Tyrosine phosphatase MEG2 modulates murine development and platelet and lymphocyte activation through secretory vesicle function

PTPN9 promotes melanoma progression by regulating the ferroptosis pathway

In recent years, there has been a gradual increase in the incidence and mortality rates of melanoma, posing a significant threat to human health and life. Protein tyrosine phosphatases (PTPNs) have been implicated in the progression of various human cancers, including breast, lung, and cervical cancer. To investigate PTPN9 expression in melanoma, impacting the disease's survival and prognosis. Our study, which involved an analysis of The Cancer Genome Atlas database and immunohistochemical staining of pathological sections, identified an upregulation of PTPN9 expression in melanoma, impacting the disease's survival and prognosis. At the cellular level, we investigated the effects of PTPN9 on the proliferation, invasion, and metastasis of A375 and SK-MEL-28 cells. Through various experimental techniques such as Western blot protein detection, electron microscopy, and oil red O staining, we observed that PTPN9 potentially contributes to the development of skin cutaneous melanoma (SKCM) by regulating ferroptosis-related proteins ACSL4, FTH1, and P53, thereby influencing lipid metabolism. The results of this study highlight the unique role of PTPN9 in SKCM and suggest its potential as a biomarker for the disease.

Genetic insights into associations of multisite chronic pain with common diseases and biomarkers using data from the UK Biobank

BACKGROUND

Chronic pain is a common, complex, and challenging condition, for which specialised healthcare is required. We investigated the relationship between multisite chronic pain (MCP) and different disease traits identify safe biomarker interventions that can prevent MCP.

METHODS

Univariable and multivariable Mendelian randomisation (MR) analysis were conducted to investigate associations between MCP and 36 common diseases in the UK Biobank. Subsequently, we estimated the potential effect of expression of 4774 proteins on MCP utilising existing plasma protein quantitative trait locus data. For the significant biomarkers, we performed phenome-wide MR (Phe-MR) with 1658 outcomes to predict potential safety profiles linked to biomarker intervention.

RESULTS

Multisite chronic pain had a substantial impact on psychiatric and neurodevelopmental traits (major depression and attention deficit hyperactivity disorder), cardiovascular diseases (myocardial infarction, coronary artery disease, and heart failure), respiratory outcomes (asthma, chronic obstructive pulmonary disease, and sleep apnoea), arthropathies, type 2 diabetes mellitus, and cholelithiasis. Higher genetically predicted levels of S100A6, DOCK9, ferritin, and ferritin light chain were associated with a risk of MCP, whereas PTN9 and NEUG were linked to decreased MCP risk. Phe-MR results suggested that genetic inhibition of DOCK9 increased the risk of 21 types of disease, whereas the other biomarker interventions were relatively safe.

CONCLUSIONS

We established that MCP has an effect on health conditions covering various physiological systems and identified six novel biomarkers for intervention. In particular, S100A6, PTN9, NEUG, and ferritin light chain represent promising targets for MCP prevention, as no significant side-effects were predicted in our study.

Hereditable variants of classical protein tyrosine phosphatase genes: Will they prove innocent or guilty?

Protein tyrosine phosphatases, together with protein tyrosine kinases, control many molecular signaling steps that control life at cellular and organismal levels. Impairing alterations in the genes encoding the involved proteins is expected to profoundly affect the quality of life-if compatible with life at all. Here, we review the current knowledge on the effects of germline variants that have been reported for genes encoding a subset of the protein tyrosine phosphatase superfamily; that of the thirty seven classical members. The conclusion must be that the newest genome research tools produced an avalanche of data that suggest 'guilt by association' for individual genes to specific disorders. Future research should face the challenge to investigate these accusations thoroughly and convincingly, to reach a mature genotype-phenotype map for this intriguing protein family.

Effect of L3MBTL3/PTPN9 polymorphisms on risk to alcohol-induced ONFH in Chinese Han population

PURPOSE

Alcohol-induced osteonecrosis femoral head necrosis (ONFH) is a disease that seriously affects human health. Abnormal expression of L3MBTL3/PTPN9 gene can cause a variety of human diseases. The purpose of this study is to investigate the effect of L3MBTL3/PTPN9 gene polymorphism on the susceptibility of alcohol-induced ONFH in Chinese Han population.

METHODS

A total of 308 alcohol-induced ONFH patients and 425 healthy controls were enrolled in this case-control study. Alleles, genotypes, genetic models, haplotypes, and multifactor dimensionality reduction analyses (MDR) based on age-corrected by using odds ratio (OR) and 95% confidence interval (CI) were performed.

RESULTS

Our result revealed rs2068957 in the L3MBTL3 gene increased the risk of alcohol ONFH under the recessive model after correction. Besides, we also found that rs75393192 in the PTPN9 gene was a protective site in stratification over 40 years of age and stage. In stratified analysis of necrotic sites, we only found that rs2068957 was associated with increased susceptibility of alcohol-induced ONFH under the co-dominant model and recessive model. Haplotype "GC" in the block (rs76107647|rs10851882 in PTPN9 gene) significantly decreased the susceptibility of alcoholic ONFH.

CONCLUSIONS

Our results provide evidence that L3MBTL3/PTPN9 polymorphisms are associated with alcohol-induced ONFH risk in Chinese Han population.

PTP-MEG2 regulates quantal size and fusion pore opening through two distinct structural bases and substrates

Tyrosine phosphorylation of secretion machinery proteins is a crucial regulatory mechanism for exocytosis. However, the participation of protein tyrosine phosphatases (PTPs) in different exocytosis stages has not been defined. Here we demonstrate that PTP-MEG2 controls multiple steps of catecholamine secretion. Biochemical and crystallographic analyses reveal key residues that govern the interaction between PTP-MEG2 and its substrate, a peptide containing the phosphorylated NSF-pY⁸³ site, specify PTP-MEG2 substrate selectivity, and modulate the fusion of catecholamine-containing vesicles. Unexpectedly, delineation of PTP-MEG2 mutants along with the NSF binding interface reveals that PTP-MEG2 controls the fusion pore opening through NSF independent mechanisms. Utilizing bioinformatics search and biochemical and electrochemical screening approaches, we uncover that PTP-MEG2 regulates the opening and extension of the fusion pore by dephosphorylating the DYNAMIN2-pY¹²⁵ and MUNC18-1-pY¹⁴⁵ sites. Further structural and biochemical analyses confirmed the interaction of PTP-MEG2 with MUNC18-1-pY¹⁴⁵ or DYNAMIN2-pY¹²⁵ through a distinct structural basis compared with that of the NSF-pY⁸³ site. Our studies thus provide mechanistic insights in complex exocytosis processes.

