HERP1 is a cell type-specific primary target of Notch

Multifaceted analysis of noncoding and coding de novo variants implicates NOTCH signaling pathway in tetralogy of Fallot in Chinese population

Tetralogy of Fallot (TOF) is the most common cyanotic heart defect in neonates. While there is compelling evidence of genetic contribution to the etiology of TOF, the contribution of noncoding variants to the development of the defect remains unexplored. Potentially damaging noncoding de novo variants (NC DNVs) were detected from 141 Chinese nonsyndromic TOF trios (CHN-TOF) and compared with those detected in the Pediatric Cardiac Genomics Consortium (PCGC). Bioinformatic analyses on noncoding and previously detected coding DNVs were performed to identify developmental pathways affected in TOF. Chinese but not PCGC-TOF patients showed a notably increased burden of putative damaging NC DNVs (n = 249). In Chinese, NC and coding DNVs were predominantly associated with cardiomyocyte differentiation and with chamber/valve/aorta development, respectively, producing a combined enrichment in NOTCH signaling (p = 1.1 × 10-6) and outflow tract morphogenesis (p = 2.2 × 10-5). Genes with NC DNVs (e.g., EFNB2, HEY2, and PITX2) interacted with NOTCH1 and FLT4 in a tight STRING protein-protein interaction (PPI) network. During the in vitro cardiac differentiation process, these noncoding candidate genes, which harbored potentially damaging regulatory NC DNVs, exhibited co-expression with NOTCH signaling genes and demonstrated dysregulated gene expression at various differentiation stages following NOTCH1 downregulation. In summary, our findings highlight a significant contribution of NC DNVs to TOF and suggest the presence of population genetic heterogeneity. Integrative analyses implicate dysregulation of NOTCH signaling, with converging influences from both coding and noncoding variants, in TOF within the Chinese population.

Heuristic shortest hyperpaths in cell signaling hypergraphs

BACKGROUND

Cell signaling pathways, which are a series of reactions that start at receptors and end at transcription factors, are basic to systems biology. Properly modeling the reactions in such pathways requires directed hypergraphs, where an edge is now directed between two sets of vertices. Inferring a pathway by the most parsimonious series of reactions corresponds to finding a shortest hyperpath in a directed hypergraph, which is NP-complete. The current state-of-the-art for shortest hyperpaths in cell signaling hypergraphs solves a mixed-integer linear program to find an optimal hyperpath that is restricted to be acyclic, and offers no efficiency guarantees.

RESULTS

We present, for the first time, a heuristic for general shortest hyperpaths that properly handles cycles, and is guaranteed to be efficient. We show the heuristic finds provably optimal hyperpaths for the class of singleton-tail hypergraphs, and also give a practical algorithm for tractably generating all source-sink hyperpaths. The accuracy of the heuristic is demonstrated through comprehensive experiments on all source-sink instances from the standard NCI-PID and Reactome pathway databases, which show it finds a hyperpath that matches the state-of-the-art mixed-integer linear program on over 99% of all instances that are acyclic. On instances where only cyclic hyperpaths exist, the heuristic surpasses the state-of-the-art, which finds no solution; on every such cyclic instance, enumerating all source-sink hyperpaths shows the solution found by the heuristic was in fact optimal.

CONCLUSIONS

The new shortest hyperpath heuristic is both fast and accurate. This makes finding source-sink hyperpaths, which in general may contain cycles, now practical for real cell signaling networks.

AVAILABILITY

Source code for the hyperpath heuristic in a new tool we call Hhugin (as well as for hyperpath enumeration, and all dataset instances) is available free for non-commercial use at http://hhugin.cs.arizona.edu.

Dissecting Tumor Growth: The Role of Cancer Stem Cells in Drug Resistance and Recurrence

Simple Summary

Cancer is one of the most debated problems all over the world. Cancer stem cells are considered responsible of tumor initiation, metastasis, drug resistance, and recurrence. This subpopulation of cells has been found into the tumor bulk and showed the capacity to self-renew, differentiate, up to generate a new tumor. In the last decades, several studies have been set on the molecular mechanisms behind their specific characteristics as the Wnt/β-catenin signaling, Notch signaling, Hedgehog signaling, transcription factors, etc. The most powerful part of CSCs is represented by the niches as “promoter” of their self-renewal and “protector” from the common oncological treatment as chemotherapy and radiotherapy. In our review article we highlighted the primary mechanisms involved in CSC tumorigenesis for the setting of further targets to control the metastatic process.

Abstract

Emerging evidence suggests that a small subpopulation of cancer stem cells (CSCs) is responsible for initiation, progression, and metastasis cascade in tumors. CSCs share characteristics with normal stem cells, i.e., self-renewal and differentiation potential, suggesting that they can drive cancer progression. Consequently, targeting CSCs to prevent tumor growth or regrowth might offer a chance to lead the fight against cancer. CSCs create their niche, a specific area within tissue with a unique microenvironment that sustains their vital functions. Interactions between CSCs and their niches play a critical role in regulating CSCs’ self-renewal and tumorigenesis. Differences observed in the frequency of CSCs, due to the phenotypic plasticity of many cancer cells, remain a challenge in cancer therapeutics, since CSCs can modulate their transcriptional activities into a more stem-like state to protect themselves from destruction. This plasticity represents an essential step for future therapeutic approaches. Regarding self-renewal, CSCs are modulated by the same molecular pathways found in normal stem cells, such as Wnt/β-catenin signaling, Notch signaling, and Hedgehog signaling. Another key characteristic of CSCs is their resistance to standard chemotherapy and radiotherapy treatments, due to their capacity to rest in a quiescent state. This review will analyze the primary mechanisms involved in CSC tumorigenesis, with particular attention to the roles of CSCs in tumor progression in benign and malignant diseases; and will examine future perspectives on the identification of new markers to better control tumorigenesis, as well as dissecting the metastasis process.

PIF7 controls leaf cell proliferation through an AN3 substitution repression mechanism

Phytochrome photoreceptors can markedly alter leaf blade growth in response to far-red (FR) rich neighbor shade, yet we have a limited understanding of how this is accomplished. This study identifies ANGUSTIFOLIA3 (AN3) as a central component in phytochrome promotion of leaf cell proliferation and PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) as a potent repressor. AN3 and PIF7 impose opposing regulation on a shared suite of genes through common cis-acting promoter elements. In response to FR light, activated PIF7 blocks AN3 action by evicting and substituting for AN3 at target promoters. This molecular switch module provides a mechanism through which changes in external light quality can dynamically manipulate gene expression, cell division, and leaf size.

Plants are agile, plastic organisms able to adapt to everchanging circumstances. Responding to far-red (FR) wavelengths from nearby vegetation, shade-intolerant species elicit the adaptive shade-avoidance syndrome (SAS), characterized by elongated petioles, leaf hyponasty, and smaller leaves. We utilized end-of-day FR (EODFR) treatments to interrogate molecular processes that underlie the SAS leaf response. Genetic analysis established that PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) is required for EODFR-mediated constraint of leaf blade cell division, while EODFR messenger RNA sequencing data identified ANGUSTIFOLIA3 (AN3) as a potential PIF7 target. We show that PIF7 can suppress AN3 transcription by directly interacting with and sequestering AN3. We also establish that PIF7 and AN3 impose antagonistic control of gene expression via common cis-acting promoter motifs in several cell-cycle regulator genes. EODFR triggers the molecular substitution of AN3 to PIF7 at G-box/PBE-box promoter regions and a switch from promotion to repression of gene expression.

Mechanisms of Binding Specificity among bHLH Transcription Factors

The transcriptome of every cell is orchestrated by the complex network of interaction between transcription factors (TFs) and their binding sites on DNA. Disruption of this network can result in many forms of organism malfunction but also can be the substrate of positive natural selection. However, understanding the specific determinants of each of these individual TF-DNA interactions is a challenging task as it requires integrating the multiple possible mechanisms by which a given TF ends up interacting with a specific genomic region. These mechanisms include DNA motif preferences, which can be determined by nucleotide sequence but also by DNA’s shape; post-translational modifications of the TF, such as phosphorylation; and dimerization partners and co-factors, which can mediate multiple forms of direct or indirect cooperative binding. Binding can also be affected by epigenetic modifications of putative target regions, including DNA methylation and nucleosome occupancy. In this review, we describe how all these mechanisms have a role and crosstalk in one specific family of TFs, the basic helix-loop-helix (bHLH), with a very conserved DNA binding domain and a similar DNA preferred motif, the E-box. Here, we compile and discuss a rich catalog of strategies used by bHLH to acquire TF-specific genome-wide landscapes of binding sites.

