depends on a two-step process starting with induction of effector precursors that express Hopx and are imprinted with multiple instructions for their subsequent terminal effector differentiation. Such molecular circuits advancing specific terminal effector differentiation upon re-stimulation include programmed expression of interferon-γ, whose production then promotes expression of T-bet in the precursors. We further show that effector programming coincides with regulatory conversion among T cells sharing the same antigen specificity. However, conventional type 2 dendritic cells (cDC2) and T cell functions of mammalian target of rapamycin complex 1 (mTORC1) increase effector precursor induction while decreasing the proportion of T cells that can become peripheral Foxp3⁺ regulatory T (pTreg) cells.

The mechanisms in the steady state that govern the formation of effector T cells with potentially autoimmune functions remain unclear. Opejin et al. reveal a two-step process starting with induction of effector precursors that express Hopx and are imprinted with multiple instructions for their subsequent terminal effector differentiation.

Beyond the Cell Surface: Targeting Intracellular Negative Regulators to Enhance T cell Anti-Tumor Activity

It is well established that extracellular proteins that negatively regulate T cell function, such as Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) and Programmed Cell Death protein 1 (PD-1), can be effectively targeted to enhance cancer immunotherapies and Chimeric Antigen Receptor T cells (CAR-T cells). Intracellular proteins that inhibit T cell receptor (TCR) signal transduction, though less well studied, are also potentially useful therapeutic targets to enhance T cell activity against tumor. Four major classes of enzymes that attenuate TCR signaling include E3 ubiquitin kinases such as the Casitas B-lineage lymphoma proteins (Cbl-b and c-Cbl), and Itchy (Itch), inhibitory tyrosine phosphatases, such as Src homology region 2 domain-containing phosphatases (SHP-1 and SHP-2), inhibitory protein kinases, such as C-terminal Src kinase (Csk), and inhibitory lipid kinases such as Src homology 2 (SH2) domain-containing inositol polyphosphate 5-phosphatase (SHIP) and Diacylglycerol kinases (DGKs). This review describes the mechanism of action of eighteen intracellular inhibitory regulatory proteins in T cells within these four classes, and assesses their potential value as clinical targets to enhance the anti-tumor activity of endogenous T cells and CAR-T cells.

PTPN3 acts as a tumor suppressor and boosts TGF-β signaling independent of its phosphatase activity

TGF-β controls a variety of cellular functions during development. Abnormal TGF-β responses are commonly found in human diseases such as cancer, suggesting that TGF-β signaling must be tightly regulated. Here, we report that protein tyrosine phosphatase non-receptor 3 (PTPN3) profoundly potentiates TGF-β signaling independent of its phosphatase activity. PTPN3 stabilizes TGF-β type I receptor (TβRI) through attenuating the interaction between Smurf2 and TβRI. Consequently, PTPN3 facilitates TGF-β-induced R-Smad phosphorylation, transcriptional responses, and subsequent physiological responses. Importantly, the leucine-to-arginine substitution at amino acid residue 232 (L232R) of PTPN3, a frequent mutation found in intrahepatic cholangiocarcinoma (ICC), disables its role in enhancing TGF-β signaling and abolishes its tumor-suppressive function. Our findings have revealed a vital role of PTPN3 in regulating TGF-β signaling during normal physiology and pathogenesis.

T cell receptor signaling for γδT cell development

T cells are central to the vertebrate immune system. Two distinct types of T cells, αβT and γδT cells, express different types of T cell antigen receptors (TCRs), αβTCR and γδTCR, respectively, that are composed of different sets of somatically rearranged TCR chains and CD3 subunits. γδT cells have recently attracted considerable attention due to their ability to produce abundant cytokines and versatile roles in host defense, tissue regeneration, inflammation, and autoimmune diseases. Both αβT and γδT cells develop in the thymus. Unlike the development of αβT cells, which depends on αβTCR-mediated positive and negative selection, the development of γδT cells, including the requirement of γδTCR, has been less well understood. αβT cells differentiate into effector cells in the peripheral tissues, whereas γδT cells acquire effector functions during their development in the thymus. In this review, we will discuss the current state of knowledge of the molecular mechanism of TCR signal transduction and its role in the thymic development of γδT cells, particularly highlighting a newly discovered mechanism that controls proinflammatory γδT cell development.

SHP-1: the next checkpoint target for cancer immunotherapy?

The immense power of the immune system is harnessed in healthy individuals by a range of negative regulatory signals and checkpoints. Manipulating these checkpoints through inhibition has resulted in striking immune-mediated clearance of otherwise untreatable tumours and metastases; unfortunately, not all patients respond to treatment with the currently available inhibitors of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1). Combinatorial studies using both anti-CTLA-4 and anti-PD-1 demonstrate synergistic effects of targeting multiple checkpoints, paving the way for other immune checkpoints to be targeted. Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) is a widely expressed inhibitory protein tyrosine phosphatase (PTP). In T-cells, it is a negative regulator of antigen-dependent activation and proliferation. It is a cytosolic protein, and therefore not amenable to antibody-mediated therapies, but its role in activation and proliferation makes it an attractive target for genetic manipulation in adoptive transfer strategies, such as chimeric antigen receptor (CAR) T-cells. This review will discuss the potential value of SHP-1 inhibition in future tumour immunotherapy.

