SHP2 forecast for the immune system: fog gradually clearing

The pathogenic T42A mutation in SHP2 rewires the interaction specificity of its N-terminal regulatory domain

Mutations in the tyrosine phosphatase Src homology-2 domain-containing protein tyrosine phosphatase-2 (SHP2) are associated with a variety of human diseases. Most mutations in SHP2 increase its basal catalytic activity by disrupting autoinhibitory interactions between its phosphatase domain and N-terminal SH2 (phosphotyrosine recognition) domain. By contrast, some disease-associated mutations located in the ligand-binding pockets of the N- or C-terminal SH2 domains do not increase basal activity and likely exert their pathogenicity through alternative mechanisms. We lack a molecular understanding of how these SH2 mutations impact SHP2 structure, activity, and signaling. Here, we characterize five SHP2 SH2 domain ligand-binding pocket mutants through a combination of high-throughput biochemical screens, biophysical and biochemical measurements, and molecular dynamics simulations. We show that while some of these mutations alter binding affinity to phosphorylation sites, the T42A mutation in the N-SH2 domain is unique in that it also substantially alters ligand-binding specificity, despite being 8 to 10 Å from the specificity-determining region of the SH2 domain. This mutation exerts its effect on sequence specificity by remodeling the phosphotyrosine-binding pocket, altering the mode of engagement of both the phosphotyrosine and surrounding residues on the ligand. The functional consequence of this altered specificity is that the T42A mutant has biased sensitivity toward a subset of activating ligands and enhances downstream signaling. Our study highlights an example of a nuanced mechanism of action for a disease-associated mutation, characterized by a change in protein-protein interaction specificity that alters enzyme activation.

Spatial interaction and functional status of CD68+SHP2+ macrophages in tumor microenvironment correlate with overall survival of NSCLC

Background

Tumor-associated macrophages (TAMs) constitute a plastic and heterogeneous cell population of the tumor microenvironment (TME) that can regulate tumor proliferation and support resistance to therapy, constituting promising targets for the development of novel anticancer agents. Our previous results suggest that SHP2 plays a crucial role in reprogramming the phenotype of TAMs. Thus, we hypothesized that SHP2+ TAM may predict the treatment efficacy of non-small cell lung cancer NSCLC patients as a biomarker.

Methods

We analyzed cancer tissue samples from 79 NSCLC patients using multiplex fluorescence (mIF) staining to visualize various SHP-2+ TAM subpopulations (CD68+SHP2+, CD68+CD86+, CD68 + 206+, CD68+ CD86+SHP2+, CD68+ CD206+SHP2+) and T cells (CD8+ Granzyme B +) of immune cells. The immune cells proportions were quantified in the tumor regions (Tumor) and stromal regions (Stroma), as well as in the overall tumor microenvironment (Tumor and Stroma, TME). The analysis endpoint was overall survival (OS), correlating them with levels of cell infiltration or effective density. Cox regression was used to evaluate the associations between immune cell subsets infiltration and OS. Correlations between different immune cell subsets were examined by Spearman's tests.

Results

In NSCLC, the distribution of different macrophage subsets within the TME, tumor regions, and stroma regions exhibited inconsistency. The proportions of CD68+ SHP2+ TAMs (P < 0.05) were higher in tumor than in stroma. And the high infiltration of CD68+SHP2+ TAMs in tumor areas correlated with poor OS (P < 0.05). We found that the expression level of SHP2 was higher in M2-like macrophages than in M1-like macrophages. The CD68+SHP2+ subset proportion was positively correlated with the CD68+CD206+ subset within TME (P < 0.0001), tumor (P < 0.0001) and stroma (P < 0.0001).

Conclusions

The high infiltration of CD68+SHP2+ TAMs predict poor OS in NSCLC. Targeting SHP2 is a potentially effective strategy to inhibit M2-phenotype polarization. And it provides a new thought for SHP2 targeted cancer immunotherapy.

The pathogenic T42A mutation in SHP2 rewires the interaction specificity of its N-terminal regulatory domain

Mutations in the tyrosine phosphatase SHP2 are associated with a variety of human diseases. Most mutations in SHP2 increase its basal catalytic activity by disrupting auto-inhibitory interactions between its phosphatase domain and N-terminal SH2 (phosphotyrosine recognition) domain. By contrast, some disease-associated mutations located in the ligand-binding pockets of the N- or C-terminal SH2 domains do not increase basal activity and likely exert their pathogenicity through alternative mechanisms. We lack a molecular understanding of how these SH2 mutations impact SHP2 structure, activity, and signaling. Here, we characterize five SHP2 SH2 domain ligand-binding pocket mutants through a combination of high-throughput biochemical screens, biophysical and biochemical measurements, and molecular dynamics simulations. We show that, while some of these mutations alter binding affinity to phosphorylation sites, the T42A mutation in the N-SH2 domain is unique in that it also substantially alters ligand-binding specificity, despite being 8-10 Å from the specificity-determining region of the SH2 domain. This mutation exerts its effect on sequence specificity by remodeling the phosphotyrosine binding pocket, altering the mode of engagement of both the phosphotyrosine and surrounding residues on the ligand. The functional consequence of this altered specificity is that the T42A mutant has biased sensitivity toward a subset of activating ligands and enhances downstream signaling. Our study highlights an example of a nuanced mechanism of action for a disease-associated mutation, characterized by a change in protein-protein interaction specificity that alters enzyme activation.

Targeting Protein Tyrosine Phosphatases to Improve Cancer Immunotherapies

Advances in immunotherapy have brought significant therapeutic benefits to many cancer patients. Nonetheless, many cancer types are refractory to current immunotherapeutic approaches, meaning that further targets are required to increase the number of patients who benefit from these technologies. Protein tyrosine phosphatases (PTPs) have long been recognised to play a vital role in the regulation of cancer cell biology and the immune response. In this review, we summarize the evidence for both the pro-tumorigenic and tumour-suppressor function of non-receptor PTPs in cancer cells and discuss recent data showing that several of these enzymes act as intracellular immune checkpoints that suppress effective tumour immunity. We highlight new data showing that the deletion of inhibitory PTPs is a rational approach to improve the outcomes of adoptive T cell-based cancer immunotherapies and describe recent progress in the development of PTP inhibitors as anti-cancer drugs.

