Lateral inhibition of Notch signaling in neoplastic cells

Notch signalling: multifaceted role in development and disease

Notch pathway is an evolutionarily conserved signalling system that operates to influence an astonishing array of cell fate decisions in different developmental contexts. Notch signalling plays important roles in many developmental processes, making it difficult to name a tissue or a developing organ that does not depend on Notch function at one stage or another. Thus, dysregulation of Notch signalling is associated with many developmental defects and various pathological conditions, including cancer. Although many recent advances have been made to reveal different aspects of the Notch signalling mechanism and its intricate regulation, there are still many unanswered questions related to how the Notch signalling pathway functions in so many developmental events. The same pathway can be deployed in numerous cellular contexts to play varied and critical roles in an organism's development and this is only possible because of the complex regulatory mechanisms of the pathway. In this review, we provide an overview of the mechanism and regulation of the Notch signalling pathway along with its multifaceted functions in different aspects of development and disease.

NOTCH pathway inactivation reprograms stem-like oral cancer cells to JAK-STAT dependent state and provides the opportunity of synthetic lethality

BACKGROUND

We have recently provided the evidence of interconvertible cellular states, driving non-genetic heterogeneity among stem-like oral cancer cells (oral-SLCCs). Here, NOTCH pathway-activity status is explored as one of the possible mechanisms behind this stochastic plasticity.

METHODS

Oral-SLCCs were enriched in 3D-spheroids. Constitutively-active and inactive status of NOTCH pathway was achieved by genetic or pharmacological approaches. RNA sequencing and real-time PCR was performed for gene expression studies. in vitro cytotoxicity assessments were performed by AlamarBlue assay and in vivo effects were studied by xenograft growth in zebrafish embryo.

RESULTS

We have observed stochastic plasticity in oral-SLCCs, spontaneously maintaining both NOTCH-active and inactive states. While cisplatin refraction was associated with post-treatment adaptation to the active-state of NOTCH pathway, oral-SLCCs with inactive NOTCH pathway status showed aggressive tumor growth and poor prognosis. RNAseq analysis clearly suggested the upregulation of JAK-STAT pathway in NOTCH pathway-inactive subset. The 3D-spheroids with lower NOTCH-activity status displayed significantly higher sensitivity to JAK-selective drugs, Ruxolitinib or Tofacitinib or siRNA mediated downregulation of tested partners STAT3/4. Oral-SLCCs were programmed to adapt the inactive status of NOTCH pathway by exposing to γ-secretase inhibitors, LY411575 or RO4929097, followed by targeting with JAK-inhibitors, Ruxolitinib or Tofacitinib. This approach resulted in a very significant inhibition in viability of 3D-spheroids as well as xenograft initiation in Zebrafish embryos.

CONCLUSION

Study revealed for the first time that NOTCH pathway-inactive state exhibit activation of JAK-STAT pathways, as synthetic lethal pair. Therefore, co-inhibition of these pathway may serve as novel therapeutic strategy against aggressive oral cancer.

Immunotherapy and the Combination with Targeted Therapies for Advanced Hepatocellular Carcinoma

One of the most important abilities of a tumor is to establish a state of immunosuppression inside the tumor microenvironment. This is made possible through numerous mechanisms of tumor immune escape that have been identified in experimental studies during the last decades. In addition, the hepatic microenvironment is commonly oriented towards a state of immune tolerance because the liver receives blood from the hepatic arteries and portal veins containing a variety of endogenous antigens. Therefore, the hepatic microenvironment establishes an autoimmune tolerance, preventing an autoimmune reaction in the liver. On this basis, hepatic tumor cells may escape the immune system, avoiding being recognized and destroyed by immune cells. Moreover, since the etiology of Hepatocellular Carcinoma (HCC) is often related to cirrhosis, and hepatitis B or C, this tumor develops in the context of chronic inflammation. Thus, the HCC microenvironment is characterized by important immune cell infiltration. Given these data and the poor prognosis of advanced HCC, different immunotherapeutic strategies have been developed and evaluated for these patients. In this review, we describe all the clinical applications of immunotherapy for advanced HCC, from the drugs that have already been approved to the ongoing clinical trials.

