T-cell protein tyrosine phosphatase is a key regulator in immune cell signaling: lessons from the knockout mouse model and implications in human disease

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.

Association between the PTPN2 gene and Crohn's disease: dissection of potential causal variants

BACKGROUND

Although genome-wide association studies (GWAS) and subsequent meta-analyses have confirmed associations between the PTPN2 (protein tyrosine phosphatase, nonreceptor type 2) gene and Crohn's disease (CD), the potential causal variants remain unidentified. We aimed to dissect potential causal CD-associated PTPN2 variants, assess their functional significance, and relate PTPN2 protein expression with inflammation in CD.

METHODS

A 3-stage study was carried out. In stage 1, we genotyped tagging single nucleotide polymorphisms (tag-SNPs) in the PTPN2 gene in a sample of patients with CD (<20 years, n = 556) and controls (n = 602). In stage 2, we resequenced the putative promoter, target exons and introns in the PTPN2 gene, and examined associations with high-frequency variants with CD in the stage 1 cohort. In stage 3 we studied the relationship between PTPN2 protein expression and mucosal inflammation and carried out in silico analyses to study the functional characteristics of the PTPN2 CD-associated SNPs.

RESULTS

In stage 1, we observed associations between 5 intronic SNPs and CD including rs1893217 (P = 2 × 10⁻⁴), the SNP that is in perfect linkage disequilibrium with the lead genome-wide association studies SNP rs2542151. Resequencing revealed 2 known promoter polymorphisms. No associations between these promoter SNPs and CD were evident. In silico analyses revealed that the 5 associated intronic SNPs influenced PTPN2 expression and binding to important transcription factors. PTPN2 protein was overexpressed in inflamed intestinal tissues of patients with CD.

CONCLUSIONS

Our findings suggest that noncoding variation in the PTPN2 gene may represent the causal variations influencing susceptibility for CD.

Multi-parametric phospho-flow cytometry: a crucial tool for T lymphocyte signaling studies

Tools such as protein immunoblotting have proven benefits for investigating T lymphocyte signaling but have several drawbacks such as the number of cells required and the difficulty of distinguishing subset-specific differences without expensive and invasive cell sorting. Recent advances in immunology and the identification of T lymphocyte sub-populations making up only a very small fraction of the total population highlight the importance of studying signaling in those small subsets in a feasible, cost-effective, high-throughput manner. To this end, we have developed a simplified protocol to study both intracellular phosphorylation patterns of important signal transduction molecules concomitantly with T cell surface marker expression. A multi-parametric analysis may allow the quantification of the phosphorylation of up to five signaling molecules in CD4 and CD8 T lymphocytes and their naïve, central memory, effector memory, and TEMRA subsets. This enables precise identification of subset-specific signaling and alterations of signaling pathways in physiological and pathological situations. The importance of such detailed analysis is discussed.

Emerging role of tyrosine phosphatase, TCPTP, in the organelles of the early secretory pathway

T-cell protein tyrosine phosphatase, TCPTP, is a ubiquitously expressed non-receptor type tyrosine phosphatase. There are two splice variants of TCPTP, TC48 and TC45, which differ in their sub-cellular localizations and functions. TC45 is a nuclear protein, which has both nuclear and cytoplasmic substrates, and is involved in many signaling events including endocytic recycling of platelet-derived growth factor β-receptor. TC48 is a predominantly endoplasmic reticulum (ER)-localizing protein, which dephosphorylates some of the substrates of TC45 at the ER. However, recently few specific substrates for TC48 have been identified. These include C3G (RapGEF1), syntaxin 17 and BCR-Abl. TC48 moves from the ER to post-ER compartments, the ER-Golgi intermediate compartment (ERGIC) and Golgi, and it is retrieved back to the ER. The retrieval of ER proteins from post-ER compartments is generally believed as a mechanism of targeting these proteins to the ER. However, it is possible that this shuttling of TC48 serves to regulate signaling in the early secretory pathway. For example, TC48 dephosphorylates phosphorylated C3G at the Golgi and inhibits neurite outgrowth. TC48 interacts with and dephosphorylates syntaxin 17, which is an ER and ERGIC-localizing protein involved in vesicle transport. A yeast two-hybrid screen identified several unique interacting partners of TC48 belonging to two groups - proteins involved in vesicle trafficking and proteins involved in cell adhesion. These interacting proteins could be substrates or regulators of TC48 function and localization. Thus, the role of TC48 seems to be more diverse, which is still to be explored.

