Protein tyrosine phosphatase containing SH2 domains: characterization, preferential expression in hematopoietic cells, and localization to human chromosome 12p12-p13

Antagonizing roles of SHP1 in the pathogenesis of Helicobacter pylori infection

BACKGROUND

SHP1 has been documented as a tumor suppressor and it was thought to play an antagonistic role in the pathogenesis of Helicobacter pylori infection. In this study, the exact mechanism of this antagonistic action was studied.

MATERIALS AND METHODS

AGS, MGC803, and GES-1 cells were infected with H. pylori, intracellular distribution changes of SHP1 were first detected by immunofluorescence. SHP1 overexpression and knockdown were then constructed in these cells to investigate its antagonistic roles in H. pylori infection. Migration and invasion of infected cells were detected by transwell assay, secretion of IL-8 was examined via ELISA, the cells with hummingbird-like alteration were determined by microexamination, and activation of JAK2/STAT3, PI3K/Akt, and ERK pathways were detected by immunoblotting. Mice infection model was established and gastric pathological changes were evaluated. Finally, the SHP1 activator sorafenib was used to analyze the attenuating effect of SHP1 activation on H. pylori pathogenesis in vitro and in vivo.

RESULTS

The sub-localization of SHP1 changed after H. pylori infection, specifically that the majority of the cytoplasmic SHP1 was transferred to the cell membrane. SHP1 inhibited H. pylori-induced activation of JAK2/STAT3 pathway, PI3K/Akt pathway, nuclear translocation of NF-κB, and then reduced EMT, migration, invasion, and IL-8 secretion. In addition, SHP1 inhibited the formation of CagA-SHP2 complex by dephosphorylating phosphorylated CagA, reduced ERK phosphorylation and the formation of CagA-dependent hummingbird-like cells. In the mice infection model, gastric pathological changes were observed and increased IL-8 secretion, indicators of cell proliferation and EMT progression were also detected. By activating SHP1 with sorafenib, a significant curative effect against H. pylori infection was obtained in vitro and in vivo.

CONCLUSIONS

SHP1 plays an antagonistic role in H. pylori pathogenesis by inhibiting JAK2/STAT3 and PI3K/Akt pathways, NF-κB nuclear translocation, and CagA phosphorylation, thereby reducing cell EMT, migration, invasion, IL-8 secretion, and hummingbird-like changes.

Epigenetics in psoriasis: perspective of DNA methylation

Psoriasis is a chronic inflammatory skin disease characterized by excessive proliferation of keratinocytes (KCs). Onset of psoriasis is related to genetic, immune and environmental factors. The environment can interact with the genome through epigenetic modifications, including DNA methylation, and this modification is involved in the pathogenesis of psoriasis. In addition to a skin disease, psoriasis is also considered a systemic disease. We reviewed the current literature of psoriatic DNA methylation for studies from several aspects on the DNA methylation distribution patterns in different tissues/cells, single-nucleotide polymorphisms, and candidate disease genes and identified target genes regulated by DNA methylation that have been directly/indirectly validated. This review contributes to a comprehensive understanding of the important a role that DNA methylation plays in psoriasis from a holistic perspective and will promote the implementation of DNA methylation in diagnostic and therapeutic strategies for psoriatic patients.

Assembly of fibronectin fibrils selectively attenuates platelet-derived growth factor-induced intracellular calcium release in fibroblasts

Cellular responses to platelet-derived growth factor (PDGF) are altered in a variety of pathological conditions, including cancers, fibroses, and vascular diseases, making PDGF-induced signaling pathways important therapeutic targets. The limited success of therapies designed to impact PDGF pathways may be overcome with a clearer understanding of how cells integrate signals from PDGF and the extracellular matrix (ECM). Here, we assessed the effects of fibronectin matrix assembly on the responsiveness of mesenchymal cells to PDGF. Our results indicate that fibroblast-mediated assembly of fibronectin fibrils attenuates intracellular calcium release in response to PDGF. The dose-dependent inhibition of PDGF-induced intracellular calcium release was specific to the ECM form of fibronectin. Further, a recombinant protein engineered to mimic ECM fibronectin similarly attenuated intracellular calcium release in response to PDGF. Of note, fibronectin attenuated the PDGF-calcium signaling axis at the level of phosphoinositide 3-kinase (PI3K) activation. Interestingly, ECM fibronectin did not alter other intracellular signals activated by PDGF, including activation of PDGF receptor β, AKT Ser/Thr kinase, phospholipase Cγ1, and extracellular signal-regulated kinase 1/2 (ERK1/2). Rather, fibronectin inhibited activation of the p55 regulatory subunit of PI3K in response to a variety of stimuli, indicating that ECM fibronectin selectively attenuates the intracellular calcium release cascade while leaving intact other PDGF signaling pathways. Selective regulation of calcium signaling by ECM fibronectin via the p55 regulatory subunit of PI3K represents a mechanism by which cells tune their response to PDGF and may therefore serve as a target to selectively regulate one branch of PDGF signaling.

Protein Tyrosine Phosphatases: Regulators of CD4 T Cells in Inflammatory Bowel Disease

Protein tyrosine phosphatases (PTPs) play a critical role in co-ordinating the signaling networks that maintain lymphocyte homeostasis and direct lymphocyte activation. By dephosphorylating tyrosine residues, PTPs have been shown to modulate enzyme activity and both mediate and disrupt protein-protein interactions. Through these molecular mechanisms, PTPs ultimately impact lymphocyte responses to environmental cues such as inflammatory cytokines and chemokines, as well as antigenic stimulation. Mouse models of acute and chronic intestinal inflammation have been shown to be exacerbated in the absence of PTPs such as PTPN2 and PTPN22. This increase in disease severity is due in part to hyper-activation of lymphocytes in the absence of PTP activity. In accordance, human PTPs have been linked to intestinal inflammation. Genome wide association studies (GWAS) identified several PTPs within risk loci for inflammatory bowel disease (IBD). Therapeutically targeting PTP substrates and their associated signaling pathways, such as those implicated in CD4⁺ T cell responses, has demonstrated clinical efficacy. The current review focuses on the role of PTPs in controlling CD4⁺ T cell activity in the intestinal mucosa and how disruption of PTP activity in CD4⁺ T cells can contribute to intestinal inflammation.

Protein Tyrosine Signaling and its Potential Therapeutic Implications in Carcinogenesis

Protein tyrosine phosphorylation is a crucial signaling mechanism that plays a role in epithelial carcinogenesis. Protein tyrosine kinases (PTKs) control various cellular processes including growth, differentiation, metabolism, and motility by activating major signaling pathways including STAT3, AKT, and MAPK. Genetic mutation of PTKs and/or prolonged activation of PTKs and their downstream pathways can lead to the development of epithelial cancer. Therefore, PTKs became an attractive target for cancer prevention. PTK inhibitors are continuously being developed, and they are currently used for the treatment of cancers that show a high expression of PTKs. Protein tyrosine phosphatases (PTPs), the homeostatic counterpart of PTKs, negatively regulate the rate and duration of phosphotyrosine signaling. PTPs initially were considered to be only housekeeping enzymes with low specificity. However, recent studies have demonstrated that PTPs can function as either tumor suppressors or tumor promoters, depending on their target substrates. Together, both PTK and PTP signal transduction pathways are potential therapeutic targets for cancer prevention and treatment.

Post-Receptor Inhibitors of the GHR-JAK2-STAT Pathway in the Growth Hormone Signal Transduction

The growth hormone (GH) plays a key role in the regulation of metabolic processes in an organism. Determination of the correct structure and functioning of the growth hormone receptor (GHR) allowed for a more detailed research of its post-receptor regulators, which substantially influences its signal transduction. This review is focused on the description of the post-receptor inhibitors of the GHR-JAK2-STAT pathway, which is one of the most important pathways in the transduction of the somatotropic axis signal. The aim of this review is the short characterization of the main post-receptor inhibitors, such as: cytokine-inducible SH2-containing protein (CIS), Suppressors of Cytokine Signaling (SOCS) 1, 2 and 3, sirtuin 1 (SIRT1), protein inhibitors of activated STAT (PIAS) 1, 3 and PIAS4, protein tyrosine phosphatases (PTP) 1B and H1, Src homology 2 (SH2) domain containing protein tyrosine phosphatase (SHP) 1, 2 and signal regulatory protein (SIRP) α1. The equilibrium between these regulators activity and inhibition is of special concern because, as many studies showed, even slight imbalance may disrupt the GH activity causing serious diseases. The regulation of the described inhibitors expression and activity may be a point of interest for pharmaceutical industry.

