Regulation of mature T cell responses by the Wnt signaling pathway

TCF7 and LEF-1 downregulation in sepsis promotes immune suppression by inhibiting CD4+ T cell proliferation

BACKGROUND

Previous studies have shown that sepsis is implicated in a reduction in the number and function of CD4+ T cells. TCF7 and LEF-1 facilitate early T cell development and lineage selection of CD4+ T cells. However, the function and mechanism of TCF7 and LEF-1 in sepsis are uncharacterized. This study intended to delineate effect of TCF7 and LEF-1 on sepsis and the impact on proliferation of CD4+ T cells in sepsis.

METHODS

A mouse sepsis model was constructed by cecal ligation and puncture (CLP) method. Expression of TCF7 and LEF-1 in sepsis was investigated using bioinformatics analysis and molecular experiments. We then constructed TCF7 and LEF-1 overexpression cell lines to investigate their effects on proliferation, apoptosis, effector activation, and immunosuppressive molecules of CD4+ T cells in sepsis.

RESULTS

TCF7 and LEF-1 were downregulated in sepsis. As the duration of sepsis induction increased, the levels of TCF7 and LEF-1 gradually decreased, as did the number of CD4+ T cells. Cell experiments showed that overexpression of TCF7 and LEF-1 enhanced proliferation and effector activation of CD4+ T cells, reduced apoptosis, decreased PD-1 and LAG3 expression, and promoted immune response in sepsis.

CONCLUSION

In conclusion, this study confirmed that downregulation of TCF7 and LEF-1 expression in sepsis inhibited proliferation of CD4+ T cells, leading to immune suppression. This finding suggested that TCF7 and LEF-1 were potential biological targets for sepsis and indicated that immunotherapy aimed at improving CD4+ T cell proliferation may be a new strategy for immune therapy in sepsis patients.

PD1 is transcriptionally regulated by LEF1 in mature T cells

The role of programmed cell death 1 (PD1) in cancer immune evasion is of considerable importance, prompting the development of monoclonal antibodies that specifically target PD-1 to enhance the immune system for cancer therapy. Nevertheless, the efficacy of PD1/programmed cell death-Ligand 1 (PD-L1) blocking antibodies is limited to certain patients or tumor types. Although researchers have demonstrated the influence of PD-1 on the positive selection of T cells, its effect on the T-cell repertoire remains uncertain. Lymphoid enhancer binding factor 1 (LEF1) has been known to play a critical role as a transcription factor in the development and maturation of T cells. Despite the greater focus on the study of its homologous protein, T cell factor 1 (TCF1), we discovered that LEF1 had a positive regulatory effect on the transcription of PD1 in mature T cells, including CD4+ T cells, CD8+ T cells, and Treg cells. This finding was observed in LEF1 knockout and LEF1-stimulated mice models. Additionally, we confirmed the direct regulation of PD1 by LEF1 in tumor-infiltrating lymphocytes through tumor-implantation experiments. The direct regulation of PD1 by LEF1 was further validated in the LEF1 knockout cell line. The results of our study provide novel perspectives on the regulation of PD1 in immune responses and investigate potential approaches for clinical anti-PD1 therapy.

The extracellular matrix of lymph node reticular fibers modulates follicle border interactions and germinal center formation

Germinal center (GC) formation and antibody production in lymph node follicles require coordinated interactions between B-cells, T-cells and dendritic cells (DCs), orchestrated by the extracellular matrix-rich reticular fiber (RF) network. We describe a unique laminin 523-containing RF network around and between follicles that associates with PDGFrecβ^highCCL19^lowgp38^low fibroblastic reticular cells (FRC). In the absence of FRC expression of laminin α5 (pdgfrb-cre:Lama5^fl/fl), pre-Tfh-cells, B-cells and DCs are displaced from follicle borders, correlating with fewer Tfh-cells and GC B-cells. Total DCs are not altered in pdgfrb-cre:Lama5^fl/fl mice, but cDC2s, which localize to laminin α5 in RFs at follicle borders, are reduced. In addition, PDGFrecβ^highCCL19^lowgp38^low FRCs show lower Ch25h expression, required for 7α,25-dihydroxycholesterol synthesis that attracts pre-Tfh-cells, B-cells and DCs to follicle borders. We propose that RF basement membrane components represent a type of tissue memory that guides the localization and differentiation of both specialized FRC and DC populations, required for normal lymph node function.

Regulation of effector and memory CD8 + T cell differentiation: a focus on orphan nuclear receptor NR4A family, transcription factor, and metabolism

CD8 + T cells undergo rapid expansion followed by contraction and the development of memory cells after their receptors are activated. The development of immunological memory following acute infection is a complex phenomenon that involves several molecular, transcriptional, and metabolic mechanisms. As memory cells confer long-term protection and respond to secondary stimulation with strong effector function, understanding the mechanisms that influence their development is of great importance. Orphan nuclear receptors, NR4As, are immediate early genes that function as transcription factors and bind with the NBRE region of chromatin. Interestingly, the NBRE region of activated CD8 + T cells is highly accessible at the same time the expression of NR4As is induced. This suggests a potential role of NR4As in the early events post T cell activation that determines cell fate decisions. In this review, we will discuss the influence of NR4As on the differentiation of CD8 + T cells during the immune response to acute infection and the development of immunological memory. We will also discuss the signals, transcription factors, and metabolic mechanisms that control cell fate decisions. HIGHLIGHTS: Memory CD8 + T cells are an essential subset that mediates long-term protection after pathogen encounters. Some specific environmental cues, transcriptional factors, and metabolic pathways regulate the differentiation of CD8 + T cells and the development of memory cells. Orphan nuclear receptor NR4As are early genes that act as transcription factors and are highly expressed post-T cell receptor activation. NR4As influence the effector function and differentiation of CD8 + T cells and also control the development of immunological memory following acute infection.

Tcf1-CTCF cooperativity shapes genomic architecture to promote CD8+ T cell homeostasis

CD8⁺ T cell homeostasis is maintained by the cytokines IL-7 and IL-15. Here we show that transcription factors Tcf1 and Lef1 were intrinsically required for homeostatic proliferation of CD8⁺ T cells. Multiomics analyses showed that Tcf1 recruited the genome organizer CTCF and that homeostatic cytokines induced Tcf1-dependent CTCF redistribution in the CD8⁺ T cell genome. Hi-C coupled with network analyses indicated that Tcf1 and CTCF acted cooperatively to promote chromatin interactions and form highly connected, dynamic interaction hubs in CD8⁺ T cells before and after cytokine stimulation. Ablating CTCF phenocopied the proliferative defects caused by Tcf1 and Lef1 deficiency. Tcf1 and CTCF controlled a similar set of genes that regulated cell cycle progression and promoted CD8⁺ T cell homeostatic proliferation in vivo. These findings identified CTCF as a Tcf1 cofactor and uncovered an intricate interplay between Tcf1 and CTCF that modulates the genomic architecture of CD8⁺ T cells to preserve homeostasis.

Vascular Calcification in Chronic Kidney Disease: An Update and Perspective

Chronic kidney disease is a devastating condition resulting from irreversible loss of nephron numbers and function and leading to end-stage renal disease and mineral disorders. Vascular calcification, an ectopic deposition of calcium-phosphate salts in blood vessel walls and heart valves, is an independent risk factor of cardiovascular morbidity and mortality in chronic kidney disease. Moreover, aging and related metabolic disorders are essential risk factors for chronic kidney disease and vascular calcification. Marked progress has been recently made in understanding and treating vascular calcification in chronic kidney disease. However, there is a paucity of systematic reviews summarizing this progress, and investigating unresolved issues is warranted. In this systematic review, we aimed to overview the underlying mechanisms of vascular calcification in chronic kidney diseases and discuss the impact of chronic kidney disease on the pathophysiology of vascular calcification. Additionally, we summarized potential clinical diagnostic biomarkers and therapeutic applications for vascular calcification with chronic kidney disease. This review may offer new insights into the pathogenesis, diagnosis, and therapeutic intervention of vascular calcification.

