Gastric cancer cell growth and epithelial-mesenchymal transition are inhibited by γ-secretase inhibitor DAPT

Elevated Notch-1 expression promotes the lymph node metastasis of gastric cancer and the Notch-1-PTEN-ERK1/2 signalling axis promotes the progression of gastric cancer

BACKGROUND

Gastric cancer (GC) is one of the most common malignant tumours and has a high fatality rate worldwide. This study investigated the role of the Notch-1 signalling pathway in the pathogenesis and progression of GC.

METHODS

A total of 64 patients with GC were included in this study. Immunohistochemistry staining was used to detect Notch-1 expression in tumour tissues and adjacent non-tumour tissues, and Notch-1 knockdown in GC cells was identified using short hairpin RNA. A cell scratch assay, transwell assay and flow cytometry analysis were used to analyse the effect of Notch-1 knockdown on cell proliferation, migration and cell cycle distribution. The expression of Notch-1, PTEN, Akt, ERK1/2, E-cadherin and other proteins was detected using Western blotting.

RESULTS

The expression level of Notch-1 in GC tissues was higher than that in adjacent non-tumour tissues (P < 0.05). High levels of Notch-1 were also found to be associated with sex (male) and lymph node metastasis (P < 0.05). Notch-1 knockdown in the AGS and BGC-823 GC cell lines inhibited the migration and proliferation of GC cells, and Notch-1 knockdown arrested the cell cycle in the G0/G1 phase. PTEN protein expression was elevated in the presence of Notch-1 knockdown, resulting in the inhibition of phosphorylated Akt protein expression. In addition, phosphorylated ERK protein levels decreased in the presence of Notch-1 knockdown. Further inhibition of ERK1/2 signalling by the MEK1/2 inhibitor U0126 decreased the proliferation of AGS cells. The results of in vivo experiments with xenotransplantation in nude mice are consistent with these results.

CONCLUSIONS

Notch-1 plays a key role in the development of GC and was found to promote the lymph node metastasis of GC. Notch-1 knockdown can effectively attenuate the progression of GC cells, which may function in part through the Notch-1-PTEN-ERK1/2 signalling axis.

LncRNA SRA mediates cell migration, invasion, and progression of ovarian cancer via NOTCH signaling and epithelial-mesenchymal transition

Long non-coding RNA (lncRNA) is a newly identified regulator of tumor formation and tumor progression. The function and expression of lncRNAs remain to be fully elucidated, but recent studies have begun to address their importance in human health and disease. The lncRNA, SRA, known as steroid receptor activator, acts as an important modulator of gynecological cancer, and its expression may affect biological functions including proliferation, apoptosis, steroid formation, and muscle development. However, it is still not well known whether SRA is involved in the regulation of ovarian cancer. The present study investigated the molecular function and association between SRA expression and clinicopathological factors. In ovarian cancer cell lines, SRA knockdown and overexpression regulated cell migration, proliferation, and invasion. Both in vivo and in vitro experiments using knockdown and overexpression showed that SRA potently regulated epithelial-mesenchymal transition (EMT) and NOTCH pathway components. Further, clinical data confirmed that SRA was a significant predictor of overall survival (OS) and progression-free survival and patients with ovarian cancer exhibiting high expression of SRA exhibited higher recurrence rates than patients with low SRA expression. In conclusion, the present study indicates that SRA has clinical significance as its expression can predict the prognosis of ovarian cancer patients. High expression of the lncRNA SRA is strongly correlated with recurrence-free survival of ovarian cancer patients.

Gamma-Secretase Inhibitor (DAPT), a potential therapeutic target drug, caused neurotoxicity in planarian regeneration by inhibiting Notch signaling pathway

DAPT (N-[N-(3, 5-difluorophenacetyl)-l-alanyl]-s-phenylglycinet-butyl ester) is a γ-secretase inhibitor that indirectly blocks the activity of Notch pathway. It is a potential therapeutic target drug for many diseases, such as cancer, neurological, cardiovascular, and cerebrovascular diseases. However, the pharmacological action and specific mechanisms of DAPT are not clear. Planarians have strong regenerative capacity and can regenerate a new individual with a complete nervous system in one week. Thus, they are used as an ideal indicator of environmental toxicants and a novel model for studying neurodevelopmental toxicology. In this study, different concentrations and treatment times of DAPT are used to analyze the gene expression levels of major components in Notch pathway. The results show that the optimal concentration and exposure time of DAPT is 100 nM for 10 days in planarians and indicate that the inhibitory of DAPT treatment on Notch pathway is time- and concentration-dependent. The potential impact of DAPT is effectively analyzed by qPCR, WISH, and Immunofluorescence. The results indicate that DAPT exposure causes intact planarian wavy or swollen, and regenerative planarians asymmetric growth or muti-eye. Moreover, DAPT exposure increases cell proliferation and apoptosis, results in neurodevelopmental defects and dynamic changes of some marker genes. These results suggest that the balance of proliferation and apoptosis is disturbed, and then, affecting tissue homeostasis and differentiation. These findings demonstrate that DAPT has serious side effects in organisms and relies on Notch pathway to determine cell fate, it is cautious in the use of DAPT as a potential therapeutic approach for the disease in clinical trials.

