The JNK pathway regulates the In vivo deletion of immature CD4(+)CD8(+) thymocytes

Inhibition of the MAP2K7-JNK pathway with 5Z-7-oxozeaenol induces apoptosis in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive pediatric leukemia with a worse prognosis than most frequent B-cell ALL due to a high incidence of treatment failures and relapse. Our previous work showed that loss of the pioneer factor KLF4 in a NOTCH1-induced T-ALL mouse model accelerated the development of leukemia through expansion of leukemia-initiating cells and activation of the MAP2K7 pathway. Similarly, epigenetic silencing of the KLF4 gene in children with T-ALL was associated with MAP2K7 activation. Here, we showed the small molecule 5Z-7-oxozeaenol (5Z7O) induces dose-dependent cytotoxicity in a panel of T-ALL cell lines mainly through inhibition of the MAP2K7-JNK pathway, which further validates MAP2K7 as a therapeutic target. Mechanistically, 5Z7O-mediated apoptosis was caused by the downregulation of regulators of the G2/M checkpoint and the inhibition of survival pathways. The anti-leukemic capacity of 5Z7O was evaluated using leukemic cells from two mouse models of T-ALL and patient-derived xenograft cells generated using lymphoblasts from pediatric T-ALL patients. Finally, a combination of 5Z7O with dexamethasone, a drug used in frontline therapy, showed synergistic induction of cytotoxicity. In sum, we report here that MAP2K7 inhibition thwarts survival mechanisms in T-ALL cells and warrants future pre-clinical studies for high-risk and relapsed patients.

Integrative Single-Cell Transcriptomic Analysis of Human Fetal Thymocyte Development

Intrathymic differentiation of T lymphocytes begins as early as intrauterine stage, yet the T cell lineage decisions of human fetal thymocytes at different gestational ages are not currently understood. Here, we performed integrative single-cell analyses of thymocytes across gestational ages. We identified conserved candidates underlying the selection of T cell receptor (TCR) lineages in different human fetal stages. The trajectory of early thymocyte commitment during fetal growth was also characterized. Comparisons with mouse data revealed conserved and species-specific transcriptional dynamics of thymocyte proliferation, apoptosis and selection. Genome-wide association study (GWAS) data associated with multiple autoimmune disorders were analyzed to characterize susceptibility genes that are highly expressed at specific stages during fetal thymocyte development. In summary, our integrative map describes previously underappreciated aspects of human thymocyte development, and provides a comprehensive reference for understanding T cell lymphopoiesis in a self-tolerant and functional adaptive immune system.

The role of MKK4 in T-cell development and immunity to viral infections

The stress-activated protein kinases (SAPKs)/c-Jun-N-terminal-kinases (JNK) are members of the mitogen-activated protein kinase family. These kinases are responsible for transducing cellular signals through a phosphorylation-dependent signaling cascade. JNK activation in immune cells can lead to a range of critical cellular responses that include proliferation, differentiation and apoptosis. MKK4 is a SAPK that can activate both JNK1 and JNK2; however, its role in T-cell development and function has been controversial. Additionally, loss of either JNK1 or JNK2 has opposing effects in the generation of T-cell immunity to viral infection and cancer. We used mice with a conditional loss of MKK4 in T cells to investigate the in vivo role of MKK4 in T-cell development and function during lymphocytic choriomeningitis virus (LCMV) infection. We found no physiologically relevant differences in T-cell responses or immunity to either acute or chronic LCMV in the absence of MKK4.

ASK1 Mediates Nur77 Expression in T-Cell Receptor Mediated Thymocyte Apoptosis

: Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK) that activates downstream JNK and p38 mitogen-activated protein kinase (MAPK) to relay death signals into cells in response to various environmental stress. However, whether ASK1 plays a role in T cell receptor (TCR)-mediated apoptosis of thymocytes is unclear. Here, we show that ASK1 is activated upon TCR stimulation and plays an important role in TCR-mediated apoptosis of thymocytes by triggering downstream JNK and p38 signaling cascades. Mechanistically, ASK1-JNK/p38 signaling leads to the upregulation of neuron-derived clone 77 (Nur77), a critical pro-apoptotic protein involved in TCR-mediated apoptosis of thymocytes. Furthermore, we demonstrate that the activation of ASK1 is negatively modulated by Akt upon TCR stimulation. Thus, our results identify a previously unappreciated signaling mechanism involving ASK1 in TCR-mediated apoptosis of thymocytes.

JNK and phosphorylated Bcl-2 predict multiple sclerosis clinical activity and glatiramer acetate therapeutic response

In this study, we investigated the role of JNK and phospho-Bcl-2 as possible biomarkers of multiple sclerosis (MS) relapse and of glatiramer acetate (GA) therapeutic response in relapsing-remitting MS patients. We enrolled a cohort of 15 GA-treated patients and measured the expression of JNK1, JNK2, phospho-JNK and phospho-Bcl-2 through Western blotting of lysates from peripheral blood mononuclear cells collected at 0, 3, 6, and 12 months after initiating GA therapy. We found significantly higher levels of JNK1 p54 and JNK2 p54 and significantly lower levels of p-Bcl-2 in relapse patients and in GA non-responders. By using receiver operating characteristic analysis, we found that the probability of accurately detecting relapse and response to GA was: 92% and 75.5%, respectively, for JNK1 p54 and 86% and 94.6%, respectively, for p-Bcl-2. Our data suggest that JNK1 and p-Bcl-2 could serve as potential biomarkers for MS relapse and the therapeutic response to GA.