A Molecular Test for Quantifying Functional Notch Signaling Pathway Activity in Human Cancer

Simple Summary

The Notch signal transduction pathway is important for various physiological processes, including immune responses, and plays a role in many diseases, for example cancer. We have developed a new assay to quantitatively measure Notch pathway activity, and we validated it using data from various human cancer cell lines. The assay can be applied across different cell types, and offers numerous possibilities to explore the contribution of the Notch pathway to tumor formation and the stratification of cancer patients. We assessed Notch pathway activity in a cohort of T cell acute lymphoblastic leukemia (T-ALL) patient samples, and found that the pathway activity score more accurately reflects Notch pathway activity than a prediction on the basis of NOTCH1 mutations alone. Finally, we found that patients with low Notch pathway activity had a significantly shorter event-free survival compared to patients who had T-ALL cells with higher activity.

Abstract

Background: The Notch signal transduction pathway is pivotal for various physiological processes, including immune responses, and has been implicated in the pathogenesis of many diseases. The effectiveness of various targeted Notch pathway inhibitors may vary due to variabilities in Notch pathway activity among individual patients. The quantitative measurement of Notch pathway activity is therefore essential to identify patients who could benefit from targeted treatment. Methods: We here describe a new assay that infers a quantitative Notch pathway activity score from the mRNA levels of generally conserved direct NOTCH target genes. Following the calibration and biological validation of our Notch pathway activity model over a wide spectrum of human cancer types, we assessed Notch pathway activity in a cohort of T-ALL patient samples and related it to biological and clinical parameters, including outcome. Results: We developed an assay using 18 select direct target genes and high-grade serous ovarian cancer for calibration. For validation, seven independent human datasets (mostly cancer series) were used to quantify Notch activity in agreement with expectations. For T-ALL, the median Notch pathway activity was highest for samples with strong NOTCH1-activating mutations, and T-ALL patients of the TLX subtype generally had the highest levels of Notch pathway activity. We observed a significant relationship between ICN1 levels and the absence/presence of NOTCH1-activating mutations with Notch pathway activity scores. Patients with the lowest Notch activity scores had the shortest event-free survival compared to other patients. Conclusions: High Notch pathway activity was not limited to T-ALL samples harboring strong NOTCH1 mutations, including juxtamembrane domain mutations or hetero-dimerization combined with PEST-domain or FBXW7 mutations, indicating that additional mechanisms may activate Notch signaling. The measured Notch pathway activity was related to intracellular NOTCH levels, indicating that the pathway activity score more accurately reflects Notch pathway activity than when it is predicted on the basis of NOTCH1 mutations. Importantly, patients with low Notch pathway activity had a significantly shorter event-free survival compared to patients showing higher activity.

Notch3 signalling and vascular remodelling in pulmonary arterial hypertension

Notch signalling is critically involved in vascular morphogenesis and function. Four Notch isoforms (Notch1–4) regulating diverse cellular processes have been identified. Of these, Notch3 is expressed almost exclusively in vascular smooth muscle cells (VSMCs), where it is critically involved in vascular development and differentiation. Under pathological conditions, Notch3 regulates VSMC switching between the contractile and synthetic phenotypes. Abnormal Notch3 signalling plays an important role in vascular remodelling, a hallmark of several cardiovascular diseases, including pulmonary arterial hypertension (PAH). Because of the importance of Notch3 in VSMC (de)differentiation, Notch3 has been implicated in the pathophysiology of pulmonary vascular remodelling in PAH. Here we review the current literature on the role of Notch in VSMC function with a focus on Notch3 signalling in pulmonary artery VSMCs, and discuss potential implications in pulmonary artery remodelling in PAH.

IMPAD1 functions as mitochondrial electron transport inhibitor that prevents ROS production and promotes lung cancer metastasis through the AMPK-Notch1-HEY1 pathway

The tumor microenvironment (TME) and metabolic reprogramming have been implicated in cancer development and progression. However, the link between TME, metabolism, and cancer progression in lung cancer is unclear. In the present study, we identified IMPAD1 from the conditioned medium of highly invasive CL1-5. High expression of IMPAD1 was associated with a poorer clinical phenotype in lung cancer patients, with reduced survival and increased lymph node metastasis. Knockdown of IMPAD1 significantly inhibited migration/invasion abilities and metastasis in vitro and in vivo. Upregulation of IMPAD1 and subsequent accumulation of AMP in cells increased the pAMPK, leading to Notch1 and HEY1 upregulation. As AMP is an ADORA1 agonist, treatment with ADORA1 inhibitor reduced the expression of pAMPK and HEY1 expression in IMPAD1-overexpressing cells. IMPAD1 caused mitochondria dysfunction by inhibiting mitochondrial Complex I activity, which reduced mitochondrial ROS levels and activated the AMPK-HEY1 pathway. Collectively this study supports the multipotent role of IMPAD1 in promotion of lung cancer metastasis by simultaneously increasing AMP levels, inhibition of Complex I activity to decrease ROS levels, thereby activating AMPK-Notch1-HEY1 signaling, and providing an alternative metabolic pathway in energy stress conditions.

The NOTCH1-HEY1 pathway regulates self-renewal and epithelial-mesenchymal transition of salivary adenoid cystic carcinoma cells

Our previous study demonstrated a close relationship between the NOTCH signaling pathway and salivary adenoid cystic carcinoma (SACC). Its receptor gene, NOTCH1, and its downstream gene, HES1, contribute to the proliferation, invasion and metastasis of SACC. Accumulating evidence supports HEY1 as another effector of the signaling pathway. The purpose of this study was to explore the effects of the NOTCH1-HEY1 pathway on the proliferation, invasion and metastasis of SACC cells. Our results verified that HEY1 is a specific molecular target of the NOTCH signaling pathway in SACC cells and that its expression in carcinoma is much higher than that in paracarcinoma tissues. The expression of NOTCH1 and HEY1 are positively correlated in the salivary adenoid cystic carcinoma tissues. NOTCH1 is significantly related to the activation of HEY1 in SACC, and that HEY1 reciprocally regulates NOTCH1 expression in SACC. HEY1 promotes cell proliferation and spheroid formation and inhibits cell apoptosis in vitro. In addition, HEY1 enhances the tumorigenicity of SACC in vivo. Furthermore, HEY1 increases cell invasion and metastasis by driving the expression of epithelial-mesenchymal transition (EMT)-related genes and MMPs. The results of this study indicate that the NOTCH1-HEY1 pathway is specifically upregulated in SACC and promotes cell proliferation, self-renewal, invasion, metastasis and the expression of EMT-related genes and MMPs. Our findings suggest that a NOTCH1-HEY1 pathway inhibitor might therefore have potential therapeutic applications in treating SACC patients by inhibiting cancer cell growth and metastasis.

Neural stem cell quiescence and stemness are molecularly distinct outputs of the Notch3 signalling cascade in the vertebrate adult brain

Neural stem cells (NSCs) in the adult vertebrate brain are found in a quiescent state and can preserve long-lasting progenitor potential (stemness). Whether and how these two properties are linked, and to what extent they can be independently controlled by NSC maintenance pathways, is unresolved. We have previously identified Notch3 signalling as a major quiescence-promoting pathway in adult NSCs of the zebrafish pallium. We now show that Notch3 also controls NSC stemness. Using parallel transcriptomic characterizations of notch3 mutant NSCs and adult NSC physiological states, we demonstrate that a set of potentially direct Notch3 target genes distinguishes quiescence and stemness control. As a proof of principle, we focus on one 'stemness' target, encoding the bHLH transcription factor Hey1, that has not yet been analysed in adult NSCs. We show that abrogation of Hey1 function in adult pallial NSCs in vivo, including quiescent NSCs, leads to their differentiation without affecting their proliferation state. These results demonstrate that quiescence and stemness are molecularly distinct outputs of Notch3 signalling, and identify Hey1 as a major Notch3 effector controlling NSC stemness in the vertebrate adult brain.