Allosteric inhibition of SHP2 rescues functional T-cell abnormalities in SAP deficiency

BACKGROUND

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency arising from SH2D1A mutations leading to loss of SLAM-associated protein (SAP). SAP is an intracellular adaptor protein that binds to SLAM family receptors and is expressed in specific lymphoid lineages. In T cells, SAP relays activatory signals from the T-cell receptor but in its absence SH2 containing protein tyrosine phosphase-1 (SHP1), SH2 containing protein tyrosine phosphase-2 (SHP2), and SH2 containing inositol 5'-phosphatase proteins (SHIP) induce T-cell inhibitory signals leading to abnormal T-cell responses. This results in severe clinical manifestations including immune dysregulation, dysgammaglobulinemia, lymphoma, and hemophagocytic lymphohistiocytosis. Current treatment relies on supportive therapies including immunoglobulin replacement and symptom-directed therapy, with hematopoietic stem cell transplant offering the only curative option.

OBJECTIVES

As most XLP symptoms are due to defective T-cell function, this study investigated whether inhibition of SHP2 can restore cellular function in the absence of SAP.

METHODS

Healthy donor and XLP patient T cells were activated with anti-CD3/CD28 in T-cell media supplemented with a SHP2 inhibitor (RMC-4550 in vitro for 24 hours) and functional assays were performed to assess follicular T_H (T_FH) cell function, CD8 cytotoxicity, and sensitivity to restimulation-induced cell death. Additionally, SAP-deficient (SAP^y/-) mice were treated with RMC-4550 before T-cell mediated challenge with 4-hydroxy-3-nitrophenylacetly conjugated chicken gammaglobulin and subsequent assessment of humoral immunity analyzing T_FH cell population, germinal center formation, and antigen-dependent immunoglobulin secretion.

RESULTS

This study shows that the use of RMC-4550 restores T-cell function in XLP patient cells and a SAP^y/- model, demonstrating restoration of T_FH cell function through immunoglobulin and cytokine secretion analysis alongside rescue of cytotoxicity and restimulation-induced cell death.

CONCLUSIONS

These data suggest that SHP2 inhibitors could offer a novel and effective targeted treatment approach for patients with XLP.

Molecular associations, clinical, and prognostic implications of PTPN11 mutations in acute myeloid leukemia (Alliance)

Patients with N-terminal SH2 domain PTPN11 mutations had an early death (<30 days) more often than those with phosphatase domain mutations.

PTPN11 mutations are associated with inferior outcomes in AML patients with wild-type NPM1.

Prognostic factors associated with chemotherapy outcomes in patients with acute myeloid leukemia (AML) are extensively reported, and one gene whose mutation is recognized as conferring resistance to several newer targeted therapies is protein tyrosine phosphatase non-receptor type 11 (PTPN11). The broader clinical implications of PTPN11 mutations in AML are still not well understood. The objective of this study was to determine which cytogenetic abnormalities and gene mutations co-occur with PTPN11 mutations and how PTPN11 mutations affect outcomes of patients treated with intensive chemotherapy. We studied 1725 patients newly diagnosed with AML (excluding acute promyelocytic leukemia) enrolled onto the Cancer and Leukemia Group B/Alliance for Clinical Trials in Oncology trials. In 140 PTPN11-mutated patient samples, PTPN11 most commonly co-occurred with mutations in NPM1, DNMT3A, and TET2. PTPN11 mutations were relatively common in patients with an inv(3)(q21q26)/t(3;3)(q21;q26) and a normal karyotype but were very rare in patients with typical complex karyotype and core-binding factor AML. Mutations in the N-terminal SH2 domain of PTPN11 were associated with a higher early death rate than those in the phosphatase domain. PTPN11 mutations did not affect outcomes of NPM1-mutated patients, but these patients were less likely to have co-occurring kinase mutations (ie, FLT3-ITD), suggesting activation of overlapping signaling pathways. However, in AML patients with wild-type NPM1, PTPN11 mutations were associated with adverse patient outcomes, providing a rationale to study the biology and treatment approaches in this molecular group. This trial was registered at www.clinicaltrials.gov as #NCT00048958 (CALGB 8461), #NCT00899223 (CALGB 9665), and #NCT00900224 (CALGB 20202).

IL-10 Signaling Elicited by Nivolumab-Induced Activation of the MAP Kinase Pathway Does Not Fully Contribute to Nivolumab-Modulated Heterogeneous T Cell Responses

Immune checkpoint inhibitor (ICI) therapy has revolutionized anti-cancer treatment for many late-stage cancer patients. However, ICI therapy has thus far demonstrated limited efficacy for most patients, and it remains unclear why this is so. Interleukin 10 (IL-10) is a cytokine that has been recognized as a central player in cancer biology with its ability to inhibit anti-tumor T cell responses. Recent studies suggest that IL-10 might also exert some intrinsic anti-tumor T cell responses, and clinical studies using recombinant IL-10 alone or in combination with ICI are underway. This paradoxical effect of IL-10 and its underlying mechanisms impacting ICI-modulated T cell responses remain poorly understood. In this study, using an in vitro mixed lymphocyte reaction assay, we found that treatment with ICIs such as the anti-programmed cell death receptor-1 (PD-1) mAb nivolumab elicits a strong expression of IL-10. While neutralization of IL-10 signaling with an anti-IL-10 specific mAb significantly decreases the production of IFN-γ by T cells in a cohort of donor cells, the opposite effect was observed in other donor cells. Similarly, neutralization of IL-10 signaling significantly decreases the expression of T cell activation markers Ki67 and CD25, as well as the production of Granzyme B in a cohort of donor cells, whereas the opposite effect was observed in others. Furthermore, we found that nivolumab and IL-10 differentially modulate the signal transducer and activator of transcription 3 (STAT3) and AKT serine–threonine kinase pathways. Finally, we found that nivolumab activates the mitogen-activated protein kinase (MAPK) pathway, which in turn is responsible for the observed induction of IL-10 production by nivolumab. These findings provide new insights into the mechanisms underlying anti-PD-1-modulated T cell responses by IL-10, which could lead to the discovery of novel combination treatments that target IL-10 and immune checkpoint molecules.

Discovery of 6-[(3S,4S)-4-Amino-3-methyl-2-oxa-8-azaspiro[4.5]decan-8-yl]-3-(2,3-dichlorophenyl)-2-methyl-3,4-dihydropyrimidin-4-one (IACS-15414), a Potent and Orally Bioavailable SHP2 Inhibitor

Src homology 2 (SH2) domain-containing phosphatase 2 (SHP2) plays a role in receptor tyrosine kinase (RTK), neurofibromin-1 (NF-1), and Kirsten rat sarcoma virus (KRAS) mutant-driven cancers, as well as in RTK-mediated resistance, making the identification of small-molecule therapeutics that interfere with its function of high interest. Our quest to identify potent, orally bioavailable, and safe SHP2 inhibitors led to the discovery of a promising series of pyrazolopyrimidinones that displayed excellent potency but had a suboptimal in vivo pharmacokinetic (PK) profile. Hypothesis-driven scaffold optimization led us to a series of pyrazolopyrazines with excellent PK properties across species but a narrow human Ether-à-go-go-Related Gene (hERG) window. Subsequent optimization of properties led to the discovery of the pyrimidinone series, in which multiple members possessed excellent potency, optimal in vivo PK across species, and no off-target activities including no hERG liability up to 100 μM. Importantly, compound 30 (IACS-15414) potently suppressed the mitogen-activated protein kinase (MAPK) pathway signaling and tumor growth in RTK-activated and KRAS^mut xenograft models in vivo.

