Non-Canonical Notch Signaling Drives Activation and Differentiation of Peripheral CD4(+) T Cells

Another Notch in the Belt of Rheumatoid Arthritis

Notch ligands and receptors, including JAG1/2, DLL1/4, and Notch1/3, are enriched on macrophages (MΦs), fibroblast-like synoviocytes (FLS), and/or endothelial cells in rheumatoid arthritis (RA) compared with normal synovial tissues (ST). Power Doppler ultrasound-guided ST studies reveal that the Notch family is highly involved in early active RA, especially during neovascularization. In contrast, the Notch family is not implicated during the erosive stage, evidenced by their lack of correlation with radiographic damage in RA ST. Toll-like receptors and tumor necrosis factor (TNF) are the common inducers of Notch expression in RA MΦs, FLS, and endothelial cells. Among Notch ligands, JAG1 and/or DLL4 are most inducible by inflammatory responses in RA MΦs or endothelial cells and transactivate their receptors on RA FLS. TNF plays a central role on Notch ligands, as anti-TNF good responders display JAG1/2 and DLL1/4 transcriptional downregulation in RA ST myeloid cells. In in vitro studies, TNF increases Notch3 expression in MΦs, which is further amplified by RA FLS addition. Specific disease-modifying antirheumatic drugs reduced JAG1 and Notch3 expression in MΦ and RA FLS cocultures. Organoids containing FLS and endothelial cells have increased expression of JAG1 and Notch3. Nonetheless, Methotrexate, interleukin-6 receptor (IL-6R) antibodies, and B cell blockers are mostly ineffective at decreasing Notch family expression. NF-κB, MAPK, and AKT pathways are involved in Notch signaling, whereas JAK/STATs are not. Although Notch blockade has been effective in RA preclinical studies, its small molecule inhibitors have failed in phase I and II studies, suggesting that alternative strategies may be required to intercept their function.

Sulindac sulfide as a non-immune suppressive γ-secretase modulator to target triple-negative breast cancer

Introduction

Triple-negative breast cancer (TNBC) comprises a heterogeneous group of clinically aggressive tumors with high risk of recurrence and metastasis. Current pharmacological treatment options remain largely limited to chemotherapy. Despite promising results, the efficacy of immunotherapy and chemo-immunotherapy in TNBC remains limited. There is strong evidence supporting the involvement of Notch signaling in TNBC progression. Expression of Notch1 and its ligand Jagged1 correlate with poor prognosis. Notch inhibitors, including g-secretase inhibitors (GSIs), are quite effective in preclinical models of TNBC. However, the success of GSIs in clinical trials has been limited by their intestinal toxicity and potential for adverse immunological effects, since Notch plays key roles in T-cell activation, including CD8 T-cells in tumors. Our overarching goal is to replace GSIs with agents that lack their systemic toxicity and ideally, do not affect tumor immunity. We identified sulindac sulfide (SS), the active metabolite of FDA-approved NSAID sulindac, as a potential candidate to replace GSIs.

Methods

We investigated the pharmacological and immunotherapeutic properties of SS in TNBC models in vitro, ex-vivo and in vivo.

Results

We confirmed that SS, a known γ-secretase modulator (GSM), inhibits Notch1 cleavage in TNBC cells. SS significantly inhibited mammosphere growth in all human and murine TNBC models tested. In a transplantable mouse TNBC tumor model (C0321), SS had remarkable single-agent anti-tumor activity and eliminated Notch1 protein expression in tumors. Importantly, SS did not inhibit Notch cleavage in T- cells, and the anti-tumor effects of SS were significantly enhanced when combined with a-PD1 immunotherapy in our TNBC organoids and in vivo.

Discussion

Our data support further investigation of SS for the treatment of TNBC, in conjunction with chemo- or -chemo-immunotherapy. Repurposing an FDA-approved, safe agent for the treatment of TNBC may be a cost-effective, rapidly deployable therapeutic option for a patient population in need of more effective therapies.

Modulation of Notch Signaling by Small-Molecular Compounds and Its Potential in Anticancer Studies

Notch signaling is responsible for conveying messages between cells through direct contact, playing a pivotal role in tissue development and homeostasis. The modulation of Notch-related processes, such as cell growth, differentiation, viability, and cell fate, offer opportunities to better understand and prevent disease progression, including cancer. Currently, research efforts are mainly focused on attempts to inhibit Notch signaling in tumors with strong oncogenic, gain-of-function (GoF) or hyperactivation of Notch signaling. The goal is to reduce the growth and proliferation of cancer cells, interfere with neo-angiogenesis, increase chemosensitivity, potentially target cancer stem cells, tumor dormancy, and invasion, and induce apoptosis. Attempts to pharmacologically enhance or restore disturbed Notch signaling for anticancer therapies are less frequent. However, in some cancer types, such as squamous cell carcinomas, preferentially, loss-of-function (LoF) mutations have been confirmed, and restoring but not blocking Notch functions may be beneficial for therapy. The modulation of Notch signaling can be performed at several key levels related to NOTCH receptor expression, translation, posttranslational (proteolytic) processing, glycosylation, transport, and activation. This further includes blocking the interaction with Notch-related nuclear DNA transcription. Examples of small-molecular chemical compounds, that modulate individual elements of Notch signaling at the mentioned levels, have been described in the recent literature.

A regulatory circuit controlled by extranuclear and nuclear retinoic acid receptor α determines T cell activation and function

Ligation of retinoic acid receptor alpha (RARα) by RA promotes varied transcriptional programs associated with immune activation and tolerance, but genetic deletion approaches suggest the impact of RARα on TCR signaling. Here, we examined whether RARα would exert roles beyond transcriptional regulation. Specific deletion of the nuclear isoform of RARα revealed an RARα isoform in the cytoplasm of T cells. Extranuclear RARα was rapidly phosphorylated upon TCR stimulation and recruited to the TCR signalosome. RA interfered with extranuclear RARα signaling, causing suboptimal TCR activation while enhancing FOXP3+ regulatory T cell conversion. TCR activation induced the expression of CRABP2, which translocates RA to the nucleus. Deletion of Crabp2 led to increased RA in the cytoplasm and interfered with signalosome-RARα, resulting in impaired anti-pathogen immunity and suppressed autoimmune disease. Our findings underscore the significance of subcellular RA/RARα signaling in T cells and identify extranuclear RARα as a component of the TCR signalosome and a determinant of immune responses.

Comparative analysis of the DNA methylation landscape in CD4, CD8, and B memory lineages

BACKGROUND

There is considerable evidence that epigenetic mechanisms and DNA methylation are critical drivers of immune cell lineage differentiation and activation. However, there has been limited coordinated investigation of common epigenetic pathways among cell lineages. Further, it remains unclear if long-lived memory cell subtypes differentiate distinctly by cell lineages.