A novel four-gene signature predicts immunotherapy response of patients with different cancers

Background

Immune checkpoint blockade (ICB) therapy has demonstrated favorable clinical efficacy, particularly for advanced or difficult‐to‐treat cancer types. However, this therapy is ineffective for many patients displaying lack of immune response or resistance to ICB. This study aimed to establish a novel four‐gene signature (CD8A, CD8B, TCF7, and LEF1) to provide a prognostic immunotherapy biomarker for different cancers.

Methods

Transcriptome profiles and clinical data were obtained from The Cancer Genome Atlas database. Multivariate Cox regression analysis was used to establish a four‐gene signature. The R package estimate was used to obtain the immune score for every patient.

Results

Risk scores of the novel four‐gene signature could effectively divided all patients into high‐ and low‐risk groups, with distinct outcomes. The immune score calculated via the estimate package demonstrated that the four‐gene signature was significantly associated with the immune infiltration level. Furthermore, the four‐gene signature could predict the response to atezolizumab immunotherapy in patients with metastatic urothelial cancer.

Conclusions

The novel four‐gene signature developed in this study is a good prognostic biomarker, as it could identify many kinds of patients with cancer who are likely to respond to and benefit from immunotherapy.

Current and Near-Future Treatment of Alzheimer's Disease

Recent findings have improved our understanding of the multifactorial nature of AD. While in early asymptomatic stages of AD, increased amyloid-β synthesis and tau hyperphosphorylation play a key role, while in the latter stages of the disease, numerous dysfunctions of homeostatic mechanisms in neurons, glial cells, and cerebrovascular endothelium determine the rate of progression of clinical symptoms. The main driving forces of advanced neurodegeneration include increased inflammatory reactions in neurons and glial cells, oxidative stress, deficiencies in neurotrophic growth and regenerative capacity of neurons, brain insulin resistance with disturbed metabolism in neurons, or reduction of the activity of the Wnt-β catenin pathway, which should integrate the homeostatic mechanisms of brain tissue. In order to more effectively inhibit the progress of neurodegeneration, combination therapies consisting of drugs that rectify several above-mentioned dysfunctions should be used. It should be noted that many widely-used drugs from various pharmacological groups, "in addition" to the main therapeutic indications, have a beneficial effect on neurodegeneration and may be introduced into clinical practice in combination therapy of AD. There is hope that complex treatment will effectively inhibit the progression of AD and turn it into a slowly progressing chronic disease. Moreover, as the mechanisms of bidirectional communication between the brain and microbiota are better understood, it is expected that these pathways will be harnessed to provide novel methods to enhance health and treat AD.

TCF1 in T cell immunity: a broadened frontier

TCF1 and its homologue LEF1 are historically known as effector transcription factors downstream of the WNT signalling pathway and are essential for early T cell development. Recent advances bring TCF1 into the spotlight for its versatile, context-dependent functions in regulating mature T cell responses. In the cytotoxic T cell lineages, TCF1 is required for the self-renewal of stem-like CD8⁺ T cells generated in response to viral or tumour antigens, and for preserving heightened responses to checkpoint blockade immunotherapy. In the helper T cell lineages, TCF1 is indispensable for the differentiation of T follicular helper and T follicular regulatory cells, and crucially regulates immunosuppressive functions of regulatory T cells. Mechanistic investigations have also identified TCF1 as the first transcription factor that directly modifies histone acetylation, with the capacity to bridge transcriptional and epigenetic regulation. TCF1 also has the potential to become an important clinical biomarker for assessing the prognosis of tumour immunotherapy and the success of viral control in treating HIV and hepatitis C virus infection. Here, we summarize the key findings on TCF1 across the fields of T cell immunity and reflect on the possibility of exploring TCF1 and its downstream transcriptional programmes as therapeutic targets for improving antiviral and antitumour immunity.

The prognostic role of the Transducin-like Enhancer of split protein family in lung adenocarcinoma

Background

Lung cancer claims more lives than any other cancer worldwide. Lung adenocarcinoma (LUAD) accounts for approximately 40% of all lung cancers. Members of the Transducin-like Enhancer of split (TLE) protein family repress transcription through multiple mechanisms; however, their prognostic value in LUAD is still unclear.

Methods

A dataset from The Cancer Genome Atlas was used to analyze the relationship between the expression of TLE family members and outcomes of LUAD. The expression of TLE family members in 59 normal and 513 tumor samples in the TCGA dataset was selected. For paired analysis, 57 normal and 57 tumor paired tissues were selected. Gene Ontology (GO) term and Reactome pathway enrichment analyses of the TLE family members were performed. Progression-free survival (PFS) and overall survival (OS) served as endpoints in this study. All statistical analyses were performed with R 3.6.0.

Results

The expression levels of TLE family proteins differed between 59 normal and 513 tumor samples. High TLE1 and low TLE2 levels were associated with poor progression-free and OS (all P<0.050). Multivariate analysis demonstrated that high TLE1 expression and low TLE2 expression were independent risk factors for a poor outcome in LUAD. Moreover, the combined expression of these two proteins was a good tool for prognostication.

Conclusions

High TLE1 expression and low TLE2 are independent adverse prognostic factors in LUAD and can serve as prognostic biomarkers.

Transcriptomic Analysis of Peripheral Monocytes upon Fingolimod Treatment in Relapsing Remitting Multiple Sclerosis Patients

Fingolimod (FTY), a second-line oral drug approved for relapsing remitting Multiple Sclerosis (RRMS) acts in preventing lymphocyte migration outside lymph nodes; moreover, several lines of evidence suggest that it also inhibits myeloid cell activation. In this study, we investigated the transcriptional changes induced by FTY in monocytes in order to better elucidate its mechanism of action. CD14⁺ monocytes were collected from 24 RRMS patients sampled at baseline and after 6 months of treatment and RNA profiles were obtained through next-generation sequencing. We conducted pathway and sub-paths analysis, followed by centrality analysis of cell-specific interactomes on differentially expressed genes (DEGs). We investigated also the predictive role of baseline monocyte transcription profile in influencing the response to FTY therapy. We observed a marked down-regulation effect (60 down-regulated vs. 0 up-regulated genes). Most of the down-regulated DEGs resulted related with monocyte activation and migration like IL7R, CCR7 and the Wnt signaling mediators LEF1 and TCF7. The involvement of Wnt signaling was also confirmed by subpaths analyses. Furthermore, pathway and network analyses showed an involvement of processes related to immune function and cell migration. Baseline transcriptional profile of the HLA class II gene HLA-DQA1 and HLA-DPA1 were associated with evidence of disease activity after 2 years of treatment. Our data support the evidence that FTY induces major transcriptional changes in monocytes, mainly regarding genes involved in cell trafficking and immune cell activation. The baseline transcriptional levels of genes associated with antigen presenting function were associated with disease activity after 2 years of FTY treatment.