Grass carp (Ctenopharyngodon idellus) SHP2 suppresses IFN I expression via decreasing the phosphorylation of GSK3β in a non-contact manner

As a tyrosine phosphatase, Src homology 2-containing protein tyrosine phosphatase 2 (SHP2) serves as an inhibitor in PI3K-Akt pathway. In mammals, SHP2 can phosphorylate GSK3β at Y216 site to control the expression of IFN. So far, the multiple functions of SHP2 have been reported in mammals. However, little is known about fish SHP2. In this study, we cloned and identified a grass carp (Ctenopharyngodon idellus) SHP2 gene (CiSHP2, MT373151). SHP2 is conserved among different vertebrates by amino acid sequences alignment and the phylogenetic tree analysis. CiSHP2 shared the closest homology with Danio rerio SHP2. Simultaneously, SHP2 was also tested in grass carp tissues and CIK (C. idellus kidney) cells. We found that it responded to poly I:C stimulation. CiSHP2 was located in the cytoplasm just as the same as those of mammals. Interestingly, it inhibited the phosphorylation level of GSK3β in a non-contact manner. Meanwhile CiGSK3β interacted with and directly phosphorylated CiTBK1. In addition, we found that CiSHP2 also reduced the phosphorylation level of CiTBK1 by CiGSK3β, and then it depressed the expression of IFN I via GSK3β-TBK1 axis. These results suggested that CiSHP2 was involved in CiGSK3β and CiTBK1 activity but not regulated their transcriptional level. At the same time, we also found that CiSHP2 also influenced the activity of CiIRF3. Therefore, fish SHP2 inhibited IFN I expression through blocking GSK3β-TBK1 signal axis.

Emerging principles of brain immunology and immune checkpoint blockade in brain metastases

Brain metastases are the most common type of brain tumours, harbouring an immune microenvironment that can in principle be targeted via immunotherapy. Elucidating some of the immunological intricacies of brain metastases has opened a therapeutic window to explore the potential of immune checkpoint inhibitors in this globally lethal disease. Multiple lines of evidence suggest that tumour cells hijack the immune regulatory mechanisms in the brain for the benefit of their own survival and progression. Nonetheless, the role of the immune checkpoint in the complex interplays between cancers cells and T cells and in conferring resistance to therapy remains under investigation. Meanwhile, early phase trials with immune checkpoint inhibitors have reported clinical benefit in patients with brain metastases from melanoma and non-small cell lung cancer. In this review, we explore the workings of the immune system in the brain, the immunology of brain metastases, and the current status of immune checkpoint inhibitors in the treatment of brain metastases.

Activating Mutation of SHP2 Establishes a Tumorigenic Phonotype Through Cell-Autonomous and Non-Cell-Autonomous Mechanisms

Gain-of-function mutation of SHP2 is a central regulator in tumorigenesis and cancer progression through cell-autonomous mechanisms. Activating mutation of SHP2 in microenvironment was identified to promote cancerous transformation of hematopoietic stem cell in non-autonomous mechanisms. It is interesting to see whether therapies directed against SHP2 in tumor or microenvironmental cells augment antitumor efficacy. In this review, we summarized different types of gain-of-function SHP2 mutations from a human disease. In general, gain-of-function mutations destroy the auto-inhibition state from wild-type SHP2, leading to consistency activation of SHP2. We illustrated how somatic or germline mutation of SHP2 plays an oncogenic role in tumorigenesis, stemness maintenance, invasion, etc. Moreover, the small-molecule SHP2 inhibitors are considered as a potential strategy for enhancing the efficacy of antitumor immunotherapy and chemotherapy. We also discussed the interconnection between phase separation and activating mutation of SHP2 in drug resistance of antitumor therapy.

SH2 domain-containing protein tyrosine phosphatase-2 (SHP-2) prevents cardiac remodeling after myocardial infarction through ERK/SMAD signaling pathway

In this study, we aimed to investigate the role of SH2 domain-containing protein tyrosine phosphatase-2 (SHP-2) in cardiac remodeling after myocardial infarction (MI) and explore the underlying molecular mechanism. MI model was established by ligation of the left anterior descending coronary artery. C57/BL6J mice were randomly administered with 3.0 mg/kg/day PHPS1 (PHPS1-treated group) or normal saline (model group) by intraperitoneal injection. After 4 weeks of infusion, the effects of PHPS1 on cardiac remodeling were evaluated. Echocardiography results showed that PHPS1 treatment aggravated the MI-induced deterioration of cardiac function, with worse cardiac function parameters. PHPS1 treatment significantly increased the infarcted area, as well as the fibrotic area and the expression of collagen I and collagen III. Western blots and immunofluorescence staining showed that PHPS1 treatment up-regulated the expression of p-GRK2, p-SMAD2/3 and p-ERK1/2, while U0126 reversed the effect of PHPS1. The present study indicated that PHPS1 treatment contributed to myocardial fibrosis and infarction by activating ERK/SMAD signaling pathway, suggesting that SHP-2 may be a promising treatment target for cardiac remodeling after MI.

Structural Understanding of Interleukin 6 Family Cytokine Signaling and Targeted Therapies: Focus on Interleukin 11

Cytokines are small signaling proteins that have central roles in inflammation and cell survival. In the half-century since the discovery of the first cytokines, the interferons, over fifty cytokines have been identified. Amongst these is interleukin (IL)-6, the first and prototypical member of the IL-6 family of cytokines, nearly all of which utilize the common signaling receptor, gp130. In the last decade, there have been numerous advances in our understanding of the structural mechanisms of IL-6 family signaling, particularly for IL-6 itself. However, our understanding of the detailed structural mechanisms underlying signaling by most IL-6 family members remains limited. With the emergence of new roles for IL-6 family cytokines in disease and, in particular, roles of IL-11 in cardiovascular disease, lung disease, and cancer, there is an emerging need to develop therapeutics that can progress to clinical use. Here we outline our current knowledge of the structural mechanism of signaling by the IL-6 family of cytokines. We discuss how this knowledge allows us to understand the mechanism of action of currently available inhibitors targeting IL-6 family cytokine signaling, and most importantly how it allows for improved opportunities to pharmacologically disrupt cytokine signaling. We focus specifically on the need to develop and understand inhibitors that disrupt IL-11 signaling.