Lung cancer and epithelial-mesenchymal transition

Lung cancer (LC) is a leading cause of cancer-related death worldwide. Epithelial-mesenchymal transition (EMT) is a well-known phenomenon that promotes the invasive and metastatic capabilities of LC. Especially, EMT is assumed to be a pivotal mechanism for tumor cell invasion and metastasis, thereby limiting the efficacy of surgery and medical treatments, resulting in poor patient prognoses. Thus, the elucidation and reversal of EMT could provide changes in therapeutic strategies for LC. To overcome the limitations of currents treatment regimens for LC, it is important for surgeons to be familiar with this complex tumor characteristic. In this review, the activating signaling pathways underlying EMT and the associated tumor phenotypes are briefly described.

Tomatidine Represses Invasion and Migration of Human Osteosarcoma U2OS and HOS Cells by Suppression of Presenilin 1 and c-Raf-MEK-ERK Pathway

Osteosarcoma, which is the most prevalent malignant bone tumor, is responsible for the great majority of bone cancer-associated deaths because of its highly metastatic potential. Although tomatidine is suggested to serve as a chemosensitizer in multidrug-resistant tumors, the anti-metastatic effect of tomatidine in osteosarcoma is still unknown. Here, we tested the hypothesis that tomatidine suppresses migration and invasion, features that are associated with metastatic process in human osteosarcoma cells and also investigate its underlying pathway. Tomatidine, up to 100 μM, without cytotoxicity, inhibited the invasion and migration capabilities of human osteosarcoma U2OS and HOS cells and repressed presenilin 1 (PS-1) expression of U2OS cells. After the knockdown of PS-1, U2OS and HOS cells’ biological behaviors of cellular invasion and migratory potential were significantly reduced. While tomatidine significantly decreased the phosphorylation of c-Raf, mitogen/extracellular signal-regulated kinase (MEK), and extracellular signal-regulated protein kinase (ERK)1/2 in U2OS cells, no obvious influences on p-Jun N-terminal kinase, p38, and Akt, including their phosphorylation, were observed. In ERK 1 silencing U2 OS cells, tomatidine further enhanced the decrease of their migratory potential and invasive activities. We conclude that both PS-1 derived from U2OS and HOS cells and the c-Raf–MEK–ERK pathway contribute to cellular invasion and migration and tomatidine could inhibit the phenomenons. These findings indicate that tomatidine might be a potential candidate for anti-metastasis treatment of human osteosarcoma.

Elevated Expression of NOTCH1 Associates with Lymph Node Metastasis of Gastric Cancer and Knock-Down of NOTCH1 Attenuates Tumor Cell Progression

BACKGROUND Gastric cancer is the third leading cause of cancer-related death, while its molecular mechanism has not been fully clarified. This study aims to explore the role of Notch signaling in the pathogenesis of gastric cancer. MATERIAL AND METHODS A total of 64 patients with gastric cancer were enrolled. The expressions of NOTCH1 in tumor tissues and adjacent non-tumor tissues were detected by immunohistochemistry staining. The correlation between NOTCH1 expression and clinicopathological features of patients was analyzed. NOTCH1 was knocked down in gastric cancer cells. The effects of NOTCH1 blockade on cell proliferation, migration and cell cycle distribution were analyzed. The expressions of ERK1/2 and phospho-ERK1/2 (p-ERK1/2) were detected using western blotting. RESULTS Gastric cancer tissues expressed higher level of NOTCH1 than adjacent non-tumor tissues (P<0.05). The high level of NOTCH1 was found to be correlated with gender (male) and lymph node metastasis. However, the expression level of NOTCH1 did not affect the overall survival of patients with gastric cancer. NOTCH1 knock-down repressed the migration and proliferation of gastric cancer cells. Moreover, the cell cycle was arrested at G0/G1 phase by NOTCH1 blockade. The expressions of ERK1/2 and p-ERK1/2 decreased with NOTCH1 knock-down. Further inhibition of ERK1/2 signaling by a MEK1/2 inhibitor U0126 reduced the proliferation of AGS cells, which aggravated the inhibition effect of NOTCH1 knock-down on cell proliferation. CONCLUSIONS NOTCH1 may play an oncogenic role in gastric cancer. Inhibition of NOTCH1 can efficiently attenuate gastric cancer cell progression, probably in part through cross-talking with ERK1/2 signaling pathway.