T Cells and Regulated Cell Death: Kill or Be Killed

Cell death plays two major complementary roles in T cell biology: mediating the removal of cells that are targeted by T cells and the removal of T cells themselves. T cells serve as major actors in the adaptive immune response and function by selectively killing cells which are infected or dysfunctional. This feature is highly involved during homeostatic maintenance, and is relied upon and modulated in the context of cancer immunotherapy. The vital recognition and elimination of both autoreactive T cells and cells which are unable to recognize threats is a highly selective and regulated process. Moreover, detection of potential threats will result in the activation and expansion of T cells, which on resolution of the immune response will need to be eliminated. The culling of these T cells can be executed via a multitude of cell death pathways which are used in context-specific manners. Failure of these processes may result in an accumulation of misdirected or dysfunctional T cells, leading to complications such as autoimmunity or cancer. This review will focus on the role of cell death regulation in the maintenance of T cell homeostasis, as well as T cell-mediated elimination of infected or dysfunctional cells, and will summarize and discuss the current knowledge of the cellular mechanisms which are implicated in these processes.

Xihuang pill promotes apoptosis of Treg cells in the tumor microenvironment in 4T1 mouse breast cancer by upregulating MEKK1/SEK1/JNK1/AP-1 pathway

OBJECTIVE

To determine the role of the MEKK1/SEK1/JNK1/AP-1 pathway in the action of Xihuang pill (XHP) in reducing regulatory T (Treg) cell numbers in the tumor microenvironment in a 4T1 mouse breast cancer model, and to clarify the anti-tumor mechanism of XHP in breast cancer.

METHODS

We established a mouse 4T1 breast cancer model. Model mice were administered XHP for 2 weeks, and tumor tissues were then removed, weighed, sliced, and homogenized. Treg cells in the tumor microenvironment were isolated by magnetic cell sorting and analyzed by immunohistochemistry and flow cytometry. Treg cell apoptosis was detected by TdT-mediated dUTP nick end labeling. mRNA expression levels of MEKK1, SEK1, JNK1, and AP-1 in Treg cells in the tumor microenvironment were detected by quantitative real-time PCR and their protein expression levels were detected by immunofluorescence staining and western blot.

RESULTS

Tumor weights were significantly lower in the XHP groups compared with the untreated control group. The overall number of Treg cells in the tumor microenvironment decreased while the number of apoptotic Treg cells increased with increasing doses of XHP. mRNA and protein expression levels of MEKK1, SEK1, JNK1, and AP-1 in Treg cells in the tumor microenvironment increased with increasing doses of XHP.

CONCLUSION

XHP might promote Treg cell apoptosis in the tumor microenvironment and further inhibit the tumor growth of 4T1 mouse breast cancer. The mechanism of XHP may be related to upregulation of gene and protein expression of MEKK1, SEK1, JNK1, and AP-1 in Treg cells in the tumor microenvironment.

Novel tumor-suppressor function of KLF4 in pediatric T-cell acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common hematological malignancy in pediatric patients. Despite advances in the treatment of this disease, many children with T-cell ALL (T-ALL) die from disease relapse due to low responses to standard chemotherapy and the lack of a targeted therapy that selectively eradicates the chemoresistant leukemia-initiating cells (LICs) responsible for disease recurrence. We reported recently that the reprogramming factor Krüppel-like factor 4 (KLF4) has a tumor-suppressive function in children with T-ALL. KLF4 silencing by promoter deoxyribonucleic acid (DNA) methylation in patients with T-ALL leads to aberrant activation of the mitogen-activated protein kinase kinase MAP2K7 and the downstream c-Jun NH₂-terminal kinase (JNK) pathway that controls the expansion of leukemia cells via c-Jun and activating transcription factor 2. This pathway can be inhibited with small molecules and therefore has the potential to eliminate LICs and eradicate disease in combination with standard therapy for patients with refractory and relapsed disease. The present review summarizes the role of the KLF4-MAP2K7 pathway in T-ALL pathogenesis and the function of JNK and MAP2K7 in carcinogenesis and therapy.

Expression of Twist2 is controlled by T-cell receptor signaling and determines the survival and death of thymocytes

Self-reactive thymocytes are eliminated by negative selection, whereas competent thymocytes survive by positive selection. The strength of the T-cell receptor (TCR) signal determines the fate of thymocytes undergoing either positive or negative selection. The TCR signal strength is relatively higher in negative selection than in positive selection and induces pro-apoptotic molecules such as Nur77 and Nor-1, which are members of the orphan nuclear receptor family, that then cause TCR-mediated apoptosis. However, at the molecular level, it remains unclear how positive or negative selection is distinguished based on the TCR signal. We found that the expression of Twist2 is differentially regulated in positively and negatively selected thymocytes. In particular, TCR signal strength that elicits positive selection induces Twist2 expression via the Ca²⁺-Cacineurin-NFATc3 pathway, whereas strength of the TCR signal that results in negative selection abolishes NFATc3-dependent Twist2 induction via specific activation of the JNK pathway. Using Twist2-deficient and Twist2 transgenic mice, we also found that Twist2 determines thymocyte sensitivity to TCR-mediated apoptosis by regulating the expression of Nur77 and Nor-1. Twist2 partially retains histone deacetylase 7 (HDAC7) in the nucleus and recruits it to the Nur77 promoter region to repress Nur77 in positively selected thymocytes. Thus our results suggest a molecular mechanism of how thymocytes interpret the strength of the TCR signal and how TCR sensitivity is controlled during thymic selection.

POSH Regulates CD4+ T Cell Differentiation and Survival

The scaffold molecule POSH is crucial for the regulation of proliferation and effector function in CD8(+) T cells. However, its role in CD4(+) T cells is not known. In this study, we found that disruption of the POSH scaffold complex established a transcriptional profile that strongly skewed differentiation toward Th2, led to decreased survival, and had no effect on cell cycle entry. This is in stark contrast to CD8(+) T cells in which POSH regulates cell cycle and does not affect survival. Disruption of POSH in CD4(+) T cells resulted in the loss of Tak1-dependent activation of JNK1/2 and Tak1-mediated survival. However, in CD8(+) T cells, POSH regulates only JNK1. Remarkably, each type of T cell had a unique composition of the POSH scaffold complex and distinct posttranslational modifications of POSH. These data indicate that the mechanism that regulates POSH function in CD4(+) T cells is different from CD8(+) T cells. All together, these data strongly suggest that POSH is essential for the integration of cell-type-specific signals that regulate the differentiation, survival, and function of T cells.