RESULTS

We used the Illumina EPIC array to investigate the consistency of DNA methylation in B cell, CD4 T, and CD8 T naïve and memory cells states. In the process of naïve to memory activation across the three lineages, we identify considerable shared epigenetic regulation at the DNA level for immune memory generation. Further, in central to effector memory differentiation, our analyses revealed specific CpG dinucleotides and genes in CD4 T and CD8 T cells with DNA methylation changes. Finally, we identified unique DNA methylation patterns in terminally differentiated effector memory (TEMRA) CD8 T cells compared to other CD8 T memory cell subtypes.

CONCLUSIONS

Our data suggest that epigenetic alterations are widespread and essential in generating human lymphocyte memory. Unique profiles are involved in methylation changes that accompany memory genesis in the three subtypes of lymphocytes.

Notch Signaling Promotes Mature T-Cell Lymphomagenesis

Peripheral T-cell lymphomas (PTCL) are agressive lymphomas that develop from mature T cells. The most common PTCLs are genetically, molecularly, and clinically diverse and are generally associated with dismal outcomes. While Notch signaling plays a critically important role in both the development of immature T cells and their malignant transformation, its role in PTCL is poorly understood, despite the increasingly appreciated function of Notch in regulating the proliferation and differentiation of mature T cells. Here, we demonstrate that Notch receptors and their Delta-like family ligands (DLL1/DLL4) play a pathogenic role in PTCL. Notch1 activation was observed in common PTCL subtypes, including PTCL-not otherwise specified (NOS). In a large cohort of PTCL-NOS biopsies, Notch1 activation was significantly associated with surrogate markers of proliferation. Complementary genetically engineered mouse models and spontaneous PTCL models were used to functionally examine the role of Notch signaling, and Notch1/Notch2 blockade and pan-Notch blockade using dominant-negative MAML significantly impaired the proliferation of malignant T cells and PTCL progression in these models. Treatment with DLL1/DLL4 blocking antibodies established that Notch signaling is ligand-dependent. Together, these findings reveal a role for ligand-dependent Notch signaling in driving peripheral T-cell lymphomagenesis.

SIGNIFICANCE

This work demonstrates that ligand-dependent Notch activation promotes the growth and proliferation of mature T-cell lymphomas, providing new therapeutic strategies for this group of aggressive lymphomas.

NOTCH1 Signalling: A key pathway for the development of high-risk chronic lymphocytic leukaemia

NOTCH1 is a cell surface receptor that releases its intracellular domain as transcription factor upon activation. With the advent of next-generation sequencing, the NOTCH1 gene was found recurrently mutated in chronic lymphocytic leukaemia (CLL). Here, virtually all NOTCH1 mutations affect the protein’s PEST-domain and impair inactivation and degradation of the released transcription factor, thus increasing NOTCH1 signalling strength. Besides sequence alterations directly affecting the NOTCH1 gene, multiple other genomic and non-genomic alterations have by now been identified in CLL cells that could promote an abnormally strong NOTCH1 signalling strength. This renders NOTCH1 one of the key signalling pathways in CLL pathophysiology. The frequency of genomic alterations affecting NOTCH1 signalling is rising over the CLL disease course culminating in the observation that besides TP53 loss, 8q gain and CDKN2A/B loss, NOTCH1 mutation is a hallmark genomic alteration associated with transformation of CLL into an aggressive lymphoma (Richter transformation). Both findings associate de-regulated NOTCH1 signalling with the development of high-risk CLL. This narrative review provides data on the role of NOTCH1 mutation for CLL development and progression, discusses the impact of NOTCH1 mutation on treatment response, gives insight into potential modes of NOTCH1 pathway activation and regulation, summarises alterations that have been discussed to contribute to a de-regulation of NOTCH1 signalling in CLL cells and provides a perspective on how to assess NOTCH1 signalling in CLL samples.

Targeting the Cbl-b-Notch1 axis as a novel immunotherapeutic strategy to boost CD8+ T-cell responses

A critical feature of cancer is the ability to induce immunosuppression and evade immune responses. Tumor-induced immunosuppression diminishes the effectiveness of endogenous immune responses and decreases the efficacy of cancer immunotherapy. In this study, we describe a new immunosuppressive pathway in which adenosine promotes Casitas B-lineage lymphoma b (Cbl-b)-mediated Notch1 degradation, causing suppression of CD8+ T-cells effector functions. Genetic knockout and pharmacological inhibition of Cbl-b prevents Notch1 degradation in response to adenosine and reactivates its signaling. Reactivation of Notch1 results in enhanced CD8+ T-cell effector functions, anti-cancer response and resistance to immunosuppression. Our work provides evidence that targeting the Cbl-b-Notch1 axis is a novel promising strategy for cancer immunotherapy.

Critical Role of Notch-1 in Mechanistic Target of Rapamycin Hyperactivity and Vascular Inflammation in Patients With Takayasu Arteritis

OBJECTIVE

Takayasu arteritis (TA) is a major type of large vessel vasculitis characterized by progressive inflammation in vascular layers. In our recent study we identified a central role of mechanistic target of rapamycin (mTOR) hyperactivity in proinflammatory T cell differentiation in TA. This study was undertaken to explore potential mechanisms underpinning T cell-intrinsic mTOR hyperactivity and vascular inflammation in TA, with a focus on Notch-1.

METHODS

Notch-1 expression and activity was determined according to Notch-1, activated Notch-1, and HES-1 levels. We detected mTOR activity with intracellular expression of phosphorylated ribosomal protein S6. Differentiation of proinflammatory T cells was analyzed by detecting Th1 and Th17 lineage-determining transcription factors. The function of Notch-1 was evaluated using γ-secretase inhibitor DAPT and gene knockdown using a short hairpin RNA (shRNA) strategy. We performed our translational study using humanized NSG mouse chimeras in which human vasculitis was induced using immune cells from TA patients.

RESULTS

CD4+ T cells from TA patients exerted Notch-1^high , leading to mTOR hyperactivity and spontaneous maldifferentiation of Th1 cells and Th17 cells. Blockade of Notch-1 using DAPT and Notch-1 shRNA efficiently abrogated mTOR complex 1 (mTORC1) activation and proinflammatory T cell differentiation. Mechanistically, Notch-1 promoted mTOR expression, interacted with mTOR, and was associated with lysosomal localization of mTOR. Accordingly, systemic administration of DAPT and CD4+ T cell-specific gene knockdown of Notch-1 could alleviate vascular inflammation in humanized TA chimeras.

CONCLUSION

Expression of Notch-1 is elevated in CD4+ T cells from TA patients, resulting in mTORC1 hyperactivity and proinflammatory T cell differentiation. Targeting Notch-1 is a promising therapeutic strategy for the clinical management of TA.