DNA-methylation-mediated silencing of miR-7-5p promotes gastric cancer stem cell invasion via increasing Smo and Hes1

Cancer stem cells are undifferentiated cancer cells that have self-renewal ability, a high tumorigenic activity, and a multilineage differentiation potential. MicroRNAs play a critical role in regulating gene expression during carcinogenesis. Here, we investigated the role of miR-7 and the mechanism by which it is dysregulated in gastric cancer stem cells (GCSCs). The stem cell marker, CD44, was used to sort GCSCs by fluorescence-activated cell sorting. We found that CD44 (+) cells have higher invasiveness and form more number of sphere colonies than CD44 (-) cells. Quantitative real-time polymerase chain reaction (PCR) revealed that the miR-7-5p expression was remarkably downregulated in GCSCs but was significantly increased in the methionine-deprived medium. The downregulation of miR-7-5p results from the increased DNA methylation in the promoter region using the methylation-specific PCR. Overexpression of miR-7-5p reduced the formation of colony and decreased the invasion of GCSCs through targeting Smo and Hes1 and subsequent repressing Notch and Hedgehog signaling pathways in vitro. Notably, upregulating miR-7-5p inhibited the growth of tumor in the xenograft model. Hence, these data demonstrated that miR-7-5p represses GCSC invasion through inhibition of Smo and Hes1, which provides a potential therapeutic target of gastric cancer treatment.

DAPT, a γ-Secretase Inhibitor, Suppresses Tumorigenesis, and Progression of Growth Hormone-Producing Adenomas by Targeting Notch Signaling

Advances in the understanding of growth hormone-producing adenomas (GHomas) are ongoing, but current therapy is limited by moderate and variable efficacy and in need of life-long treatment. In this study, the molecular signaling pathway related to GHoma was investigated by proteomics and transcriptomics. The differentially expressed proteins and genes were significantly enriched in Extracellular Matrix-Receptor Interactions, Notch Signaling, Basal Cell Carcinoma Signaling, JAK-STAT3, Wnt Signaling, and Glioblastoma Multiforme Signaling by Ingenuity Pathway Analysis. Furthermore, the Notch2/Delta-like canonical Notch ligand (DLL) signaling pathway was identified to be associated with tumorigenesis and invasiveness of GHoma. In 76 patients, Notch2 and DLL3 were upregulated in invasive compared to those in non-invasive GHoma (p < 0.05). Disease-free survival was significantly longer in patients with low, compared with high, DLL3 expression (p = 0.027). Notch 2 knockdown inhibited cell migration in both GH3 cells and primary GHoma cells, along with downregulation of the mRNA expression of related genes. DAPT, a γ-secretase inhibitor, inhibited tumor growth and invasion in vivo and in vitro and suppressed the release of growth hormone in primary GHoma cells. The involvement of Notch2/DLL3 signaling in GHoma progression warrants additional study of Notch inhibitor, DAPT, as a potential GHoma treatment.

Folic acid deficiency enhanced microglial immune response via the Notch1/nuclear factor kappa B p65 pathway in hippocampus following rat brain I/R injury and BV2 cells

Recent studies revealed that folic acid deficiency (FD) increased the likelihood of stroke and aggravated brain injury after focal cerebral ischaemia. The microglia-mediated inflammatory response plays a crucial role in the complicated pathologies that lead to ischaemic brain injury. However, whether FD is involved in the activation of microglia and the neuroinflammation after experimental stroke and the underlying mechanism is still unclear. The aim of the present study was to assess whether FD modulates the Notch1/nuclear factor kappa B (NF-κB) pathway and enhances microglial immune response in a rat middle cerebral artery occlusion-reperfusion (MCAO) model and oxygen-glucose deprivation (OGD)-treated BV-2 cells. Our results exhibited that FD worsened neuronal cell death and exaggerated microglia activation in the hippocampal CA1, CA3 and Dentate gyrus (DG) subregions after cerebral ischaemia/reperfusion. The hippocampal CA1 region was more sensitive to ischaemic injury and FD treatment. The protein expressions of proinflammatory cytokines such as tumour necrosis factor-α, interleukin-1β and interleukin-6 were also augmented by FD treatment in microglial cells of the post-ischaemic hippocampus and in vitro OGD-stressed microglia model. Moreover, FD not only dramatically enhanced the protein expression levels of Notch1 and NF-κB p65 but also promoted the phosphorylation of pIkBα and the nuclear translocation of NF-κB p65. Blocking of Notch1 with N-[N-(3, 5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester partly attenuated the nuclear translocation of NF-κB p65 and the protein expression of neuroinflammatory cytokines in FD-treated hypoxic BV-2 microglia. These results suggested that Notch1/NF-κB p65 pathway-mediated microglial immune response may be a molecular mechanism underlying cerebral ischaemia-reperfusion injury worsened by FD treatment.