Conversations that count: Cellular interactions that drive T cell fate

The relationship between the extrinsic environment and the internal transcriptional network is circular. Naive T cells first engage with antigen‐presenting cells to set transcriptional differentiation networks in motion. In turn, this regulates specific chemokine receptors that direct migration into distinct lymph node niches. Movement into these regions brings newly activated T cells into contact with accessory cells and cytokines that reinforce the differentiation programming to specify T cell function. We and others have observed similarities in the transcriptional networks that specify both CD4+ T follicular helper (T_FH) cells and CD8+ central memory stem‐like (T_SCM) cells. Here, we compare and contrast the current knowledge for these shared differentiation programs, compared to their effector counterparts, CD4+ T‐helper 1 (T_H1) and CD8+ short‐lived effector (T_SLEC) cells. Understanding the interplay between cellular interactions and transcriptional programming is essential to harness T cell differentiation that is fit for purpose; to stimulate potent T cell effector function for the elimination of chronic infection and cancer; or to amplify the formation of humoral immunity and longevity of cellular memory to prevent infectious diseases.

β-catenin and γ-catenin are dispensable for T lymphocytes and AML leukemic stem cells

The β-catenin transcriptional coregulator is involved in various biological and pathological processes; however, its requirements in hematopoietic cells remain controversial. We re-targeted the Ctnnb1 gene locus to generate a true β-catenin-null mutant mouse strain. Ablation of β-catenin alone, or in combination with its homologue γ-catenin, did not affect thymocyte maturation, survival or proliferation. Deficiency in β/γ-catenin did not detectably affect differentiation of CD4⁺T follicular helper cells or that of effector and memory CD8⁺ cytotoxic cells in response to acute viral infection. In an MLL-AF9 AML mouse model, genetic deletion of β-catenin, or even all four Tcf/Lef family transcription factors that interact with β-catenin, did not affect AML onset in primary recipients, or the ability of leukemic stem cells (LSCs) in propagating AML in secondary recipients. Our data thus clarify on a long-standing controversy and indicate that β-catenin is dispensable for T cells and AML LSCs.

Ectopic Tcf1 expression instills a stem-like program in exhausted CD8+ T cells to enhance viral and tumor immunity

Exhausted CD8⁺ T (Tex) cells are dysfunctional due to persistent antigen exposure in chronic viral infection and tumor contexts. A stem cell-like Tex (Tex-stem) subset can self-renew and differentiate into terminally exhausted (Tex-term) cells. Here, we show that ectopic Tcf1 expression potently promoted the generation of Tex-stem cells in both a chronic viral infection and preclinical tumor models. Tcf1 overexpression diminished coinhibitory receptor expression and enhanced polycytokine-producing capacity while retaining a heightened responses to checkpoint blockade, leading to enhanced viral and tumor control. Mechanistically, ectopically expressed Tcf1 exploited existing and novel chromatin accessible sites as transcriptional enhancers or repressors and modulated the transcriptome by enforcing pre-existing expression patterns in Tex-stem cells, such as enhanced suppression of Blimp1 and Bim and acquisition of new downstream genes, including Mx1, Tox2, and Runx3. These findings reveal a pronounced impact of ectopic Tcf1 expression on Tex functional restoration and highlight the therapeutic potential of harnessing Tcf1-enforced transcriptional programs.

Polymorphisms in the CTLA4 promoter sequence are associated with canine hypoadrenocorticism

Background

Canine hypoadrenocorticism is an immune-mediated endocrinopathy that shares both clinical and pathophysiological similarities with Addison’s disease in humans. Several dog breeds are overrepresented in the disease population, suggesting that a genetic component is involved, although this is likely to be polygenic. Previous research has implicated CTLA4 as a potential susceptibility gene. CTLA4 is an important regulator of T cell function and polymorphisms/mutations in CTLA4 have been associated with a number of autoimmune phenotypes in both humans and rodent models of autoimmunity. The aim of the current study was to undertake a case:control association study of CTLA4 promotor polymorphisms in three dog breeds, cocker spaniels, springer spaniels and West Highland white terriers (WHWT).

Results

Polymorphisms in the CTLA4 promoter were determined by PCR and sequence-based typing. There were significant associations with three promoter haplotypes in cocker spaniels (p = 0.003). A series of SNPs were also associated with hypoadrenocorticism in cocker spaniels and springer spaniels, including polymorphisms in predicted NFAT and SP1 transcription factor binding sites.

Conclusions

This study provides further evidence that CTLA4 promotor polymorphisms are associated with this complex genetic disease and supports an immune mediated aetiopathogenesis of canine hypoadrenocorticism.

Attenuation of Wnt/β-catenin signaling in patients with Stevens-Johnson syndrome and toxic epidermal necrolysis

Stevens-Johnson syndrome (SJS) and toxic epidermal necrosis (TEN) are rare but life-threatening severe cutaneous adverse reactions. Current studies have suggested that the pathobiology of drug-mediated SJS/TEN involves a dysregulation of cellular immunity with overwhelming activation of cytotoxic T lymphocytes. The canonical Wnt signaling pathway plays important roles in T cell development and activation, which may provide potential avenues for alleviating dysregulated immunity in SJS/TEN. In this study, we aimed to assess the implication of Wnt signaling in drug-reactive T cells in SJS/TEN. We showed downregulation of Wnt signaling components, including T cell factor 1 (TCF-1)/lymphoid enhancer binding factor 1 (LEF-1) transcription factors, in SJS/TEN patients, suggesting that canonical Wnt signaling is regulated during cytotoxic T cell responses in SJS/TEN. Further analyses demonstrated that engagement of the T cell receptor by antigen encounter and treatment of a prognostic marker of SJS/TEN, IL-15, in vitro led to the downregulation of LEF-1 and TCF-1 expression in CD8+ T cells. Enhancement of Wnt signaling by adding the Wnt activators attenuated ex vivo activation of drug-specific T cells from SJS/TEN patients, indicating a functional involvement of Wnt signaling in the pathomechanism of SJS/TEN. These findings provide additional insight into the immunopathogenesis and therapeutic intervention of this devastating condition.

Control of Lymphocyte Fate, Infection, and Tumor Immunity by TCF-1

T cell factor-1 (TCF-1), encoded by Tcf7, is a transcription factor and histone deacetylase (HDAC) essential for commitment to both the T cell and the innate lymphoid cell (ILC) lineages in mammals. In this review, we discuss the multifunctional role of TCF-1 in establishing these lineages and the requirement for TCF-1 throughout lineage differentiation and maintenance of lineage stability. We highlight recent reports showing promise for TCF-1 as a novel biomarker to identify recently characterized subsets of exhausted CD8⁺ T cells that may help to predict patient responses to immune checkpoint blockade (ICB).

Cutting Edge: Tcf1 Instructs T Follicular Helper Cell Differentiation by Repressing Blimp1 in Response to Acute Viral Infection

Differentiation of T follicular helper (T_FH) cells is regulated by a complex transcriptional network, with mutually antagonistic Bcl6-Blimp1 as a core regulatory axis. It is well established that Tcf1 acts upstream of Bcl6 for its optimal induction to program T_FH cell differentiation. In this study, we show that whereas genetic ablation of Tcf1 in mice greatly diminished T_FH cells in response to viral infection, compound deletion of Blimp1 with Tcf1 restored T_FH cell frequency, numbers, and generation of germinal center B cells. Aberrant upregulation of T-bet and Id2 in Tcf1-deficient T_FH cells was also largely rectified by ablating Blimp1. Tcf1 chromatin immunoprecipitation sequencing in T_FH cells identified two strong Tcf1 binding sites in the Blimp1 gene at a 24-kb upstream and an intron-3 element. Deletion of the intron-3 element, but not the 24-kb upstream element, compromised production of T_FH cells. Our data demonstrate that Tcf1-mediated Blimp1 repression is functionally critical for safeguarding T_FH cell differentiation.

