Notch activity influences the alphabeta versus gammadelta T cell lineage decision

The physiological and pathological roles of RNA modifications in T cells

RNA molecules undergo dynamic chemical modifications in response to various external or cellular stimuli. Some of those modifications have been demonstrated to post-transcriptionally modulate the RNA transcription, localization, stability, translation, and degradation, ultimately tuning the fate decisions and function of mammalian cells, particularly T cells. As a crucial part of adaptive immunity, T cells play fundamental roles in defending against infections and tumor cells. Recent findings have illuminated the importance of RNA modifications in modulating T cell survival, proliferation, differentiation, and functional activities. Therefore, understanding the epi-transcriptomic control of T cell biology enables a potential avenue for manipulating T cell immunity. This review aims to elucidate the physiological and pathological roles of internal RNA modifications in T cell development, differentiation, and functionality drawn from current literature, with the goal of inspiring new insights for future investigations and providing novel prospects for T cell-based immunotherapy.

New insights into the function and pathophysiology of the ectodomain sheddase A Disintegrin And Metalloproteinase 10 (ADAM10)

The 'A Disintegrin And Metalloproteinase 10' (ADAM10) has gained considerable attention due to its discovery as an 'α-secretase' involved in the nonamyloidogenic processing of the amyloid precursor protein, thereby possibly preventing the excessive generation of the amyloid beta peptide, which is associated with the pathogenesis of Alzheimer's disease. ADAM10 was found to exert many additional functions, cleaving about 100 different membrane proteins. ADAM10 is involved in many pathophysiological conditions, ranging from cancer and autoimmune disorders to neurodegeneration and inflammation. ADAM10 cleaves its substrates close to the plasma membrane, a process referred to as ectodomain shedding. This is a central step in the modulation of the functions of cell adhesion proteins and cell surface receptors. ADAM10 activity is controlled by transcriptional and post-translational events. The interaction of ADAM10 with tetraspanins and the way they functionally and structurally depend on each other is another topic of interest. In this review, we will summarize findings on how ADAM10 is regulated and what is known about the biology of the protease. We will focus on novel aspects of the molecular biology and pathophysiology of ADAM10 that were previously poorly covered, such as the role of ADAM10 on extracellular vesicles, its contribution to virus entry, and its involvement in cardiac disease, cancer, inflammation, and immune regulation. ADAM10 has emerged as a regulator controlling cell surface proteins during development and in adult life. Its involvement in disease states suggests that ADAM10 may be exploited as a therapeutic target to treat conditions associated with a dysfunctional proteolytic activity.

The role of quiescent thymic progenitors in TAL/LMO2-induced T-ALL chemotolerance

Relapse in T-cell acute lymphoblastic leukemia (T-ALL) may signify the persistence of leukemia-initiating cells (L-ICs). Ectopic TAL1/LMO expression defines the largest subset of T-ALL, but its role in leukemic transformation and its impact on relapse-driving L-ICs remain poorly understood. In TAL1/LMO mouse models, double negative-3 (DN3; CD4-CD8-CD25+CD44-) thymic progenitors harbored L-ICs. However, only a subset of DN3 leukemic cells exhibited L-IC activity, and studies linking L-ICs and chemotolerance are needed. To investigate L-IC heterogeneity, we used mouse models and applied single-cell RNA-sequencing and nucleosome labeling techniques in vivo. We identified a DN3 subpopulation with a cell cycle-restricted profile and heightened TAL1/LMO2 activity, that expressed genes associated with stemness and quiescence. This dormant DN3 subset progressively expanded throughout leukemogenesis, displaying intrinsic chemotolerance and enrichment in genes linked to minimal residual disease. Examination of TAL/LMO patient samples revealed a similar pattern in CD7+CD1a- thymic progenitors, previously recognized for their L-IC activity, demonstrating cell cycle restriction and chemotolerance. Our findings substantiate the emergence of dormant, chemotolerant L-ICs during leukemogenesis, and demonstrate that Tal1 and Lmo2 cooperate to promote DN3 quiescence during the transformation process. This study provides a deeper understanding of TAL1/LMO-induced T-ALL and its clinical implications in therapy failure.

γδ T cells: origin and fate, subsets, diseases and immunotherapy

The intricacy of diseases, shaped by intrinsic processes like immune system exhaustion and hyperactivation, highlights the potential of immune renormalization as a promising strategy in disease treatment. In recent years, our primary focus has centered on γδ T cell-based immunotherapy, particularly pioneering the use of allogeneic Vδ2+ γδ T cells for treating late-stage solid tumors and tuberculosis patients. However, we recognize untapped potential and optimization opportunities to fully harness γδ T cell effector functions in immunotherapy. This review aims to thoroughly examine γδ T cell immunology and its role in diseases. Initially, we elucidate functional differences between γδ T cells and their αβ T cell counterparts. We also provide an overview of major milestones in γδ T cell research since their discovery in 1984. Furthermore, we delve into the intricate biological processes governing their origin, development, fate decisions, and T cell receptor (TCR) rearrangement within the thymus. By examining the mechanisms underlying the anti-tumor functions of distinct γδ T cell subtypes based on γδTCR structure or cytokine release, we emphasize the importance of accurate subtyping in understanding γδ T cell function. We also explore the microenvironment-dependent functions of γδ T cell subsets, particularly in infectious diseases, autoimmune conditions, hematological malignancies, and solid tumors. Finally, we propose future strategies for utilizing allogeneic γδ T cells in tumor immunotherapy. Through this comprehensive review, we aim to provide readers with a holistic understanding of the molecular fundamentals and translational research frontiers of γδ T cells, ultimately contributing to further advancements in harnessing the therapeutic potential of γδ T cells.

Transcriptional regulation of Notch1 by nuclear factor-κB during T cell activation

Notch1 plays important roles in T cell development and is highly expressed in activated CD4⁺ T cells. However, the underlying mechanism of Notch1 transcription in T cells has not been fully characterized. Therefore, we aimed to determine how Notch1 expression is regulated during the activation of CD4⁺ T cells. Both the surface expression and mRNA transcription of Notch1 were significantly higher in activated CD4⁺ T cells, but the inhibition of phosphatidylinositol 3-kinase (PI3K) by LY294002 or deletion of the Pdk1 gene impaired this upregulation of Notch1. Interrogation of the Notch1 promoter region using serially deleted Notch1 promoter reporters revealed that the - 300 to - 270 region is crucial for its transcription in activated T cells. In addition, we found that nuclear factor (NF)-κB subunits containing RelA bind directly to this promoter region, thereby upregulating transcription. In addition, inhibition of NF-κB by SN50 impaired upregulation of Notch1 surface protein and mRNA in activated CD4⁺ T cells. Thus, we provide evidence that Notch1 transcription in activated CD4⁺ T cells is upregulated via the PI3K-PDK1-NF-κB signaling pathway.