Immune markers and differential signaling networks in ulcerative colitis and Crohn's disease

BACKGROUND

Cytokine signaling pathways play a central role in the pathogenesis of inflammatory bowel disease (IBD). Ulcerative colitis (UC) and Crohn's disease (CD) have unique as well as overlapping phenotypes, susceptibility genes, and gene expression profiles. This study aimed to delineate patterns within cytokine signaling pathways in colonic mucosa of UC and CD patients, explore molecular diagnostic markers, and identify novel immune mediators in IBD pathogenesis.

METHODS

We quantified 70 selected immune genes that are important in IBD signaling from formalin-fixed, paraffin-embedded (FFPE) colon biopsy samples from normal control subjects and UC and CD patients having either severe colitis or quiescent disease (n = 98 subjects). We utilized and validated a new modified real-time reverse-transcription polymerase chain reaction (RT-PCR) technique for gene quantification.

RESULTS

Expression levels of signaling molecules including IL-6/10/12/13/17/23/33, STAT1/3/6, T-bet, GATA3, Foxp3, SOCS1/3, and downstream inflammatory mediators such as chemokines CCL-2/11/17/20, oxidative stress inducers, proteases, and mucosal genes were differentially regulated between UC and CD and between active and quiescent disease. We also document the possible role of novel genes in IBD, including SHP-1, IRF-1,TARC, Eotaxin, NOX2, arginase I, and ADAM 8.

CONCLUSIONS

This comprehensive approach to quantifying gene expression provides insights into the pathogenesis of IBD by elucidating distinct immune signaling networks in CD and UC. Furthermore, this is the first study demonstrating that gene expression profiling in FFPE colon biopsies might be a practical and effective tool in the diagnosis and prognosis of IBD and may help identify molecular markers that can predict and monitor response to individualized therapeutic treatments.

Autologous regulatory T cells for the treatment of type 1 diabetes

The immune system is tasked with defending the host from a wide array of pathogens and environmental insults. When uncontrolled, this endeavor may lead to off-target reactivity to self-tissues resulting in multiple autoimmune diseases including type 1 diabetes (T1D). This multifactorial disease process involves over 40 susceptibility genes and is influenced by poorly characterized environmental factors. While many questions regarding the pathogenesis of the disease process remain, it has become increasingly clear that the progression to disease results from a breakdown in the processes that maintain peripheral immune tolerance. The end result of this process is localized tissue inflammation, islet dysfunction, and ultimately the destruction of pancreatic β cells due to concomitant defects in innate and adaptive immune responses. A number of immunomodulatory intervention trials have now been conducted in patients at risk for or with recent onset T1D, often with the goal of restoring immune tolerance by inducing regulatory T cells (Tregs). Unfortunately, many of these trials have fallen short of inducing persistent immune regulation. This shortfall has led to additional efforts to more directly shift the balance from destructive effector T cell (Teff) responses to favor Tregs, including the use of autologous Treg cell therapy. In this review we will discuss key concepts related to the use of autologous Treg cell therapy for the treatment of T1D. Among these topics, we will discuss the notions of genetic control of Treg activity, Treg cellular plasticity, and requirements for antigen-specificity.

Genome-wide association analyses of esophageal squamous cell carcinoma in Chinese identify multiple susceptibility loci and gene-environment interactions

We conducted a genome-wide association study (GWAS) and a genome-wide gene-environment interaction analysis of esophageal squamous-cell carcinoma (ESCC) in 2,031 affected individuals (cases) and 2,044 controls with independent validation in 8,092 cases and 8,620 controls. We identified nine new ESCC susceptibility loci, of which seven, at chromosomes 4q23, 16q12.1, 17q21, 22q12, 3q27, 17p13 and 18p11, had a significant marginal effect (P=1.78×10(-39) to P=2.49×10(-11)) and two of which, at 2q22 and 13q33, had a significant association only in the gene-alcohol drinking interaction (gene-environment interaction P (PG×E)=4.39×10(-11) and PG×E=4.80×10(-8), respectively). Variants at the 4q23 locus, which includes the ADH cluster, each had a significant interaction with alcohol drinking in their association with ESCC risk (PG×E=2.54×10(-7) to PG×E=3.23×10(-2)). We confirmed the known association of the ALDH2 locus on 12q24 to ESCC, and a joint analysis showed that drinkers with both of the ADH1B and ALDH2 risk alleles had a fourfold increased risk for ESCC compared to drinkers without these risk alleles. Our results underscore the direct genetic contribution to ESCC risk, as well as the genetic contribution to ESCC through interaction with alcohol consumption.