Receptor signaling, transcriptional, and metabolic regulation of T cell exhaustion

Exhaustion cripples T cell effector responses against metastatic cancers and chronic infections alike. There has been considerable interest in understanding the molecular and cellular mechanisms driving T cell exhaustion in human cancers fueled by the success of immunotherapy drugs especially the checkpoint receptor blockade (CRB) inhibitory antibodies that reverses T cell functional exhaustion. The current understanding of molecular mechanism of T cell exhaustion has been elucidated from the studies utilizing murine models of chronic viral infections. These studies have formed the basis for much of our understanding of the process of exhaustion and proven vital to developing anti-exhaustion therapies against human cancers. In this review, we discuss the T cell exhaustion differentiation pathway in cancers and chronic viral infections and explore how the transcription factors expression dynamics play role in T cell exhaustion fate choices and maturation. Finally, we summarize the role of some of the most important transcription factors involved in T cell functional exhaustion and construct exhaustion specific signaling pathway maps.

The glucocorticoids prednisone and dexamethasone differentially modulate T cell function in response to anti-PD-1 and anti-CTLA-4 immune checkpoint blockade

On-treatment steroids for countering immune checkpoint inhibitor-induced inflammatory responses (irAEs) are a hallmark of cancer immunotherapy. However, the suppressive nature of steroids has raised questions regarding their ability to compromise the function of the 'proliferative burst' of effector T cells induced by immune checkpoint antibodies. We investigated the effector functions and the co-inhibitory receptor profile of stimulated peripheral blood mononuclear cells (PBMCs) pre-treated with prednisone and dexamethasone alone or in the presence of anti-PD-1/CTLA-4 antibodies. Also, clinical analysis of a patient who exhibited irAEs following combination (anti-PD-1/CTLA-4) in the presence of glucocorticoids was done. We found that prednisone in contrast to dexamethasone did not compromise T cell cytokine production (IL-2, IFN-γ and TNF-α) and proliferation in the absence or presence of anti-PD-1/CTLA-4 antibodies, when a physiological concentration was used. Neither single prednisone treatment nor co-treatment with checkpoint inhibitors impacted the expression of co-inhibitory receptors PD-1, CTLA-4, TIM-3 and LAG-3. In contrast, dexamethasone treatment promoted downregulation of LAG-3 expression by T cells. In addition, co-treatment of PD-1 + Jurkat cells with prednisone and/or dexamethasone with anti-PD-1 before stimulation significantly reduced SHP-2 phosphorylation, indicative of increased T cell function. Our findings hereby demonstrate a differential steroid effect on T cell function, which should be taken into consideration for patients undergoing immunotherapy. Also, the clinical analysis of a patient who exhibited irAEs following combination (anti-PD-1/CTLA-4) therapy indicated complete metabolic response in the presence of glucocorticoids. Therefore, concomitant use of prednisone does not appear to interfere with the function of immune checkpoint blockade.

RPTPε promotes M2-polarized macrophage migration through ROCK2 signaling and podosome formation

Cysteinyl-leukotrienes (cys-LTs) have well-characterized physiopathological roles in the development of inflammatory diseases. We have previously found that protein tyrosine phosphatase ε (PTPε) is a signaling partner of CysLT₁R, a high affinity receptor for leukotriene D4 (LTD₄). There are two major isoforms of PTPε, receptor-like (RPTPε) and cytoplasmic (cyt-)PTPε, both of which are encoded by the PTPRE gene but from different promoters. In most cells, their expression is mutually exclusive, except in human primary monocytes, which express both isoforms. Here, we show differential PTPε isoform expression patterns between monocytes, M1 and M2 human monocyte-derived macrophages (hMDMs), with the expression of glycosylated forms of RPTPε predominantly in M2-polarized hMDMs. Using PTPε-specific siRNAs and expression of RPTPε and cyt-PTPε, we found that RPTPε is involved in monocyte adhesion and migration of M2-polarized hMDMs in response to LTD₄ Altered organization of podosomes and higher phosphorylation of the inhibitory Y-722 residue of ROCK2 was also found in PTPε-siRNA-transfected cells. In conclusion, we show that differentiation and polarization of monocytes into M2-polarized hMDMs modulates the expression of PTPε isoforms and RPTPε is involved in podosome distribution, ROCK2 activation and migration in response to LTD₄.

Targeting SHP2 as a promising strategy for cancer immunotherapy

Src homology-2-containing protein tyrosine phosphatase 2 (SHP2) is a major phosphatase involved in several cellular processes. In recent years, SHP2 has been the focus of significant attention in human diseases, particular in cancer. Several studies have shown that SHP2 plays an important role in regulating immune cell functions in tumor microenvironment. A few clinical trials conducted using SHP2 allosteric inhibitors have shown remarkable anti-tumor benefits and good safety profiles. This review focuses on the current understanding of the regulation of SHP2 and highlights the vital roles of SHP2 in T lymphocytes, macrophages and cancer cells. It also summarizes the current development of SHP2 inhibitors as a promising strategy for cancer immunotherapy.

SHP-2 in Lymphocytes' Cytokine and Inhibitory Receptor Signaling

Somewhat counterintuitively, the tyrosine phosphatase SHP-2 (SH2 domain-containing protein tyrosine phosphatase-2) is crucial for the activation of extracellular signal-regulated kinase (ERK) downstream of various growth factor receptors, thereby exerting essential developmental functions. This phosphatase also deploys proto-oncogenic functions and specific inhibitors have recently been developed. With respect to the immune system, the role of SHP-2 in the signaling of cytokines relevant for myelopoiesis and myeloid malignancies has been intensively studied. The function of this phosphatase downstream of cytokines important for lymphocytes is less understood, though multiple lines of evidence suggest its importance. In addition, SHP-2 has been proposed to mediate the suppressive effects of inhibitory receptors (IRs) that sustain a dysfunctional state in anticancer T cells. Molecules involved in IR signaling are of potential pharmaceutical interest as blockade of these inhibitory circuits leads to remarkable clinical benefit. Here, we discuss the dichotomy in the functions ascribed to SHP-2 downstream of cytokine receptors and IRs, with a focus on T and NK lymphocytes. Further, we highlight the importance of broadening our understanding of SHP-2′s relevance in lymphocytes, an essential step to inform on side effects and unanticipated benefits of its therapeutic blockade.