HEY2, a target of miR-137, indicates poor outcomes and promotes cell proliferation and migration in hepatocellular carcinoma

HEY2, a bHLH transcription factor, has been implicated in the progression of human cancers. Here, we showed that HEY2 expression was markedly increased in HCC, compared with the adjacent nontumorous tissues. High HEY2 expression was closely correlated with tumor multiplicity, tumor differentiation and TNM stage. Kaplan-Meier analyses revealed that HEY2 expression was significantly associated with poor overall and disease-free survival in a training cohort of 361 patients with HCC. The prognostic implication of HEY2 was validated in another cohort of 169 HCC patients. Multivariate Cox regression model indicated HEY2 as an independent factor for overall survival in HCC (Hazard ratio = 1.645, 95% confident interval: 1.309-2.067, P<0.001). We also demonstrated that HEY2 expression was inhibited by miR-137. In clinical samples, HEY2 expression was reversely associated to miR-137 expression. Furthermore, overexpression of HEY2 increased cell viabilities, colony formation and cell migration, whereas knockdown of HEY2 resulted in the opposite phenotypes. Collectively, our data suggest HEY2 as a promising biomarker for unfavorable outcomes and a novel therapeutic target for the clinical management of HCC.

Notch signaling regulates Hey2 expression in a spatiotemporal dependent manner during cardiac morphogenesis and trabecular specification

Hey2 gene mutations in both humans and mice have been associated with multiple cardiac defects. However, the currently reported localization of Hey2 in the ventricular compact zone cannot explain the wide variety of cardiac defects. Furthermore, it was reported that, in contrast to other organs, Notch doesn’t regulate Hey2 in the heart. To determine the expression pattern and the regulation of Hey2, we used novel methods including RNAscope and a Hey2^CreERT2 knockin line to precisely determine the spatiotemporal expression pattern and level of Hey2 during cardiac development. We found that Hey2 is expressed in the endocardial cells of the atrioventricular canal and the outflow tract, as well as at the base of trabeculae, in addition to the reported expression in the ventricular compact myocardium. By disrupting several signaling pathways that regulate trabeculation and/or compaction, we found that, in contrast to previous reports, Notch signaling and Nrg1/ErbB2 regulate Hey2 expression level in myocardium and/or endocardium, but not its expression pattern: weak expression in trabecular myocardium and strong expression in compact myocardium. Instead, we found that FGF signaling regulates the expression pattern of Hey2 in the early myocardium, and regulates the expression level of Hey2 in a Notch1 dependent manner.

Expression of the Transcription Factor HEY1 in Glioblastoma: A Preliminary Clinical Study

Aims and background

The hairy/enhancer of split (E(spl))-related family of transcription factors (HES and HEY) are established targets of the notch signaling pathway, which has been implicated in different developmental processes, tumor formation and the self-renewal of neural stem cells. We determined the expression of HEY1 in human malignant gliomas to investigate whether its expression might be related to prognosis.

Methods

The expression of HEY1 was studied by in situ hybridization on 62 cases of glioblastoma. Patients were treated with surgery followed by chemotherapy and radiotherapy. We considered as end points of the study the overall survival time and progression-free interval. Correlations between HEY1 expression and tumor grade/patient overall survival and free interval before recurrence were analyzed using univariate analysis.

Results

Based on the in situ hybridization results, HEY1 expression rate was reported as negative staining in 13 cases (20.6%), as weak staining in 11 cases (17.3%), as moderate staining in 21 cases (33.3%), and as strong staining in 17 cases. We considered in the analysis the cumulative expression of HEY1 at in situ hybridization (Hey Index) as negative in 13 cases and positive in 49 cases (77.78%). The overall survival (P = 0.002) and the free-interval (P = 0.012) were significantly longer in patients who were negative for HEY1 expression.

Conclusions

Our data suggest that expression of HEY1 might be used as a marker to distinguish glioblastoma patients with a relatively good prognosis from those at high-risk, and that, in the future, HEY1 might represent a therapeutic target.

MiR-34c represses muscle development by forming a regulatory loop with Notch1

Since pork accounts for about 40% of global meat consumption, the pig is an important economic animal for meat production. Pig is also a useful medical model for humans due to its similarity in size and physiology. Understanding the mechanism of muscle development has great implication for animal breeding and human health. Previous studies showed porcine muscle satellite cells (PSCs) are important for postnatal skeletal muscle growth, and Notch1 signaling pathway and miRNAs regulate the skeletal muscle development. Notch1 signal pathway regulates the transcription of certain types of miRNAs which further affects target gene expression. However, the specific relationship between Notch1 and miRNAs during muscle development has not been established. We found miR-34c is decreased in PSCs overexpressed N1ICD. Through the overexpression and inhibition of mi-34c, we demonstrated that miR-34c inhibits PSCs proliferation and promotes PSCs differentiation. Using dual-luciferase reporter assay and Chromatin immunoprecipitation, we demonstrate there is a reciprocal regulatory loop between Notch1 and miR-34c. Furthermore, injection of miR-34c lentivirus into mice caused repression of gastrocnemius muscle development. In summary, our data revealed that miR-34c can form a regulatory loop with Notch1 to repress muscle development, and this result expands our understanding of muscle development mechanism.

17β-estradiol regulates the differentiation of cementoblasts via Notch signaling cascade

Estrogen has been well recognized as a key factor in the homeostasis of bone and periodontal tissue, but the way it regulates the activities of cementoblasts, the cell population maintaining cementum has not been fully understood. In this study, we examined the expression of estrogen receptor in OCCM-30 cells and the effect of 17β-estradiol (E2) on the proliferation and differentiation of OCCM-30 cells. We found that both estrogen receptor α and β were expressed in OCCM-30 cells. E2 exerted no significant influence on the proliferation of OCCM-30 cells, but inhibited the transcription and translation of BSP and Runx2 in the early phase of osteogenic induction except the BSP mRNA. Afterwards in the late phase of osteogenic induction, E2 enhanced the transcription and translation of BSP and Runx2 and promoted the calcium deposition. In addition, the expression level of Notch1, NICD and Hey1 mRNAs responded to exogenous E2 in a pattern similar to that of the osteoblastic markers. DAPT could attenuate the effect of E2 on the expression of osteoblastic markers. These findings indicated that E2 might regulate the differentiation of cementoblasts via Notch signaling.

Not all NOTCH Is Created Equal: The Oncogenic Role of NOTCH2 in Bladder Cancer and Its Implications for Targeted Therapy

PURPOSE

Recent molecular analyses of bladder cancer open the door to significant advances in targeted therapies. NOTCH has been identified as a tumor suppressor in bladder cancer, but prior reports have focused on NOTCH1 Here we hypothesized that NOTCH2 is an oncogene suitable for therapeutic targeting in bladder cancer.

EXPERIMENTAL DESIGN

We studied genomic aberrations of NOTCH, compared survival and tumor progression according to NOTCH2 expression levels, and studied NOTCH2 function in vitro and vivo

RESULTS

We report a high rate of NOTCH2 copy number gain in bladder cancer. High NOTCH2 expression was identified especially in the basal subtype and in mesenchymal tumors. NOTCH2 activation correlated with adverse disease parameters and worse prognosis by immunohistochemistry. Forced overexpression of the intracellular domain of NOTCH2 (N2ICD) induced cell growth and invasion by cell-cycle progression, maintenance of stemness and epithelial-to-mesenchymal transition (EMT). These effects were abrogated by silencing of CSL, indicating that the effects were mediated through the canonical NOTCH signaling pathway. In an orthotopic xenograft model, forced overexpression of N2ICD increased growth, invasion, and metastasis. To explore the potential for therapeutic targeting of NOTCH2, we first silenced the receptor with shRNA and subsequently treated with a specific inhibitory antibody. Both interventions decreased cell growth, invasion, and metastasis in vitro and in the orthotopic xenograft model.