Notch signalling induces epithelial‑mesenchymal transition to promote metastasis in oral squamous cell carcinoma

The activation of Notch signalling induces epithelial‑mesenchymal transition (EMT), but this signalling pathway and its association with EMT in the context of cell motility in oral squamous cell carcinoma (OSCC) remains unclear. The present study aimed to investigate the role of the Notch signalling pathway and EMT in the metastatic potential of OSCC using 2 cell lines, Tca8113 and CAL27. The data demonstrated that zinc finger domain SNAI1 (Snail) knockdown by small interfering RNA decreased the expression of vimentin and increased the expression of epithelial cadherin (E‑cadherin). In addition, silencing Snail also significantly inhibited cell migration in the 2 OSCC cell lines. It was also identified that blocking Notch signalling with the g‑secretase inhibitor DAPT decreased the expression of the EMT markers Snail and vimentin and increased E‑cadherin expression, accompanied by a significant inhibition of cell migration in the 2 OSCC cell lines. These data clearly indicate that Notch signalling mediates EMT to promote metastasis in OSCC cells. Therefore, targeting Notch signalling and its association with EMT may provide novel insights into the mechanism of invasion and metastasis in OSCC and potential therapeutic interventions.

Cervical Cancer Cell Growth, Drug Resistance, and Epithelial-Mesenchymal Transition Are Suppressed by y-Secretase Inhibitor RO4929097

BACKGROUND The Notch signaling pathway has been reported to play a pivotal role in tumorigenesis. Emerging evidence has demonstrated that the Notch signaling pathway regulates several cellular processes. The present study investigated the effect of the Notch signaling pathway on cell growth, invasiveness, and drug resistance, as well as epithelial-mesenchymal transition (EMT), of cervical cancer cells. MATERIAL AND METHODS We used quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis to measure the expression level of Notch2. CCK-8, clonality, wound healing, and Transwell assays were used to evaluate the effect of γ-secretase inhibitor (GSI) RO4929097 on cervical cancer cell lines HeLa and Caski. To explore the role of the Notch signaling pathway in EMT, the epithelial and mesenchymal markers were detected by qRT-PCR and Western blot after cervical cancer cell lines were treated with GSI RO4929097. RESULTS The expression of Notch2 was found to increase in cervical cancer cell lines compared with the normal immortalized human cervical epithelial cells. GSI RO4929097 was confirmed to inhibit the Notch signaling pathway and impaired the proliferation, drug resistance, migration, and invasion abilities of cervical cancer cells. The protein expression levels of the mesenchymal biomarkers Snail, Twist, and neural cadherin (N-cadherin) decreased; however, the expression of the epithelial biomarker epithelial cadherin (E-cadherin) increased in the cervical cancer cells treated with GSI RO4929097. CONCLUSIONS Notch signaling pathway plays an important role in the development and progression of cervical cancer. Blockade of the Notch pathway using GSI RO4929097 inhibited cell growth and reduced chemoresistance, invasion, metastasis, and EMT in cervical cancer cells.

Concurrent Treatment with Anti-DLL4 Enhances Antitumor and Proapoptotic Efficacy of a γ-Secretase Inhibitor in Gastric Cancer

