Deregulated Notch Signaling Research Articles

Identification of Notch target genes in uncommitted T-cell progenitors: no direct induction of a T-cell specific gene program

Deregulated Notch signaling occurs in the majority of human T-ALL. During normal lymphoid development, activation of the Notch signaling pathway poses a T-cell fate on hematopoietic progenitors. However, the transcriptional targets of the Notch pathway are largely unknown. We sought to identify Notch target genes by inducing Notch signaling in human hematopoietic progenitors using two different methods: an intracellular signal through transfection of activated Notch and a Notch-receptor dependent signal by interaction with its ligand Delta1. Gene expression profiles were generated and evaluated with respect to expression profiles of immature thymic subpopulations. We confirmed HES1, NOTCH1 and NRARP as Notch target genes, but other reported Notch targets, including the genes for Deltex1, pre-T-cell receptor alpha and E2A, were not found to be differentially expressed. Remarkably, no induction of T-cell receptor gene rearrangements or transcription of known T-cell specific genes was found after activation of the Notch pathway. A number of novel Notch target genes, including the transcription factor TCFL5 and the HOXA cluster, were identified and functionally tested. Apparently, Notch signaling is essential to open the T-cell pathway, but does not initiate the T-cell program itself.

Intracellular Activated Notch1 Is Critical for Proliferation of Kaposi's Sarcoma-Associated Herpesvirus-Associated B-Lymphoma Cell Lines In Vitro

Kaposi's sarcoma-associated herpesvirus (KSHV) is a human tumor virus expressing latent antigens critical for pathogenesis. The mechanism by which KSHV mediates oncogenesis has not been fully elucidated. Notch signaling is an evolutionarily conserved pathway controlling diverse events related to development, proliferation, and tissue homeostasis. Deregulation of Notch signaling has also been shown to be highly correlated with oncogenesis. Here we show that the activated intracellular domain of Notch1 (ICN) is aberrantly accumulated in latently KSHV-infected pleural effusion lymphoma cells and results in increased proliferation. Specifically, growth of the infected cells was dramatically inhibited at the G(1) phase by treatment with a gamma-secretase inhibitor which specifically blocks the production of ICN. Increased ICN also up-regulated the cyclin D1 cell cycle regulator. Taken together, these studies define an important mechanism directly linking latent KSHV infection to induction of oncogenesis through dysregulation of the conserved Notch signaling pathway.

All pathways to cancer apoptosis meeting in Thiruvananthapuram (India)

An extensive amount of research in the past three decades has revealed many pathways of cell death. Although ‘apoptosis’ is the term used for most types of cell death, the pathways that lead to it are not always the same. The list of agents that mediate apoptosis is constantly growing. Because cancer is a hyperproliferative disorder, apoptosis of cancer cells and not of normal cells is a critical issue. Both physiologic and pharmacologic inducers of apoptosis have been identified. At an international conference held in Kerala, India, scientists discussed how apoptosis occurs, what mediates it, what pharmacologic agents induce it, how it is genetically regulated, and its role in tumorigenesis and cancer. It is said that multiple pathways can lead to enlightenment. What better place to discuss this than Thirvananthapuram (Trivandrum), Kerala. Created by Parsuram, the legendary Brahmin ‘protector,’ Kerala, the southernmost state in India, sits where the Indian Ocean and Arabian Sea meet, where Vasco de Gama landed in search of spices, where St. Thomas landed in search of enlightenment, where the world’s second oldest mosque is located, and where one of the world’s oldest synagogues is located. The purpose of 31⁄2-day conference that convened on December 18, 2005 was to bring together laboratory and clinical scientists to share current knowledge and future strategies for promoting the death of cancer cells. The participants included over 450 physicians and researchers from 16 different countries worldwide. The format of the meeting was daily major symposia, parallel minisymposia, and poster sessions. Dr. Abdul Kalam, the President of India and an aerospace engineer, inaugurated the meeting and reminded the importance of stem cell cloning and nontoxic drugs in cancer treatment and the role of patient databases and genomics in cancer care. The conference began with a keynote speech delivered by Dr. John Mendelsohn (Houston, TX, USA). He enlightened the audience by describing the journey that led to the discovery of Erbitux, a monoclonal antibody against epidermal growth factor receptor (EGFR). Major highlight of Dr. Mendelsohn’s talk was that although this antibody induces apoptosis of EGFR-overexpressing tumor cells in the laboratory, its effect on tumor cells in patients was not mediated through EGFR but through antibody-dependent cell-mediated cytotoxicity. Erbitux when combined with chemotherapeutic agents is effective in some patients with colorectal cancer. Another interesting revelation was that this antibody induces antitumor response in patients that is unrelated to the level of EGFR expression in tumor cells. In a plenary lecture, Dr. Bharat Aggarwal (Houston, TX, USA), explained the connection between inflammation and cancer. A common molecule in these two processes is the tumor necrosis factor (TNF). He pointed out that natural products could serve as good drugs for treatment of both inflammation and cancer. One such product is curcumin, which exhibits a blocking effect on the TNF. Curcumin is being tested in early clinical trials in patients with multiple myeloma, breast cancer, and pancreatic cancer. Dr. S Krishna (Banglore, India) delineated the Notch oncogenic signaling pathway in human epithelial neoplasms. His group has identified deregulated Notch signaling in cervical cancer. The midmorning session began with a speech by Dr. Premkumar Reddy (Philadelphia, PA, USA), who discussed the human kinome. Eucaryotic and atypical protein kinases of the human kinome constitute more than 500 proteins mostly belonging to tyrosine kinases or serine/threonine kinases. Many of these kinases are either mutated, constitutively active, or overexpressed in human cancers. The best example of such an agent is imatinib, the inhibitor of Bcr-Abl tyrosine kinase, he pointed out. Dr. Raj Puri (Bethesda, MD, USA) discussed early laboratory, preclinical, and animal model studies that were conducted with an immunotoxin composed of IL-13 and a mutated form of Pseudomonas exotoxin. These preclinical results were translated into phase I/II investigations in patients with solid tumors. Dr. Kapil Mehta (Houston, TX, USA) discussed the implications of elevated tissue transglutaminase expression in the development of drug resistance and metastatic phenotypes in tumor cells. Cell Death and Differentiation (2006), 1–2 & 2006 Nature Publishing Group All rights reserved 1350-9047/06 $30.00

