Upregulation Of Notch1 Expression Research Articles

Unidirectional and stage-dependent roles of Notch1 in Wnt-responsive Lgr5+ cells during mouse inner ear development.

Wnt and Notch signaling play crucial roles in the determination of the prosensory domain and in the differentiation of hair cells (HCs) and supporting cells during mouse inner ear development; however, the relationship between the two signaling pathways in the mouse cochlea remains largely unknown. Here, we investigated the interactions between Notch and Wnt signaling on the basis of the bidirectional regulation of Notch1 specifically in Wnt-responsive Lgr5+ progenitors during different cochlear development stages. We found that the downregulation of Notch1 in Lgr5+ cells from embryonic day (E) 14.5 to E18.5 can drive the quiescent Lgr5+ cells to re-enter the cell cycle and differentiate into extra HCs, whereas the upregulation of Notch1 expression did not affect the proliferation or differentiation of otic progenitor cells. No effect was observed on the upregulation or downregulation of Notch1 in Lgr5+ cells from E10.5 to E14.5. We concluded that the roles of Notch1 in Wnt-responsive Lgr5+ cells are unidirectional and stage dependent and Notch1 serves as a negative regulator for Lgr5+ progenitor activation during cochlear differentiation. Our findings improved the understanding of the interactions between Notch and Wnt signaling in cochlear development.

Electroacupuncture promotes neural stem cell proliferation and neurogenesis in the dentate gyrus of rats following stroke via upregulation of Notch1 expression.

Neural stem cells (NSCs) are important in rehabilitation following stroke. Electroacupuncture (EA) treatment has been observed to promote the recovery of neurological functions subsequent to stroke, however, the effects of EA on the proliferation and differentiation of NSCs and its potential mechanisms remain to be elucidated. In the present study, rats, in which a stroke was induced through middle cerebral artery occlusion (MCAO), were treated with EA or control manipulation for 21 days. The modified Neurological Severity score and Morris water maze tests were used to assess the neurological functions of the rats. Bromodeoxyuridine (BrdU)/glial fibrillary acidic protein (GFAP) or BrdU/neuronal marker (NeuN) double immunofluorescence staining were used to examine the proliferation and differentiation of the NSCs. Reverse transcription quantitative polymerase chain reaction (RT‑qPCR) and western blot analyses were performed to detect the expression levels of Notch1 and Hes1 in the dentate gyrus (DG) of the hippocampus of rats following MCAO. The results demonstrated that EA treatment significantly improved the neurological functional recovery of rats following stroke. A significant increase was observed in the number of BrdU+/GAFP+ and BrdU+/NeuN+ cells in the DG area in the EA‑treated rats compared with that of the control group. RT‑qPCR analysis revealed that EA treatment significantly increased the expression levels of Notch1 and Hes1, which may account for the enhanced proliferation and differentiation of NSCs. In conclusion, to the best of our knowledge, the present study was the first to demonstrate that EA treatment promoted NSC proliferation and neurogenesis in the DG area through the upregulation of Notch signaling following a stroke; therefore, EA may be a useful novel therapeutic strategy in future stroke treatment.

Simvastatin induces growth inhibition and apoptosis in HepG2 and Huh7 hepatocellular carcinoma cells via upregulation of Notch1 expression.

Statins, cholesterol‑lowering drugs, are one of the most commonly prescribed types of medications. Previous studies have suggested that simvastatin may inhibit the cell function and tumor growth of hepatocellular carcinoma (HCC) cells; however, the molecular mechanisms underlying simvastatin‑induced apoptosis in HCC cells remains to be elucidated. The aim of the present study was to investigate the role of simvastatin in the regulation of cell viability, proliferation and apoptosis in HepG2 and Huh7 HCC cells, and to elucidate the specific regulatory mechanisms by which simvastatin proceeds. MTT, trypan blue and flow cytometric analyses were performed in order to detect viability, proliferation and apoptosis in HepG2 and Huh7 cells. The results of the present study demonstrated that simvastatin significantly decreased cell viability and proliferation as well as increased apoptosis in HepG2 and Huh7 cells compared to that in untreated cells. In addition, reverse transcription quantitative polymerase chain reaction and western blot analysis revealed that simvastatin‑treated cells exhibited increased expression levles of Notch1, p53, and Bax, as well as decreased expression levels of B cell lymphoma 2; furthermore, Notch1 upregulation resulted in the inhibition of Akt phosphorylation. In conclusion, the results of the present study indicated that simvastatin significantly promoted apoptosis in HCC cells, the mechanism of which may have proceeded via the upregualtion of the Notch1 gene in the Akt‑dependent signaling pathway.