The Notch signaling pathway has been identified as a therapeutic target for cancers. γ-Secretase inhibitors (GSIs) have been progressively recognized as potential anticancer drugs. The present study aimed to investigate the effects of anti-delta like legend 4 (anti-DLL4) treatment on the anticancer efficacy of GSIs in gastric cancer. SGC-7901-GFP human gastric cancer cells were tested for DLL4 expression by rosette formation test and immunofluorescence, and then were treated with anti-DLL4 antibody N-[N-(3,5-difluorophenacetyl)-L-ananyl]-S-phenylglycine t-butyl ester (DAPT, a type of GSI), or a combination of anti-DLL4 antibody and DAPT. The effects of in vitro treatments on cell apoptosis, cell cycle, and cell invasion were analyzed. For in vivo study, an orthotopic mouse model of gastric cancer was established with green fluorescence expressing SGC-7901. Ultrasound targeted microbubble destruction was used to treat tumor-bearing mice with anti-DLL4 antibody conjugated microbubbles, DAPT, and a combination of the two. Real-time fluorescence imaging was performed to assess tumor cell inhibition in each group. Following in vivo treatments, apoptosis of tumor cells and the expression of apoptosis-related genes BAX, Bcl-2, and P53 were detected by TUNEL and immunohistochemical staining. In vivo combined treatment of anti-DLL4 and DAPT led to a higher rate of cell apoptosis and greater inhibition of cell invasion than that observed with DAPT treatment alone. DAPT and anti-DLL4 combination therapy resulted in decreased cell distribution at G1 phase and increased cell distribution at S phase, compared to the untreated control group (P < .01). In vivo combined therapy with anti-DLL4 and DAPT significantly increased tumor growth inhibition and tumor cell apoptosis when compared to DAPT therapy alone (P < .05). In addition, combined treatment significantly increased expression of BAX and P53 and reduced Bcl-2 expression (P < .05). Conversely, treatment with DAPT alone only increased expression of BAX and P53 (P < .05), suggesting that the reduction of Bcl-2 expression may play an important role in the synergetic antitumor and proapoptosis effects of the combined treatment. Concurrent treatment with anti-DLL4 enhances the antitumor and proapoptotic efficacy of the γ-secretase inhibitor in gastric cancer both in vitro and in vivo.

The function of Notch1 intracellular domain in the differentiation of gastric cancer

Due to the complex function of the Notch signal pathway in gastric cancer (GC), the association between Notch homolog 1 (Notch1) intracellular domain (NICD) and differentiation of GC remains unknown. The present study aimed to investigate the potential association between NICD and GC differentiation, and demonstrated that poorly differentiated GC expressed increased NICD levels compared with well differentiated GC. A γ-secretase inhibitor inhibited the growth of AGS cells through downregulating NICD level. Additional data suggested that a COX-2 inhibitor caused a marked reduction of NICD level in comparison with a control group treated with dimethyl sulfoxide. Combined administration of γ-secretase and COX-2 inhibitor produced a marked inhibition of growth in AGS cells, which suggests that patients with poorly differentiated GC may benefit from the blockage of NICD, which potentially serves a role in GC differentiation.

Hypoxia Enhances Fusion of Oral Squamous Carcinoma Cells and Epithelial Cells Partly via the Epithelial-Mesenchymal Transition of Epithelial Cells

Increasing evidence and indications showed that cell fusion is crucial in tumor development and metastasis, and hypoxia, a closely linked factor to tumor microenvironment, which can lead to EMT, induces angiogenesis and metastasis in tumor growth. However, the relationship between hypoxia and fusion has not been reported yet. EMT will change some proteins in the epithelial cell surface and the changes of proteins in cell surface may increase cell fusion. This study found that hypoxia promotes the spontaneous cell fusion between Oral Squamous Carcinoma Cells (OSCCs) and Human Immortalized Oral Epithelial Cells (HIOECs). At the same time, Hypoxia can lead to EMT, and hypoxia-pretreated HIOECs increased fusion rate with OSCC, while the fusion rate was significantly reduced by DAPT, a kind of EMT blocker. Therefore, epithelial cells can increase spontaneously cell fusion with OSCC by EMT. Our study may provide a new insight to link among tumor microenvironment, cell fusion, and cancer.

Combination treatment of all-trans retinoic acid (ATRA) and γ-secretase inhibitor (DAPT) cause growth inhibition and apoptosis induction in the human gastric cancer cell line

Current medication for gastric cancer patients has a low success rate with resistance and side effects. According to recent studies, γ-secretase inhibitors is used as therapeutic drugs in cancer. Moreover, all-trans retinoic acid (ATRA) is a natural compound proposed for the treatment/chemo-prevention of cancers. The aim of this study was to explore the effects of ATRA in combination with N-[N-(3,5-difluorophenacetyl-l-alanyl)]-S-phenylglycine t-butyl ester (DAPT) as γ-secretase inhibitor on viability and apoptosis of the AGS and MKN-45 derived from human gastric cancer. AGS and MKN-45 gastric cancer cell lines were treated with different concentrations of ATRA or DAPT alone or ATRA plus DAPT. The viability, death detection and apoptosis of cells was examined by MTT assay and Ethidium bromide/acridine orange staining. The distribution of cells in different phases of cell cycle was also evaluated through flow cytometry analyses. In addition, caspase 3/7 activity and the expression of caspase-3 and bcl-2 were examined. DAPT and ATRA alone decreased gastric cancer cells viability in a concentration dependent manner. The combination of DAPT and ATRA exhibited significant synergistic inhibitory effects. The greater percentage of cells were accumulated in G0/G1 phase of cell cycle in combination treatment. The combination of DAPT and ATRA effectively increased the proportion of apoptotic cells and the level of caspase 3/7 activities compared to single treatment. Moreover, augmented caspase-3 up-regulation and bcl-2 down-regulation were found following combined application of DAPT and ATRA. The combination of DAPT and ATRA led to more reduction in viability and apoptosis in respect to DAPT or ATRA alone in the investigated cell lines.