Generation of T-cell-receptor-negative CD8αβ-positive CAR T cells from T-cell-derived induced pluripotent stem cells

The production of autologous T cells expressing a chimaeric antigen receptor (CAR) is time-consuming, costly and occasionally unsuccessful. T-cell-derived induced pluripotent stem cells (TiPS) are a promising source for the generation of 'off-the-shelf' CAR T cells, but the in vitro differentiation of TiPS often yields T cells with suboptimal features. Here we show that the premature expression of the T-cell receptor (TCR) or a constitutively expressed CAR in TiPS promotes the acquisition of an innate phenotype, which can be averted by disabling the TCR and relying on the CAR to drive differentiation. Delaying CAR expression and calibrating its signalling strength in TiPS enabled the generation of human TCR- CD8αβ+ CAR T cells that perform similarly to CD8αβ+ CAR T cells from peripheral blood, achieving effective tumour control on systemic administration in a mouse model of leukaemia and without causing graft-versus-host disease. Driving T-cell maturation in TiPS in the absence of a TCR by taking advantage of a CAR may facilitate the large-scale development of potent allogeneic CD8αβ+ T cells for a broad range of immunotherapies.

Development of γδ T cells in the thymus - A human perspective

γδ T cells are increasingly emerging as crucial immune regulators that can take on innate and adaptive roles in the defence against pathogens. Although they arise within the thymus from the same hematopoietic precursors as conventional αβ T cells, the development of γδ T cells is less well understood. In this review, we focus on summarising the current state of knowledge about the cellular and molecular processes involved in the generation of γδ T cells in human.

RNA m6A demethylase ALKBH5 regulates the development of γδ T cells

γδ T cells are an abundant T cell population at the mucosa and are important in providing immune surveillance as well as maintaining tissue homeostasis. However, despite γδ T cells' origin in the thymus, detailed mechanisms regulating γδ T cell development remain poorly understood. N⁶-methyladenosine (m⁶A) represents one of the most common posttranscriptional modifications of messenger RNA (mRNA) in mammalian cells, but whether it plays a role in γδ T cell biology is still unclear. Here, we show that depletion of the m⁶A demethylase ALKBH5 in lymphocytes specifically induces an expansion of γδ T cells, which confers enhanced protection against gastrointestinal Salmonella typhimurium infection. Mechanistically, loss of ALKBH5 favors the development of γδ T cell precursors by increasing the abundance of m⁶A RNA modification in thymocytes, which further reduces the expression of several target genes including Notch signaling components Jagged1 and Notch2. As a result, impairment of Jagged1/Notch2 signaling contributes to enhanced proliferation and differentiation of γδ T cell precursors, leading to an expanded mature γδ T cell repertoire. Taken together, our results indicate a checkpoint role of ALKBH5 and m⁶A modification in the regulation of γδ T cell early development.

The Legend of Delta: Finding a New TCR Gene

This Pillars of Immunology article is a commentary on “A new T-cell receptor gene located within the alpha locus and expressed early in T-cell differentiation,” a pivotal article written by Y.-H. Chien, M. Iwashima, K. B. Kaplan, J. F. Elliott, and M. M. Davis, and published in Nature, in 1987. https://www.nature.com/articles/327677a0.

Meprin and ADAM proteases as triggers of systemic inflammation in sepsis

Systemic inflammatory disorders (SIDs) comprise a broad range of diseases characterized by dysregulated excessive innate immune responses. Severe forms of SIDs can lead to organ failure and death, and their increasing incidence represents a major issue for the healthcare system. Protease-mediated ectodomain shedding of cytokines and their receptors represents a central mechanism in the regulation of inflammatory responses. The metalloprotease A disintegrin and metalloproteinase (ADAM) 17 is the best-characterized ectodomain sheddase capable of releasing TNF-α and soluble IL-6 receptor, which are decisive factors of systemic inflammation. Recently, meprin metalloproteases were also identified as IL-6 receptor sheddases and activators of the pro-inflammatory cytokines IL-1β and IL-18. In different mouse models of SID, particularly those mimicking a sepsis-like phenotype, ADAM17 and meprins have been found to promote disease progression. In this review, we summarize the role of ADAM10, ADAM17, and meprins in the onset and progression of sepsis and discuss their potential as therapeutic targets.

A Co-Association Network Analysis Reveals Putative Regulators for Health-Related Traits in Pigs

In recent years, the increase in awareness of antimicrobial resistance together with the societal demand of healthier meat products have driven attention to health-related traits in livestock production. Previous studies have reported medium to high heritabilities for these traits and described genomic regions associated with them. Despite its genetic component, health- and immunity-related traits are complex and its study by association analysis with genomic markers may be missing some information. To analyse multiple phenotypes and gene-by-gene interactions, systems biology approaches, such as the association weight matrix (AWM), allows combining genome wide association study results with network inference algorithms. The present study aimed to identify gene networks, key regulators and candidate genes associated to immunocompetence in pigs by integrating multiple health-related traits, enriched for innate immune phenotypes, using the AWM approach. The co-association network analysis unveiled a network comprised of 3,636 nodes (genes) and 451,407 edges (interactions), including a total of 246 regulators. From these, five genes (ARNT2, BRMS1L, MED12L, SUPT3H and TRIM25) were selected as key regulators as they were associated with the maximum number of genes with the minimum overlapping (1,827 genes in total). The five regulators were involved in pathways related to immunity such as lymphocyte differentiation and activation, platelet activation and degranulation, megakaryocyte differentiation, FcγR-mediated phagocytosis and response to nitric oxide, among others, but also in immunometabolism. Furthermore, we identified genes co-associated with the key regulators previously reported as candidate genes (e.g., ANGPT1, CD4, CD36, DOCK1, PDE4B, PRKCE, PTPRC and SH2B3) for immunity traits in humans and pigs, but also new candidate ones (e.g., ACSL3, CXADR, HBB, MMP12, PTPN6, WLS) that were not previously described. The co-association analysis revealed new regulators associated with health-related traits in pigs. This approach also identified gene-by-gene interactions and candidate genes involved in pathways related to cell fate and metabolic and immune functions. Our results shed new light in the regulatory mechanisms involved in pig immunity and reinforce the use of the pig as biomedical model.