Role of B-cell receptors for B-cell development and antigen-induced differentiation

B-cell development is characterized by a number of tightly regulated selection processes. Signals through the B-cell receptor (BCR) guide and are required for B-cell maturation, survival, and fate decision. Here, we review the role of the BCR during B-cell development, leading to the emergence of B1, marginal zone, and peripheral follicular B cells. Furthermore, we discuss BCR-derived signals on activated B cells that lead to germinal center and plasma cell differentiation.

Regorafenib (Stivarga) pharmacologically targets epithelial-mesenchymal transition in colorectal cancer

Epithelial-to-mesenchymal transition (EMT) is well-known to evoke cancer invasion/metastasis, leading to a high frequency of mortality in patients with metastatic colorectal cancer (mCRC). Protein tyrosine phosphatase (PTPase)-targeted therapy has been identified as a novel cancer therapeutic. Previously, we proved that sorafenib with anti-EMT potency prevents TGF-β1-induced EMT/invasion by directly activating SH2-domain-containing phosphatase 1 (SHP-1)-dependent p-STAT3Tyr705 suppression in hepatocellular carcinoma. Regorafenib has a closely related chemical structure as sorafenib and is approved for the pharmacotherapy of mCRC. Herein, we evaluate whether regorafenib activates PTPase SHP-1 in the same way as sorafenib to abolish EMT-related invasion/metastasis in CRC. Notably, regorafenib exerted potent anti-EMT activity to curb TGF-β1-induced EMT/invasion in vitro as well inhibited lung metastatic outgrowth of SW480 mesenchymal cells in vivo. Mechanistically, regorafenib-enhanced SHP-1 activity significantly impeded TGF-β1-induced EMT/invasion via low p-STAT3Tyr705 level as proved by a SHP-1 inhibitor or siRNA-mediated SHP-1 depletion. Conversely, overexpression of SHP-1 further enhanced the inhibitory effects of regorafenib on TGF-β1-induced p-STAT3Tyr705 and EMT/invasion. Regorafenib directly activates SHP-1 by potently relieving the autoinhibited N-SH2 domain of SHP-1 to inhibit TGF-β1-induced p-STAT3Tyr705 and EMT/invasion. Importantly, the clinical evidence indicated that SHP-1 was positively correlated with E-cadherin and that significantly determined the overall survival of CRC patients. This result further confirms our in vitro data that SHP-1 is a negative regulatory PTPase in EMT regulation and serves as a pharmacological target for mCRC therapy. Collectively, activating PTPase SHP-1 by regorafenib focusing on its anti-EMT activity might be a useful pharmacotherapy for mCRC.

Modulation of VEGF receptor 2 signaling by protein phosphatases

Phosphorylation of serines, threonines, and tyrosines is a central event in signal transduction cascades in eukaryotic cells. The phosphorylation state of any particular protein reflects a balance of activity between kinases and phosphatases. Kinase biology has been exhaustively studied and is reasonably well understood, however, much less is known about phosphatases. A large body of evidence now shows that protein phosphatases do not behave as indiscriminate signal terminators, but can function both as negative or positive regulators of specific signaling pathways. Genetic models have also shown that different protein phosphatases play precise biological roles in health and disease. Finally, genome sequencing has unveiled the existence of many protein phosphatases and associated regulatory subunits comparable in number to kinases. A wide variety of roles for protein phosphatase roles have been recently described in the context of cancer, diabetes, hereditary disorders and other diseases. In particular, there have been several recent advances in our understanding of phosphatases involved in regulation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling. The receptor is the principal signaling molecule mediating a wide spectrum of VEGF signal and, thus, is of paramount significance in a wide variety of diseases ranging from cancer to cardiovascular to ophthalmic. This review focuses on the current knowledge about protein phosphatases' regulation of VEGFR2 signaling and how these enzymes can modulate its biological effects.

Enhancing SHP-1 expression with 5-azacytidine may inhibit STAT3 activation and confer sensitivity in lestaurtinib (CEP-701)-resistant FLT3-ITD positive acute myeloid leukemia

Background

Tumor-suppressor genes are inactivated by methylation in several cancers including acute myeloid leukemia (AML). Src homology-2 (SH2)-containing protein-tyrosine phosphatase 1 (SHP-1) is a negative regulator of the JAK/STAT pathway. Transcriptional silencing of SHP-1 plays a critical role in the development and progression of cancers through STAT3 activation. 5-Azacytidine (5-Aza) is a DNA methyltransferase inhibitor that causes DNA demethylation resulting in re-expression of silenced SHP-1. Lestaurtinib (CEP-701) is a multi-targeted tyrosine kinase inhibitor that potently inhibits FLT3 tyrosine kinase and induces hematological remission in AML patients harboring the internal tandem duplication of the FLT3 gene (FLT3-ITD). However, the majority of patients in clinical trials developed resistance to CEP-701. Therefore, the aim of this study, was to assess the effect of re-expression of SHP-1 on sensitivity to CEP-701 in resistant AML cells.

Methods

Resistant cells harboring the FLT3-ITD were developed by overexposure of MV4-11 to CEP-701, and the effects of 5-Aza treatment were investigated. Apoptosis and cytotoxicity of CEP-701 were determined using Annexin V and MTS assays, respectively. Gene expression was performed by quantitative real-time PCR. STATs activity was examined by western blotting and the methylation profile of SHP-1 was studied using MS-PCR and pyrosequencing analysis. Repeated-measures ANOVA and Kruskal–Wallis tests were used for statistical analysis.

Results

The cytotoxic dose of CEP-701 on resistant cells was significantly higher in comparison with parental and MV4-11R-cep + 5-Aza cells (p = 0.004). The resistant cells showed a significant higher viability and lower apoptosis compared with other cells (p < 0.001). Expression of SHP-1 was 7-fold higher in MV4-11R-cep + 5-Aza cells compared to parental and resistant cells (p = 0.011). STAT3 was activated in resistant cells. Methylation of SHP-1 was significantly decreased in MV4-11R-cep + 5-Aza cells (p = 0.002).

Conclusions

The restoration of SHP-1 expression induces sensitivity towards CEP-701 and could serve as a target in the treatment of AML. Our findings support the hypothesis that, the tumor-suppressor effect of SHP-1 is lost due to epigenetic silencing and its re-expression might play an important role in re-inducing sensitivity to TKIs. Thus, SHP-1 is a plausible candidate for a role in the development of CEP-701 resistance in FLT3-ITD+ AML patients.

Effect of NADPH oxidase inhibitor-apocynin on the expression of Src homology-2 domain-containing phosphatase-1 (SHP-1) exposed renal ischemia/reperfusion injury in rats

This study was designed to evaluate whether NADPH oxidase inhibitor (apocynin) preconditioning induces expression of Src homology-2 domain-containing phosphatase-1 (SHP-1) to protect against renal ischemia/reperfusion (I/R) injury (RI/RI) in rats. Rats were pretreated with 50 mg/kg apocynin, then subjected to 45 min ischemia and 24 h reperfusion. The results indicated that apocynin preconditioning improved the recovery of renal function and nitroso-redox balance, reduced oxidative stress injury and inflammation damage, and upregulated expression of SHP-1 as compared to RI/RI group. Therefore our study demonstrated that apocynin preconditioning provided a protection to the kidney against I/R injury in rats partially through inducing expression of SHP-1.