Normal and deregulated Notch signaling in regulation of hematopoietic stem cells and development of leukemia

Normal and deregulated Notch signaling in regulation of hematopoietic stem cells and development of leukemia

Deregulated NOTCH Signaling in Acute T-Cell Lymphoblastic Leukemia/Lymphoma: New Insights, Questions, and Opportunities

Recent work has shown that the majority of human acute T-cell lymphoblastic leukemias and lymphomas (T-ALL) have gain-of-function mutations in NOTCH1, a type I transmembrane receptor that normally signals through a gamma-secretase-dependent mechanism that relies on ligand-induced regulated intramembranous proteolysis. Cleavage by gamma-secretase releases the intracellular domain of NOTCH1 (ICN1), permitting it to translocate to the nucleus and form a short-lived transcriptional activation complex that is essential for normal T-cell development. Two types of mutations are prevalent in human T-ALL: extracellular domain mutations that increase ICN1 production and C-terminal mutations that sustain ICN1 action. Inhibitors of ICN1 production and activity abrogate the growth of established T-ALL cell lines, and a clinical trial of a NOTCH pathway inhibitor in patients with refractory T-ALL has opened recently. These insights raise a number of new questions relevant to T-ALL pathogenesis and offer exciting opportunities for rational targeted therapy.

Modulation of Notch Signaling Elicits Signature Tumors and Inhibits Hras1-Induced Oncogenesis in the Mouse Mammary Epithelium

Deregulation of Notch signaling, which normally affects a broad spectrum of cell fates, has been implicated in various neoplastic conditions. Here we describe a transgenic mouse model, which demonstrates that expression of a constitutively active form of the Notch1 receptor in the mammary epithelium induces the rapid development of pregnancy/lactation-dependent neoplasms that consistently exhibit a characteristic histopathological pattern. These signature tumors retain the ability to respond to apoptotic stimuli and regress on initiation of mammary gland involution, but eventually appear to progress in subsequent pregnancies to nonregressing malignant adenocarcinomas. Additionally, we present evidence indicating that cyclin D1 is an in vivo target of Notch signals in the mammary glands and demonstrate that we can effectively inhibit Hras1-driven, cyclin D1-dependent mammary oncogenesis by transgenic expression of the Notch antagonist Deltex.

Human papillomavirus type 16 E6 amino acid 83 variants enhance E6-mediated MAPK signaling and differentially regulate tumorigenesis by notch signaling and oncogenic Ras.

Oncogenically high-risk human papillomaviruses (HPVs) are causally associated with the progression of major human neoplasia-like cancers of the cervix. Several studies have defined functions of the key E6 and E7 oncoproteins in epithelial cell immortalization. The roles of these oncogenes in the progression of immortalized epithelial cells to invasive tumors are still poorly understood. Here, we establish a novel link between the E6 oncoprotein and activation of mitogen-activated protein kinase (MAPK) signaling and show that this signaling involves Rap1. We find that activated MAPK signaling cooperates with deregulated Notch1 signaling to recreate features of HPV-driven invasive cervical carcinomas. We extend our analysis to evaluate an E6 (amino acid [aa] 83) variant that has been linked to invasive tumors. The variant enhances MAPK signaling and cooperative transformation with deregulated Notch1 signaling. Unlike E6, this variant surprisingly inhibits oncogenic Ras-mediated transformation. Our data reveal that the quantitative differences in activation of MAPK signaling by E6 and its variant correlate with differences in cooperative transformation with other signaling pathways, thus suggesting that thresholds of MAPK activation may define permissive conditions for other signaling pathways in tumorigenesis. Epidemiological studies have suggested the importance of E6 aa 83 variants in invasive carcinomas; our data support a key deterministic role for this variant in human cervical tumorigenesis. These observations, along with our recent data showing that deregulated Notch signaling activates phosphatidylinositol 3-kinase signaling, strengthen the possibility of the existence of Ras-independent mechanisms to recreate signaling through classical Ras effector pathways.