Downregulation of prostaglandin E receptor subtype EP3 during colon cancer development

Targeting cyclooxygenase-2 for chemoprevention of inflammation-associated intestinal carcinogenesis: An update

Mounting evidence from preclinical and clinical studies suggests that persistent inflammation functions as a driving force in the journey to cancer. Cyclooxygenase-2 (COX-2) is a key enzyme involved in inflammatory signaling. While being transiently upregulated upon inflammatory stimuli, COX-2 has been found to be consistently overexpressed in human colorectal cancer and several other malignancies. The association between chronic inflammation and cancer has been revisited: cancer can arise when inflammation fails to resolve. Besides its proinflammatory functions, COX-2 also catalyzes the production of pro-resolving as well as anti-inflammatory metabolites from polyunsaturated fatty acids. This may account for the side effects caused by long term use of some COX-2 inhibitory drugs during the cancer chemopreventive trials. This review summarizes the latest findings highlighting the dual functions of COX-2 in the context of its implications in the development, maintenance, and progression of cancer.

Cooperation between Prostaglandin E2 and Epidermal Growth Factor Receptor in Cancer Progression: A Dual Target for Cancer Therapy

It is recognized that prostaglandin E2 (PGE2) is one key lipid mediator involved in chronic inflammation, and it is directly implicated in tumor development by regulating cancer cell growth and migration, apoptosis, epithelial-mesenchymal transition, angiogenesis, and immune escape. In addition, the expression of the enzymes involved in PGE2 synthesis, cyclooxygenase 2 (COX-2) and microsomal prostaglandin E synthase 1 (mPGES1), positively correlates with tumor progression and aggressiveness, clearly indicating the crucial role of the entire pathway in cancer. Moreover, several lines of evidence suggest that the COX2/mPGES1/PGE2 inflammatory axis is involved in the modulation of epidermal growth factor receptor (EGFR) signaling to reinforce the oncogenic drive of EGFR activation. Similarly, EGFR activation promotes the induction of COX2/mPGES1 expression and PGE2 production. In this review, we describe the interplay between COX2/mPGES1/PGE2 and EGFR in cancer, and new therapeutic strategies that target this signaling pathway, to outline the importance of the modulation of the inflammatory process in cancer fighting.

The Atypical MAP Kinase MAPK15 Is Required for Lung Adenocarcinoma Metastasis via Its Interaction with NF-κB p50 Subunit and Transcriptional Regulation of Prostaglandin E2 Receptor EP3 Subtype

Studying the relatively underexplored atypical MAP Kinase MAPK15 on cancer progression/patient outcomes and its potential transcriptional regulation of downstream genes would be highly valuable for the diagnosis, prognosis, and potential oncotherapy of malignant tumors such as lung adenocarcinoma (LUAD). Here, the expression of MAPK15 in LUAD was detected by immunohistochemistry and its correlation with clinical parameters such as lymph node metastasis and clinical stage was analyzed. The correlation between the prostaglandin E2 receptor EP3 subtype (EP3) and MAPK15 expression in LUAD tissues was examined, and the transcriptional regulation of EP3 and cell migration by MAPK15 in LUAD cell lines were studied using the luciferase reporter assay, immunoblot analysis, qRT-PCR, and transwell assay. We found that MAPK15 is highly expressed in LUAD with lymph node metastasis. In addition, EP3 is positively correlated with the expression of MAPK15 in LUAD tissues, and we confirmed that MAPK15 transcriptionally regulates the expression of EP3. Upon the knockdown of MAPK15, the expression of EP3 was down-regulated and the cell migration ability was decreased in vitro; similarly, the mesenteric metastasis ability of the MAPK15 knockdown cells was inhibited in in vivo animal experiments. Mechanistically, we demonstrate for the first time that MAPK15 interacts with NF-κB p50 and enters the nucleus, and NF-κB p50 binds to the EP3 promoter and transcriptionally regulates the expression of EP3. Taken together, we show that a novel atypical MAPK and NF-κB subunit interaction promotes LUAD cell migration through transcriptional regulation of EP3, and higher MAPK15 level is associated with lymph node metastasis in patients with LUAD.

