The COX-2 selective inhibitor-independent COX-2 effect on colon carcinoma cells is associated with the Delta1/Notch1 pathway

Notch receptor/ligand diversity: contribution to colorectal cancer stem cell heterogeneity

Cancer cell heterogeneity is a key contributor to therapeutic failure and post-treatment recurrence. Targeting cell subpopulations responsible for chemoresistance and recurrence seems to be an attractive approach to improve treatment outcome in cancer patients. However, this remains challenging due to the complexity and incomplete characterization of tumor cell subpopulations. The heterogeneity of cells exhibiting stemness-related features, such as self-renewal and chemoresistance, fuels this complexity. Notch signaling is a known regulator of cancer stem cell (CSC) features in colorectal cancer (CRC), though the effects of its heterogenous signaling on CRC cell stemness are only just emerging. In this review, we discuss how Notch ligand-receptor specificity contributes to regulating stemness, self-renewal, chemoresistance and cancer stem cells heterogeneity in CRC.

NS398 as a potential drug for autosomal-dominant polycystic kidney disease: Analysis using bioinformatics, and zebrafish and mouse models

Autosomal‐dominant polycystic kidney disease (ADPKD) is characterized by uncontrolled renal cyst formation, and few treatment options are available. There are many parallels between ADPKD and clear‐cell renal cell carcinoma (ccRCC); however, few studies have addressed the mechanisms linking them. In this study, we aimed to investigate their convergences and divergences based on bioinformatics and explore the potential of compounds commonly used in cancer research to be repurposed for ADPKD. We analysed gene expression datasets of ADPKD and ccRCC to identify the common and disease‐specific differentially expressed genes (DEGs). We then mapped them to the Connectivity Map database to identify small molecular compounds with therapeutic potential. A total of 117 significant DEGs were identified, and enrichment analyses results revealed that they are mainly enriched in arachidonic acid metabolism, p53 signalling pathway and metabolic pathways. In addition, 127 ccRCC‐specific up‐regulated genes were identified as related to the survival of patients with cancer. We focused on the compound NS398 as it targeted DEGs and found that it inhibited the proliferation of Pkd1^−/− and 786‐0 cells. Furthermore, its administration curbed cystogenesis in Pkd2 zebrafish and early‐onset Pkd1‐deficient mouse models. In conclusion, NS398 is a potential therapeutic agent for ADPKD.

Curcumin attenuates hypoxia/reoxygenation‑induced cardiomyocyte injury by downregulating Notch signaling

Recovery of the blood supply is the most effective treatment against ischemic heart disease; however, it is also a major cause of myocardial ischemia/reperfusion injury in clinical therapy. Curcumin has been reported to possess beneficial effects against hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury by regulating cell proliferation, apoptosis and antioxidant enzyme activity. The aim of the present study was to investigate the molecular mechanisms underlying the effects of curcumin on H/R-injured cardiomyocytes. H9C2 cardiomyocytes were pretreated with curcumin, and then cultured under H/R conditions. The viability of H9C2 cells was measured using a Cell Counting kit-8 assay, and the levels of intracellular lactate dehydrogenase (LDH), malondialdehyde (MDA) and superoxide dismutase (SOD) were measured to assess cell injury. Levels of reactive oxygen species (ROS) and apoptosis were evaluated by flow cytometry. The expression levels of Notch intracellular domain (NICD) and numerous downstream genes were analyzed via reverse transcription-quantitative polymerase chain reaction and western blotting. The results revealed that curcumin protected H9C2 cells against H/R-induced injury, reversing the H/R-induced increases in LDH and MDA levels, and decreases in SOD levels. ROS levels in H/R-induced cells were also significantly downregulated by curcumin treatment (P<0.01), and the apoptotic rate was significantly decreased from 15.13% in the H/R group to 7.7% in the H/R + curcumin group (P<0.01). The expression levels of NICD, hairy and enhancer of split (Hes)-1, Hes-5 and hairy/enhancer-of-split related with YRPW motif protein 1 (Hey-1) were significantly decreased in H/R-treated cells following curcumin treatment. Treatment with Jagged1 attenuated the effects of curcumin on cell viability, ROS levels and apoptosis; the Notch pathway was also reactivated. The present study indicated that there was a role for the Notch pathway in the protective effects of curcumin against H/R-induced cardiomyocyte injury, suggesting that downregulation of the Notch pathway may alleviate H/R-induced injury in H9C2 cells.