Hippocampal transcriptome-wide association study and neurobiological pathway analysis for Alzheimer's disease

Genome-wide association studies (GWASs) have identified multiple susceptibility loci for Alzheimer’s disease (AD), which is characterized by early and progressive damage to the hippocampus. However, the association of hippocampal gene expression with AD and the underlying neurobiological pathways remain largely unknown. Based on the genomic and transcriptomic data of 111 hippocampal samples and the summary data of two large-scale meta-analyses of GWASs, a transcriptome-wide association study (TWAS) was performed to identify genes with significant associations between hippocampal expression and AD. We identified 54 significantly associated genes using an AD-GWAS meta-analysis of 455,258 individuals; 36 of the genes were confirmed in another AD-GWAS meta-analysis of 63,926 individuals. Fine-mapping models further prioritized 24 AD-related genes whose effects on AD were mediated by hippocampal expression, including APOE and two novel genes (PTPN9 and PCDHA4). These genes are functionally related to amyloid-beta formation, phosphorylation/dephosphorylation, neuronal apoptosis, neurogenesis and telomerase-related processes. By integrating the predicted hippocampal expression and neuroimaging data, we found that the hippocampal expression of QPCTL and ERCC2 showed significant difference between AD patients and cognitively normal elderly individuals as well as correlated with hippocampal volume. Mediation analysis further demonstrated that hippocampal volume mediated the effect of hippocampal gene expression (QPCTL and ERCC2) on AD. This study identifies two novel genes associated with AD by integrating hippocampal gene expression and genome-wide association data and reveals candidate hippocampus-mediated neurobiological pathways from gene expression to AD.

The hippocampus is a potential neuroimaging endophenotype for Alzheimer’s disease (AD). This study identifies genes whose expression in hippocampal tissue is associated with AD and establishes the pathways from hippocampal gene expression to hippocampal volume to AD. We demonstrate that 24 genes are associated with AD in hippocampal tissue, and these genes are enriched for AD-related biological processes of amyloid-beta formation, phosphorylation/dephosphorylation, neuronal apoptosis, neurogenesis and telomerase-related processes. We further show that hippocampal volume mediates the effects of the hippocampal gene expression of QPCTL and ERCC2 on AD. These findings improve our understanding of the genetic and neural mechanisms of AD.

The role of phospho-tyrosine signaling in platelet biology and hemostasis

Platelets are small enucleated cell fragments specialized in the control of hemostasis, but also playing a role in angiogenesis, inflammation and immunity. This plasticity demands a broad range of physiological processes. Platelet functions are mediated through a variety of receptors, the concerted action of which must be tightly regulated, in order to allow specific and timely responses to different stimuli. Protein phosphorylation is one of the main key regulatory mechanisms by which extracellular signals are conveyed. Despite the importance of platelets in health and disease, the molecular pathways underlying the activation of these cells are still under investigation. Here, we review current literature on signaling platelet biology and in particular emphasize the newly emerging role of phosphatases in these processes.

Lipid transfer proteins and instructive regulation of lipid kinase activities: Implications for inositol lipid signaling and disease

Cellular membranes are critical platforms for intracellular signaling that involve complex interfaces between lipids and proteins, and a web of interactions between a multitude of lipid metabolic pathways. Membrane lipids impart structural and functional information in this regulatory circuit that encompass biophysical parameters such as membrane thickness and fluidity, as well as chaperoning the interactions of protein binding partners. Phosphatidylinositol and its phosphorylated derivatives, the phosphoinositides, play key roles in intracellular membrane signaling, and these involvements are translated into an impressively diverse set of biological outcomes. The phosphatidylinositol transfer proteins (PITPs) are key regulators of phosphoinositide signaling. Found in a diverse array of organisms from plants, yeast and apicomplexan parasites to mammals, PITPs were initially proposed to be simple transporters of lipids between intracellular membranes. It now appears increasingly unlikely that the soluble versions of these proteins perform such functions within the cell. Rather, these serve to facilitate the activity of intrinsically biologically insufficient inositol lipid kinases and, in so doing, promote diversification of the biological outcomes of phosphoinositide signaling. The central engine for execution of such functions is the lipid exchange cycle that is a fundamental property of PITPs. How PITPs execute lipid exchange remains very poorly understood. Molecular dynamics simulation approaches are now providing the first atomistic insights into how PITPs, and potentially other lipid-exchange/transfer proteins, operate.

PTPN9-mediated dephosphorylation of VTI1B promotes ATG16L1 precursor fusion and autophagosome formation

Macroautophagy/autophagy is an evolutionarily conserved intracellular pathway for the degradation of cytoplasmic materials. Under stress conditions, autophagy is upregulated and double-membrane autophagosomes are formed by the expansion of phagophores. The ATG16L1 precursor fusion contributes to development of phagophore structures and is critical for the biogenesis of autophagosomes. Here, we discovered a novel role of the protein tyrosine phosphatase PTPN9 in the regulation of homotypic ATG16L1 vesicle fusion and early autophagosome formation. Depletion of PTPN9 and its Drosophila homolog Ptpmeg2 impaired autophagosome formation and autophagic flux. PTPN9 colocalized with ATG16L1 and was essential for homotypic fusion of ATG16L1⁺ vesicles during starvation-induced autophagy. We further identified the Q-SNARE VTI1B as a substrate target of PTPN9 phosphatase. Like PTPN9, the VTI1B nonphosphorylatable mutant but not the phosphomimetic mutant enhanced SNARE complex assembly and autophagic flux. Our findings highlight the important role of PTPN9 in the regulation of ATG16L1⁺ autophagosome precursor fusion and autophagosome biogenesis through modulation of VTI1B phosphorylation status.Abbreviations: csw: corkscrew; EBSS: Earle's balanced salt solution; ERGIC: ER-Golgi intermediate compartment; ESCRT: endosomal sorting complexes required for transport; mop: myopic; NSF: N-ethylmaleimide-sensitive factor; PAS: phagophore assembly site; PolyQ: polyglutamine; PtdIns3P: phosphatidylinositol-3-phosphate; PTK: protein tyrosine kinase; PTM: posttranslational modification; PTP: protein tyrosine phosphatase; PTPN23/HD-PTP: protein tyrosine phosphatase non-receptor type 23; SNARE: soluble N-ethylmaleimide sensitive factor attachment protein receptor; STX7: syntaxin 7; STX8: syntaxin 8; STX17: syntaxin 17; VAMP3: vesicle associated membrane protein 3; VAMP7: vesicle associated membrane protein 7; VTI1B: vesicle transport through interaction with t-SNAREs 1B; YKT6: YKT6 v-SNARE homolog; ZFYVE1/DFCP1: zinc finger FYVE-type containing 1.

Coenzyme Q10 attenuates platelet integrin αIIbβ3 signaling and platelet hyper-reactivity in ApoE-deficient mice

CoQ10 supplementation in ApoE^−/− mice attenuates high-fat diet-induced platelet hyper-reactivity via down-regulating platelet αIIbβ3 signaling, and thus protecting against atherothrombosis.