Suppression of the mTORC1/STAT3/Notch1 pathway by activated AMPK prevents hepatic insulin resistance induced by excess amino acids

Nutrient overload is associated with the development of obesity, insulin resistance, and type 2 diabetes. However, the underlying mechanisms for developing insulin resistance in the presence of excess nutrients are incompletely understood. We investigated whether activation of AMP-activated protein kinase (AMPK) prevents the hepatic insulin resistance that is induced by the consumption of a high-protein diet (HPD) and the presence of excess amino acids. Exposure of HepG2 cells to excess amino acids reduced AMPK phosphorylation, upregulated Notch1 expression, and impaired the insulin-stimulated phosphorylation of Akt Ser(473) and insulin receptor substrate-1 (IRS-1) Tyr(612). Inhibition of Notch1 prevented amino acid-induced insulin resistance, which was accompanied by reduced expression of Rbp-Jk, hairy and enhancer of split-1, and forkhead box O1. Mechanistically, mTORC1 signaling was activated by excess amino acids, which then positively regulated Notch1 expression through the activation of the signal transducer and activator of transcription 3 (STAT3). Activation of AMPK by metformin inhibited mTORC1-STAT3 signaling, thereby preventing excess amino acid-impaired insulin signaling. Finally, HPD feeding suppressed AMPK activity, activated mTORC1/STAT3/Notch1 signaling, and induced insulin resistance. Chronic administration of either metformin or rapamycin inhibited the HPD-activated mTORC1/STAT3/Notch1 signaling pathway and prevented hepatic insulin resistance. We conclude that the upregulation of Notch1 expression by hyperactive mTORC1 signaling is an essential event in the development of hepatic insulin resistance in the presence of excess amino acids. Activation of AMPK prevents amino acid-induced insulin resistance through the suppression of the mTORC1/STAT3/Notch1 signaling pathway.

Abstract 618: Anti-tumor effects of Notch pathway activation in Gastrointestinal Stromal Tumors cells

Abstract Gastrointestinal Stromal Tumors (GISTs) are the most common sarcomas of the GI tract and harbor a gain-of-function mutation of the KIT receptor tyrosine kinase. The introduction of imatinib, a specific inhibitor of KIT, has significantly extended survival of many GIST patients. Unfortunately, patients inevitably develop resistance, prompting interest in understanding GIST biology and developing new therapeutic options. Notch signaling may act as an oncogene or a tumor suppressor depending cellular context. In neuroendocrine tumors Notch signaling acts constantly as a tumor suppressor. Additionally, histone deacetylase inhibitors (HDACi) were recently shown to induce Notch signaling in neuroendocrine neoplasms. Given that GIST is of neuroectodermal origin, we hypothesized that inhibition of growth in GIST cells by HDAC inhibitors is mediated by activation of Notch signaling. To characterize Notch signaling in GIST, we assessed the expression of Notch-1, and its effector human hairy enhancer of split-1 (HES1) in human GIST cell lines (GIST-T1 and GIST 882) by quantitative RT-PCR. To determine the activity of Notch signaling in GIST, we assayed the effect of Notch activation in GIST cells by transduction with retroviral vectors to overexpress active forms of Notch1 and HES1 in GIST cells. The proportion of GFP-positive cells in unselected culture was assessed to determine the transgene's effect on cell growth. To study the effect of HDAC inhibition, we quantified viability, caspase activity, cell cycle analysis and expression of Notch pathway genes after HDAC inhibition with suberoylanilide hydroxamic acid (SAHA). Notch signaling genes (Notch1, HES1) were weakly expressed at the basal level in cells compared to other sarcomas. Notch signaling with a constitutively active, truncated form of the receptor (ICN-1) and HES1 potently induced growth arrest in GIST cell lines. The proportion of ICN-1 GFP+ cells dramatically declined after transduction compared to GFP- cells, (decrease of 69% at day 7 and 78% at day 9 after transduction). Vector empty-transduced GFP+ cells gave no change in the proportion of positive cells. SAHA caused dose dependent decrease in viability, activation of caspase 3 and 7, increase of sub-G1 population (6 fold increase at 1µM, p<0.01), as well as upregulation of Notch-1 expression (5 fold at 1µM, p<0.01). Retroviral silencing of downstream targets of Notch (dnHes-1 and dnMastermind [dnMAM]) partially rescued GIST-T1 cells from the inhibitory effects of SAHA (61% v 105%, p<0.05 for dnHes-1 and 61 v 87%, p<0.01 for dnMAM after 2 days of treatment with SAHA 0.6 µM). These results suggest that Notch signaling is a tumor suppressor in GIST cells and the activation of Notch signaling by HDAC inhibitors may represent a new strategy for treating GIST patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 618. doi:10.1158/1538-7445.AM2011-618