Opportunities and challenges for the development of covalent chemical immunomodulators

Compounds that react irreversibly with cysteines have reemerged as potent and selective tools for altering protein function, serving as chemical probes and even clinically approved drugs. The exquisite sensitivity of human immune cell signaling pathways to oxidative stress indicates the likely, yet still underexploited, general utility of covalent probes for selective chemical immunomodulation. Here, we provide an overview of immunomodulatory cysteines, including identification of electrophilic compounds available to label these residues. We focus our discussion on three protein classes essential for cell signaling, which span the 'druggability' spectrum from amenable to chemical probes (kinases), somewhat druggable (proteases), to inaccessible (phosphatases). Using existing inhibitors as a guide, we identify general strategies to guide the development of covalent probes for selected undruggable classes of proteins and propose the application of such compounds to alter immune cell functions.

SHP2 inhibition triggers anti-tumor immunity and synergizes with PD-1 blockade

Tyrosine phosphatase SHP2 is a promising drug target in cancer immunotherapy due to its bidirectional role in both tumor growth promotion and T-cell inactivation. Its allosteric inhibitor SHP099 is known to inhibit cancer cell growth both in vitro and in vivo. However, whether SHP099-mediated SHP2 inhibition retards tumor growth in vivo via anti-tumor immunity remains elusive. To address this, a CT-26 colon cancer xenograft model was established in mice since this cell line is insensitive to SHP099. Consequently, SHP099 minimally affected CT-26 tumor growth in immuno-deficient nude mice, but significantly decreased the tumor burden in CT-26 tumor-bearing mice with intact immune system. SHP099 augmented anti-tumor immunity, as shown by the elevated proportion of CD8⁺IFN-γ⁺ T cells and the upregulation of cytotoxic T-cell related genes including Granzyme B andPerforin, which decreased the tumor load. In addition, tumor growth in mice with SHP2-deficient T-cells was markedly slowed down because of enhanced anti-tumor responses. Finally, the combination of SHP099 and anti-PD-1 antibody showed a higher therapeutic efficacy than either monotherapy in controlling tumor growth in two colon cancer xenograft models, indicating that these agents complement each other. Our study suggests that SHP2 inhibitor SHP099 is a promising candidate drug for cancer immunotherapy.

System network analysis of genomics and transcriptomics data identified type 1 diabetes-associated pathway and genes

Genome-wide association studies (GWASs) have discovered >50 risk loci for type 1 diabetes (T1D). However, those variations only have modest effects on the genetic risk of T1D. In recent years, accumulated studies have suggested that gene-gene interactions might explain part of the missing heritability. The purpose of our research was to identify potential and novel risk genes for T1D by systematically considering the gene-gene interactions through network analyses. We carried out a novel system network analysis of summary GWAS statistics jointly with transcriptomic gene expression data to identify some of the missing heritability for T1D using weighted gene co-expression network analysis (WGCNA). Using WGCNA, seven modules for 1852 nominally significant (P ≤ 0.05) GWAS genes were identified by analyzing microarray data for gene expression profile. One module (tagged as green module) showed significant association (P ≤ 0.05) between the module eigengenes and the trait. This module also displayed a high correlation (r = 0.45, P ≤ 0.05) between module membership (MM) and gene significant (GS), which indicated that the green module of co-expressed genes is of significant biological importance for T1D status. By further describing the module content and topology, the green module revealed a significant enrichment in the "regulation of immune response" (GO:0050776), which is a crucially important pathway in T1D development. Our findings demonstrated a module and several core genes that act as essential components in the etiology of T1D possibly via the regulation of immune response, which may enhance our fundamental knowledge of the underlying molecular mechanisms for T1D.

SHP2 associates with nuclear localization of STAT3: significance in progression and prognosis of colorectal cancer

Tyrosine phosphatase SHP2, encoded by PTPN11, has been implicated in many physiologic and pathologic processes in neoplastic progression. However, controversies are emerging from many studies, indicating SHP2 has a dual role in different types of tumors. We aimed to explore the role of SHP2 in progression and prognosis of colorectal cancer (CRC). SHP2 inhibited CRC cell proliferation and migration, and the phosphorylation of STAT3 was negatively regulated by SHP2 in CRC. SHP2 and nuclear STAT3 were examined in 270 CRC tissues. SHP2 was significantly correlated with nuclear STAT3 (Spearman’s rho = −0.408, P ≤ 0.001). Based on Cox regression analysis, patients with high levels of SHP2 and low levels of nuclear STAT3 had longer disease-specific survival (DSS) (HR, 0.362; 95% CI, 0.165–0.794) and disease-free survival (DFS) (HR, 0.447; 95% CI, 0.227–0.877). Further, low levels of SHP2 and high levels of nuclear STAT3 were independently associated with adverse outcomes in the whole cohort (DFS; HR, 2.353; 95% CI, 1.199–4.619). These results suggest that combination of SHP2 and nuclear STAT3 is a strong prognostic predictor in CRC.

Atorvastatin downregulates co-inhibitory receptor expression by targeting Ras-activated mTOR signalling

Regulation of T cell function in the steady state is mediated by co-inhibitory receptors or immune checkpoints such as PD-1, CTLA-4, TIM-3 and LAG-3. Persistent antigen stimulation, during chronic viral infections and cancer, results in sustained expression of multiple co-inhibitory receptors and subsequently poor effector T cell function. Immune checkpoint blockade using monoclonal antibodies against PD-1, PDL-1 and CTLA-4 has been implemented as an immunotherapy strategy- resulting in restoration of T cell function and reduction of viral load or tumour growth. Immunomodulatory roles of commonly used cholesterol-lowering medications, atorvastatin and other statins, are widely documented. We have previously shown that atorvastatin can inhibit HIV-1 infection and replication. Here, for the very first time we discovered that atorvastatin also regulates activated T cell function by mediating downregulation of multiple co-inhibitory receptors, which corresponded with increased IL-2 production by stimulated T cells. In addition, we found that atorvastatin treatment reduces expression of mTOR and downstream T cell effector genes. We demonstrate a novel mechanism showing that atorvastatin inhibition of Ras-activated MAPK and PI3K-Akt pathways, and subsequent mTOR signalling promotes gross downregulation of co-inhibitory receptors. Thus, our results suggest that statins may hold particular promise in reinvigorating T cell function in chronic conditions.