Regulation of CD4+ T Cell Signaling and Immunological Synapse by Protein Tyrosine Phosphatases: Molecular Mechanisms in Autoimmunity

T cell activation and effector function is mediated by the formation of a long-lasting interaction established between T cells and antigen-presenting cells (APCs) called immunological synapse (IS). During T cell activation, different signaling molecules as well as the cytoskeleton and the endosomal compartment are polarized to the IS. This molecular dynamics is tightly regulated by phosphorylation networks, which are controlled by protein tyrosine phosphatases (PTPs). While some PTPs are known to be important regulators of adhesion, ligand discrimination or the stimulation threshold, there is still little information about the regulatory role of PTPs in cytoskeleton rearrangements and endosomal compartment dynamics. Besides, spatial and temporal regulation of PTPs and substrates at the IS is only barely known. Consistent with an important role of PTPs in T cell activation, multiple mutations as well as altered expression levels or dynamic behaviors have been associated with autoimmune diseases. However, the precise mechanism for the regulation of T cell activation and effector function by PTPs in health and autoimmunity is not fully understood. Herein, we review the current knowledge about the regulatory role of PTPs in CD4⁺ T cell activation, IS assembly and effector function. The potential molecular mechanisms mediating the action of these enzymes in autoimmune disorders are discussed.

Heterozygous Meg2 Ablation Causes Intraocular Pressure Elevation and Progressive Glaucomatous Neurodegeneration

Glaucomatous neurodegeneration represents one of the major causes of irreversible blindness worldwide. Yet, the detailed molecular mechanisms that initiate optic nerve damage and retinal ganglion cell (RGC) loss are not fully understood. Members of the protein tyrosine phosphatase (PTP) superfamily are key players in numerous neurodegenerative diseases. In order to investigate the potential functional relevance of the PTP megakaryocyte 2 (Meg2) in retinal neurodegeneration, we analyzed Meg2 knockout (KO) and heterozygous (HET)-synonym protein-tyrosine phosphatase non-receptor type 9 (Ptpn9)-mice. Interestingly, via global microarray and quantitative real-time PCR (RT-qPCR) analyses of Meg2 KO and HET retinae, we observed a dysregulation of several candidate genes that are highly associated with retinal degeneration and intraocular pressure (IOP) elevation, the main risk factor for glaucoma. Subsequent IOP measurements in Meg2 HET mice verified progressive age-dependent IOP elevation. Ultrastructural analyses and immunohistochemistry showed severe optic nerve degeneration accompanied by a dramatic loss of RGCs. Additionally, HET mice displayed reactive micro-/macrogliosis and early activation of the classical complement cascade with pronounced deposition of the membrane attack complex (MAC) in the retina and optic nerve. When treated with latanoprost, significant IOP lowering prevented RGC loss and microglial invasion in HET mice. Finally, electroretinogram (ERG) recordings revealed reduced a- and b-wave amplitudes, indicating impaired retinal functionality in Meg2 HET mice. Collectively, our findings indicate that the heterozygous loss of Meg2 in mice is sufficient to cause IOP elevation and glaucomatous neurodegeneration. Thus, Meg2 HET mice may serve as a novel animal model to study the pathomechanism involved in the onset and progression of glaucoma.

PTPN9 induces cell apoptosis by mitigating the activation of Stat3 and acts as a tumor suppressor in colorectal cancer

Background

Accumulating evidence has shown that protein tyrosine phosphatases (PTPs) are involved in regulating the transduction of many signaling pathways and play important roles in modulating the progression of some cancers, but the functions of PTPs in cancers have not been well elucidated until now. Here, we aimed to identify the roles of protein tyrosine phosphatase nonreceptor type 9 (PTPN9), a cytoplasmic PTP, in the development of colorectal cancer and elucidate the regulatory mechanism involved.

Materials and methods

Cell viability assessment, colony formation assay, caspase-3 and caspase-9 activity assay, real-time PCR, and Western blot analysis were applied.

Results

Our results showed that PTPN9 expression was frequently downregulated in colorectal cancer tissues compared with adjacent normal tissues. Overexpression of PTPN9 mitigated cell growth and colony formation and induced cell apoptosis in colorectal cancer. Conversely, PTPN9 knockdown promoted cell growth and survival. Moreover, PTPN9 negatively regulated the activation of Stat3 and depressed its nuclear translocation in colorectal cancer. The effects of PTPN9 knockdown on cell apoptosis were attenuated by inhibition of the Stat3 pathway.

Conclusion

These results indicate that PTPN9 inhibits cell growth and survival by repressing the activation of Stat3 in colorectal cancer, which suggests an important underlying mechanism of regulating cell growth and provides a novel candidate therapeutic target for colorectal cancer.

MEG2 inhibits the growth and metastasis of hepatocellular carcinoma by inhibiting AKT pathway

MEG2 was recently found to have important functions in human cancers. However, the expression status and biological functions of MEG2 in hepatocellular carcinoma (HCC) remain unknown. In this study, we demonstrated that MEG2 expression was reduced in HCC tissues and cell lines using qRT-PCR, western blot and immunohistochemical staining. Decreased MEG2 expression predicted unfavorable clinical features and decreased overall survival and disease-free survival of HCC patients. In vitro functional assays showed that overexpression of MEG2 inhibited the cell viability, migration and invasion of HCCLM3 cells while MEG2 knockdown promoted these biological functions of Hep3B cells. Subcutaneous injection model and tail vein injection model showed that forced expression of MEG2 in HCCLM3 decreased the growth and lung metastasis of HCCLM3 cells in nude mice. Mechanically, MEG2 inhibited the EMT and AKT phosphorylation of HCC cells. The promoting effects of MEG2 knockdown on EMT, cell viability, proliferation, migration and invasion of Hep3B cells was blocked by AKT phosphorylation inhibition. In all, this study demonstrates that MEG2 inhibits the growth and metastasis of hepatocellular carcinoma by inhibiting AKT pathway.

Protein Tyrosine Phosphatases as Potential Regulators of STAT3 Signaling

The signal transducer and activator of transcription 3 (STAT3) protein is a major transcription factor involved in many cellular processes, such as cell growth and proliferation, differentiation, migration, and cell death or cell apoptosis. It is activated in response to a variety of extracellular stimuli including cytokines and growth factors. The aberrant activation of STAT3 contributes to several human diseases, particularly cancer. Consequently, STAT3-mediated signaling continues to be extensively studied in order to identify potential targets for the development of new and more effective clinical therapeutics. STAT3 activation can be regulated, either positively or negatively, by different posttranslational mechanisms including serine or tyrosine phosphorylation/dephosphorylation, acetylation, or demethylation. One of the major mechanisms that negatively regulates STAT3 activation is dephosphorylation of the tyrosine residue essential for its activation by protein tyrosine phosphatases (PTPs). There are seven PTPs that have been shown to dephosphorylate STAT3 and, thereby, regulate STAT3 signaling: PTP receptor-type D (PTPRD), PTP receptor-type T (PTPRT), PTP receptor-type K (PTPRK), Src homology region 2 (SH-2) domain-containing phosphatase 1(SHP1), SH-2 domain-containing phosphatase 2 (SHP2), MEG2/PTP non-receptor type 9 (PTPN9), and T-cell PTP (TC-PTP)/PTP non-receptor type 2 (PTPN2). These regulators have great potential as targets for the development of more effective therapies against human disease, including cancer.