Zfat-deficient CD4⁺ CD8⁺ double-positive thymocytes are susceptible to apoptosis with deregulated activation of p38 and JNK

Zfat, which is a nuclear protein harboring an AT-hook domain and 18-repeats of C2H2 zinc-finger motif, is highly expressed in immune-related tissues, including the thymus and spleen. T cell specific deletion of the Zfat gene by crossing Zfat(f/f) mice with LckCre mice yields a significant reduction in the number of CD4(+) CD8(+) double-positive (DP) thymocytes. However, physiological role for Zfat in T cell development in the thymus remains unknown. Here, we found that Zfat-deficient DP thymocytes in Zfat(f/f)-LckCre mice were susceptible to apoptosis both at an unstimulated state and in response to T cell receptor (TCR)-stimulation. The phosphorylation levels of p38 and JNK were elevated in Zfat-deficient thymocytes at an unstimulated state with an enhanced phosphorylation of ATF2 and with an over-expression of Gadd45α⋅ On the other hand, the activation of JNK in the Zfat-deficient thymocytes, but not p38, was strengthened and prolonged in response to TCR-stimulation. All these results demonstrate that Zfat critically participates in the development of DP thymocytes through regulating the activities of p38 and JNK.

Dominant negative form of alpha4 inhibits the BCR crosslinking-induced phosphorylation of Bcl-xL and apoptosis in an immature B cell line WEHI-231

We previously demonstrated that c-Jun N-terminal kinase (JNK) phosphorylates serine 62 of Bcl-xL to induce the degradation of Bcl-xL and apoptosis in WEHI-231 cells upon BCR crosslinking. In order to elucidate the regulatory mechanisms underlying the phosphorylation of Bcl-xL, we prepared an assay system in which JNK phosphorylated Bcl-xL in HEK293T cells. Consequently, we found that a signal transduction molecule, alpha4, enhanced the phosphorylation of Bcl-xL by JNK, while the co-expression of C-terminal alpha4 (220-340) diminished the phosphorylation of Bcl-xL induced by JNK. Furthermore, full-length alpha4 associated with both JNK and Bcl-xL, whereas C-terminal alpha4 (220-340) associated only with Bcl-xL, not JNK. In addition, WEHI-231 cells transfected with the cDNA of C-terminal alpha4 (220-340) exhibited decreased phosphorylation of Bcl-xL and stronger resistance to apoptosis induced by BCR crosslinking. These results indicate that alpha4 is an important regulatory molecule of apoptosis induced by BCR crosslinking in WEHI-231 cells and that C-terminal alpha4 (220-340) functions as a dominant negative form.

Increased Thymic Cell Turnover under Boron Stress May Bypass TLR3/4 Pathway in African Ostrich

Previous studies revealed that thymus is a targeted immune organ in malnutrition, and high-boron stress is harmful for immune organs. African ostrich is the living fossil of ancient birds and the food animals in modern life. There is no report about the effect of boron intake on thymus of ostrich. The purpose of present study was to evaluate the effect of excessive boron stress on ostrich thymus and the potential role of TLR3/4 signals in this process. Histological analysis demonstrated that long-term boron stress (640 mg/L for 90 days) did not disrupt ostrich thymic structure during postnatal development. However, the numbers of apoptotic cells showed an increased tendency, and the expression of autophagy and proliferation markers increased significantly in ostrich thymus after boron treatment. Next, we examined the expression of TLR3 and TLR4 with their downstream molecular in thymus under boron stress. Since ostrich genome was not available when we started the research, we first cloned ostrich TLR3 TLR4 cDNA from thymus. Ostrich TLR4 was close to white-throated Tinamou. Whole avian TLR4 codons were under purify selection during evolution, whereas 80 codons were under positive selection. TLR3 and TLR4 were expressed in ostrich thymus and bursa of fabricius as was revealed by quantitative real-time PCR (qRT-PCR). TLR4 expression increased with age but significantly decreased after boron treatment, whereas TLR3 expression showed the similar tendency. Their downstream molecular factors (IRF1, JNK, ERK, p38, IL-6 and IFN) did not change significantly in thymus, except that p100 was significantly increased under boron stress when analyzed by qRT-PCR or western blot. Taken together, these results suggest that ostrich thymus developed resistance against long-term excessive boron stress, possibly by accelerating intrathymic cell death and proliferation, which may bypass the TLR3/4 pathway. In addition, attenuated TLRs activity may explain the reduced inflammatory response to pathogens under boron stress.