CONCLUSIONS

We have demonstrated that NOTCH2 acts as an oncogene that promotes bladder cancer growth and metastasis through EMT, cell-cycle progression, and maintenance of stemness. Inhibition of NOTCH2 is a rational novel treatment strategy for invasive bladder cancer. Clin Cancer Res; 22(12); 2981-92. ©2016 AACR.

Hajdu Cheney Mouse Mutants Exhibit Osteopenia, Increased Osteoclastogenesis, and Bone Resorption

Notch receptors are determinants of cell fate and function and play a central role in skeletal development and bone remodeling. Hajdu Cheney syndrome, a disease characterized by osteoporosis and fractures, is associated with NOTCH2 mutations resulting in a truncated stable protein and gain-of-function. We created a mouse model reproducing the Hajdu Cheney syndrome by introducing a 6955C→T mutation in the Notch2 locus leading to a Q2319X change at the amino acid level. Notch2(Q2319X) heterozygous mutants were smaller and had shorter femurs than controls; and at 1 month of age they exhibited cancellous and cortical bone osteopenia. As the mice matured, cancellous bone volume was restored partially in male but not female mice, whereas cortical osteopenia persisted in both sexes. Cancellous bone histomorphometry revealed an increased number of osteoclasts and bone resorption, without a decrease in osteoblast number or bone formation. Osteoblast differentiation and function were not affected in Notch2(Q2319X) cells. The pre-osteoclast cell pool, osteoclast differentiation, and bone resorption in response to receptor activator of nuclear factor κB ligand in vitro were increased in Notch2(Q2319X) mutants. These effects were suppressed by the γ-secretase inhibitor LY450139. In conclusion, Notch2(Q2319X) mice exhibit cancellous and cortical bone osteopenia, enhanced osteoclastogenesis, and increased bone resorption.

Hey bHLH transcription factors

Hey bHLH transcription factors are direct targets of canonical Notch signaling. The three mammalian Hey proteins are closely related to Hes proteins and they primarily repress target genes by either directly binding to core promoters or by inhibiting other transcriptional activators. Individual candidate gene approaches and systematic screens identified a number of Hey target genes, which often encode other transcription factors involved in various developmental processes. Here, we review data on interaction partners and target genes and conclude with a model for Hey target gene regulation. Furthermore, we discuss how expression of Hey proteins affects processes like cell fate decisions and differentiation, e.g., in cardiovascular, skeletal, and neural development or oncogenesis and how this relates to the observed developmental defects and phenotypes observed in various knockout mice.

Co-ordinating Notch, BMP, and TGF-β signaling during heart valve development

Congenital heart defects affect approximately 1-5 % of human newborns each year, and of these cardiac defects 20-30 % are due to heart valve abnormalities. Recent literature indicates that the key factors and pathways that regulate valve development are also implicated in congenital heart defects and valve disease. Currently, there are limited options for treatment of valve disease, and therefore having a better understanding of valve development can contribute critical insight into congenital valve defects and disease. There are three major signaling pathways required for early specification and initiation of endothelial-to-mesenchymal transformation (EMT) in the cardiac cushions: BMP, TGF-β, and Notch signaling. BMPs secreted from the myocardium set up the environment for the overlying endocardium to become activated; Notch signaling initiates EMT; and both BMP and TGF-β signaling synergize with Notch to promote the transition of endothelia to mesenchyme and the mesenchymal cell invasiveness. Together, these three essential signaling pathways help form the cardiac cushions and populate them with mesenchyme and, consequently, set off the cascade of events required to develop mature heart valves. Furthermore, integration and cross-talk between these pathways generate highly stratified and delicate valve leaflets and septa of the heart. Here, we discuss BMP, TGF-β, and Notch signaling pathways during mouse cardiac cushion formation and how they together produce a coordinated EMT response in the developing mouse valves.

Osteogenesis of Adipose-Derived Stem Cells

Current treatment options for skeletal repair, including immobilization, rigid fixation, alloplastic materials and bone grafts, have significant limitations. Bone tissue engineering offers a promising method for the repair of bone deficieny caused by fractures, bone loss and tumors. The use of adipose derived stem cells (ASCs) has received attention because of the self-renewal ability, high proliferative capacity and potential of osteogenic differentiation in vitro and in vivo studies of bone regeneration. Although cell therapies using ASCs are widely promising in various clinical fields, no large human clinical trials exist for bone tissue engineering. The aim of this review is to introduce how they are harvested, examine the characterization of ASCs, to review the mechanisms of osteogenic differentiation, to analyze the effect of mechanical and chemical stimuli on ASC osteodifferentiation, to summarize the current knowledge about usage of ASC in vivo studies and clinical trials, and finally to conclude with a general summary of the field and comments on its future direction.

Notch suppresses nuclear factor of activated T cells (NFAT) transactivation and Nfatc1 expression in chondrocytes

Notch1 to Notch4 transmembrane receptors determine cell fate, and release of the Notch intracellular domain (NICD) in the cytoplasm induces gene expression. Notch regulates endochondral ossification, but it is not clear whether Notch interacts with signals controlling chondrocyte differentiation. Nuclear factor of activated T cells (Nfatc) transcription factors regulate chondrogenesis, and we asked whether Notch modifies Nfat signaling in chondrocytes. Notch was induced in teratocarcinoma ATDC5 chondrogenic cells infected with a retroviral vector, where the cytomegalovirus (CMV) promoter directs NICD expression. NICD suppressed chondrocyte differentiation and inhibited Nfat transactivation and Nfatc1 expression. Notch was activated in chondrocytes from Rosa(Notch) mice, where the Rosa26 promoter is upstream of a loxP-flanked STOP cassette and NICD. To excise the STOP cassette and express NICD, Rosa(Notch) chondrocytes were infected with an adenoviral vector where the CMV promoter directs Cre expression (Ad-CMV-Cre). Notch1 and Notch2 mediate the effects of Notch in skeletal cells, and to inhibit Notch signaling, chondrocytes from mice homozygous for Notch1 and Notch2 alleles targeted with loxP sites were infected with Ad-CMV-Cre. NICD suppressed chondrogenic nodules formation and expression of selected chondrocyte gene markers, induced Col10a1 and Mmp13, and suppressed Nfat transactivation and Nfatc1 expression, whereas inactivation of Notch1 and Notch2 did not affect chondrocyte differentiation. To investigate Nfatc1 function in chondrocytes, Nfatc1 was induced in Rosa(Notch) chondrocytes overexpressing NICD or controls. Nfatc1 suppressed chondrocyte differentiation and opposed Col10a1 induction by Notch. In conclusion, Notch suppresses Nfat transactivation in chondrocytes and Notch and Nfatc1 regulate chondrocyte differentiation.

Nuclear factor of activated T-cells (NFAT)C2 inhibits Notch receptor signaling in osteoblasts

Notch receptors regulate osteoblastogenesis, and Notch activation induces cleavage and nuclear translocation of the Notch intracellular domain (NICD), which associates with Epstein-Barr virus latency C-promoter binding factor-1/suppressor of hairless/lag-1 (CSL) and induces transcription of Notch target genes, such as hairy enhancer of split-related with YRPW motif (Hey)1 and Hey2. Nuclear factors of activated T-cells (NFAT) are transcription factors that regulate osteoclastogenesis, but their function in osteoblasts is not clear. Notch inhibits NFATc1 transcription, but interactions between Notch and NFAT are understood poorly. To determine the regulation of NFAT expression by Notch, osteoblasts from Rosa(Notch) mice, where NICD is transcribed following excision of a loxP flanked STOP cassette, were used. Alternatively, wild-type C57BL/6 osteoblasts were exposed to the Notch ligand Delta-like (Dll)1 to induce Notch signaling or to bovine serum albumin as control. In Rosa(Notch) osteoblasts, Notch suppressed NFATc1 expression, increased Nfatc2 mRNA by post-transcriptional mechanisms, and had no effect on NFATc3 and NFATc4 transcripts. Induction of Nfatc2 transcripts by Notch was confirmed in C57BL/6 osteoblasts exposed to Dll1. To investigate NFATc2 function in osteoblasts, constitutively active NFATc2 was overexpressed in Rosa(Notch) osteoblasts. NFATc2 suppressed Notch transactivation and expression of Hey genes. Electrophoretic mobility shift assays revealed that NFATc2 and CSL bind to similar DNA sequences, and chromatin immunoprecipitation indicated that NFATc2 displaced CSL from the Hey2 promoter. The effects of NICD and NFATc2 in Rosa(Notch) osteoblasts were assessed, and both proteins inhibited osteoblast function. In conclusion, Notch stabilizes Nfatc2 transcripts, NFATc2 suppresses Notch signaling, and both proteins inhibit osteoblast function.