DLL3 regulates Notch signaling in small cell lung cancer

Tumor heterogeneity plays a critical role in tumor development and response to treatment. In small-cell lung cancer (SCLC), intratumoral heterogeneity is driven in part by the Notch signaling pathway, which reprograms neuroendocrine cancer cells to a less/non-neuroendocrine state. Here we investigated the atypical Notch ligand DLL3 as a biomarker of the neuroendocrine state and a regulator of cell-cell interactions in SCLC. We first built a mathematical model to predict the impact of DLL3 expression on SCLC cell populations. We next tested this model using a single-chain variable fragment (scFv) to track DLL3 expression in vivo and a new mouse model of SCLC with inducible expression of DLL3 in SCLC tumors. We found that high levels of DLL3 promote the expansion of a SCLC cell population with lower expression levels of both neuroendocrine and non-neuroendocrine markers. This work may influence how DLL3-targeting therapies are used in SCLC patients.

Reversible and bidirectional signaling of notch ligands

The Notch signaling pathway is a direct cell-cell communication system involved in a wide variety of biological processes, and its disruption is observed in several pathologies. The pathway is comprised of a ligand-expressing (sender) cell and a receptor-expressing (receiver) cell. The canonical ligands are members of the Delta/Serrate/Lag-1 (DSL) family of proteins. Their binding to a Notch receptor in a neighboring cell induces a conformational change in the receptor, which will undergo regulated intramembrane proteolysis (RIP), liberating the Notch intracellular domain (NICD). The NICD is translocated to the nucleus and promotes gene transcription. It has been demonstrated that the ligands can also undergo RIP and nuclear translocation, suggesting a function for the ligands in the sender cell and possible bidirectionality of the Notch pathway. Although the complete mechanism of ligand processing is not entirely understood, and its dependence on Notch receptors has not been ruled out. Also, ligands have autonomous functions beyond Notch activation. Here we review the concepts of reverse and bidirectional signalization of DSL proteins and discuss the characteristics that make them more than just ligands of the Notch pathway.

MAPK and Notch-Mediated Effects of Meso-Xanthin F199 Compounds on Proliferative Activity and Apoptosis of Human Melanocytes in Three-Dimensional Culture

Meso-Xanthin (Meso-Xanthin F199™) is a highly active antiaging injection drug of the latest generation. The main acting compound is fucoxanthin, supplemented with several growth factors, vitamins, and hyaluronic acid. Previous examination of fucoxanthin on melanocytes showed its ability to inhibit skin pigmentation through different signaling pathways focused on suppression of melanogenic-stimulating receptors. In turn, the anticancer property of fucoxanthin is realized through MAPK and PI3K pathways. We aimed to evaluate the effect of fucoxanthin and supplemented growth factors on melanocyte growth and transformation at a proteomic level. The effect of fucoxanthin on melanocytes cultivated in three-dimensional (3D) condition was examined using high-throughput proteomic and system biology approaches to disclose key molecular events of the targeted action. Our results demonstrated significant inhibition of cell differentiation and ubiquitination processes. We found that the negative regulation of PSME1 and PTGIS largely determines the inhibition of NF-κB and MAPK2. Besides, fucoxanthin selectively inhibits cell differentiation via negative regulation of Raf signaling and the upstream activation of IL-1 signaling. It is assumed that inhibition of Raf influences the Notch-4 signaling and switches off the MAPK/MAPK2 cascade. Blockage of MAPK/MAPK2 is feasible due to suppression of Ras and NF-κB by the addressed action of IKKB, IKK2, and TRAF6. Suggestively, Meso-Xanthin F199™ can manage processes of proliferative activity and inhibition of apoptosis due to composition of fucoxanthin and growth-stimulating factors, which may increase the risk of skin cancer development under certain condition.