The role of Notch signaling in gastric carcinoma: molecular pathogenesis and novel therapeutic targets

Notch signaling, an evolutionarily conserved signaling cascade system, is involved in promoting the progression of different types of cancers. Within the past decades, the Notch signaling pathway has increasingly been shown to have a primary role in deciding the fate of cancer cells and cancer stem cells in the stomach. Most components of Notch signaling are strongly expressed at different levels in gastric carcinoma tissue samples and are associated with a considerable number of clinical parameters. Moreover, crosstalk signaling between the Notch pathway and the Wnt, Ras, and NF-κB pathways promotes the process of gastric carcinogenesis. Consequently, this increases proliferation and prevents apoptosis in gastric cancer cells, and it contributes to the induction of angiogenesis and accelerates the progression of the epithelial-to-mesenchymal transition. Although the Notch signaling pathway presents novel therapeutic targets for cancer therapeutic intervention, there is still a dearth of in-depth understanding of the molecular mechanisms of Notch signaling in gastric carcinoma. In this review, we summarize the landscape of the Notch signaling pathway and recent findings on Notch signaling in gastric cancer. Furthermore, advanced studies and clinical treatments targeting the Notch signaling pathway arediscussed.

Notch as a Driver of Gastric Epithelial Cell Proliferation

The gastric epithelium is sustained by a population of stem cells that replenish the various mature epithelial lineages throughout adulthood. Regulation of stem and progenitor cell proliferation occurs via basic developmental signaling pathways, including the Notch pathway, which recently was described to promote gastric stem cell proliferation in both mice and human beings. Current cancer theory proposes that adult stem cells that maintain gastrointestinal tissues accumulate mutations that promote cancerous growth, and that basic signaling pathways, such as Notch, which stimulate stem cell proliferation, can promote tumorigenesis. Accordingly, constitutive Notch activation leads to unchecked cellular proliferation and gastric tumors in genetic mouse models. Furthermore, there is emerging evidence suggesting that the Notch pathway may be activated in some human gastric cancers, supporting a potential role for Notch in gastric tumorigenesis. In this review, we first summarize the current understanding of gastric stem cells defined by genetic mouse studies, followed by discussion of the literature regarding Notch pathway regulation of gastric stem cell function in the mouse and human beings. Notch action to maintain gastric epithelial cell homeostasis and the cellular consequences of dysregulated signaling to promote tumorigenesis are discussed, including studies associating Notch activation with human gastric cancer. Finally, we compare and contrast Notch function in the stomach with other gastrointestinal tissues, including the intestine, to highlight the sensitivity of the stomach to Notch-induced tumors.

Gastric cancer stem cells: Signal pathways and targeted therapies

Gastric cancer is still one of the most common malignant neoplasms worldwide and the third leading cause of cancer-related death. Therefore, it is of great significance to clarify the mechanism of gastric cancer oncogenesis. In the past decades, the theory of cancer stem cell has enhanced our knowledge of gastric cancer. Cancer stem cells are defined as cells within a tumor that possess the capacity to self-renew and to cause the heterogeneous lineages of cancer cells that comprise the tumor. The dysregulation of certain signal pathways occurs during tumor formation. Recently, the research on gastric cancer stem cells (GCSCs) and related signal pathways has provided a new theoretical basis for clarifying the mechanism of gastric cancer and treating this malignancy. This review will discuss the role of related signal pathways in GCSCs and therapies targeting the key molecules of these pathways.