Protein phosphatase 6 controls BCR-induced apoptosis of WEHI-231 cells by regulating ubiquitination of Bcl-xL

Crosslinking BCR in the immature B cell line WEHI-231 causes apoptosis. We found that Bcl-xL was degraded by polyubiquitination upon BCR crosslinking and in this study explored the mechanism that controls the degradation of Bcl-xL. Ser(62) of Bcl-xL was phosphorylated by JNK to trigger polyubiquitination, and this was opposed by serine/threonine protein phosphatase 6 (PP6) that physically associated with Bcl-xL. We show BCR crosslinking decreased PP6 activity to allow Ser(62) phosphorylation of Bcl-xL. CD40 crosslinking rescues BCR-induced apoptosis, and we found PP6 associated with CD40 and PP6 activation in response to CD40. Our data suggest that PP6 activity is regulated to control apoptosis by modulating Ser(62) phosphorylation of Bcl-xL, which results in its polyubiquitination and degradation.

c-Jun NH2 -terminal kinase is a critical node in the death of CD4+ CD8+ thymocytes during Salmonella enterica serovar Typhimurium infection

Thymic atrophy, due to the depletion of CD4(+) CD8(+) thymocytes, is observed during infections with numerous pathogens. Several mechanisms, such as glucocorticoids and inflammatory cytokines, are known to be involved in this process; however, the roles of intracellular signaling molecules have not been investigated. In this study, the functional role of c-Jun NH2 -terminal kinase (JNK) during infection-induced thymic atrophy was addressed. The levels of phosphorylated JNK in immature CD4(+) CD8(+) thymocytes from C57BL/6 (Nramp-deficient) and 129/SvJ (Nramp-sufficient) mice were increased upon oral infection of mice with Salmonella enterica serovar Typhimurium (S. typhimurium). Furthermore, inhibition of JNK signaling, but not ERK or p38 MAPK, prevented the in vitro death of infected thymocytes. Importantly, the in vivo inhibition of JNK signaling with SP600125 protected C57BL/6 CD4(+) CD8(+) thymocytes from depletion via multiple mechanisms as follows: lower intracellular ROS, inflammatory cytokines, Bax and caspase 3 activity, increase in Bcl-xL amounts, and prevention of the loss in mitochondrial membrane potential. Notably, thymic architecture was preserved in infected mice treated with SP600125. Overall, this study identifies a novel role for JNK as a crucial regulator of the death of CD4(+) CD8(+) thymocytes during S. typhimurium infection.

JNK inhibitors as anti-inflammatory and neuroprotective agents

JNK is involved in a broad range of physiological processes. Several inflammatory and neurodegenerative diseases, such as multiple sclerosis, Alzheimer's and Parkinson's disease have been linked with the dysregulated JNK pathway. Research on disease models using the relevant knockout mice has highlighted the importance of specific JNK isoformsin-particular disorders and has stimulated further efforts in the drug-discovery area. However, most of the experimental evidence for the efficacy of JNK inhibition in animal models is from studies using JNK inhibitors, which are not isoform selective. Some of the more recent compounds exhibit good oral bioavailability, CNS penetration and selectivity against the rest of the kinome. Efforts to design isoform-selective inhibitors have produced a number of examples with various selectivity profiles. This article presents recent progress in this area and comment on the role of isoform selectivity for efficacy.

Nuclear export of histone deacetylase 7 during thymic selection is required for immune self-tolerance

Histone deacetylase 7 (HDAC7) is a T-cell receptor (TCR) signal-dependent regulator of differentiation that is highly expressed in CD4/CD8 double-positive (DP) thymocytes. Here, we examine the effect of blocking TCR-dependent nuclear export of HDAC7 during thymic selection, through expression of a signal-resistant mutant of HDAC7 (HDAC7-ΔP) in thymocytes. We find that HDAC7-ΔP transgenic thymocytes exhibit a profound block in negative thymic selection, but can still undergo positive selection, resulting in the escape of autoreactive T cells into the periphery. Gene expression profiling reveals a comprehensive suppression of the negative selection-associated gene expression programme in DP thymocytes, associated with a defect in the activation of MAP kinase pathways by TCR signals. The consequence of this block in vivo is a lethal autoimmune syndrome involving the exocrine pancreas and other abdominal organs. These experiments establish a novel molecular model of autoimmunity and cast new light on the relationship between thymic selection and immune self-tolerance.

Reduced TCR signaling potential impairs negative selection but does not result in autoimmune disease

TCR signal attenuation selectively favors Foxp3 expression and T reg cell lineage commitment.

Negative selection and regulatory T (T reg) cell development are two thymus-dependent processes necessary for the enforcement of self-tolerance, and both require high-affinity interactions between the T cell receptor (TCR) and self-ligands. However, it remains unclear if they are similarly impacted by alterations in TCR signaling potential. We generated a knock-in allele (6F) of the TCR ζ chain gene encoding a mutant protein lacking signaling capability whose expression is controlled by endogenous ζ regulatory sequences. Although negative selection was defective in 6F/6F mice, leading to the survival of autoreactive T cells, 6F/6F mice did not develop autoimmune disease. We found that 6F/6F mice generated increased numbers of thymus-derived T reg cells. We show that attenuation of TCR signaling potential selectively impacts downstream signaling responses and that this differential effect favors Foxp3 expression and T reg cell lineage commitment. These results identify a potential compensatory pathway for the enforcement of immune tolerance in response to defective negative selection caused by reduced TCR signaling capability.

Interchangeability of Themis1 and Themis2 in thymocyte development reveals two related proteins with conserved molecular function

Themis1, a recently identified T cell protein, has a critical function in the generation of mature CD4(+)CD8(-) and CD4(-)CD8(+) (CD4 and CD8 single-positive [SP]) thymocytes and T cells. Although Themis1 has been shown to bind to the adaptor proteins LAT and Grb2, previous studies have yielded conflicting results regarding whether thymocytes from Themis1(-/-) mice exhibit TCR-mediated signaling defects. In this study, we demonstrate that, in the absence of Themis1, TCR-mediated signaling is selectively impaired in CD4 SP and CD8 SP thymocytes but is not affected in CD4(+)CD8(+) double-positive thymocytes despite high expression of Themis1 in double-positive thymocytes. Like Themis1, Themis2, a related member of the Themis family, which is expressed in B cells and macrophages, contains two conserved cysteine-based domains, a proline-rich region, and a nuclear localization signal. To determine whether Themis1 and Themis2 can perform similar functions in vivo, we analyzed T cell development and TCR-mediated signaling in Themis1(-/-) mice reconstituted with either Themis1 or Themis2 transgenes. Notably, Themis1 and Themis2 exhibited the same potential to restore T cell development and TCR-mediated signaling in Themis1(-/-) mice. Both proteins were tyrosine phosphorylated and were recruited within Grb2 signaling complexes to LAT following TCR engagement. These results suggest that conserved molecular features of the Themis1 and Themis2 proteins are important for their biological activity and predict that Themis1 and Themis2 may perform similar functions in T and B cells, respectively.