The genetic basis of graves' disease

The presented comprehensive review of current knowledge about genetic factors predisposing to Graves’ disease (GD) put emphasis on functional significance of observed associations. In particular, we discuss recent efforts aimed at refining diseases associations found within the HLA complex and implicating HLA class I as well as HLA-DPB1 loci. We summarize data regarding non-HLA genes such as PTPN22, CTLA4, CD40, TSHR and TG which have been extensively studied in respect to their role in GD. We review recent findings implicating variants of FCRL3 (gene for FC receptor-like-3 protein), SCGB3A2 (gene for secretory uteroglobin-related protein 1- UGRP1) as well as other unverified possible candidate genes for GD selected through their documented association with type 1 diabetes mellitus: Tenr–IL2–IL21, CAPSL (encoding calcyphosine-like protein), IFIH1(gene for interferon-induced helicase C domain 1), AFF3, CD226 and PTPN2. We also review reports on association of skewed X chromosome inactivation and fetal microchimerism with GD. Finally we discuss issues of genotype-phenotype correlations in GD.

The role of autophagy in Crohn's disease

(Macro)-autophagy is a homeostatic process by which eukaryotic cells dispose of protein aggregates and damaged organelles. Autophagy is also used to degrade micro-organisms that invade intracellularly in a process termed xenophagy. Genome-wide association scans have recently identified autophagy genes as conferring susceptibility to Crohn’s disease (CD), one of the chronic inflammatory bowel diseases, with evidence suggesting that CD arises from a defective innate immune response to enteric bacteria. Here we review the emerging role of autophagy in CD, with particular focus on xenophagy and enteric E. coli strains with an adherent and invasive phenotype that have been consistently isolated from CD patients with ileal disease.

Protein tyrosine phosphatases in lymphocyte activation and autoimmunity

Lymphocyte activation must be tightly regulated to ensure sufficient immunity to pathogens and prevent autoimmunity. Protein tyrosine phosphatases (PTPs) serve critical roles in this regulation by controlling the functions of key receptors and intracellular signaling molecules in lymphocytes. In some cases, PTPs inhibit lymphocyte activation, whereas in others they promote it. Here we discuss recent progress in elucidating the roles and mechanisms of action of PTPs in lymphocyte activation. We also review the accumulating evidence that genetic alterations in PTPs are involved in human autoimmunity.

PTPN2, a candidate gene for type 1 diabetes, modulates pancreatic β-cell apoptosis via regulation of the BH3-only protein Bim

OBJECTIVE

Genome-wide association studies allowed the identification of several associations between specific loci and type 1 diabetes (T1D). However, the mechanisms by which most candidate genes predispose to T1D remain unclear. We presently evaluated the mechanisms by which PTPN2, a candidate gene for T1D, modulates β-cell apoptosis after exposure to type I and II interferons (IFNs), cytokines that contribute to β-cell loss in early T1D.

RESEARCH DESIGN AND METHODS

Small interfering RNAs were used to inhibit PTPN2, STAT1, Bim, and Jun NH(2)-terminal kinase 1 (JNK1) expression. Cell death was assessed by Hoechst and propidium iodide staining. BAX translocation, Bim phosphorylation, cytochrome c release, and caspases 9 and 3 activation were measured by Western blot or immunofluorescence.

RESULTS

PTPN2 knockdown exacerbated type I IFN-induced apoptosis in INS-1E, primary rat, and human β-cells. PTPN2 silencing and exposure to type I and II IFNs induced BAX translocation to the mitochondria, cytochrome c release, and caspase 3 activation. There was also an increase in Bim phosphorylation that was at least in part regulated by JNK1. Of note, both Bim and JNK1 knockdown protected β-cells against IFN-induced apoptosis in PTPN2-silenced cells.

