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It is well established that Notch functions as a transcriptional activator through the formation of a ternary complex that comprises Notch, Maml, and CSL. This ternary complex then serves to recruit additional transcriptional cofactors that link to higher order transcriptional complexes. The mechanistic details of these events remain unclear. This report reveals that the Notch ternary complex can direct the formation of a repressor complex to terminate gene expression of select target genes. Herein, it is demonstrated that p19 Arf and Klf4 are transcriptionally repressed in a Notch-dependent manner. Furthermore, results indicate that Notch recruits Polycomb Repressor Complex 2 (PRC2) and Lysine Demethylase 1 (KDM1A/LSD1) to these promoters, which leads to changes in the epigenetic landscape and repression of transcription. The demethylase activity of LSD1 is a prerequisite for Notch-mediated transcriptional repression. In addition, a stable Notch transcriptional repressor complex was identified containing LSD1, PRC2, and the Notch ternary complex. These findings demonstrate a novel function of Notch and provide further insight into the mechanisms of Notch-mediated tumorigenesis. Implications: This study provides rationale for the targeting of epigenetic enzymes to inhibit Notch activity or use in combinatorial therapy to provide a more profound therapeutic response. Mol Cancer Res; 15(9); 1173-83. ©2017 AACR ., (©2017 American Association for Cancer Research.)

In many cancers, aberrant Notch activity has been demonstrated to play a role in the initiation and maintenance of the neoplastic phenotype and in cancer stem cells, which may allude to its additional involvement in metastasis and resistance to therapy. Therefore, Notch is an exceedingly attractive therapeutic target in cancer, but the full range of potential targets within the pathway has been underexplored. To date, there are no small-molecule inhibitors that directly target the intracellular Notch pathway or the assembly of the transcriptional activation complex. Here, we describe an in vitro assay that quantitatively measures the assembly of the Notch transcriptional complex on DNA. Integrating this approach with computer-aided drug design, we explored potential ligand-binding sites and screened for compounds that could disrupt the assembly of the Notch transcriptional activation complex. We identified a small-molecule inhibitor, termed Inhibitor of Mastermind Recruitment-1 (IMR-1), that disrupted the recruitment of Mastermind-like 1 to the Notch transcriptional activation complex on chromatin, thereby attenuating Notch target gene transcription. Furthermore, IMR-1 inhibited the growth of Notch-dependent cell lines and significantly abrogated the growth of patient-derived tumor xenografts. Taken together, our findings suggest that a novel class of Notch inhibitors targeting the transcriptional activation complex may represent a new paradigm for Notch-based anticancer therapeutics, warranting further preclinical characterization. Cancer Res; 76(12); 3593-603. ©2016 AACR., (©2016 American Association for Cancer Research.)

The Notch signaling pathway plays a critical role in embryonic development, self-renewal of stem cells, and carcinogenesis. Aberrant Notch signaling has been linked to a wide variety of cancers, and can either suppress or promote tumors depending on the cell type and the context. Increasingly it is being realized that Notch signaling not only involves in the pathogenesis and development of esophageal adenocarcinoma (EAC), it also promotes the growth of EAC cells and also involved in the maintenance of EAC cancer stem cells. The efficacy of gamma-secretase inhibitor (GSI) in EAC treatment could have a major impact on easing the burden of this devastating disease. Therefore, it appears that inhibition of Notch sensitizes EAC cells to chemotherapeutic agents, which should lead to a better and more durable response to neoadjuvant chemotherapy (NAC). In this review, we bring to highlight how Notch plays a role in the development, tumorigenicity, and stemness of EAC cells, and how Notch signaling pathway could be a promising therapeutic target for the treatment of human EAC.

Deregulated Notch signaling has been extensively linked to T-cell acute lymphoblastic leukemia (T-ALL). Here, we show a direct relationship between Notch3 receptor and Jagged1 ligand in human cell lines and in a mouse model of T-ALL. We provide evidence that Notch-specific ligand Jagged1 is a new Notch3 signaling target gene. This essential event justifies an aberrant Notch3/Jagged1 cis-expression inside the same cell. Moreover, we demonstrate in Notch3-IC-overexpressing T lymphoma cells that Jagged1 undergoes a raft-associated constitutive processing. The proteolytic cleavage allows the Jagged1 intracellular domain to empower Notch signaling activity and to increase the transcriptional activation of Jagged1 itself (autocrine effect). On the other hand, the release of the soluble Jagged1 extracellular domain has a positive impact on activating Notch signaling in adjacent cells (paracrine effect), finally giving rise to a Notch3/Jagged1 auto-sustaining loop that supports the survival, proliferation, and invasion of lymphoma cells and contributes to the development and progression of Notch-dependent T-ALL. These observations are also supported by a study conducted on a cohort of patients in which Jagged1 expression is associated to adverse prognosis., (Copyright © 2014 Neoplasia Press, Inc. Published by Elsevier Inc. All rights reserved.)

Esophageal adenocarcinoma ranks sixth in cancer mortality in the world and its incidence has risen dramatically in the Western population over the last decades. Data presented herein strongly suggest that Notch signaling is critical for esophageal adenocarcinoma and underlies resistance to chemotherapy. We present evidence that Notch signaling drives a cancer stem cell phenotype by regulating genes that establish stemness. Using patient-derived xenograft models, we demonstrate that inhibition of Notch by gamma-secretase inhibitors (GSI) is efficacious in downsizing tumor growth. Moreover, we demonstrate that Notch activity in a patient's ultrasound-assisted endoscopic-derived biopsy might predict outcome to chemotherapy. Therefore, this study provides a proof of concept that inhibition of Notch activity will have efficacy in treating esophageal adenocarcinoma, offering a rationale to lay the foundation for a clinical trial to evaluate the efficacy of GSI in esophageal adenocarcinoma treatment., (©2014 American Association for Cancer Research.)