Thymocyte responsiveness to endogenous glucocorticoids is required for immunological fitness

Generation of a self-tolerant but antigen-responsive T cell repertoire occurs in the thymus. Although glucocorticoids are usually considered immunosuppressive, there is also evidence that they play a positive role in thymocyte selection. To address the question of how endogenous glucocorticoids might influence the adaptive immune response, we generated GRlck-Cre mice, in which the glucocorticoid receptor gene (GR) is deleted in thymocytes prior to selection. These mice were immunocompromised, with reduced polyclonal T cell proliferative responses to alloantigen, defined peptide antigens, and viral infection. This was not due to an intrinsic proliferation defect, because GR-deficient T cells responded normally when the TCR was cross-linked with antibodies or when the T cell repertoire was "fixed" with αβ TCR transgenes. Varying the affinity of self ligands in αβ TCR transgenic mice showed that affinities that would normally lead to thymocyte-positive selection caused negative selection, and alterations in the TCR repertoire of polyclonal T cells were confirmed by analysis of TCR Vβ CDR3 regions. Thus, endogenous glucocorticoids are required for a robust adaptive immune response because of their promotion of the selection of T cells that have sufficient affinity for self, and the absence of thymocyte glucocorticoid signaling results in an immunocompromised state.

CD24 on thymic APCs regulates negative selection of myelin antigen-specific T lymphocytes

Negative selection plays a key role in the clonal deletion of autoreactive T cells in the thymus. However, negative selection is incomplete; as high numbers of autoreactive T cells can be detected in normal individuals, mechanisms that regulate negative selection must exist. In this regard, we previously reported that CD24, a GPI-anchored glycoprotein, is required for thymic generation of autoreactive T lymphocytes. The CD24-deficient 2D2 TCR transgenic mice (2D2(+) CD24(-/-) ), whose TCR recognizes myelin oligodendrocyte glycoprotein (MOG), fail to generate functional 2D2 T cells. However, it was unclear if CD24 regulated negative selection, and if so, what cellular mechanisms were involved. Here, we show that elimination of MOG or Aire gene expression in 2D2(+) CD24(-/-) mice - through the creation of 2D2(+) CD24(-/-) MOG(-/-) or 2D2(+) CD24(/) ∼Aire(-/-) mice - completely restores thymic cellularity and function of 2D2 T cells. Restoration of CD24 expression on DCs, but not on thymocytes also partially restores 2D2 T-cell generation in 2D2(+) CD24(-/-) mice. Taken together, we propose that CD24 expression on thymic antigen-presenting cells (mTECs, DCs) down-regulates autoantigen-mediated clonal deletion of autoreactive thymocytes.

TEC and MAPK Kinase Signalling Pathways in T helper (TH) cell Development, TH2 Differentiation and Allergic Asthma

Significant advances in our understanding of the signalling events during T cell development and differentiation have been made in the past few decades. It is clear that ligation of the T cell receptor (TCR) triggers a series of proximal signalling cascades regulated by an array of protein kinases. These orchestrated and highly regulated series of events, with differential requirements of particular kinases, highlight the disparities between αβ+CD4+ T cells. Throughout this review we summarise both new and old studies, highlighting the role of Tec and MAPK in T cell development and differentiation with particular focus on T helper 2 (TH2) cells. Finally, as the allergy epidemic continues, we feature the role played by TH2 cells in the development of allergy and provide a brief update on promising kinase inhibitors that have been tested in vitro, in pre-clinical disease models in vivo and into clinical studies.

Transcription factor Foxp1 exerts essential cell-intrinsic regulation of the quiescence of naive T cells

The molecular mechanisms that underlie T cell quiescence are poorly understood. Here we report that mature naive CD8(+) T cells lacking the transcription factor Foxp1 gained effector phenotype and function and proliferated directly in response to interleukin 7 (IL-7) in vitro. Foxp1 repressed expression of the IL-7 receptor α-chain (IL-7Rα) by antagonizing Foxo1 and negatively regulated signaling by the kinases MEK and Erk. Acute deletion of Foxp1 induced naive T cells to gain an effector phenotype and proliferate in lympho-replete mice. Foxp1-deficient naive CD8(+) T cells proliferated even in lymphopenic mice deficient in major histocompatibility complex class I. Our results demonstrate that Foxp1 exerts essential cell-intrinsic regulation of naive T cell quiescence, providing direct evidence that lymphocyte quiescence is achieved through actively maintained mechanisms that include transcriptional regulation.

Distinct roles of Cdc42 in thymopoiesis and effector and memory T cell differentiation

Cdc42 of the Rho GTPase family has been implicated in cell actin organization, proliferation, survival, and migration but its physiological role is likely cell-type specific. By a T cell-specific deletion of Cdc42 in mouse, we have recently shown that Cdc42 maintains naïve T cell homeostasis through promoting cell survival and suppressing T cell activation. Here we have further investigated the involvement of Cdc42 in multiple stages of T cell differentiation. We found that in Cdc42^−/− thymus, positive selection of CD4⁺CD8⁺ double-positive thymocytes was defective, CD4⁺ and CD8⁺ single-positive thymocytes were impaired in migration and showed an increase in cell apoptosis triggered by anti-CD3/-CD28 antibodies, and thymocytes were hyporesponsive to anti-CD3/-CD28-induced cell proliferation and hyperresponsive to anti-CD3/-CD28-stimulated MAP kinase activation. At the periphery, Cdc42-deficient naive T cells displayed an impaired actin polymerization and TCR clustering during the formation of mature immunological synapse, and showed an enhanced differentiation to Th1 and CD8⁺ effector and memory cells in vitro and in vivo. Finally, Cdc42^−/− mice exhibited exacerbated liver damage in an induced autoimmune disease model. Collectively, these data establish that Cdc42 is critically involved in thymopoiesis and plays a restrictive role in effector and memory T cell differentiation and autoimmunity.