Inhibition of gamma-secretase activity without interfering in Notch signalling decreases inflammatory response in patients with cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) patients present an exacerbated inflammatory response associated with tissue damage and ulcer development. Increasing numbers of patients have exhibited treatment failure, which remains not well understood. We hypothesized that adjuvant anti-inflammatory therapy would benefit CL patients. The aim of the present study was to investigate the contribution of Notch signalling and gamma-secretase activity to the inflammatory response observed in CL patients. Notch signalling is a molecular signalling pathway conserved among animal species. Gamma-secretase forms a complex of proteins that, among other pathways, modulates Notch signalling and immune response. We found that Notch 1 cell receptor signalling protects against the pathologic inflammatory response, and JLK6, a gamma-secretase inhibitor that does not interfere with Notch signalling, was shown to decrease the in-vitro inflammatory response in CL. Our data suggest that JLK6 may serve as an adjuvant treatment for CL patients.

Ontogenic timing, T cell receptor signal strength, and Notch signaling direct γδ T cell functional differentiation in vivo

γδ T cells form an integral arm of the immune system and are critical during protective and destructive immunity. However, how γδ T cells are functionally programmed in vivo remains unclear. Here, we employ RBPJ-inducible and KN6-transgenic mice to assess the roles of ontogenic timing, T cell receptor (TCR) signal strength, and Notch signaling. We find skewing of Vγ1+ cells toward the PLZF+Lin28b+ lineage at the fetal stage. Generation of interleukin-17 (IL-17)-producing γδ T cells is favored during, although not exclusive to, the fetal stage. Surprisingly, Notch signaling is dispensable for peripheral γδ T cell IL-17 production. Strong TCR signals, together with Notch, promote IL-4 differentiation. Conversely, less strong TCR signals promote Notch-independent IL-17 differentiation. Single-cell transcriptomic analysis reveals differential programming instilled by TCR signal strength and Notch for specific subsets. Thus, our results precisely define the roles of ontogenic timing, TCR signal strength, and Notch signaling in γδ T cell functional programming in vivo.

Inaccessible LCG Promoters Act as Safeguards to Restrict T Cell Development to Appropriate Notch Signaling Environments

T cell development is restricted to the thymus and is dependent on high levels of Notch signaling induced within the thymic microenvironment. To understand Notch function in thymic restriction, we investigated the basis for target gene selectivity in response to quantitative differences in Notch signal strength, focusing on the chromatin architecture of genes essential for T cell differentiation. We find that high Notch signal strength is required to activate promoters of known targets essential for T cell commitment, including Il2ra, Cd3ε, and Rag1, which feature low CpG content (LCG) and DNA inaccessibility in hematopoietic stem progenitor cells. Our findings suggest that promoter DNA inaccessibility at LCG T lineage genes provides robust protection against stochastic activation in inappropriate Notch signaling contexts, limiting T cell development to the thymus.

Biological Significance of NOTCH Signaling Strength

The evolutionarily conserved NOTCH signaling displays pleotropic functions in almost every organ system with a simple signaling axis. Different from many other signaling pathways that can be amplified via kinase cascades, NOTCH signaling does not contain any intermediate to amplify signal. Thus, NOTCH signaling can be activated at distinct signaling strength levels, disruption of which leads to various developmental disorders. Here, we reviewed mechanisms establishing different NOTCH signaling strengths, developmental processes sensitive to NOTCH signaling strength perturbation, and transcriptional regulations influenced by NOTCH signaling strength changes. We hope this could add a new layer of diversity to explain the pleotropic functions of NOTCH signaling pathway.

Identifying the Immunological Gene Signatures of Immune Cell Subtypes

The immune system is a complicated defensive system that comprises multiple functional cells and molecules acting against endogenous and exogenous pathogenic factors. Identifying immune cell subtypes and recognizing their unique immunological functions are difficult because of the complicated cellular components and immunological functions of the immune system. With the development of transcriptomics and high-throughput sequencing, the gene expression profiling of immune cells can provide a new strategy to explore the immune cell subtyping. On the basis of the new profiling data of mouse immune cell gene expression from the Immunological Genome Project (ImmGen), a novel computational pipeline was applied to identify different immune cell subtypes, including αβ T cells, B cells, γδ T cells, and innate lymphocytes. First, the profiling data was analyzed by a powerful feature selection method, Monte-Carlo Feature Selection, resulting in a feature list and some informative features. For the list, the two-stage incremental feature selection method, incorporating random forest as the classification algorithm, was applied to extract essential gene signatures and build an efficient classifier. On the other hand, a rule learning scheme was applied on the informative features to construct quantitative expression rules. A group of gene signatures was found as qualitatively related to the biological processes of four immune cell subtypes. The quantitative expression rules can efficiently cluster immune cells. This work provides a novel computational tool for immune cell quantitative subtyping and biomarker recognition.

Field cancerization: Definition, epidemiology, risk factors, and outcomes

Field cancerization was first described in 1953 when pathologic atypia was identified in clinically normal tissue surrounding oropharyngeal carcinomas. The discovery of mutated fields surrounding primary tumors raised the question of whether the development of subsequent tumors within the field represented recurrences or additional primary tumors. Since this initial study, field cancerization has been applied to numerous other epithelial tissues, including the skin. Cutaneous field cancerization occurs in areas exposed to chronic ultraviolet radiation, which leads to clonal proliferations of p53-mutated fields and is characterized by multifocal actinic keratoses, squamous cell carcinomas in situ, and cutaneous squamous cell carcinomas. In the first article in this continuing medical education series, we define field cancerization, review the available grading systems, and discuss the epidemiology, risk factors, and outcomes associated with this disease.