Shp1 signalling is required to establish the long-lived bone marrow plasma cell pool

Germline or B-cell-specific loss of Ptpn6 gene encoding the Shp1 protein tyrosine phosphatase leads to skewed B lymphopoiesis and systemic autoimmunity. Here, to study its role in B-cell terminal differentiation, we generated Ptpn6^f/fAicda^Cre/+ mice with Shp1 ablated only in activated B cells. We show that Ptpn6^f/fAicda^Cre/+ mice have normal B-cell development but exhibit defective class-switched primary and recalled antibody response to a T-cell-dependent antigen. Germinal centres are present but do not persist and memory B cells are not formed. Interestingly, Shp1-deficient plasma cells are generated in the spleen but do not contribute to the bone marrow long-lived pool. Plasma cells lacking Shp1 exhibit aberrant α4β1 integrin activation due to dysregulated Src- and PI3-kinase signalling and manifest attenuated migration in vitro and defective bone marrow homing when reconstituted in vivo. Interrupting α4β1–VCAM-1 interaction rectifies this defect. These data suggest that Shp1 signalling is required for the establishment of a life-long protective humoral immunity.

SHP-1 signalling is required for the normal development of B lymphocytes but its role in the terminal differentiation of these cells has not been fully established. Here, the authors show that SHP-1 ablation impairs the establishment of long-lived bone marrow-resident plasma cells due to aberrant integrin activation.

Role of protein tyrosine phosphatases in the modulation of insulin signaling and their implication in the pathogenesis of obesity-linked insulin resistance

Insulin resistance is a major disorder that links obesity to type 2 diabetes mellitus (T2D). It involves defects in the insulin actions owing to a reduced ability of insulin to trigger key signaling pathways in major metabolic tissues. The pathogenesis of insulin resistance involves several inhibitory molecules that interfere with the tyrosine phosphorylation of the insulin receptor and its downstream effectors. Among those, growing interest has been developed toward the protein tyrosine phosphatases (PTPs), a large family of enzymes that can inactivate crucial signaling effectors in the insulin signaling cascade by dephosphorylating their tyrosine residues. Herein we briefly review the role of several PTPs that have been shown to be implicated in the regulation of insulin action, and then focus on the Src homology 2 (SH2) domain-containing SHP1 and SHP2 enzymes, since recent reports have indicated major roles for these PTPs in the control of insulin action and glucose metabolism. Finally, the therapeutic potential of targeting PTPs for combating insulin resistance and alleviating T2D will be discussed.

Stage-specific quantitative changes in renal and urinary proteome during the progression and development of streptozotocin-induced diabetic nephropathy in rats

Diabetic nephropathy (DN) is a microvascular complication associated with diabetes causing slow deterioration of kidneys leading to end-stage renal disease. Timely intervention and diagnosis are crucial in order to ameliorate and halt the progression of DN. Current diagnosis of DN consists of urine assays for detection of microalbuminuria, which have inadequate specificity and sensitivity. Hence, there arises a need to discover stage-specific biomarkers which can aid in the early detection of DN and also in identifying the mechanisms underlying pathogenesis of DN. Therefore the present study was undertaken to identify the differentially expressed proteins in the urine and to examine the pattern of proteomic changes occurring in the rat kidneys during the course of progression of streptozotocin-induced model of DN in rats. Two-dimensional gel electrophoresis coupled to MALDI-TOF mass spectrometry was employed to identify the differentially expressed proteins under diabetic conditions. Among the identified proteins Calgranulin A and Calgranulin B appeared in the urinary proteome at the fourth week of induction of diabetes while we recorded a time-dependent decrease in the expression of major urinary protein (alpha 2u globulin) in the urine as well as kidneys of diabetic rats. Parallel monitoring of targeted proteomic changes in the renal proteome revealed an increase in histone H2B phosphorylation at serine14 along with a gradual decrease in Bcl-2 and MMP-13 expression during the course of progression and development of streptozotocin-induced DN.

Biological significance of RNA editing in cells

RNA editing is one of the post-transcriptional RNA processes. RNA editing generates RNA and protein diversity in eukaryotes and results in specific amino acid substitutions, deletions, and changes in gene expression levels. Adenosine-to-inosine RNA editing represents the most important class of editing in human and affects function of many genes. The importance of balancing RNA modification levels across time and space is becoming increasingly evident. In this review, we overview the biological significance of RNA editing including RNA editing in tumorigenesis, RNA editing in neuronal tissues, RNA editing as a regulator of gene expression, and RNA editing in dsRNA-mediated gene silencing, which may increase our understanding of RNA biology.

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.

Hepatocyte-specific Ptpn6 deletion protects from obesity-linked hepatic insulin resistance

The protein-tyrosine phosphatase Shp1 negatively regulates insulin action on glucose homeostasis in liver and muscle, but its potential role in obesity-linked insulin resistance has not been examined. To investigate the role of Shp1 in hepatic insulin resistance, we generated hepatocyte-specific Shp1 knockout mice (Ptpn6(H-KO)), which were subjected to extensive metabolic monitoring throughout an 8-week standard chow diet (SD) or high-fat diet (HFD) feeding. We report for the first time that Shp1 expression is upregulated in metabolic tissues of HFD-fed obese mice. When compared with their Shp1-expressing Ptpn6(f/f) littermates, Ptpn6(H-KO) mice exhibited significantly lowered fasting glycemia and heightened hepatic insulin sensitivity. After HFD feeding, Ptpn6(H-KO) mice developed comparable levels of obesity as Ptpn6(f/f) mice, but they were remarkably protected from liver insulin resistance, as revealed by euglycemic clamps and hepatic insulin signaling determinations. Although Ptpn6(H-KO) mice still acquired diet-induced peripheral insulin resistance, they were less hyperinsulinemic during a glucose tolerance test because of reduced insulin secretion. Ptpn6(H-KO) mice also exhibited increased insulin clearance in line with enhanced CC1 tyrosine phosphorylation in liver. These results show that hepatocyte Shp1 plays a critical role in the development of hepatic insulin resistance and represents a novel therapeutic target for obesity-linked diabetes.

Tetraspanin CD37 directly mediates transduction of survival and apoptotic signals

Tetraspanins are commonly believed to act only as "molecular facilitators," with no direct role in signal transduction. We herein demonstrate that upon ligation, CD37, a tetraspanin molecule expressed on mature normal and transformed B cells, becomes tyrosine phosphorylated, associates with proximal signaling molecules, and initiates a cascade of events leading to apoptosis. Moreover, we have identified two tyrosine residues with opposing regulatory functions: one lies in the N-terminal domain of CD37 in a predicted "ITIM-like" motif and mediates SHP1-dependent death, whereas the second lies in a predicted "ITAM motif" in the C-terminal domain of CD37 and counteracts death signals by mediating phosphatidylinositol 3-kinase-dependent survival.

SHP-1 as a critical regulator of Mycoplasma pneumoniae-induced inflammation in human asthmatic airway epithelial cells

Asthma is a chronic inflammatory disease in which airway epithelial cells are the first line of defense against exposure of the airway to infectious agents. Src homology protein (SHP)-1, a protein tyrosine phosphatase, is a negative regulator of signaling pathways that are critical to the development of asthma and host defense. We hypothesize that SHP-1 function is defective in asthma, contributing to the increased inflammatory response induced by Mycoplasma pneumoniae, a pathogen known to exacerbate asthma. M. pneumoniae significantly activated SHP-1 in airway epithelial cells collected from nonasthmatic subjects by bronchoscopy with airway brushing but not in cells from asthmatic subjects. In asthmatic airway epithelial cells, M. pneumoniae induced significant PI3K/Akt phosphorylation, NF-κB activation, and IL-8 production compared with nonasthmatic cells, which were reversed by SHP-1 overexpression. Conversely, SHP-1 knockdown significantly increased IL-8 production and PI3K/Akt and NF-κB activation in the setting of M. pneumoniae infection in nonasthmatic cells, but it did not exacerbate these three parameters already activated in asthmatic cells. Thus, SHP-1 plays a critical role in abrogating M. pneumoniae-induced IL-8 production in nonasthmatic airway epithelial cells through inhibition of PI3K/Akt and NF-κB activity, but it is defective in asthma, resulting in an enhanced inflammatory response to infection.