Notch signaling in oral pre-cancer and oral cancer

Notch signaling involves cell to cell contact. It is an ancient signaling mechanism that is conserved throughout the animal kingdom. The basic function of Notch signaling is to decide cell fate and execute asymmetrical division. Notch signaling is indispensable for embryo growth. Aberrant Notch signaling involves in cancer progression by altering cell proliferation rate, tumor micro-environment, stem cell activities. The role of Notch signaling in cancer progression is context-dependent. In breast cancer and T cell lymphoma Notch signaling is highly active, whereas in squamous cell carcinoma (SCC) as oral and skin cancer, the signaling is suppressed. It is believed that in SCC, Notch-mediated tumor growth is due to the cell non-autonomous function. Oral cancer is the 6th most risky cancer worldwide. In many patients, oral cancer is preceded by pre-cancer conditions. In this review, we have summarized the research knowledge related to the role of Notch signaling in oral cancer and pre-cancer conditions and the therapeutic options available targeting different components of Notch pathways.

Therapeutic Targeting of Notch Signaling: From Cancer to Inflammatory Disorders

Over the past two decades, the Notch signaling pathway has been investigated as a therapeutic target for the treatment of cancers, and more recently in the context of immune and inflammatory disorders. Notch is an evolutionary conserved pathway found in all metazoans that is critical for proper embryonic development and for the postnatal maintenance of selected tissues. Through cell-to-cell contacts, Notch orchestrates cell fate decisions and differentiation in non-hematopoietic and hematopoietic cell types, regulates immune cell development, and is integral to shaping the amplitude as well as the quality of different types of immune responses. Depriving some cancer types of Notch signals has been shown in preclinical studies to stunt tumor growth, consistent with an oncogenic function of Notch signaling. In addition, therapeutically antagonizing Notch signals showed preclinical potential to prevent or reverse inflammatory disorders, including autoimmune diseases, allergic inflammation and immune complications of life-saving procedures such allogeneic bone marrow and solid organ transplantation (graft-versus-host disease and graft rejection). In this review, we discuss some of these unique approaches, along with the successes and challenges encountered so far to target Notch signaling in preclinical and early clinical studies. Our goal is to emphasize lessons learned to provide guidance about emerging strategies of Notch-based therapeutics that could be deployed safely and efficiently in patients with immune and inflammatory disorders.

Targeting the Notch Signaling Pathway in Chronic Inflammatory Diseases

The Notch signaling pathway regulates developmental cell-fate decisions and has recently also been linked to inflammatory diseases. Although therapies targeting Notch signaling in inflammation in theory are attractive, their design and implementation have proven difficult, at least partly due to the broad involvement of Notch signaling in regenerative and homeostatic processes. In this review, we summarize the supporting role of Notch signaling in various inflammation-driven diseases, and highlight efforts to intervene with this pathway by targeting Notch ligands and/or receptors with distinct therapeutic strategies, including antibody designs. We discuss this in light of lessons learned from Notch targeting in cancer treatment. Finally, we elaborate on the impact of individual Notch members in inflammation, which may lay the foundation for development of therapeutic strategies in chronic inflammatory diseases.

TAO-kinase 3 governs the terminal differentiation of NOTCH2-dependent splenic conventional dendritic cells

Antigen-presenting conventional dendritic cells (cDCs) are broadly divided into type 1 and type 2 subsets that further adapt their phenotype and function to perform specialized tasks in the immune system. The precise signals controlling tissue-specific adaptation and differentiation of cDCs are currently poorly understood. We found that mice deficient in the Ste20 kinase Thousand and One Kinase 3 (TAOK3) lacked terminally differentiated ESAM+ CD4+ cDC2s in the spleen and failed to prime CD4+ T cells in response to allogeneic red-blood-cell transfusion. These NOTCH2- and ADAM10-dependent cDC2s were absent selectively in the spleen, but not in the intestine of Taok3-/- and CD11c-cre Taok3fl/fl mice. The loss of splenic ESAM+ cDC2s was cell-intrinsic and could be rescued by conditional overexpression of the constitutively active NOTCH intracellular domain in CD11c-expressing cells. Therefore, TAOK3 controls the terminal differentiation of NOTCH2-dependent splenic cDC2s.

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.

CD28 Signaling Drives Notch Ligand Expression on CD4 T Cells

Notch signaling provides an important cue in the mammalian developmental process. It is a key player in T cell development and function. Notch ligands such as Delta-like ligands (DLL) 1, 3, 4, and JAG1, 2 can impact Notch signaling positively or negatively, by trans-activation or cis-inhibition. Trans and cis interactions are receptor-ligand interaction on two adjacent cells and interaction on the same cell, respectively. The former sends an activation signal and the later, a signal for inhibition of Notch. However, earlier reports suggested that Notch is activated in the absence of Notch ligand-expressing APCs in a purified population of CD4 T cells. Thus, the role of ligands in Notch activation, in a purified population of CD4 T cells, remains obscure. In this study, we demonstrate that mature CD4 T cells are capable of expressing Notch ligands on their surface very early upon activation with soluble antibodies against CD3 and CD28. Moreover, signaling solely through CD28 induces Notch ligand expression and CD3 signaling inhibits ligand expression, in contrast to Notch which is induced by CD3 signaling. Additionally, by using decoys, mimicking the Notch extracellular domain, we demonstrated that DLL1, DLL4, and JAG1, expressed on the T cells, can cis-interact with the Notch receptor and inhibit activation of Notch. Thus, our data indicate a novel mechanism of the regulation of Notch ligand expression on CD4 T cells and its impact on activated Notch.

Notch signaling pathway regulates T cell dysfunction in septic patients

Sepsis disrupts innate and adaptive immune response, and immune disorders may also impact clinical course of sepsis. Notch signaling pathway plays a vital role in T cell modulation and differentiation. The aim of current study was to investigate the immunoregulatory function of Notch signaling pathway to T cells in patients with sepsis and septic shock. Twenty-seven sepsis patients, twenty-five septic shock patients, and twenty-one normal controls (NCs) were enrolled. Notch receptors mRNA levels were semi-quantified by real-time PCR. The absolute numbers of CD3⁺, CD4⁺, and CD8⁺ T cells were measured by flow cytometry. Key transcriptional factors of CD4⁺ T cells, cytotoxic molecules in CD8⁺ T cells, and cytotoxicity of CD8⁺ T cells were investigated. The regulatory activities of Notch signaling inhibition by γ-secretase inhibitor (GSI) on purified CD4⁺ and CD8⁺ T cells from sepsis and septic shock patients were also assessed. Notch1 mRNA relative level was significantly elevated in sepsis and septic shock patients when compared with NCs. CD4⁺ and CD8⁺ T cells were dysfunctional in sepsis and septic shock, which presented as decreased cell accounts, down-regulation of Th1/Th17 transcriptional factors and cytotoxic molecules (perforin, granzyme B, and FasL), and reduced cytotoxicity of CD8⁺ T cells. Notch signaling inhibition by GSI increased Th1 and Th17 differentiation of CD4⁺ T cells. Moreover, GSI stimulation not only promoted perforin, granzyme B, and FasL mRNA expression in CD8⁺ T cells, but also elevated CD8⁺ T cell-induced target cell death and IFN-γ/TNF-α production in sepsis and septic shock. The current data suggest that Notch signaling pathway contributes to T cell dysfunction and limited immune response in sepsis.