ΔNp63α Repression of the Notch1 Gene Supports the Proliferative Capacity of Normal Human Keratinocytes and Cervical Cancer Cells

The p53 family member p63 is a master regulator of epithelial development. One of its isoforms, DeltaNp63alpha, is predominantly expressed in the basal cells of stratified epithelia and plays a fundamental role in control of regenerative potential and epithelial integrity. In contrast to p53, p63 is rarely mutated in human cancers, but it is frequently overexpressed in squamous cell carcinomas (SCC). However, its functional relevance to tumorigenesis remains largely unclear. We previously identified the Notch1 gene as a novel transcriptional target of p53. Here, we show that DeltaNp63alpha functions as a transcriptional repressor of the Notch1 gene through the p53-responsive element. Knockdown of p63 caused upregulation of Notch1 expression and marked reduction in proliferation and clonogenicity of both normal human keratinocytes and cervical cancer cell lines overexpressing DeltaNp63alpha. Concomitant silencing of Notch1 significantly rescued this phenotype, indicating the growth defect induced by p63 deficiency to be, at least in part, attributable to Notch1 function. Conversely, overexpression of DeltaNp63alpha decreased basal levels of Notch1, increased proliferative potential of normal human keratinocytes, and inhibited both p53-dependent and p53-independent induction of Notch1 and differentiation markers upon genotoxic stress and serum exposure, respectively. These results suggest that DeltaNp63alpha maintains the self-renewing capacity of normal human keratinocytes and cervical cancer cells partly through transcriptional repression of the Notch1 gene and imply a novel pathogenetical significance of frequently observed overexpression of DeltaNp63alpha together with p53 inactivation in SCCs.

Potential role of Notch1 signaling pathway in laryngeal squamous cell carcinoma cell line Hep-2 involving proliferation inhibition, cell cycle arrest, cell apoptosis, and cell migration

Head and neck cancer is the sixth most common cancer worldwide and laryngeal cancer represents the largest subgroup. However, the molecular mechanism underlying its malignant behavior and progression is not clarified. Accumulating evidence has shown that Notch1 signaling pathway plays a central role in carcinogenesis, but its potential role in regulating the development of laryngeal carcinoma, has not been characterized. Here, we identified that Notch1 signaling pathway was activated in laryngeal carcinoma accompanied with up-regulation of Notch1 and Hes1 expression. Overexpression of Notch1 in laryngeal carcinoma cell line Hep-2 led to suppression of tumor cellular proliferation and arrested cell cycle in the G0/G1 phase and induced cell apoptosis, which were coupled with the down-regulation of cyclin D1, cyclin E, cdk2 and bcl-2 and up-regulation of caspase-3, caspase-9 and p53. Most importantly, up-regulation of Notch1 expression also reduced the migration of Hep-2 cells, which was closely associated with down-regulation of MMP-2 and MMP-9. The finding may lay a foundation for further investigations into the Notch1 signaling pathway as a potential target for laryngeal carcinoma.

Evidence for the notch signaling pathway on the role of estrogen in angiogenesis.

We have investigated the molecular mechanisms involved in 17 beta-estradiol-induced angiogenic pathway. We show here that 17 beta-estradiol promoted a 6-fold increase in Jagged1 expression and an 8-fold increase in Notch1 expression by cDNA arrays in breast cancer MCF7 cells. Interestingly, Jagged1 was abrogated by incubation with the estrogen antagonist, ICI182,780. A similar up-regulation of both Notch1 receptor and Jagged1 ligand was found in endothelial cells. Additionally, imperfect estrogen-responsive elements were found in the 5' untranslated region of Notch1 and Jagged1 genes. Treatment with 17 beta-estradiol also led to an activation of Notch signaling in MCF7 cells expressing Notch1 reporter gene or by promoting Jagged1-induced Notch signaling in coculture assays. Inoculation of MCF7 cells in 17 beta-estradiol-treated nude mice resulted in up-regulation of Notch1 expression as well as increased number of tumor microvessels in comparison to placebo-treated mice. Notch1-expressing endothelial cell cultures formed cord-like structures on Matrigel in contrast to cells expressing a dominant-negative form of Notch1, emphasizing the relevance of Notch1 pathway in vessel assembly. Finally, Notch1-expressing MCF7 cells up-regulated hypoxia-inducible factor 1 alpha gene, a well-known angiogenic factor that clustered with Notch1 gene. This study implicates Notch signaling in the cross talk between 17 beta-estradiol and angiogenesis.