Inhibition of protein tyrosine phosphatase improves angiogenesis via enhancing Ang-1/Tie-2 signaling in diabetes

Diabetes is associated with impairment of angiogenesis such as reduction of myocardial capillary formation. Our previous studies demonstrate that disruption of Angiopoietin-1 (Ang-1)/Tie-2 signaling pathway contributes to the diabetes-associated impairment of angiogenesis. Protein tyrosine phosphatase (PTP) has a critical role in the regulation of insulin signal by inhibition of tyrosine kinase phosphorylation. In present study, we examined the role of protein tyrosine phosphatase-1 (SHP-1) in diabetes-associated impairment of Ang-1/Tie-2 angiogenic signaling and angiogenesis. SHP-1 expression was significantly increased in diabetic db/db mouse hearts. Furthermore, SHP-1 bond to Tie-2 receptor and stimulation with Ang-1 led to SHP-1 dissociation from Tie-2 in mouse heart microvascular endothelial cell (MHMEC). Exposure of MHMEC to high glucose (HG, 30 mmol/L) increased SHP-1/Tie-2 association accompanied by a significant reduction of Tie-2 phosphorylation. Exposure of MHMEC to HG also blunted Ang-1-mediated SHP-1/Tie-2 dissociation. Knockdown of SHP-1 significantly attenuated HG-induced caspase-3 activation and apoptosis in MHMEC. Treatment with PTP inhibitors restored Ang-1-induced Akt/eNOS phosphorylation and angiogenesis. Our data implicate a critical role of SHP-1 in diabetes-associated vascular complications, and that upregulation of Ang-1/Tie-2 signaling by targeting SHP-1 should be considered as a new therapeutic strategy for the treatment of diabetes-associated impairment of angiogenesis.

Spontaneous insertion of a b2 element in the ptpn6 gene drives a systemic autoinflammatory disease in mice resembling neutrophilic dermatosis in humans

We found a spontaneous autosomal mutation in a mouse leading to neutrophil infiltration with ulceration in the upper dermis of homozygous offspring. These animals had increased neutrophil numbers, associated with normal lymphocyte count, in peripheral blood and bone marrow, suggesting a myeloproliferative disorder; however, granulocyte precursor proliferation in bone marrow was actually reduced (because circulating neutrophils were less susceptible to apoptosis). Neutrophil infiltration of the skin and other organs and high serum levels of immunoglobulins and autoantibodies, cytokines, and acute-phase proteins were additional abnormalities, all of which could be reduced by high-dose corticosteroid treatment or neutrophil depletion by antibodies. Use of genome-wide screening localized the mutation within an 0.4-Mbp region on mouse chromosome 6. We identified insertion of a B2 element in exon 6 of the Ptpn6 gene (protein tyrosine phosphatase, non-receptor type 6; also known as Shp-1). This insertion involves amino acid substitutions that significantly reduced the enzyme activity in mice homozygous for the mutation. Disease onset was delayed, and the clinical phenotype was milder than the phenotypes of other Ptpn6-mutants described in motheaten (me, mev) mice; we designated this new genotype as Ptpn6(meB2/meB2) and the phenotype as meB2. This new phenotype encompasses an autoinflammatory disease showing similarities to many aspects of the so-called neutrophilic dermatoses, a heterogeneous group of skin diseases with unknown etiology in humans.

Protein Tyrosine Phosphatase SHP-2 (PTPN11) in Hematopoiesis and Leukemogenesis

SHP-2 (PTPN11), a ubiquitously expressed protein tyrosine phosphatase, is critical for hematopoietic cell development and function owing to its essential role in growth factor/cytokine signaling. More importantly, germline and somatic mutations in this phosphatase are associated with Noonan syndrome, Leopard syndrome, and childhood hematologic malignancies. The molecular mechanisms by which SHP-2 mutations induce these diseases are not fully understood, as the biochemical bases of SHP-2 functions still remain elusive. Further understanding SHP-2 signaling activities and identification of its interacting proteins/substrates will shed light on the pathogenesis of PTPN11-associated hematologic malignancies, which, in turn, may lead to novel therapeutics for these diseases.

Evasion of Host Defence by Leishmania donovani: Subversion of Signaling Pathways

Protozoan parasites of the genus Leishmania are responsible for causing a variety of human diseases known as leishmaniasis, which range from self-healing skin lesions to severe infection of visceral organs that are often fatal if left untreated. Leishmania donovani (L. donovani), the causative agent of visceral leishmaniasis, exemplifys a devious organism that has developed the ability to invade and replicate within host macrophage. In fact, the parasite has evolved strategies to interfere with a broad range of signaling processes in macrophage that includes Protein Kinase C, the JAK2/STAT1 cascade, and the MAP Kinase pathway. This paper focuses on how L. donovani modulates these signaling pathways that favour its survival and persistence in host cells.

Alteration in the gene encoding protein tyrosine phosphatase nonreceptor type 6 (PTPN6/SHP1) may contribute to neutrophilic dermatoses

We have found a B2 repeat insertion in the gene encoding protein tyrosine phosphatase nonreceptor type 6 (PTPN6) in a mouse that developed a skin disorder with clinical and histopathological features resembling those seen in human neutrophilic dermatoses. Neutrophilic dermatoses are a group of complex heterogeneous autoinflammatory diseases that all demonstrate excessive neutrophil infiltration of the skin. Therefore, we tested the cDNA and genomic DNA sequences of PTPN6 from patients with Sweet's syndrome (SW) and pyoderma gangrenosum and found numerous novel splice variants in different combinations. Isoforms resulting from deletions of exons 2, 5, 11, and 15 and retention of intron 1 or 5 were the most common in a patients with a familial case of SW, who had a neonatal onset of an inflammatory disorder with skin lesions and a biopsy specimen consistent with SW. These isoforms were associated with a heterozygous E441G mutation and a heterozygous 1.7-kbp deletion in the promoter region of the PTPN6 gene. Although full-length PTPN6 was detected in all other patients with either pyoderma gangrenosum or SW, it was always associated with splice variants: a partial deletion of exon 4 with the complete deletion of exon 5, alterations that were not detected in healthy controls. The defect in transcriptional regulation of the hematopoietic PTPN6 appears to be involved in the pathogenesis of certain subsets of the heterogeneous group of neutrophilic dermatoses.

Angiotensin-II-induced apoptosis requires regulation of nucleolin and Bcl-xL by SHP-2 in primary lung endothelial cells

Angiotensin II (Ang II) is a key proapoptotic factor in fibrotic tissue diseases. However, the mechanism of Ang-II-induced cell death in endothelial cells has not been previously elucidated. Using the neutral comet assay and specific receptor antagonists and agonists, we found that Ang-II-mediated apoptosis in primary pulmonary endothelial cells required the AT2 receptor. Ang II caused cytochrome c release from the mitochondria concurrent with caspase-3 activation and DNA fragmentation, and apoptosis was suppressed by an inhibitor of Bax-protein channel formation, implicating mitochondrial-mediated apoptosis. There was no evidence that the extrinsic apoptotic pathway was involved, because caspase-9, but not caspase-8, was activated by Ang-II treatment. Apoptosis required phosphoprotein phosphatase activation, and inhibition of the SHP-2 phosphatase (encoded by Ptpn11) blocked cell death. Reduced levels of anti-apoptotic Bcl-2-family members can initiate intrinsic apoptosis, and we found that Ang-II treatment lowered cytosolic Bcl-x(L) protein levels. Because the protein nucleolin has been demonstrated to bind Bcl-x(L) mRNA and prevent its degradation, we investigated the role of nucleolin in Ang-II-induced loss of Bcl-x(L). RNA-immunoprecipitation experiments revealed that Ang II reduced the binding of nucleolin to Bcl-x(L) mRNA in an AU-rich region implicated in instability of Bcl-x(L) mRNA. Inhibition of SHP-2 prevented Ang-II-induced degradation of Bcl-x(L) mRNA. Taken together, our findings suggest that nucleolin is a primary target of Ang-II signaling, and that Ang-II-activated SHP-2 inhibits nucleolin binding to Bcl-x(L) mRNA, thus affecting the equilibrium between pro- and anti-apoptotic members of the Bcl-2 family.

