Interleukin-7 regulates Bim proapoptotic activity in peripheral T-cell survival

Advances in IL-7 Research on Tumour Therapy

Interleukin-7 (IL-7) is a versatile cytokine that plays a crucial role in regulating the immune system's homeostasis. It is involved in the development, proliferation, and differentiation of B and T cells, as well as being essential for the differentiation and survival of naïve T cells and the production and maintenance of memory T cells. Given its potent biological functions, IL-7 is considered to have the potential to be widely used in the field of anti-tumour immunotherapy. Notably, IL-7 can improve the tumour microenvironment by promoting the development of Th17 cells, which can in turn promote the recruitment of effector T cells and NK cells. In addition, IL-7 can also down-regulate the expression of tumour growth factor-β and inhibit immunosuppression to promote anti-tumour efficacy, suggesting potential clinical applications for anti-tumour immunotherapy. This review aims to discuss the origin of IL-7 and its receptor IL-7R, its anti-tumour mechanism, and the recent advances in the application of IL-7 in tumour therapy.

Shaping Heterogeneity of Naive CD8+ T Cell Pools

Immune diversification helps protect the host against a myriad of pathogens. CD8⁺ T cells are essential adaptive immune cells that inhibit the spread of pathogens by inducing apoptosis in infected host cells, ultimately ensuring complete elimination of infectious pathogens and suppressing disease development. Accordingly, numerous studies have been conducted to elucidate the mechanisms underlying CD8⁺ T cell activation, proliferation, and differentiation into effector and memory cells, and to identify various intrinsic and extrinsic factors regulating these processes. The current knowledge accumulated through these studies has led to a huge breakthrough in understanding the existence of heterogeneity in CD8⁺ T cell populations during immune response and the principles underlying this heterogeneity. As the heterogeneity in effector/memory phases has been extensively reviewed elsewhere, in the current review, we focus on CD8⁺ T cells in a "naïve" state, introducing recent studies dealing with the heterogeneity of naive CD8⁺ T cells and discussing the factors that contribute to such heterogeneity. We also discuss how this heterogeneity contributes to establishing the immense complexity of antigen-specific CD8⁺ T cell response.

Med1 controls CD8 T cell maintenance through IL-7R-mediated cell survival signalling

Under steady‐state conditions, the pool size of peripheral CD8⁺ T cells is maintained through turnover and survival. Beyond TCR and IL‐7R signals, the underlying mechanisms are less well understood. In the present study, we found a significant reduction of CD8⁺ T cell proportion in spleens but not in thymi of mice with T cell‐specific deletion of Mediator Subunit 1 (Med1). A competitive transfer of wild‐type (WT) and Med1‐deficient CD8⁺ T cells reproduced the phenotype in the same recipients and confirmed intrinsic role of Med1. Furthermore, we observed a comparable degree of migration and proliferation but a significant increase of cell death in Med1‐deficient CD8⁺ T cells compared with WT counterparts. Finally, Med1‐deficient CD8⁺ T cells exhibited a decreased expression of interleukin‐7 receptor α (IL‐7Rα), down‐regulation of phosphorylated‐STAT5 (pSTAT5) and Bim up‐regulation. Collectively, our study reveals a novel role of Med1 in the maintenance of CD8⁺ T cells through IL‐7Rα/STAT5 pathway‐mediated cell survival.

Interleukin (IL)-7 Signaling in the Tumor Microenvironment

Interleukin (IL)-7 plays an important immunoregulatory role in different types of cells. Therefore, it attracts researcher's attention, but despite the fact, many aspects of its modulatory action, as well as other functionalities, are still poorly understood. The review summarizes current knowledge on the interleukin-7 and its signaling cascade in context of cancer development. Moreover, it provides a cancer-type focused description of the involvement of IL-7 in solid tumors, as well as hematological malignancies.The interleukin has been discovered as a growth factor crucial for the early lymphocyte development and supporting the growth of malignant cells in certain leukemias and lymphomas. Therefore, its targeting has been explored as a treatment modality in hematological malignancies, while the unique ability to expand lymphocyte populations selectively and without hyperinflammation has been used in experimental immunotherapies in patients with lymphopenia. Ever since the early research demonstrated a reduced growth of solid tumors in the presence of IL-7, the interleukin application in boosting up the anticancer immunity has been investigated. However, a growing body of evidence indicative of IL-7 upregulation in carcinomas, facilitating tumor growth and metastasis and aiding drug-resistance, is accumulating. It therefore becomes increasingly apparent that the response to the IL-7 stimulus strongly depends on cell type, their developmental stage, and microenvironmental context. The interleukin exerts its regulatory action mainly through phosphorylation events in JAK/STAT and PI3K/Akt pathways, while the significance of MAPK pathway seems to be limited to solid tumors. Given the unwavering interest in IL-7 application in immunotherapy, a better understanding of interleukin role, source in tumor microenvironment, and signaling pathways, as well as the identification of cells that are likely to respond should be a research priority.