Purity of transferred CD8(+) T cells is crucial for safety and efficacy of combinatorial tumor immunotherapy in the absence of SHP-1

Adoptive transfer of tumor-specific cytotoxic T cells is a promising advance in cancer therapy. Similarly, checkpoint inhibition has shown striking clinical results in some patients. Here we combine adoptive cell transfer with ablation of the checkpoint protein Src homology 2-domain-containing phosphatase 1 (SHP-1, Ptpn6). Naturally occurring motheaten mice lack SHP-1 and do not survive weaning due to extensive immunopathology. To circumvent this limitation, we created a novel SHP-1^null mouse that is viable up to 12 weeks of age by knocking out IL1r1. Using this model, we demonstrate that the absence of SHP-1 augments the ability of adoptively transferred CD8⁺ T cells to control tumor growth. This therapeutic effect was only observed in situations where T-cell numbers were limited, analogous to clinical settings. However, adoptive transfer of non-CD8⁺ SHP-1^null hematopoietic cells resulted in lethal motheaten-like pathology, indicating that systemic inhibition of SHP-1 could have serious adverse effects. Despite this caveat, our findings support the development of SHP-1 inhibition strategies in human T cells to complement adoptive transfer therapies in the clinic.

Genome-Wide Association Study of Staphylococcus aureus Carriage in a Community-Based Sample of Mexican-Americans in Starr County, Texas

Staphylococcus aureus is the number one cause of hospital-acquired infections. Understanding host pathogen interactions is paramount to the development of more effective treatment and prevention strategies. Therefore, whole exome sequence and chip-based genotype data were used to conduct rare variant and genome-wide association analyses in a Mexican-American cohort from Starr County, Texas to identify genes and variants associated with S. aureus nasal carriage. Unlike most studies of S. aureus that are based on hospitalized populations, this study used a representative community sample. Two nasal swabs were collected from participants (n = 858) 11–17 days apart between October 2009 and December 2013, screened for the presence of S. aureus, and then classified as either persistent, intermittent, or non-carriers. The chip-based and exome sequence-based single variant association analyses identified 1 genome-wide significant region (KAT2B) for intermittent and 11 regions suggestively associated with persistent or intermittent S. aureus carriage. We also report top findings from gene-based burden analyses of rare functional variation. Notably, we observed marked differences between signals associated with persistent and intermittent carriage. In single variant analyses of persistent carriage, 7 of 9 genes in suggestively associated regions and all 5 top gene-based findings are associated with cell growth or tight junction integrity or are structural constituents of the cytoskeleton, suggesting that variation in genes associated with persistent carriage impact cellular integrity and morphology.

Multiple Changes of Gene Expression and Function Reveal Genomic and Phenotypic Complexity in SLE-like Disease

The complexity of clinical manifestations commonly observed in autoimmune disorders poses a major challenge to genetic studies of such diseases. Systemic lupus erythematosus (SLE) affects humans as well as other mammals, and is characterized by the presence of antinuclear antibodies (ANA) in patients’ sera and multiple disparate clinical features. Here we present evidence that particular sub-phenotypes of canine SLE-related disease, based on homogenous (ANA^H) and speckled ANA (ANA^S) staining pattern, and also steroid-responsive meningitis-arteritis (SRMA) are associated with different but overlapping sets of genes. In addition to association to certain MHC alleles and haplotypes, we identified 11 genes (WFDC3, HOMER2, VRK1, PTPN3, WHAMM, BANK1, AP3B2, DAPP1, LAMTOR3, DDIT4L and PPP3CA) located on five chromosomes that contain multiple risk haplotypes correlated with gene expression and disease sub-phenotypes in an intricate manner. Intriguingly, the association of BANK1 with both human and canine SLE appears to lead to similar changes in gene expression levels in both species. Our results suggest that molecular definition may help unravel the mechanisms of different clinical features common between and specific to various autoimmune disease phenotypes in dogs and humans.

Autoimmune disorders display complex phenotypes with clinically diverse manifestations, which together with complex genetic inheritance and environmental factors triggering the disease may complicate the diagnosis and investigation of the disease mechanism. The use of dog breeds may facilitate the analysis of genetic factors based on genetic homogeneity within a breed. We performed genetic analysis of two diseases common in dogs, immune-mediated rheumatic disease (IMRD) and steroid-responsive meningitis-arteritis (SRMA) that are similar to human SLE and a group of vasulitides such as Kawasaki disease, Henoch-Schönlein purpura and Behçet’s disease, correspondingly. We identified eleven genes along with specific alleles and genotypes for the major histocompatibility complex II involved in susceptibility, and studied their expression. The genes shared between the two diseases may be involved in the common immune signaling pathways and hence account for the common clinical signs, whereas the phenotype-specific genes may be implicated in particular pathways active in certain tissues and organs, and thereby may be responsible for characteristic manifestations seen only in one of the diseases. Further, the similarity between human and dog SLE at the genetic and functional levels demonstrated by the association of the BANK1 gene in both species indicates the common cross-species mechanisms of autoimmunity and may help identification of novel disease genes and pathways.