GPIbα is required for platelet-mediated hepatic thrombopoietin generation

Thrombopoietin (TPO), a hematopoietic growth factor produced predominantly by the liver, is essential for thrombopoiesis. Prevailing theory posits that circulating TPO levels are maintained through its clearance by platelets and megakaryocytes via surface c-Mpl receptor internalization. Interestingly, we found a two- to threefold decrease in circulating TPO in GPIbα^-/- mice compared with wild-type (WT) controls, which was consistent in GPIbα-deficient human Bernard-Soulier syndrome (BSS) patients. We showed that lower TPO levels in GPIbα-deficient conditions were not due to increased TPO clearance by GPIbα^-/- platelets but rather to decreased hepatic TPO mRNA transcription and production. We found that WT, but not GPIbα^-/-, platelet transfusions rescued hepatic TPO mRNA and circulating TPO levels in GPIbα^-/- mice. In vitro hepatocyte cocultures with platelets or GPIbα-coupled beads further confirm the disruption of platelet-mediated hepatic TPO generation in the absence of GPIbα. Treatment of GPIbα^-/- platelets with neuraminidase caused significant desialylation; however, strikingly, desialylated GPIbα^-/- platelets could not rescue impaired hepatic TPO production in vivo or in vitro, suggesting that GPIbα, independent of platelet desialylation, is a prerequisite for hepatic TPO generation. Additionally, impaired hepatic TPO production was recapitulated in interleukin-4/GPIbα-transgenic mice, as well as with antibodies targeting the extracellular portion of GPIbα, demonstrating that the N terminus of GPIbα is required for platelet-mediated hepatic TPO generation. These findings reveal a novel nonredundant regulatory role for platelets in hepatic TPO homeostasis, which improves our understanding of constitutive TPO regulation and has important implications in diseases related to GPIbα, such as BSS and auto- and alloimmune-mediated thrombocytopenias.

Synthesis, bioactivity, 3D-QSAR studies of novel dibenzofuran derivatives as PTP-MEG2 inhibitors

PTP-MEG2 plays a critical role in the diverse cell signalling processes, so targeting PTP-MEG2 is a promising strategy for various human diseases treatments. In this study, a series of novel dibenzofuran derivatives was synthesized and assayed for their PTP-MEG2 inhibitory activities. 10a with highest inhibitory activity (320 nM) exhibited significant selectivity for PTP-MEG2 over its close homolog SHP2, CDC25 (IC₅₀ > 50 μM). By means of the powerful “HipHop” technique, a 3D-QSAR study was carried out to explore structure activity relationship of these molecules. The generated pharmacophore model revealed that the one RA, three Hyd, and two HBA features play an important role in binding to the active site of the target protein-PTP-MEG2. Docking simulation study indicated that 10a achieved its potency and specificity for PTP-MEG2 by targeting unique nearby peripheral binding pockets and the active site. The absorption, distribution, metabolism and excretion (ADME) predictions showed that the 11 compounds hold high potential to be novel lead compounds for targeting PTP-MEG2. Our findings here can provide a new strategy or useful insights for designing the effective PTP-MEG2 inhibitors.

The Roles of Protein Tyrosine Phosphatases in Hepatocellular Carcinoma

The protein tyrosine phosphatase (PTP) family is involved in multiple cellular functions and plays an important role in various pathological and physiological processes. In many chronic diseases, for example cancer, PTP is a potential therapeutic target for cancer treatment. In the last two decades, dozens of PTP inhibitors which specifically target individual PTP molecules were developed as therapeutic agents. Hepatocellular carcinoma (HCC) is one of the most common malignant tumors and is the second most lethal cancer worldwide due to a lack of effective therapies. Recent studies have unveiled both oncogenic and tumor suppressive functions of PTP in HCC. Here, we review the current knowledge on the involvement of PTP in HCC and further discuss the possibility of targeting PTP in HCC.

Plant-based Food Cyanidin-3-Glucoside Modulates Human Platelet Glycoprotein VI Signaling and Inhibits Platelet Activation and Thrombus Formation

Background: Platelets play an important role in hemostasis, thrombosis, and atherosclerosis. Glycoprotein VI (GPVI) is a major platelet receptor that interacts with exposed collagen on injured vessel walls. Our previous studies have shown that anthocyanins (a type of natural plant pigment) attenuate platelet function; however, whether anthocyanins affect collagen-induced GPVI signaling remains unknown.Objective: The objective of this study was to explore the effects of cyanidin-3-glucoside (Cy-3-g, one of the major bioactive compounds in anthocyanins) on platelet activation and thrombosis and the GPVI signaling pathway.Methods: Platelets from healthy men and women were isolated and incubated with different concentrations (0, 0.5, 5, and 50 μM) of Cy-3-g. The expression of activated integrin αIIbβ3, P-selectin, CD63, and CD40L, fibrinogen binding to platelets, and platelet aggregation were evaluated in vitro. Platelet adhesion and aggregation in whole blood under flow conditions were assessed in collagen-coated perfusion chambers. Thrombosis and hemostasis were assessed in 3-4-wk-old male C57BL/6J mice through FeCl₃-induced intravital microscopy and tail bleeding time. The effect of Cy-3-g on collagen-induced human platelet GPVI signaling was explored with Western blot.Results: Cy-3-g attenuated platelet function in a dose-dependent manner. The 0.5-μM dose of Cy-3-g inhibited (P < 0.05) human platelet adhesion and aggregation to collagen at both venous (-54.02%) and arterial (-22.90%) shear stresses. The 5-μM dose inhibited (P < 0.05) collagen-induced human platelet activation (PAC-1: -48.21%, P-selectin: -50.63%), secretion (CD63: -73.89%, CD40L: -43.70%), fibrinogen binding (-56.79%), and aggregation (-17.81%). The 5-μM dose attenuated (P < 0.01) thrombus growth (-66.67%) without prolonging bleeding time in mice. The 50-μM dose downregulated (P < 0.05) collagen-induced GPVI signaling in human platelets and significantly decreased phosphorylation of Syk-linker for activation of T cells (LAT)-SLP76 (Syk: -39.08%, LAT: -32.25%, SLP76: -40.00%) and the expression of Lyn (-31.89%), Fyn (-36.27%), and phospholipase C-γ2 (-39.08%).Conclusions: Cy-3-g inhibits human platelet activation, aggregation, secretion, and thrombus formation, and downregulates the collagen-GPVI signaling pathway. Supplementation of Cy-3-g may have protective effects against atherothrombosis.