Notch signaling at the crossroads of innate and adaptive immunity

Notch signaling is an evolutionarily conserved cell-to-cell signaling pathway that regulates cellular differentiation and function across multiple tissue types and developmental stages. In this review, we discuss our current understanding of Notch signaling in mammalian innate and adaptive immunity. The importance of Notch signaling is pervasive throughout the immune system, as it elicits lineage and context-dependent effects in a wide repertoire of cells. Although regulation of binary cell fate decisions encompasses many of the functions first ascribed to Notch in the immune system, recent advances in the field have refined and expanded our view of the Notch pathway beyond this initial concept. From establishing T cell identity in the thymus to regulating mature T cell function in the periphery, the Notch pathway is an essential, recurring signal for the T cell lineage. Among B cells, Notch signaling is required for the development and maintenance of marginal zone B cells in the spleen. Emerging roles for Notch signaling in innate and innate-like lineages such as classical dendritic cells and innate lymphoid cells are likewise coming into view. Lastly, we speculate on the molecular underpinnings that shape the activity and versatility of the Notch pathway.

Targeting ADAM10 in Cancer and Autoimmunity

Generating inhibitors for A Disintegrin And Metalloproteinase 10 (ADAM10), a zinc-dependent protease, was heavily invested in by the pharmaceutical industry starting over 20 years ago. There has been much enthusiasm in basic research for these inhibitors, with a multitude of studies generating significant data, yet the clinical trials have not replicated the same results. ADAM10 is ubiquitously expressed and cleaves many important substrates such as Notch, PD-L1, EGFR/HER ligands, ICOS-L, TACI, and the "stress related molecules" MIC-A, MIC-B and ULBPs. This review goes through the most recent pre-clinical data with inhibitors as well as clinical data supporting the use of ADAM10 inhibitor use in cancer and autoimmunity. It additionally addresses how ADAM10 inhibitor therapy can be improved and if inhibitor therapy can be paired with other drug treatments to maximize effectiveness in various disease states. Finally, it examines the ADAM10 substrates that are important to each disease state and if any of these substrates or ADAM10 itself is a potential biomarker for disease.

Metabolic signaling directs the reciprocal lineage decisions of αβ and γδ T cells

The interaction between extrinsic factors and intrinsic signal strength governs thymocyte development, but the mechanisms linking them remain elusive. We report that mechanistic target of rapamycin complex 1 (mTORC1) couples microenvironmental cues with metabolic programs to orchestrate the reciprocal development of two fundamentally distinct T cell lineages, the αβ and γδ T cells. Developing thymocytes dynamically engage metabolic programs including glycolysis and oxidative phosphorylation, as well as mTORC1 signaling. Loss of RAPTOR-mediated mTORC1 activity impairs the development of αβ T cells but promotes γδ T cell generation, associated with disrupted metabolic remodeling of oxidative and glycolytic metabolism. Mechanistically, we identify mTORC1-dependent control of reactive oxygen species production as a key metabolic signal in mediating αβ and γδ T cell development, and perturbation of redox homeostasis impinges upon thymocyte fate decisions and mTORC1-associated phenotypes. Furthermore, single-cell RNA sequencing and genetic dissection reveal that mTORC1 links developmental signals from T cell receptors and NOTCH to coordinate metabolic activity and signal strength. Our results establish mTORC1-driven metabolic signaling as a decisive factor for reciprocal αβ and γδ T cell development and provide insight into metabolic control of cell signaling and fate decisions.

Innate Lymphoid Cell Development: A T Cell Perspective

Innate lymphoid cells (ILCs) and natural killer (NK) cells have garnered considerable interest due to their unique functional properties in immune defense and tissue homeostasis. Our current understanding of how these cells develop has been greatly facilitated by knowledge of T cell biology. Models of T cell differentiation provided the basis for a conceptual classification of these innate effectors and inspired a scheme of their activation and regulation. In this review, we discuss NK cell and ILC development from a "T cell standpoint" in an attempt to extend the analogy between adaptive T cells and their innate ILC and NK cell counterparts.

The multifaceted role of Notch signal in regulating T cell fate

Notch signaling pathway facilitates important cellular functions of the host. Notch signal is essential for the development of T cells, and the role of Notch in fine tuning of αβ versus γδ T cell lineage commitment is fundamentally different in mice and human. The Notch family of cell surface receptor likewise plays a critical role in regulating T cell activation, and influences T cell response both intrinsically and through the local environment. In this review, we take an overview of Notch signaling pathway and also emphasize the role of Notch signal in T cell lineage differentiation and activating effector function of peripheral T cells.

Intrathymic Notch3 and CXCR4 combinatorial interplay facilitates T-cell leukemia propagation

Notch hyperactivation dominates T-cell acute lymphoblastic leukemia development, but the mechanisms underlying “pre-leukemic” cell dissemination are still unclear. Here we describe how deregulated Notch3 signaling enhances CXCR4 cell-surface expression and migratory ability of CD4⁺CD8⁺ thymocytes, possibly contributing to “pre-leukemic” cell propagation, early in disease progression. In transgenic mice overexpressing the constitutively active Notch3 intracellular domain, we detect the progressive increase in circulating blood and bone marrow of CD4⁺CD8⁺ cells, characterized by high and combined surface expression of Notch3 and CXCR4. We report for the first time that transplantation of such CD4⁺CD8⁺ cells reveals their competence in infiltrating spleen and bone marrow of immunocompromised recipient mice. We also show that CXCR4 surface expression is central to the migratory ability of CD4⁺CD8⁺ cells and such an expression is regulated by Notch3 through β-arrestin in human leukemia cells. De novo, we propose that hyperactive Notch3 signaling by boosting CXCR4-dependent migration promotes anomalous egression of CD4⁺CD8⁺ cells from the thymus in early leukemia stages. In fact, in vivo CXCR4 antagonism prevents bone marrow colonization by such CD4⁺CD8⁺ cells in young Notch3 transgenic mice. Therefore, our data suggest that combined therapies precociously counteracting intrathymic Notch3/CXCR4 crosstalk may prevent dissemination of “pre-leukemic” CD4⁺CD8⁺ cells, by a “thymus-autonomous” mechanism.