Life and death in the thymus--cell death signaling during T cell development

The thymus is an organ vital to proper T cell development, and the regulation of cell survival and death contributes significantly to its efficient function. Vital to many of the developmental processes that occur in the thymus, control over cell survival and death is orchestrated by several signaling processes. In this review, we focus on the regulation of death in early thymocytes known as CD4/CD8 double negative cells, including the roles of interleukin-7 and Bcl-2 family members in this developmental stage. We next consider the survival and death of later thymocytes that express both CD4 and CD8, the 'double-positive' thymocytes. These findings are discussed within the context of recent studies demonstrating the existence of caspase-independent cell death pathways.

Characterization of immune cell subsets during the active phase of multiple sclerosis reveals disease and c-Jun N-terminal kinase pathway biomarkers

BACKGROUND

Autoimmune activation and deregulated apoptosis of T lymphocytes are involved in multiple sclerosis (MS). c-Jun N-terminal kinase (JNK) plays a role in T-cell survival and apoptosis.

OBJECTIVES

The aim of this work was to investigate the role of the JNK-dependent apoptosis pathway in relapsing-remitting MS (RRMS).

METHODS

The immunomodulatory effect of AS602801, a JNK inhibitor, was firstly evaluated on activated peripheral blood mononuclear cells (PBMCs) from healthy volunteers (HVs) and secondly in unstimulated purified CD4+, CD8+ and CD11b+ cells from RRMS patients and HVs. Moreover JNK/inflammation/apoptosis related genes were investigated in RRMS and HV samples.

RESULTS

In activated PBMCs from HVs, we showed that AS602801 blocked T-lymphocyte proliferation and induced apoptosis. In RRMS CD4+ and CD8+ cells, AS602801 induced apoptosis genes and expression of surface markers, while in RRMS CD11b+ cells it induced expression of innate immunity receptors and co-stimulatory molecules. Untreated cells from RRMS active-phase patients significantly released interleukin-23 (IL-23) and interferon-gamma (IFN-γ) and expressed less apoptosis markers compared to the cells of HVs. Moreover, gene expression was significantly different in cells from RRMS active-phase patients vs. HVs. By comparing RRMS PBMCs in the active and stable phases, a specific genomic signature for RRMS was indentified. Additionally, CASP8AP2, CD36, ITGAL, NUMB, OLR1, PIAS-1, RNASEL, RTN4RL2 and THBS1 were identified for the first time as being associated to the active phase of RRMS.

CONCLUSIONS

The analysis of the JNK-dependent apoptosis pathway can provide biomarkers for activated lymphocytes in the active phase of RRMS and a gene expression signature for disease status. The reported results might be useful to stratify patients, thereby supporting the development of novel therapies.

Grb2, a simple adapter with complex roles in lymphocyte development, function, and signaling

Lymphocyte development, activation, and tolerance depend on antigen receptor signaling transduced via multiple intracellular signalosomes. These signalosomes are assembled by different adapters. Given that signaling molecules can be either positive or negative regulators for a biochemical target, the complex of a target with different regulator may dictate the final signaling outcome. Grb2 is a simple adapter known to be involved in a variety of growth factor receptor signaling. However, its role in antigen receptor signaling as well as lymphocyte development and function has emerged only recently. Despite its simple molecular structure, recent experiments show that Grb2 may play a complex role in T and B-cell antigen receptor signaling. In this article, we review recent findings about the physiological role of Grb2 in T and B-cell development and activation and summarize the current mechanistic understanding of how Grb2 exerts its function following T and B-cell antigen receptor stimulation.

Mitochondria-centric activation induced cell death of cytolytic T lymphocytes and its implications for cancer immunotherapy

Premature death of the adoptively transferred cytolytic T lymphocytes (CTL) by means of activation induced cell death (AICD) represents one of the major constraints in devising an effective anti-cancer immune intervention strategy. Understanding the mechanism of AICD is, therefore, critical for developing methods to interfere with this death process. Although the existing paradigm on AICD centers around the initiation of the cascade of events originating from the engagement of death receptors leading to the activation of effector caspases and eventually resulting in cell death, recent findings have questioned the universal role of caspases as the cell death executioners. We here review our current understanding of the contribution of caspase-dependent and caspase-independent death executioners in AICD of T cells. We will also discuss the involvement of mitochondria-centric death pathway in AICD of human tumor associated antigen-specific primary CTL and its implications in cancer immunotherapy.

A novel TCR transgenic model reveals that negative selection involves an immediate, Bim-dependent pathway and a delayed, Bim-independent pathway

A complete understanding of negative selection has been elusive due to the rapid apoptosis and clearance of thymocytes in vivo. We report a TCR transgenic model in which expression of the TCR during differentiation occurs only after V(D)J-like recombination. TCR expression from this transgene closely mimics expression of the endogenous TCRalpha locus allowing for development that is similar to wild type thymocytes. This model allowed us to characterize the phenotypic changes that occurred after TCR-mediated signaling in self-reactive thymocytes prior to their deletion in a highly physiological setting. Self-reactive thymocytes were identified as being immature, activated and CD4(lo)CD8(lo). These cells had upregulated markers of negative selection and were apoptotic. Elimination of Bim reduced the apoptosis of self-reactive thymocytes, but it did not rescue their differentiation and the cells remained at the immature CD4(lo)CD8(lo) stage of development. These cells upregulate Nur77 and do not contribute to the peripheral T cell repertoire in vivo. Remarkably, development past the CD4(lo)CD8(lo) stage was possible once the cells were removed from the negatively selecting thymic environment. In vitro development of these cells occurred despite their maintenance of high intracellular levels of Nur77. Therefore, in vivo, negatively selected Bim-deficient thymocytes are eliminated after prolonged developmental arrest via a Bim-independent pathway that is dependent on the thymic microenvironment. These data newly reveal a layering of immediate, Bim-dependent, and delayed Bim-independent pathways that both contribute to elimination of self-reactive thymocytes in vivo.