Computational Model for Predicting the Relationship Between Micro-RNAs and Their Target Messenger RNAs in Breast and Colon Cancers

Motivation

Uncovering the relationship between micro-RNAs (miRNAs) and their target messenger RNAs (mRNAs) can provide critical information regarding the mechanisms underlying certain types of cancers. In this context, we have proposed a computational method, referred to as prediction analysis by optimization method (PAOM), to predict miRNA-mRNA relations using data from normal and cancer tissues, and then applying the relevant algorithms to colon and breast cancers. Specifically, we used 26 miRNAs and 26 mRNAs with 676 (= 26 × 26) relationships to be recovered as unknown parameters.

Results

Optimization methods were used to detect 61 relationships in breast cancer and 32 relationships in colon cancer. Using sequence filtering, we detected 18 relationships in breast cancer and 15 relationships in colon cancer. Among the 18 relationships, CD24 is the target gene of let-7a and miR-98, and E2F1 is the target gene of miR-20. In addition, the frequencies of the target genes of miR-223, miR-23a, and miR-20 were significant in breast cancer, and the frequencies of the target genes of miR-17, miR-124, and miR-30a were found to be significant in colon cancer.

Availability

The numerical code is available from the authors on request.

Stromal COX-2 signaling are correlated with colorectal cancer: A review

Cyclooxygenase-2 (COX-2) and its product prostaglandin E₂ (PGE₂) play a critical role in development and progression of colorectal cancer. Yet the detailed mechanistic pathways of COX-2 mediated signaling are still controversial and the role of COX-2 interaction in epithelial-stromal compartments on colorectal carcinogenesis is not well-understood either. In this review, we provide experimental evidence to support that (1) COX-2 signaling plays a major role in development and progression of colorectal cancer; (2) Stromal fibroblasts are a major source of COX-2 and PGE₂; (3) Stromal-epithelial interaction mediated by COX-2 signaling promotes colorectal carcinogenesis and (4) Inhibition of stromal COX-2 signaling is necessary to control colorectal cancer. In conclusion, the evidences summarized in the review reflect recent advances and insight in mechanistic studies of colorectal cancer which can help the audiences to further understand the etiology and the control of this disease.

DAPT suppresses the proliferation of human glioma cell line SHG-44

OBJECTIVE

To explore the suppressing effect of γ-secretase inhibitor DAPT on proliferation of human glioma cell line SHG-44 in vitro and its mechanism.

METHODS

The SHG-44 cell was treated by DAPT with different concentration. The proliferation of cells was detected by MTT assay; cell cycle and TSC of CD133(+) were determined by flow cytometry analysis technique; the key factor in Notch signaling pathway (Notch-1, Delta-1, Hes-1) was measured by reverse transcriptase-polymerase chain reaction and western blotting.

RESULTS

DAPT inhibited the growth and proliferation of SHG-44 cells significantly(P<0.05). And the inhibiting effect on SHG-44 cells produced by DAPT showed a dose-dependent manner. DAPT increased the rate of cells in G0/G1 phase of SHG-44 cells, while it decreased the rate of cells in S phase. TSC of CD133(+) was significantly reduced after DAPT treated SHG-44 cells. The expression of protein and mRNA of Notch-1, Delta-1 and Hes-1 were gradually downregulated with the increase of DAPT doses.

CONCLUSIONS

DAPT can downregulate these key factor in Notch signaling pathway, reduce the TSC of CD133+ and inhibit the proliferation of SHG-44 cells.

Modulators affecting the immune dialogue between human immune and colon cancer cells