Notch Signaling Regulates Immune Responses in Atherosclerosis

Atherosclerosis is a chronic autoimmune inflammatory disease that can cause coronary artery disease, stroke, peripheral artery disease, depending on which arteries are affected. At the beginning of atherosclerosis plasma lipoproteins accumulate in the sub-endothelial space. In response, monocytes migrate from the circulation through the endothelium into the intima where they differentiate into macrophages. These early events trigger a complex immune response that eventually involves many cellular subtypes of both innate and adaptive immunity. The Notch signaling pathway is an evolutionary conserved cell signaling system that mediates cell-to-cell communication. Recent studies have revealed that Notch modulate atherosclerosis by controlling macrophages polarization into M1 or M2 subtypes. Furthermore, it is known that Notch signaling controls differentiation and activity of T-helper and cytotoxic T-cells in inflammatory diseases. In this review, we will discuss the role of Notch in modulating immunity in the context of atherosclerosis and whether targeting Notch may represent a therapeutic strategy.

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.

Notch Signaling Regulates Mitochondrial Metabolism and NF-κB Activity in Triple-Negative Breast Cancer Cells via IKKα-Dependent Non-canonical Pathways

Triple negative breast cancer (TNBC) patients have high risk of recurrence and metastasis, and current treatment options remain limited. Cancer stem-like cells (CSCs) have been linked to cancer initiation, progression and chemotherapy resistance. Notch signaling is a key pathway regulating TNBC CSC survival. Treatment of TNBC with PI3K or mTORC1/2 inhibitors results in drug-resistant, Notch-dependent CSC. However, downstream mechanisms and potentially druggable Notch effectors in TNBC CSCs are largely unknown. We studied the role of the AKT pathway and mitochondrial metabolism downstream of Notch signaling in TNBC CSC from cell lines representative of different TNBC molecular subtypes as well as a novel patient-derived model. We demonstrate that exposure of TNBC cells to recombinant Notch ligand Jagged1 leads to rapid AKT phosphorylation in a Notch1-dependent but RBP-Jκ independent fashion. This requires mTOR and IKKα. Jagged1 also stimulates mitochondrial respiration and fermentation in an AKT- and IKK-dependent fashion. Notch1 co-localizes with mitochondria in TNBC cells. Pharmacological inhibition of Notch cleavage by gamma secretase inhibitor PF-03084014 in combination with AKT inhibitor MK-2206 or IKK-targeted NF-κB inhibitor Bay11-7082 blocks secondary mammosphere formation from sorted CD90^hi or CD44⁺CD24^low (CSCs) cells. A TNBC patient-derived model gave comparable results. Besides mitochondrial oxidative metabolism, Jagged1 also triggers nuclear, NF-κB-dependent transcription of anti-apoptotic gene cIAP-2. This requires recruitment of Notch1, IKKα and NF-κB to the cIAP-2 promoter. Our observations support a model where Jagged1 triggers IKKα-dependent, mitochondrial and nuclear Notch1 signals that stimulate AKT phosphorylation, oxidative metabolism and transcription of survival genes in PTEN wild-type TNBC cells. These data suggest that combination treatments targeting the intersection of the Notch, AKT and NF-κB pathways have potential therapeutic applications against CSCs in TNBC cases with Notch1 and wild-type PTEN expression.

Jagged1-expressing adenovirus-infected dendritic cells induce expansion of Foxp3+ regulatory T cells and alleviate T helper type 2-mediated allergic asthma in mice

Dendritic cells (DCs) are professional antigen-presenting cells that play a key role in directing T-cell responses. Regulatory T (Treg) cells possess an immunosuppressive ability to inhibit effector T-cell responses, and Notch ligand Jagged1 (Jag1) is implicated in Treg cell differentiation. In this study, we evaluated whether bone marrow-derived DCs genetically engineered to express Jag1 (Jag1-DCs) would affect the maturation and function of DCs in vitro and further investigated the immunoregulatory ability of Jag1-DCs to manipulate T helper type 2 (Th2) -mediated allergic asthma in mice. We produced Jag1-DCs by adenoviral transduction. Overexpression of Jag1 by ovalbumin (OVA) -stimulated Jag1-DCs exhibited increased expression of programmed cell death ligand 1 (PD-L1) and OX40L molecules. Subsequently, co-culture of these OVA-pulsed Jag1-DCs with allogeneic or syngeneic CD4⁺ T cells promoted the generation of Foxp3⁺ Treg cells, and blocking PD-L1 using specific antibodies partially reduced Treg cell expansion. Furthermore, adoptive transfer of OVA-pulsed Jag1-DCs to mice with OVA-induced asthma reduced allergen-specific immunoglobulin E production, airway hyperresponsiveness, airway inflammation, and secretion of Th2-type cytokines (interleukin-4, interleukin-5, and interleukin-13). Notably, an increased number of Foxp3⁺ Treg cells associated with enhanced levels of transforming growth factor-β production was observed in Jag1-DC-treated mice. These data indicate that transgenic expression of Jag1 by DCs promotes induction of Foxp3⁺ Treg cells, which ameliorated Th2-mediated allergic asthma in mice. Our study supports an attractive strategy to artificially generate immunoregulatory DCs and provides a novel approach for manipulating Th2 cell-driven deleterious immune diseases.

Notch and NF-κB: Coach and Players of Regulatory T-Cell Response in Cancer

The Notch signaling pathway plays multiple roles in driving T-cell fate decisions, proliferation, and aberrant growth. NF-κB is a cell-context key player interconnected with Notch signaling either in physiological or in pathological conditions. This review focuses on how the multilayered crosstalk between different Notches and NF-κB subunits may converge on Foxp3 gene regulation and orchestrate CD4⁺ regulatory T (Treg) cell function, particularly in a tumor microenvironment. Notably, Treg cells may play a pivotal role in the inhibition of antitumor immune responses, possibly promoting tumor growth. A future challenge is represented by further dissection of both Notch and NF-κB pathways and consequences of their intersection in tumor-associated Treg biology. This may shed light on the molecular mechanisms regulating Treg cell expansion and migration to peripheral lymphoid organs thought to facilitate tumor development and still to be explored. In so doing, new opportunities for combined and/or more selective therapeutic approaches to improve anticancer immunity may be found.

Enhanced TAT-Cre Protein Transduction for Efficient Gene Recombination in T cells

Genetic manipulation has increased our understanding of gene function and led to the discovery of new therapeutic targets. Cre/LoxP DNA recombination is widely used for genetic studies in mammalian cells. The direct delivery of Cre recombinase fused to protein transduction domains (PTDs), such as TAT, has been described as a valid alternative to the conditional, site-specific Cre expression in transgenic mice. However, efficiently conveying proteins into live cells, especially primary T cells, remains a major challenge. In this study, we show that one of our recently developed PTDs synthetic mimic greatly enhances the cellular uptake of the TAT-Cre fusion protein, enabling significantly smaller amounts of the protein to be used. We used this technique in primary mouse T cells to successfully delete, ex vivo, two essential genes involved in regulating T cell activation, Notch1 and Rbpjκ. Ex vivo gene deletion resulted in substantial protein reduction, comparable to that obtained in vivo when Cre-expressing Notch1-floxed (MxCre^±Notch1^fl/fl) mice were treated with polyinosinic-polycytidylic acid (polyl/C), but in considerably less time, and without altering normal cell physiology. These results highlight several key advantages that include the ability to use less expensive protein (TAT-Cre), a major reduction in total experimental time and labor, and fewer side effects on the treated cells. This method should offer new opportunities for immunological studies, especially in the context of identifying novel therapeutic targets.