Pseudophosphatases: methods of analysis and physiological functions

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.

pCAP-based peptide substrates: the new tool in the box of tyrosine phosphatase assays

Robust, facile high throughput assays based on non-peptidic probes are available to detect the enzyme activity of protein tyrosine phosphatases. However, these assays cannot replace the use of peptide-based probes in many applications; for example when a closer mimic of the physiological target is desired or in substrate profiling expeditions. Phosphotyrosine peptides are often used in these assays, but their use is complicated by either poor sensitivity or the need for indirect detection methods, among other pitfalls. Novel peptide-based probes for protein tyrosine phosphatases are needed to replace phosphotyrosine peptides and accelerate the field of tyrosine phosphatase substrate profiling. Here we review a type of peptidic probe for tyrosine phosphatases, which is based on the incorporation of the phosphotyrosine-mimic phosphocoumaryl amino propionic acid (pCAP) into peptides. The resulting fluorogenic pCAP peptides are dephosphorylated by tyrosine phosphatases with similar efficiency as the homologous phosphotyrosine peptides. pCAP peptides outperform phosphotyrosine peptides, providing an assay that is as robust, sensitive and facile as the non-peptidic fluorogenic probes on the market. Finally the use of pCAP can expand the range of phosphatase assays, facilitating the investigation of multiphosphorylated peptides and providing an in-gel assay for phosphatase activity.

Protein tyrosine phosphatases as novel targets in breast cancer therapy

Breast cancer is linked to hyperactivation of protein tyrosine kinases (PTKs), and recent studies have unveiled that selective tyrosine dephosphorylation by protein tyrosine phosphatases (PTPs) of specific substrates, including PTKs, may activate or inactivate oncogenic pathways in human breast cancer cell growth-related processes. Here, we review the current knowledge on the involvement of PTPs in breast cancer, as major regulators of breast cancer therapy-targeted PTKs, such as HER1/EGFR, HER2/Neu, and Src. The functional interplay between PTKs and PTK-activating or -inactivating PTPs, and its implications in novel breast cancer therapies based on targeting of specific PTPs, are discussed.

Regulation of TCR signalling by tyrosine phosphatases: from immune homeostasis to autoimmunity

More than half of the known protein tyrosine phosphatases (PTPs) in the human genome are expressed in T cells, and significant progress has been made in elucidating the biology of these enzymes in T-cell development and function. Here we provide a systematic review of the current understanding of the roles of PTPs in T-cell activation, providing insight into their mechanisms of action and regulation in T-cell receptor signalling, the phenotypes of their genetically modified mice, and their possible involvement in T-cell-mediated autoimmune disease. Our projection is that the interest in PTPs as mediators of T-cell homeostasis will continue to rise with further functional analysis of these proteins, and PTPs will be increasingly considered as targets of immunomodulatory therapies.

Abrogation of SRC homology region 2 domain-containing phosphatase 1 in tumor-specific T cells improves efficacy of adoptive immunotherapy by enhancing the effector function and accumulation of short-lived effector T cells in vivo

T cell expression of inhibitory proteins can be a critical component for the regulation of immunopathology owing to self-reactivity or potentially exuberant responses to pathogens, but it may also limit T cell responses to some malignancies, particularly if the tumor Ag being targeted is a self-protein. We found that the abrogation of Src homology region 2 domain-containing phosphatase-1 (SHP-1) in tumor-reactive CD8(+) T cells improves the therapeutic outcome of adoptive immunotherapy in a mouse model of disseminated leukemia, with benefit observed in therapy employing transfer of CD8(+) T cells alone or in the context of also providing supplemental IL-2. SHP-1(-/-) and SHP-1(+/+) effector T cells were expanded in vitro for immunotherapy. Following transfer in vivo, the SHP-1(-/-) effector T cells exhibited enhanced short-term accumulation, followed by greater contraction, and they ultimately formed similar numbers of long-lived, functional memory cells. The increased therapeutic effectiveness of SHP-1(-/-) effector cells was also observed in recipients that expressed the tumor Ag as a self-antigen in the liver, without evidence of inducing autoimmune toxicity. SHP-1(-/-) effector CD8(+) T cells expressed higher levels of eomesodermin, which correlated with enhanced lysis of tumor cells. Furthermore, reduction of SHP-1 expression in tumor-reactive effector T cells by retroviral transduction with vectors that express SHP-1-specific small interfering RNA, a translatable strategy, also exhibited enhanced antitumor activity in vivo. These studies suggest that abrogating SHP-1 in effector T cells may improve the efficacy of tumor elimination by T cell therapy without affecting the ability of the effector cells to persist and provide a long-term response.

Protein tyrosine phosphatase assays

Tyrosine phosphorylation and dephosphorylation of proteins play a critical role in many processes of the immune system, from early development to fully differentiated effector function. Since the opposing actions of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) determine the steady-state level of tyrosine phosphorylation on a given protein, it is often important for mechanistic studies to determine the specific activities of PTKs and PTPs. PTPs are defined by their enzymatic activity that catalyzes the dephosphorylation of phosphotyrosine residues. This unit focuses on methods to determine the enzymatic activity of PTPs. While there are many varieties of PTP assays, the focus in this unit is on immune complex PTP assays, which do not require elaborate biochemical purifications and are commonly used to test the activities of specific PTPs in the immune system.

SHP-1 in T cells limits the production of CD8 effector cells without impacting the formation of long-lived central memory cells

During responses against viruses and malignancies, naive CD8 T lymphocytes expand to form both short-lived effector cells and a population containing cells with the potential to be long-lived and participate in memory responses (memory precursor effector cells). The strength of antigenic, costimulatory, and cytokine signals during responses impacts the magnitude and type of CD8 populations formed. In vitro studies have revealed that the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 (SHP-1) regulates signal transduction from receptors on T cells including the TCR, helping set the activation threshold, and therefore may shape responses of mature CD8 T cells in vivo. Analysis of CD8 T cells from motheaten mice, which are globally deficient in SHP-1, proved problematic due to cell-extrinsic effects of SHP-1 deficiency in non-T cells on CD8 T cells. Therefore, a conditional knockout of SHP-1 in mature single-positive T cells was developed to analyze cell-intrinsic consequences of complete and partial SHP-1 deficiency on CD8 T cell responses to acute viral infection. The results demonstrated that SHP-1 has disparate effects on subpopulations of responding cells, limiting the magnitude and quality of primary and secondary responses by reducing the number of short-lived effector cells generated without affecting the size of the memory precursor effector cell pool that leads to formation of long-term memory.