Jagged-1-mediated activation of notch signalling induces adipogenesis of adipose-derived stem cells

OBJECTIVES

Notch signalling plays an important role in many cell activities, involving proliferation, migration, differentiation and cell death. The aim of this study was to investigate effects of such signalling on adipogenesis of mouse adipose-derived stem cells (mASCs).

MATERIALS AND METHODS

Jagged1 (50 and 100 ng/ml) was added to mASCs to activate Notch signalling, 2 days before adipogenic induction. At 5 and 7 days after induction, oil red-O staining was performed to evaluate lipid accumulation. Then real-time PCR was performed to examine expression of Notch downstream genes (Notch-1, -2, Hes-1 and Hey-1) and adipogenic transcription factor (PPAR-γ). Expressions of Hes-1 and PPAR-γ at protein level were confirmed by immunofluorescence staining.

RESULTS

Our data indicated that Jagged1 promoted adipogenic differentiation of mASCs. Moreover, Jagged1 also increased expression of Notch downstream genes and PPAR-γ. Expressions of Hes-1 and PPAR-γ were found to be enhanced in Jagged1 pre-treated mASCs when compared to controls.

DISCUSSION

The results led to the conclusion that activation of Notch signalling had stimulated adipogenesis of mASCs in the presence of adipogenic medium by promoting expression of PPAR-γ.

The Notch pathway attenuates interleukin 1β (IL1β)-mediated induction of adenylyl cyclase 8 (AC8) expression during vascular smooth muscle cell (VSMC) trans-differentiation

Vascular smooth muscle cell (VSMC) trans-differentiation, or their switch from a contractile/quiescent to a secretory/inflammatory/migratory state, is known to play an important role in pathological vascular remodeling including atherosclerosis and postangioplasty restenosis. Several reports have established the Notch pathway as tightly regulating VSMC response to various stress factors through growth, migration, apoptosis, and de-differentiation. More recently, we showed that alterations of the Notch pathway also govern VSMC acquisition of the inflammatory state, one of the major events accelerating atherosclerosis. We also evidenced that the inflammatory context of atherosclerosis triggers a de novo expression of adenylyl cyclase isoform 8 (AC8), associated with the properties developed by trans-differentiated VSMCs. As an initial approach to understanding the regulation of AC8 expression, we examined the role of the Notch pathway. Here we show that inhibiting the Notch pathway enhances the effect of IL1β on AC8 expression, amplifies its deleterious effects on the VSMC trans-differentiated phenotype, and decreases Notch target genes Hrt1 and Hrt3. Conversely, Notch activation resulted in blocking AC8 expression and up-regulated Hrt1 and Hrt3 expression. Furthermore, overexpressing Hrt1 and Hrt3 significantly decreased IL1β-induced AC8 expression. In agreement with these in vitro findings, the in vivo rat carotid balloon-injury model of restenosis evidenced that AC8 de novo expression coincided with down-regulation of the Notch3 pathway. These results, demonstrating that the Notch pathway attenuates IL1β-mediated AC8 up-regulation in trans-differentiated VSMCs, suggest that AC8 expression, besides being induced by the proinflammatory cytokine IL1β, is also dependent on down-regulation of the Notch pathway occurring in an inflammatory context.

Soluble Jagged-1 inhibits neointima formation by attenuating Notch-Herp2 signaling

OBJECTIVE

Notch has been implicated in neointima formation as reflected by increased Notch/Jagged expression on vascular injury and the promigratory effect of Notch signaling on smooth muscle cells. Soluble Jagged-1 (sJag1) has been shown to inhibit Notch signaling in vitro; however, its capacity to suppress neointima formation remains unknown.

METHODS AND RESULTS

Balloon injury of rat carotid arteries induced Notch1, Notch3, and Jagged-1 expression at days 3 and 14 postinjury. Notch signaling was activated as shown by increased expression of the Notch target gene Herp2. Adenoviral sJag1 (Ad-sJag1) transfection reduced neointima formation in carotid artery and enhanced reendothelialization, whereas adenoviral full-length Jagged-1 (Ad-Fl-Jag1) or LacZ had no effect. Injury-induced Herp2 expression was absent in vessels treated with Ad-sJag1. Consistently, Herp2 expression was reduced in Ad-sJag1-infected or recombinant sJag1 -treated coronary artery smooth muscle cells (CASMCs). Ad-sJag1 had no effect on human umbilical endothelial cell behavior, but it significantly reduced proliferation and migration of CASMCs. Overexpression of Herp2 in sJag1-treated CASMCs rescued the migratory and proliferative capacity in vitro.

CONCLUSIONS

Our results demonstrate that sJag1 can inhibit neointima formation after balloon injury by decreasing smooth muscle cell proliferation and migration through interference with Notch-Herp2 signaling.

HeyL promotes neuronal differentiation of neural progenitor cells

Members of the Hes and Hey families of basic helix-loop-helix transcription factors are regarded as Notch target genes that generally inhibit neuronal differentiation of neural progenitor cells. We found that HeyL, contrary to the classic function of Hes and Hey factors, promotes neuronal differentiation of neural progenitor cells both in culture and in the embryonic brain in vivo. Furthermore, null mutation of HeyL decreased the rate of neuronal differentiation of cultured neural progenitor cells. HeyL binds to and activates the promoter of the proneural gene neurogenin2, which is inhibited by other Hes and Hey family members, and HeyL is a weak inhibitor of the Hes1 promoter. HeyL is able to bind other Hes and Hey family members, but it cannot bind the Groucho/Tle1 transcriptional corepressor, which mediates the inhibitory effects of the Hes family of factors. Furthermore, although HeyL expression is only weakly augmented by Notch signaling, we found that bone morphogenic protein signaling increases HeyL expression by neural progenitor cells. These observations suggest that HeyL promotes neuronal differentiation of neural progenitor cells by activating proneural genes and by inhibiting the actions of other Hes and Hey family members.

Reciprocal regulation of Notch and nuclear factor of activated T-cells (NFAT) c1 transactivation in osteoblasts

Notch are transmembrane receptors involved in the determination of cell fate. Nuclear factor of activated T-cells (NFAT)c are transcription factors that control cell differentiation and function. We tested whether Notch and NFAT signaling pathways interacted in osteoblastic cells. Notch signaling was induced in ST-2 cells using vectors expressing Notch1 intracellular domain (NICD), and in Rosa(Notch) osteoblastic cells by Cre recombinase-mediated excision of a loxP-flanked STOP cassette cloned between the Rosa26 promoter and NICD. NFATc1 was induced in Rosa(Notch) osteoblastic cells by transducing an adenoviral vector expressing constitutively active NFATc1. Notch inhibited NFAT transactivation and NFATc1 transcription. In ST-2 cells, suppression of NFAT transactivation by Notch was reversed by constitutively active cGMP-dependent protein kinase type II. NFATc1 inhibited the transactivation of Notch target genes, and competed for binding to DNA with the Notch interacting protein Epstein-Barr virus latency C promoter binding factor-1, suppressor of hairless, Lag-1 (CSL). Co-immunoprecipitation and confocal microscopy demonstrated that NFATc1 and CSL interacted. Studies on the effects of NICD and NFATc1 on the differentiation and function of osteoblastic cells demonstrated that NICD and NFATc1 inhibited expression of osteoblast gene markers in Rosa(Notch) osteoblasts, but only NICD suppressed the commitment of bone marrow stromal cells to the osteoblastic lineage. In conclusion, NICD and NFATc1 reciprocally inhibit their signaling pathways, and form a regulatory network to control their activity in osteoblasts.

gamma-secretase inhibitor induces adipogenesis of adipose-derived stem cells by regulation of Notch and PPAR-gamma

OBJECTIVE

To determine the inhibitory effect and mechanism of Notch signalling on adipogenesis of mouse adipose-derived stem cells (mASCs).