The link between chronic inflammation and colorectal cancer has been well established. The events proceeding along tumorigenesis are complicated and involve cells activated at the cancer microenvironment, tumor infiltrating polymorphonuclears, immune cells including lymphocyte subtypes and peripheral blood mononuclear cells (PBMC), as well as tumor-associated macrophages. The immune cells generate inflammatory cytokines, several of them playing a crucial role in tumorigenesis. Additional factors, such as gene expression regulated by cytokines, assembling of tumor growth- and transforming factors, accelerated angiogenesis, delayed apoptosis, contribute all to initiation, development and migration of tumor cells. Oxygen radical species originating from the inflammatory area promote cell mutation and cancer proliferation. Tumor cells may over-express pro-inflammatory mediators that in turn activate immune cells for inflammatory cytokines production. Consequently, an immune dialogue emerges between immune and cancer cells orchestrated through a number of activated molecular pathways. Cytokines, encompassing migration inhibitory factor, transforming growth factor beta 1, tumor necrosis factor-α, Interleukin (IL)-6, IL-10, IL-12, IL-17, IL-23 have been reported to be involved in human cancer development. Some cytokines, namely IL-5, IL-6, IL-10, IL-22 and growth factors promote tumor development and metastasis, and inhibit apoptosis via activation of signal transducer activator transcription-3 transcription factor. Colon cancer environment comprises mesenchymal, endothelial and immune cells. Assessment of the interaction between components in the tumor environment and malignant cells requires a reconsideration of a few topics elucidating the role of chronic inflammation in carcinogenesis, the function of the immune cells expressed by inflammatory cytokine production, the immunomodulation of cancer cells and the existence of a cross-talk between immune and malignant cells leading to a balance in cytokine production. It is conceivable that the prevalence of anti-inflammatory cytokine production by PBMC in the affected colonic mucosa will contribute to the delay, or even to halt down malignant expansion. Targeting the interplay between immune and cancer cells by mediators capable to alter cytokine secretion toward increased anti-inflammatory cytokine release by PBMC and tumor associated macrophages, may serve as an additional strategy for treatment of malignant diseases. This review will focus on the inflammatory events preceding tumorigenesis in general, and on a number of modulators capable to affect colon cancer cell-induced production of inflammatory cytokines by PBMC through alteration of the immune cross-talk between PBMC and cancer cells.

Chemopreventive drugs: Mechanisms via inhibition of cancer stem cells in colorectal cancer

Recent epidemiological studies, basic research and clinical trials on colorectal cancer (CRC) prevention have helped identify candidates for effective chemopreventive drugs. However, because of the conflicting results of clinical trials or side effects, the effective use of chemopreventive drugs has not been generalized, except for patients with a high-risk for developing hereditary CRC. Advances in genetic and molecular technologies have highlighted the greater complexity of carcinogenesis, especially the heterogeneity of tumors. We need to target cells and processes that are critical to carcinogenesis for chemoprevention and treatment of advanced cancer. Recent research has shown that intestinal stem cells may serve an important role in tumor initiation and formation of cancer stem cells. Moreover, studies have shown that the tumor microenvironment may play additional roles in dedifferentiation, to enable tumor cells to take on stem cell features and promote the formation of tumorigenic stem cells. Therefore, early tumorigenic changes of stem cells and signals for dedifferentiation may be good targets for chemoprevention. In this review, I focus on cancer stem cells in colorectal carcinogenesis and the effect of major chemopreventive drugs on stem cell-related pathways.

Ibuprofen inhibits colitis-induced overexpression of tumor-related Rac1b

The serrated pathway to colorectal tumor formation involves oncogenic mutations in the BRAF gene, which are sufficient for initiation of hyperplastic growth but not for tumor progression. A previous analysis of colorectal tumors revealed that overexpression of splice variant Rac1b occurs in around 80% of tumors with mutant BRAF and both events proved to cooperate in tumor cell survival. Here, we provide evidence for increased expression of Rac1b in patients with inflamed human colonic mucosa as well as following experimentally induced colitis in mice. The increase of Rac1b in the mouse model was specifically prevented by the nonsteroidal anti-inflammatory drug ibuprofen, which also inhibited Rac1b expression in cultured HT29 colorectal tumor cells through a cyclooxygenase inhibition.independent mechanism. Accordingly, the presence of ibuprofen led to a reduction of HT29 cell survival in vitro and inhibited Rac1b-dependent tumor growth of HT29 xenografts. Together, our results suggest that stromal cues, namely, inflammation, can trigger changes in Rac1b expression in the colon and identify ibuprofen as a highly specific and efficient inhibitor of Rac1b overexpression in colorectal tumors. Our data suggest that the use of ibuprofen may be beneficial in the treatment of patients with serrated colorectal tumors or with inflammatory colon syndromes.