Characterization of protein tyrosine phosphatase H1 knockout mice in animal models of local and systemic inflammation

Background

PTPH1 is a protein tyrosine phosphatase expressed in T cells but its effect on immune response is still controversial. PTPH1 dephosphorylates TCRzeta in vitro, inhibiting the downstream inflammatory signaling pathway, however no immunological phenotype has been detected in primary T cells derived from PTPH1-KO mice. The aim of the present study is to characterize PTPH1 phenotype in two in vivo inflammatory models and to give insights in possible PTPH1 functions in cytokine release.

Methods

We challenged PTPH1-KO mice with two potent immunomodulatory molecules, carrageenan and LPS, in order to determine PTPH1 possible role in inflammatory response in vivo. Cytokine release, inflammatory pain and gene expression were investigated in challenged PTPH1-WT and KO mice.

Results

The present study shows that carrageenan induces a trend of slightly increased spontaneous pain sensitivity in PTPH1-KO mice compared to WT (wild-type) littermates, but no differences in cytokine release, induced pain perception and cellular infiltration have been detected between the two genotypes in this mouse model. On the other hand, LPS-induced TNFα, MCP-1 and IL10 release was significantly reduced in PTPH1-KO plasma compared to WTs 30 and 60 minutes post challenge. No cytokine release modulation was detectable 180 minutes post LPS challenge.

Conclusion

In conclusion, the present study points out a slight potential role for PTPH1 in spontaneous pain sensitivity and it indicates that this phosphatase might play a role in the positive regulation of the LPS-induced cytokines release in vivo, in contrast to previous reports indicating PTPH1 as potential negative regulator of immune response.

PTPH1 dephosphorylates and cooperates with p38gamma MAPK to increase ras oncogenesis through PDZ-mediated interaction

Protein phosphatases are believed to coordinate with kinases to execute biological functions, but examples of such integrated activities, however, are still missing. In this report, we have identified protein tyrosine phosphatase H1 (PTPH1) as a specific phosphatase for p38gamma mitogen-activated protein kinase (MAPK) and shown their cooperative oncogenic activity through direct binding. p38gamma, a Ras effector known to act independent of its phosphorylation, was first shown to require its unique PDZ-binding motif to increase Ras transformation. Yeast two-hybrid screening and in vitro and in vivo analyses further identified PTPH1 as a specific p38gamma phosphatase through PDZ-mediated binding. Additional experiments showed that PTPH1 itself plays a role in Ras-dependent malignant growth in vitro and/or in mice by a mechanism depending on its p38gamma-binding activity. Moreover, Ras increases both p38gamma and PTPH1 protein expression and there is a coupling of increased p38gamma and PTPH1 protein expression in primary colon cancer tissues. These results reveal a coordinative oncogenic activity of a MAPK with its specific phosphatase and suggest that PDZ-mediated p38gamma/PTPH1 complex may be a novel target for Ras-dependent malignancies.

The FERM and PDZ domain-containing protein tyrosine phosphatases, PTPN4 and PTPN3, are both dispensable for T cell receptor signal transduction

PTPN3 and PTPN4 are two closely-related non-receptor protein tyrosine phosphatases (PTP) that, in addition to a PTP domain, contain FERM (Band 4.1, Ezrin, Radixin, and Moesin) and PDZ (PSD-95, Dlg, ZO-1) domains. Both PTP have been implicated as negative-regulators of early signal transduction through the T cell antigen receptor (TCR), acting to dephosphorylate the TCRzeta chain, a component of the TCR complex. Previously, we reported upon the production and characterization of PTPN3-deficient mice which show normal TCR signal transduction and T cell function. To address if the lack of a T cell phenotype in PTPN3-deficient mice can be explained by functional redundancy of PTPN3 with PTPN4, we generated PTPN4-deficient and PTPN4/PTPN3 double-deficient mice. As in PTPN3 mutants, T cell development and homeostasis and TCR-induced cytokine synthesis and proliferation were found to be normal in PTPN4-deficient and PTPN4/PTPN3 double-deficient mice. PTPN13 is another FERM and PDZ domain-containing non-receptor PTP that is distantly-related to PTPN3 and PTPN4 and which has been shown to function as a negative-regulator of T helper-1 (Th1) and Th2 differentiation. Therefore, to determine if PTPN13 might compensate for the loss of PTPN3 and PTPN4 in T cells, we generated mice that lack functional forms of all three PTP. T cells from triple-mutant mice developed normally and showed normal cytokine secretion and proliferative responses to TCR stimulation. Furthermore, T cell differentiation along the Th1, Th2 and Th17 lineages was largely unaffected in triple-mutants. We conclude that PTPN3 and PTPN4 are dispensable for TCR signal transduction.

Knockout mice reveal a role for protein tyrosine phosphatase H1 in cognition

Background

The present study has investigated the protein tyrosine phosphatase H1 (PTPH1) expression pattern in mouse brain and its impact on CNS functions.