The Role of Inflammatory Mediators in Colorectal Cancer Hepatic Metastasis

Colorectal cancer (CRC) is the second leading cause of death in cancer patients in the USA, whereas the major cause of CRC deaths is hepatic metastases. The liver is the most common site of metastasis in patients with CRC due to hepatic portal veins receiving blood from the digestive tract. Understanding the cellular and molecular mechanisms of hepatic metastases is of dire need for the development of potent targeted therapeutics. Immuno-signaling molecules including cytokines and chemokines play a pivotal role in hepatic metastases from CRC. This brief review discusses the involvement of three representative cytokines (TNF-α, IL-6 and IL-1β), a lipid molecule PGE2 and two chemokines (CXCL1 and CXCL2) in the process of CRC liver metastases.

Participation of lipopolysaccharide in hyperplasic adipose expansion: Involvement of NADPH oxidase/ROS/p42/p44 MAPK-dependent Cyclooxygenase-2

Obesity is a world‐wide problem, especially the child obesity, with the complication of various metabolic diseases. Child obesity can be developed as early as the age between 2 and 6. The expansion of fat mass in child age includes both hyperplasia and hypertrophy of adipose tissue, suggesting the importance of proliferation and adipogenesis of preadipocytes. The changed composition of gut microbiota is associated with obesity, revealing the roles of lipopolysaccharide (LPS) on manipulating adipose tissue development. Studies suggest that LPS enters the circulation and acts as a pro‐inflammatory regulator to facilitate pathologies. Nevertheless, the underlying mechanisms behind LPS‐modulated obesity are yet clearly elucidated. This study showed that LPS enhanced the expression of cyclooxygenase‐2 (COX‐2), an inflammatory regulator of obesity, in preadipocytes. Pretreating preadipocytes with the scavenger of reactive oxygen species (ROS) or the inhibitors of NADPH oxidase or p42/p44 MAPK markedly decreased LPS‐stimulated gene expression of COX‐2 together with the phosphorylation of p47^phox and p42/p44 MAPK, separately. LPS activated p42/p44 MAPK via NADPH oxidase‐dependent ROS accumulation in preadipocytes. Reduction of intracellular ROS or attenuation of p42/p44 MAPK activation both reduced LPS‐mediated COX‐2 expression and preadipocyte proliferation. Moreover, LPS‐induced preadipocyte proliferation and adipogenesis were abolished by the inhibition of COX‐2 or PEG₂ receptors. Taken together, our results suggested that LPS enhanced the proliferation and adipogenesis of preadipocytes via NADPH oxidase/ROS/p42/p44 MAPK‐dependent COX‐2 expression.

The COX-2-PGE2 Pathway Promotes Tumor Evasion in Colorectal Adenomas

The mechanisms underlying the regulation of a checkpoint receptor, PD-1, in tumor-infiltrating immune cells during the development of colorectal cancer are not fully understood. Here we demonstrate that COX-2-derived PGE2, an inflammatory mediator and tumor promoter, induces PD-1 expression by enhancing NFκB's binding to the PD-1 promoter via an EP4-PI3K-Akt signaling pathway in both CD8+ T cells and macrophages. Moreover, PGE2 suppresses CD8+ T-cell proliferation and cytotoxicity against tumor cells and impairs macrophage phagocytosis of cancer cells via an EP4-PI3K-Akt-NFκB-PD-1 signaling pathway. In contrast, inhibiting the COX-2-PGE2-EP4 pathway increases intestinal CD8+ T-cell activation and proliferation and enhances intestinal macrophage phagocytosis of carcinoma cells accompanied by reduction of PD-1 expression in intestinal CD8+ T cells and macrophages in ApcMin/+ mice. PD-1 expression correlates well with COX-2 levels in human colorectal cancer specimens. Both elevated PD-1 and COX-2 are associated with poorer overall survival in patients with colorectal cancer. Our results uncover a novel role of PGE2 in tumor immune evasion. They may provide the rationale for developing new therapeutic approaches to subvert this process by targeting immune checkpoint pathways using EP4 antagonists. In addition, our findings reveal a novel mechanism explaining how NSAIDs reduce colorectal cancer risk by suppressing tumor immune evasion.

PREVENTION RELEVANCE

These findings provide a potential explanation underlying the chemopreventive effect of NSAIDs on reducing colorectal cancer incidence during premalignancy and provide a rationale for developing EP4 antagonists for colorectal cancer prevention and treatment. Simply targeting PGE2 signaling alone may be efficacious in colorectal cancer prevention and treatment, avoiding side effects associated with NSAIDs.