Stress-induced dynamic regulation of mitochondrial STAT3 and its association with cyclophilin D reduce mitochondrial ROS production

Signal transducer and activator of transcription 3 (STAT3) is associated with various physiological and pathological functions, mainly as a transcription factor that translocates to the nucleus upon tyrosine phosphorylation induced by cytokine stimulation. In addition, a small pool of STAT3 resides in the mitochondria, where it serves as a sensor for various metabolic stressors including reactive oxygen species (ROS). Mitochondrially localized STAT3 largely exerts its effects through direct or indirect regulation of the activity of the electron transport chain (ETC). It has been assumed that the amounts of STAT3 in the mitochondria are static. We showed that various stimuli, including oxidative stress and cytokines, triggered a signaling cascade that resulted in a rapid loss of mitochondrially localized STAT3. Recovery of the mitochondrial pool of STAT3 over time depended on phosphorylation of Ser727 in STAT3 and new protein synthesis. Under these conditions, mitochondrially localized STAT3 also became competent to bind to cyclophilin D (CypD). Binding of STAT3 to CypD was mediated by the amino terminus of STAT3, which was also important for reducing mitochondrial ROS production after oxidative stress. These results outline a role for mitochondrially localized STAT3 in sensing and responding to external stimuli.

Protein-protein interaction between caveolin-1 and SHP-2 is dependent on the N-SH2 domain of SHP-2

Src homology 2-containing protein tyrosine phosphatase 2 (SHP-2) is known to protect neurons from neurodegeneration during ischemia/reperfusion injury. We recently reported that ROS-mediated oxidative stress promotes phosphorylation of endogenous SHP-2 in astrocytes and complex formation between caveolin-1 and SHP-2 in response to oxidative stress. To examine the region of SHP-2 participating in complex formation with caveolin-1, we generated three deletion mutant constructs and six point mutation constructs of SHP-2. Compared with wild-type SHP-2, binding of the N-SH2 domain deletion mutant of SHP-2 to p-caveolin-1 was reduced greatly, using flow cytometric competitive binding assays and surface plasmon resonance (SPR). Moreover, deletion of the N-SH2 domain of SHP-2 affected H2O2-mediated ERK phosphorylation and Src phosphorylation at Tyr 419 in primary astrocytes, suggesting that N-SH2 domain of SHP-2 is responsible for the binding of caveolin-1 and contributes to the regulation of Src phosphorylation and activation following ROS-induced oxidative stress in brain astrocytes.

Critical role of SHP2 (PTPN11) signaling in germinal center-derived lymphoma

Germinal center lymphoma is a heterogeneous human lymphoma entity. Here we report that constitutive activity of SHP2 (PTPN11) and its downstream kinase ERK is essential for the viability of germinal center lymphoma cells and disease progression. Mechanistically, SHP2/ERK inhibition impedes c-Myc transcriptional activity, which results in the repression of proliferative phenotype signatures of germinal center lymphoma. Furthermore, SHP2/ERK signaling is required to maintain the CD19/c-Myc loop, which preferentially promotes survival of a distinct subtype of germinal center lymphoma cells carrying the MYC/IGH translocation. These findings demonstrate a critical function for SHP2/ERK signaling upstream of c-Myc in germinal center lymphoma cells and provide a rationale for targeting SHP2 in the therapy of germinal center lymphoma.

SHP-2 binds to caveolin-1 and regulates Src activity via competitive inhibition of CSK in response to H2O2 in astrocytes

Reactive oxygen species (ROS) regulate diverse cellular functions by triggering signal transduction events, such as Src and mitogen-activated protein (MAP) kinases. Here, we report the role of caveolin-1 and Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP-2) in H₂O₂-induced signaling pathway in brain astrocytes. H₂O₂-mediated oxidative stress induced phosphorylation of caveolin-1 and association between p-caveolin-1 and SHP-2. SHP-2 specifically bound to wild-type caveolin-1 similarly to c-Src tyrosine kinase (CSK), but not to phosphorylation-deficient mutant of caveolin-1 (Y14A), and interfered with complex formation between caveolin-1 and CSK. In the presence of CSK siRNA, binding between caveolin-1 and SHP-2 was enhanced by H₂O₂ treatment, which led to reduced Src phosphorylation at tyrosine (Tyr) 530 and enhanced Src phosphorylation at Tyr 419. In contrast, siRNA targeting of SHP-2 facilitated H₂O₂-mediated interaction between caveolin-1 and CSK and enhanced Src phosphorylation at Tyr 530, leading to subsequent decrease in Src downstream signaling, such as focal adhesion kinase (FAK) and extracellular signal-related kinase (ERK). Our results collectively indicate that SHP-2 alters Src kinase activity by interfering with the complex formation between CSK and phosphotyrosine caveolin-1 in the presence of H₂O₂, thus functions as a positive regulator in Src signaling under oxidative stress in brain astrocytes.

Loss of SHP-2 activity in CD4+ T cells promotes melanoma progression and metastasis

The Src homology 2 domain-containing tyrosine phosphatase 2 (SHP-2) has been reported to have both tumor-promoting and tumor-suppressing roles in tumorigenesis. However, the role of SHP-2 in tumor immunity remains unclear. Here we observed progressively lower levels of phosphorylated SHP-2 in tumor-associated CD4⁺ T cells during melanoma development in a murine model. Similarly, the levels of phosphorylated SHP-2 in the CD4⁺ T cells of human melanoma specimens revealed a decrease paralleling cancer development. The CD4⁺ T cell-specific deletion of SHP-2 promoted melanoma metastasis in mice. Furthermore, SHP-2 deficiency in CD4⁺ T cells resulted in the increased release of inflammatory cytokines, especially IL-6, and the enhanced accumulation of tumor-promoting myeloid-derived suppressor cells (MDSCs) in tumor-bearing mice. An IL-6-neutralizing antibody reduced MDSC accumulation and inhibited tumor growth in CD4⁺ T-cell-specific SHP-2-knockout mice. Our results suggest that SHP-2 in CD4⁺ T cells plays an important role in preventing melanoma progression and metastasis.

SHP-2 phosphatase promotes cervical cancer cell proliferation through inhibiting interferon-β production

AIM

The aim of this study was to explore the effect of Src-homology-2-domain-containing protein, tyrosine phosphatase 2 (SHP-2) on the proliferation of cervical cancer cells.

MATERIAL AND METHODS

A total of 45 patients with cervical cancer (stage I-III), 32 with cervical intraepithelial neoplasia and 20 healthy subjects were consecutively recruited. The levels of SHP-2 and interferon (IFN)-β expression in cervical tissues were characterized by immunohistochemistry and statistically analyzed by logistic regression. Following knockdown of SHP-2 expression by a siRNA or pre-treatment with a specific peptide, the effect of SHP-2 expression in THP-1 cells on the growth and survival of SiHa cells and on IFN-β production was determined by co-culture assays, 3-(4,5)-dimethylthiazol (-z-y 1)-3,5-diphenyltetrazolium bromide, and enzyme immunosorbent assay.