Methods

We have previously described a PTPH1-KO mouse, generated by replacing the PTP catalytic and the PDZ domain with a LacZ neomycin cassette. PTPH1 expression pattern was evaluated by LacZ staining in the brain and PTPH1-KO and WT mice (n = 10 per gender per genotype) were also behaviorally tested for CNS functions.

Results

In CNS, PTPH1 is expressed during development and in adulthood and mainly localized in hippocampus, thalamus, cortex and cerebellum neurons. The behavioral tests performed on the PTPH1-KO mice showed an impact on working memory in male mice and an impaired learning performance at rotarod in females.

Conclusion

These results demonstrate for the first time a neuronal expression of PTPH1 and its functionality at the level of cognition.

Haemophilus ducreyi LspA proteins are tyrosine phosphorylated by macrophage-encoded protein tyrosine kinases

The LspA proteins (LspA1 and LspA2) of Haemophilus ducreyi are necessary for this pathogen to inhibit the phagocytic activity of macrophage cell lines, an event that can be correlated with a reduction in the level of active Src family protein tyrosine kinases (PTKs) in these eukaryotic cells. During studies investigating this inhibitory mechanism, it was discovered that the LspA proteins themselves were tyrosine phosphorylated after wild-type H. ducreyi cells were incubated with macrophages. LspA proteins in cell-free concentrated H. ducreyi culture supernatant fluid could also be tyrosine phosphorylated by macrophages. This ability to tyrosine phosphorylate the LspA proteins was not limited to immune cell lineages but could be accomplished by both HeLa and COS-7 cells. Kinase inhibitor studies with macrophages demonstrated that the Src family PTKs were required for this tyrosine phosphorylation activity. In silico methods and site-directed mutagenesis were used to identify EPIYG and EPVYA motifs in LspA1 that contained tyrosines that were targets for phosphorylation. A total of four tyrosines could be phosphorylated in LspA1, with LspA2 containing eight predicted tyrosine phosphorylation motifs. Purified LspA1 fusion proteins containing either the EPIYG or EPVYA motifs were shown to be phosphorylated by purified Src PTK in vitro. Macrophage lysates could also tyrosine phosphorylate the LspA proteins and an LspA1 fusion protein via a mechanism that was dependent on the presence of both divalent cations and ATP. Several motifs known to interact with or otherwise affect eukaryotic kinases were identified in the LspA proteins.

The protein tyrosine phosphatase PTPN4/PTP-MEG1, an enzyme capable of dephosphorylating the TCR ITAMs and regulating NF-kappaB, is dispensable for T cell development and/or T cell effector functions

T cell receptor signaling processes are controlled by the integrated actions of families of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPases). Several distinct cytosolic protein tyrosine phosphatases have been described that are able to negatively regulate TCR signaling pathways, including SHP-1, SHP-2, PTPH1, and PEP. Using PTPase substrate-trapping mutants and wild type enzymes, we determined that PTPN4/PTP-MEG1, a PTPH1-family member, could complex and dephosphorylate the ITAMs of the TCR zeta subunit. In addition, the substrate-trapping derivative augmented basal and TCR-induced activation of NF-kappaB in T cells. To characterize the contribution of this PTPase in T cells, we developed PTPN4-deficient mice. T cell development and TCR signaling events were comparable between wild type and PTPN4-deficient animals. The magnitude and duration of TCR-regulated ITAM phosphorylation, as well as overall protein phosphorylation, was unaltered in the absence of PTPN4. Finally, Th1- and Th2-derived cytokines and in vivo immune responses to Listeria monocytogenes were equivalent between wild type and PTPN4-deficient mice. These findings suggest that additional PTPases are involved in controlling ITAM phosphorylations.

TCR-induced downregulation of protein tyrosine phosphatase PEST augments secondary T cell responses

We report that the protein tyrosine phosphatase PTP-PEST is expressed in resting human and mouse CD4(+) and CD8(+) T cells, but not in Jurkat T leukemia cells, and that PTP-PEST protein, but not mRNA, was dramatically downregulated in CD4(+) and CD8(+) primary human T cells upon T cell activation. This was also true in mouse CD4(+) T cells, but less striking in mouse CD8(+) T cells. PTP-PEST reintroduced into Jurkat at levels similar to those in primary human T cells, was a potent inhibitor of TCR-induced transactivation of reporter genes driven by NFAT/AP-1 and NF-kappaB elements and by the entire IL-2 gene promoter. Introduction of PTP-PEST into previously activated primary human T cells also reduced subsequent IL-2 production by these cells in response to TCR and CD28 stimulation. The inhibitory effect of PTP-PEST was associated with dephosphorylation the Lck kinase at its activation loop site (Y394), reduced early TCR-induced tyrosine phosphorylation, reduced ZAP-70 phosphorylation and inhibition of MAP kinase activation. We propose that PTP-PEST tempers T cell activation by dephosphorylating TCR-proximal signaling molecules, such as Lck, and that down-regulation of PTP-PEST may be a reason for the increased response to TCR triggering of previously activated T cells.