Identification of a genomic enhancer that enforces proper apoptosis induction in thymic negative selection

During thymic negative selection, autoreactive thymocytes carrying T cell receptor (TCR) with overtly strong affinity to self-MHC/self-peptide are removed by Bim-dependent apoptosis, but how Bim is specifically regulated to link TCR activation and apoptosis induction is unclear. Here we identify a murine T cell-specific genomic enhancer EBAB (Bub1-Acoxl-Bim), whose deletion leads to accumulation of thymocytes expressing high affinity TCRs. Consistently, EBAB knockout mice have defective negative selection and fail to delete autoreactive thymocytes in various settings, with this defect accompanied by reduced Bim expression and apoptosis induction. By contrast, EBAB is dispensable for maintaining peripheral T cell homeostasis via Bim-dependent pathways. Our data thus implicate EBAB as an important, developmental stage-specific regulator of Bim expression and apoptosis induction to enforce thymic negative selection and suppress autoimmunity. Our study unravels a part of genomic enhancer codes that underlie complex and context-dependent gene regulation in TCR signaling.

IL-7-induced proliferation of peripheral Th17 cells is impaired in HAART-controlled HIV infection

OBJECTIVES

Th17 cells are key regulators of functional immunity in mucosal tissues, including the gut-associated lymphoid tissue (GALT), an important site of immune impairment in HIV infection. During HIV infection, Th17 cells are lost in large numbers from the GALT. Despite the recovery of peripheral CD4 T cells that accompanies suppression of viral replication with HAART, Th17 cells in GALT are not completely restored. IL-7 is essential for the survival and proliferation of T cells, but its signaling through its receptor IL-7Rα (CD127), is impaired in CD8 T cells and thymocytes during HIV infection. We set out to determine if decreased CD127 expression or impaired CD127 signaling may be the cause of Th17 impairment in HAART-controlled HIV infection.

DESIGN

Healthy and HIV donors on HAART were selected for this study of Th17 cell function in HIV.

METHODS

Peripheral CD4 T cells and Th17 cells were isolated using magnetic beads, then stimulated with IL-7. CD127 expression and the phosphorylation of signaling molecules was determined using flow cytometry. Proliferation was determined with a CFSE dilution assay.

RESULTS

CD127 was not decreased on Th17 cells from HAART-controlled HIV individuals, in fact, the percentage of Th17 cells that express CD127 was increased in treated HIV individuals. Furthermore, Th17 cells from HAART-controlled individuals, have normal IL-7-induced STAT5 and Bcl-2 responses, but vastly decreased proliferative responses.

CONCLUSION

This reduced IL-7 responsiveness may explain the lack of Th17 cell recovery and ongoing systemic immune activation that persists despite well treated HIV infection.

Life and Death of Activated T Cells: How Are They Different from Naïve T Cells?

T cells are pivotal in immunity and immunopathology. After activation, T cells undergo a clonal expansion and differentiation followed by a contraction phase, once the pathogen has been cleared. Cell survival and cell death are critical for controlling the numbers of naïve T cells, effector, and memory T cells. While naïve T cell survival has been studied for a long time, more effort has gone into understanding the survival and death of activated T cells. Despite this effort, there is still much to be learnt about T cell survival, as T cells transition from naïve to effector to memory. One key advance is the development of inhibitors that may allow the temporal study of survival mechanisms operating in these distinct cell states. Naïve T cells were highly reliant on BCL-2 and sensitive to BCL-2 inhibition. Activated T cells are remarkably different in their regulation of apoptosis by pro- and antiapoptotic members of the BCL-2 family, rendering them differentially sensitive to antagonists blocking the function of one or more members of this family. Recent progress in understanding other programmed cell death mechanisms, especially necroptosis, suggests a unique role for alternative pathways in regulating death of activated T cells. Furthermore, we highlight a mechanism of epigenetic regulation of cell survival unique to activated T cells. Together, we present an update of our current understanding of the survival requirement of activated T cells.

