Regulating naïve and memory CD8 T cell homeostasis - a role for protein tyrosine phosphatases

LAR inhibitory peptide promotes recovery of diaphragm function and multiple forms of respiratory neural circuit plasticity after cervical spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs), up-regulated in and around the lesion after traumatic spinal cord injury (SCI), are key extracellular matrix inhibitory molecules that limit axon growth and consequent recovery of function. CSPG-mediated inhibition occurs via interactions with axonal receptors, including leukocyte common antigen- related (LAR) phosphatase. We tested the effects of a novel LAR inhibitory peptide in rats after hemisection at cervical level 2, a SCI model in which bulbospinal inspiratory neural circuitry originating in the medullary rostral ventral respiratory group (rVRG) becomes disconnected from phrenic motor neuron (PhMN) targets in cervical spinal cord, resulting in persistent partial-to-complete diaphragm paralysis. LAR peptide was delivered by a soaked gelfoam, which was placed directly over the injury site immediately after C2 hemisection and replaced at 1 week post-injury. Axotomized rVRG axons originating in ipsilateral medulla or spared rVRG fibers originating in contralateral medulla were separately assessed by anterograde tracing via AAV2-mCherry injection into rVRG. At 8 weeks post-hemisection, LAR peptide significantly improved ipsilateral hemidiaphragm function, as assessed in vivo with electromyography recordings. LAR peptide promoted robust regeneration of ipsilateral-originating rVRG axons into and through the lesion site and into intact caudal spinal cord to reach PhMNs located at C3-C5 levels. Furthermore, regenerating rVRG axons re-established putative monosynaptic connections with their PhMNs targets. In addition, LAR peptide stimulated robust sprouting of both modulatory serotonergic axons and contralateral-originating rVRG fibers within the PhMN pool ipsilateral/ caudal to the hemisection. Our study demonstrates that targeting LAR-based axon growth inhibition promotes multiple forms of respiratory neural circuit plasticity and provides a new peptide-based therapeutic strategy to ameliorate the devastating respiratory consequences of SCI.

PRL-2 phosphatase is required for vascular morphogenesis and angiogenic signaling

Protein tyrosine phosphatases are essential modulators of angiogenesis and have been identified as novel therapeutic targets in cancer and anti-angiogenesis. The roles of atypical Phosphatase of Regenerative Liver (PRL) phosphatases in this context remain poorly understood. Here, we investigate the biological function of PRL phosphatases in developmental angiogenesis in the postnatal mouse retina and in cell culture. We show that endothelial cells in the retina express PRL-2 encoded by the Ptp4a2 gene, and that inducible endothelial and global Ptp4a2 mutant mice exhibit defective retinal vascular outgrowth, arteriovenous differentiation, and sprouting angiogenesis. Mechanistically, PTP4A2 deletion limits angiogenesis by inhibiting endothelial cell migration and the VEGF-A, DLL-4/NOTCH-1 signaling pathway. This study reveals the importance of PRL-2 as a modulator of vascular development.

Proteomic Study of Fetal Membrane: Inflammation-Triggered Proteolysis of Extracellular Matrix May Present a Pathogenic Pathway for Spontaneous Preterm Birth

INTRODUCTION

Spontaneous preterm birth (sPTB), which predominantly presents as spontaneous preterm labor (sPTL) or prelabor premature rupture of membranes (PPROM), is a syndrome that accounts for 5-10% of live births annually. The long-term morbidity in surviving preterm infants is significantly higher than that in full-term neonates. The causes of sPTB are complex and not fully understood. Human placenta, the maternal and fetal interface, is an environmental core of fetal intrauterine life, mediates fetal oxygen exchange, nutrient uptake, and waste elimination and functions as an immune-defense organ. In this study, the molecular signature of preterm birth placenta was assessed and compared to full-term placenta by proteomic profiling.