Role of prostaglandin E2 in the progression of gastrointestinal cancer

Chronic inflammation is a well-established risk factor for several diseases, including cancer. It influences tumor cell biology and the type and density of immune cells in the tumor microenvironment (TME), promoting cancer development. While pro-inflammatory cytokines and chemokines modulate cancer development, emerging evidence has shown that prostaglandin E2 (PGE2) is a known mediator connecting chronic inflammation to cancerization. This review highlights recent advances in our understanding of how the elevation of PGE2 production promotes gastrointestinal cancer initiation, progression, invasion, metastasis, and recurrence, including modulation of immune checkpoint signaling and the type and density of immune cells in the tumor/tissue microenvironment.

Immunological significance of alternative splicing prognostic signatures for bladder cancer

Background

Bladder cancer (BLCA) is the most common malignant tumor in the genitourinary system, and the complex tumor microenvironment (TME) of BLCA is the main factor in its difficult treatment. Accumulated evidence supports that alternative splicing (AS) events frequently occur in cancer and are closely related to the TME. Therefore, there is an urgent need to comprehensively analyze the prognostic value of AS events in BLCA.

Method

The clinical, transcriptome and AS data of BLCA were downloaded from the Cancer Genome Atlas database, and a Cox proportional hazard regression model and LASSO regression were used to establish a prognostic signature. Then, the prognostic value of the signature was verified by clinical survival status, clinicopathologic features, tumor immune microenvironment (TIME), and immune checkpoint. Next, we screened the AS-related genes with the largest expression differences between tumor and normal samples by gene differential expression analysis. Finally, the regulatory network of AS-splicing factors (SFs) was established to unravel the potential regulatory mechanism of AS events in BLCA.

Results

A BLCA prognostic signature related to seven AS events was constructed, and the prognostic value of the signature was also verified from multiple perspectives. Moreover, there was significant abnormal expression of PTGER3, a gene implicated in AS events, the expression of which was associated with the survival, clinicopathological features, TIME, and immunotherapy of BLCA, suggesting that it has potential clinical application value. Furthermore, the AS-SF regulatory network indicated that splicing factors (PRPF39, LUC7L, HSPA8 and DDX21) might be potential biomarkers of BLCA.

Conclusions

Our study revealed the potential role of AS events in the prognosis, TIME and immunotherapy of BLCA and yielded new insights into the molecular mechanisms of and personalized immunotherapy for BLCA.

Phospholipase A2, a nonnegligible enzyme superfamily in gastrointestinal diseases

Gastrointestinal tract is important for digestion, absorption, detoxification and immunity. Gastrointestinal diseases are mainly caused by the imbalance of protective and attacking factors in gastrointestinal mucosa, which can seriously harm human health. Phospholipase A₂ (PLA₂) is a large family closely involved in lipid metabolism and is found in almost all human cells. A growing number of studies have revealed that its metabolites are deeply implicated in various inflammatory pathways and also regulates the maintenance of numerous biological events such as dietary digestion, membrane remodeling, barrier action, and host immunity. In addition to their phospholipase activity, some members of the superfamily also have other catalytic activities. Based on the in-depth effects of phospholipase A2 on bioactive lipid metabolism and inflammatory cytokines, PLA₂ and its metabolites are likely to be involved in the pathogenesis, development or prevention of gastrointestinal diseases. Therefore, this review will focus on the physiological and pathogenic roles of several important PLA₂ enzymes in the gastrointestinal tract, and reveals the potential of PLA₂ as a therapeutic target for gastrointestinal diseases.

Prostaglandin Pathways: Opportunities for Cancer Prevention and Therapy

Because of profound effects observed in carcinogenesis, prostaglandins (PGs), prostaglandin-endoperoxide synthases, and PG receptors are implicated in cancer development and progression. Understanding the molecular mechanisms of PG actions has potential clinical relevance for cancer prevention and therapy. This review focuses on the current status of PG signaling pathways in modulating cancer progression and aims to provide insights into the mechanistic actions of PGs and their receptors in influencing tumor progression. We also examine several small molecules identified as having anticancer activity that target prostaglandin receptors. The literature suggests that targeting PG pathways could provide opportunities for cancer prevention and therapy.