Tcf1 and Lef1 are required for the immunosuppressive function of regulatory T cells

Tcf1 and Lef1 are underexpressed in T reg cells compared with conventional CD4⁺ T cells. Xing et al. demonstrate that genetic ablation of both factors impairs immunosuppressive function of T reg cells and leads to spontaneous multi-organ autoimmunity.

Tcf1 and Lef1 have versatile functions in regulating T cell development and differentiation, but intrinsic requirements for these factors in regulatory T (T reg) cells remain to be unequivocally defined. Specific ablation of Tcf1 and Lef1 in T reg cells resulted in spontaneous multi-organ autoimmunity that became more evident with age. Tcf1/Lef1-deficient T regs showed reduced protection against experimentally induced colitis, indicative of diminished immuno-suppressive capacity. Transcriptomic analysis revealed that Tcf1 and Lef1 were responsible for positive regulation of a subset of T reg–overrepresented signature genes such as Ikzf4 and Izumo1r. Unexpectedly, Tcf1 and Lef1 were necessary for restraining expression of cytotoxic CD8⁺ effector T cell–associated genes in T reg cells, including Prdm1 and Ifng. Tcf1 ChIP-seq revealed substantial overlap between Tcf1 and Foxp3 binding peaks in the T reg cell genome, with Tcf1-Foxp3 cooccupancy observed at key T reg signature and cytotoxic effector genes. Our data collectively indicate that Tcf1 and Lef1 are critical for sustaining T reg suppressive functions and preventing loss of self-tolerance.

Stress and immunosenescence: The role of telomerase

Chronic stress is associated with the accelerated aging of the immune system and represents a potent risk factor for the development and progression of a wide range of physical and mental disorders. The elucidation of molecular pathways and mechanisms underlying the link between stress and cellular aging is an area of considerable interest and investigation. In this context, telomere biology has emerged as a particularly attractive candidate mechanism. Several studies have linked immune cell telomere length with stress-related conditions and states, and also with several physical and mental disorders. Because the cellular reverse transcriptase enzyme telomerase is the primary regulator of telomere length (by adding telomeric DNA to telomeres and thereby attenuating telomere shortening), the understanding of its regulation and regulatory functions constitutes a prime target for developing strategies to prevent, attenuate or reverse the adverse consequences of immune system aging (immunosenescence). In this review we provide an overview of the mechanistic pathways linking telomerase with stress and cellular aging, with an emphasis on the immune system. We summarize and synthesize the current state of the literature on immune cell telomerase in different stress- and aging-related disease states and provide recommendations for future research directions.

Ezh2 programs TFH differentiation by integrating phosphorylation-dependent activation of Bcl6 and polycomb-dependent repression of p19Arf

Ezh2 is an histone methyltransferase (HMT) that catalyzes H3K27me3 and functions in T_H1, T_H2, and Treg cells primarily via HMT activity. Here we show that Ezh2 ablation impairs T follicular helper (T_FH) cell differentiation and activation of the T_FH transcription program. In T_FH cells, most Ezh2-occupied genomic sites, including the Bcl6 promoter, are associated with H3K27ac rather than H3K27me3. Mechanistically, Ezh2 is recruited by Tcf1 to directly activate Bcl6 transcription, with this function requiring Ezh2 phosphorylation at Ser21. Meanwhile, Ezh2 deploys H3K27me3 to repress Cdkn2a expression in T_FH cells, where aberrantly upregulated p19Arf, a Cdkn2a protein product, triggers T_FH cell apoptosis and antagonizes Bcl6 function via protein-protein interaction. Either forced expression of Bcl6 or genetic ablation of p19Arf in Ezh2-deficient cells improves T_FH cell differentiation and helper function. Thus, Ezh2 orchestrates T_FH-lineage specification and function maturation by integrating phosphorylation-dependent transcriptional activation and HMT-dependent gene repression.

Ezh2 is an histone methyltransferase that catalyzes H3K27me3. Here the authors show that Ezh2 promotes T follicular helper (T_FH) differentiation and helper activity, by cooperating with Tcf1 to activate Bcl6 transcription and epigenetically repressing p19Arf, an antagonist of Bcl6 function and T_FH cell survival.

The role of LRRK2 in cell signalling

Parkinson's disease (PD) is a common late-onset neurodegenerative disorder known primarily for its motor features. Mutations and risk variants in LRRK2 cause familial and idiopathic forms of PD. Mutations segregating with disease are found in the LRRK2 GTPase and kinase domains, affecting catalytic activity and protein-protein interactions. This likely results in an overall gain of LRRK2 cell signalling function contributing to PD pathogenesis. This concept supports the development of LRRK2 kinase inhibitors as disease-modifying treatments, at least for a subset of patients. However, the function of LRRK2 as a cell signalling protein with two catalytic and several protein-protein interaction domains is highly complex. For example, LRRK2 plays important roles in several inflammatory diseases, raising the possibility that it may mediate immune responses in PD. Consistently, LRRK2-mediated cell signalling was not only shown to be important for neuronal function, including neuronal development and homeostasis, but also for peripheral and central immune responses. The catalytic activity of LRRK2 is regulated by autophosphorylation, protein monomer/dimer cycling, and upstream kinases and GTPases, affecting its subcellular localisation and downstream signalling. Part of LRRK2-mediated signalling is likely facilitated by Rab protein phosphorylation, affecting primarily membrane trafficking, including vesicle release at the trans-Golgi network. However, LRRK2 also displays intrinsic GTPase activity and functions as a signalling scaffold. As an example, LRRK2 was suggested to be part of the NRON complex and β-catenin destruction complex, inhibiting NFAT and canonical Wnt signalling, respectively. In summary, continuous research into LRRK2 signalling function contributes to novel diagnostic and therapeutic concepts in PD.

Simulation of Stimulation: Cytokine Dosage and Cell Cycle Crosstalk Driving Timing-Dependent T Cell Differentiation

Triggering an appropriate protective response against invading agents is crucial to the effectiveness of human innate and adaptive immunity. Pathogen recognition and elimination requires integration of a myriad of signals from many different immune cells. For example, T cell functioning is not qualitatively, but quantitatively determined by cellular and humoral signals. Tipping the balance of signals, such that one of these is favored or gains advantage on another one, may impact the plasticity of T cells. This may lead to switching their phenotypes and, ultimately, modulating the balance between proliferating and memory T cells to sustain an appropriate immune response. We hypothesize that, similar to other intracellular processes such as the cell cycle, the process of T cell differentiation is the result of: (i) pleiotropy (pattern) and (ii) magnitude (dosage/concentration) of input signals, as well as (iii) their timing and duration. That is, a flexible, yet robust immune response upon recognition of the pathogen may result from the integration of signals at the right dosage and timing. To investigate and understand how system's properties such as T cell plasticity and T cell-mediated robust response arise from the interplay between these signals, the use of experimental toolboxes that modulate immune proteins may be explored. Currently available methodologies to engineer T cells and a recently devised strategy to measure protein dosage may be employed to precisely determine, for example, the expression of transcription factors responsible for T cell differentiation into various subtypes. Thus, the immune response may be systematically investigated quantitatively. Here, we provide a perspective of how pattern, dosage and timing of specific signals, called interleukins, may influence T cell activation and differentiation during the course of the immune response. We further propose that interleukins alone cannot explain the phenotype variability observed in T cells. Specifically, we provide evidence that the dosage of intercellular components of both the immune system and the cell cycle regulating cell proliferation may contribute to T cell activation, differentiation, as well as T cell memory formation and maintenance. Altogether, we envision that a qualitative (pattern) and quantitative (dosage) crosstalk between the extracellular milieu and intracellular proteins leads to T cell plasticity and robustness. The understanding of this complex interplay is crucial to predict and prevent scenarios where tipping the balance of signals may be compromised, such as in autoimmunity.