The Notch signaling pathway governs many distinct cellular processes by regulating transcriptional programs. The transcriptional response initiated by Notch is highly cell context dependent, indicating that multiple factors influence Notch target gene selection and activity. However, the mechanism by which Notch drives target gene transcription is not well understood. Herein, we identify and characterize a novel Notch-interacting protein, Notch activation complex kinase (NACK), which acts as a Notch transcriptional coactivator. We show that NACK associates with the Notch transcriptional activation complex on DNA, mediates Notch transcriptional activity, and is required for Notch-mediated tumorigenesis. We demonstrate that Notch1 and NACK are coexpressed during mouse development and that homozygous loss of NACK is embryonic lethal. Finally, we show that NACK is also a Notch target gene, establishing a feed-forward loop. Thus, our data indicate that NACK is a key component of the Notch transcriptional complex and is an essential regulator of Notch-mediated tumorigenesis and development., (©2014 American Association for Cancer Research.)

The Notch signal transduction pathway mediates important cellular functions through direct cell-to-cell contact. Deregulation of Notch activity can lead to an altered cell proliferation and has been linked to many human cancers. Casein kinase 2 (CK2), a ubiquitous kinase, regulates several cellular processes by phosphorylating proteins involved in signal transduction, gene expression, and protein synthesis. In this report we identify Notch(ICD) as a novel target of phosphorylation by CK2. Using mapping and mutational studies, we identified serine 1901, located in the ankyrin domain of Notch, as the target amino acid. Interestingly, phosphorylation of serine 1901 by CK2 appears to generate a second phosphorylation site at threonine 1898. Furthermore, threonine 1898 phosphorylation only occurs when Notch forms a complex with Mastermind and CSL. Phosphorylation of both threonine 1898 and serine 1901 resulted in decreased binding of the Notch-Mastermind-CSL ternary complex to DNA and consequently lower transcriptional activity. These data indicate that the phosphorylation of serine 1901 and threonine 1898 negatively regulates Notch function by dissociating the complex from DNA. This study identifies a new component involved in regulation of Notch(ICD) transcriptional activity, reinforcing the notion that a precise and tight regulation is required for this essential signaling pathway.

The discovery of Notch in Drosophila melanogaster nearly a century ago opened the door to an ever-widening understanding of cellular processes that are controlled or influenced by Notch signalling. As would be expected with such a pleiotropic pathway, the deregulation of Notch signalling leads to several pathological conditions, including cancer. A role for Notch is well established in haematological malignancies, and more recent studies have provided evidence for the importance of Notch activity in solid tumours. As it is thought to act as an oncogene in some cancers but as a tumour suppressor in others, the role of Notch in solid tumours seems to be highly context dependent.

Notch transmembrane receptors direct essential cellular processes, such as proliferation and differentiation, through direct cell-to-cell interactions. Inappropriate release of the intracellular domain of Notch (N(ICD)) from the plasma membrane results in the accumulation of deregulated nuclear N(ICD) that has been linked to human cancers, notably T-cell acute lymphoblastic leukemia (T-ALL). Nuclear N(ICD) forms a transcriptional activation complex by interacting with the coactivator protein Mastermind-like 1 and the DNA binding protein CSL (for CBF-1/Suppressor of Hairless/Lag-1) to regulate target gene expression. Although it is well understood that N(ICD) forms a transcriptional activation complex, little is known about how the complex is assembled. In this study, we demonstrate that N(ICD) multimerizes and that these multimers function as precursors for the stepwise assembly of the Notch activation complex. Importantly, we demonstrate that the assembly is mediated by N(ICD) multimers interacting with Skip and Mastermind. These interactions form a preactivation complex that is then resolved by CSL to form the Notch transcriptional activation complex on DNA.

T-cell acute lymphoblastic leukemia (T-ALL) is a hematologic neoplasm characterized by malignant expansion of immature T cells. Activated NOTCH (Notch(IC)) and c-MYC expression are increased in a large percentage of human T-ALL tumors. Furthermore, c-MYC has been shown to be a NOTCH target gene. Although activating mutations of Notch have been found in human T-ALL tumors, there is little evidence that the c-MYC locus is altered in this neoplasm. It was previously demonstrated that Notch and c-Myc-regulated genes have a broadly overlapping profile, including genes involved in cell cycle progression and metabolism. Given that Notch and c-Myc appear to function similarly in T-ALL, we sought to determine whether these two oncogenes could substitute for each other in T-ALL tumors. Here we report that NOTCH(IC) is able to maintain T-ALL tumors formed in the presence of exogenous NOTCH(IC) and c-MYC when exogenous c-MYC expression is extinguished. In contrast, c-MYC is incapable of maintaining these tumors in the absence of NOTCH(IC). We propose that failure of c-MYC to maintain these tumors is the result of p53-mediated apoptosis. These results demonstrate that T-ALL maintenance is dependent on NOTCH(IC), but not c-MYC, demonstrating that NOTCH is oncogenic dominant in T-ALL tumors.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive subset of ALL with poor clinical outcome compared to B-ALL. Therefore, to improve treatment, it is imperative to delineate the molecular blueprint of this disease. This review describes the central role that the Notch pathway plays in T-ALL development. We also discuss the interactions between Notch and the tumor suppressors Ikaros and p53. Loss of Ikaros, a direct repressor of Notch target genes, and suppression of p53-mediated apoptosis are essential for development of this neoplasm. In addition to the activating mutations of Notch previously described, this review will outline combinations of mutations in pathways that contribute to Notch signaling and appear to drive T-ALL development by 'mimicking' Notch effects on cell cycle and apoptosis.