Macrophages of multiple sclerosis patients display deficient SHP-1 expression and enhanced inflammatory phenotype

Recent studies in mice have demonstrated that the protein tyrosine phosphatase SHP-1 is a crucial negative regulator of proinflammatory cytokine signaling, TLR signaling, and inflammatory gene expression. Furthermore, mice genetically lacking SHP-1 (me/me) display a profound susceptibility to inflammatory CNS demyelination relative to wild-type mice. In particular, SHP-1 deficiency may act predominantly in inflammatory macrophages to increase CNS demyelination as SHP-1-deficient macrophages display coexpression of inflammatory effector molecules and increased demyelinating activity in me/me mice. Recently, we reported that PBMCs of multiple sclerosis (MS) patients have a deficiency in SHP-1 expression relative to normal control subjects indicating that SHP-1 deficiency may play a similar role in MS as to that seen in mice. Therefore, it became essential to examine the specific expression and function of SHP-1 in macrophages from MS patients. Herein, we document that macrophages of MS patients have deficient SHP-1 protein and mRNA expression relative to those of normal control subjects. To examine functional consequences of the lower SHP-1, the activation of STAT6, STAT1, and NF-kappaB was quantified and macrophages of MS patients showed increased activation of these transcription factors. In accordance with this observation, several STAT6-, STAT1-, and NF-kappaB-responsive genes that mediate inflammatory demyelination were increased in macrophages of MS patients following cytokine and TLR agonist stimulation. Supporting a direct role of SHP-1 deficiency in altered macrophage function, experimental depletion of SHP-1 in normal subject macrophages resulted in an increased STAT/NF-kappaB activation and increased inflammatory gene expression to levels seen in macrophages of MS patients. In conclusion, macrophages of MS patients display a deficiency of SHP-1 expression, heightened activation of STAT6, STAT1, and NF-kappaB and a corresponding inflammatory profile that may be important in controlling macrophage-mediated demyelination in MS.

Interferon-beta treatment in multiple sclerosis attenuates inflammatory gene expression through inducible activity of the phosphatase SHP-1

Interferon-beta is a current treatment for multiple sclerosis (MS). Interferon-beta is thought to exert its therapeutic effects on MS by down-modulating the immune response by multiple potential pathways. Here, we document that treatment of MS patients with interferon beta-1a (Rebif) results in a significant increase in the levels and function of the protein tyrosine phosphatase SHP-1 in PBMCs. SHP-1 is a crucial negative regulator of cytokine signaling, inflammatory gene expression, and CNS demyelination as evidenced in mice deficient in SHP-1. In order to examine the functional significance of SHP-1 induction in MS PBMCs, we analyzed the activity of proinflammatory signaling molecules STAT1, STAT6, and NF-kappaB, which are known SHP-1 targets. Interferon-beta treatment in vivo resulted in decreased NF-kappaB and STAT6 activation and increased STAT1 activation. Further analysis in vitro showed that cultured PBMCs of MS patients and normal subjects had a significant SHP-1 induction following interferon-beta treatment that correlated with decreased NF-kappaB and STAT6 activation. Most importantly, experimental depletion of SHP-1 in cultured PBMCs abolished the anti-inflammatory effects of interferon-beta treatment, indicating that SHP-1 is a predominant mediator of interferon-beta activity. In conclusion, interferon-beta treatment upregulates SHP-1 expression resulting in decreased transcription factor activation and inflammatory gene expression important in MS pathogenesis.

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.

Mechanisms of SHP-1 P2 promoter regulation in hematopoietic cells and its silencing in HTLV-1-transformed T cells

The Src homology-2-containing protein-tyrosine phosphatase 1 (SHP-1), is a negative regulator of cell signaling. It is also considered a tumor suppressor gene because of its ability to antagonize the action of tyrosine kinases. Although SHP-1 is expressed strongly in hematopoietic cells, decreased expression has been observed in various hematological malignancies, which suggests a central involvement of SHP-1 in leukemogenesis. We have shown previously that human T cell lymphotropic virus type-1 (HTLV-1) Tax-induced promoter silencing (TIPS) is an early event causing down-regulation of SHP-1 expression, which is dependent on NF-kappaB. In this study, DNase I footprinting and EMSA also revealed binding of transcription factors, specificity protein 1 (Sp1) and octamer-binding transcription factor 1 (Oct-1) to the P2 promoter, and site-directed mutagenesis confirmed that these factors contribute to the basal P2 promoter activity. Chromatin immunoprecipitation (CHIP) assays showed that Sp1, Oct-1, NF-kappaB, CREB-1, and RNA polymerase II interacted with the core SHP-1 P2 promoter in CD4+ T cells and Jurkat cells but not in HTLV-1-transformed MT-2 and HUT102 cells when HTLV-1 Tax is present. Furthermore, bisulfite sequencing of the SHP-1 P2 core region revealed heavy CpG methylation in HTLV-1-transformed cells compared with freshly isolated CD4+ T cells and HTLV-1-noninfected T cell lines. A significant inverse correlation between degree of CpG methylation and expression of SHP-1 mRNA or protein was observed. Taken together, our data support the notion that in HTLV-1-transformed CD4+ T cells, TIPS causes dissociation of transcription factors from the core SHP-1 P2 promoter, which in turn leads to subsequent DNA methylation, an important early step for leukemogenesis.

The role and target potential of protein tyrosine phosphatases in cancer

Protein tyrosine phosphatases (PTPases) are attractive targets for developing novel cancer therapeutics. Activated via gain-of-function point mutations or overexpression, several PTPases have been identified as critical oncogenic molecules in human malignancies that may be targeted with small chemical inhibitors as a therapeutic strategy. Tumor suppressor PTPases have also been discovered as contributing factors in cancer development that may be targeted via intervention of downstream signaling events for therapeutic purposes. In addition, PTPases have been identified as key negative regulators of cytokines or immune cells. Targeting these negative PTPases may improve the efficacy of cytokine therapy and immunotherapy, which currently have modest response rates and limited survival benefit. Inhibitors of selective PTPases have demonstrated significant preclinical antitumor activity, leading to early-phase clinical trials. Further research and development could lead to PTPase-targeted cancer therapeutics in the near future.

SHP-1 deficiency and increased inflammatory gene expression in PBMCs of multiple sclerosis patients

Recent studies in mice have demonstrated that the protein tyrosine phosphatase SHP-1 is a crucial negative regulator of cytokine signaling, inflammatory gene expression, and demyelination in central nervous system. The present study investigates a possible similar role for SHP-1 in the human disease multiple sclerosis (MS). The levels of SHP-1 protein and mRNA in PBMCs of MS patients were significantly lower compared to normal subjects. Moreover, promoter II transcripts, expressed from one of two known promoters, were selectively deficient in MS patients. To examine functional consequences of the lower SHP-1 in PBMCs of MS patients, we measured the intracellular levels of phosphorylated STAT6 (pSTAT6). As expected, MS patients had significantly higher levels of pSTAT6. Accordingly, siRNA to SHP-1 effectively increased the levels of pSTAT6 in PBMCs of controls to levels equal to MS patients. Additionally, transduction of PBMCs with a lentiviral vector expressing SHP-1 lowered pSTAT6 levels. Finally, multiple STAT6-responsive inflammatory genes were increased in PBMCs of MS patients relative to PBMCs of normal subjects. Thus, PBMCs of MS patients display a stable deficiency of SHP-1 expression, heightened STAT6 phosphorylation, and an enhanced state of activation relevant to the mechanisms of inflammatory demyelination.

The Src homology 2 domain tyrosine phosphatases SHP-1 and SHP-2: diversified control of cell growth, inflammation, and injury

Interest in the diverse biology of protein tyrosine phosphatases that are encoded by more than 100 genes in the human genome continues to grow at an accelerated pace. In particular, two cytoplasmic protein tyrosine phosphatases composed of two Src homology 2 (SH2) NH2-terminal domains and a C-terminal protein-tyrosine phosphatase domain referred to as SHP-1 and SHP-2 are known to govern a host of cellular functions. SHP-1 and SHP-2 modulate progenitor cell development, cellular growth, tissue inflammation, and cellular chemotaxis, but more recently the role of SHP-1 and SHP-2 to directly control cell survival involving oxidative stress pathways has come to light. SHP-1 and SHP-2 are fundamental for the function of several growth factor and metabolic pathways yielding far reaching implications for disease pathways and disorders such as diabetes, neurodegeneration, and cancer. Although SHP-1 and SHP-2 can employ similar or parallel cellular pathways, these proteins also clearly exert opposing effects upon downstream cellular cascades that affect early and late apoptotic programs. SHP-1 and SHP-2 modulate cellular signals that involve phosphatidylinositol 3-kinase, Akt, Janus kinase 2, signal transducer and activator of transcription proteins, mitogen-activating protein kinases, extracellular signal-related kinases, c-Jun-amino terminal kinases, and nuclear factor-kappaB. Our progressive understanding of the impact of SHP-1 and SHP-2 upon multiple cellular environments and organ systems should continue to facilitate the targeted development of treatments for a variety of disease entities.