Tle corepressors are differentially partitioned to instruct CD8+ T cell lineage choice and identity

Xing et al demonstrate the requirements for Tle transcriptional corepressors in CD8⁺ T cell development. Tle proteins are differentially partitioned to the Runx and Tcf/Lef complexes to promote CD8⁺ lineage choice and establish CD8⁺ T cell identity, respectively.

Tle/Groucho proteins are transcriptional corepressors interacting with Tcf/Lef and Runx transcription factors, but their physiological roles in T cell development remain unknown. Conditional targeting of Tle1, Tle3 and Tle4 revealed gene dose–dependent requirements for Tle proteins in CD8⁺ lineage cells. Upon ablating all three Tle proteins, generation of CD8⁺ T cells was greatly diminished, largely owing to redirection of MHC-I–selected thymocytes to CD4⁺ lineage; the remaining CD8-positive T cells showed aberrant up-regulation of CD4⁺ lineage-associated genes including Cd4, Thpok, St8sia6, and Foxp3. Mechanistically, Tle3 bound to Runx-occupied Thpok silencer, in post-selection double-positive thymocytes to prevent excessive ThPOK induction and in mature CD8⁺ T cells to silence Thpok expression. Tle3 also bound to Tcf1-occupied sites in a few CD4⁺ lineage-associated genes, including Cd4 silencer and St8sia6 introns, to repress their expression in mature CD8⁺ T cells. These findings indicate that Tle corepressors are differentially partitioned to Runx and Tcf/Lef complexes to instruct CD8⁺ lineage choice and cooperatively establish CD8⁺ T cell identity, respectively.

Prostaglandin E1 and Its Analog Misoprostol Inhibit Human CML Stem Cell Self-Renewal via EP4 Receptor Activation and Repression of AP-1

Effective treatment of chronic myelogenous leukemia (CML) largely depends on the eradication of CML leukemic stem cells (LSCs). We recently showed that CML LSCs depend on Tcf1 and Lef1 factors for self-renewal. Using a connectivity map, we identified prostaglandin E1 (PGE1) as a small molecule that partly elicited the gene expression changes in LSCs caused by Tcf1/Lef1 deficiency. Although it has little impact on normal hematopoiesis, we found that PGE1 treatment impaired the persistence and activity of LSCs in a pre-clinical murine CML model and a xenograft model of transplanted CML patient CD34⁺ stem/progenitor cells. Mechanistically, PGE1 acted on the EP4 receptor and repressed Fosb and Fos AP-1 factors in a β-catenin-independent manner. Misoprostol, an FDA-approved EP4 agonist, conferred similar protection against CML. These findings suggest that activation of this PGE1-EP4 pathway specifically targets CML LSCs and that the combination of PGE1/misoprostol with conventional tyrosine-kinase inhibitors could provide effective therapy for CML.

Identification of Interleukin-27 (IL-27)/IL-27 Receptor Subunit Alpha as a Critical Immune Axis for In Vivo HIV Control

Intact and broad immune cell effector functions and specific individual cytokines have been linked to HIV disease outcome, but their relative contribution to HIV control remains unclear. We asked whether the proteome of secreted cytokines and signaling factors in peripheral blood can be used to discover specific pathways critical for host viral control. A custom glass-based microarray, able to measure >600 plasma proteins involved in cell-to-cell communication, was used to measure plasma protein profiles in 96 HIV-infected, treatment-naive individuals with high (>50,000) or low (<10,000 HIV RNA copies/ml) viral loads. Univariate and regression model analysis demonstrate that plasma levels of soluble interleukin-27 (IL-27) are significantly elevated in individuals with high plasma viremia (P < 0.0001) and are positively correlated with proviral HIV-DNA copy numbers in peripheral blood mononuclear cells (PBMC) (Rho = 0.4011; P = 0.0027). Moreover, soluble IL-27 plasma levels are negatively associated with the breadth and magnitude of the total virus-specific T-cell responses and directly with plasma levels of molecules involved in Wnt/β-catenin signaling. In addition to IL-27, gene expression levels of the specific IL-27 receptor (IL27RA) in PBMC correlated directly with both plasma viral load (Rho = 0.3531; P = 0.0218) and the proviral copy number in the peripheral blood as an indirect measure of partial viral reservoir (Rho = 0.4580; P = 0.0030). These results were validated in unrelated cohorts of early infected subjects as well as subjects before and after initiation of antiretroviral treatment, and they identify IL-27 and its specific receptor as a critical immune axis for the antiviral immune response and as robust correlates of viral load and proviral reservoir size in PBMC.

IMPORTANCE The detailed knowledge of immune mechanisms that contribute to HIV control is a prerequisite for the design of effective treatment strategies to achieve HIV cure. Cells communicate with each other by secreting signaling proteins, and the blood is a key conduit for transporting such factors. Investigating the communication factors promoting effective immune responses and having potentially antiviral functions against HIV using a novel focused omics approach (“communicome”) has the potential to significantly improve our knowledge of effective host immunity and accelerate the HIV cure agenda. Including 140 subjects with variable viral loads and measuring the plasma levels of >600 soluble proteins, our data highlight the importance of Th17 cells and Wnt/β-catenin signaling in HIV control and especially identify the IL-27/IL-27 receptor subunit alpha (IL-27RA) axis as a predictor of plasma viral load and proviral copy number in the peripheral blood. These data may provide important guidance to therapeutic approaches in the HIV cure agenda.

Differential Requirements for Tcf1 Long Isoforms in CD8+ and CD4+ T Cell Responses to Acute Viral Infection

In response to acute viral infection, activated naive T cells give rise to effector T cells that clear the pathogen and memory T cells that persist long-term and provide heightened protection. T cell factor 1 (Tcf1) is essential for several of these differentiation processes. Tcf1 is expressed in multiple isoforms, with all isoforms sharing the same HDAC and DNA-binding domains and the long isoforms containing a unique N-terminal β-catenin-interacting domain. In this study, we specifically ablated Tcf1 long isoforms in mice, while retaining expression of Tcf1 short isoforms. During CD8⁺ T cell responses, Tcf1 long isoforms were dispensable for generating cytotoxic CD8⁺ effector T cells and maintaining memory CD8⁺ T cell pool size, but they contributed to optimal maturation of central memory CD8⁺ T cells and their optimal secondary expansion in a recall response. In contrast, Tcf1 long isoforms were required for differentiation of T follicular helper (T_FH) cells, but not T_H1 effectors, elicited by viral infection. Although Tcf1 short isoforms adequately supported Bcl6 and ICOS expression in T_FH cells, Tcf1 long isoforms remained important for suppressing the expression of Blimp1 and T_H1-associated genes and for positively regulating Id3 to restrain germinal center T_FH cell differentiation. Furthermore, formation of memory T_H1 and memory T_FH cells strongly depended on Tcf1 long isoforms. These data reveal that Tcf1 long and short isoforms have distinct, yet complementary, functions and may represent an evolutionarily conserved means to ensure proper programming of CD8⁺ and CD4⁺ T cell responses to viral infection.