RESULTS

The levels of SHP-2 expression in cervical cancer tissues were significantly higher than that in cervical intraepithelial neoplasia and uterine myoma tissues (P<0.05, respectively), and negatively correlated with the levels of IFN-β expression in these tissues (R=-0.582, P<0.05). Knockdown of SHP-2 expression with SHP-2 siRNA or treatment with the SHP-2-specific blocking peptide in THP-1 cells significantly increased the production of IFN-β (P<0.05, respectively) and inhibited the proliferation of SiHa cells in a co-culture system of THP-1 and SiHa cells (P<0.05, respectively).

CONCLUSIONS

SHP-2 phosphatase promotes cervical cancer cell proliferation through inhibiting IFN-β production.

Crystal structure of human protein tyrosine phosphatase SHP-1 in the open conformation

SHP-1 belongs to the family of non-receptor protein tyrosine phosphatases (PTPs) and generally acts as a negative regulator in a variety of cellular signaling pathways. Previously, the crystal structures of the tail-truncated SHP-1 and SHP-2 revealed an autoinhibitory conformation. To understand the regulatory mechanism of SHP-1, we have determined the crystal structure of the full-length SHP-1 at 3.1 Å. Although the tail was disordered in current structure, the huge conformational rearrangement of the N-SH2 domain and the incorporation of sulfate ions into the ligand-binding site of each domain indicate that the SHP-1 is in the open conformation. The N-SH2 domain in current structure is shifted away from the active site of the PTP domain to the other side of the C-SH2 domain, resulting in exposure of the active site. Meanwhile, the C-SH2 domain is twisted anticlockwise by about 110°. In addition, a set of new interactions between two SH2 domains and between the N-SH2 and the catalytic domains is identified, which could be responsible for the stabilization of SHP-1 in the open conformation. Based on the structural comparison, a model for the activation of SHP-1 is proposed.

CD31 is required on CD4+ T cells to promote T cell survival during Salmonella infection

Hematopoietic cells constitutively express CD31/PECAM1, a signaling adhesion receptor associated with controlling responses to inflammatory stimuli. Although expressed on CD4(+) T cells, its function on these cells is unclear. To address this, we have used a model of systemic Salmonella infection that induces high levels of T cell activation and depends on CD4(+) T cells for resolution. Infection of CD31-deficient (CD31KO) mice demonstrates that these mice fail to control infection effectively. During infection, CD31KO mice have diminished numbers of total CD4(+) T cells and IFN-γ-secreting Th1 cells. This is despite a higher proportion of CD31KO CD4(+) T cells exhibiting an activated phenotype and an undiminished capacity to prime normally and polarize to Th1. Reduced numbers of T cells reflected the increased propensity of naive and activated CD31KO T cells to undergo apoptosis postinfection compared with wild-type T cells. Using adoptive transfer experiments, we show that loss of CD31 on CD4(+) T cells alone is sufficient to account for the defective CD31KO T cell accumulation. These data are consistent with CD31 helping to control T cell activation, because in its absence, T cells have a greater propensity to become activated, resulting in increased susceptibility to become apoptotic. The impact of CD31 loss on T cell homeostasis becomes most pronounced during severe, inflammatory, and immunological stresses such as those caused by systemic Salmonella infection. This identifies a novel role for CD31 in regulating CD4 T cell homeostasis.

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.

The CagA protein of Helicobacter pylori suppresses the functions of dendritic cell in mice

CagA protein is the most assessed effecter molecule of Helicobacter pylori. In this report, we demonstrate how CagA protein regulates the functions of dendritic cells (DC) against H. pylori infection. In addition, we found that CagA protein was tyrosine-phosphorylated in DC. The responses to cagA-positive H. pylori in DC were reduced in comparison to those induced by cagA-negative H. pylori. CagA-overexpressing DC also exhibited a decline in the responses against LPS stimulation and the differentiation of CD4(+) T cells toward Th1 type cells compared to wild type DC. In addition, the level of phosphorylated IRF3 decreased in CagA-overexpressing DC stimulated with LPS, indicating that activated SHP-2 suppressed the enzymatic activity of TBK1 and consequently IRF3 phosphorylation. These data suggest that CagA protein negatively regulates the functions of DC via CagA phosphorylation and that cagA-positive H. pylori strains suppress host immune responses resulting in their chronic colonization of the stomach.

Siglec-E is up-regulated and phosphorylated following lipopolysaccharide stimulation in order to limit TLR-driven cytokine production

Although production of cytokines by TLR is essential for viral and bacterial clearance, overproduction can be detrimental, thus controlling these responses is essential. CD33-related sialic acid binding Ig-like lectin receptors (Siglecs) have been implicated in the control of leukocyte responses. In this study, we report that murine Siglec-E is induced by TLRs in a MyD88-specific manner, is tyrosine phosphorylated following LPS stimulation, and negatively regulates TLR responses. Specifically, we demonstrate the Siglec-E expression inhibits TLR-induced NF-kappaB and more importantly, the induction of the antiviral cytokines IFN-beta and RANTES. Siglec-E mediates its inhibitory effects on TIR domain containing adaptor inducing IFN-beta (TRIF)-dependent cytokine production via recruitment of the tyrosine [corrected] phosphatase SHP2 and subsequent inhibition of TBK1 activity as evidenced by enhanced TBK1 phosphorylation in cells following knockdown of Siglec-E expression. Taken together, our results demonstrate a novel role for Siglec-E in controlling the antiviral response to TLRs and thus helping to maintain a healthy cytokine balance following infection.

Expression and purification of 15N-labeled 2-SH2 protein domain of SHP-2 from Homo sapiens in Escherichia coli for NMR studies and applications

A method for 2-SH2 protein domain study was described as per the order of expression, purification and structural detection. The 2-SH2 protein of Homo sapiens SHP-2 was successfully expressed and purified. It could specifically bind to anti-SHP-2/SHPTP-2 antibody according to the MS and Western blot analysis. The NMR spectrum result reveals that the protein exists in a well-ordered structure. This can provide foundations to find out the reaction mechanism of the D phosphorylated-EPIYA motif accessible to 2-SH2, support the research and development of the novel detection chip as well as target inhibition medicine for the future clinical applications.

Negative signaling by inhibitory receptors: the NK cell paradigm

Receptors carrying immunoreceptor tyrosine-based inhibition motifs (ITIMs) in their cytoplasmic tail control a vast array of cellular responses, ranging from autoimmunity, allergy, phagocytosis of red blood cells, graft versus host disease, to even neuronal plasticity in the brain. The inhibitory function of many receptors has been deduced on the basis of cytoplasmic ITIM sequences. Tight regulation of natural killer (NK) cell cytotoxicity and cytokine production by inhibitory receptors specific for major histocompatibility complex class I molecules has served as a model system to study the negative signaling pathway triggered by an ITIM-containing receptor in the physiological context of NK-target cell interactions. Advances in our understanding of the molecular details of inhibitory signaling in NK cells have provided a conceptual framework to address how ITIM-mediated regulation controls cellular reactivity in diverse cell types.