Investigations into the regulation and function of the SH2 domain-containing protein-tyrosine phosphatase, SHP-1

Our laboratory is interested in identifying genes relevant to diseases. Our approach is to use spontaneous mouse mutants with immunological defects and decipher the molecular basis of the phenotypes. In the early 1990s, our attention was focused on the motheaten and viable motheaten mouse mutants. We used these mutant mice as a model system for elucidating the genetic and cellular events contributing to expression of normal hematopoietic and immune function. Our initial goal was to identify the gene responsible for the motheaten and viable motheaten phenotype. In 1993, we and others reported that both motheaten and viable motheaten mice have mutations in the SHP-1 gene. Currently, there are more than 600 publications involving SHP-1. In this review, rather than summarizing all these studies, we highlight work involving SHP-1 that were/are carried out in our and our collaborators' laboratories.

SHP-1 promoter 2 methylation in normal epithelial tissues and demethylation in psoriasis

SHP-1 promoter hypermethylation has been studied in hematopoietic cells and observed only in various types of lymphoma and leukemia. This study reports a contrasting situation in normal epithelial tissues and an association with skin pathogenesis, particularly in psoriasis. We investigated several cell lines, five of them were epithelial and six were hematopoietic, white blood cells from normal, healthy donors, and normal microdissected epithelium of kidney, liver, breast, cervix, lung, prostate, bladder, and skin. Interestingly, promoter 2 hypermethylation was apparent in all epithelial cell lines and tissues. However, distinctive degrees of demethylation were noted in some skin samples. The methylation patterns of each cell line corresponded to their mRNA isoforms, in that isoforms I and II could not be detected with either promoter 1 or 2 hypermethylation, respectively. We further explored whether an enhanced degree of demethylation could be observed in various dermatopathology lesions. While the promoter 2 methylation levels of squamous cell cancers, eczemas, and normal skins were not different, a significant degree of demethylation can be observed in psoriasis (p<0.005). In addition, psoriasis displays a higher level of SHP-1 isoform II than normal skin (p<0.05). In conclusion, this study discovered an unprecedented role of SHP-1 methylation in tissue-specific expression and its alteration in a nonmalignant human disease besides the transcription inhibition in leukemia and lymphoma. Furthermore, the promoter demethylation may play an important role in skin pathogenesis by enhancing SHP-1 isoform II transcription in psoriatic skin lesions.

Tyrosine phosphorylation regulates maturation of receptor tyrosine kinases

Constitutive activation of receptor tyrosine kinases (RTKs) is a frequent event in human cancer cells. Activating mutations in Fms-like tyrosine kinase 3 (FLT-3), notably, internal tandem duplications in the juxtamembrane domain (FLT-3 ITD), have been causally linked to acute myeloid leukemia. As we describe here, FLT-3 ITD exists predominantly in an immature, underglycosylated 130-kDa form, whereas wild-type FLT-3 is expressed predominantly as a mature, complex glycosylated 150-kDa molecule. Endogenous FLT-3 ITD, but little wild-type FLT-3, is detectable in the endoplasmic reticulum (ER) compartment. Conversely, cell surface expression of FLT-3 ITD is less efficient than that of wild-type FLT-3. Inhibition of FLT-3 ITD kinase by small molecules, inactivating point mutations, or coexpression with the protein-tyrosine phosphatases (PTPs) SHP-1, PTP1B, and PTP-PEST but not RPTPalpha promotes complex glycosylation and surface localization. However, PTP coexpression has no effect on the maturation of a surface glycoprotein of vesicular stomatitis virus. The maturation of wild-type FLT-3 is impaired by general PTP inhibition or by suppression of endogenous PTP1B. Enhanced complex formation of FLT-3 ITD with the ER-resident chaperone calnexin indicates that its retention in the ER is related to inefficient folding. The regulation of RTK maturation by tyrosine phosphorylation was observed with other RTKs as well, defines a possible role for ER-resident PTPs, and may be related to the altered signaling quality of constitutively active, transforming RTK mutants.

Subversion mechanisms by which Leishmania parasites can escape the host immune response: a signaling point of view

The obligate intracellular parasite Leishmania must survive the antimicrobial activities of its host cell, the macrophage, and prevent activation of an effective immune response. In order to do this, it has developed numerous highly successful strategies for manipulating activities, including antigen presentation, nitric oxide and oxygen radical generation, and cytokine production. This is generally the result of interactions between Leishmania cell surface molecules, particularly gp63 and LPG, and less well identified macrophage surface receptors, causing the distortion of specific intracellular signaling cascades. We describe some of the signaling pathways and intermediates that are repressed in infected cells, including JAK/STAT, Ca(2+)-dependent protein kinase C (PKC) isoforms, and mitogen-activated protein kinases (especially ERK1/2), and proteasome-mediated transcription factor degradation. We also discuss protein tyrosine phosphatases (particularly SHP-1), intracellular Ca2+, Ca(2+)-independent PKC, ceramide, and the suppressors of cytokine signaling family of repressors, which are all reported to be activated following infection, and the role of parasite-secreted cysteine proteases.

Lack of phosphotyrosine phosphatase SHP-1 expression in malignant T-cell lymphoma cells results from methylation of the SHP-1 promoter

SHP-1 is an important negative regulator of signaling by several receptors including receptors for interleukin-2 (IL-2R) and other cytokines. SHP-1 acts by dephosphorylating the receptors and receptor-associated kinases such as IL-2R-associated Jak3 kinase. We found that SHP-1 protein was not detectable or greatly diminished in most (six of seven) T cell lines derived from various types of T cell lymphomas and all (eight of eight) cutaneous T-cell lymphoma tissues with a transformed, large-cell morphology. All T-cell lymphoma lines tested (eight of eight) expressed diminished amounts or no detectable SHP-1 mRNA. These T cell lines did not, however, carry any mutations in the SHP-1 gene-coding, splice-junction, and promoter regions. Importantly, SHP-1 DNA promoter region in the T cell lines was resistant to digestion with three different methylation-sensitive restriction enzymes. This resistance was reversed by treatment of the cells with a demethylating agent, 5-deoxyazacytidine. The treatment resulted also in the expression of SHP-1 mRNA and, less frequently, SHP-1 protein. The expression of SHP-1 protein was associated with dephosphorylation of the Jak3 kinase. These results show that lack of SHP-1 expression is frequent in malignant T cells and results from methylation of the SHP-1 gene promoter. Furthermore, they indicate that SHP-1 loss may play a role in the pathogenesis of T cell lymphomas by permitting persistence of signals generated by IL-2R and, possibly, other receptor complexes.

p27KIP1 deletions in childhood acute lymphoblastic leukemia

The p27KIP1 gene, which encodes a cyclin-dependent kinase (CDK) inhibitor, has been assigned to chromosome band 12p12, a region often affected by cytogenetically apparent deletions or translocations in childhood acute lymphoblastic leukemia (ALL). As described here, fluorescence in situ hybridization (FISH) analysis of 35 primary ALL samples with cytogenetic evidence of 12p abnormalities revealed hemizygous deletions of p27KIP1 in 29 cases. Further analysis of 19 of these cases with two additional gene-specific probes from the 12p region (hematopoietic cell phosphatase, HCP and cyclin D2, CCND2) showed that p27KIP1 is located more proximally on the short arm of chromosome 12 and is deleted more frequently than either HCP or CCND2. Of 16 of these cases with hemizygous deletion of p27KIP1, only eight showed loss of HCP or CCND2, whereas loss of either of the latter two loci was uniformly associated with loss of p27KIP1. Missense mutations or mutations leading to premature termination codons were not detected in the coding sequences of the retained p27KIP1 alleles in any of the 16 ALL cases examined, indicating a lack of homozygous inactivation. By Southern blot analysis, one case of primary T-cell ALL had hemizygous loss of a single p27KIP1 allele and a 34.5-kb deletion, including the second coding exon of the other allele. Despite homozygous inactivation of p27KP1 in this case, our data suggest that haploinsufficiency for p27KIP1 is the primary consequence of 12p chromosomal deletions in childhood ALL. The oncogenic role of reduced, but not absent, levels of p27KIP1 is supported by recent studies in murine models and evidence that this protein not only inhibits the activity of complexes containing CDK2 and cyclin E, but also promotes the assembly and catalytic activity of CDK4 or CDK6 in complexes with cyclin D.