Notch1 Deficiency Induces Tumor Cell Accumulation Inside the Bronchiolar Lumen and Increases TAZ Expression in an Autochthonous Kras LSL-G12V Driven Lung Cancer Mouse Model

Purpose: Abrogation of Notch signaling, which is pivotal for lung development and pulmonary epithelial cell fate decisions was shown to be involved in the aggressiveness and the differentiation of lung carcinomas. Additionally, the transcription factors YAP and TAZ which are involved in the Hippo pathway, were recently shown to be tightly linked with Notch signaling and to regulate the cell fate in epidermal stem cells. Thus, we aim to elucidate the effects of conditional Notch1 deficiency on carcinogenesis and TAZ expression in lung cancer. Methods: We investigated the effect of conditional Cre-recombinase mediated Notch1 knock-out on lung cancer cells in vivo using an autochthonous mouse model of lung adenocarcinomas driven by Kras ^LSL-G12V and comprehensive immunohistochemical analysis. In addition, we analyzed clinical samples and human lung cancer cell lines for TAZ expression and supported our findings by publicly available data from The Cancer Genome Atlas (TCGA). Results: In mice, we found induction of papillary adenocarcinomas and protrusions of tumor cells from the bronchiolar lining upon Notch1 deficiency. Moreover, the mutated Kras driven lung tumors with deleted Notch1 showed increased TAZ expression and focal nuclear translocation which was frequently observed in human pulmonary adenocarcinomas and squamous cell carcinomas of the lung, but not in small cell lung carcinomas. In addition, we used data from TCGA to show that putative inactivating NOTCH1 mutations co-occur with KRAS mutations and genomic amplifications in lung adenocarcinomas. Conclusion: Our in vivo study provides evidence that Notch1 deficiency in mutated Kras driven lung carcinomas contributes to lung carcinogenesis in a subgroup of patients by increasing TAZ expression who might benefit from TAZ signaling blockade.

Oncogenic and Tumor-Suppressive Functions of NOTCH Signaling in Glioma

Although the role of NOTCH signaling has been extensively studied in health and disease, many questions still remain unresolved. Being crucial for tissue homeostasis, NOTCH signaling is also implicated in multiple cancers by either promoting or suppressing tumor development. In this review we illustrate the context-dependent role of NOTCH signaling during tumorigenesis with a particular focus on gliomas, the most frequent and aggressive brain tumors in adults. For a long time, NOTCH has been considered an oncogene in glioma mainly by virtue of its neural stem cell-promoting activity. However, the recent identification of NOTCH-inactivating mutations in some glioma patients has challenged this notion, prompting a re-examination of the function of NOTCH in brain tumor subtypes. We discuss recent findings that might help to reconcile the controversial role of NOTCH signaling in this disease, and pose outstanding questions that still remain to be addressed.

Cancer Stem Cells, Quo Vadis? The Notch Signaling Pathway in Tumor Initiation and Progression

The Notch signaling pathway regulates cell proliferation, cytodifferentiation and cell fate decisions in both embryonic and adult life. Several aspects of stem cell maintenance are dependent from the functionality and fine tuning of the Notch pathway. In cancer, Notch is specifically involved in preserving self-renewal and amplification of cancer stem cells, supporting the formation, spread and recurrence of the tumor. As the function of Notch signaling is context dependent, we here provide an overview of its activity in a variety of tumors, focusing mostly on its role in the maintenance of the undifferentiated subset of cancer cells. Finally, we analyze the potential of molecules of the Notch pathway as diagnostic and therapeutic tools against the various cancers.

IL-4-dependent Jagged1 expression/processing is associated with survival of chronic lymphocytic leukemia cells but not with Notch activation