Cyclooxygenases and Prostaglandins in Tumor Immunology and Microenvironment of Gastrointestinal Cancer

Chronic inflammation is a known risk factor for gastrointestinal cancer. The evidence that nonsteroidal anti-inflammatory drugs suppress the incidence, growth, and metastasis of gastrointestinal cancer supports the concept that a nonsteroidal anti-inflammatory drug target, cyclooxygenase, and its downstream bioactive lipid products may provide one of the links between inflammation and cancer. Preclinical studies have demonstrated that the cyclooxygenase-2-prostaglandin E₂ pathway can promote gastrointestinal cancer development. Although the role of this pathway in cancer has been investigated extensively for 2 decades, only recent studies have described its effects on host defenses against transformed epithelial cells. Overcoming tumor-immune evasion remains one of the major challenges in cancer immunotherapy. This review summarizes the impacts of the cyclooxygenase-2-prostaglandin E₂ pathway on gastrointestinal cancer development. Our focus was to highlight recent advances in our understanding of how this pathway induces tumor immune evasion.

Genetic architectures of proximal and distal colorectal cancer are partly distinct

OBJECTIVE

An understanding of the etiologic heterogeneity of colorectal cancer (CRC) is critical for improving precision prevention, including individualized screening recommendations and the discovery of novel drug targets and repurposable drug candidates for chemoprevention. Known differences in molecular characteristics and environmental risk factors among tumors arising in different locations of the colorectum suggest partly distinct mechanisms of carcinogenesis. The extent to which the contribution of inherited genetic risk factors for CRC differs by anatomical subsite of the primary tumor has not been examined.

DESIGN

To identify new anatomical subsite-specific risk loci, we performed genome-wide association study (GWAS) meta-analyses including data of 48 214 CRC cases and 64 159 controls of European ancestry. We characterised effect heterogeneity at CRC risk loci using multinomial modelling.

RESULTS

We identified 13 loci that reached genome-wide significance (p<5×10-8) and that were not reported by previous GWASs for overall CRC risk. Multiple lines of evidence support candidate genes at several of these loci. We detected substantial heterogeneity between anatomical subsites. Just over half (61) of 109 known and new risk variants showed no evidence for heterogeneity. In contrast, 22 variants showed association with distal CRC (including rectal cancer), but no evidence for association or an attenuated association with proximal CRC. For two loci, there was strong evidence for effects confined to proximal colon cancer.

CONCLUSION

Genetic architectures of proximal and distal CRC are partly distinct. Studies of risk factors and mechanisms of carcinogenesis, and precision prevention strategies should take into consideration the anatomical subsite of the tumour.

Prostaglandin E2 receptor 3 (EP3) signaling promotes migration of cervical cancer via urokinase-type plasminogen activator receptor (uPAR)

Purpose

Cervical cancer metastasis results in poor prognosis and increased mortality, which is not separated from inflammatory reactions accumulated by prostaglandin E2 (PGE2). As a specific G-protein coupled PGE2 receptor, EP3 is demonstrated as a negative prognosticator of cervical malignancy. Now, we aimed to investigate the pathological mechanism of EP3 in modulating cervical cancer carcinogenesis.

Methods

Bioinformatics analysis was used to identify PAI-1 and uPAR correlations with EP3 expression, as well as the prognosis of cervical cancer patients. In vitro analyses were carried out to investigate the role of EP3 on cervical cancer proliferation and migration.

Results

In vitro studies showed that sulprostone (an EP3 agonist) enhanced the proliferation and migration of cervical cancer cells, whereas silencing of EP3 inhibited their proliferation and migration. Furthermore, EP3 knockdown increased the expression of plasminogen activator inhibitor type 1 (PAI-1), urokinase-type plasminogen activator receptor (uPAR), and phosphorylated extracellular signal-regulated kinases 1/2 (p-ERK1/2), but decreased p53 expression. Bioinformatics analysis showed that both PAI-1 and uPAR were correlated with EP3 expression, as well as the prognosis of cervical cancer patients. The survival analysis further showed that uPAR overexpression (IRS≥2) was correlated with a lower overall survival rate of cervical cancer patients with advanced stages (FIGO III-IV).

Conclusion

These results indicated that EP3 signaling pathway might facilitate the migration of cervical cancer cells through modulating uPAR expression. Therefore, EP3 and uPAR could represent novel therapeutic targets in the treatment of cervical cancer in advantaged stages.

Electronic supplementary material

The online version of this article (10.1007/s00432-020-03272-0) contains supplementary material, which is available to authorized users.