CONCLUSIONS

The present findings suggest that local IFN production may interact with a genetic factor (PTPN2) to induce aberrant proapoptotic activity of the BH3-only protein Bim, resulting in increased β-cell apoptosis via JNK activation and the intrinsic apoptotic pathway. This is the first indication of a direct interaction between a candidate gene for T1D and the activation of a specific downstream proapoptotic pathway in β-cells.

Unraveling the functional implications of GWAS: how T cell protein tyrosine phosphatase drives autoimmune disease

Genome-wide association studies (GWAS) have identified a large number of SNPs that are linked to human autoimmune diseases. However, the functional consequences of most of these genetic variations remain undefined. T cell protein tyrosine phosphatase (TCPTP, which is encoded by PTPN2) is a JAK/STAT and growth factor receptor phosphatase that has been linked to the pathogenesis of type 1 diabetes, rheumatoid arthritis, and Crohn's disease by GWAS. In this issue of the JCI, Wiede and colleagues have generated a T cell-specific deletion of TCPTP and identified a novel role for this phosphatase as a negative regulator of TCR signaling. These data provide new insight as to how noncoding PTPN2 SNPs identified in GWAS could drive human autoimmune diseases.

Mutation analysis of the tyrosine phosphatase PTPN2 in Hodgkin's lymphoma and T-cell non-Hodgkin's lymphoma

We recently reported deletion of the protein tyrosine phosphatase gene PTPN2 in T-cell acute lymphoblastic leukemia. Functional analyses confirmed that PTPN2 acts as classical tumor suppressor repressing the proliferation of T cells, in part through inhibition of JAK/STAT signaling. We investigated the expression of PTPN2 in leukemia as well as lymphoma cell lines. We identified bi-allelic inactivation of PTPN2 in the Hodgkin's lymphoma cell line SUP-HD1 which was associated with activation of the JAK/STAT pathway. Subsequent sequence analysis of Hodgkin's lymphoma and T-cell non-Hodgkin's lymphoma identified bi-allelic inactivation of PTPN2 in 2 out of 39 cases of peripheral T-cell lymphoma not otherwise specified, but not in Hodgkin's lymphoma. These results, together with our own data on T-cell acute lymphoblastic leukemia, demonstrate that PTPN2 is a tumor suppressor gene in T-cell malignancies.

Shared genetics in coeliac disease and other immune-mediated diseases

Identifying disease-associated variants can improve the predictive models of disease risk and provide mechanistic insights into disease development. Coeliac disease (CD) is the only autoimmune trait with a known environmental trigger, which makes it an excellent model for studying the complexity of genetic and environmental factors in the development of autoimmunity. In this review, we will focus on the genetic loci that have recently been associated with CD and that contain genes involved in innate and adaptive immunity. Some of these loci are shared with other immune-mediated diseases, suggesting an overlap of the genetic mechanisms involved in the development of such diseases. Some therapies, e.g. tumour necrosis factor inhibitors or a gluten-free diet, are already proving effective for more than one autoimmune disease. Follow-up of individuals with a high genetic risk of CD and other autoimmune diseases could help to elucidate the role of environmental factors (such as infectious agents or alterations in the microbiome) and prevent disease development.

An autoimmune-associated variant in PTPN2 reveals an impairment of IL-2R signaling in CD4(+) T cells