Nonsteroidal anti-inflammatory drugs suppress cancer stem cells via inhibiting PTGS2 (cyclooxygenase 2) and NOTCH/HES1 and activating PPARG in colorectal cancer

Cancer stem cells (CSCs) play a pivotal role in cancer relapse or metastasis. We investigated the CSC-suppressing effect of nonsteroidal anti-inflammatory drugs (NSAIDs) and the relevant mechanisms in colorectal cancer. We measured the effect of NSAIDs on CSC populations in Caco-2 or SW620 cells using colosphere formation and flow cytometric analysis of PROM1 (CD133)(+) CD44(+) cells after indomethacin treatment with/without prostaglandin E2 (PGE2) or peroxisome proliferator-activated receptor γ (PPARG) antagonist, and examined the effect of indomethacin on transcriptional activity and protein expression of NOTCH/HES1 and PPARG. These effects of indomethacin were also evaluated in a xenograft mouse model. NSAIDs (indomethacin, sulindac and aspirin), celecoxib, γ-secretase inhibitor and PPARG agonist significantly decreased the number of colospheres formation compared to controls. In Caco-2 and SW620 cells, compared to controls, PROM1 (CD133)(+) CD44(+) cells were significantly decreased by indomethacin treatment, and increased by 5-fluorouracil (5-FU) treatment. This 5-FU-induced increase of PROM1 (CD133)(+) CD44(+) cells was significantly attenuated by combination with indomethacin. This CSC-inhibitory effect of indomethacin was reversed by addition of PGE2 and PPARG antagonist. Indomethacin significantly decreased CBFRE and increased PPRE transcriptional activity and their relative protein expressions. In xenograft mouse experiments using 5-FU-resistant SW620 cells, the 5-FU treatment combined with indomethacin significantly reduced tumor growth, compared to 5-FU alone. In addition, treatment of indomethacin alone or combination of 5-FU and indomethacin decreased the expressions of PROM1 (CD133), CD44, PTGS2 (cyclooxygenase 2) and HES1, and increased PPARG expression. NSAIDs could selectively reduce the colon CSCs and suppress 5-FU-induced increase of CSCs via inhibiting PTGS2 (cyclooxygenase 2) and NOTCH/HES1, and activating PPARG.

The effects of piroxicam and deracoxib on canine mammary tumour cell line

Cyclooxygenase (COX) inhibitors, already widely used for the treatment of pain and inflammation, are considered as promising compounds for the prevention and treatment of neoplasia. The aim of our study was to determine the direct antiproliferative effects of nonsteroidal anti-inflammatory drugs (NSAIDs), piroxicam and deracoxib, at a variety of concentrations as both single and combined treatments on canine mammary carcinoma cell line CMT-U27 and to understand the mechanisms of cell death. MTT assay was performed to determine cell viability, and flow cytometric analyses were performed to evaluate apoptosis and cell cycle alterations. Significant decrease in cell viability was observed at high concentrations of piroxicam and deracoxib in both single and combined treatments after 72 h incubation. Combined treatment produced a significantly greater inhibition than that caused by either agent alone. Also apoptotic cell number was increased by both drugs at the cytotoxic concentrations. However, concomitant treatment of cells with piroxicam and deracoxib resulted in significant induction of apoptosis at lower concentrations and accumulation of cells in the G₀/G₁ phase. Significant cytotoxic effects exhibited by the combination of piroxicam and deracoxib against canine mammary carcinoma cells in vitro suggest an attractive approach for the treatment of canine mammary carcinoma.

Chemoprevention in colorectal cancer--where we stand and what we have learned from twenty year's experience

INTRODUCTION

Colorectal chemoprevention is a strategy aimed at preventing tumour progression before irreversible changes to the proteome are in full progress. Chemoprevention is not a new concept. In fact, medical practitioners since the early 19th century have tried various herbal and medicinal products as methods that could prevent tumours. The current understanding of tumourigenesis and cellular signalling focuses on a more targeted approach and paves the way for better understanding of colorectal chemoprevention.

METHODS

The online databases PubMed, Medline, Medscape Oncology and Scirrus were searched for articles of relevance. The Keyword involved the following words: "Colorectal Cancer Chemoprevention", "Colorectal Cancer", "Chemoprevention", "Adenoma-Carcinoma Sequence" and "Colorectal Polyps". The search was started from the period of June 1995 until September 2010 inclusive.

RESULTS

More than 50 natural and synthetic compounds have been shown to have chemotherapeutic effect but the majority of these agents are still in their early experimental stages and hence far from our subject of discussion. Our discussion will focus on large scale randomised trials on human subjects or established compounds. Within the context of chemoprevention, Non-steroidal anti-inflammatory agents have undergone extensive research and have shown promising results with large scale randomised trials. Additionally, metformin, resveratrol, Histone deacetylase inhibitors, Src kinases as well monoclonal antibodies have shown promising results as well.