Role of cellular events in the pathophysiology of sepsis

INTRODUCTION

Sepsis is a dysregulated host immune response due to an uncontrolled infection. It is a leading cause of mortality in adult intensive care units globally. When the host immune response induced against a local infection fails to contain it locally, it progresses to sepsis, severe sepsis, septic shock and death.

METHOD

Literature survey was performed on the roles of different innate and adaptive immune cells in the development and progression of sepsis. Additionally, the effects of septic changes on reprogramming of different immune cells were also summarized to prepare the manuscript.

FINDINGS

Scientific evidences to date suggest that the loss of balance between inflammatory and anti-inflammatory responses results in reprogramming of immune cell activities that lead to irreversible tissue damaging events and multi-organ failure during sepsis. Many surface receptors expressed on immune cells at various stages of sepsis have been suggested as biomarkers for sepsis diagnosis. Various immunomodulatory therapeutics, which could improve the functions of immune cells during sepsis, were shown to restore immunological homeostasis and improve survival in animal models of sepsis.

CONCLUSION

In-depth and comprehensive knowledge on the immune cell activities and their correlation with severity of sepsis will help clinicians and scientists to design effective immunomodulatory therapeutics for treating sepsis.

Posttranscriptional and Translational Control of Gene Regulation in CD4+ T Cell Subsets

The immune system is under strict regulatory control to ensure homeostasis of inflammatory responses, lying dormant when not needed but quick to act when called upon. Small changes in gene expression can lead to drastic changes in lineage commitment, cellular function, and immunity. Conventional assessment of these changes centered on the analysis of mRNA levels through a variety of methodologies, including microarrays. However, mRNA synthesis does not always correlate directly to protein synthesis and downstream functional activity. Work conducted in recent years has begun to shed light on the various posttranscriptional changes that occur in response to a dynamic external environment that a given cell type encounters. We provide a critical review of key posttranscriptional mechanisms (i.e., microRNA) and translational mechanisms of regulation of gene expression in the immune system, with a particular emphasis on these regulatory processes in various CD4(+) T cell subsets.

Critical Illness-Induced Immune Suppression: Current State of the Science

Critical illness comprises a heterogeneous group of serious medical conditions that typically involve an initial proinflammatory process. A compensatory anti-inflammatory response may occur that, if severe and persistent, places the patient at high risk for adverse outcomes including secondary infection and death. Monitoring strategies can identify these patients through measurement of innate and adaptive immune function. Reductions in monocyte HLA-DR expression, reduced cytokine production capacity, increased inhibitory cell surface molecule expression, and lymphopenia have all been associated with this immune-suppressed state. Intriguing data suggest that critical illness-induced immune suppression may be reversible with agents such as interferon-γ, granulocyte macrophage colony-stimulating factor, interleukin 7, or anti-programmed death-1 therapy. Future approaches for characterization of patient-specific immune derangements and individualized treatment could revolutionize how we recognize and prevent complications in critically ill patients.

Emerging therapeutic targets of sepsis-associated acute kidney injury

Sepsis-associated acute kidney injury (SA-AKI) is linked to high morbidity and mortality. To date, singular approaches to target specific pathways known to contribute to the pathogenesis of SA-AKI have failed. Because of the complexity of the pathogenesis of SA-AKI, a reassessment necessitates integrative approaches to therapeutics of SA-AKI that include general supportive therapies such as the use of vasopressors, fluids, antimicrobials, and target-specific and time-dependent therapeutics. There has been recent progress in our understanding of the pathogenesis and treatment of SA-AKI including the temporal nature of proinflammatory and anti-inflammatory processes. In this review, we discuss the clinical and experimental basis of emerging therapeutic approaches that focus on targeting early proinflammatory and late anti-inflammatory processes, as well as therapeutics that may enhance cellular survival and recovery. Finally, we include ongoing clinical trials in sepsis.