As previously reported, chronic lymphocytic leukemia (CLL) cells show constitutive Notch1/2 activation and express the Notchligand Jagged1. Despite increasing knowledge of the impact of Notch alterations on CLL biology and pathogenesis, the role of Jagged1 expressed in CLL cells remains undefined. In other cell types, it has been shown that after Notch engagement, Jagged1 not only activates Notch in signal-receiving cell, but also undergoes proteolytic activation in signal-sending cell, triggering a signaling with biological effects. We investigated whether Jagged1 expressed in CLL cells undergoes proteolytic processing and/or is able to induce Notch activation through autocrine/paracrine loops, focusing on the effect that CLL prosurvival factor IL-4 could exert on the Notch-Jagged1 system in these cells. We found that Jagged1 was constitutively processed in CLL cells and generated an intracellular fragment that translocated into the nucleus, and an extracellular fragment released into the culture supernatant. IL-4 enhanced expression of Jagged1 and its intracellular fragments, as well as Notch1/2 activation. The IL-4-induced increase in Notch1/2 activation was independent of the concomitant upregulated Jagged1 levels. Indeed, blocking Notch-Jagged1 interactions among CLL cells with Jagged1 neutralizing antibodies did not affect the expression of the Notch target Hes1. Notably, anti-Jagged1 antibodies partially prevented the IL-4-induced increase in Jagged1 processing and cell viability, suggesting that Jagged1 processing is one of the events contributing to IL-4-induced CLL cell survival. Consistent with this, Jagged1 silencing by small interfering RNA partially counteracted the capacity of IL-4 to promote CLL cell survival. Investigating the pathways whereby IL-4 promoted Notch1/2 activation in CLL cells independent of Jagged1, we found that PI3Kδ/AKT and PKCδ were involved in upregulating Notch1 and Notch2 proteins, respectively. Overall, this study provides new insights into the Notch-ligand system in CLL cells and suggests that targeting this system may be exploited as a novel/additional therapy approach for CLL.

Notch signaling promotes a HIF2α-driven hypoxic response in multiple tumor cell types

Hyperactivation of Notch signaling and the cellular hypoxic response are frequently observed in cancers, with increasing reports of connections to tumor initiation and progression. The two signaling mechanisms are known to intersect, but while it is well established that hypoxia regulates Notch signaling, less is known about whether Notch can regulate the cellular hypoxic response. We now report that Notch signaling specifically controls expression of HIF2α, a key mediator of the cellular hypoxic response. Transcriptional upregulation of HIF2α by Notch under normoxic conditions leads to elevated HIF2α protein levels in primary breast cancer cells as well as in human breast cancer, medulloblastoma, and renal cell carcinoma cell lines. The elevated level of HIF2α protein was in certain tumor cell types accompanied by downregulation of HIF1α protein levels, indicating that high Notch signaling may drive a HIF1α-to-HIF2α switch. At the transcriptome level, the presence of HIF2α was required for approximately 21% of all Notch-induced genes: among the 1062 genes that were upregulated by Notch in medulloblastoma cells during normoxia, upregulation was abrogated in 227 genes when HIF2α expression was knocked down by HIF2α siRNA. In conclusion, our data show that Notch signaling affects the hypoxic response via regulation of HIF2α, which may be important for future cancer therapies.

Deregulation of the Notch pathway as a common road in viral carcinogenesis

The Notch pathway is a conserved signaling pathway and a form of direct cell-cell communication related to many biological processes during development and adulthood. Deregulation of the Notch pathway is involved in many diseases, including cancer. Almost 20% of all cancer cases have an infectious etiology, with viruses responsible for at least 1.5 million new cancer cases per year. Seven groups of viruses have been classified as oncogenic: hepatitis B and C viruses (HBV and HCV respectively), Epstein-Barr virus (EBV), Kaposi sarcoma-associated herpesvirus (KSHV), human T lymphotropic virus (HTLV-1), human papillomavirus (HPV), and Merkel cell polyomavirus (MCPyV). These viruses share the ability to manipulate a variety of cell pathways that are critical in proliferation and differentiation, leading to malignant transformation. Viral proteins interact directly or indirectly with different members of the Notch pathway, altering their normal function. This review focuses exclusively on the direct interactions of viral oncoproteins with Notch elements, providing a deeper understanding of the dual behavior of the Notch pathway as activator or suppressor of neoplasia in virus-related cancers.