Suppression of hepatitis B viral gene expression by protein-tyrosine phosphatase PTPN3

Protein-tyrosine phosphatase PTPN3 is a membrane-associated non-receptor protein-tyrosine phosphatase. PTPN3 contains a N-terminal FERM domain, a middle PDZ domain, and a C-terminal phosphatase domain. Upon co-expression of PTPN3, the level of human hepatitis B viral (HBV) RNAs, 3.5 kb, 2.4/2.1 kb, and 0.7 kb transcribed from a replicating HBV expression plasmid is significantly reduced in human hepatoma HuH-7 cells. When the expression of endogenous PTPN3 protein is diminished by specific small interfering RNA, the expression of HBV genes is enhanced, indicating that the endogenous PTPN3 indeed plays a suppressive role on HBV gene expression. PTPN3 can interact with HBV core protein. The interaction is mediated via the PDZ domain of PTPN3 and the carboxyl-terminal last four amino acids of core. Either deletion of PDZ domain of PTPN3 or substitution of PDZ ligand in core has no effect on PTPN3-mediated suppression. These results clearly show that the interaction of PTPN3 with core is not required for PTPN3 suppressive effect. Mutation of (359)serine and (835)serine of 14-3-3beta binding sites to alanine, which slightly reduces the interaction with 14-3-3beta, does not influence the PTPN3 effect. In contrast, mutation of the invariant (842)cysteine residue in phosphatase domain to serine, which makes the phosphatase activity inactive, does not change its subcellular localization and interaction with core or 14-3-3beta, but completely abolishes PTPN3-mediated suppression. Furthermore, deletion of FERM domain does not affect the phosphatase activity or interaction with 14-3-3beta, but changes the subcellular localization from cytoskeleton-membrane interface to cytoplasm and nucleus, abolishes binding to core, and diminishes the PTPN3 effect on HBV gene expression. Taken together, these results demonstrate that the phosphatase activity and FERM domain of PTPN3 are essential for its suppression of HBV gene expression.

Normal TCR signal transduction in mice that lack catalytically active PTPN3 protein tyrosine phosphatase

PTPN3 (PTPH1) is a cytoskeletal protein tyrosine phosphatase that has been implicated as a negative regulator of early TCR signal transduction and T cell activation. To determine whether PTPN3 functions as a physiological negative regulator of TCR signaling in primary T cells, we generated gene-trapped and gene-targeted mouse strains that lack expression of catalytically active PTPN3. PTPN3 phosphatase-negative mice were born in expected Mendelian ratios and exhibited normal growth and development. Furthermore, numbers and ratios of T cells in primary and secondary lymphoid organs were unaffected by the PTPN3 mutations and there were no signs of spontaneous T cell activation in the mutant mice with increasing age. TCR-induced signal transduction, cytokine production, and proliferation was normal in PTPN3 phosphatase-negative mice. This was observed using both quiescent T cells and recently stimulated T cells where expression of PTPN3 is substantially up-regulated. We conclude, therefore, that the phosphatase activity of PTPN3 is dispensable for negative regulation of TCR signal transduction and T cell activation.

Nonreceptor Protein-Tyrosine Phosphatases in Immune Cell Signaling

Tyrosyl phosphorylation plays a critical role in multiple signaling pathways regulating innate and acquired immunity. Although tyrosyl phosphorylation is a reversible process, we know much more about the functions of protein-tyrosine kinases (PTKs) than about protein-tyrosine phosphatases (PTPs). Genome sequencing efforts have revealed a large and diverse superfamily of PTPs, which can be subdivided into receptor-like (RPTPs) and nonreceptor (NRPTPs). The role of the RPTP CD45 in immune cell signaling is well known, but those of most other PTPs remain poorly understood. Here, we review the mechanism of action, regulation, and physiological functions of NRPTPs in immune cell signaling. Such an analysis indicates that PTPs are as important as PTKs in regulating the immune system.

Degradation of tyrosine phosphatase PTPN3 (PTPH1) by association with oncogenic human papillomavirus E6 proteins

Oncoproteins from DNA tumor viruses associate with critical cellular proteins to regulate cell proliferation, survival, and differentiation. Human papillomavirus (HPV) E6 oncoproteins have been previously shown to associate with a cellular HECT domain ubiquitin ligase termed E6AP (UBE3A). Here we show that the E6-E6AP complex associates with and targets the degradation of the protein tyrosine phosphatase PTPN3 (PTPH1) in vitro and in living cells. PTPN3 is a membrane-associated tyrosine phosphatase with FERM, PDZ, and PTP domains previously implicated in regulating tyrosine phosphorylation of growth factor receptors and p97 VCP (valosin-containing protein, termed Cdc48 in Saccharomyces cerevisiae) and is mutated in a subset of colon cancers. Degradation of PTPN3 by E6 requires E6AP, the proteasome, and an interaction between the carboxy terminus of E6 and the PDZ domain of PTPN3. In transduced keratinocytes, E6 confers reduced growth factor requirements, a function that requires the PDZ ligand of E6 and that can in part be replicated by inhibiting the expression of PTPN3. This report demonstrates the potential of E6 to regulate phosphotyrosine metabolism through the targeted degradation of a tyrosine phosphatase.

Cardiac sodium channel Na(v)1.5 interacts with and is regulated by the protein tyrosine phosphatase PTPH1

In order to identify proteins interacting with the cardiac voltage-gated sodium channel Na(v)1.5, we used the last 66 amino acids of the C-terminus of the channel as bait to screen a human cardiac cDNA library. We identified the protein tyrosine phosphatase PTPH1 as an interacting protein. Pull-down experiments confirmed the interaction, and indicated that it depends on the PDZ-domain binding motif of Na(v)1.5. Co-expression experiments in HEK293 cells showed that PTPH1 shifts the Na(v)1.5 availability relationship toward hyperpolarized potentials, whereas an inactive PTPH1 or the tyrosine kinase Fyn does the opposite. The results of this study suggest that tyrosine phosphorylation destabilizes the inactivated state of Na(v)1.5.