Responsiveness of Developing T Cells to IL-7 Signals Is Sustained by miR-17∼92

miRNAs regulate a large variety of developmental processes including development of the immune system. T cell development is tightly controlled through the interplay of transcriptional programs and cytokine-mediated signals. However, the role of individual miRNAs in this process remains largely elusive. In this study, we demonstrated that hematopoietic cell-specific loss of miR-17∼92, a cluster of six miRNAs implicated in B and T lineage leukemogenesis, resulted in profound defects in T cell development both at the level of prethymic T cell progenitors as well as intrathymically. We identified reduced surface expression of IL-7R and concomitant limited responsiveness to IL-7 signals as a common mechanism resulting in reduced cell survival of common lymphoid progenitors and thymocytes at the double-negative to double-positive transition. In conclusion, we identified miR-17∼92 as a critical modulator of multiple stages of T cell development.

Regulation of Bim in Health and Disease

The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.

c-FLIP protects T lymphocytes from apoptosis in the intrinsic pathway

Apoptosis can be induced by either death receptors on the plasma membrane (extrinsic pathway) or the damage of the genome and/or cellular organelles (intrinsic pathway). Previous studies suggest that cellular caspase 8 (FLICE)-like inhibitory protein (c-FLIP) promotes cell survival in death receptor-induced apoptosis pathway in T lymphocytes. Independent of death receptor signaling, mitochondria sense apoptotic stimuli and mediate the activation of effector caspases. Whether c-FLIP regulates mitochondrion-dependent apoptotic signals remains unknown. In this study, c-FLIP gene was deleted in mature T lymphocytes in vitro, and the role of c-FLIP protein in intrinsic apoptosis pathway was studied. In resting T cells treated with the intrinsic apoptosis inducer, c-FLIP suppressed cytochrome c release from mitochondria. Bim-deletion rescued the enhanced apoptosis in c-FLIP-deficient T cells, whereas inhibition of caspase 8 did not. Different from activated T cells, there was no necroptosis or increase in reactive oxygen species in c-FLIP-deficient resting T cells. These data suggest that c-FLIP is a negative regulator of intrinsic apoptosis pathway in T lymphocytes.

The new normal: immunomodulatory agents against sepsis immune suppression

Sepsis is the leading cause of death among critically ill patients in intensive care units, and treatment options are limited. Therapies developed against the proinflammatory stage have failed clinically; therefore, new approaches that target the host immune response in sepsis are necessary. Increasing evidence suggests that a major pathophysiological event in sepsis is immune suppression, often resulting in secondary fungal, bacterial, or viral infections. Recent studies from animal sepsis models and patient samples suggest that cytokines such as interleukin-7 (IL-7), IL-15, granulocyte macrophage colony-stimulating factor (GM-CSF), as well as co-inhibitory molecule blockade, such as anti-programmed cell death receptor-1 (anti-PD-1) and anti-B and T lymphocyte attenuator (anti-BTLA), may have utility in alleviating the clinical morbidity associated with sustained sepsis. This review discusses some of these novel immunomodulatory agents and evaluates their potential use as therapeutics.

Mutually exclusive regulation of T cell survival by IL-7R and antigen receptor-induced signals

Two major processes govern T cell proliferation and survival: interleukin-7-mediated homeostasis and antigen-induced selection. How cells transit between the two states is unknown. Here we show that T cell receptor ligation actively inhibits homeostatic survival signals while initiating a new, dominant survival programme. This switch is mediated by a change in the expression of pro- and anti-apoptosis proteins through the downregulation of Bcl-2 and the induction of Bim, A1 and Bcl-xL. Calcineurin inhibitors prevent the initiation of the new survival programme, while permitting the dominant repression of Bcl-2. Thus, in the presence of these drugs the response to antigen receptor ligation is cell death. Our results identify a molecular switch that can serve as an attractive target for inducing antigen-specific tolerance in treating autoimmune disease patients and transplant recipients.