CONCLUSION

Colorectal cancer is the fourth most common cancer in the world. In the UK alone the number of cases reported in 2008 was almost 40,000 which make it the third most common tumour nationwide. Curative intent surgery or Colectomy is the treatment of choice for most cases of bowel cancer; however, in a select subpopulation of patients who have been colonoscopically diagnosed to harbour pre-malignant lesions, have a family history of colorectal cancer, or have been genetically diagnosed and treated surgically for colorectal tumours; chemoprevention might play a crucial role in deterring further tumour progression. The very latest studies that are in publication or are just accruing results are giving us encouraging data that might suggest whether mass scale ingestion of a specific medication might deter colorectal tumour progression.

Role of Notch and its oncogenic signaling crosstalk in breast cancer

The Notch signaling plays a key role in cell differentiation, survival, and proliferation through diverse mechanisms. Notch signaling is also involved in vasculogenesis and angiogenesis. Moreover, Notch expression is regulated by hypoxia and inflammatory cytokines (IL-1, IL-6 and leptin). Entangled crosstalk between Notch and other developmental signaling (Hedgehog and Wnt), and signaling triggered by growth factors, estrogens and oncogenic kinases, could impact on Notch targeted genes. Thus, alterations of the Notch signaling can lead to a variety of disorders, including human malignancies. Notch signaling is activated by ligand binding, followed by ADAM/tumor necrosis factor-α-converting enzyme (TACE) metalloprotease and γ-secretase cleavages that produce the Notch intracellular domain (NICD). Translocation of NICD into the nucleus induces the transcriptional activation of Notch target genes. The relationships between Notch deregulated signaling, cancer stem cells and the carcinogenesis process reinforced by Notch crosstalk with many oncogenic signaling pathways suggest that Notch signaling may be a critical drug target for breast and other cancers. Since current status of knowledge in this field changes quickly, our insight should be continuously revised. In this review, we will focus on recent advancements in identification of aberrant Notch signaling in breast cancer and the possible underlying mechanisms, including potential role of Notch in breast cancer stem cells, tumor angiogenesis, as well as its crosstalk with other oncogenic signaling pathways in breast cancer. We will also discuss the prognostic value of Notch proteins and therapeutic potential of targeting Notch signaling for cancer treatment.

Celecoxib inhibits β-catenin-dependent survival of the human osteosarcoma MG-63 cell line

Cyclo-oxygenase (COX)-2 inhibitors may exert antitumour effects through COX-2-independent mechanisms. This study investigated the effects of the COX-2 inhibitor celecoxib on the viability of the human osteosarcoma MG-63 cell line and its β-catenin signalling pathway. Cell viability and apoptosis were examined in celecoxib-treated cells or after β-catenin knockdown in vitro. Analyses were performed to detect glycogen synthase kinase (GSK)-3β, phosphorylated GSK-3β, β-catenin, c-Myc and cyclin D1 proteins, and mRNA levels of β-catenin, c-Myc and CCND1 (encoding cyclin D1). β-Catenin was shown to be required for MG63 cell survival and celecoxib exerted an inhibitory effect on the viability of cultured MG-63 cells in a time- and dose-dependent manner. β-Catenin protein decreased in the cytosol and nucleus following celecoxib treatment (from 6 h after initiation of treatment onwards; lowest protein levels were reached at > 72 h). Significant reductions in β-catenin, c-Myc and CCND1 mRNA were observed. Celecoxib inhibited MG-63 cell viability, possibly by activating GSK-3β and inhibiting β-catenin-dependent gene transcription, suggesting a role for celecoxib in osteosarcoma treatment.