MEG2 is regulated by miR-181a-5p and functions as a tumour suppressor gene to suppress the proliferation and migration of gastric cancer cells

BACKGROUND

Protein-tyrosine phosphatase MEG2 (MEG2) is a classic tyrosine-specific protein tyrosine phosphatase (PTP). It has been reported that MEG2 participates in the carcinogenesis of the breast and liver. However, functions of MEG2 in gastric cancer remain poorly understood.

METHODS

We examined the expression of MEG2 protein by western blotting and that of miR-181a-5p by qRT-PCR. We used bioinformatic analyses to search for miRNAs that potentially target MEG2. We performed a luciferase reporter assay to investigate the interaction between miR-181a-5p and MEG2. In addition, we assessed the effects of MEG2 and miR-181a-5p on gastric cancer cells in vitro and in vivo.

RESULTS

We found that MEG2 is downregulated in human gastric cancer and that miR-181a-5p is predicted to be a potential regulator of MEG2. We also observed that expression of MEG2 is reversely correlated with that of miR-181a-5p in gastric cancer. Moreover, we observed that MEG2 regulation by miR-181a-5p significantly suppresses the proliferation and migration of gastric cancer cells in vitro and decelerates tumour growth in vivo.

CONCLUSIONS

Our results revealed that MEG2 is a tumour suppressor gene and negatively regulated by miR-181a-5p in gastric cancer.

Gene Expression Profiles of Human Phosphotyrosine Phosphatases Consequent to Th1 Polarisation and Effector Function

Phosphotyrosine phosphatases (PTPs) constitute a complex family of enzymes that control the balance of intracellular phosphorylation levels to allow cell responses while avoiding the development of diseases. Despite the relevance of CD4 T cell polarisation and effector function in human autoimmune diseases, the expression profile of PTPs during T helper polarisation and restimulation at inflammatory sites has not been assessed. Here, a systematic analysis of the expression profile of PTPs has been carried out during Th1-polarising conditions and upon PKC activation and intracellular raise of Ca²⁺ in effector cells. Changes in gene expression levels suggest a previously nonnoted regulatory role of several PTPs in Th1 polarisation and effector function. A substantial change in the spatial compartmentalisation of ERK during T cell responses is proposed based on changes in the dose of cytoplasmic and nuclear MAPK phosphatases. Our study also suggests a regulatory role of autoimmune-related PTPs in controlling T helper polarisation in humans. We expect that those PTPs that regulate T helper polarisation will constitute potential targets for intervening CD4 T cell immune responses in order to generate new therapies for the treatment of autoimmune diseases.

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.

The Protein Tyrosine Phosphatase MEG2 Regulates the Transport and Signal Transduction of Tropomyosin Receptor Kinase A

Protein tyrosine phosphatase MEG2 (PTP-MEG2) is a unique nonreceptor tyrosine phosphatase associated with transport vesicles, where it facilitates membrane trafficking by dephosphorylation of the N-ethylmaleimide-sensitive fusion factor. In this study, we identify the neurotrophin receptor TrkA as a novel cargo whose transport to the cell surface requires PTP-MEG2 activity. In addition, TrkA is also a novel substrate of PTP-MEG2, which dephosphorylates both Tyr-490 and Tyr-674/Tyr-675 of TrkA. As a result, overexpression of PTP-MEG2 down-regulates NGF/TrkA signaling and blocks neurite outgrowth and differentiation in PC12 cells and cortical neurons.

Fibronectin maintains the balance between hemostasis and thrombosis

Fibronectin is a dimeric protein widely distributed in solid tissues and blood. This major extracellular matrix protein is indispensable for embryogenesis and plays crucial roles in many physiological and pathological processes. Fibronectin pre-mRNA undergoes alternative splicing to generate over 20 splicing variants, which are categorized as either plasma fibronectin (pFn) or cellular fibronectin (cFn). All fibronectin variants contain integrin binding motifs, as well as N-terminus collagen and fibrin binding motifs. With motifs that can be recognized by platelet integrins and coagulation factors, fibronectin, especially pFn, has long been suspected to be involved in hemostasis and thrombosis, but the exact function of fibronectin in these processes is controversial. The advances made using intravital microscopy models and fibronectin deficient and mutant mice have greatly facilitated the direct investigation of fibronectin function in vivo. Recent studies revealed that pFn is a vital hemostatic factor that is especially crucial for hemostasis in both genetic and anticoagulant-induced deficiencies of fibrin formation. pFn may also be an important self-limiting regulator to prevent hemorrhage as well as excessive thrombus formation and vessel occlusion. In addition to pFn, cFn is found to be prothrombotic and may contribute to thrombotic complications in various diseases. Further investigations of the role of pFn and cFn in thrombotic and hemorrhagic diseases may provide insights into development of novel therapeutic strategies (e.g., pFn transfusion) for the maintenance of the fine balance between hemostasis and thrombosis.

Platelets are versatile cells: New discoveries in hemostasis, thrombosis, immune responses, tumor metastasis and beyond

Platelets are small anucleate blood cells generated from megakaryocytes in the bone marrow and cleared in the reticuloendothelial system. At the site of vascular injury, platelet adhesion, activation and aggregation constitute the first wave of hemostasis. Blood coagulation, which is initiated by the intrinsic or extrinsic coagulation cascades, is the second wave of hemostasis. Activated platelets can also provide negatively-charged surfaces that harbor coagulation factors and markedly potentiate cell-based thrombin generation. Recently, deposition of plasma fibronectin, and likely other plasma proteins, onto the injured vessel wall has been identified as a new "protein wave of hemostasis" that may occur even earlier than the first wave of hemostasis, platelet accumulation. Although no experimental evidence currently exists, it is conceivable that platelets may also contribute to this protein wave of hemostasis by releasing their granule fibronectin and other proteins that may facilitate fibronectin self- and non-self-assembly on the vessel wall. Thus, platelets may contribute to all three waves of hemostasis and are central players in this critical physiological process to prevent bleeding. Low platelet counts in blood caused by enhanced platelet clearance and/or impaired platelet production are usually associated with hemorrhage. Auto- and allo-immune thrombocytopenias such as idiopathic thrombocytopenic purpura and fetal and neonatal alloimmune thrombocytopenia may cause life-threatening bleeding such as intracranial hemorrhage. When triggered under pathological conditions such as rupture of an atherosclerotic plaque, excessive platelet activation and aggregation may result in thrombosis and vessel occlusion. This may lead to myocardial infarction or ischemic stroke, the major causes of mortality and morbidity worldwide. Platelets are also involved in deep vein thrombosis and thromboembolism, another leading cause of mortality. Although fibrinogen has been documented for more than half a century as essential for platelet aggregation, recent studies demonstrated that fibrinogen-independent platelet aggregation occurs in both gene deficient animals and human patients under physiological and pathological conditions (non-anti-coagulated blood). This indicates that other unidentified platelet ligands may play important roles in thrombosis and might be novel antithrombotic targets. In addition to their critical roles in hemostasis and thrombosis, emerging evidence indicates that platelets are versatile cells involved in many other pathophysiological processes such as innate and adaptive immune responses, atherosclerosis, angiogenesis, lymphatic vessel development, liver regeneration and tumor metastasis. This review summarizes the current knowledge of platelet biology, highlights recent advances in the understanding of platelet production and clearance, molecular and cellular events of thrombosis and hemostasis, and introduces the emerging roles of platelets in the immune system, vascular biology and tumorigenesis. The clinical implications of these basic science and translational research findings will also be discussed.