Before antigen exposure, T cell survival is dependent on signalling stimulated by IL-7. Koenen et al. show that upon encountering specific antigen, T cell receptor signalling initiates a different set of survival pathways, which actively suppress those that sustain naive T cells.

Pim1 permits generation and survival of CD4+ T cells in the absence of γc cytokine receptor signaling

γ-Chain (γc) cytokine receptor signaling is required for the development of all lymphocytes. Why γc signaling plays such an essential role is not fully understood, but induction of the serine/threonine kinase Pim1 is considered a major downstream event of γc as Pim1 prevents apoptosis and increases metabolic activity. Consequently, we asked whether Pim1 overexpression would suffice to restore lymphocyte development in γc-deficient mice. By analyzing Pim1-transgenic γc-deficient mice (Pim1(Tg) γc(KO) ), we show that Pim1 promoted T-cell development and survival in the absence of γc. Interestingly, such effects were largely limited to CD4(+) lineage αβ T cells as CD4(+) T-cell numbers improved to near normal levels but CD8(+) T cells remained severely lymphopenic. Notably, Pim1 over-expression failed to promote development and survival of any T-lineage cells other than αβ T cells, as we observed complete lack of γδ, NKT, FoxP3(+) T regulatory cells and TCR-β(+) CD8αα IELs in Pim1(Tg) γc(KO) mice. Collectively, these results uncover distinct requirements for γc signaling between CD4(+) αβ T cells and all other T-lineage cells, and they identify Pim1 as a novel effector molecule sufficient to drive CD4(+) αβ T-cell development and survival in the absence of γc cytokine receptor signaling.

TGF-β sensitivity restrains CD8+ T cell homeostatic proliferation by enforcing sensitivity to IL-7 and IL-15

The pleiotropic cytokine TGF-β has been implicated in the regulation of numerous aspects of the immune response, including naïve T cell homeostasis. Previous studies found that impairing TGF-β responsiveness (through expression of a dominant-negative TGF-β RII [DNRII] transgene) leads to accumulation of memory phenotype CD8 T cells, and it was proposed that this resulted from enhanced IL-15 sensitivity. Here we show naïve DNRII CD8 T cells exhibit enhanced lymphopenia-driven proliferation and generation of “homeostatic” memory cells. However, this enhanced response occurred in the absence of IL-15 and, unexpectedly, even in the combined absence of IL-7 and IL-15, which were thought essential for CD8 T cell homeostatic expansion. DNRII transgenic CD8 T cells still require access to self Class I MHC for homeostatic proliferation, arguing against generalized dysregulation of homeostatic cues. These findings suggest TGF-β responsiveness is critical for enforcing sensitivity to homeostatic cytokines that limit maintenance and composition of the CD8 T cell pool. (154 words).

The major isoforms of Bim contribute to distinct biological activities that govern the processes of autophagy and apoptosis in interleukin-7 dependent lymphocytes

Bim is a BH3-only member of the Bcl-2 family that enables the death of T-cells. Partial rescue of cytokine-deprived T-cells occurs when Bim and the receptor for the T-cell growth factor, interleukin-7, are deleted, implicating Bim as a possible target of interleukin-7-mediated signaling. Alternative splicing yields three major isoforms: BimEL, BimL and BimS. To study the effect of Bim deficiency and define the function of the major isoforms, Bim-containing and Bim-deficient T-cells, dependent on interleukin-7 for growth, were used. Loss of total Bim in interleukin-7-deprived T-cells resulted in delayed apoptosis. However, loss of Bim also impeded the later degradative phase of autophagy. p62, an autophagy-adaptor protein which is normally degraded, accumulated in Bim deficient cells. To explain this, BimL was found to support acidification of lysosomes that later may associate with autophagic vesicles. Key findings showed that inhibition of lysosomal acidification accelerated death upon interleukin-7 withdrawal only in Bim-containing T-cells. intereukin-7 dependent T-cells lacking Bim were less sensitive to inhibition of lysosomal acidification. BimL co-immunoprecipitated with dynein and Lamp1-containing vesicles, indicating BimL could be an adaptor for dynein to facilitate loading of lysosomes. In Bim deficient T-cells, lysosome-tracking probes revealed vesicles of less acidic pH. Over-expression of BimL restored acidic vesicles in Bim deficient T-cells, while other isoforms, BimEL and BimS, promoted intrinsic cell death. These results reveal a novel role for BimL in lysosomal positioning that may be required for the formation of degradative autolysosomes.