Enhancement of 5-fluorouracil efficacy on high COX-2 expressing HCA-7 cells by low dose indomethacin and NS-398 but not on low COX-2 expressing HT-29 cells

The antiproliferative effect of 5-fluorouracil (5-FU) in the presence of low dose non-steroidal anti-inflammatory drugs (NSAIDs) on high cyclooxygenase-2 (COX-2)-expressing HCA-7 and low COX-2-expressing HT-29 colon carcinoma cell lines was investigated. Pharmacogenetic parameters were studied to characterize the 5-FU sensitivity of the two cell lines. Thymidylate synthase (TS) and methylenetetrahydrofolate reductase (MTHFR) polymorphisms were determined by PCR analysis. Cell proliferation was measured by SRB assay, cell cycle distribution and apoptosis by FACS analysis. Cyclooxygenase expression was detected by Western blot and also by fluorescence microscopy. Prostaglandin E(2) (PGE(2)) levels were investigated with ELISA kit. The HT-29 cell line was found to be homozygous for TS 2R and 1494ins6 and T homozygous for MTHFR 677 polymorphisms predicting high 5-FU sensitivity (IC(50): 10 microM). TS 3R homozygosity, TS 1496del6 and MTHFR 677CT heterozygosity may explain the modest 5-FU sensitivity (IC(50): 1.1 mM) of the HCA-7 cell line. Indomethacin and NS-398 (10 microM and 1.77 microM, respectively) reduced the PGE(2) level in HCA-7 cells (>90%). Low concentrations of NSAIDs without antiproliferative potency increased the S-phase arrest and enhanced the cytotoxic action of 5-FU only in HCA-7 cells after 48-hours treatment. The presented data suggested that the enhancement of 5-FU cytotoxicity by indomethacin or NS-398 applied in low dose is related to the potency of NSAIDs to modulate the cell-cycle distribution and the apoptosis; however, it seems that this effect might be dependent on cell phenotype, namely on the COX-2 expression.

NOTCH signaling is required for formation and self-renewal of tumor-initiating cells and for repression of secretory cell differentiation in colon cancer

NOTCH signaling is critical for specifying the intestinal epithelial cell lineage and for initiating colorectal adenomas and colorectal cancers (CRC). Based on evidence that NOTCH is important for the maintenance and self-renewal of cancer-initiating cells in other malignancies, we studied the role of NOTCH signaling in colon cancer-initiating cells (CCIC). Tumors formed by CCICs maintain many properties of the primary CRCs from which they were derived, such as glandular organization, cell polarity, gap junctions, and expression of characteristic CRC molecular markers. Furthermore, CCICs have the property of self-renewal. In this study, we show that NOTCH signaling is 10- to 30-fold higher in CCIC compared with widely used colon cancer cell lines. Using small-molecule inhibition and short hairpin RNA knockdown, we show that NOTCH prevents CCIC apoptosis through repression of cell cycle kinase inhibitor p27 and transcription factor ATOH1. NOTCH is also critical to intrinsic maintenance of CCIC self-renewal and the repression of secretory cell lineage differentiation genes such as MUC2. Our findings describe a novel human cell system to study NOTCH signaling in CRC tumor initiation and suggest that inhibition of NOTCH signaling may improve CRC chemoprevention and chemotherapy.

Arachidonic acid potentiates hypoxia-induced VEGF expression in mouse embryonic stem cells: involvement of Notch, Wnt, and HIF-1α

Recent investigations suggest that hypoxia increases the release of fatty acids, which participate in the regulation of cytokine synthesis and cell growth. Therefore, in this study, we examined the effect of arachidonic acid (AA) on hypoxia-induced vascular endothelial growth factor (VEGF) expression and its related signaling pathways in mouse embryonic stem (ES) cells. Hypoxia increased the level of [3H]AA release and VEGF expression. AA treatment concurrent with hypoxia further increased the PGE2 production and VEGF expression level, which was inhibited by the suppression of cPLA2 and cyclooxygenase 2 (COX-2) pathways. Hypoxia increased the level of Notch-1 and Wnt-1/β-catenin expression, which was blocked by the inhibition of COX-2, and inhibition of Notch-1 by γ-secretase inhibitor blocked Wnt-1 activation. Moreover, the hypoxia-induced increase of hypoxia-inducible factor 1α (HIF-1α) expression induced Notch-1 activation and was regulated by Wnt-1 activation. The expression of each signaling molecule induced an increase in VEGF expression that was greater in hypoxia with AA than in hypoxia alone. The inhibition of VEGF expression using VEGF-targeted small interfering RNA decreased the hypoxia-induced increase in cell cycle regulatory protein expression, DNA synthesis, and cell number, suggesting that hypoxia-induced VEGF expression stimulates proliferation of mouse ES cells. In conclusion, AA potentiates hypoxia-induced VEGF expression in mouse ES cells through the Notch-1, Wnt-1, and HIF-1α pathways.