MATERIALS AND METHODS

Four groups of fetal membranes (the amniochorionic membranes), with five cases in each group in the discovery study and 30 cases in each group for validation, were included: groups A: sPTL; B: PPROM; C: full-term birth (FTB); and D: full-term premature rupture of membrane (PROM). Fetal membranes were dissected and used for proteome quantification study. Maxquant and Perseus were used for protein quantitation and statistical analysis. Both fetal membranes and placental villi samples were used to validate proteomic discovery.

RESULTS

Proteomics analysis of fetal membranes identified 2,800 proteins across four groups. Sixty-two proteins show statistical differences between the preterm and full-term groups. Among these differentially expressed proteins are (1) proteins involved in inflammation (HPGD), T cell activation (PTPRC), macrophage activation (CAPG, CD14, and CD163), (2) cell adhesion (ICAM and ITGAM), (3) proteolysis (CTSG, ELANE, and MMP9), (4) antioxidant (MPO), (5) extracellular matrix (ECM) proteins (APMAP, COL4A1, LAMA2, LMNB1, LMNB2, FBLN2, and CSRP1) and (6) metabolism of glycolysis (PKM and ADPGK), fatty acid synthesis (ACOX1 and ACSL3), and energy biosynthesis (ATP6AP1 and CYBB).

CONCLUSION

Our molecular signature study of preterm fetal membranes revealed inflammation as a major event, which is inconsistent with previous findings. Proteolysis may play an important role in fetal membrane rupture. Extracellular matrix s have been altered in preterm fetal membranes due to proteolysis. Metabolism was also altered in preterm fetal membranes. The molecular changes in the fetal membranes provided a significant molecular signature for PPROM in preterm syndrome.

Unleashing the Therapeutic Potential of Dendritic and T Cell Therapies Using RNA Interference

Therapeutic dendritic cell (DC) cancer vaccines work to boost the body's immune system to fight a cancer. Although this type of immunotherapy often leads to the activation of tumor-specfic T cells, clinical responses are fairly low, arguing for the need to improve the design of DC-based vaccines. Recent studies revealed a promising strategy of combining DC vaccines with small interfering RNAs (siRNAs) targeting immunosuppressive signals such as checkpoint receptors. Similarly, incorporating checkpoint siRNA blockers in adoptive T-cell therapy to amplify cytotoxic T lymphocyte responses is now being tested in the clinic. The development of the next generation of cancer immunotherapies using siRNA technology will hopefuly benefit patients with various cancer types including those who did not respond to current therapies. This review highlights the latest advances in RNA interference technology to improve the therapeutic efficacy of DC cancer vaccines and T cell therapy.

Human regulatory T cells (Treg) and their response to cancer

INTRODUCTION

Regulatory T cells (Treg) and their role in health and disease is being intensively investigated. Today, human Treg emerge as a highly heterogeneous subset of CD4+ T cells which mediate immune suppression but also regulate responses of non-immune cells. In cancer, Treg occupy a critical although not yet entirely understood role.

AREAS COVERED

Newly acquired insights into Treg indicate a much greater plasticity and functional heterogeneity of this T cell subset than was previously known. Functional redundancy of Treg and their interactions with a variety of immune and non-immune cellular targets emphasize the central role Treg play in cancer. Treg not only regulate the host responses to cancer; they may also regulate responses to immune therapies. The impact of immune checkpoint blockade on Treg survival, stability and suppressive activity remains to be elucidated. T cell reprogramming by tumor-derived factors, including tumor-derived exosomes (TEX), plays a key role in shaping the Treg repertoire in the tumor microenvironment (TME). The reprogrammed or induced iTreg acquire capabilities to strongly down-regulate anti-tumor immune responses by mechanisms that are specific for each TME. Therapeutic silencing of such Treg calls for the discrimination of "bad" from "good" Treg subsets, an approach that remains elusive in the absence of a definitive "Treg signature."

EXPERT OPINION

Context-related plasticity and heterogeneity of Treg in the TME are significant barriers to selective therapeutic depletion of those Treg subsets that are reprogramed by the tumor to suppress anti-tumor immunity.