Intrathymic IL-7: the where, when, and why of IL-7 signaling during T cell development

The thymus is the birthplace of all T lineage cells. But the thymus is also a cradle as it provides the environment for further maturation and differentiation of immature thymocytes. While many factors contribute to make the thymus a unique place for T cell development, here we review the essential role of intrathymic interleukin-7 (IL-7). In the absence of IL-7 signaling, survival, proliferation and differentiation of immature thymocytes are all severely impaired. Consequently, IL-7 is critical to nurture and guide T precursor cells through the diverse steps of thymic maturation. Interestingly, even as IL-7 signaling is such a critical factor, IL-7 signaling must be also actively suppressed during specific stages of T cell differentiation. These contradictory observations are puzzling but can be satisfactorily explained when understanding the developmental context of IL-7 signaling. In this regard, here we will discuss the spatiotemporal expression of intrathymic IL-7 and address the stage-specific effects of IL-7 signaling in developing thymocytes. Specifically, we will review other facets of intrathymic IL-7 beyond its role as a pro-survival factor and so clarify and reaffirm the unique role of IL-7 as a prime factor in T cell development and differentiation.

Angiotensin II regulates activation of Bim via Rb/E2F1 during apoptosis: involvement of interaction between AMPKβ1/2 and Cdk4

Apoptotic cell death is essential for mammalian development and tissue homeostasis. Dysregulation of apoptosis has been identified in pathologies including in pulmonary fibrotic remodeling. We previously reported that a key proapoptotic factor in fibrosis, angiotensin II (Ang II), mediates apoptosis in primary pulmonary artery endothelial cells (PAEC) via the AT(2) receptor and requires activation of AMP-regulated protein kinase (AMPK). We now demonstrate that Ang II induces E2F1 transcription factor binding to and activation of the promoter for the Bcl-2 homology 3 (BH3)-only protein Bim. In PAEC, Ang II treatment induced cyclin-dependent kinase 4 (Cdk4)-mediated hyperphosphorylation of retinoblastoma protein (Rb) and its disassociation from E2F1, a key step in facilitating E2F1-directed transcriptional activity. Indeed, ectopic expression of a dominant negative Cdk4 mutant inhibited Ang II-mediated hyperphosphorylation of Rb and Bim promoter activation. Our data also show that the β-subunit of AMPK was constitutively associated with Cdk4 in PAEC and that Ang II treatment induced AMPKβ phosphorylation and subsequent disassociation of this complex. Both Ang II-induced Rb hyperphosphorylation and Cdk4-AMPK disassociation were blocked by the AMPK inhibitor compound C. Together these findings illuminate a novel proapoptotic signaling pathway in endothelial cells, whereby Ang II triggers E2F1-mediated transcriptional upregulation of Bim via activation of AMPKβ1/2 and Cdk4.

IL-7 signaling and CD127 receptor regulation in the control of T cell homeostasis

After their development in the thymus, mature T cells are maintained in the periphery by two sets of survival signals, namely TCR signals from contact with self-peptide/MHC ligands and the cytokine receptor signals from binding IL-7 and IL-15. These signals cooperate to maximize the utility of finite resources to support a diverse pool of mature T cells. It is becoming increasingly clear that multiple mechanisms exist to regulate expression of IL-7R at the transcriptional and post-translational levels. The interplay between TCR signals and IL-7R signals are also important in regulation of IL-7R expression. This review will focus on regulation of T cell homeostasis by IL-7R signaling, with an emphasis on the cross talk between signals from TCR and IL-7R.