Identification of the key genes and pathways involved in the tumorigenesis and prognosis of kidney renal clear cell carcinoma

Kidney renal clear cell carcinoma (KIRC) is the most common renal cell carcinoma (RCC). However, patients with KIRC usually have poor prognosis due to limited biomarkers for early detection and prognosis prediction. In this study, we analysed key genes and pathways involved in KIRC from an array dataset including 26 tumour and 26 adjacent normal tissue samples. Weighted gene co-expression network analysis (WGCNA) was performed with the WGCNA package, and 20 modules were characterized as having the highest correlation with KIRC. The upregulated genes in the tumour samples are involved in the innate immune response, whereas the downregulated genes contribute to the cellular catabolism of glucose, amino acids and fatty acids. Furthermore, the key genes were evaluated through a protein-protein interaction (PPI) network combined with a co-expression network. The comparatively lower expression of AGXT, PTGER3 and SLC12A3 in tumours correlates with worse prognosis in KIRC patients, while higher expression of ALOX5 predicts reduced survival. Our integrated analysis illustrated the hub genes involved in KIRC tumorigenesis, shedding light on the development of prognostic markers. Further understanding of the function of the identified KIRC hub genes could provide deep insights into the molecular mechanisms of KIRC.

Prostaglandin E2/EP Signaling in the Tumor Microenvironment of Colorectal Cancer

The number of colorectal cancer (CRC) patients is increasing worldwide. Accumulating evidence has shown that the tumor microenvironment (TME), including macrophages, neutrophils, and fibroblasts, plays an important role in the development and progression of CRC. Although targeting the TME could be a promising therapeutic approach, the mechanisms by which inflammatory cells promote CRC tumorigenesis are not well understood. When inflammation occurs in tissues, prostaglandin E2 (PGE2) is generated from arachidonic acid by the enzyme cyclooxygenase-2 (COX-2). PGE2 regulates multiple functions in various immune cells by binding to the downstream receptors EP1, EP2, EP3, and EP4, and plays an important role in the development of CRC. The current therapies targeting PGE2 using non-steroidal anti-inflammatory drugs (NSAIDs) or COX-2 inhibitors have failed due to the global prostanoid suppression resulting in the severe adverse effects despite the fact they could prevent tumorigenesis. Therefore, therapies targeting the specific downstream molecules of PGE2 signaling could be a promising approach. This review highlights the role of each EP receptor in the TME of CRC tumorigenesis and their therapeutic potential.

Possible predisposition for colorectal carcinogenesis due to altered gene expressions in normal appearing mucosa from patients with colorectal neoplasia

Background

Investigations of colorectal carcinogenesis have mainly focused on examining neoplastic tissue. With our aim of identifying potentially cancer-predisposing molecular compositions, we chose a different approach by examining endoscopically normal appearing colonic mucosa of patients with and without colorectal neoplasia (CRN). Directed by this focus, we selected 18 genes that were previously found with altered expression in colorectal cancer affected mucosa.

Methods

Biopsies of colonic mucosa were sampled from 27 patients referred for colonoscopy on suspicion of colorectal disease. Of these, 14 patients had present or previous CRN and the remaining 13 patients served as controls. Using qPCR and Western blot technique, we investigated mRNA and protein expressions. Expressions were investigated for selected kinases in the extracellular signal-regulated kinase/mitogen activated protein kinase (ERK/MAPK), the phosphoinositide 3-kinase/Akt, and the Wnt/β-catenin pathways as well as for selected phosphatases and several entities associated with prostaglandin E2 (PGE₂) signaling. Colonic mucosal contents of PGE₂ and PGE₂ metabolites were determined by use of ELISA.

Results

We found up-regulation of ERK1, ERK2, Akt1, Akt2, PLA2G4A, prostanoid receptor EP3 and phosphatase scaffold subunit PPP2R1B mRNA expression in normal appearing colonic mucosa of CRN patients compared to controls.

Conclusion

Present study supports that even normal appearing mucosa of CRN patients differs from that of non-CRN patients at a molecular level. Especially expression of ERK1 mRNA was increased (p = 0.007) in CRN group. ERK1 may therefore be considered a potential candidate gene as predictive biomarker for developing CRN. Further validation in larger cohorts are required to determine such predictive use in translational medicine and clinics.