Can CpG methylation serve as surrogate markers for immune infiltration in cancer?

Recent reports describe how genome-wide transcriptional analysis of cancer tissues can be exploited to identify molecular signatures of immune infiltration in cancer. We hypothesize that immune infiltration in cancer may also be defined by changes in certain epigenetic signatures. In this context, a primary objective is to identify site-specific CpG markers whose levels of methylation may be highly indicative of known transcriptional markers of immune infiltration such as GZMA, PRF1, T cell receptor genes, PDCD1, and CTLA4. This has been accomplished by integrating genome-wide transcriptional expression and methylation data for different types of cancer (melanoma, kidney cancers, lung cancers, gliomas, head and neck cancer). Our findings establish that cancers of related histology also have a high degree of similarity in immune-infiltration CpG markers. For example, the epigenetic immune infiltration signatures in lung adenocarcinoma (LUAD), mesothelioma (MESO), lung squamous cell carcinoma (LUSC), and head and neck squamous cell carcinoma (HNSC) are distinctly similar. So are glioblastoma multiforme (GBM) and brain lower grade glioma (LGG); and kidney renal papillary cell carcinoma (KIRP) and kidney renal clear cell carcinoma (KIRC). Kidney chromophobe (KICH), on the other hand has markers that are unique to this cohort. The strong relationships between immune infiltration and CpG methylation (for certain sites) in cancer tissues were not observed upon integrated analysis of publicly available cancer cell line datasets. Results from comparative pathways analyses offer further justification to methylation at certain CpG sites as being indicators of cancer immune infiltration, and possibly of predicting patient response to immunotherapeutic drugs. Achieving this target objective would significantly enhance therapeutic outcomes employing immunotherapy through focused patient-centric personalized medicine.

Releasing the Immune System Brakes Using siRNAs Enhances Cancer Immunotherapy

Therapeutic dendritic cell (DC) cancer vaccines rely on the immune system to eradicate tumour cells. Although tumour antigen-specific T cell responses have been observed in most studies, clinical responses are fairly low, arguing for the need to improve the design of DC-based vaccines. The incorporation of small interfering RNAs (siRNAs) against immunosuppressive factors in the manufacturing process of DCs can turn the vaccine into potent immune stimulators. Additionally, siRNA modification of ex vivo-expanded T cells for adoptive immunotherapy enhanced their killing potency. Most of the siRNA-targeted immune inhibitory factors have been successful in that their blockade produced the strongest cytotoxic T cell responses in preclinical and clinical studies. Cancer patients treated with the siRNA-modified DC vaccines showed promising clinical benefits providing a strong rationale for further development of these immunogenic vaccine formulations. This review covers the progress in combining siRNAs with DC vaccines or T cell therapy to boost anti-tumour immunity.

Rational combination immunotherapeutic approaches for effective cancer treatment

Immunotherapy is an important mode of cancer treatment. Over the past decades, immunotherapy has improved the clinical outcome for cancer patients. However, in many cases, mutations in cancer cells, lack of selectivity, insufficiency of tumor-reactive T cells, and host immunosuppression limit the clinical benefit of immunotherapy. Combination approaches in immunotherapy may overcome these obstacles. Accumulating evidence demonstrates that combination immunotherapy is the future of cancer treatment. However, designing safe and rational combinations of immunotherapy with other treatment modalities is critical. This review will discuss the optimal immunotherapy-based combinations mainly with respect to the mechanisms of action of individual therapeutic agents that target multiple steps in evasion and progression of tumor.

Diverse functions of protein tyrosine phosphatase σ in the nervous and immune systems

Tyrosine phosphorylation is a common means of regulating protein functions and signal transduction in multiple cells. Protein tyrosine phosphatases (PTPs) are a large family of signaling enzymes that remove phosphate groups from tyrosine residues of target proteins and change their functions. Among them, receptor-type PTPs (RPTPs) exhibit a distinct spatial pattern of expression and play essential roles in regulating neurite outgrowth, axon guidance, and synaptic organization in developmental nervous system. Some RPTPs function as essential receptors for chondroitin sulfate proteoglycans that inhibit axon regeneration following CNS injury. Interestingly, certain RPTPs are also important to regulate functions of immune cells and development of autoimmune diseases. PTPσ, a RPTP in the LAR subfamily, is expressed in various immune cells and regulates their differentiation, production of various cytokines and immune responses. In this review, we highlight the physiological and pathological significance of PTPσ and related molecules in both nervous and immune systems.