Notch Signaling as a Regulator of the Tumor Immune Response: To Target or Not To Target?

The Notch signaling pathway regulates important cellular processes involved in stem cell maintenance, proliferation, development, survival, and inflammation. These responses to Notch signaling involving both canonical and non-canonical pathways can be spatially and temporally variable and are highly cell-type dependent. Notch signaling can elicit opposite effects in regulating tumorigenicity (tumor-promoting versus tumor-suppressing function) as well as controlling immune cell responses. In various cancer types, Notch signaling elicits a "cancer stem cell (CSC)" phenotype that results in decreased proliferation, but resistance to various therapies, hence potentially contributing to cell dormancy and relapse. CSCs can reshape their niche by releasing paracrine factors and inflammatory cytokines, and the niche in return can support their quiescence and resistance to therapies as well as the immune response. Moreover, Notch signaling is one of the key regulators of hematopoiesis, immune cell differentiation, and inflammation and is implicated in various autoimmune diseases, carcinogenesis (leukemia), and tumor-induced immunosuppression. Notch can control the fate of various T cell types, including Th1, Th2, and the regulatory T cells (Tregs), and myeloid cells including macrophages, dendritic cells, and myeloid-derived suppressor cells (MDSCs). Both MDSCs and Tregs play an important role in supporting tumor cells (and CSCs) and in evading the immune response. In this review, we will discuss how Notch signaling regulates multiple aspects of the tumor-promoting environment by elucidating its role in CSCs, hematopoiesis, normal immune cell differentiation, and subsequently in tumor-supporting immunogenicity.

Long-Term Culture of Distal Airway Epithelial Cells Allows Differentiation Towards Alveolar Epithelial Cells Suited for Influenza Virus Studies

As the target organ for numerous pathogens, the lung epithelium exerts critical functions in health and disease. However, research in this area has been hampered by the quiescence of the alveolar epithelium under standard culture conditions. Here, we used human distal airway epithelial cells (DAECs) to generate alveolar epithelial cells. Long-term, robust growth of human DAECs was achieved using co-culture with feeder cells and supplementation with epidermal growth factor (EGF), Rho-associated protein kinase inhibitor Y27632, and the Notch pathway inhibitor dibenzazepine (DBZ). Removal of feeders and priming with DBZ and a cocktail of lung maturation factors prevented the spontaneous differentiation into airway club cells and instead induced differentiation to alveolar epithelial cells. We successfully transferred this approach to chicken distal airway cells, thus generating a zoonotic infection model that enables studies on influenza A virus replication. These cells are also amenable for gene knockdown using RNAi technology, indicating the suitability of the model for mechanistic studies into lung function and disease.

Rotenone Treatment Reveals a Role for Electron Transport Complex I in the Subcellular Localization of Key Transcriptional Regulators During T Helper Cell Differentiation

Recent advances in our understanding of tumor cell mitochondrial metabolism suggest it may be an attractive therapeutic target. Mitochondria are central hubs of metabolism that provide energy during the differentiation and maintenance of immune cell phenotypes. Mitochondrial membranes harbor several enzyme complexes that are involved in the process of oxidative phosphorylation, which takes place during energy production. Data suggest that, among these enzyme complexes, deficiencies in electron transport complex I may differentially affect immune responses and may contribute to the pathophysiology of several immunological conditions. Once activated by T cell receptor signaling, along with co-stimulation through CD28, CD4 T cells utilize mitochondrial energy to differentiate into distinct T helper (Th) subsets. T cell signaling activates Notch1, which is cleaved from the plasma membrane to generate its intracellular form (N1ICD). In the presence of specific cytokines, Notch1 regulates gene transcription related to cell fate to modulate CD4 Th type 1, Th2, Th17, and induced regulatory T cell (iTreg) differentiation. The process of differentiating into any of these subsets requires metabolic energy, provided by the mitochondria. We hypothesized that the requirement for mitochondrial metabolism varies between different Th subsets and may intersect with Notch1 signaling. We used the organic pesticide rotenone, a well-described complex I inhibitor, to assess how compromised mitochondrial integrity impacts CD4 T cell differentiation into Th1, Th2, Th17, and iTreg cells. We also investigated how Notch1 localization and downstream transcriptional capabilities regulation may be altered in each subset following rotenone treatment. Our data suggest that mitochondrial integrity impacts each of these Th subsets differently, through its influence on Notch1 subcellular localization. Our work further supports the notion that altered immune responses can result from complex I inhibition. Therefore, understanding how mitochondrial inhibitors affect immune responses may help to inform therapeutic approaches to cancer treatment.

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.

Notch1 primes CD4 T cells for T helper type I differentiation through its early effects on miR-29

The transmembrane receptor, Notch1 plays an important role during the differentiation of CD4 T cells into T helper (Th) subsets in the presence of appropriate cytokines, including differentiation into Th1 cells. MicroRNAs have also been shown to be important regulators of immune responses, including negatively regulating cytokine production by Th1 cells. The miR-29 family of microRNAs can act to inhibit tbx21 and ifng transcription, two important pro-inflammatory genes that are abundantly expressed in Th1 cells. Here we show that Notch1 may prime CD4 T cells to be responsive to Th1-polarizing cues through its early repressive effects on the miR-29 family of microRNAs. Using a combination of cell lines and primary cells, we demonstrate that Notch1 can repress miR-29a, miR-29b, and miR-29c transcription through a mechanism that is independent of NF-κB. We further show that this repression is mediated by canonical Notch signaling and requires active Mastermind like (MAML) 1, but this process is superseded by positive regulation of miR-29 in response to IFNγ at later stages of CD4 T cell activation and differentiation. Collectively, our data suggest an additional mechanism by which Notch1 signaling may fine-tune Th1 cell differentiation.