NOTCH1 and NOTCH2 regulate epithelial cell proliferation in mouse and human gastric corpus

The Notch signaling pathway is known to regulate stem cells and epithelial cell homeostasis in gastrointestinal tissues; however, Notch function in the corpus region of the stomach is poorly understood. In this study we examined the consequences of Notch inhibition and activation on cellular proliferation and differentiation and defined the specific Notch receptors functioning in the mouse and human corpus. Notch pathway activity was observed in the mouse corpus epithelium, and gene expression analysis revealed NOTCH1 and NOTCH2 to be the predominant Notch receptors in both mouse and human. Global Notch inhibition for 5 days reduced progenitor cell proliferation in the mouse corpus, as well as in organoids derived from mouse and human corpus tissue. Proliferation effects were mediated through both NOTCH1 and NOTCH2 receptors, as demonstrated by targeting each receptor alone or in combination with Notch receptor inhibitory antibodies. Analysis of differentiation by marker expression showed no change to the major cell lineages; however, there was a modest increase in the number of transitional cells coexpressing markers of mucous neck and chief cells. In contrast to reduced proliferation after pathway inhibition, Notch activation in the adult stomach resulted in increased proliferation coupled with reduced differentiation. These findings suggest that NOTCH1 and NOTCH2 signaling promotes progenitor cell proliferation in the mouse and human gastric corpus, which is consistent with previously defined roles for Notch in promoting stem and progenitor cell proliferation in the intestine and antral stomach.

NEW & NOTEWORTHY

Here we demonstrate that the Notch signaling pathway is essential for proliferation of stem cells in the mouse and human gastric corpus. We identify NOTCH1 and NOTCH2 as the predominant Notch receptors expressed in both mouse and human corpus and show that both receptors are required for corpus stem cell proliferation. We show that chronic Notch activation in corpus stem cells induces hyperproliferation and tissue hypertrophy, suggesting that Notch may drive gastric tumorigenesis.

NOTCH receptors in gastric and other gastrointestinal cancers: oncogenes or tumor suppressors?

Gastric cancer (GC) ranks the most common cancer types and is one of the leading causes of cancer-related death. Due to delayed diagnosis and high metastatic frequency, 5-year survival rate of GC is rather low. It is a complex disease resulting from the interaction between environmental factors and host genetic alterations that deregulate multiple signaling pathways. The Notch signaling pathway, a highly conserved system in the regulation of the fate in several cell types, plays a pivotal role in cell differentiation, survival and proliferation. Notch is also one of the most commonly activated signaling pathways in tumors and its aberrant activation plays a key role in cancer advancement. Whether Notch cascade exerts oncogenic or tumor suppressive function in different cancer types depends on the cellular context. Mammals have four NOTCH receptors that modulate Notch pathway activity. In this review, we provide a comprehensive summary on the functional role of NOTCH receptors in gastric and other gastrointestinal cancers. Increasing knowledge of NOTCH receptors in gastrointestinal cancers will help us recognize the underlying mechanisms of Notch signaling and develop novel therapeutic strategies for GC.

Roles of Signaling Pathways in the Epithelial-Mesenchymal Transition in Cancer

The epithelial-mesenchymal transition (EMT) is a cellular process though which an epithelial phenotype can be converted into a phenotype of mesenchymal cells. Under physiological conditions EMT is important for embryogenesis, organ development, wound repair and tissue remodeling. However, EMT may also be activated under pathologic conditions, especially in carcinogenesis and metastatic progression. Major signaling pathways involved in EMT include transforming growth factor β(TGF-β), Wnt, Notch, Hedgehog and other signaling pathways. These pathways are related to several transcription factors, including Twist, Smads and zinc finger proteins snail and slug. These interact with each other to provide crosstalk between the relevant signaling pathways. This review lays emphasis on studying the relationship between EMT and signaling pathways in carcinogenesis and metastatic progression.

Prognostic values of four Notch receptor mRNA expression in gastric cancer

Notch ligands and receptors are frequently deregulated in several human malignancies including gastric cancer. The activation of Notch signaling has been reported to contribute to gastric carcinogenesis and progression. However, the prognostic roles of individual Notch receptors in gastric cancer patients remain elusive. In the current study, we accessed the prognostic roles of four Notch receptors, Notch 1-4, in gastric cancer patients through "The Kaplan-Meier plotter" (KM plotter) database, in which updated gene expression data and survival information include a total of 876 gastric cancer patients. All four Notch receptors' high mRNA expression was found to be correlated to worsen overall survival (OS) for all gastric cancer patients followed for 20 years. We further accessed the prognostic roles of individual Notch receptors in different clinicopathological features using Lauren classification, pathological grades, clinical grades, HER2 status and different choices of treatments of gastric cancer patients. These results indicate that there are critical prognostic values of the four Notch receptors in gastric cancer. This information will be useful for better understanding of the heterogeneity and complexity in the molecular biology of gastric cancer and to develop tools to more accurately predict their prognosis.