A Review of Notch Processing With New Insights Into Ligand-Independent Notch Signaling in T-Cells

The Notch receptor is an evolutionarily highly conserved transmembrane protein essential to a wide spectrum of cellular systems, and its deregulation has been linked to a vast number of developmental disorders and malignancies. Regulated Notch function is critical for the generation of T-cells, in which abnormal Notch signaling results in leukemia. Notch activation through trans-activation of the receptor by one of its ligands expressed on adjacent cells has been well defined. In this canonical ligand-dependent pathway, Notch receptor undergoes conformational changes upon ligand engagement, stimulated by a pulling-force on the extracellular fragment of Notch that results from endocytosis of the receptor-bound ligand into the ligand-expressing cell. These conformational changes in the receptor allow for two consecutive proteolytic cleavage events to occur, which release the intracellular region of the receptor into the cytoplasm. It can then travel to the nucleus, where it induces gene transcription. However, there is accumulating evidence that other pathways may induce Notch signaling. A ligand-independent mechanism of Notch activation has been described in which receptor processing is initiated via cell-internal signals. These signals result in the internalization of Notch into endosomal compartments, where chemical changes existing in this microenvironment result in the conformational modifications required for receptor processing. This review will present mechanisms underlying both canonical ligand-dependent and non-canonical ligand-independent Notch activation pathways and discuss the latter in the context of Notch signaling in T-cells.

Peripheral PDGFRα+gp38+ mesenchymal cells support the differentiation of fetal liver-derived ILC2

Group 2 innate lymphoid cells (ILC2s) are derived from common lymphoid progenitors (CLPs) via several specific precursors, and the transcription factors essential for ILC2 differentiation have been extensively studied. However, the external factors regulating commitment to the ILC lineage as well as the sites and stromal cells that constitute the optimal microenvironment for ILC2-specific differentiation are not fully defined. In this study, we demonstrate that three key external factors, the concentration of interleukin 7 (IL-7) and strength and duration of Notch signaling, coordinately determine the fate of CLP toward the T, B, or ILC lineage. Additionally, we identified three stages of ILC2 in the fetal mesentery that require STAT5 signals for maturation: ILC progenitors, CCR9⁺ ILC2 progenitors, and KLRG1^- immature ILC2. We further demonstrate that ILC2 development is supported by mesenteric platelet-derived growth factor receptor α (PDGFRα)⁺ glycoprotein 38 (gp38)⁺ mesenchymal cells. Collectively, our results suggest that early differentiation of ILC2 occurs in the fetal liver via IL-7 and Notch signaling, whereas final differentiation occurs in the periphery with the aid of PDGFRα⁺gp38⁺ cells.

The Notch3 Receptor and Its Intracellular Signaling-Dependent Oncogenic Mechanisms

During evolution, gene duplication of the Notch receptor suggests a progressive functional diversification. The Notch3 receptor displays a number of structural differences with respect to Notch1 and Notch2, most of which have been reported in the transmembrane and in the intracellular regions, mainly localized in the negative regulatory region (NRR) and trans-activation domain (TAD). Targeted deletion of Notch3 does not result in embryonic lethality, which is in line with its highly restricted tissue expression pattern. Importantly, deregulated Notch3 expression and/or activation, often results in disrupted cell differentiation and/or pathological development, most notably in oncogenesis in different cell contexts. Mechanistically this is due to Notch3-related genetic alterations or epigenetic or posttranslational control mechanisms. In this chapter we discuss the possible relationships between the structural differences and the pathological role of Notch3 in the control of mouse and human cancers. In future, targeting the unique features of Notch3-oncogenic mechanisms could be exploited to develop anticancer therapeutics.

PKCθ links proximal T cell and Notch signaling through localized regulation of the actin cytoskeleton

Notch is a critical regulator of T cell differentiation and is activated through proteolytic cleavage in response to ligand engagement. Using murine myelin-reactive CD4 T cells, we demonstrate that proximal T cell signaling modulates Notch activation by a spatiotemporally constrained mechanism. The protein kinase PKCθ is a critical mediator of signaling by the T cell antigen receptor and the principal costimulatory receptor CD28. PKCθ selectively inactivates the negative regulator of F-actin generation, Coronin 1A, at the center of the T cell interface with the antigen presenting cell (APC). This allows for effective generation of the large actin-based lamellum required for recruitment of the Notch-processing membrane metalloproteinase ADAM10. Such enhancement of Notch activation is critical for efficient T cell proliferation and Th17 differentiation. We reveal a novel mechanism that, through modulation of the cytoskeleton, controls Notch activation at the T cell:APC interface thereby linking T cell receptor and Notch signaling pathways.

Control of Adhesion GPCR Function Through Proteolytic Processing

Proteolytic processing events in adhesion GPCRs. aGPCRs can undergo multiple autoproteolytic (red asterisks) and proteolytic processing events by exogenous proteases (yellow asterisks) that may be involved in signaling events of the receptors. Proteolytic processing is an unusual property of adhesion family G protein-coupled receptors (aGPCRs) that was observed upon their cloning and biochemical characterization.Ever since, much effort has been dedicated to delineate the mechanisms and requirements for cleavage events in the control of aGPCR function. Most notably, all aGPCRs possess a juxtamembrane protein fold, the GPCR autoproteolysis-inducing (GAIN) domain, which operates as an autoprotease for many aGPCR homologs investigated thus far. Analysis of its autoproteolytic reaction, the consequences for receptor fate and function, and the allocation of physiological effects to this peculiar feature of aGPCRs has occupied the experimental agenda of the aGPCR field and shaped our current understanding of the signaling properties and cell biological effects of aGPCRs. Interestingly, individual aGPCRs may undergo additional proteolytic steps, one of them resulting in shedding of the entire ectodomain that is secreted and can function independently. Here, we summarize the current state of knowledge on GAIN domain-mediated and GAIN domain-independent aGPCR cleavage events and their significance for the pharmacological and cellular actions of aGPCRs. Further, we compare and contrast the proteolytic profile of aGPCRs with known signaling routes that are governed through proteolysis of surface molecules such as the Notch and ephrin pathways.