Deficiency of SHP-1 protein-tyrosine phosphatase activity results in heightened osteoclast function and decreased bone density

Mice homozygous for the motheaten (Hcphme) or viable motheaten (Hcphme-v) mutations are deficient in functional SHP-1 protein-tyrosine phosphatase and show severe defects in hematopoiesis. Comparison of femurs from mev/mev mice revealed significant decreases in bone mineral density (0.33 +/- 0.03 mg/mm3 for mev/mevversus 0.41 +/- 0.01 mg/mm3 for controls) and mineral content (1.97 +/- 0.36 mg for mev/mevversus 10.64 +/- 0.67 for controls) compared with littermate controls. Viable motheaten mice also showed reduced amounts of trabecular bone and decreased cortical thickness. These bone abnormalities were associated with a 14% increase in numbers of multinucleated osteoclasts and an increase in osteoclast resorption activity. In co-cultures of normal osteoblasts with mutant or control bone marrow cells, numbers of osteoclasts developing from mutant mice were increased compared with littermate control mice. Although mev/mev osteoclasts develop in the absence of colony-stimulating factor (CSF)-1, nevertheless cultured osteoclasts show increased size in the presence of CSF-1. CSF-1-deficient osteopetrosis (op/op) mutant mice develop severe osteosclerosis. However, doubly homozygous mev/mevop/op mice show an expansion of bone marrow cavities and reduced trabecular bone mass compared with op/op mice. Western blot analysis showed that several proteins that were markedly hyperphosphorylated on tyrosine residues were detected in the motheaten osteoclasts, including a novel 126-kd phosphotyrosine protein. The marked hyperphosphorylation of a 126-kd protein in motheaten osteoclasts suggests that this protein depends on SHP-1 for dephosphorylation. These findings demonstrate that the decreased SHP-1 catalytic activity in me/me and mev/mev mice results in an increased population of activated osteoclasts and consequent reduction in bone density.

Identification of major binding proteins and substrates for the SH2-containing protein tyrosine phosphatase SHP-1 in macrophages

The protein tyrosine phosphatase SHP-1 is a critical regulator of macrophage biology, but its detailed mechanism of action remains largely undefined. SHP-1 associates with a 130-kDa tyrosyl-phosphorylated species (P130) in macrophages, suggesting that P130 might be an SHP-1 regulator and/or substrate. Here we show that P130 consists of two transmembrane glycoproteins, which we identify as PIR-B/p91A and the signal-regulatory protein (SIRP) family member BIT. These proteins also form separate complexes with SHP-2. BIT, but not PIR-B, is in a complex with the colony-stimulating factor 1 receptor (CSF-1R), suggesting that BIT may direct SHP-1 to the CSF-1R. BIT and PIR-B bind preferentially to substrate-trapping mutants of SHP-1 and are hyperphosphorylated in macrophages from motheaten viable mice, which express catalytically impaired forms of SHP-1, indicating that these proteins are SHP-1 substrates. However, BIT and PIR-B are hypophosphorylated in motheaten macrophages, which completely lack SHP-1 expression. These data suggest a model in which SHP-1 dephosphorylates specific sites on BIT and PIR-B while protecting other sites from dephosphorylation via its SH2 domains. Finally, BIT and PIR-B associate with two tyrosyl phosphoproteins and a tyrosine kinase activity. Tyrosyl phosphorylation of these proteins and the level of the associated kinase activity are increased in the absence of SHP-1. Our data suggest that BIT and PIR-B recruit multiple signaling molecules to receptor complexes, where they are regulated by SHP-1 and/or SHP-2.

Targeted disruption of SHIP leads to hemopoietic perturbations, lung pathology, and a shortened life span

SHIP is a 145-kD SH2-containing inositol-5-phosphatase widely expressed in hemopoietic cells. It was first identified as a tyrosine phosphoprotein associated with Shc in response to numerous cytokines. SHIP has been implicated in FcgammaRIIB receptor-mediated negative signaling in B cells and mast cells and is postulated to down-regulate cytokine signal transduction in myeloid cells. To define further its role in the proliferation and differentiation of hemopoietic progenitors, as well as its function in mature cells, we have generated embryonic stem cells and mice bearing a targeted disruption of both SHIP alleles. Here we show that although SHIP null mice are viable and fertile, they fail to thrive and survival is only 40% by 14 weeks of age. Mortality is associated with extensive consolidation of the lungs resulting from infiltration by myeloid cells. Increased numbers of granulocyte-macrophage progenitors are observed in both the bone marrow and spleen of SHIP-/- mice, perhaps as a consequence of hyper-responsiveness to stimulation by macrophage-colony stimulating factor, granulocyte-macrophage colony stimulating factor, interleukin-3, or Steel factor as observed in vitro. In contrast, numbers of bone marrow lymphoid and late erythroid progenitors (CFU-E) are reduced. Thus, homozygous disruption of SHIP establishes the crucial role of this molecule in modulating cytokine signaling within the hemopoietic system and provides a powerful model for further delineating its function.

Requirement of SH2-containing protein tyrosine phosphatases SHP-1 and SHP-2 for paired immunoglobulin-like receptor B (PIR-B)-mediated inhibitory signal

Paired immunoglobulin-like receptor B (PIR-B) (p91) molecule has been proposed to function as an inhibitory receptor in B cells and myeloid lineage cells. We demonstrate here that the cytoplasmic region of PIR-B is capable of inhibiting B cell activation. Mutational analysis of five cytoplasmic tyrosines indicate that tyrosine 771 in the motif VxYxxL plays the most crucial role in mediating the inhibitory signal. PIR-B-mediated inhibition was markedly reduced in the SH2-containing protein tyrosine phosphatases SHP-1 and SHP-2 double-deficient DT40 B cells, whereas this inhibition was unaffected in the inositol polyphosphate 5'-phosphatase SHIP-deficient cells. These data demonstrate that PIR-B can negatively regulate B cell receptor activation and that this PIR-B-mediated inhibition requires redundant functions of SHP-1 and SHP-2.

Downregulated expression of SHP-1 in Burkitt lymphomas and germinal center B lymphocytes

We wish to identify developmental changes in germinal center B cells that may contribute to their rapid growth. SHP-1 is an SH2 domain-containing phosphotyrosine phosphatase that negatively regulates activation of B cells and other cells of hematopoietic lineages. We have found that in all 13 EBV-negative and 11 EBV-positive Burkitt lymphomas with a nonlymphoblastoid phenotype, the mean concentration of SHP-1 was reduced to 5% of that of normal B and T cells. The possibility that this diminished expression of SHP-1 was related to the germinal center phenotype of Burkitt lymphomas was supported by the low to absent immunofluorescent staining for SHP-1 in germinal centers, and by the inverse relationship between the concentration of SHP-1 and the expression of the germinal center marker CD38 on purified tonsillar B cells. In CD38-high B cells, SHP-1 concentration was 20% of that of mantle zone B cells from the same donor. This reduction in SHP-1 is comparable to that of cells from motheaten viable mev/mev mice in which there is dysregulated, spontaneous signaling by cytokine and antigen receptors. Therefore, germinal center B cells may have a developmentally regulated, low threshold for cellular activation.