The microvascular niche instructs T cells in large vessel vasculitis via the VEGF-Jagged1-Notch pathway

Microvascular networks in the adventitia of large arteries control access of inflammatory cells to the inner wall layers (media and intima) and thus protect the immune privilege of the aorta and its major branches. In autoimmune vasculitis giant cell arteritis (GCA), CD4 T helper 1 (T_H1) and T_H17 cells invade into the wall of the aorta and large elastic arteries to form tissue-destructive granulomas. Whether the disease microenvironment provides instructive cues for vasculitogenic T cells is unknown. We report that adventitial microvascular endothelial cells (mvECs) perform immunoregulatory functions by up-regulating the expression of the Notch ligand Jagged1. Vascular endothelial growth factor (VEGF), abundantly present in GCA patients' blood, induced Jagged1 expression, allowing mvECs to regulate effector T cell induction via the Notch-mTORC1 (mammalian target of rapamycin complex 1) pathway. We found that circulating CD4 T cells in GCA patients have left the quiescent state, actively signal through the Notch pathway, and differentiate into T_H1 and T_H17 effector cells. In an in vivo model of large vessel vasculitis, exogenous VEGF functioned as an effective amplifier to recruit and activate vasculitogenic T cells. Thus, systemic VEGF co-opts endothelial Jagged1 to trigger aberrant Notch signaling, biases responsiveness of CD4 T cells, and induces pathogenic effector functions. Adventitial microvascular networks function as an instructive tissue niche, which can be exploited to target vasculitogenic immunity in large vessel vasculitis.

Mechanisms of Non-canonical Signaling in Health and Disease: Diversity to Take Therapy up a Notch?

Non-canonical Notch signaling encompasses a wide range of cellular processes, diverging considerably from the established paradigm. It can dispense of ligand, proteolytic or nuclear activity. Non-canonical Notch signaling events have been studied mostly in the fruit fly Drosophila melanogaster, the organism in which Notch was identified first and a powerful model for understanding signaling outcomes. However, non-canonical events are ill-defined and their involvement in human physiology is not clear, hampering our understanding of diseases arising from Notch signaling alterations. At a time in which therapies based on specific targeting of Notch signaling are still an unfulfilled promise, detailed understanding of non-canonical Notch events might be key to devising more specific and less toxic pharmacologic options. Based on the blueprint of non-canonical signaling in Drosophila, here, we review and rationalize current evidence about non-canonical Notch signaling. Our effort might inform Notch biologists developing new research avenues and clinicians seeking future treatment of Notch-dependent diseases.

Notch and T Cell Function - A Complex Tale

Notch drives critical decisions in a multitude of developmental decisions in many invertebrate and vertebrate organisms including flies, worms, fish, mice and humans. Therefore, it is not surprising that Notch family members also play a key role in cell fate choices in the vertebrate immune system. This review highlights the critical function of Notch in the development of mature T lymphocytes from hematopoietic precursors and describes the role of Notch in mature T cell activation, proliferation and differentiation.

Inhibition of Notch signalling has ability to alter the proximal and distal TCR signalling events in human CD3+ αβ T-cells

The Notch signalling pathway is an important regulator of T cell function and is known to regulate the effector functions of T cells driven by T cell receptor (TCR). However, the mechanism integrating these pathways in human CD3⁺ αβ T cells is not well understood. The present study was carried out to investigate how Notch and TCR driven signalling are synchronized in human αβ T cells. Differential expression of Notch receptors, ligands, and target genes is observed on human αβ T cells which are upregulated on stimulation with α-CD3/CD28 mAb. Inhibition of Notch signalling by GSI-X inhibited the activation of T cells and affected proximal T cell signalling by regulating CD3-ζ chain expression. Inhibition of Notch signalling decreased the protein expression of CD3-ζ chain and induced expression of E3 ubiquitin ligase (GRAIL) in human αβ T cells. Apart from affecting proximal TCR signalling, Notch signalling also regulated the distal TCR signalling events. In the absence of Notch signalling, α-CD3/CD28 mAb induced activation and IFN-γ production by αβ T cells was down-modulated. The absence of Notch signalling in human αβ T cells inhibited proliferative responses despite strong signalling through TCR and IL-2 receptor. This study shows how Notch signalling cooperates with TCR signalling by regulating CD3-ζ chain expression to support proliferation and activation of human αβ T cells.

Notch Signaling in Development, Tissue Homeostasis, and Disease

Notch signaling is an evolutionarily highly conserved signaling mechanism, but in contrast to signaling pathways such as Wnt, Sonic Hedgehog, and BMP/TGF-β, Notch signaling occurs via cell-cell communication, where transmembrane ligands on one cell activate transmembrane receptors on a juxtaposed cell. Originally discovered through mutations in Drosophila more than 100 yr ago, and with the first Notch gene cloned more than 30 yr ago, we are still gaining new insights into the broad effects of Notch signaling in organisms across the metazoan spectrum and its requirement for normal development of most organs in the body. In this review, we provide an overview of the Notch signaling mechanism at the molecular level and discuss how the pathway, which is architecturally quite simple, is able to engage in the control of cell fates in a broad variety of cell types. We discuss the current understanding of how Notch signaling can become derailed, either by direct mutations or by aberrant regulation, and the expanding spectrum of diseases and cancers that is a consequence of Notch dysregulation. Finally, we explore the emerging field of Notch in the control of tissue homeostasis, with examples from skin, liver, lung, intestine, and the vasculature.

T Cell-Restricted Notch Signaling Contributes to Pulmonary Th1 and Th2 Immunity during Cryptococcus neoformans Infection

Cryptococcus neoformans is a ubiquitous, opportunistic fungal pathogen but the cell signaling pathways that drive T cell responses regulating antifungal immunity are incompletely understood. Notch is a key signaling pathway regulating T cell development, and differentiation and functional responses of mature T cells in the periphery. The targeting of Notch signaling within T cells has been proposed as a potential treatment for alloimmune and autoimmune disorders, but it is unknown whether disturbances to T cell immunity may render these patients vulnerable to fungal infections. To elucidate the role of Notch signaling during fungal infections, we infected mice expressing the pan-Notch inhibitor dominant negative mastermind-like within mature T cells with C. neoformans Inhibition of T cell-restricted Notch signaling increased fungal burdens in the lungs and CNS, diminished pulmonary leukocyte recruitment, and simultaneously impaired Th1 and Th2 responses. Pulmonary leukocyte cultures from T cell Notch-deprived mice produced less IFN-γ, IL-5, and IL-13 than wild-type cells. This correlated with lower frequencies of IFN-γ-, IL-5-, and IL-13-producing CD4⁺ T cells, reduced expression of Th1 and Th2 associated transcription factors, Tbet and GATA3, and reduced production of IFN-γ by CD8⁺ T cells. In contrast, Th17 responses were largely unaffected by Notch signaling. The changes in T cell responses corresponded with impaired macrophage activation and reduced leukocyte accumulation, leading to diminished fungal control. These results identify Notch signaling as a previously unappreciated regulator of Th1 and Th2 immunity and an important element of antifungal defenses against cryptococcal infection and CNS dissemination.

A New View of Pathway-Driven Drug Resistance in Tumor Proliferation

Defeating drug resistance in tumor cell proliferation is challenging. We propose that signaling in cell proliferation takes place via two core pathways, each embodying multiple alternative pathways. We consider drug resistance through an alternative proliferation pathway - within the same or within the other core pathway. Most drug combinations target only one core pathway; blocking both can restrain proliferation. We define core pathways as independent and acting similarly in cell-cycle control, which can explain why their products (e.g., ERK and YAP1) can substitute for each other in resistance. Core pathways can forecast possible resistance because acquired resistance frequently occurs through alternative proliferation pathways. This concept may help to predict the efficacy of drug combinations. The selection of distinct combinations for specific mutated pathways would be guided by clinical diagnosis.