The Jekyll and Hyde story of IL17-Producing γδT Cells

In comparison to conventional αβT cells, γδT cells are considered as specialized T cells based on their contributions in regulating immune response. γδT cells sense early environmental signals and initiate local immune-surveillance. The development of functional subtypes of γδT cells takes place in the thymus but they also exhibit plasticity in response to the activating signals and cytokines encountered in the extrathymic region. Thymic development of Tγδ1 requires strong TCR, CD27, and Skint-1 signals. However, differentiation of IL17-producing γδT cells (Tγδ17) is independent of Skint-1 or CD27 but requires notch signaling along with IL6 and TGFβ cytokines in the presence of weak TCR signal. In response to cytokines like IL23, IL6, and IL1β, Tγδ17 outshine Th17 cells for early activation and IL17 secretion. Despite expressing similar repertoire of lineage transcriptional factors, cytokines, and chemokine receptors, Tγδ17 cells differ from Th17 in spatial and temporal fashion. There are compelling reasons to consider significant role of Tγδ17 cells in regulating inflammation and thereby disease outcome. Tγδ17 cells regulate mobilization of innate immune cells and induce keratinocytes to secrete anti-microbial peptides thus exhibiting protective functions in anti-microbial immunity. In contrast, dysregulated Tγδ17 cells inhibit Treg cells, exacerbate autoimmunity, and are also known to support carcinogenesis by enhancing angiogenesis. The mechanism associated with this dual behavior of Tγδ17 is not clear. To exploit, Tγδ17 cells for beneficial use requires comprehensive analysis of their biology. Here, we summarize the current understanding on the characteristics, development, and functions of Tγδ17 cells in various pathological scenarios.

Transcription factor networks directing the development, function, and evolution of innate lymphoid effectors

Mammalian lymphoid immunity is mediated by fast and slow responders to pathogens. Fast innate lymphocytes are active within hours after infections in mucosal tissues. Slow adaptive lymphocytes are conventional T and B cells with clonal antigen receptors that function days after pathogen exposure. A transcription factor (TF) regulatory network guiding early T cell development is at the core of effector function diversification in all innate lymphocytes, and the kinetics of immune responses is set by developmental programming. Operational units within the innate lymphoid system are not classified by the types of pathogen-sensing machineries but rather by discrete effector functions programmed by regulatory TF networks. Based on the evolutionary history of TFs of the regulatory networks, fast effectors likely arose earlier in the evolution of animals to fortify body barriers, and in mammals they often develop in fetal ontogeny prior to the establishment of fully competent adaptive immunity.

Role of gamma-delta (γδ) T cells in autoimmunity

γδ T cells represent a small population of overall T lymphocytes (0.5-5%) and have variable tissue distribution in the body. γδ T cells can perform complex functions, such as immune surveillance, immunoregulation, and effector function, without undergoing clonal expansion. Heterogeneous distribution and anatomic localization of γδ T cells in the normal and inflamed tissues play an important role in alloimmunity, autoimmunity, or immunity. The cross-talk between γδ T cells and other immune cells and phenotypic and functional plasticity of γδ T cells have been given recent attention in the field of immunology. In this review, we discussed the cellular and molecular interaction of γδ T cells with other immune cells and its mechanism in the pathogenesis of various autoimmune diseases.

Postnatal Notch1 activation induces T‑cell malignancy in conditional and inducible mouse models

The Notch1 signaling pathway is essential for hematopoietic development. However, the effects of postnatal activation of Notch1 signaling on hematopoietic system is not yet fully understood. We previously generated ZEG‑IC‑Notch1 transgenic mice that have a floxed β‑geo/stop signal between a CMV promoter and intracellular domain of Notch1 (IC‑Notch1). Constitutively active IC‑Notch1 is silent until the introduction of Cre recombinase. In this study, endothelial/hematopoietic specific expression of IC‑Notch1 in double transgenic ZEG‑IC‑Notch1/Tie2‑Cre embryos induced embryonic lethality at E9.5 with defects in vascular system but not in hematopoietic system. Inducible IC‑Notch1 expression in adult mice was achieved by using tetracycline regulated Cre system. The ZEG‑IC‑Notch1/Tie2‑tTA/tet‑O‑Cre triple transgenic mice survived embryonic development when maintained on tetracycline. Post‑natal withdrawal of tetracycline induced expression of IC‑Notch1 transgene in hematopoietic cells of adult mice. The triple transgenic mice displayed extensive T‑cell infiltration in multiple organs and T‑cell malignancy of lymph nodes. In addition, the protein levels of p53 and alternative reading frame (ARF) were decreased in lymphoma‑like neoplasms from the triple transgenic mice while their mRNA expression remained unchanged, suggesting that IC‑Notch1 might repress ARF‑p53 pathway by a post‑transcriptional mechanism. This study demonstrated that activation of constitutive Notch1 signaling after embryonic development alters adult hematopoiesis and induces T‑cell malignancy.

Enforcement of γδ-lineage commitment by the pre-T-cell receptor in precursors with weak γδ-TCR signals

Developing thymocytes bifurcate from a bipotent precursor into αβ- or γδ-lineage T cells. Considering this common origin and the fact that the T-cell receptor (TCR) β-, γ-, and δ-chains simultaneously rearrange at the double negative (DN) stage of development, the possibility exists that a given DN cell can express and transmit signals through both the pre-TCR and γδ-TCR. Here, we tested this scenario by defining the differentiation outcomes and criteria for lineage choice when both TCR-β and γδ-TCR are simultaneously expressed in Rag2(-/-) DN cells via retroviral transduction. Our results showed that Rag2(-/-) DN cells expressing both TCRs developed along the γδ-lineage, down-regulated CD24 expression, and up-regulated CD73 expression, showed a γδ-biased gene-expression profile, and produced IFN-γ in response to stimulation. However, in the absence of Inhibitor of DNA-binding 3 expression and strong γδ-TCR ligand, γδ-expressing cells showed a lower propensity to differentiate along the γδ-lineage. Importantly, differentiation along the γδ-lineage was restored by pre-TCR coexpression, which induced greater down-regulation of CD24, higher levels of CD73, Nr4a2, and Rgs1, and recovery of functional competence to produce IFN-γ. These results confirm a requirement for a strong γδ-TCR ligand engagement to promote maturation along the γδ T-cell lineage, whereas additional signals from the pre-TCR can serve to enforce a γδ-lineage choice in the case of weaker γδ-TCR signals. Taken together, these findings further cement the view that the cumulative signal strength sensed by developing DN cells serves to dictate its lineage choice.

