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1.  Modulating the Strength and Threshold of NOTCH Oncogenic Signals by mir-181a-1/b-1 
PLoS Genetics  2012;8(8):e1002855.
Oncogenes, which are essential for tumor initiation, development, and maintenance, are valuable targets for cancer therapy. However, it remains a challenge to effectively inhibit oncogene activity by targeting their downstream pathways without causing significant toxicity to normal tissues. Here we show that deletion of mir-181a-1/b-1 expression inhibits the development of Notch1 oncogene-induced T cell acute lymphoblastic leukemia (T-ALL). mir-181a-1/b-1 controls the strength and threshold of Notch activity in tumorigenesis in part by dampening multiple negative feedback regulators downstream of NOTCH and pre-T cell receptor (TCR) signaling pathways. Importantly, although Notch oncogenes utilize normal thymic progenitor cell genetic programs for tumor transformation, comparative analyses of mir-181a-1/b-1 function in normal thymocyte and tumor development demonstrate that mir-181a-1/b-1 can be specifically targeted to inhibit tumor development with little toxicity to normal development. Finally, we demonstrate that mir-181a-1/b-1, but not mir-181a-2b-2 and mir-181-c/d, controls the development of normal thymic T cells and leukemia cells. Together, these results illustrate that NOTCH oncogene activity in tumor development can be selectively inhibited by targeting the molecular networks controlled by mir-181a-1/b-1.
Author Summary
Oncogenes elicit driving signals required for tumor initiation, development, and maintenance and are valuable targets for cancer therapy. However, oncogenes often have essential functions in normal cellular physiology and produce intracellular proteins that are difficult to inhibit with small molecule drugs without causing significant toxicity to normal tissues. Thus, one of the challenges in cancer therapy is to identify downstream networks that can be targeted to specifically dampen the oncogenic signals in tumor cells without harming normal tissues. In this study we demonstrate that deletion of a microRNA (miRNA) gene, mir-181a-1/b-1, specifically inhibits the activity of the Notch oncogene in tumorigenesis without causing significant defects in normal development. Although earlier studies have elegantly shown the essential role of NOTCH and pre-TCR signals in NOTCH-induced tumorigenesis, neither NOTCH nor pre-TCR signals can be targeted effectively for treatment of T-ALL with available drugs due to their weak therapeutic effects and severe toxicities. Our findings illustrate that dissecting the downstream targets of miRNAs can reveal the molecular networks that can be targeted to control tumor transformation caused by oncogenes. More importantly, our results illustrate that comparative studies on the pathways utilized by normal cells and tumor cells may reveal novel insights into how tumorigenic pathways may be selectively inhibited with limited damage to normal tissues.
doi:10.1371/journal.pgen.1002855
PMCID: PMC3415433  PMID: 22916024
2.  A critical role for TCF-1 in T-lineage specification and differentiation 
Nature  2011;476(7358):63-68.
The vertebrate thymus provides an inductive environment for T-cell development. Within the thymus, Notch signals are indispensable for imposing the T-cell fate on multipotential hematopoietic progenitors, but the downstream effectors that impart T-lineage specification and commitment are not well understood. Here we show that transcription factor, T-cell factor 1 (TCF-1), is a critical regulator in T-cell specification. TCF-1 is highly expressed in the earliest thymic progenitors, and its expression is upregulated by Notch signals. Most importantly, when TCF-1 is forcibly expressed in BM progenitors, it drives the development of T-lineage cells in the absence of T-inductive Notch1 signals. Further characterization of these TCF-1-induced cells revealed expression of many T-lineage genes, including T-cell specific transcription factors Gata3, Bcl11b, and components of the T-cell receptor. Our data suggest a model where Notch signals induce TCF-1, and TCF-1 in turn imprints the T-cell fate by upregulating expression of T-cell essential genes.
doi:10.1038/nature10279
PMCID: PMC3156435  PMID: 21814277
3.  NOTCH1 and NOTCH3 coordinate esophageal squamous differentiation through a CSL-dependent transcriptional network 
Gastroenterology  2010;139(6):2113-2123.
Background & Aims
The Notch receptor family regulates cell fate through cell-cell communication. CSL (CBF-1/RBP-jκ, Su(H), Lag-1) drives canonical Notch-mediated gene transcription during cell lineage specification, differentiation and proliferation in the hematopoietic system, the intestine, the pancreas and the skin. However, the functional roles of Notch in esophageal squamous epithelial biology remain unknown.
Methods
Normal esophageal keratinocytes were stimulated with calcium chloride to induce terminal differentiation. The squamous epithelia were reconstituted in organotypic three-dimensional culture, a form of human tissue engineering. Notch was inhibited in culture with a γ-secretase inhibitor or dominant negative mastermind-like1 (DNMAML1). The roles of Notch receptors were evaluated by in vitro gain-of-function and loss-of-function experiments. Additionally, DNMAML1 was targeted to the mouse esophagus by cytokeratin K14 promoter-driven Cre (K14Cre) recombination of Lox-STOP-Lox-DNMAML1. Notch-regulated gene expression was determined by reporter transfection, chromatin immunoprecipitation (ChIP) assays, quantitative reverse-transcription polymerase chain reactions (RT-PCR), Western blotting, immunofluorescence and immunohistochemistry.