The IL-2/IL-2R signaling pathway has an important role in autoimmunity. Several genes identified in genome-wide association (GWA) studies encode proteins in the IL-2/IL-2R signaling cascade that are associated with autoimmune diseases. One of these, PTPN2, encodes a protein tyrosine phosphatase that is highly expressed in T cells and regulates cytokine signaling. An intronic risk allele in PTPN2, rs1893217(C), correlated with decreased IL-2R signaling in CD4(+) T cells as measured by phosphorylation of STAT5 (phosphorylated STAT5 (pSTAT5)). We modeled an additive single nucleotide polymorphism (SNP) genotype, in which each copy of the risk allele conferred a decrease in IL-2R signaling (P=4.4 × 10(-8)). Decreased pSTAT5 impacted IL-2Rβ chain signaling resulting in reduced FOXP3 expression in activated cells. This phenotype was not due to overt differences in expression of the IL-2R, molecules in the IL-2R signaling cascade or defects in STAT5. However, the rs1893217(C) risk variant did correlate with decreased PTPN2 expression in CD4(+)CD45RO T cells (P=0.0002). Thus, the PTPN2rs1893217(C) risk allele associated with reduced pSTAT5 in response to IL-2 and reduced PTPN2 expression. Together, these data suggest that decreased expression of PTPN2 may indirectly modulate IL-2 responsiveness. These findings, identified through genotype/phenotype relationships, may lead to identification of novel mechanisms underlying dysregulation of cytokine signaling in autoimmunity.

Molecular and cellular pathobiology of Ehrlichia infection: targets for new therapeutics and immunomodulation strategies

Ehrlichia are small obligately intracellular bacteria in the order Rickettsiales that are transmitted by ticks and associated with emerging life-threatening human zoonoses. Vaccines are not available for human ehrlichiosis, and therapeutic options are limited to a single antibiotic class. New technologies for exploring host-pathogen interactions have yielded recent advances in understanding the molecular interactions between Ehrlichia and the eukaryotic host cell and identified new targets for therapeutic and vaccine development, including those that target pathogen virulence mechanisms or disrupt the processes associated with ehrlichial effector proteins. Animal models have also provided insight into immunopathological mechanisms that contribute significantly to understanding severe disease manifestations, which should lead to the development of immunomodulatory approaches for treating patients nearing or experiencing severe disease states. In this review, we discuss the recent advances in our understanding of molecular and cellular pathobiology and the immunobiology of Ehrlichia infection. We identify new molecular host-pathogen interactions that can be targets of new therapeutics, and discuss prospects for treating the immunological dysregulation during acute infection that leads to life-threatening complications.

A polymorphism in PTPN2 gene is associated with an earlier onset of type 1 diabetes

The Wellcome Trust Case Control Consortium (WTCCC) genome-wide study found association of PTPN2 with three autoimmune diseases, among them is type 1 diabetes (T1D). This result was confirmed by a follow-up study that pointed to new independent signals within the region. However, both studies were performed in patients with an early-onset T1D. We aimed at replicating the previous results and studying the influence of these polymorphisms in the age at T1D debut. We genotyped 439 T1D Spanish subjects (age at onset, 1 to 65 years) and 861 controls for two PTPN2 single nucleotide polymorphisms (SNPs), rs2542151 and rs478582, and studied the effect of both polymorphisms in age at onset through stratified and continuous analyses. The frequency of rs2542151*G carriers was significantly higher in the early-onset group compared with late-onset patients (p = 0.023) and with controls (OR = 1.61 [1.14-2.26]; p = 0.005). No significant differences were found between controls and late-onset patients. The log-rank chi-square test for the Kaplan-Meier plots (carriers of susceptibility allele vs non carriers) was statistically significant (χ (1df) (2)  = 4.485; p = 0.034), yielding an earlier disease debut for G carriers. The analysis of the SNP rs478582 did not reach statistical significance. In summary, we replicate the association detected by the WTCCC and propose that the rs2542151*G allele confers risk to an earlier onset of T1D.

Animal models of IBD: linkage to human disease

Spontaneous development of intestinal inflammation in many different kinds of genetically engineered mice as well as the presence of numerous susceptibility genes in humans suggests that inflammatory bowel disease (IBD) is mediated by more complicated mechanisms than previously predicted. The human genetic studies implicate some major pathways in the pathogenesis of IBD, including epithelial defense against commensal microbiota, the IL-23/Th17 axis, and immune regulation. Murine IBD models, which are genetically engineered to lack some susceptibility genes, have been generated, and have provided useful insights into the therapeutic potential of targeting the susceptibility genes directly or their downstream pathways indirectly for IBD. This review summarizes current information related to the function of IBD-associated genes as derived from genetically engineered mouse models.