Involvement of Notch in activation and effector functions of γδ T cells

Notch signaling plays a pivotal role in cell fate decision and lineage commitment of lymphocytes. Although the role of Notch in CD4(+) and CD8(+) αβ T cells is well documented, there are no reports on how Notch signaling regulates effector functions of γδ T cells. γδ T cells are a minor fraction in the peripheral blood but are known to play a major role in defense against pathogens and tumors. In this study, we show that Notch receptors (mRNA and protein) are expressed in peripheral γδ T cells. Inhibition of Notch signaling by γ-secretase inhibitor inhibited the proliferation and IFN-γ secretion of γδ T cells in response to stimulation with phosphoantigens and anti-CD3 mAb. In the presence of γ-secretase inhibitor, the antitumor cytolytic ability of γδ T cells was inhibited with a decreased CD107a expression. Knockdown of Notch1 and Notch2 genes in γδ T cells using small interfering RNA inhibited their antitumor cytotoxic potential. Our study describes for the first time, to our knowledge, the role of Notch as an additional signal contributing to Ag-specific effector functions of γδ T cells.

The emerging roles of Notch signaling in leukemia and stem cells

The Notch signaling pathway plays a critical role in maintaining the balance between cell proliferation, differentiation and apoptosis, and is a highly conserved signaling pathway that regulates normal development in a context- and dose-dependent manner. Dysregulation of Notch signaling has been suggested to be key events in a variety of hematological malignancies. Notch1 signaling appears to be the central oncogenic trigger in T cell acute lymphoblastic leukemia (T-ALL), in which the majority of human malignancies have acquired mutations that lead to constitutive activation of Notch1 signaling. However, emerging evidence unexpectedly demonstrates that Notch signaling can function as a potent tumor suppressor in other forms of leukemia. This minireview will summarize recent advances related to the roles of activated Notch signaling in human lymphocytic leukemia, myeloid leukemia, stem cells and stromal microenvironment, and we will discuss the perspectives of Notch signaling as a potential therapeutic target as well.

Specific Notch receptor-ligand interactions control human TCR-αβ/γδ development by inducing differential Notch signal strength

Jagged2 preferentially signals through Notch3 to promote γδ T cell development.

In humans, high Notch activation promotes γδ T cell development, whereas lower levels promote αβ-lineage differentiation. How these different Notch signals are generated has remained unclear. We show that differential Notch receptor–ligand interactions mediate this process. Whereas Delta-like 4 supports both TCR-αβ and -γδ development, Jagged1 induces mainly αβ-lineage differentiation. In contrast, Jagged2-mediated Notch activation primarily results in γδ T cell development and represses αβ-lineage differentiation by inhibiting TCR-β formation. Consistently, TCR-αβ T cell development is rescued through transduction of a TCR-β transgene. Jagged2 induces the strongest Notch signal through interactions with both Notch1 and Notch3, whereas Delta-like 4 primarily binds Notch1. In agreement, Notch3 is a stronger Notch activator and only supports γδ T cell development, whereas Notch1 is a weaker activator supporting both TCR-αβ and -γδ development. Fetal thymus organ cultures in JAG2-deficient thymic lobes or with Notch3-blocking antibodies confirm the importance of Jagged2/Notch3 signaling in human TCR-γδ differentiation. Our findings reveal that differential Notch receptor–ligand interactions mediate human TCR-αβ and -γδ T cell differentiation and provide a mechanistic insight into the high Notch dependency of human γδ T cell development.

Expression of Notch receptor and its target gene Hes-1 in bone marrow CD34+ cells from patients with psoriasis

Psoriasis is an autoimmune disease mediated mainly by dysfunctional peripheral blood T cells. Both CD4+/CD8+ T cells and CD4+CD25+ regulatory T cells derived from psoriatic CD34+ bone marrow cells in vitro have been found to be functionally similar to those psoriatic circulating and lesional T cells. Notch signaling participates in diverse cell fate decisions during T cell development and has been reported to influence the proliferation of hematopoietic stem cells and the differentiation of T cells. The purpose of this study was to investigate the expression levels of Notch receptor 1, 2 and its target gene Hes-1 in CD34+ cells from patients with psoriasis. The total RNA and protein of CD34+ cells were extracted, and the mRNA as well as protein expression of Notch1, Notch2 and Hes-1 were investigated using real-time PCR and Western blot assays. We found that the mRNA and protein expression levels of Notch1 and Hes-1 in psoriasis patients were higher compared to normal controls, while the Notch2 mRNA and protein expression levels in psoriasis patients were similar to those of normal controls. The elevated Notch1 and Hes-1 expression levels in psoriatic CD34+ cells might be one reason for the immune disorders which are mainly mediated by T cells.

Modulation of PKC-α promotes lineage reprogramming of committed B lymphocytes

During hematopoietic lineage development, hematopoietic stem cells sequentially commit toward myeloid or lymphoid lineages in a tightly regulated manner, which under normal circumstances is irreversible. However, studies have established that targeted deletion of the B-lineage specific transcription factor, paired box gene 5 (Pax5), enables B cells to differentiate toward other hematopoietic lineages, in addition to generating progenitor B-cell lymphomas. Our previous studies showed that subversion of protein kinase C (PKC)-α in developing B cells transformed B-lineage cells. Here, we demonstrate that PKC-α modulation in committed CD19(+) B lymphocytes also promoted lineage conversion toward myeloid, NK-, and T-cell lineages upon Notch ligation. This occurred via a reduction in Pax5 expression resulting from a downregulation of E47, a product of the E2A gene. T-cell lineage commitment was indicated by the expression of T-cell associated genes Ptcra, Cd3e, and gene rearrangement at the Tcrb gene locus. Importantly, the lineage-converted T cells carried Igh gene rearrangements reminiscent of their B-cell origin. Our findings suggest that modulation of PKC-α induces hematopoietic-lineage plasticity in committed B-lineage cells by perturbing expression of critical B-lineage transcription factors, and deregulation of PKC-α activity/expression represents a potential mechanism for lineage trans-differentiation during malignancies.