Downregulation of PTP1B and TC-PTP phosphatases potentiate dendritic cell-based immunotherapy through IL-12/IFNγ signaling

PTP1B and TC-PTP are highly related protein-tyrosine phosphatases (PTPs) that regulate the JAK/STAT signaling cascade essential for cytokine-receptor activation in immune cells. Here, we describe a novel immunotherapy approach whereby monocyte-derived dendritic cell (moDC) function is enhanced by modulating the enzymatic activities of PTP1B and TC-PTP. To downregulate or delete the activity/expression of these PTPs, we generated mice with PTP-specific deletions in the dendritic cell compartment or used PTP1B and TC-PTP specific inhibitor. While total ablation of PTP1B or TC-PTP expression leads to tolerogenic DCs via STAT3 hyperactivation, downregulation of either phosphatase remarkably shifts the balance toward an immunogenic DC phenotype due to hyperactivation of STAT4, STAT1 and Src kinase. The resulting increase in IL-12 and IFNγ production subsequently amplifies the IL-12/STAT4/IFNγ/STAT1/IL-12 positive autocrine loop and enhances the therapeutic potential of mature moDCs in tumor-bearing mice. Furthermore, pharmacological inhibition of both PTPs improves the maturation of defective moDCs derived from pancreatic cancer (PaC) patients. Our study provides a new advance in the use of DC-based cancer immunotherapy that is complementary to current cancer therapeutics.

Engineering better immunotherapies via RNA interference

The therapeutic potential of dendritic cell (DC) cancer vaccines has gained momentum in recent years. However, clinical data indicate that antitumor immune responses generally fail to translate into measurable tumor regression. This has been ascribed to a variety of tolerance mechanisms, one of which is the expression of immunosuppressive factors by DCs and T cells. With respect to cancer immunotherapies, these factors antagonise the ability to induce robust and sustained immunity required for tumor cell eradication. Gene silencing of immunosuppressive factors in either DCs or adoptive transferred T cells enhanced anti-tumor immune responses and significantly inhibited tumor growth. Therefore, engineered next generation of DC vaccines or adoptive T-cell therapy should include immunomodulatory siRNAs to release the "brakes" imposed by the immune system. Moreover, the combination of gene silencing, antigen targeting to DCs and cytoplasmic cargo delivery will improve clinical benefits.

Cellular signaling in the aging immune system

Causes for immunosenescence and inflamm-aging have to be established. Efficient function of the immune system requires homeostatic regulation from receptor recognition of antigenic challenge to cell responses and adaptation to its changing environment. It is reasonable to assume that one of the most important molecular causes of immunosenescence is alteration in the regulation of signaling pathways. Indeed, alterations in feed-forward and negative feedback (inhibitory) signaling have been highlighted in all cells involved in the immune response including short-lived (neutrophils) and long-lived (T lymphocytes) cells. These dysregulations tip the balance in favor of altered (less efficient) function of the immune system. In this review, we summarize our knowledge on signal transduction changes in the aging immune system and propose a unifying mechanism as one of the causes of immunosenescence. Modulation of these pathways with aging represents a major challenge to restore the immune response to functional levels.

Protein tyrosine phosphatase inhibition by metals and metal complexes

SIGNIFICANCE

Protein tyrosine phosphatases (PTPs) play essential roles in controlling cell proliferation, differentiation, communication, and adhesion. The dysregulated activities of PTPs are involved in the pathogenesis of a number of human diseases such as cancer, diabetes, and autoimmune diseases.