Downregulated Expression of PTPN9 Contributes to Human Hepatocellular Carcinoma Growth and Progression

Human hepatocellular carcinoma (HCC) is one of the most common malignant cancers, whose molecular mechanisms is remains largely. PTPN9 has recently been reported to play a critical role in breast cancer development. However, the role of PTPN9 in human HCC remains elusive. The present study aimed at investigating the potential role of PTPN9 in HCC. Western blot and immunohistochemistry were used to examine the expression of PTPN9 protein in HCC and adjacent non-tumorous tissues in 45 patients. Furthermore, Cell Counting Kit-8, flow cytometry and RNA interference experiments were performed to analyze the role of PTPN9 in the regulation of HCC cell proliferation. We showed that the expression level of PTPN9 was significantly reduced in HCC, compared with adjacent non-tumorous tissues. PTPN9 expression was inversely associated with Tumor size (P = 0.014), serum AFP level (P = 0.004) and Ki-67 expression. Low expression of PTPN9 predicted poor survival in HCC patients. Moreover, PTPN9 interference assay that PTPN9 inhibited cell proliferation in HepG2 cells. Cell apoptosis assay revealed that, silencing of PTPN9 expression significantly reduced cell apoptosis, compared with control ShRNA treatment group. Our results suggested that PTPN9 expression was down-regulated in HCC tumor tissues, and reduced PTPN9 expression was associated with worsened overall survival in HCC patients. Depletion of PTPN9 inhibits the apoptosis and promotes the proliferation of HCC cells.

Desialylation is a mechanism of Fc-independent platelet clearance and a therapeutic target in immune thrombocytopenia

Immune thrombocytopenia (ITP) is a common bleeding disorder caused primarily by autoantibodies against platelet GPIIbIIIa and/or the GPIb complex. Current theory suggests that antibody-mediated platelet destruction occurs in the spleen, via macrophages through Fc-FcγR interactions. However, we and others have demonstrated that anti-GPIbα (but not GPIIbIIIa)-mediated ITP is often refractory to therapies targeting FcγR pathways. Here, we generate mouse anti-mouse monoclonal antibodies (mAbs) that recognize GPIbα and GPIIbIIIa of different species. Utilizing these unique mAbs and human ITP plasma, we find that anti-GPIbα, but not anti-GPIIbIIIa antibodies, induces Fc-independent platelet activation, sialidase neuraminidase-1 translocation and desialylation. This leads to platelet clearance in the liver via hepatocyte Ashwell-Morell receptors, which is fundamentally different from the classical Fc-FcγR-dependent macrophage phagocytosis. Importantly, sialidase inhibitors ameliorate anti-GPIbα-mediated thrombocytopenia in mice. These findings shed light on Fc-independent cytopenias, designating desialylation as a potential diagnostic biomarker and therapeutic target in the treatment of refractory ITP.

Protein-tyrosine phosphatases: a new frontier in platelet signal transduction

Platelet activation must be tightly controlled in order to allow platelets to respond rapidly to vascular injury and prevent thrombosis from occurring. Protein-tyrosine phosphorylation is one of the main ways in which activation signals are transmitted in platelets. Although much is known about the protein-tyrosine kinases (PTKs) that initiate and propagate activation signals, relatively little is known about the protein-tyrosine phosphatases (PTPs) that modulate these signals in platelets. PTPs are a family of enzymes that dephosphorylate tyrosine residues in proteins and regulate signals transmitted within cells. PTPs have been implicated in a variety of pathological conditions, including cancer, diabetes and autoimmunity, but their functions in hemostasis and thrombosis remain largely undefined. Exciting new findings from a number of groups have revealed that PTPs are in fact critical regulators of platelet activation and thrombosis. The primary aim of this review is to highlight the unique and important functions of PTPs in regulating platelet activity. Establishing the functions of PTPs in platelets is essential to better understand the molecular basis of thrombosis and may lead to the development of improved antithrombotic therapies.

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.

Tyrosine phosphatase PTP-MEG2 negatively regulates vascular endothelial growth factor receptor signaling and function in endothelial cells

Protein tyrosine phosphorylation is a fundamental mechanism for diverse physiological processes, which is regulated by protein tyrosine kinases and protein tyrosine phosphatases (PTPs). In this study, we searched for protein substrates of PTP-MEG2 (also called PTPN9), a nonreceptor PTP, and investigated its function in endothelial cells (ECs). By using a PTP-MEG2 substrate-trapping DA mutant, we found that a couple of tyrosine-phosphorylated proteins were associated with the DA mutant but not wild-type PTP-MEG2 and that the association was enhanced by vascular endothelial growth factor (VEGF) in ECs. We further found that VEGF receptor 2 (VEGFR2) was coimmunopricipitated with the DA mutant but not wild-type PTP-MEG2. The VEGF-induced phosphorylation of VEGFR2 on Tyr1175, a critical autophosphorylation site for VEGFR2 signaling, was inhibited 70% by overexpression of wild-type PTP-MEG2 but was enhanced (2.2-fold) by the DA mutant of PTP-MEG2. We also found that PTP-MEG2 DA mutant preferentially associated with Janus kinase 1 (JAK1) but not with other JAK kinases (Tyk2 and JAK2) present in ECs and regulated JAK1 tyrosine phosphorylation. Lastly, the VEGF-induced signal transduction and the production of interleukin (IL)-6 were significantly enhanced by PTP-MEG2 knockdown in ECs, whereas the VEGF-induced IL-6 production was inhibited 50% by PTP-MEG2 overexpression. Thus we have indentified VEGFR2 as a PTP-MEG2 substrate, and our findings indicate that PTP-MEG2 is a negative regulator of VEGFR2 signaling and function in ECs.

Protein tyrosine phosphatase Meg2 dephosphorylates signal transducer and activator of transcription 3 and suppresses tumor growth in breast cancer

Introduction

Signal transducer and activator of transcription 3 (STAT3) is over-activated or phosphorylated in breast cancers. The hyper-phosphorylation of STAT3 was attributed to either up-regulated phosphorylation by several tyrosine-kinases or down-regulated activity of phosphatases. Although several factors have been identified to phosphorylate STAT3, it remains unclear how STAT3 is dephosphorylated by PTPMeg2. The aim of this study was to determine the role of PTPMeg2 as a phosphatase in regulation of the activity of STAT3 in breast cancers.