NOTCH1 Aberrations in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is an incurable B-cell neoplasm characterized by highly variable clinical outcomes. In recent years, genomic and molecular studies revealed a remarkable heterogeneity in CLL, which mirrored the clinical diversity of this disease. These studies profoundly enhanced our understanding of leukemia cell biology and led to the identification of new biomarkers with potential prognostic and therapeutic significance. Accumulating evidence indicates a key role of deregulated NOTCH1 signaling and NOTCH1 mutations in CLL. This review highlights recent discoveries that improve our understanding of the pathophysiological NOTCH1 signaling in CLL and the clinical impact of NOTCH1 mutations in retrospective and prospective trials. In addition, we discuss the rationale for a therapeutic strategy aiming at inhibiting NOTCH1 signaling in CLL, along with an overview on the currently available NOTCH1-directed approaches.

Highly Tumorigenic Diffuse Large B Cell Lymphoma Cells Are Produced by Coculture with Stromal Cells

BACKGROUND/AIMS

Diffuse large B cell lymphoma (DLBCL) is heterogeneous. We aimed to explore how tumor microenvironment promotes lymphoma cell aggressiveness and heterogeneity.

METHODS

We created a coculture system using human DLBCL cells and mouse bone marrow stromal cells. Proliferative capacity, drug resistance, clonogenicity, and tumorigenicity were compared in lymphoma cells from the coculture system and lymphoma cells cultured alone. Expression of Notch signaling associated genes was evaluated using real-time reverse transcriptase PCR and Western blot.

RESULTS

Lymphoma cells in the coculture system differentiated into a suspended cell group and an adherent cell group. They acquired a stronger proliferative capacity and drug resistance than lymphoma cells cultured alone, and differences existed between the adherent cell and suspended cell groups. The suspended cell group acquired the most powerful clonogenic and tumorigenic potential. However, Notch3 was exclusively expressed in the adherent lymphoma cell group and the use of N-[N-(3, 5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester, an inhibitor of Notch pathway, could abolish the emergence of highly aggressive lymphoma cells.

CONCLUSION

Highly tumorigenic lymphoma cells could be generated by coculture with stromal cells, and it was dependent on Notch3 expression in the adjacent lymphoma cells through interaction with stromal cells.

Targeting Notch signaling as a novel therapy for retinoblastoma

Retinoblastoma is the most common intraocular malignancy of childhood. Notch plays a key role in retinal cells from which retinoblastomas arise, and we therefore studied the role of Notch signaling in promoting retinoblastoma proliferation. Moderate or strong nuclear expression of Hes1 was found in 10 of 11 human retinoblastoma samples analyzed immunohistochemically, supporting a role for Notch in retinoblastoma growth. Notch pathway components were present in WERI Rb1 and Y79 retinoblastoma lines, with Jag2 and DLL4 more highly expressed than other ligands, and Notch1 and Notch2 more abundant than Notch3. The cleaved/active form of Notch1 was detectable in both lines. Inhibition of the pathway, achieved using a γ-secretase inhibitor (GSI) or by downregulating Jag2, DLL4 or CBF1 using short hairpin RNA, potently reduced growth, proliferation and clonogenicity in both lines. Upregulation of CXCR4 and CXCR7 and downregulation of PI3KC2β were identified by microarray upon Jag2 suppression. The functional importance of PI3KC2β was confirmed using shRNA. Synergy was found by combining GSI with Melphalan at their IC₅₀. These findings indicate that Notch pathway is active in WERI Rb1 and Y79, and in most human retinoblastoma samples, and suggest that Notch antagonists may represent a new approach to more effectively treat retinoblastoma.

Notch and Senescence

Cellular senescence, previously thought of as an autonomous tumour suppressor mechanism, is emerging as a phenotype and effector present throughout the life of an organism from embryogenesis to senile decline. Senescent cells have powerful non-autonomous effects upon multiple players within their microenvironment mainly through their secretory phenotype. How senescent cells co-ordinate numerous, sometimes functionally contrasting outputs through their secretome had previously been unclear. The Notch pathway, originally identified for its involvement in Drosophila wing development, has more recently been found to underpin diverse effects in human cancer. Here we discuss recent findings that suggest that Notch is intimately involved in the development of senescence and how it acts to co-ordinate the composition and functional effects of the senescence secretome. We also highlight the complex physical and functional interplay between Notch and p53, critical to both senescence and cancer. Understanding the interplay between Notch, p53 and senescence could allow us develop the therapeutics of the future for cancer and ageing.