RECENT ADVANCES

Many PTPs have emerged as potential new targets for novel drug discovery. PTP inhibitors have attracted much attention. Many PTP inhibitors have been developed. Some of them have been proven to be efficient in lowering blood glucose levels in vivo or inhibiting tumor xenograft growth.

CRITICAL ISSUES

Some metal ions and metal complexes potently inhibit PTPs. The metal atoms within metal complexes play an important role in PTP binding, while ligand structures influence the inhibitory potency and selectivity. Some metal complexes can penetrate the cell membrane and selectively bind to their targeting PTPs, enhancing the phosphorylation of the related substrates and influencing cellular metabolism. PTP inhibition is potentially involved in the pathophysiological and toxicological processes of metals and some PTPs may be cellular targets of certain metal-based therapeutic agents.

FUTURE DIRECTIONS

Investigating the structural basis of the interactions between metal complexes and PTPs would facilitate a comprehensive understanding of the structure-activity relationship and accelerate the development of promising metal-based drugs targeting specific PTPs.

Protein tyrosine phosphatase 1B is a regulator of the interleukin-10-induced transcriptional program in macrophages

Both pro- and anti-inflammatory cytokines activate the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway; however, they elicit distinct transcriptional programs. Posttranslational modifications of STAT proteins, such as tyrosine phosphorylation, are critical to ensure the differential expression of STAT target genes. Although JAK-STAT signaling is dependent on reversible tyrosine phosphorylation, whether phosphatases contribute to the specificity of STAT-dependent gene expression is unclear. We examined the role of protein tyrosine phosphatase 1B (PTP1B) in regulating the interleukin-10 (IL-10)-dependent, STAT3-mediated anti-inflammatory response. We found that IL-10-dependent STAT3 phosphorylation and anti-inflammatory gene expression were enhanced in macrophages from PTP1B(-/-) mice compared to those in macrophages from wild-type mice. Consistent with this finding, the IL-10-dependent suppression of lipopolysaccharide-induced macrophage activation was increased in PTP1B(-/-) macrophages compared to that in wild-type macrophages, as was the IL-10-dependent increase in the cell surface expression of the anti-inflammatory cytokine receptor IL-4Rα. Furthermore, RNA sequencing revealed the expression of genes encoding proinflammatory factors in IL-10-treated PTP1B(-/-) macrophages, which correlated with increased phosphorylation of STAT1, which is not normally highly activated in response to IL-10. These findings identify PTP1B as a central regulator of IL-10R-STAT3 and IL-10R-STAT1 signaling, and demonstrate that phosphatases can tailor the quantitative and qualitative properties of cytokine-induced transcriptional responses.

PTP1B: a simple enzyme for a complex world

Our understanding of the fundamental regulatory roles that tyrosine phosphatases play within cells has advanced significantly in the last two decades. Out-dated ideas that tyrosine phosphatases acts solely as the "off" switch counterbalancing the action of tyrosine kinases has proved to be flawed. PTP1B is the most characterized of all the tyrosine phosphatases and it acts as a critical negative and positive regulator of numerous signaling cascades. PTP1B's direct regulation of the insulin and the leptin receptors makes it an ideal therapeutic target for type II diabetes and obesity. Moreover, the last decade has also seen several reports establishing PTP1B as key player in cancer serving as both tumor suppressor and tumor promoter depending on the cellular context. Despite many key advances in these fields one largely ignored area is what role PTP1B may play in the modulation of immune signaling. The important recognition that PTP1B is a major negative regulator of Janus kinase - signal transducer and activator of transcription (JAK-STAT) signaling throughout evolution places it as a key link between metabolic diseases and inflammation, as well as a unique regulator between immune response and cancer. This review looks at the emergence of PTP1B through evolution, and then explore at the cell and systemic levels how it is controlled physiologically. The second half of the review will focus on the role(s) PTP1B can play in disease and in particular its involvement in metabolic syndromes and cancer. Finally we will briefly examine several novel directions in the development of PTP1B pharmacological inhibitors.