The motheaten mutation rescues B cell signaling and development in CD45-deficient mice

The cytosolic SHP-1 and transmembrane CD45 protein tyrosine phosphatases (PTP) play critical roles in regulating signal transduction via the B cell antigen receptor (BCR). These PTPs differ, however, in their effects on BCR function. For example, BCR-mediated mitogenesis is essentially ablated in mice lacking CD45 (CD45(-)), but is enhanced in SHP-1-deficient motheaten (me) and viable motheaten (mev) mice. To determine whether these PTPs act independently or coordinately in modulating the physiologic outcome of BCR engagement, we assessed B cell development and signaling in CD45-deficient mev (CD45-/SHP-1-) mice. Here we report that the CD45-/SHP-1-) cells undergo appropriate induction of protein kinase activity, mitogen-activated protein kinase activation, and proliferative responses after BCR aggregation. However, BCR-elicited increases in the tyrosine phosphorylation of several SHP-1-associated phosphoproteins, including CD19, were substantially enhanced in CD45-/SHP-1-, compared to wild-type and CD45- cells. In addition, we observed that the patterns of cell surface expression of mu, delta, and CD5, which distinguish the PTP-deficient from normal mice, are largely restored to normal levels in the double mutant animals. These findings indicate a critical role for the balance of SHP-1 and CD45 activities in determining the outcome of BCR stimulation and suggest that these PTPs act in a coordinate fashion to couple antigen receptor engagement to B cell activation and maturation.

A role for the SHP-2 tyrosine phosphatase in nerve growth-induced PC12 cell differentiation

SHP-1 and SHP-2 are intracellular protein tyrosine phosphatases containing two adjacent src homology 2 domains that target these phosphatases to cell surface receptor signaling complexes and play a role in receptor signal transduction. In this report the PC12 cell system was used to investigate the potential roles of SHP-1 and SHP-2 in the induction of neuronal differentiation by nerve growth factor (NGF). By using neurite outgrowth as a marker for differentiation, the effects of transfected constructs of SHP-1 and SHP-2 were assessed. Overexpression of a catalytically inactive SHP-2, but not a catalytically inactive SHP-1, blocked NGF-stimulated neurite outgrowth. The mitogen-activated protein kinase (MAPK) signaling cascade is important for the morphological differentiation in PC12 cells, and both SHP-1 and SHP-2 have been implicated to act upstream of MAPK in other receptor signaling systems. A positive role for SHP-2 but not SHP-1 in the activation of MAPK by NGF was demonstrated by introduction of the SHP-2 phosphatase mutants along with hemagglutinin-tagged MAPK. Coexpression studies with the SHP-2 mutant along with mutant forms of MAPK kinase suggested that SHP-2 functions upstream of MAPK kinase and MAPK in NGF-induced neurite outgrowth.

Mouse Ly-49A interrupts early signaling events in natural killer cell cytotoxicity and functionally associates with the SHP-1 tyrosine phosphatase

The lytic activity of natural killer (NK) cells is inhibited by the expression of class I major histocompatibility complex (MHC) antigens on target cells. In murine NK cells, Ly-49A mediates inhibition of cytotoxicity in response to the class I MHC antigen H-2Dd. In this report, we studied the function of mouse Ly-49A in both the rat NK cell tumor line, RNK-16, transfected with Ly-49A cDNA, and in primary NK cells. We show that ligation of Ly-49A by H-2Dd inhibits early signaling events during target cell stimulation, including polyphosphoinositide turnover and tyrosine phosphorylation. We also show that Ly-49A directly associates with the cytoplasmic tyrosine phosphatase SHP-1, and that Ly-49A function is impaired in NK cells from SHP-1 mutant viable motheaten mice and from SHP-1-deficient motheaten mice. Finally, we demonstrate that mutational substitution of the tyrosine within the proposed SHP-1 binding motif in Ly-49A completely abrogates inhibition of NK cell cytotoxicity through this receptor. These results demonstrate that Ly-49A interrupts early activating signals in NK cells, and that SHP-1 is an important mediator of Ly-49A function.

STEP61: a member of a family of brain-enriched PTPs is localized to the endoplasmic reticulum

The STEP family of protein tyrosine phosphatases is highly enriched within the CNS. Members of this family are alternatively spliced to produce both transmembrane and cytosolic variants. This manuscript describes the distinctive intracellular distribution and enzymatic activity of the membrane-associated isoform STEP61. Transfection experiments in fibroblasts, as well as subcellular fractionations, sucrose density gradients, immunocytochemical labeling, and electron microscopy in brain tissue, show that STEP61 is an intrinsic membrane protein of striatal neurons and is associated with the endoplasmic reticulum. In addition, structural analysis of the novel N-terminal region of STEP61 reveals several motifs not present in the cytosolic variant STEP46. These include two putative transmembrane domains, two sequences rich in Pro, Glu, Asp, Ser, and Thr (PEST sequences), and two polyproline-rich domains. Like STEP46, STEP61 is enriched in the brain, but the recombinant protein has less enzymatic activity than STEP46. Because STEP46 is contained in its entirety within STEP61 and differs only in the extended N terminus of STEP61, this amino acid sequence is responsible for the association of STEP61 with membrane compartments and may also regulate its enzymatic activity.

Regulation of cell signaling by the protein tyrosine phosphatases, CD45 and SHP-1

An equilibrium between positive and negative regulation of immunoreceptor signaling leads to the proper execution of lymphocyte activation. Tyrosine phosphorylation is the initial event in antigen receptor-induced lymphocyte activation. It is generally accepted that protein tyrosine kinases are involved in positive regulation, whereas protein tyrosine phosphatases are important for the negative regulation of tyrosine phosphorylation-dependent processes. However, the interaction between protein tyrosine kinases and protein tyrosine phosphatases is complex. This article discusses the role of two protein tyrosine phosphatases. CD45 and SHP-1, in the regulation of immunoreceptor signaling. SHP-1 acts as a negative regulator for several immunoreceptors, including those for T- and B-cell antigen receptors. The major role of CD45 is in the positive regulation of T- and B-cell antigen receptor signaling.

Prolactin mediated intracellular signaling in mammary epithelial cells

Prolactin binds to a member of the cytokine receptor superfamily. The cytoplasmic domain of the prolactin receptor (PrlR) displays no enzymatic activity yet prolactin treatment leads to the induction of protein tyrosine phosphorylation. PrlR is associated with JAK2, a protein tyrosine kinase whose activity is stimulated following receptor dimerization. JAK2 subsequently phosphorylates PrlR and other cellular proteins which are recruited to the activated receptor complex. Among the JAK2 substrates is the transcription factor Stat5 whose phosphorylation mediates the transcriptional activation of beta-casein gene expression. In this review we discuss the prolactin induced signaling pathways which mediate differentiation of the mammary gland.

Direct association with and dephosphorylation of Jak2 kinase by the SH2-domain-containing protein tyrosine phosphatase SHP-1

SHP-1 is an SH2-containing cytoplasmic tyrosine phosphatase that is widely distributed in cells of the hematopoietic system. SHP-1 plays an important role in the signal transduction of many cytokine receptors, including the receptor for erythropoietin, by associating via its SH2 domains to the receptors and dephosphorylating key substrates. Recent studies have suggested that SHP-1 regulates the function of Jak family tyrosine kinases, as shown by its constitutive association with the Tyk2 kinase and the hyperphosphorylation of Jak kinases in the motheaten cells that lack functional SHP-1. We have examined the interactions of SHP-1 with two tyrosine kinases activated during engagement of the erythropoietin receptor, the Janus family kinase Jak-2 and the c-fps/fes kinase. Immunoblotting studies with extracts from mouse hematopoietic cells demonstrated that Jak2, but not c-fes, was present in anti-SHP-1 immunoprecipitates, suggesting that SHP-1 selectively associates with Jak2 in vivo. Consistent with this, when SHP-1 was coexpressed with these kinases in Cos-7 cells, it associated with and dephosphorylated Jak2 but not c-fes. Transient cotransfection of truncated forms of SHP-1 with Jak2 demonstrated that the SHP-1-Jak2 interaction is direct and is mediated by a novel binding activity present in the N terminus of SHP-1, independently of SH2 domain-phosphotyrosine interaction. Such SHP-1-Jak2 interaction resulted in induction of the enzymatic activity of the phosphatase in in vitro protein tyrosine phosphatase assays. Interestingly, association of the SH2n domain of SHP-1 with the tyrosine phosphorylated erythropoietin receptor modestly potentiated but was not essential for SHP-1-mediated dephosphorylation of Jak2 and had no effect on c-fes phosphorylation. These data indicate that the main mechanism for regulation of Jak2 phosphorylation by SHP-1 involves a direct, SH2-independent interaction with Jak2 and suggest the existence of similar mechanisms for other members of the Jak family of kinases. They also suggest that such interactions may provide one of the mechanisms that control SHP-1 substrate specificity.