Notch Signaling in T Helper Cell Subsets: Instructor or Unbiased Amplifier?

For protection against pathogens, it is essential that naïve CD4⁺ T cells differentiate into specific effector T helper (Th) cell subsets following activation by antigen presented by dendritic cells (DCs). Next to T cell receptor and cytokine signals, membrane-bound Notch ligands have an important role in orchestrating Th cell differentiation. Several studies provided evidence that DC activation is accompanied by surface expression of Notch ligands. Intriguingly, DCs that express the delta-like or Jagged Notch ligands gain the capacity to instruct Th1 or Th2 cell polarization, respectively. However, in contrast to this model it has also been hypothesized that Notch signaling acts as a general amplifier of Th cell responses rather than an instructive director of specific T cell fates. In this alternative model, Notch enhances proliferation, cytokine production, and anti-apoptotic signals or promotes co-stimulatory signals in T cells. An instructive role for Notch ligand expressing DCs in the induction of Th cell differentiation is further challenged by evidence for the involvement of Notch signaling in differentiation of Th9, Th17, regulatory T cells, and follicular Th cells. In this review, we will discuss the two opposing models, referred to as the “instructive” and the “unbiased amplifier” model. We highlight both the function of different Notch receptors on CD4⁺ T cells and the impact of Notch ligands on antigen-presenting cells.

The lysine deacetylase Sirtuin 1 modulates the localization and function of the Notch1 receptor in regulatory T cells

The ability to tune cellular functions in response to nutrient availability has important consequences for immune homeostasis. The activity of the receptor Notch in regulatory T (T_reg) cells, which suppress the functions of effector T cells, is indispensable for T_reg cell survival under conditions of diminished nutrient supply. Anti-apoptotic signaling induced by the Notch1 intracellular domain (NIC) originates from the cytoplasm and is spatially decoupled from the nuclear, largely transcriptional functions of NIC. We showed that Sirtuin 1 (Sirt1), which is an NAD⁺ (nicotinamide adenine dinucleotide)-dependent lysine deacetylase that inhibits NIC-dependent gene transcription, stabilized NIC proximal to the plasma membrane to promote the survival and function of activated T_reg cells. Sirt1 was required for NIC-dependent protection from apoptosis in cell lines but not for the activity of the anti-apoptotic protein Bcl-xL. In addition, a variant NIC protein in which four lysines were mutated to arginines (NIC4KR) retained anti-apoptotic activity, but was not regulated by Sirt1, and reconstituted the functions of nonnuclear NIC in Notch1-deficient T_reg cells. Loss of Sirt1 compromised T_reg cell survival, resulting in antigen-induced T cell proliferation and inflammation in two mouse models. Thus, the Sirt1-Notch interaction may constitute an important checkpoint that tunes noncanonical Notch1 signaling.

Notch regulates Th17 differentiation and controls trafficking of IL-17 and metabolic regulators within Th17 cells in a context-dependent manner

Th17 cells play critical roles in host defense and autoimmunity. Emerging data support a role for Notch signaling in Th17 cell differentiation but whether it is a positive or negative regulator remains unclear. We report here that T cell-specific deletion of Notch receptors enhances Th17 cell differentiation in the gut, with a corresponding increase in IL-17 secretion. An increase in Th17 cell frequency was similarly observed following immunization of T cell specific Notch mutant mice with OVA/CFA. However, in this setting, Th17 cytokine secretion was impaired, and increased intracellular retention of IL-17 was observed. Intracellular IL-17 co-localized with the CD71 iron transporter in the draining lymph node of both control and Notch-deficient Th17 cells. Immunization induced CD71 surface expression in control, but not in Notch-deficient Th17 cells, revealing defective CD71 intracellular transport in absence of Notch signaling. Moreover, Notch receptor deficient Th17 cells had impaired mTORC2 activity. These data reveal a context-dependent impact of Notch on vesicular transport during high metabolic demand suggesting a role for Notch signaling in the bridging of T cell metabolic demands and effector functions. Collectively, our findings indicate a prominent regulatory role for Notch signaling in the fine-tuning of Th17 cell differentiation and effector function.

Activation of an endothelial Notch1-Jagged1 circuit induces VCAM1 expression, an effect amplified by interleukin-1β

The Notch1 and Notch4 signaling pathways regulate endothelial cell homeostasis. Inflammatory cytokines induce the expression of endothelial adhesion molecules, including VCAM1, partly by downregulating Notch4 signaling. We investigated the role of endothelial Notch1 in this IL-1β-mediated process. Brief treatment with IL-1β upregulated endothelial VCAM1 and Notch ligand Jagged1. IL-1β decreased Notch1 mRNA levels, but levels of the active Notch1ICD protein remained constant. IL-1β-mediated VCAM1 induction was downregulated in endothelial cells subjected to pretreatment with a pharmacological inhibitor of the γ-secretase, which activates Notch receptors, producing NotchICD. It was also downregulated in cells in which Notch1 and/or Jagged1 were silenced.Conversely, the forced expression of Notch1ICD in naïve endothelial cells upregulated VCAM1 per se and amplified IL-1β-mediated VCAM1 induction. Jagged1 levels increased and Notch4 signaling was downregulated in parallel. Finally, Notch1ICD and Jagged1 expression was upregulated in the endothelium of the liver in a model of chronic liver inflammation.In conclusion, we describe here a cell-autonomous, pro-inflammatory endothelial Notch1-Jagged1 circuit (i) triggering the expression of VCAM1 even in the absence of inflammatory cytokines and (ii) enhancing the effects of IL-1β. Thus, IL-1β regulates Notch1 and Notch4 activity in opposite directions, consistent with a selective targeting of Notch1 in inflamed endothelium.

Requirement of HDAC6 for activation of Notch1 by TGF-β1

TGF-β1 is enriched in the tumor microenvironment and acts as a key inducer of epithelial to mesenchymal transition (EMT) in lung cancer. The NOTCH signaling pathway is conserved across species and is an essential pathway for development, cell differentiation, and cancer biology. Dysregulation of Notch signaling is a common feature of non-small cell lung cancer (NSCLC) and is correlated with poor prognosis. Crosstalk exists between the NOTCH and TGF-β signaling pathways in EMT. Herein we report that histone deacetylase 6 (HDAC6) modulates TGF-β1-mediated activation of the Notch pathway. HDAC6, a primarily cytoplasmic deacetylase, mediates TGF-β1-induced EMT in human lung cancer cells. Inhibition of HDAC6 with a small molecule inhibitor, namely tubacin or with siRNA attenuated TGF-β1-induced Notch-1 signaling. We show that TGFβ-1-induced EMT is accompanied by rapid HDAC6-dependent deacetylation of heat shock protein 90 (HSP90). Consistently, inhibition of HSP90 with its small molecule inhibitor 17AAG attenuated expression of TGF-β1-induced Notch-1 target genes, HEY-1 and HES-1. These findings reveal a novel function of HDAC6 in EMT via mediating the TGF-β-Notch signaling cascade, and support HDAC6 as a key regulator of TGFβ-induced EMT in NSCLC. This work suggests that HDAC6 may be an attractive therapeutic target against tumor progression and metastasis.