Deletion of the protein tyrosine phosphatase gene PTPN2 in T-cell acute lymphoblastic leukemia

PTPN2 (protein tyrosine phosphatase non-receptor type 2, also known as TC-PTP) is a cytosolic tyrosine phosphatase that functions as a negative regulator of a variety of tyrosine kinases and other signaling proteins. In agreement with its role in the regulation of the immune system, PTPN2 was identified as a susceptibility locus for autoimmune diseases. In this work, we describe the identification of focal deletions of PTPN2 in human T-cell acute lymphoblastic leukemia (T-ALL). Deletion of PTPN2 was specifically found in T-ALLs with aberrant expression of the TLX1 transcription factor oncogene, including four cases also expressing the NUP214-ABL1 tyrosine kinase. Knockdown of PTPN2 increased the proliferation and cytokine sensitivity of T-ALL cells. In addition, PTPN2 was identified as a negative regulator of NUP214-ABL1 kinase activity. Our study provides genetic and functional evidence for a tumor suppressor role of PTPN2 and suggests that expression of PTPN2 may modulate response to treatment.

Differences in genetic background between active smokers, passive smokers, and non-smokers with Crohn's disease

OBJECTIVES

Smoking behavior and genetic variations are important factors for the development of Crohn's disease (CD), but studies investigating the interaction between smoking and genetic background are scarce. We studied allelic associations of 19 confirmed variants located in 14 CD-associated genes or loci, in CD patients stratified for active smoking at diagnosis and passive smoking in childhood.

METHODS

Genotyping data of 19 CD-associated single-nucleotide polymorphisms (SNPs) were available for 310 CD patients and 976 controls. Data on active smoking at diagnosis and passive smoking in childhood were obtained through a written questionnaire and a review of medical charts.

RESULTS

The loci associated in smoking, but not in non-smoking, CD patients were 5p13.1 (rs17234657), DLG5 (rs2165047), NKX2-3 (rs10883365), and NOD2 (R702W). The loci associated in non-smoking, but not in smoking, CD patients were IL23R (rs7517847), 5p13.1 (rs9292777), IRGM (rs13361189 and rs4958847), IL12B (rs6887695), and CCNY (rs3936503). PTPN2 (rs2542151) was only associated in the smoking CD cohort (P=0.041), and not in the entire cohort (P=0.23) or in the non-smoking CD cohort (P=0.80). In passively smoking CD patients, associations with 13 SNPs in 9 loci were found, including PTPN2. In non-passive smoking CD patients, only associations with NOD2 (1007fsinsC and G908R) were found.

CONCLUSIONS

The difference in associated genes between smoking and non-smoking CD patients implies a complex gene-environment interaction. Therefore, genetic studies of CD should be stratified for smoking behavior, as otherwise moderately associated genes such as PTPN2 can be missed.

Defects in IL-2R signaling contribute to diminished maintenance of FOXP3 expression in CD4(+)CD25(+) regulatory T-cells of type 1 diabetic subjects

OBJECTIVE

In humans, multiple genes in the interleukin (IL)-2/IL-2 receptor (IL-2R) pathway are associated with type 1 diabetes. However, no link between IL-2 responsiveness and CD4(+)CD25(+)FOXP3(+) regulatory T-cells (Tregs) has been demonstrated in type 1 diabetic subjects despite the role of these IL-2-dependent cells in controlling autoimmunity. Here, we address whether altered IL-2 responsiveness impacts persistence of FOXP3 expression in Tregs of type 1 diabetic subjects.

RESEARCH DESIGN AND METHODS

Persistence of Tregs was assessed by culturing sorted CD4(+)CD25(hi) natural Tregs with IL-2 and measuring FOXP3 expression over time by flow cytometry for control and type 1 diabetic populations. The effects of IL-2 on FOXP3 induction were assessed 48 h after activation of CD4(+)CD25(-) T-cells with anti-CD3 antibody. Cytokine receptor expression and signaling upon exposure to IL-2, IL-7, and IL-15 were determined by flow cytometry and Western blot analysis.

RESULTS

Maintenance of FOXP3 expression in CD4(+)CD25(+) Tregs of type 1 diabetic subjects was diminished in the presence of IL-2, but not IL-7. Impaired responsiveness was not linked to altered expression of the IL-2R complex. Instead, IL-2R signaling was reduced in Tregs and total CD4(+) T-cells of type 1 diabetic subjects. In some individuals, decreased signal transducer and activator of transcription 5 phosphorylation correlated with significantly higher expression of protein tyrosine phosphatase N2, a negative regulator of IL-2R signaling.