Results
NOTCH1 (N1) was activated at the onset of squamous differentiation in the esophagus. Intracellular domain of N1 (ICN1) directly activated NOTCH3 (N3) transcription, inducing HES5 and early differentiation markers such as involucrin (IVL) and cytokeratin CK13 in a CSL-dependent fashion. N3 enhanced ICN1 activity and was required for squamous differentiation. Loss of Notch signaling in K14Cre;DNMAML1 mice perturbed esophageal squamous differentiation and resulted in N3 loss and basal cell hyperplasia.
Conclusions
Notch signaling is important for esophageal epithelial homeostasis. In particular, the crosstalk of N3 with N1 during differentiation provides novel, mechanistic insights into Notch signaling and squamous epithelial biology.
doi:10.1053/j.gastro.2010.08.040
PMCID: PMC2997138  PMID: 20801121
NOTCH1; NOTCH3; esophageal epithelium; squamous differentiation
4.  Active Notch1 Confers a Transformed Phenotype to Primary Human Melanocytes 
Cancer research  2009;69(13):5312-5320.
The importance of MAPK signaling in melanoma is underscored by the prevalence of activating mutations in N-Ras and B-Raf; yet, clinical development of inhibitors of this pathway has been largely ineffective, suggesting that alternative oncogenes may also promote melanoma. Notch is an interesting candidate that has only been correlated with melanoma development and progression; a thorough assessment of tumor-initiating effects of activated Notch on human melanocytes would clarify the mounting correlative evidence and perhaps identify a novel target for an otherwise untreatable disease. Analysis of a substantial panel of cell lines and patient lesions demonstrated that Notch activity is significantly higher in melanomas than their non-transformed counterparts. The use of a constitutively-active, truncated Notch transgene construct (NIC) was exploited to determine if Notch activation is a ‘driving’ event in melanocytic transformation or instead a ‘passenger’ event associated with melanoma progression. NIC-infected melanocytes displayed increased proliferative capacity and biological features more reminiscent of melanoma such as dysregulated cell adhesion and migration. Gene expression analyses supported these observations and aided in the identification of MCAM, an adhesion molecule associated with acquisition of the malignant phenotype, as a direct target of Notch transactivation. NIC-positive melanocytes grew at clonal density, proliferated in limiting media conditions, and also exhibited anchorage-independent growth suggesting that Notch, alone, is a transforming oncogene in human melanocytes, a phenomenon not previously described for any melanoma oncogene; this new information yields valuable insight into the basic epidemiology of melanoma and launches a realm of possibilities for drug intervention in this deadly disease.
doi:10.1158/0008-5472.CAN-08-3767
PMCID: PMC2755513  PMID: 19549918
Notch; melanoma; transformation; MCAM; therapy
5.  Notch Directly Regulates Gata3 Expression during T Helper 2 Cell Differentiation 
Immunity  2007;27(1):100-110.
SUMMARY
Notch signaling plays multiple roles to direct diverse decisions regarding cell fate during T cell development. During helper T (Th) cell differentiation, Notch is involved in generating optimal Th2 cell responses. Here, we present data investigating how Notch mediates Th2 cell differentiation. Notch showed a CD4+ T cell intrinsic role in promoting IL-4 expression that required GATA-3. In the absence of Notch signals, Gata3 expression was markedly diminished. Introduction of an activated allele of Notch1 into CD4+ T cells led to the specific and direct upregulation of a developmentally regulated Gata3 transcript that included the exon 1a sequences. Furthermore, Notch acted in parallel with GATA-3 to synergistically activate IL-4 expression. Together, these data implicate Gata3 as a direct transcriptional Notch target that acts in concert with Notch signaling to generate optimal Th2 cell responses.
doi:10.1016/j.immuni.2007.04.018
PMCID: PMC2801546  PMID: 17658278
6.  The requirement for Notch signaling at the β-selection checkpoint in vivo is absolute and independent of the pre–T cell receptor 
The Journal of Experimental Medicine  2006;203(10):2239-2245.
Genetic inactivation of Notch signaling in CD4−CD8− double-negative (DN) thymocytes was previously shown to impair T cell receptor (TCR) gene rearrangement and to cause a partial block in CD4+CD8+ double-positive (DP) thymocyte development in mice. In contrast, in vitro cultures suggested that Notch was absolutely required for the generation of DP thymocytes independent of pre-TCR expression and activity. To resolve the respective role of Notch and the pre-TCR, we inhibited Notch-mediated transcriptional activation in vivo with a green fluorescent protein–tagged dominant-negative Mastermind-like 1 (DNMAML) that allowed us to track single cells incapable of Notch signaling. DNMAML expression in DN cells led to decreased production of DP thymocytes but only to a modest decrease in intracellular TCRβ expression. DNMAML attenuated the pre-TCR–associated increase in cell size and CD27 expression. TCRβ or TCRαβ transgenes failed to rescue DNMAML-related defects. Intrathymic injections of DNMAML− or DNMAML+ DN thymocytes revealed a complete DN/DP transition block, with production of DNMAML+ DP thymocytes only from cells undergoing late Notch inactivation. These findings indicate that the Notch requirement during the β-selection checkpoint in vivo is absolute and independent of the pre-TCR, and it depends on transcriptional activation by Notch via the CSL/RBP-J–MAML complex.
doi:10.1084/jem.20061020
PMCID: PMC2118105  PMID: 16966428

Results 1-6 (6)