LFA-1/ICAM-1 Ligation in Human T Cells Promotes Th1 Polarization through a GSK3β Signaling-Dependent Notch Pathway

In this study, we report that the integrin LFA-1 cross-linking with its ligand ICAM-1 in human PBMCs or CD4(+) T cells promotes Th1 polarization by upregulating IFN-γ secretion and T-bet expression. LFA-1 stimulation in PBMCs, CD4(+) T cells, or the T cell line HuT78 activates the Notch pathway by nuclear translocation of cleaved Notch1 intracellular domain (NICD) and upregulation of target molecules Hey1 and Hes1. Blocking LFA-1 by a neutralizing Ab or specific inhibition of Notch1 by a γ-secretase inhibitor substantially inhibits LFA-1/ICAM-1-mediated activation of Notch signaling. We further demonstrate that the Notch pathway activation is dependent on LFA-1/ICAM-1-induced inactivation of glycogen synthase kinase 3β (GSK3β), which is mediated via Akt and ERK. Furthermore, in silico analysis in combination with coimmunoprecipitation assays show an interaction between NICD and GSK3β. Thus, there exists a molecular cross-talk between LFA-1 and Notch1 through the Akt/ERK-GSK3β signaling axis that ultimately enhances T cell differentiation toward Th1. Although clinical use of LFA-1 antagonists is limited by toxicity related to immunosuppression, these findings support the concept that Notch inhibitors could be attractive for prevention or treatment of Th1-related immunologic disorders and have implications at the level of local inflammatory responses.

Notch Signaling in Neuroendocrine Tumors

Carcinoids and neuroendocrine tumors (NETs) are a heterogeneous group of tumors that arise from the neuroendocrine cells of the GI tract, endocrine pancreas, and the respiratory system. NETs remain significantly understudied with respect to molecular mechanisms of pathogenesis, particularly the role of cell fate signaling systems such as Notch. The abundance of literature on the Notch pathway is a testament to its complexity in different cellular environments. Notch receptors can function as oncogenes in some contexts and tumor suppressors in others. The genetic heterogeneity of NETs suggests that to fully understand the roles and the potential therapeutic implications of Notch signaling in NETs, a comprehensive analysis of Notch expression patterns and potential roles across all NET subtypes is required.

Oncogenic KRAS signaling and YAP1/β-catenin: Similar cell cycle control in tumor initiation

Why are YAP1 and c-Myc often overexpressed (or activated) in KRAS-driven cancers and drug resistance? Here, we propose that there are two independent pathways in tumor proliferation: one includes MAPK/ERK and PI3K/A kt/mTOR; and the other consists of pathways leading to the expression (or activation) of YAP1 and c-Myc. KRAS contributes through the first. MYC is regulated by e.g. β-catenin, Notch and Hedgehog. We propose that YAP1 and ERK accomplish similar roles in cell cycle control, as do β-catenin and PI3K. This point is compelling, since the question of how YAP1 rescues K-Ras or B-Raf ablation has recently captured much attention, as well as the mechanism of resistance to PI3K inhibitors. The similarity in cell cycle actions of β-catenin and PI3K can also clarify the increased aggressiveness of lung cancer when both K-Ras and β-catenin operate. Thus, we propose that the two pathways can substitute one another - or together amplify each other - in promoting proliferation. This new understanding of the independence and correspondence of the two pathways in cancer - MAPK/ERK and PI3K/Akt/mTOR; and YAP1 and c-Myc - provide a coherent and significant picture of signaling-driven oncogenic proliferation and may help in judicious, pathway-based drug discovery.

Signaling in T cells - is anything the m(a)TOR with the picture(s)?

The excitement surrounding checkpoint inhibitors in the treatment of patients with cancer exemplifies a triumph of the long-term value of investing in basic science and fundamental questions of T-cell signaling. The pharmaceutical future actively embraces ways of making more patients’ cancers responsive to these inhibitors. Such a process will be aided by elucidation of signaling and regulation. With thousands of articles spread across almost 30 years, this commentary can touch only on portions of the canonical picture of T-cell signaling and provide a few parables from work on mammalian (or mechanistic) target of rapamycin (mTOR) pathways as they link to early and later phases of lymphocyte activation. The piece will turn a critical eye to some issues with models about these pathways in T cells. Many of the best insights lie in the future despite all that is uncovered already, but a contention is that further therapeutic successes will be fostered by dealing with disparities among findings and attention to the temporal, spatial, and stochastic aspects of T-cell responses. Finally, thoughts on some (though not all) items urgently needed for future progress will be mooted.

Notching tumor: Signaling through Notch receptors improves antitumor T cell immunity

Notch signaling is crucial for lymphocyte effector and memory differentiation. While tumor suppress Notch signaling in antitumor lymphocytes, recent studies show that the pharmacological Delta-like ligand-1 multivalent cluster or proteasome inhibitor bortezomib can restore Notch-NF-κB signaling in T cells of tumor-bearing hosts with a potential to overcome cancer cell resistance to therapy.

Notch in T Cell Differentiation: All Things Considered

Differentiation of naïve T cells into effector cells is required for optimal protection against different classes of microbial pathogen and for the development of immune memory. Recent findings have revealed important roles for the Notch signaling pathway in T cell differentiation into all known effector subsets, raising the question of how this pathway controls such diverse differentiation programs. Studies in preclinical models support the therapeutic potential of manipulating the Notch pathway to alleviate immune pathology, highlighting the importance of understanding the mechanisms through which Notch regulates T cell differentiation and function. We review these findings here, and outline both unifying principles involved in Notch-mediated T cell fate decisions and cell type- and context-specific differences that may present the most suitable points for therapeutic intervention.

The Notch signaling pathway controls short-lived effector CD8+ T cell differentiation but is dispensable for memory generation

Following an infection, naive CD8(+) T cells expand and differentiate into two main populations of effectors: short-lived effector cells (SLECs) and memory precursor effector cells (MPECs). There is limited understanding of the molecular mechanism and cellular processes governing this cell fate. Notch is a key regulator of cell fate decision relevant in many immunological pathways. In this study, we add to the role of Notch in cell fate decision and demonstrate that the Notch signaling pathway controls the MPEC/SLEC differentiation choice following both Listeria infection and dendritic cell immunization of mice. Although fewer SLECs were generated, Notch deficiency did not alter the rate of memory CD8(+) T cell generation. Moreover, we reveal that the Notch signaling pathway plays a context-dependent role for optimal cytokine production by effector CD8(+) T cells. Together, our results unravel critical functions for the Notch signaling pathway during effector CD8(+) T cell differentiation.