Notch1 and IL-7 receptor signalling in early T-cell development and leukaemia

Notch receptors are master regulators of many aspects of development and tissue renewal in metazoans. Notch1 activation is essential for T-cell specification of bone marrow-derived multipotent progenitors that seed the thymus, and for proliferation and further progression of early thymocytes along the T-cell lineage. Deregulated activation of Notch1 significantly contributes to the generation of T-cell acute lymphoblastic leukaemia (T-ALL). In addition to Notch1 signals, survival and proliferation signals provided by the IL-7 receptor (IL-7R) are also required during thymopoiesis. Our understanding of the molecular mechanisms controlling stage-specific survival and proliferation signals provided by Notch1 and IL-7R has recently been improved by the discovery that the IL-7R is a transcriptional target of Notch1. Thus, Notch1 controls T-cell development, in part by regulating the stage- and lineage-specific expression of IL-7R. The finding that induction of IL-7R expression downstream of Notch1 also occurs in T-ALL highlights the important contribution that deregulated IL-7R expression and function may have in this pathology. Confirming this notion, oncogenic IL7R gain-of-function mutations have recently been identified in childhood T-ALL. Here we discuss the fundamental role of Notch1 and IL-7R signalling pathways in physiological and pathological T-cell development in mice and men, highlighting their close molecular underpinnings.

Notch receptor-ligand interactions during T cell development, a ligand endocytosis-driven mechanism

Notch signaling plays an important role during the development of different cell types and tissues. The role of Notch signaling in lymphocyte development, in particular in the development and commitment to the T cell lineage, has been the focus of research for many years. Notch signaling is absolutely required during the commitment and early stages of T cell development. Activation of the Notch signaling pathway is initiated by ligand-receptor interactions and appears to require active endocytosis of Notch ligands. Studies addressing the mechanism underlying endocytosis of Notch ligands have helped to identify the main players important and necessary for this process. Here, we review the Notch ligands, and the proposed models of Notch activation by Notch ligand endocytosis, highlighting key molecules involved. In particular, we discuss recent studies on Notch ligands involved in T cell development, current studies aimed at elucidating the relevance of Notch ligand endocytosis during T cell development and the identification of key players necessary for ligand endocytosis in the thymus and during T cell development.

Notch signaling in acute lymphoblastic leukemia: any role for stromal microenvironment?

Notch signaling pathway regulates many different events of embryonic and adult development; among them, Notch plays an essential role in the onset of hematopoietic stem cells and influences multiple maturation steps of developing lymphoid and myeloid cells. Deregulation of Notch signaling determines several human disorders, including cancer. In the last decade it became evident that Notch signaling plays pivotal roles in the onset and development of T- and B-cell acute lymphoblastic leukemia by regulating the intracellular molecular pathways involved in leukemia cell survival and proliferation. On the other hand, bone marrow stromal cells are equally necessary for leukemia cell survival by preventing blast cell apoptosis and favoring their reciprocal interactions and cross-talk with bone marrow microenvironment. Quite surprisingly, the link between Notch signaling pathway and bone marrow stromal cells in acute lymphoblastic leukemia has been pointed out only recently. In fact, bone marrow stromal cells express Notch receptors and ligands, through which they can interact with and influence normal and leukemia T- and B-cell survival. Here, the data concerning the development of T- and B-cell acute lymphoblastic leukemia has been critically reviewed in light of the most recent findings on Notch signaling in stromal microenvironment.

Notch induces human T-cell receptor γδ+ thymocytes to differentiate along a parallel, highly proliferative and bipotent CD4 CD8 double-positive pathway

In wild-type mice, T-cell receptor (TCR) γδ(+) cells differentiate along a CD4 CD8 double-negative (DN) pathway whereas TCRαβ(+) cells differentiate along the double-positive (DP) pathway. In the human postnatal thymus (PNT), DN, DP and single-positive (SP) TCRγδ(+) populations are present. Here, the precursor-progeny relationship of the various PNT TCRγδ(+) populations was studied and the role of the DP TCRγδ(+) population during T-cell differentiation was elucidated. We demonstrate that human TCRγδ(+) cells differentiate along two pathways downstream from an immature CD1(+) DN TCRγδ(+) precursor: a Notch-independent DN pathway generating mature DN and CD8αα SP TCRγδ(+) cells, and a Notch-dependent, highly proliferative DP pathway generating immature CD4 SP and subsequently DP TCRγδ(+) populations. DP TCRγδ(+) cells are actively rearranging the TCRα locus, and differentiate to TCR(-) DP cells, to CD8αβ SP TCRγδ(+) cells and to TCRαβ(+) cells. Finally, we show that the γδ subset of T-cell acute lymphoblastic leukemias (T-ALL) consists mainly of CD4 SP or DP phenotypes carrying significantly more activating Notch mutations than DN T-ALL. The latter suggests that activating Notch mutations in TCRγδ(+) thymocytes induce proliferation and differentiation along the DP pathway in vivo.

Loss-of-function mutations in Notch receptors in cutaneous and lung squamous cell carcinoma

Squamous cell carcinomas (SCCs) are one of the most frequent forms of human malignancy, but, other than TP53 mutations, few causative somatic aberrations have been identified. We identified NOTCH1 or NOTCH2 mutations in ~75% of cutaneous SCCs and in a lesser fraction of lung SCCs, defining a spectrum for the most prevalent tumor suppressor specific to these epithelial malignancies. Notch receptors normally transduce signals in response to ligands on neighboring cells, regulating metazoan lineage selection and developmental patterning. Our findings therefore illustrate a central role for disruption of microenvironmental communication in cancer progression. NOTCH aberrations include frameshift and nonsense mutations leading to receptor truncations as well as point substitutions in key functional domains that abrogate signaling in cell-based assays. Oncogenic gain-of-function mutations in NOTCH1 commonly occur in human T-cell lymphoblastic leukemia/lymphoma and B-cell chronic lymphocytic leukemia. The bifunctional role of Notch in human cancer thus emphasizes the context dependency of signaling outcomes and suggests that targeted inhibition of the Notch pathway may induce squamous epithelial malignancies.

Molecular aspects of epithelial γδ T cell regulation

γδ T cells lie at the interface between innate and adaptive immunity, sharing features with both arms of the immune system. The vast majority of γδ T cells reside in epithelial layers of tissues such as skin, gut, lung, tongue and reproductive tract where they provide a first line of defense against environmental attack. The existence of epithelium-resident γδ T cells has been known for over 20 years but our understanding of the molecular events regulating development and function of these cells is incomplete. We review recent advances in the field, with particular emphasis on the γδ T cell population resident in mouse epidermis. These studies have enhanced our knowledge and understanding of the life cycle of this enigmatic population of cells.