MATERIALS AND METHODS

Varied concentrations of N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butylester (DAPT) were added to mASCs 3 days before adipogenic induction with insulin-containing differentiation medium. The process of adipogenesis and ability of lipid droplet accumulation were analysed using oil red-O staining. The Notch signalling pathway (Notch-1, -2, -3, -4, Hes-1 and Hey-1) and adipogenesis-related factors (PPAR-gamma, DLK-1/Pref-1 and Acrp) were tested using real-time PCR, Western blot analysis and immunofluorescence staining assays.

RESULTS

We demonstrated that Notch-2-Hes-1 signalling pathway was inhibited dose-dependently by DAPT in mASCs. In addition, transcription of PPAR-gamma was promoted by DAPT before adipogenic induction, while inhibitor of adipogenesis DLK-1/Pref-1 was further depressed. At early stages of differentiation (2-4 days), adipogenesis in mASCs was advanced and significantly enhanced in 5 and 10 mum DAPT pre-treated cases. On day 4, in differentiated mASCs cases with DAPT pre-treatment, we also found promotion of activation of de-PPAR-gamma and depression of HES-1, DLK-1/Pref-1 mRNA and protein expression.

CONCLUSIONS

We conclude that blocking Notch signalling with DAPT enhances adipogenesis of differentiated mASCs at an early stage. It may be due to depression of DLK-1/Pref-1 and promotion of de-PPAR-gamma activation, which work through inhibition of Notch-2-Hes-1 pathway by DAPT.

The Notch effector Hey1 associates with myogenic target genes to repress myogenesis

Members of the Hey family of transcriptional repressors are basic helix-loop-helix proteins that are thought to act downstream of Notch in diverse tissues. Although forced expression of Hey1, a target of Notch in myoblasts, is sufficient to recapitulate inhibitory effects of the pathway on differentiation, how Hey1 interferes with myogenic transcription has not been fully elucidated. We provide multiple lines of evidence that Hey1 does not target the intrinsic transcriptional activity of the skeletal muscle master regulator MyoD. Our results indicate instead that Hey1 is recruited to the promoter regions of myogenin and Mef2C, two genes whose induction is critical for myogenesis. Expression of Hey1 in C2C12 myoblasts correlates with reduced recruitment of MyoD to these promoters, arguing that Hey1 inhibits myogenesis by associating with and repressing expression of key myogenic targets.

KSHV manipulates Notch signaling by DLL4 and JAG1 to alter cell cycle genes in lymphatic endothelia

Increased expression of Notch signaling pathway components is observed in Kaposi sarcoma (KS) but the mechanism underlying the manipulation of the canonical Notch pathway by the causative agent of KS, Kaposi sarcoma herpesvirus (KSHV), has not been fully elucidated. Here, we describe the mechanism through which KSHV directly modulates the expression of the Notch ligands JAG1 and DLL4 in lymphatic endothelial cells. Expression of KSHV-encoded vFLIP induces JAG1 through an NFkappaB-dependent mechanism, while vGPCR upregulates DLL4 through a mechanism dependent on ERK. Both vFLIP and vGPCR instigate functional Notch signalling through NOTCH4. Gene expression profiling showed that JAG1- or DLL4-stimulated signaling results in the suppression of genes associated with the cell cycle in adjacent lymphatic endothelial cells, indicating a role for Notch signaling in inducing cellular quiescence in these cells. Upregulation of JAG1 and DLL4 by KSHV could therefore alter the expression of cell cycle components in neighbouring uninfected cells during latent and lytic phases of viral infection, influencing cellular quiescence and plasticity. In addition, differences in signaling potency between these ligands suggest a possible complementary role for JAG1 and DLL4 in the context of KS.

Hes1 is expressed in the second heart field and is required for outflow tract development

BACKGROUND

Rapid growth of the embryonic heart occurs by addition of progenitor cells of the second heart field to the poles of the elongating heart tube. Failure or perturbation of this process leads to congenital heart defects. In order to provide further insight into second heart field development we characterized the insertion site of a transgene expressed in the second heart field and outflow tract as the result of an integration site position effect.

RESULTS

Here we show that the integration site of the A17-Myf5-nlacZ-T55 transgene lies upstream of Hes1, encoding a basic helix-loop-helix containing transcriptional repressor required for the maintenance of diverse progenitor cell populations during embryonic development. Transgene expression in a subset of Hes1 expression sites, including the CNS, pharyngeal epithelia, pericardium, limb bud and lung endoderm suggests that Hes1 is the endogenous target of regulatory elements trapped by the transgene. Hes1 is expressed in pharyngeal endoderm and mesoderm including the second heart field. Analysis of Hes1 mutant hearts at embryonic day 15.5 reveals outflow tract alignment defects including ventricular septal defects and overriding aorta. At earlier developmental stages, Hes1 mutant embryos display defects in second heart field proliferation, a reduction in cardiac neural crest cells and failure to completely extend the outflow tract.

CONCLUSIONS

Hes1 is expressed in cardiac progenitor cells in the early embryo and is required for development of the arterial pole of the heart.

Notch signaling regulates the differentiation of bone marrow-derived cells into smooth muscle-like cells during arterial lesion formation

Bone marrow- (BM-) derived cells can differentiate into smooth muscle-like cells (SMLC), resulting in vascular pathogenesis. However, the molecular mechanism of the differentiation remains unknown. We have recently reported that Notch signaling promotes while a Notch target HERP1 inhibit the differentiation of mesenchymal cells to SMC. During the differentiation of BM-derived mononuclear cells into smooth muscle alpha-actin (SMA)-positive cells, expression of Jagged1 and SMC-specific Notch3 was increased. Blocking Notch with gamma-secretase inhibitor prevented the induction of SMA. Wire-mediated vascular injury was produced in femoral arteries in mice transplanted with green fluorescent protein (GFP)-positive cells. Many double-positive cells for GFP/Jagged1 or GFP/Notch3 were detected in the thickened neointima. In contrast, only a few SMA-positive cells were positive for GFP in neointima where HERP1, a suppressor for Notch, were abundantly expressed. In conclusion, Notch-HERP1 pathway plays an important role in differentiation of BM-derived mononuclear cells into SMLC.

Notch signaling in cardiac development

The Notch signaling pathway has been demonstrated to play a critical role during mammalian cardiac development based on recent findings from gene-targeted mice. In addition, mutations in the Notch signaling pathway have been associated with human congenital heart defects such as Alagille syndrome, bicuspid aortic valve disease, calcification of the heart valves, and ventricular septal defects. Recently, it was demonstrated that Notch activation in the endocardium regulates ventricular myocardial development and that the Notch downstream target genes Hey1 and Hey2 are required for the establishment of the atrioventricular canal myocardial boundary. The Notch pathway has previously been implicated in regulating endothelial-to-mesenchymal transition during development of the heart valves, and recent reports further dissect the role of individual Notch downstream target genes during this process. In addition, a role for the Notch pathway during cardiac neural crest cell development has been identified, which provides a potential mechanism for the findings seen in Alagille syndrome. This review focuses on recently reported findings that elucidate mechanisms regulated by the Notch pathway during ventricular, atrioventricular canal, and outflow tract development.