G-CSF stimulates Jak2-dependent Gab2 phosphorylation leading to Erk1/2 activation and cell proliferation

Granulocyte colony-stimulating factor (G-CSF), the major cytokine regulator of neutrophilic granulopoiesis, stimulates both the proliferation and differentiation of myeloid precursors. A variety of signaling proteins have been identified as mediators of G-CSF signaling, but understanding of their specific interactions and organization into signaling pathways for particular cellular effects is incomplete. The present study examined the role of the scaffolding protein Grb2-associated binding protein-2 (Gab2) in G-CSF signaling. We found that a chemical inhibitor of Janus kinases inhibited G-CSF-stimulated Gab2 phosphorylation. Transfection with Jak2 antisense and dominant negative constructs also inhibited Gab2 phosphorylation in response to G-CSF. In addition, G-CSF enhanced the association of Jak2 with Gab2. In vitro, activated Jak2 directly phosphorylated specific Gab2 tyrosine residues. Mutagenesis studies revealed that Gab2 tyrosine 643 (Y643) was a major target of Jak2 in vitro, and a key residue for Jak2-dependent phosphorylation in intact cells. Mutation of Gab2 Y643 inhibited G-CSF-stimulated Erk1/2 activation and Shp2 binding to Gab2. Loss of Y643 also inhibited Gab2-mediated G-CSF-stimulated cell proliferation. Together, these results identify a novel signaling pathway involving Jak2-dependent Gab2 phosphorylation leading to Erk1/2 activation and cell proliferation in response to G-CSF.

A novel VIP signaling pathway in T cells cAMP-->protein tyrosine phosphatase (SHP-2?)-->JAK2/STAT4-->Th1 differentiation

Vasoactive intestinal peptide (VIP) is a potent anti-inflammatory agent. In addition to the deactivation of macrophages, dendritic cells, and microglia, VIP shifts the Th1/Th2 balance, promoting the preferential differentiation and survival of Th2 cells, to the detriment of the proinflammatory Th1 effectors. Several mechanisms operate in the Th1/Th2 shift induced by VIP. Here we report on a novel mechanism for the effect of VIP on T cell differentiation, and show that VIP inhibits Th1 differentiation by interfering directly with the IL-12Jak2/STAT4 signaling pathway in T cells. The effect of VIP is cAMP-dependent, and appears to be mediated through the activation of protein tyrosine phosphatases (PTP), with SHP-2 as a potential target. The activation of PTPs represents a novel cAMP-downstream target for the immunomodulatory effects of VIP.

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.

Tyr66 acts as a conformational switch in the closed-to-open transition of the SHP-2 N-SH2-domain phosphotyrosine-peptide binding cleft

Background

The N-terminal SH2 domain (N-SH2) of the non-receptor tyrosine phosphatase SHP-2 is involved both in localization of SHP-2 by recognition of phosphotyrosine (pY) peptides and self-inhibition of SHP-2 phosphatase activity through the formation of a protein – protein interface with the phosphatase domain. Mutations that disrupt this interface break the coupling between pY-peptide binding cleft conformation and self-inhibition, thereby increasing both SHP-2 phosphatase activity and pY-peptide binding affinity, and are associated with the congenital condition Noonan syndrome and various pediatric leukemias. To better characterize the molecular process involved in N-SH2 pY-dependent binding, we have applied explicit-solvent molecular dynamics simulations to study the closed-to-open transition of the N-SH2 pY-peptide binding cleft.

Results

The existence of stable conformations in the left-handed helical and the extended regions of Tyr66 φ/ψ space prevent rapid interconversion of the backbone and create a conformational switch such that Tyr66 in a left-handed helical backbone conformation results in an open cleft and in an extended backbone conformation results in a closed cleft. The stable conformations arise from deep, well-localized free-energy minima in the left-handed helical and extended regions of the Tyr66 φ/ψ map. Changing the Tyr66 backbone conformation from extended to left-handed helical induces a closed-to-open transition in the cleft, and the reverse change in backbone conformation induces the reverse, open-to-closed transition. In the open-cleft state, weak solvent-exposed interactions involving the sidechains of Tyr66, Asp40, Lys55, and Gln57 serve to anchor the Tyr66 sidechain to the surface of the protein and away from the binding cleft entrance, thereby facilitating pY-peptide access to the binding cleft.

Conclusion

The simulations point to a regulatory role for Tyr66 and surrounding residues in SHP-2 function: mutations at Tyr66, Asp40, Lys55, and/or Gln57 are predicted to break the switching mechanism and negatively impact pY-peptide binding. This in turn would interfere with cellular localization and the coupled SHP-2 phosphatase activity. The structurally well-defined binding cleft conformations resulting from the switch-like transition suggest the possibility of applying structure-based methods to develop inhibitors of N-SH2 pY-peptide binding to serve as research tools for signal transduction and precursors to therapeutics for SHP-2-related diseases.

FcRL6, a new ITIM-bearing receptor on cytolytic cells, is broadly expressed by lymphocytes following HIV-1 infection

Fc receptor–like proteins (FcRLs) are a growing family of molecules homologous to FcγRI. Whereas all 7 previously reported Fc receptor homologs are expressed by B cells, here we report a new receptor, FcRL6, that is expressed by cytolytic cells including natural killer (NK) cells and effector and effector-memory CD8+ T cells. FcRL6 contains a novel cytoplasmic cysteine-rich motif and recruits SHP-2 through a phosphorylated ITIM, indicating a potential signaling function in effector lymphocytes. In vitro, FcRL6 does not greatly influence NK-cell or CD8+ T-cell–mediated cytotoxicity and has minimal impact on cytokine secretion. However, FcRL6 expression among T lymphocytes is greatly expanded in human immunodeficiency virus type 1 (HIV-1)–infected individuals, and includes not only effector and effector-memory CD8+ T cells but also populations of CD4+ T cells. Expansion of FcRL6-positive lymphocytes is not related to viral load, but is indicative of the dysregulated expansion of terminally differentiated effector lymphocyte populations in response to chronic HIV-1 infection and may serve as an important marker for chronic immune activation and for tracking the generation of effector cells following immune stimulation.

Protein tyrosine phosphatases: from genes, to function, to disease

The protein tyrosine phosphatase (PTP) superfamily of enzymes functions in a coordinated manner with protein tyrosine kinases to control signalling pathways that underlie a broad spectrum of fundamental physiological processes. In this review, I describe recent breakthroughs in our understanding of the role of the PTPs in the regulation of signal transduction and the aetiology of human disease.