Targeting CD147 for T to NK Lineage Reprogramming and Tumor Therapy

CD147 is highly expressed on the surface of numerous tumor cells to promote invasion and metastasis. Targeting these cells with CD147-specific antibodies has been validated as an effective approach for lung and liver cancer therapy. In the immune system, CD147 is recognized as a co-stimulatory receptor and impacts the outcome of thymic selection. Using T cell-specific deletion, we showed here that in thymus CD147 is indispensable for the stable αβ T cell lineage commitment: loss of CD147 biases both multipotent DN (double negative) and fully committed DP (double positive) cells into innate NK-like lineages. Mechanistically, CD147 deficiency results in impaired Wnt signaling and expression of BCL11b, a master transcription factor in determining T cell identity. In addition, functional blocking of CD147 by antibody phenocopies genetic deletion to enrich NK-like cells in the periphery. Furthermore, using a melanoma model and orthotopic liver cancer transplants, we showed that the augmentation of NK-like cells strongly associates with resistance against tumor growth upon CD147 suppression. Therefore, besides its original function in tumorigenesis, CD147 is also an effective surface target for immune modulation in tumor therapy.

•

DN, DP cells were reprogrammed into innate NK-like cells after thymic CD147 deleted

•

Loss of CD147 results in impaired Bcl11b expression and T-lineages development, which can be rescued by Wnt3a stimulation.

•

CD147 is an vital target for immune modulation via NK-like cells in tumor therapy.

Tumor therapy is a difficult task and many methods have been used. Among them, tumor immunotherapy is a focus in the field and has made great progress. In this study, we found CD147 is an vital target for immune modulation via NK-like cells in tumor therapy, which means CD147 antibody may be through regulating immune cells to achieve tumor therapy. Although CD147 antibody has been used for liver cancer, making clear the mechanism of CD147 antibody mediated tumor therapy may be benefit for guiding clinical treatment.

Effect of mesenchymal stem cells on Sjögren-like mice and the microRNA expression profiles of splenic CD4+ T cells

Mesenchymal stem cells (MSCs) serve immuno-regulatory functions and offer a promising novel treatment for certain autoimmune diseases. The present study investigated the therapeutic effect of mice bone marrow (BM)-MSCs on mice with relatively late stage of Sjögren-like disease and the impact of BM-MSCs on the microRNA (miRNA) expression profiles of splenic CD4+ T cells. Female NOD/Ltj mice were randomized into two groups: The disease group (n=8) and the MSC-treated group (n=8). Female ICR mice served as the healthy control group (n=8). The MSC-treated group received an injection of MSCs when they were 26 weeks old. Water intake, blood glucose and salivary flow rate were measured and submandibular glands were resected and stained with hematoxylin and eosin to calculate the focus score. The concentrations of interleukin (IL)-2, IL-6, hepatocyte growth factor, interferon γ, IL-10, prostaglandin E2, transforming growth factor β1 and tumor necrosis factor-α in serum were measured using ELISA. The expression of miRNAs in splenic CD4+ T cells were measured using deep sequencing. The results demonstrated that treatment with BM-MSCs prevented a decline in the salivary flow rate and lymphocyte infiltration in the salivary glands of NOD mice, indicating that MSC-treatment had a therapeutic effect on NOD mice with relatively late stage of Sjögren-like disease. ELISA and deep sequencing results showed that the three groups of mice had different serum concentrations of cytokines/growth factors and different miRNA expression profiles of splenic CD4+ T cells. This implies that the alteration in serum levels of cytokines/growth factors and miRNA expression profiles of splenic CD4+ T cells may explain the therapeutic effect MSCs have on Sjögren's syndrome.

Cutting Edge: β-Catenin-Interacting Tcf1 Isoforms Are Essential for Thymocyte Survival but Dispensable for Thymic Maturation Transitions

T cell factor 1 (Tcf1) is essential for T cell development; however, it remains controversial whether β-catenin, a known coactivator of Tcf1, has a role. Tcf1 is expressed in multiple isoforms in T lineage cells, with the long isoforms interacting with β-catenin through an N-terminal domain. In this study, we specifically ablated Tcf1 long isoforms in mice (p45^-/-mice) to abrogate β-catenin interaction. Although thymic cellularity was diminished in p45^-/- mice, transition of thymocytes through the maturation stages was unaffected, with no overt signs of developmental blocks. p45^-/- thymocytes showed increased apoptosis and alterations in transcriptome, but these changes were substantially more modest than in thymocytes lacking all Tcf1 isoforms. These data indicate that Tcf1-β-catenin interaction is necessary for promoting thymocyte survival to maintain thymic output. Rather than being dominant-negative regulators, Tcf1 short isoforms are adequate in supporting developing thymocytes to traverse through maturation steps and in regulating the expression of most Tcf1 target genes.

1810011o10 Rik Inhibits the Antitumor Effect of Intratumoral CD8+ T Cells through Suppression of Notch2 Pathway in a Murine Hepatocellular Carcinoma Model

The mechanisms by which tumor-responsive CD8⁺ T cells are regulated are important for understanding the tumor immunity and for developing new therapeutic strategies. In current study, we identified the expression of 1810011o10 Rik, which is the homolog of human thyroid cancer 1, in intratumoral activated CD8⁺ T cells in a murine hepatocellular carcinoma (HCC) implantation model. To investigate the role of 1810011o10 Rik in the regulation of antitumor activity of CD8⁺ T cells, normal CD8⁺ T cells were transduced with 1810011o10 Rik-expressing lentiviruses. Although 1810011o10 Rik overexpression did not influence agonistic antibody-induced CD8⁺ T cell activation in vitro, it inhibited the cytotoxic efficacy of CD8⁺ T cells on HCC cells in vivo. 1810011o10 Rik overexpression impeded CD8⁺ T cell-mediated HCC cell apoptosis and favored tumor cell growth in vivo. Further investigation revealed that 1810011o10 Rik blocked the nuclear translocation of Notch2 intracellular domain, which is crucial for CD8⁺ T cell activity. Furthermore, a brief in vitro experiment suggested that both antigen-presenting cells and TGF-β might be necessary for the upregulation of Rik expression in activated CD8⁺ T cells. In general, our study disclosed a novel mechanism underlying the negative regulation of antitumor CD8⁺ T cells during HCC progression.

Critical roles of mTOR Complex 1 and 2 for T follicular helper cell differentiation and germinal center responses

T follicular helper (Tfh) cells play critical roles for germinal center responses and effective humoral immunity. We report here that mTOR in CD4 T cells is essential for Tfh differentiation. In Mtor^f/f-Cd4Cre mice, both constitutive and inducible Tfh differentiation is severely impaired, leading to defective germinal center B cell formation and antibody production. Moreover, both mTORC1 and mTORC2 contribute to Tfh and GC B cell development but may do so via distinct mechanisms. mTORC1 mainly promotes CD4 T cell proliferation to reach the cell divisions necessary for Tfh differentiation, while Rictor/mTORC2 regulates Tfh differentiation by promoting Akt activation and TCF1 expression without grossly influencing T cell proliferation. Together, our results reveal crucial but distinct roles for mTORC1 and mTORC2 in CD4 T cells during Tfh differentiation and germinal center responses.