MicroRNA and transcription factor co-regulatory network analysis reveals miR-19 inhibits CYLD in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy. The understanding of its gene expression regulation and molecular mechanisms still remains elusive. Started from experimentally verified T-ALL-related miRNAs and genes, we obtained 120 feed-forward loops (FFLs) among T-ALL-related genes, miRNAs and TFs through combining target prediction. Afterwards, a T-ALL miRNA and TF co-regulatory network was constructed, and its significance was tested by statistical methods. Four miRNAs in the miR-17–92 cluster and four important genes (CYLD, HOXA9, BCL2L11 and RUNX1) were found as hubs in the network. Particularly, we found that miR-19 was highly expressed in T-ALL patients and cell lines. Ectopic expression of miR-19 represses CYLD expression, while miR-19 inhibitor treatment induces CYLD protein expression and decreases NF-κB expression in the downstream signaling pathway. Thus, miR-19, CYLD and NF-κB form a regulatory FFL, which provides new clues for sustained activation of NF-κB in T-ALL. Taken together, we provided the first miRNA-TF co-regulatory network in T-ALL and proposed a model to demonstrate the roles of miR-19 and CYLD in the T-cell leukemogenesis. This study may provide potential therapeutic targets for T-ALL and shed light on combining bioinformatics with experiments in the research of complex diseases.

JunD/AP-1-mediated gene expression promotes lymphocyte growth dependent on interleukin-7 signal transduction

Interleukin-7 (IL-7) is an essential cytokine for lymphocyte growth that has the potential for promoting immune reconstitution. This feature makes IL-7 an ideal candidate for therapeutic development. As with other cytokines, signaling through the IL-7 receptor induces the JAK/STAT pathway. However, the broad scope of IL-7 regulatory targets likely necessitates the use of other signaling components whose identities remain poorly defined. To this end, we used an IL-7 dependent T-cell line to examine how expression of the glycolytic enzyme, Hexokinase II (HXKII) was regulated by IL-7 in a STAT5-independent manner. Our studies revealed that IL-7 promoted the activity of JNK (Jun N-terminal Kinase), and that JNK, in turn, drove the expression of JunD, a component of the Activating Protein 1 (AP-1) transcription factors. Gel shifts showed that the AP-1 complex induced by IL-7 contained JunD but not c-Fos or c-Jun. Inhibition of JNK/JunD blocked glucose uptake and HXKII gene expression, indicating that this pathway was responsible for promoting HXKII expression. Because others had shown that JunD was a negative regulator of cell growth, we performed a bioinformatics analysis to uncover possible JunD-regulated gene targets. Our search revealed that JunD could control the expression of proteins involved in signal transduction, cell survival and metabolism. One of these growth promoters was the oncogene, Pim-1. Pim-1 is an IL-7-induced protein that was inhibited when the activities of JNK or JunD were blocked, showing that in IL-7 dependent T-cells JunD can promote positive signals transduced through Pim-1. This was confirmed when the IL-7-induced proliferation of CD8 T-cells was impaired upon JunD inhibition. These results show that engagement of the IL-7 receptor drives a signal that is more complex than the JAK/STAT pathway, activating JNK and JunD to induce rapid growth stimulation through the expression of metabolic and signaling factors like HXKII and Pim-1.

Apoptosis - an Ubiquitous T cell Immunomodulator

Apoptosis is a natural process where cells that are no longer required can be eliminated in a highly regulated, controlled manner. Apoptosis is important in maintaining the mammalian immune system and plays a significant role in immune response, positive and negative T cell selection, and cytotoxic death of target cells. When the apoptotic pathways are impaired or are not tightly regulated, autoimmune diseases, inflammatory diseases, viral and bacterial infections and cancers ensue. An imbalance in the anti-apoptotic and pro-apoptotic factors has been implicated in these diseases. Moreover, current therapies directed towards these diseases focus on the modulation of the apoptotic death pathways to regulate the immune response. In this review, we will focus on the process of T cell activation and apoptosis in autoimmune reactions, in response to tumor progression as well as in response to bacterial and viral infections.

HIV infection perturbs interleukin-7 signaling at the step of STAT5 nuclear relocalization

OBJECTIVE

Interleukin-7 (IL-7) responses are impaired in CD4(+) T cells from HIV-infected patients, which may play a significant role in the loss of CD4(+) T-cell homeostasis. We set to investigate the nature of IL-7-dependent signaling defects in patients with progressive HIV-1 infection.