Identification of substrates of human protein-tyrosine phosphatase PTPN22

Stimulation of mature T cells activates a downstream signaling cascade involving temporally and spatially regulated phosphorylation and dephosphorylation events mediated by protein-tyrosine kinases and phosphatases, respectively. PTPN22 (Lyp), a non-receptor protein-tyrosine phosphatase, is expressed exclusively in cells of hematopoietic origin, notably in T cells where it represses signaling through the T cell receptor. We used substrate trapping coupled with mass spectrometry-based peptide identification in an unbiased approach to identify physiological substrates of PTPN22. Several potential substrates were identified in lysates from pervanadate-stimulated Jurkat cells using PTPN22-D195A/C227S, an optimized substrate trap mutant of PTPN22. These included three novel PTPN22 substrates (Vav, CD3epsilon, and valosin containing protein) and two known substrates of PEP, the mouse homolog of PTPN22 (Lck and Zap70). T cell antigen receptor (TCR) zeta was also identified as a potential substrate in Jurkat lysates by direct immunoblotting. In vitro experiments with purified recombinant proteins demonstrated that PTPN22-D195A/C227S interacted directly with activated Lck, Zap70, and TCRzeta, confirming the initial substrate trap results. Native PTPN22 dephosphorylated Lck and Zap70 at their activating tyrosine residues Tyr-394 and Tyr-493, respectively, but not at the regulatory tyrosines Tyr-505 (Lck) or Tyr-319 (Zap70). Native PTPN22 also dephosphorylated TCRzeta in vitro and in cells, and its substrate trap variant co-immunoprecipitated with TCRzeta when both were coexpressed in 293T cells, establishing TCRzeta as a direct substrate of PTPN22.

Haemophilus ducreyi targets Src family protein tyrosine kinases to inhibit phagocytic signaling

Haemophilus ducreyi, the etiologic agent of the sexually transmitted disease chancroid, has been shown to inhibit phagocytosis of both itself and secondary targets in vitro. Immunodepletion of LspA proteins from H. ducreyi culture supernatant fluid abolished this inhibitory effect, indicating that the LspA proteins are necessary for the inhibition of phagocytosis by H. ducreyi. Fluorescence microscopy revealed that macrophages incubated with wild-type H. ducreyi, but not with a lspA1 lspA2 mutant, were unable to complete development of the phagocytic cup around immunoglobulin G-opsonized targets. Examination of the phosphotyrosine protein profiles of these two sets of macrophages showed that those incubated with wild-type H. ducreyi had greatly reduced phosphorylation levels of proteins in the 50-to-60-kDa range. Subsequent experiments revealed reductions in the catalytic activities of both Lyn and Hck, two members of the Src family of protein tyrosine kinases that are known to be involved in the proximal signaling steps of Fcgamma receptor-mediated phagocytosis. Additional experiments confirmed reductions in the levels of both active Lyn and active Hck in three different immune cell lines, but not in HeLa cells, exposed to wild-type H. ducreyi. This is the first example of a bacterial pathogen that suppresses Src family protein tyrosine kinase activity to subvert phagocytic signaling in hostcells.

Transcriptional modulation of TCR, Notch and Wnt signaling pathways in SEB-anergized CD4+ T cells

Gene expression changes in CD4 + Vbeta8+ T cells energized by in vivo exposure to staphylococcal enterotoxin B (SEB) bacterial superantigen compared to CD4 + Vbeta8+ non-energic T cells were assessed using DNA microarrays containing 5184 murine complementary DNAs. Anergy in splenic T cells of SEB-immunized BALB/c mice was verified by dramatically reduced proliferative capacity and an 8 x overexpression of GRAIL mRNA in CD4 + Vbeta8+ T cells taken from mice 7 days after injection. At an Associative t-test threshold of P<0.0005, 96 genes were overexpressed or detected only in anergic T cells, while 256 genes were suppressed or not detected in anergic T cells. Six of eight differential expressions tested using real-time quantitative PCR were validated. Message for B-Raf was detected only in non-anergic cells, while expression of the TCR signaling modulator Slap (Src-like adapter protein) and the TCR zeta-chain specific phosphatase Ptpn3 was enhanced. Modulation of multiple genes suggests downregulation of Wnt/beta-catenin signaling and enhanced Notch signaling in the anergic cells. Consistent with previous reports in a non-superantigen in vivo anergy model, mRNA for CD18 and the transcription factor Satb1 (special AT-rich-binding protein 1) was increased in SEB-energized T cells. This is the first report of global transcriptional changes in CD4+ T cells made anergic by superantigen exposure.

Mast cell activation is differentially affected by heat shock

OBJECTIVE

Mast cells play pivotal roles in immediate-type and inflammatory allergic and nonallergic reactions. Cross-linking of the high-affinity receptor for IgE (FcepsilonRI) on mast cells activates a signaling pathway leading to Ca2+ mobilization and is followed by degranulation and the release of histamine and other preformed mediators, as well as de novo synthesis of arachidonic acid metabolites. In a previous study, we have demonstrated that heat shock activates heat shock transcription factor-1 (HSF-1), induces heat shock protein 70 (HSP70), and suppresses cytokine production in bone marrow-derived mast cells (BMMC). In this study, we further investigated the effects of heat shock on the activation of mast cells and the release of mast cell mediators.