The interplay between the cellular hypoxic response and Notch signaling

The ability to sense and adapt to low oxygen levels (hypoxia) is central for most organisms and cell types. At the center of this process is a molecular mechanism, the cellular hypoxic response, in which the hypoxia inducible factors (HIFs) are stabilized by hypoxia, allowing the HIF proteins to act as master transcriptional regulators to adjust the cell to a low oxygen environment. In recent years, it has become increasingly appreciated that the cellular hypoxic response does not always operate in splendid isolation, but intersects with signaling mechanisms such as Notch signaling, a key regulatory signaling mechanism operating in most cell types controlling stem cell maintenance and differentiation. In this review, which is dedicated to the memory of Lorenz Poellinger,¹ we discuss how the intersection between Notch and the cellular hypoxic response was discovered and our current understanding of the molecular basis for the cross-talk. We also provide examples of where Notch and hypoxia intersect in various physiological and disease contexts.

Targeting Notch3 in Hepatocellular Carcinoma: Molecular Mechanisms and Therapeutic Perspectives

The Notch signaling pathway is a very conserved system that controls embryonic cell fate decisions and the maintenance of adult stem cells through cell to cell communication. Accumulating evidence support the relevance of Notch signaling in different human diseases and it is one of the most commonly activated signaling pathways in cancer. This review focuses mainly on the role of Notch3 signaling in hepatocellular carcinoma and its potential therapeutic applications against this malignancy. In this regard, the crosstalk between Notch and p53 may play an important role.

Fine-Tuning of the Kaposi's Sarcoma-Associated Herpesvirus Life Cycle in Neighboring Cells through the RTA-JAG1-Notch Pathway

Kaposi’s sarcoma (KS)-associated herpesvirus (KSHV) is an oncogenic pathogen that displays latent and lytic life cycles. In KS lesions, infiltrated immune cells, secreted viral and/or cellular cytokines, and hypoxia orchestrate a chronic pro-lytic microenvironment that can promote KSHV reactivation. However, only a small subset of viruses spontaneously undergoes lytic replication in this pro-lytic microenvironment while the majority remains in latency. Here, we show that the expression of the Notch ligand JAG1 is induced by KSHV-encoded replication and transcription activator (RTA) during reactivation. JAG1 up-regulation activates Notch signaling in neighboring cells and prevents viral lytic replication. The suppression of JAG1 and Notch1 with inhibitors or small interfering RNA promotes lytic replication in the presence of RTA induction or under conditions of hypoxia. The underlying mechanism involves the Notch downstream effector hairy and enhancer of split 1 (Hes1), which directly binds lytic gene promoters and attenuates viral lytic gene expression. RTA interacts with lymphoid enhancer-binding factor 1 (LEF1), disrupts LEF1/Groucho/TLE suppressive complexes and releases LEF1 to activate JAG1 expression. Taken together, our results suggest that cells with viral lytic replication can inhibit KSHV reactivation in neighboring cells through an RTA-JAG1-Notch pathway. These data provide insight into the mechanism by which the virus maintains the balance between lytic and latent infection in the pro-lytic tumor microenvironment.

KSHV infected cells display significant heterogeneity in viral lytic replication within the universal pro-lytic inflammatory milieu, suggesting that the balance between latency and reactivation is carefully regulated. This fine-tuned regulatory mechanism is essential for KSHV to persist in the host and drive cells to malignancy. In the present study, we show that KSHV can usurp the Notch signaling pathway to inhibit the viral lytic life cycle in neighboring cells. Notch signaling in surrounding cells can be activated through an RTA-JAG1-Notch pathway initiated by cells in which KSHV is reactivated. Activated Notch inhibits KSHV reactivation through its downstream effector Hes1. These findings suggest that the ability of Notch to determine the fate of adjacent cells is hijacked by KSHV to maintain its life cycle, providing a mechanistic explanation for the phenomenon by which only a small fraction of viruses enters lytic replication in the common pro-lytic microenvironment.