DESIGN AND METHODS

IL-7 signaling was compared in CD4(+) T cells from viremic patients with a viral load more than 10,000 copies of HIV RNA/ml (n = 23) and from healthy blood donors (n = 23). Phosphorylation of the transcription factor STAT5 on the regulatory serine S726 and the key tyrosine Y694 was monitored by intracellular flow cytometry. Phospho-STAT5 relocalization to the nucleus was analyzed by quantitative immunofluorescence imaging.

RESULTS

In control CD4(+) T cells, S726 phosphorylation was mostly constitutive and inducible by IL-7 to a limited extent (1.3x, P < 0.05). In contrast, phosphorylation at Y694 was highly inducible by IL-7 (12.6x, P < 0.0001). Progressive HIV infection led to hyperphosphorylation of both S726 and Y694 in naive CD4(+) T cells, with these changes correlating together (R = 0.66, P = 0.01). Quantitative image analysis revealed an impairment in the nuclear relocalization of both forms of phospho-STAT5 in patient cells (P < 0.005 for S726; P < 0.05 for Y694). The nuclear relocalization defect correlated with increased HLA-DR expression (R = 0.75, P < 0.01), suggesting a role for chronic immune activation in perturbed IL-7 signal transduction.

CONCLUSION

HIV infection perturbs IL-7 signaling by impairing the access of STAT5 to the nuclear compartment. This defect may contribute to the loss of CD4(+) T-cell populations in patients with chronically high immune activation.

A role for p120 RasGAP in thymocyte positive selection and survival of naive T cells

Activation of the Ras small GTP-binding protein is necessary for normal T cell development and function. However, it is unknown which Ras GTPase-activating proteins (RasGAPs) inactivate Ras in T cells. We used a T cell-specific RASA1-deficient mouse model to investigate the role of the p120 RasGAP (RASA1) in T cells. Death of CD4(+)CD8(+) double-positive thymocytes was increased in RASA1-deficient mice. Despite this finding, on an MHC class II-restricted TCR transgenic background, evidence was obtained for increased positive selection of thymocytes associated with augmented activation of the Ras-MAPK pathway. In the periphery, RASA1 was found to be dispensable as a regulator of Ras-MAPK activation and T cell functional responses induced by full agonist peptides. However, numbers of naive T cells were substantially reduced in RASA1-deficient mice. Loss of naive T cells in the absence of RASA1 could be attributed in part to impaired responsiveness to the IL-7 prosurvival cytokine. These findings reveal an important role for RASA1 as a regulator of double-positive survival and positive selection in the thymus as well as naive T cell survival in the periphery.

Cdc25A-driven proliferation regulates CD62L levels and lymphocyte movement in response to interleukin-7

OBJECTIVE

Interleukin-7 (IL-7) is a multifunctional cytokine and a promising immunotherapeutic agent. However, because transient T-cell depletion is an immediate outcome of IL-7 administration at supraphysiological doses, we investigated the mechanism by which the IL-7 proliferative signal transduced through Cdc25A, a key activator of cyclin-dependent kinases, could modulate lymphocyte movement.

MATERIALS AND METHODS

Employing novel methods of manipulating Cdc25A gene expression, combined with in vitro and in vivo evaluation of IL-7 application, we assessed the expression of activation and homing markers and identified the mechanism by which IL-7 could induce T-cell expansion and alter lymphocyte motility.

RESULTS

Constitutively active Cdc25A drove T-cell proliferation independently of IL-7 and resulted in an activated phenotype (CD69(hi), CD44(hi)). Conversely, inhibition of Cdc25A resulted in decreased proliferation, reduced expression of activation markers, and upregulation of the lymph node homing molecule, CD62L, which promoted cell adhesion when engaged by ligand. We found that IL-7 prevented the nuclear translocation of the transcription factor, Foxo1, in a manner dependent on the activity of Cdc25A, resulting in decreased levels of CD62L. In vivo administration of IL-7 decreased lymph node cellularity, while treatment with IL-7, premixed with a neutralizing IL-7 antibody (M25), increased total lymph node cells--with more nuclear Foxo1 detected in cells from mice receiving IL-7 + M25.

CONCLUSIONS

These results are consistent with the model that IL-7 drives Cdc25A-mediated T-cell proliferation, which prevents the nuclear translocation of Foxo1, leading to reduced expression of CD62L and the migration of T cells into circulation.