Notch3 and IL-1beta exert opposing effects on a vascular smooth muscle cell inflammatory pathway in which NF-kappaB drives crosstalk

Atherogenesis begins with the transfer of monocytes from the lumen to the intimal layer of arteries. The paracrine activity acquired by these monocytes shifts vascular smooth muscle cells from a contractile-quiescent to a secretory-proliferative phenotype, allowing them to survive and migrate in the intima. Transformed and relocated, they also start to produce and/or secrete inflammatory enzymes, converting them into inflammatory cells. Activation of the Notch pathway, a crucial determinant of cell fate, regulates some of the new features acquired by these cells as it triggers vascular smooth muscle cells to grow and inhibits their death and migration. Here, we evaluate whether and how the Notch pathway regulates the cell transition towards an inflammatory or de-differentiated state. Activation of the Notch pathway by the notch ligand Delta1, as well as overexpression of the active form of Notch3, prevents this phenomenon [initiated by interleukin 1beta (IL-1beta)], whereas inhibiting the Notch pathway enhances the transition. IL-1beta decreases the expression of Notch3 and Notch target genes. As shown by using an IkappaBalpha-mutated form, the decrease of Notch3 signaling elements occurs subsequent to dissociation of the NF-kappaB complex. These results demonstrate that the Notch3 pathway is attenuated through NF-kappaB activation, allowing vascular smooth muscle cells to switch into an inflammatory state.

Downregulation by lipopolysaccharide of Notch signaling, via nitric oxide

The Notch signaling pathway appears to perform an important function in inflammation. Here, we present evidence to suggest that lipopolysaccharide (LPS) suppresses Notch signaling via the direct modification of Notch by the nitration of tyrosine residues in macrophages. In the RAW264.7 macrophage cell line and in rat primary alveolar macrophages, LPS was found to inhibit Notch1 intracellular domain (Notch1-IC) transcription activity, which could then be rescued by treatment with N(G)-nitro-l-arginine, a nitric oxide synthase (NOS) inhibitor. Nitric oxide (NO), which was produced in cells that stably express endothelial NOS (eNOS) and brain NOS (bNOS), also induced the inhibition of Notch1 signaling. The NO-induced inhibition of Notch1 signaling remained unchanged after treatment with 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), a guanylyl-cyclase inhibitor, and was not found to be mimicked by 8-bromo-cyclic GMP in the primary alveolar macrophages. With regards to the control of Notch signaling, NO appears to have a significant negative influence, via the nitration of Notch1-IC, on the binding that occurs between Notch1-IC and RBP-Jk, both in vitro and in vivo. By intrinsic fluorescence, we also determined that nitration could mediate conformational changes of Notch1-IC. The substitution of phenylalanine for tyrosine at residue 1905 in Notch1-IC abolished the nitration of Notch1-IC by LPS. Overall, our data suggest that an important relationship exists between LPS-mediated inflammation and the Notch1 signaling pathway, and that this relationship intimately involves the nitration of Notch1-IC tyrosine residues.

Evidence of Notch pathway activation in the ectatic ducts of chronic pancreatitis

Ductal concretions in chronic pancreatitis (CP) are one of the causes of ductal obstruction, resulting in pancreatic ductal hypertension (PDH) and duct ectasia. Ductal epithelium subjected to chronic stress by PDH may undergo molecular alterations, thereby not only initiating and sustaining the inflammatory process but also activating molecules that have transforming potential. Acino-ductal metaplasia and pancreatic intraepithelial neoplasia (PanIN) are frequently seen in CP. Using laser capture microdissection, cDNA microarrays and Ingenuity Pathways Analysis, we found an altered Notch pathway in the ectatic ducts of CP. The microarray data was further validated by real-time PCR. We also found elevated transcripts of Notch receptors, Notch1 and Notch3 in microdissected ectatic ducts of CP. The Notch pathway ligands, Jagged/Delta-like and a Notch target, HES-related repressor protein (HERP), were up-regulated in ectatic compared to normal pancreatic ducts, while another target of Notch, hairy/enhancer of split (HES), was down-regulated. The transcripts of Delta-like1 and Jagged1 were increased 3.7-fold and 1.3-fold, respectively, while those of HERP1 were elevated 2.4-fold in the ectatic ducts of CP, compared to normal ducts. Immunohistochemistry showed that Jagged1 was not expressed in normal pancreatic ducts, while it was highly expressed in ectatic ducts. This pattern of Notch component alteration in ectatic ducts was mimicked to some extent in vitro in a human pancreatic duct epithelial (HPDE) cell line, when subjected to a pressure of 200 mmHg for 24 h. Therefore, we conclude that in the ectatic ducts of CP, PDH activates signalling pathways such as Notch, which have transforming potential.

A TAG on to the neurogenic functions of APP

The proteolytic processing of amyloid beta precursor protein (APP) has long been studied because of its association with the pathology of Alzheimer's disease (AD). The ectodomain of APP is shed by alpha- or beta-secretase cleavage. The remaining membrane bound stub can then undergo regulated intramembrane proteolysis (RIP) by gamma-secretase. This cleavage can release amyloid beta (Abeta) from the stub left by beta-secretase cleavage but also releases the APP intracellular domain (AICD) after alpha- or beta-secretase cleavage. The physiological functions of this proteolytic processing are not well understood. We compare the proteolytic processing of APP to the ligand-dependent RIP of Notch. In this review, we discuss recent evidence suggesting that TAG1 is a functional ligand for APP. The interaction between TAG1 and APP triggers gamma-secretase-dependent release of AICD. TAG1, APP and Fe65 colocalise in the neurogenic ventricular zone and in fetal neural progenitor cells in vitro. Experiments in TAG1, APP and Fe65 null mice as well as TAG1 and APP double-null mice demonstrate that TAG1 induces a gamma-secretase- and Fe65-dependent suppression of neurogenesis.

The multifaceted role of Notch in cardiac development and disease

Notch receptors and their cognate ligands transduce crucial signals between cells in various tissues, and have been conserved across millions of years of evolution. Mutations in Notch signalling components result in congenital heart defects in humans and mice, demonstrating an essential role for Notch in cardiovascular development. The results of recent experiments implicate this signalling pathway in many stages of heart development, and provide mechanistic insight into the vital functions of Notch in the aetiology of several common forms of paediatric and adult cardiac disease.

RBP-J, the transcription factor downstream of Notch receptors, is essential for the maintenance of vascular homeostasis in adult mice

In adults, angiogenic abnormalities are involved in not only tumor growth but several human inherited diseases as well. It is unclear, however, concerning how the normal vascular structure is maintained and how angiogenesis is initiated in normal adults. Using the Cre-LoxP-mediated conditional gene deletion, we show in the present study that in adult mice disruption of the transcription factor recombination signal-binding protein Jkappa (RBP-J) in endothelial cells strikingly induced spontaneous angiogenesis in multiple tissues, including retina and cornea, as well as in internal organs, such as liver and lung. In a choroidal neovascularization model, which mimics the angiogenic process in tumor growth and age-related macular degeneration, RBP-J deficiency induced a more intensive angiogenic response to injury. This could be transmitted by bone marrow, indicating that RBP-J could modulate bone marrow-derived endothelial progenitor cells in adult angiogenesis. In addition, in the absence of RBP-J, proliferation of endothelial cells increased significantly, leading to accumulative vessel outgrowth. These findings suggest that in adults RBP-J-mediated Notch signaling may play an essential role in the maintenance of vascular homeostasis by repressing endothelial cell proliferation.

Notch signaling in the developing cardiovascular system

The Notch proteins encompass a family of transmembrane receptors that have been highly conserved through evolution as mediators of cell fate. Recent findings have demonstrated a critical role of Notch in the developing cardiovascular system. Notch signaling has been implicated in the endothelial-to-mesenchymal transition during development of the heart valves, in arterial-venous differentiation, and in remodeling of the primitive vascular plexus. Mutations of Notch pathway components in humans are associated with congenital defects of the cardiovascular system such as Alagille syndrome, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and bicuspid aortic valves. This article focuses on the role of the Notch pathway in the developing cardiovascular system and congenital human cardiovascular diseases.

Cre-conditional expression of constitutively active Notch1 in transgenic mice

The Notch signaling pathway plays a critical role during mammalian development. To bypass embryonic lethality associated with constitutive Notch1 signaling, we created transgenic mice with a floxed beta-geo/stop signal between a cytomegalo virus promoter and the constitutively active intracellular domain of Notch1 (IC-Notch1). IC-Notch1 is activated upon introduction of Cre recombinase and it is coexpressed with an enhanced green fluorescent protein or human placental alkaline phosphatase reporter. We created three IC-Notch1 transgenic mouse lines and crossed them to a general Cre deletor mouse line, pCX-Cre. The double transgenic IC-Notch1/pCX-Cre embryos have widespread expression of IC-Notch1 and reporters and die before 10.5 days of gestation. Morphological and histological analysis of the double transgenic embryos indicated growth arrest and various developmental defects, including lack of neural tube closure, disorganized somites, and disrupted vasculature. The conditional IC-Notch1 expressing transgenic mice provide a unique tool to investigate the Notch pathway using tissue-specific Cre mice and inducible Cre systems.