A Role for Lipid Mediators in Acute Myeloid Leukemia

In spite of therapeutic improvements in the treatment of different hematologic malignancies, the prognosis of acute myeloid leukemia (AML) treated solely with conventional induction and consolidation chemotherapy remains poor, especially in association with high risk chromosomal or molecular aberrations. Recent discoveries describe the complex interaction of immune effector cells, as well as the role of the bone marrow microenvironment in the development, maintenance and progression of AML. Lipids, and in particular omega-3 as well as omega-6 polyunsaturated fatty acids (PUFAs) have been shown to play a vital role as signaling molecules of immune processes in numerous benign and malignant conditions. While the majority of research in cancer has been focused on the role of lipid mediators in solid tumors, some data are showing their involvement also in hematologic malignancies. There is a considerable amount of evidence that AML cells are targetable by innate and adaptive immune mechanisms, paving the way for immune therapy approaches in AML. In this article we review the current data showing the lipid mediator and lipidome patterns in AML and their potential links to immune mechanisms.

Inhibition of PGE2/EP4 receptor signaling enhances oxaliplatin efficacy in resistant colon cancer cells through modulation of oxidative stress

The platinum-based chemotherapeutic agent, oxaliplatin, is used to treat advanced colorectal cancer (CRC). Unfortunately, nearly all patients acquire resistance to oxaliplatin after long-term use, limiting its therapeutic efficacy. Since COX-2 and PGE₂ signaling can impact colon cancer cell proliferation and survival, we examined how this pathway was affected in an oxaliplatin resistant colon cancer cell line. PGE₂ levels were significantly elevated in oxaliplatin-resistant HT29 cells (OXR) compared to naïve parental HT29 cells (PAR). This increase was associated with elevated COX-2 (17.9-fold; P = 0.008) and reduced 15-hydroxyprostaglandin dehydrogenase (2.9-fold; P < 0.0001) expression. RNAi knockdown of microsomal prostaglandin E synthase-1, the rate-limiting enzyme in PGE₂ synthesis, sensitized OXR cells to oxaliplatin. Downstream effects of PGE₂ in OXR cells were also examined. Selective inhibition of the EP4 PGE₂ receptor by the small molecule inhibitor, L-161,982 enhanced oxaliplatin-induced apoptosis in OXR cells. L-161,982 also reduced expression of the colonic stem cell markers, CD133 and CD44, and inhibited tumor sphere formation. The accumulation of intracellular reactive oxygen species (ROS), a key component of oxaliplatin cytotoxicity, was significantly increased by EP4 inhibition (2.4 -fold; P < 0.0001). Overall, our findings uncover an important role for the COX-2/PGE₂/EP4 signaling axis in oxaliplatin resistance via regulation of oxidative stress.

FTY720P inhibits the Na+/K+ ATPase in Caco-2 cells via S1PR2: PGE2 and NO are along the signaling pathway

AIMS

Sphingosine-1-phosphate (S1P) has been implicated lately in inflammatory bowel disease which has diarrhea as one of its symptoms. Diarrhea is due to altered water movements as a result of altered electrolyte transport, and in particular sodium. Sodium movements are geared by the sodium gradient established by the Na⁺/K⁺ ATPase. The aim of this work was to investigate if S1P can modulate the activity of the ATPase, using Caco-2 cells as a model and the S1P analogue, FTY720P.

MATERIALS AND METHODS

The activity of the ATPase was assayed by measuring the amount of inorganic phosphate liberated in presence and absence of ouabain. Protein expression of the various S1P receptors was studied by western blot analysis.

KEY FINDINGS

Caco-2 cells were found to express mainly S1PR2 and S1PR3. FTY720P (7.5 nM) reduced significantly the activity of the Na⁺/K⁺ ATPase when applied for 15 min. This inhibitory effect disappeared in presence of JTE-013, a specific blocker of S1PR2, and indomethacin, an inhibitor of cyclooxygenase enzymes, and was mimicked by CYM5520, a S1PR2 agonist and by exogenous PGE2. The inhibitory effect of PGE2 did not appear when EP3 receptors were blocked or when a nitric oxide scavenger was added. RpcAMP, a PKA inhibitor, reduced the activity of the Na⁺/K⁺ ATPase, while dbcAMP, a PKA activator was without any effect and when added, abrogated the effect of PGE2.

SIGNIFICANCE

It was concluded that FTY720P inhibits the Na+/K+ ATPase via activation of S1PR2 and generation of PGE2 nitric oxide.