Cutting edge: Extracellular signal-related kinase is not required for negative selection of developing T cells

Signals initiated through the TCR during development can result in either survival and differentiation or cell death. High affinity signals that induce death elicit a robust yet transient activation of signaling pathways, including Erk, whereas low affinity ligands, which promote survival, generate a gradual and weaker activation of the same pathways. It was recently demonstrated that Erk localizes to distinct cellular locations in response to high and low affinity ligands. Although a requirement for Erk in positive selection is well established, its role in negative selection is controversial and, thus, the importance of Erk relocalization during development is not understood. In this study, we examined the role of Erk in negative selection using mice that are genetically deficient in both Erk1 and Erk2 in T cells. Results from three different models reveal that thymocyte deletion remains intact in the absence of Erk.

Beta-catenin/Tcf determines the outcome of thymic selection in response to alphabetaTCR signaling

Thymic maturation of T cells depends on the intracellular interpretation of alphabetaTCR signals by processes that are poorly understood. In this study, we report that beta-catenin/Tcf signaling was activated in double-positive thymocytes in response to alphabetaTCR engagement and impacted thymocyte selection. TCR engagement combined with activation of beta-catenin signaled thymocyte deletion, whereas Tcf-1 deficiency rescued from negative selection. Survival/apoptotis mediators including Bim, Bcl-2, and Bcl-x(L) were alternatively influenced by stabilization of beta-catenin or ablation of Tcf-1, and Bim-mediated beta-catenin induced thymocyte deletion. TCR activation in double-positive cells with stabilized beta-catenin triggered signaling associated with negative selection, including sustained overactivation of Lat and Jnk and a transient activation of Erk. These observations are consistent with beta-catenin/Tcf signaling acting as a switch that determines the outcome of thymic selection downstream the alphabetaTCR cascade.

Signal integration by JNK and p38 MAPK pathways in cancer development

Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) family members function in a cell context-specific and cell type-specific manner to integrate signals that affect proliferation, differentiation, survival and migration. Consistent with the importance of these events in tumorigenesis, JNK and p38 MAPK signalling is associated with cancers in humans and mice. Studies in mouse models have been essential to better understand how these MAPKs control cancer development, and these models are expected to provide new strategies for the design of improved therapeutic approaches. In this Review we highlight the recent progress made in defining the functions of the JNK and p38 MAPK pathways in different cancers.

Signal integration by JNK and p38 MAPK pathways in cancer development

Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) family members function in a cell context-specific and cell type-specific manner to integrate signals that affect proliferation, differentiation, survival and migration. Consistent with the importance of these events in tumorigenesis, JNK and p38 MAPK signalling is associated with cancers in humans and mice. Studies in mouse models have been essential to better understand how these MAPKs control cancer development, and these models are expected to provide new strategies for the design of improved therapeutic approaches. In this Review we highlight the recent progress made in defining the functions of the JNK and p38 MAPK pathways in different cancers.

Regulation of the immune response by stress-activated protein kinases

Activation of immune cells to mediate an immune response is often triggered by potential 'danger' or 'stress' stimuli that the organism receives. Within the mitogen-activated protein kinases (MAPKs) family, the stress-activated protein kinase (SAPK) group was defined as group of kinases that activated by stimuli that cause cell stress. In the immune cells, SAPKs are activated by antigen receptors (B- or T-cell receptors), Toll-like receptors, cytokine receptors, and physical-chemical changes in the environment among other stimuli. The SAPKs are established to be important mediators of intracellular signaling during adaptive and innate immune responses. Here we summarize what is currently known about the role of two sub-groups of SAPKs - c-Jun NH(2)-terminal kinase and p38 MAPK-in the function of specific components of the immune system and the overall contribution to the immune response.

Oxidized LDL impair adipocyte response to insulin by activating serine/threonine kinases

Oxidized LDL (oxLDL) increase in patients affected by type-2 diabetes, obesity, and metabolic syndrome. Likewise, insulin resistance, an impaired responsiveness of target tissues to insulin, is associated with those pathological conditions. To investigate a possible causal relationship between oxLDL and the onset of insulin resistance, we evaluated the response to insulin of 3T3-L1 adipocytes treated with oxLDL. We observed that oxLDL inhibited glucose uptake (-40%) through reduced glucose transporter 4 (GLUT4) recruitment to the plasma membrane (-70%), without affecting GLUT4 gene expression. These findings were associated to the impairment of insulin signaling. Specifically, in oxLDL-treated cells insulin receptor (IR) substrate-1 (IRS-1) was highly degraded likely because of the enhanced Ser(307)phosphorylation. This process was largely mediated by the activation of the inhibitor of kappaB-kinase beta (IKKbeta) and the c-Jun NH(2)-terminal kinase (JNK). Moreover, the activation of IKKbeta positively regulated the nuclear content of nuclear factor kappaB (NF-kappaB), by inactivating the inhibitor of NF-kappaB (IkappaBalpha). The activated NF-kappaB further impaired per se GLUT4 functionality. Specific inhibitors of IKKbeta, JNK, and NF-kappaB restored insulin sensitivity in adipocytes treated with oxLDL. These data provide the first evidence that oxLDL, by activating serine/threonine kinases, impaired adipocyte response to insulin affecting pathways involved in the recruitment of GLUT4 to plasma membranes (PM). This suggests that oxLDL might participate in the development of insulin resistance.