Delta-Notch--and then? Protein interactions and proposed modes of repression by Hes and Hey bHLH factors

Hes and Hey genes are the mammalian counterparts of the Hairy and Enhancer-of-split type of genes in Drosophila and they represent the primary targets of the Delta–Notch signaling pathway. Hairy-related factors control multiple steps of embryonic development and misregulation is associated with various defects. Hes and Hey genes (also called Hesr, Chf, Hrt, Herp or gridlock) encode transcriptional regulators of the basic helix-loop-helix class that mainly act as repressors. The molecular details of how Hes and Hey proteins control transcription are still poorly understood, however.

Proposed modes of action include direct binding to N- or E-box DNA sequences of target promoters as well as indirect binding through other sequence-specific transcription factors or sequestration of transcriptional activators. Repression may rely on recruitment of corepressors and induction of histone modifications, or even interference with the general transcriptional machinery. All of these models require extensive protein–protein interactions. Here we review data published on protein–protein and protein–DNA interactions of Hairy-related factors and discuss their implications for transcriptional regulation. In addition, we summarize recent progress on the identification of potential target genes and the analysis of mouse models.

DNA repair Ku proteins in gastric cancer cells and pancreatic acinar cells

The DNA repair protein Ku acts as a heterodimer of Ku70 and Ku80 that binds to the DNA ends, nicks, or single-to-double-strand transition. It has a crucial role for DNA double-strand-break repair. Either Ku70 or Ku80 itself may have a unique function that is independent of the other Ku subunit. In this review, the role of Ku on cell proliferation and apoptosis will be discussed. Ku acts as a regulator of transcription by interacting with the recombination signal binding protein Jkappa and the NF-kappaB p50 homodimer to up-regulate p50 expression, which may regulate the proliferation of gastric cancer cells. Both Ku70 and Ku80 expressions are mediated by constitutively activated NF-kappaB and constitutively expressed cyclooxygenase-2 in gastric cancer cells, which may be related to gastric cell proliferation and carcinogenesis. In addition, nuclear loss of Ku may underlie the mechanism of apoptosis in pancreatic acinar cells after oxidative stress.

Activation of D 3 Dopamine Receptor Decreases Angiotensin II Type 1 Receptor Expression in Rat Renal Proximal Tubule Cells

The dopaminergic and renin angiotensin systems interact to regulate blood pressure. Disruption of the D 3 dopamine receptor gene in mice produces renin-dependent hypertension. In rats, D 2 -like receptors reduce angiotensin II binding sites in renal proximal tubules (RPTs). Because the major D 2 -like receptor in RPTs is the D 3 receptor, we examined whether D 3 receptors regulate angiotensin II type 1 (AT 1 ) receptors in rat RPT cells. The effect of D 3 receptors on AT 1 receptors was studied in vitro and in vivo. The D 3 receptor agonist PD128907 decreased AT 1 receptor protein and mRNA in WKY RPT cells and increased it in SHR cells. PD128907 increased D 3 receptors in WKY cells but had no effect in SHR cells. D 3 /AT 1 receptors colocalized in RPT cells; D 3 receptor stimulation decreased the percent amount of D 3 receptors that coimmunoprecipitated with AT 1 receptors to a greater extent in WKY than in SHR cells. However, D 3 receptor stimulation did not change the percent amount of AT 1 receptors that coimmunoprecipitated with D 3 receptors in WKY cells and markedly decreased the coimmunoprecipitation in SHR cells. The D 3 receptor also regulated the AT 1 receptor in vivo because AT 1 receptor expression was increased in kidneys of D 3 receptor–null mice compared with wild type littermates. D 3 receptors may regulate AT 1 receptor function by direct interaction with and regulation of AT 1 receptor expression. One mechanism of hypertension may be related to increased renal expression of AT 1 receptors due decreased D 3 receptor regulation.

Jagged1-selective notch signaling induces smooth muscle differentiation via a RBP-Jkappa-dependent pathway

The Notch signaling pathway plays a crucial role in specifying cellular fates by interaction between cellular neighbors; however, the molecular mechanism underlying smooth muscle cell (SMC) differentiation by Notch signaling has not been well characterized. Here we demonstrate that Jagged1-Notch signaling promotes SMC differentiation from mesenchymal cells. Overexpression of the Notch intracellular domain, an activated form of Notch, up-regulates the expression of multiple SMC marker genes including SMC-myosin heavy chain (Sm-mhc) in mesenchymal 10T1/2 cells, but not in non-mesenchymal cells. Physiological Notch stimulation by its ligand Jagged1, but not Dll4, directly induces Sm-mhc expression in 10T1/2 cells without de novo protein synthesis, indicative of a ligand-selective effect. Jagged1-induced expression of SM-MHC was blocked bygamma-secretase inhibitor, N-(N-(3,5-difluorophenyl)-l-alanyl)-S-phenylglycine t-butyl ester, which impedes Notch signaling. Using Rbp-jkappa-deficient cells and site-specific mutagenesis of the SM-MHC gene, we show that such an induction is independent of the myocardin-serum response factor-CArG complex, but absolutely dependent on RBP-Jkappa, a major mediator of Notch signaling, and its cognate binding sequence. Of importance, Notch signaling and myocardin synergistically activate SM-MHC gene expression. Taken together, these data suggest that the Jagged1-Notch pathway constitutes an instructive signal for SMC differentiation through an RBP-Jkappa-dependent mechanism and augments gene expression mediated by the myocardin-SRF-CArG complex. Given that Notch pathway components are expressed in vascular SMC during normal development and disease, Notch signaling is likely to play a pivotal role in such situations to modulate the vascular smooth muscle cell phenotype.

Physiology and pathology of notch signalling system

Notch proteins encode a family of transmembrane receptors that are part of a signalling transduction system known as Notch signalling, an extremely conserved and widely used mechanism regulating programs governing growth, apoptosis and differentiation in metazoans. Notch signalling begins when the Notch receptor binds ligands and ends when the Notch intracellular domain enters the nucleus and activates transcription of target genes. This core pathway is subjected to a wide array of regulatory influences and protein-protein interactions and is correlated with other signalling pathway. This review will summarize recent findings concerning the physiology and pathology of Notch signalling in vascular development and homeostasis. Moreover, the clinical phenotypes of Notch3 signalling system pathology will be described, with particular regard to CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy) for which the most recent pathogenetic hypotheses are reported.

Activation of Notch1 signaling in cardiogenic mesoderm induces abnormal heart morphogenesis in mouse

Notch signaling is implicated in many developmental processes. In our current study, we have employed a transgenic strategy to investigate the role of Notch signaling during cardiac development in the mouse. Cre recombinase-mediated Notch1 (NICD1) activation in the mesodermal cell lineage leads to abnormal heart morphogenesis, which is characterized by deformities of the ventricles and atrioventricular (AV) canal. The major defects observed include impaired ventricular myocardial differentiation, the ectopic appearance of cell masses in the AV cushion, the right-shifted interventricular septum (IVS) and impaired myocardium of the AV canal. However, the fates of the endocardium and myocardium were not disrupted in NICD1-activated hearts. One of the Notch target genes, Hesr1, was found to be strongly induced in both the ventricle and the AV canal of NICD1-activated hearts. However, a knockout of the Hesr1 gene from NICD-activated hearts rescues only the abnormality of the AV myocardium. We searched for additional possible targets of NICD1 activation by GeneChip analysis and found that Wnt2, Bmp6, jagged 1 and Tnni2 are strongly upregulated in NICD1-activated hearts, and that the activation of these genes was also observed in the absence of Hesr1. Our present study thus indicates that the Notch1 signaling pathway plays a suppressive role both in AV myocardial differentiation and the maturation of the ventricular myocardium.