CONCLUSIONS

Aberrant IL-2R signaling in CD4(+) T-cells of type 1 diabetic subjects contributes to decreased persistence of FOXP3 expression that may impact establishment of tolerance. These findings suggest novel targets for treatment of type 1 diabetes within the IL-2R pathway and suggest that an altered IL-2R signaling signature may be a biomarker for type 1 diabetes.

New insights into molecular Ehrlichia chaffeensis-host interactions

Ehrlichia chaffeensis is an obligately intracellular bacterium that exhibits tropism for mononuclear phagocytes and survives by reprogramming the host cell. Here we review new information regarding the newly characterized effector molecules and the complex network of molecular host-pathogen interactions that the organism exploits enabling it to thrive and persist intracellularly.

Increased susceptibility to dextran sulfate sodium induced colitis in the T cell protein tyrosine phosphatase heterozygous mouse

T cell protein tyrosine phosphatase (TC-PTP / PTPN2) is an enzyme that is essential for the proper functioning of the immune system and that participates in the control of cell proliferation, and inflammation. We previously observed that TC-PTP^−/− mice display various immunodeficiencies, hypersensitivity to LPS and die within three weeks of birth due to anemia and widespread inflammation. A recent analysis of the Wellcome Trust Case Control Consortium (WTCC) genome wide scan data, reported in 2007, indicated a potential role for TC-PTP in inflammatory bowel disease (IBD). To further investigate the potential role of TC-PTP in IBD, we studied heterozygous TC-PTP mutant mice challenged with dextran sulfate sodium (DSS) in their drinking water. In comparison to control animals, we observed significant changes in the colon mucosa of DSS-treated TC-PTP^+/− mice, in the ratio of colon to body weight, as well as an up-regulation of mRNA transcripts for IL-6, IL-23, 1L-12β, IFN-γ, TNF-α. Moreover, up-regulation of serum IL-6 levels in DSS-treated TC-PTP^+/− mice confirms that mice with a single copy of the TC-PTP gene display increased susceptibility to systemic inflammation due to bowel epithelial erosion resulting from DSS challenge. Our findings support the lack of modulation of Janus kinases 1 and 3 (Jak1, Jak3), and the downstream signal transducer and activator of transcription 1,3 and 5 (Stat1, Stat3, Stat 5) by PTPN2 in the development of IBD like condition. Pathological and molecular analysis reveal that the deficiency of TC-PTP results in pro-inflammatory condition in the bowel of heterozygous TC-PTP^+/− mice. These novel findings in TC-PTP hemi-deficiency support the hypothesis that TC-PTP is an important regulator of inflammatory cytokine signaling and that it may be implicated in the pathophysiology of IBD.

TC-PTP is required for the maintenance of MYC-driven B-cell lymphomas

We sought to determine the contributions of protein tyrosine phosphatases (PTPs) to the pathogenesis of B-cell lymphomas. We found that T-cell PTP (TC-PTP) was overexpressed in transformed B cells. We hypothesized that TC-PTP may be a tumor-promoting gene that is regulated by MYC overexpression in B cells. Knockdown of TC-PTP in murine tumors resulted in decreased cell viability in vitro because of an arrest in the G(1) phase of the cell cycle. Furthermore, cells with reduced TC-PTP expression were unable to either engraft or expand in vivo. Taken together, these data indicate that TC-PTP is required for B-cell tumor maintenance. Our data also suggested a correlation between TC-PTP expression and MYC overexpression. To investigate this further, we used malignant murine B cells that contain a doxycycline-repressible MYC transgene. We found that repression of MYC overexpression with doxycycline reduced TC-PTP expression. Moreover, enforced expression of TC-PTP showed partial rescue of the expansion of tumor cells after suppression of MYC overexpression. These results suggest that MYC overexpression induces TC-PTP overexpression, which in turn promotes tumor proliferation, implicating TC-PTP as an important effector of the MYC-driven proliferation program in B-cell lymphomas. Thus, TC-PTP may be a suitable molecular target for the treatment of B-cell lymphomas.