Genetic control of programmed cell death during animal development

The elimination of unwanted cells by programmed cell death is a common feature of animal development. Genetic studies in the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the mouse have not only revealed the molecular machineries that cause the programmed demise of specific cells, but have also allowed us to get a glimpse of the types of pathways that regulate these machineries during development. Rather than serving as a broad overview of programmed cell death during development, this review focuses on recent advances in our understanding of the regulation of specific programmed cell death events during nematode, fly, and mouse development. Recent studies have revealed that many of the regulatory pathways involved play additional important roles in development, which confirms that the programmed cell death fate is an integral aspect of animal development.

Origin of the sharp boundary that discriminates positive and negative selection of thymocytes

T lymphocytes play a key role in adaptive immunity and are activated by interactions of their T cell receptors (TCR) with peptides (p) derived from antigenic proteins bound to MHC gene products. The repertoire of T lymphocytes available in peripheral organs is tuned in the thymus. Immature T lymphocytes (thymocytes) interact with diverse endogenous peptides bound to MHC in the thymus. TCR expressed on thymocytes must bind weakly to endogenous pMHC (positive selection) but must not bind too strongly to them (negative selection) to emerge from the thymus. Negatively selecting pMHC ligands bind TCR with a binding affinity that exceeds a sharply defined (digital) threshold. In contrast, there is no sharp threshold separating positively selecting ligands from those that bind too weakly to elicit a response. We describe results of computer simulations and experiments, which suggest that the contrast between the characters of the positive and negative selection thresholds originates in differences in the way in which Ras proteins are activated by ligands of varying potency. The molecular mechanism suggested by our studies generates hypotheses for how genetic aberrations may dampen the digital negative selection response, with concomitant escape of autoimmune T lymphocytes from the thymus.

Analyzing mitogen-activated protein kinase (MAPK) activities in T cells

The recognition of peptide antigens by T cells through their antigen receptors (T cell receptors, or TCR), together with the ligation of additional surface molecules called costimulatory receptors, rapidly induces interactive signaling pathways that lead to transcriptional initiation at genes such as that of the autocrine growth factor interleukin 2 (IL-2). Activation of the ERK and JNK subfamilies of MAPK mediates some of these signals. This unit presents procedures for a solid-phase kinase assay and immune-complex kinase assay to measure JNK and ERK activities, respectively, in T cells that have been appropriately stimulated. Also described is a procedure for preparing GSThyphen;cJun/GSH-Sepharose beads needed in the solid-phase JNK protein kinase activity assay.

Trauma and hemorrhage-induced acute hepatic insulin resistance: dominant role of tumor necrosis factor-alpha

It has long been known that injury, infections, and other critical illnesses are often associated with hyperglycemia and hyperinsulinemia. Mortality of critically ill patients is greatly reduced by intensive insulin therapy, suggesting the significance of reversing or compensating for the development of acute insulin resistance. However, the development of acute injury/infection-induced insulin resistance is poorly studied, much less than the chronic diseases associated with insulin resistance, such as type 2 diabetes and obesity. We previously found that insulin resistance develops acutely in the liver after trauma and hemorrhage. The present study was designed to begin to understand the first steps in the development of trauma and hemorrhage-induced acute hepatic insulin resistance in an animal model of injury and blood loss similar to traumatic or surgical injury and hemorrhage. We present novel data that indicate that hepatic insulin resistance increased dramatically with an increasing extent of hemorrhage. With increasing extent of blood loss, there were increases in serum TNF-alpha levels, phosphorylation of liver insulin receptor substrate-1 on serine 307, and liver c-Jun N-terminal kinase activation/phosphorylation. Exogenous TNF-alpha infusion increased c-Jun N-terminal kinase phosphorylation and insulin receptor substrate-1 serine 307 phosphorylation, and inhibited insulin-induced signaling in liver. Conversely, neutralizing TNF-alpha antibody treatment reversed many of the hemorrhage-induced changes in hepatic insulin signaling. Our data indicate that the acute development of insulin resistance after trauma and hemorrhage may have some similarities to the insulin resistance that occurs in chronic diseases. However, because so little is known about this acute insulin-resistant state, much more needs to be done before we can attain a level of understanding similar to that of chronic states of insulin resistance.

T-cell development and function are modulated by dual specificity phosphatase DUSP5

Interleukin-2 (IL-2) is a pleiotropic cytokine that regulates lymphocyte proliferation and peripheral tolerance. IL-2 activates mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase, and signal transducer and activator of transcription (STAT) pathways and modulates expression of target genes. Systematic analysis of IL-2 target genes has revealed regulation of potential feedback inhibitors of IL-2 signaling, including several suppressor of cytokine signaling (SOCS) family members as well as MAPK pathway-regulating dual specificity phosphatases (DUSPs). Here we have evaluated the in vivo actions of DUSP5, an extracellular signal-regulated kinase 1/2 (ERK1/2)-specific phosphatase, by generating transgenic mice overexpressing DUSP5 within the lymphoid compartment. We show that transgenic DUSP5 expression results in a block in thymocyte development at the double positive stage. We also demonstrate that DUSP5-expressing mature T cells exhibit decreased IL-2-dependent proliferation and defective IL-2-mediated induction of genes. Finally, DUSP5 transgenic mice develop autoimmune symptoms, suggesting a role for the MAPK pathway in the regulation of tolerance. Thus, proper regulation of DUSP5 activity is critical for normal immune system development, IL-2 actions, and tolerance.