METHODS

In mouse mast cells, derived from a culture of bone marrow cells of male BALB/cBy and null HSF-1(-/-)mice, responsiveness to heat shock was monitored by measuring beta-hexosaminidase and leukotriene C4 (LTC4) release.

RESULTS

Using BMMC, we found that heat shock inhibits degranulation of BMMC without affecting leukotriene production. To further elucidate the mechanism of suppression of degranulation, we studied the effects of heat shock on the regulation of signal transduction in more detail. We found that heat shock inhibits calcium mobilization and tyrosine phosphorylation of Syk and SHIP upon IgE receptor activation, but increases the phosphorylation of SHP-1 and -2. Moreover, our results revealed that suppression of tyrosine phosphorylation of Syk and SHIP coincided with an increased tyrosine phosphatase activity.

CONCLUSION

The inhibitory action of heat shock toward mast cell degranulation is likely due to shifting the balance between kinase and phosphatase activity.

Engineering non-natural inhibitor sensitivity in protein tyrosine phosphatase H1

Protein tyrosine phosphatase H1, a member of the ubiquitous protein tyrosine phosphatase (PTP) superfamily of enzymes, is an important signaling molecule, mutant forms of which have been found in human colorectal cancers. Selective PTPH1 inhibitors would be valuable tools for investigating PTPH1's roles in cellular regulation. However, no PTPH1-specific inhibitors are known. To identify target-selective inhibitors of human PTPH1, we have redesigned a PTPH1/inhibitor interface. Structure-based protein design was used to identify two amino-acid residues, isoleucine 846 and methionine 883, that control PTPH1's sensitivity to oxalylaminoindole PTP inhibitors. Mutation of residues 846 and 883 to alanine and glycine, respectively, conferred novel inhibitor sensitivity onto PTPH1. From a small panel of putative inhibitors, compounds that potently and selectively target the inhibitor-sensitized PTPH1 mutants were identified.

Localization of Src homology 2 domain-containing phosphatase 1 (SHP-1) to lipid rafts in T lymphocytes: functional implications and a role for the SHP-1 carboxyl terminus

The protein tyrosine phosphatase Src homology 2 domain-containing phosphatase 1 (SHP-1) has previously been shown to be a negative regulator of signaling mediated via the TCR. A growing body of evidence indicates that the regulated localization of proteins within certain membrane subdomains, referred to as lipid rafts, is important for the successful transduction of signaling events downstream of the TCR. However, considerably less is known about the localization of negative regulators during these lipid raft-dependent signaling events. In this study we have investigated the subcellular localization of SHP-1 and its role in regulation of TCR-mediated signaling. Our studies demonstrate that in a murine T cell hybridoma as well as in primary murine thymocytes, a fraction of SHP-1 localizes to the lipid rafts, both basally and after TCR stimulation. Interestingly, although SHP-1 localized in the nonraft fractions is tyrosine phosphorylated, the SHP-1 isolated from the lipid rafts lacks the TCR-induced tyrosine phosphorylation, suggesting physical and/or functional differences between these two subpopulations. We identify a requirement for the C-terminal residues of SHP-1 in optimal localization to the lipid rafts. Although expression of SHP-1 that localizes to lipid rafts potently inhibits TCR-mediated early signaling events and IL-2 production, the expression of lipid raft-excluded SHP-1 mutants fails to elicit any of the inhibitory effects. Taken together these studies reveal a key role for lipid raft localization of SHP-1 in mediating the inhibitory effects on T cell signaling events.

Protein tyrosine phosphatases and the immune response

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism for numerous important aspects of eukaryotic physiology and is catalysed by kinases and phosphatases. Together, cells of the immune system express at least half of the 107 protein tyrosine phosphatase (PTP) genes in the human genome, most of which encode multidomain proteins that contain protein- and phospholipid-interaction domains. Here, we discuss the diverse but specific, and important, roles that PTPs have in immune cells, focusing mainly on T and B cells, and we highlight recent evidence that even subtle alterations in PTPs can cause immune dysfunction and human disease.

Analysis of SHP-1-mediated Down-regulation of the TRK-T3 Oncoprotein Identifies Trk-fused Gene (TFG) as a Novel SHP-1-interacting Protein

SHP-1 is a cytoplasmic SH2 domain containing protein-tyrosine phosphatase (PTP) involved in the negative regulation of multiple signaling pathways in hematopoietic, nervous, and epithelial cells. The thyroid TRK-T3 oncogene consists of the NTRK1 tyrosine kinase domain fused in-frame with sequences of the TFG (TRK-fused gene), encoding a protein of unknown function. TFG contains a coiled-coil domain responsible for TRK-T3 oligomerization. In addition, recent analysis of the sequences outside of the coiled-coil domain suggested possible interactions with other proteins. Based on the presence of a putative SHP-1 SH2-binding site within the TFG sequences, we have investigated the role of the SHP-1 phosphatase in TRK-T3 oncoprotein signaling. In this study we show that SHP-1 interacts with and down-regulates TRK-T3. We provide evidence that SHP-1 SH2 and catalytic domains, respectively, associate with the TFG- and NTRK1-derived portions of TRK-T3. Our data contribute to the definition of cellular mechanisms involved in thyroid tumorigenesis. Moreover, it reveals TFG as a novel protein able to modulate SHP-1 activity.