Methods

Immunoprecipitation assays were used to study the interaction of STAT3 with PTPMeg2. A series of biochemistry experiments were performed to evaluate the role of PTPMeg2 in the dephosphorylation of STAT3. Two breast cancer cell lines MCF7 (PTPMeg2 was depleted as it was endogenously high) and MDA-MB-231 (PTPMeg2 was overexpressed as it was endogenously low) were used to compare the level of phosphorylated STAT3 and the tumor growth ability in vitro and in vivo. Samples from breast carcinoma (n = 73) were subjected to a pair-wise Pearson correlation analysis for the correlation of levels of PTPMeg2 and phosphorylated STAT3.

Results

PTPMeg2 directly interacts with STAT3 and mediates its dephosphorylation in the cytoplasm. Over-expression of PTPMeg2 decreased tyrosine phosphorylation of STAT3 while depletion of PTPMeg2 increased its phosphorylation. The decreased tyrosine phosphorylation of STAT3 is coupled with suppression of STAT3 transcriptional activity and reduced tumor growth in vitro and in vivo. Levels of PTPMeg2 and phosphorylated STAT3 were inversely correlated in breast cancer tissues (P = 0.004).

Conclusions

PTPMeg2 is an important phosphatase for the dephosphorylation of STAT3 and plays a critical role in breast cancer development.

Mammalian diseases of phosphatidylinositol transfer proteins and their homologs

Inositol and phosphoinositide signaling pathways represent major regulatory systems in eukaryotes. The physiological importance of these pathways is amply demonstrated by the variety of diseases that involve derangements in individual steps in inositide and phosphoinositide production and degradation. These diseases include numerous cancers, lipodystrophies and neurological syndromes. Phosphatidylinositol transfer proteins (PITPs) are emerging as fascinating regulators of phosphoinositide metabolism. Recent advances identify PITPs (and PITP-like proteins) to be coincidence detectors, which spatially and temporally coordinate the activities of diverse aspects of the cellular lipid metabolome with phosphoinositide signaling. These insights are providing new ideas regarding mechanisms of inherited mammalian diseases associated with derangements in the activities of PITPs and PITP-like proteins.

Identification and expression of the family of classical protein-tyrosine phosphatases in zebrafish

Protein-tyrosine phosphatases (PTPs) have an important role in cell survival, differentiation, proliferation, migration and other cellular processes in conjunction with protein-tyrosine kinases. Still relatively little is known about the function of PTPs in vivo. We set out to systematically identify all classical PTPs in the zebrafish genome and characterize their expression patterns during zebrafish development. We identified 48 PTP genes in the zebrafish genome by BLASTing of human PTP sequences. We verified all in silico hits by sequencing and established the spatio-temporal expression patterns of all PTPs by in situ hybridization of zebrafish embryos at six distinct developmental stages. The zebrafish genome encodes 48 PTP genes. 14 human orthologs are duplicated in the zebrafish genome and 3 human orthologs were not identified. Based on sequence conservation, most zebrafish orthologues of human PTP genes were readily assigned. Interestingly, the duplicated form of ptpn23, a catalytically inactive PTP, has lost its PTP domain, indicating that PTP activity is not required for its function, or that ptpn23b has lost its PTP domain in the course of evolution. All 48 PTPs are expressed in zebrafish embryos. Most PTPs are maternally provided and are broadly expressed early on. PTP expression becomes progressively restricted during development. Interestingly, some duplicated genes retained their expression pattern, whereas expression of other duplicated genes was distinct or even mutually exclusive, suggesting that the function of the latter PTPs has diverged. In conclusion, we have identified all members of the family of classical PTPs in the zebrafish genome and established their expression patterns. This is the first time the expression patterns of all members of the large family of PTP genes have been established in a vertebrate. Our results provide the first step towards elucidation of the function of the family of classical PTPs.

Protein-tyrosine phosphatase PTPN9 negatively regulates ErbB2 and epidermal growth factor receptor signaling in breast cancer cells

ErbB family of the receptor protein-tyrosine kinase plays an important role in the progression of human cancers including breast cancer. Finding protein-tyrosine phosphatase (PTPs) that can specifically regulate the function of ErbB should help design novel therapies for treatment. By performing a small interfering RNA screen against 43 human PTPs, we find that knockdown of protein-tyrosine phosphatase PTPN9 significantly increases ErbB2 tyrosyl phosphorylation in the SKBR3 breast cancer cell line. In addition, knockdown of PTPN9 expression also enhances tyrosyl phosphorylation of the ErbB1/epidermal growth factor receptor (EGFR) in the MDA-MB-231 breast cancer cell line. Conversely, increasing expression of PTPN9 wild type (WT) inhibits tyrosyl phosphorylation of ErbB2 and EGFR. To test whether ErbB2 and EGFR are substrates of PTPN9, PTPN9 WT, and a substrate trapping mutant (PTPN9 DA) are overexpressed in SKBR3 and MDA-MB-231 cells. Compared with vector control, expression of PTPN9 WT significantly inhibits whereas expression of PTPN9 DA dramatically enhances tyrosyl phosphorylation of ErbB2 and EGFR, respectively. In contrast, expression of PTPN9 WT or DA mutant does not affect tyrosyl phosphorylation of ErbB3 and Shc. Importantly, coimmunoprecipitation and glutathione S-transferase fusion protein pulldown experiments show that tyrosol-phosphorylated ErbB2 or EGFR is preferentially associated with PTPN9 DA compared with PTPN9 WT, indicating that ErbB2 and EGFR are substrates of PTPN9. Furthermore, PTPN9 WT expression specifically impairs EGF-induced STAT3 and STAT5 activation, and inhibits the cell growth in soft agar. Last, PTPN9 WT expression also reduces invasion and MMP2 expression of MDA-MB-231 cells. Our data suggest PTPN9 as a negative regulator of breast cancer cells by targeting ErbB2 and EGFR and inhibiting STAT activation.

Protein tyrosine phosphatases expression during development of mouse superior colliculus

Protein tyrosine phosphatases (PTPs) are key regulators of different processes during development of the central nervous system. However, expression patterns and potential roles of PTPs in the developing superior colliculus remain poorly investigated. In this study, a degenerate primer-based reverse transcription-polymerase chain reaction (RT-PCR) approach was used to isolate seven different intracellular PTPs and nine different receptor-type PTPs (RPTPs) from embryonic E15 mouse superior colliculus. Subsequently, the expression patterns of 11 PTPs (TC-PTP, PTP1C, PTP1D, PTP-MEG2, PTP-PEST, RPTPJ, RPTPε, RPTPRR, RPTPσ, RPTPκ and RPTPγ) were further analyzed in detail in superior colliculus from embryonic E13 to postnatal P20 stages by quantitative real-time RT-PCR, Western blotting and immunohistochemistry. Each of the 11 PTPs exhibits distinct spatiotemporal regulation of mRNAs and proteins in the developing superior colliculus suggesting their versatile roles in genesis of neuronal and glial cells and retinocollicular topographic mapping. At E13, additional double-immunohistochemical analysis revealed the expression of PTPs in collicular nestin-positive neural progenitor cells and RC-2-immunoreactive radial glia cells, indicating the potential functional importance of PTPs in neurogenesis and gliogenesis.