The expression of presenilin 1 enhances carcinogenesis and metastasis in gastric cancer

Presenilin 1 (PS-1, encoded by PSEN1) is a part of the gamma- (γ-) secretase complex. Mutations in PSEN1 cause the majority of cases of familial Alzheimer's disease (FAD). Although in recent years PS-1 has been implicated as a tumor enhancer in various cancers, nothing is known regarding its role in gastric cancer (GC). In the present study, we investigate the role and clinical significance of PS-1 in GC. We observed that PS-1 was significantly upregulated and amplified in GC tissues and cell lines, and its aberrant expression was positively correlated with lymph node metastasis and with poor overall survival. Furthermore, PS-1 promoted tumor invasion and metastasis of GC both in vitro and vivo without affecting the proliferation of GC cells (MGC-803 and MKN-45). The results of treatment with the γ-secretase inhibitor DAPT were consistent with the outcomes of PS-1 silencing. PS-1/γ-secretase cleaves E-cadherin and releases its bound protein partner, β-catenin, from the actin cytoskeleton, thereby allowing it to translocate into the nucleus and to activate the TCF/LEF-1 transcriptional activator, which may promote GC invasion and metastasis.In conclusion, PS-1 promotes invasion and metastasis in GC and may represent a novel prognostic biomarker and potential therapeutic target for GC treatment.

Notch and Wnt signaling pathway in cancer: Crucial role and potential therapeutic targets (Review)

There is no radical cure for all cancer types. The most frequently used therapies are surgical treatment, radiotherapy and chemotherapy. However, recrudescence, radiation resistance and chemotherapy resistance are the most challenging issues in clinical practice. To address these issues, they should be further studied at the molecular level, and the signaling pathways involved represent a promising avenue for this research. In the present review, we mainly discuss the components and mechanisms of activation of the Notch and Wnt signaling pathways, and we summarize the recent research efforts on these two pathways in different cancers. We also evaluate the ideal drugs that could target these two signaling pathways for cancer therapy, summarize alterations in the Notch and Wnt signaling pathways in cancer, and discuss potential signaling inhibitors as effective drugs for cancer therapy.

Epithelial-mesenchymal transition in gastric cancer

Gastric cancer (GC) is one of the most common malignancies worldwide with poor prognosis for lack of early detection and effective treatment modalities. The significant influence of tumor microenvironment on malignant cells has been extensively investigated in this targeted-therapy era. Epithelial-mesenchymal transition (EMT) is a highly conserved and fundamental process that is critical for embryogenesis and some other pathophysiological processes, especially tumor genesis and progression. Aberrant gastric EMT activation could endow gastric epithelial cells with increased mesenchymal characteristics and less epithelial features, and promote cancer cell stemness, initiation, invasion, metastasis, and chemo-resistance with cellular adhesion molecules especially E-cadherin concomitantly repressed, which allows tumor cells to disseminate and spread throughout the body. Some pathogens, stress, and hypoxia could induce and aggravate GC via EMT, which is significantly correlated with prognosis. GC EMT is modulated by diverse micro-environmental, membrane, and intracellular cues, and could be triggered by various overexpressed transcription factors, which are downstream of several vital cross-talking signaling pathways including TGF-β, Wnt/β-catenin, Notch, etc. microRNAs also contribute significantly to GC EMT modulation. There are currently some agents which could suppress GC EMT, shedding light on novel anti-malignancy strategies. Investigating potential mechanisms modulating GC cell EMT and discovering novel EMT regulators will further elucidate GC biology, and may provide new biomarkers for early GC detection and potentially efficient targets for preventative and curative anti-GC intervention approaches to prevent local and distant invasions.

Gastric tumor-initiating CD44+ cells and epithelial-mesenchymal transition are inhibited by γ-secretase inhibitor DAPT

It has been proposed that the Notch signaling pathway may serve a pivotal role in cellular differentiation, proliferation and apoptosis. However, the function of Notch signaling in gastric cancer stem cells (GCSCs) is largely unknown. The present study aimed to delineate the role of the Notch1 pathway in GCSCs and during epithelial-mesenchymal transition (EMT). Flow cytometry was used to isolate CD44⁺ cells from the human gastric cancer cell line, MKN45. CD44⁺ cells displayed the characteristics of CSCs and exhibited higher Notch1 expression compared with CD44^- cells. To investigate the role of the Notch1 pathway in GCSCs, CD44⁺ cells were treated with the γ-secretase inhibitor DAPT. DAPT treatment inhibited the expression of the Notch1 downstream target Hes1 and EMT markers, suppressed the properties of CSCs and impaired the invasion and proliferation capabilities of CD44⁺ cells. In addition, intraperitoneal treatment with DAPT effectively inhibited the growth of CD44⁺ cell xenograft tumors. The present study indicated that CD44⁺ GCSCs possess the characteristics of CSCs and that the Notch1 pathway serves a critical role in the maintenance of CSCs and EMT.