DOI:http://dx.doi.org/10.7554/eLife.17936.001

Improvement of Sclerodermatous Graft-Versus-Host Disease in Mice by Niclosamide

Sclerodermatous graft-versus-host disease, a frequent complication of allogeneic hematopoietic stem cell graft, shares many features with systemic sclerosis, such as production of autoantibodies and fibrosis of skin and inner organs. Recent reports on the implication of signal transducer and activator of transcription 3 and of Wnt/β-catenin in fibrosis have prompted us to investigate the effects of the inhibition of both signaling pathways in a mouse model of sclerodermatous graft-versus-host disease, using niclosamide, an anthelmintic drug, with a well-defined safety profile. Sclerodermatous graft-versus-host disease was induced in BALB/c mice by B10.D2 bone marrow and spleen cell transplantation. Mice were treated every other day, 5 days a week, for 5 weeks by niclosamide. Clinical and biological features were studied 42 days after transplantation. Niclosamide reversed clinical symptoms including alopecia, vasculitis, and diarrhea and prevented fibrosis of the skin and visceral organs. Beneficial immunological effects were also observed: niclosamide decreased the production of effector memory CD4 and CD8 T cells, T-cell infiltration of the skin and visceral organs, and decreased productions of IL-4 and IL-13, and autoimmune B-cell activation. The improvement provided by niclosamide in the mouse model of sclerodermatous graft-versus-host disease provides a rationale for the evaluation of niclosamide in the management of patients affected by systemic fibrotic disease.

Dual epithelial and immune cell function of Dvl1 regulates gut microbiota composition and intestinal homeostasis

Homeostasis of the gastrointestinal (GI) tract is controlled by complex interactions between epithelial and immune cells and the resident microbiota. Here, we studied the role of Wnt signaling in GI homeostasis using Disheveled 1 knockout (Dvl1^-/-) mice, which display an increase in whole gut transit time. This phenotype is associated with a reduction and mislocalization of Paneth cells and an increase in CD8⁺ T cells in the lamina propria. Bone marrow chimera experiments demonstrated that GI dysfunction requires abnormalities in both epithelial and immune cells. Dvl1^-/- mice exhibit a significantly distinct GI microbiota, and manipulation of the gut microbiota in mutant mice rescued the GI transit abnormality without correcting the Paneth and CD8⁺ T cell abnormalities. Moreover, manipulation of the gut microbiota in wild-type mice induced a GI transit abnormality akin to that seen in Dvl1^-/- mice. Together, these data indicate that microbiota manipulation can overcome host dysfunction to correct GI transit abnormalities. Our findings illustrate a mechanism by which the epithelium and immune system coregulate gut microbiota composition to promote normal GI function.

The role of the Wnt canonical signaling in neurodegenerative diseases

The Wnt/β-catenin or Wnt canonical pathway controls multiple biological processes throughout development and adult life. Growing evidences have suggested that deregulation of the Wnt canonical pathway could be involved in the pathogenesis of neurodegenerative diseases. The Wnt canonical signaling is a pathway tightly regulated, which activation results in the inhibition of the Glycogen Synthase Kinase 3β (GSK-3β) function and in increased β-catenin activity, that migrates into the nucleus, activating the transcription of the Wnt target genes. Conversely, when the Wnt canonical pathway is turned off, increased levels of GSK-3β promote β-catenin degradation. Hence, GSK-3β could be considered as a key regulator of the Wnt canonical pathway. Of note, GSK-3β has also been involved in the modulation of inflammation and apoptosis, determining the delicate balance between immune tolerance/inflammation and neuronal survival/neurodegeneration. In this review, we have summarized the current acknowledgements about the role of the Wnt canonical pathway in the pathogenesis of some neurodegenerative diseases including Alzheimer's disease, cerebral ischemia, Parkinson's disease, Huntington's disease, multiple sclerosis and amyotrophic lateral sclerosis, with particular regard to the main in vitro and in vivo studies in this field, by reviewing 85 research articles about.

Identification of a novel mechanism of action of fingolimod (FTY720) on human effector T cell function through TCF-1 upregulation

Background

Fingolimod (FTY720), the first oral treatment for multiple sclerosis (MS), blocks immune cell trafficking and prevents disease relapses by downregulation of sphingosine-1-phosphate receptor. We determined the effect of FTY720 on human T cell activation and effector function.

Methods

T cells from MS patients and healthy controls were isolated to measure gene expression profiles in the presence or absence of FTY720 using nanostring and quantitative real-time polymerase chain reaction (qPCR). Cytokine protein expression was measured using luminex assay and flow cytometry analysis. Lentivirus vector carrying short hairpin RNA (shRNA) was used to knock down the expression of specific genes in CD4+ T cells. Chromatin immunoprecipitation was performed to assess T cell factor 1 (TCF-1) binding to promoter regions. Luciferase assays were performed to test the direct regulation of interferon gamma (IFN-γ) and granzyme B (GZMB) by TCF-1. Western blot analysis was used to assess the phosphorylation status of Akt and GSK3β.

Results

We showed that FTY720 treatment not only affects T cell trafficking but also T cell activation. Patients treated with FTY720 showed a significant reduction in circulating CD4 T cells. Activation of T cells in presence of FTY720 showed a less inflammatory phenotype with reduced production of IFN-γ and GZMB. This decreased effector phenotype of FTY720-treated T cells was dependent on the upregulation of TCF-1. FTY720-induced TCF-1 downregulated the pathogenic cytokines IFN-γ and GZMB by binding to their promoter/enhancer regions and mediating epigenetic modifications. Furthermore, we observed that TCF-1 expression was lower in T cells from multiple sclerosis patients than in those from healthy individuals, and FTY720 treatment increased TCF-1 expression in multiple sclerosis patients.

Conclusions

These results reveal a previously unknown mechanism of the effect of FTY720 on human CD4+ T cell modulation in multiple sclerosis and demonstrate the role of TCF-1 in human T cell activation and effector function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0460-z) contains supplementary material, which is available to authorized users.

The aryl hydrocarbon receptor in barrier organ physiology, immunology, and toxicology

The aryl hydrocarbon receptor (AhR) is an evolutionarily old transcription factor belonging to the Per-ARNT-Sim-basic helix-loop-helix protein family. AhR translocates into the nucleus upon binding of various small molecules into the pocket of its single-ligand binding domain. AhR binding to both xenobiotic and endogenous ligands results in highly cell-specific transcriptome changes and in changes in cellular functions. We discuss here the role of AhR for immune cells of the barrier organs: skin, gut, and lung. Both adaptive and innate immune cells require AhR signaling at critical checkpoints. We also discuss the current two prevailing views-namely, 1) AhR as a promiscuous sensor for small chemicals and 2) a role for AhR as a balancing factor for cell differentiation and function, which is controlled by levels of endogenous high-affinity ligands. AhR signaling is considered a promising drug and preventive target, particularly for cancer, inflammatory, and autoimmune diseases. Therefore, understanding its biology is of great importance.

GRP94/gp96 in Cancer: Biology, Structure, Immunology, and Drug Development

As an endoplasmic reticulum heat-shock protein 90 (HSP90) paralog, GRP94 (glucose-regulated protein 94)/gp96 (hereafter referred to as GRP94) has been shown to be an essential master chaperone for multiple receptors including Toll-like receptors, Wnt coreceptors, and integrins. Clinically, expression of GRP94 correlates with advanced stage and poor survival in a variety of cancers. Recent preclinical studies have also revealed that GRP94 expression is closely linked to cancer growth and metastasis in melanoma, ovarian cancer, multiple myeloma, lung cancer, and inflammation-associated colon cancer. Thus, GRP94 is an attractive therapeutic target in a number of malignancies. The chaperone function of GRP94 depends on its ATPase domain, which is structurally distinct from HSP90, allowing design of highly selective GRP94-targeted inhibitors. In this chapter, we discuss the biology and structure-function relationship of GRP94. We also summarize the immunological roles of GRP94 based on the studies documented over the last two decades, as these pertain to tumorigenesis and cancer progression. Finally, the structure-based rationale for the design of selective small-molecule inhibitors of GRP94 and their potential application in the treatment of cancer are highlighted.