Bracovirus gene products are highly divergent from insect proteins

Recently, several polydnavirus (PDV) genomes have been completely sequenced. The dsDNA circles enclosed in virus particles and injected by wasps into caterpillars appear to mainly encode virulence factors potentially involved in altering host immunity and/or development, thereby allowing the survival of the parasitoid larvae within the host tissues. Parasitoid wasps generally inject virulence factors produced in the venom gland. As PDV genomes are inherited vertically by wasps through a proviral form, wasp virulence genes may have been transferred to this chromosomal form, leading to their incorporation into virus particles. Indeed, many gene products from Cotesia congregata bracovirus (CcBV), such as PTPs, IkappaB-like, and cystatins, contain protein domains conserved in metazoans. Surprisingly however, CcBV virulence gene products are not more closely related to insect proteins than to human proteins. To determine whether the distance between CcBV and insect proteins is a specific feature of BV proteins or simply reflects a general high divergence of parasitoid wasp products, which might be due to parasitic lifestyle, we have analyzed the sequences of wasp genes obtained from a cDNA library. Wasp sequences having a high similarity with Apis mellifera genes involved in a variety of biological functions could be identified indicating that the high level of divergence observed for BV products is a hallmark of these viral proteins. We discuss how this divergence might be explained in the context of the current hypotheses on the origin and evolution of wasp-bracovirus associations.

The lipid-binding SEC14 domain

Protein-lipid interactions are important for protein targeting, signal transduction, lipid transport, lipid biosynthesis, lipid metabolism, and the maintenance of cellular compartments and membranes. Specific lipid-binding protein domains, such as PH, FYVE, PX, PHD, C2 and SEC14 homology domains, mediate interactions between proteins and specific phospholipids. Here we review the published literature, plus some of our most recent unpublished findings, regarding the biology of the SEC14 domain, also known as CRAL_TRIO domain.

Mouse mutants with neural tube closure defects and their role in understanding human neural tube defects

BACKGROUND

The number of mouse mutants and strains with neural tube closure defects (NTDs) now exceeds 190, including 155 involving known genes, 33 with unidentified genes, and eight "multifactorial" strains.

METHODS

The emerging patterns of mouse NTDs are considered in relation to the unknown genetics of the common human NTDs, anencephaly, and spina bifida aperta.

RESULTS

Of the 150 mouse mutants that survive past midgestation, 20% have risk of either exencephaly and spina bifida aperta or both, parallel to the majority of human NTDs, whereas 70% have only exencephaly, 5% have only spina bifida, and 5% have craniorachischisis. The primary defect in most mouse NTDs is failure of neural fold elevation. Most null mutations (>90%) produce syndromes of multiple affected structures with high penetrance in homozygotes, whereas the "multifactorial" strains and several null-mutant heterozygotes and mutants with partial gene function (hypomorphs) have low-penetrance nonsyndromic NTDs, like the majority of human NTDs. The normal functions of the mutated genes are diverse, with clusters in pathways of actin function, apoptosis, and chromatin methylation and structure. The female excess observed in human anencephaly is found in all mouse exencephaly mutants for which gender has been studied. Maternal agents, including folate, methionine, inositol, or alternative commercial diets, have specific preventative effects in eight mutants and strains.

CONCLUSIONS

If the human homologs of the mouse NTD mutants contribute to risk of common human NTDs, it seems likely to be in multifactorial combinations of hypomorphs and low-penetrance heterozygotes, as exemplified by mouse digenic mutants and the oligogenic SELH/Bc strain.

Association of Protein-tyrosine Phosphatase MEG2 via Its Sec14p Homology Domain with Vesicle-trafficking Proteins

The protein-tyrosine phosphatase PTPMEG2 is located on the cytoplasmic face of the enclosing membrane of secretory vesicles, where it regulates vesicle size by promoting homotypic vesicle fusion by dephosphorylating N-ethylmaleimide-sensitive factor, a key regulator of vesicle fusion. Here we address the question of how PTPMEG2 is targeted to this subcellular location. Using a series of deletion mutants, we pinpointed the N-terminal Sec14p homology (SEC14) domain of PTPMEG2, residues 1-261, as the region containing the secretory vesicle targeting signal. This domain, alone or appended to a heterologous protein, was localized to intracellular vesicle membranes. Yeast two-hybrid screening identified a number of secretory vesicle proteins that interacted directly with the SEC14 domain of PTPMEG2, providing a mechanism for PTPMEG2 targeting to secretory vesicles. Two such proteins, mannose 6-phosphate receptor-interacting protein TIP47 and Arfaptin2, were found to alter PTPMEG2 localization when overexpressed, and elimination of TIP47 resulted in loss of PTPMEG2 function. We conclude that the N terminus of PTPMEG2 is necessary for the targeting of this phosphatase to the secretory vesicle compartment by association with other proteins involved in intracellular transport.

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.

Protein tyrosine phosphatase function: the substrate perspective

It is now well established that the members of the PTP (protein tyrosine phosphatase) superfamily play critical roles in fundamental biological processes. Although there has been much progress in defining the function of PTPs, the task of identifying substrates for these enzymes still presents a challenge. Many PTPs have yet to have their physiological substrates identified. The focus of this review will be on the current state of knowledge of PTP substrates and the approaches used to identify them. We propose experimental criteria that should be satisfied in order to rigorously assign PTP substrates as bona fide. Finally, the progress that has been made in defining the biological roles of PTPs through the identification of their substrates will be discussed.

Protein tyrosine phosphatases as negative regulators of the immune response

In this mini-review, we provide an overview of those PTPs (protein tyrosine phosphatases) that are relevant to the immune response, highlighting the function of a number of intracellular and transmembrane PTPs that have been identified as having important negative regulatory roles on distinct aspects of host immunity.

Identification of the tyrosine phosphatase PTP-MEG2 as an antagonist of hepatic insulin signaling

Insulin resistance is a primary defect in type 2 diabetes characterized by impaired peripheral glucose uptake and insufficient suppression of hepatic glucose output. Insulin signaling inhibits liver glucose production by inducing nuclear exclusion of the gluconeogenic transcription factor FOXO1 in an Akt-dependent manner. Through the concomitant application of genome-scale functional screening and quantitative image analysis, we have identified PTP-MEG2 as a modulator of insulin-dependent FOXO1 subcellular localization. Ectopic expression of PTP-MEG2 in cells inhibited insulin-induced phosphorylation of the insulin receptor, while RNAi-mediated reduction of PTP-MEG2 transcript levels enhanced insulin action. Additionally, adenoviral-mediated depletion of PTP-MEG2 in livers of diabetic (db/db) mice resulted in insulin sensitization and normalization of hyperglycemia. These data implicate PTP-MEG2 as a mediator of blood glucose homeostasis through antagonism of insulin signaling, and suggest that modulation of PTP-MEG2 activity may be an effective strategy in the treatment of type 2 diabetes.