TCF1 Is Required for the T Follicular Helper Cell Response to Viral Infection

T follicular helper (TFH) and T helper 1 (Th1) cells generated after viral infections are critical for the control of infection and the development of immunological memory. However, the mechanisms that govern the differentiation and maintenance of these two distinct lineages during viral infection remain unclear. We found that viral-specific TFH and Th1 cells showed reciprocal expression of the transcriptions factors TCF1 and Blimp1 early after infection, even before the differential expression of the canonical TFH marker CXCR5. Furthermore, TCF1 was intrinsically required for the TFH cell response to viral infection; in the absence of TCF1, the TFH cell response was severely compromised, and the remaining TCF1-deficient TFH cells failed to maintain TFH-associated transcriptional and metabolic signatures, which were distinct from those in Th1 cells. Mechanistically, TCF1 functioned through forming negative feedback loops with IL-2 and Blimp1. Our findings demonstrate an essential role of TCF1 in TFH cell responses to viral infection.

The transcription factor TCF-1 initiates the differentiation of T(FH) cells during acute viral infection

Induction of the transcriptional repressor Bcl-6 in CD4(+) T cells is critical for the differentiation of follicular helper T cells (T(FH) cells), which are essential for B cell-mediated immunity. In contrast, the transcription factor Blimp1 (encoded by Prdm1) inhibits T(FH) differentiation by antagonizing Bcl-6. Here we found that the transcription factor TCF-1 was essential for both the initiation of T(FH) differentiation and the effector function of differentiated T(FH) cells during acute viral infection. Mechanistically, TCF-1 bound directly to the Bcl6 promoter and Prdm1 5' regulatory regions, which promoted Bcl-6 expression but repressed Blimp1 expression. TCF-1-null T(FH) cells upregulated genes associated with non-T(FH) cell lineages. Thus, TCF-1 functions as an important hub upstream of the Bcl-6-Blimp1 axis to initiate and secure the differentiation of T(FH) cells during acute viral infection.

From inception to output, Tcf1 and Lef1 safeguard development of T cells and innate immune cells

Transcription factors have recurring roles during T cell development and activation. Tcf1 and Lef1 are known to be essential for early stages of thymocyte maturation. Recent research has revealed several novel aspects of their functionality. Tcf1 is induced at the very earliest step of specifying hematopoietic progenitors to the T cell lineage as a key target gene downstream of Notch activation. In addition to promoting maturation of T-lineage-committed thymocytes, Tcf1 functions as a tumor suppressor in developing thymocytes, and this is mediated, paradoxically, by restraining Lef1 expression. After positive selection, Tcf1 and Lef1 act together to direct CD4(+)CD8(+) double positive thymocytes to a CD4(+) T cell fate. Although not required for CD8(+) T cell differentiation, Tcf1 and Lef1 cooperate with Runx factors to achieve stable silencing of the Cd4 gene in CD8(+) T cells. Tcf1 is also found to have versatile roles in innate immune cells, which partly mirror its functions in mature T helper cells. Discrepancy in requirements of Tcf1/Lef1 and β-catenin in T cells has been a long-standing enigma. We will review other protein factors interacting with Tcf1 and Lef1 and discuss their regulatory roles independent of β-catenin.

TCF1 and LEF1 act as T-cell intrinsic HTLV-1 antagonists by targeting Tax

Human T-cell leukemia virus type 1 (HTLV-1) is a delta-type retrovirus that induces malignant and inflammatory diseases during its long persistence in vivo. HTLV-1 can infect various kinds of cells; however, HTLV-1 provirus is predominantly found in peripheral CD4 T cells in vivo. Here we find that TCF1 and LEF1, two Wnt transcription factors that are specifically expressed in T cells, inhibit viral replication through antagonizing Tax functions. TCF1 and LEF1 can each interact with Tax and inhibit Tax-dependent viral expression and activation of NF-κB and AP-1. As a result, HTLV-1 replication is suppressed in the presence of either TCF1 or LEF1. On the other hand, T-cell activation suppresses the expression of both TCF1 and LEF1, and this suppression enables Tax to function as an activator. We analyzed the thymus of a simian T-cell leukemia virus type 1 (STLV-1) infected Japanese macaque, and found a negative correlation between proviral load and TCF1/LEF1 expression in various T-cell subsets, supporting the idea that TCF1 and LEF1 negatively regulate HTLV-1 replication and the proliferation of infected cells. Thus, this study identified TCF1 and LEF1 as Tax antagonistic factors in vivo, a fact which may critically influence the peripheral T-cell tropism of this virus.

Wnt5a signaling increases IL-12 secretion by human dendritic cells and enhances IFN-γ production by CD4+ T cells

Wnt5a is a secreted pleiotropic glycoprotein produced in an inflammatory state by a wide spectrum of ubiquitous cell populations. Recently, we demonstrated that Wnt5a skews the differentiation of human monocyte derived dendritic cells (moDCs) to a tolerogenic functional state. In this study we focus our interest on the role of this Wnt ligand after DC differentiation, during their maturation and function. We show that the expression of Wnt receptors is tightly regulated during the life cycle of DCs suggesting a differential responsiveness to Wnt signaling conditioned by their differentiation stage and the maturational stimuli. Furthermore, we confirm that Wnt5a is the main non-canonical Wnt protein expressed by DCs and its production increases upon specific stimuli. Exogenous Wnt5a improved the endocytic capacity of immature DCs but it is not a stimulatory signal on its own, slightly affecting the maturation and function of DCs. However, knocking down Wnt5a gene expression in maturing DCs demonstrates that DC-derived Wnt5a is necessary for normal IL-12 secretion and plays a positive role during the development of Th1 responses. Wnt5a acts both in autocrine and paracrine ways. Thus, human naive CD4(+) T cells express Wnt receptors and, the addition of Wnt5a during CD3/CD28 stimulation enhances IL-2 and IFN-γ production. Taken together these results suggest a time-dependent role for Wnt5a during inflammatory responses conditioned by the differentiation stage of cellular targets.

TCF-1 and LEF-1 act upstream of Th-POK to promote the CD4(+) T cell fate and interact with Runx3 to silence Cd4 in CD8(+) T cells

The transcription factors TCF-1 and LEF-1 are essential for early T cell development, but their roles beyond the CD4(+)CD8(+) double-positive (DP) stage are unknown. By specific ablation of these factors in DP thymocytes, we demonstrated that deficiency in TCF-1 and LEF-1 diminished the output of CD4(+) T cells and redirected CD4(+) T cells to a CD8(+) T cell fate. The role of TCF-1 and LEF-1 in the CD4-versus-CD8 lineage 'choice' was mediated in part by direct positive regulation of the transcription factor Th-POK. Furthermore, loss of TCF-1 and LEF-1 unexpectedly caused derepression of CD4 expression in T cells committed to the CD8(+) lineage without affecting the expression of Runx transcription factors. Instead, TCF-1 physically interacted with Runx3 to cooperatively silence Cd4. Thus, TCF-1 and LEF-1 adopted distinct genetic 'wiring' to promote the CD4(+) T cell fate and establish CD8(+) T cell identity.