The role of EP3-receptor expression in cervical dysplasia

PURPOSE

Prostaglandin-mediated inflammatory reactions play a major role in different cancers. Prostaglandin E2-receptor 3 (EP3) expression correlates with FIGO stages in cervical cancer and has been shown to be an independent prognostic factor for overall survival. EP3 expression levels in cervical intraepithelial neoplasia (CIN) as the precursor lesion of cervical cancer are currently unknown.

METHODS

EP3 expression was analyzed by immunohistochemistry in 124 patient samples (CIN 1-3 and healthy controls) using the IR-scoring system. Expression levels were correlated with clinical outcome to assess for prognostic relevance in patients with CIN 2. Data analysis was performed using Kruskal-Wallis and Mann-Whitney U test.

RESULTS

EP3 expression levels significantly correlated with different grades of cervical dysplasia. Median EP3-IRS in healthy cervical tissue was 12 (n = 13) compared to 9 in CIN 1 (n = 38; p = 0.031 vs. healthy control), 6 in CIN 2 (n = 45; p < 0.001 vs. CIN 1) and 4 in CIN 3 (n = 28, p = 0.008 vs. CIN 2). The percentage of EP3 expressing cells in CIN 2 lesions was significantly lower in progressive than in regressive cases (mean percentage of EP3 positive cells in progress: 3.8%, n = 18; in regress: 9.3%, n = 20; p = 0.040).

CONCLUSION

EP3 expression significantly decreases with higher grades of cervical intraepithelial neoplasia-which is in line with published IR scores in cervical cancer patients-and seems to be a prognostic marker for regression or progression of CIN 2 lesions. Our findings support the importance of the prostanoid pathway in cervical cancer and could help to identify targets for future therapies.

Role of COX-2/PGE2 Mediated Inflammation in Oral Squamous Cell Carcinoma

A significant amount of research indicates that the cyclooxygenase/prostaglandin E2 (PGE2) pathway of inflammation contributes to the development and progression of a variety of cancers, including squamous cell carcinoma of the oral cavity and oropharynx (OSCC). Although there have been promising results from studies examining the utility of anti-inflammatory drugs in the treatment of OSCC, this strategy has been met with only variable success and these drugs are also associated with toxicities that make them inappropriate for some OSCC patients. Improved inflammation-targeting therapies require continued study of the mechanisms linking inflammation and progression of OSCC. In this review, a synopsis of OSCC biology will be provided, and recent insights into inflammation related mechanisms of OSCC pathobiology will be discussed. The roles of prostaglandin E2 and cluster of differentiation factor 147 (CD147) will be presented, and evidence for their interactions in OSCC will be explored. Through continued investigation into the protumourigenic pathways of OSCC, more treatment modalities targeting inflammation-related pathways can be designed with the hope of slowing tumour progression and improving patient prognosis in patients with this aggressive form of cancer.

Role of prostanoids in gastrointestinal cancer

Chronic inflammation is a risk factor for gastrointestinal cancer and other diseases. Most studies have focused on cytokines and chemokines as mediators connecting chronic inflammation to cancer, whereas the involvement of lipid mediators, including prostanoids, has not been extensively investigated. Prostanoids are among the earliest signaling molecules released in response to inflammation. Multiple lines of evidence suggest that prostanoids are involved in gastrointestinal cancer. In this Review, we discuss how prostanoids impact gastrointestinal cancer development. In particular, we highlight recent advances in our understanding of how prostaglandin E2 induces the immunosuppressive microenvironment in gastrointestinal cancers.

EP3 (prostaglandin E2 receptor 3) expression is a prognostic factor for progression-free and overall survival in sporadic breast cancer

Background

In various cancers, overexpression of cyclooxygenase (COX)-2 and elevated prostaglandin (PG) E2 synthesis have been associated with tumor development and progression. The potential of COX-2 inhibitors in cancer prevention and treatment has been shown repeatedly; however, their clinical use is limited due to toxicity. PGE2 signals via EP receptors 1–4, whose functions are analyzed in current research in search for targeted anti-PG therapies. EP2 and EP4 rather promote tumorigenesis, while the role of EP3, especially in breast cancer, is not yet clear and both pro- and anti-tumorigenic effects have been described. Our study evaluates EP3 receptor expression in sporadic breast cancer and its association with clinicopathological parameters, progression-free and overall survival.

Methods

Two hundred eighty-nine sporadic breast cancer samples without primary distant metastasis were immunohistochemically analyzed for EP3 receptor expression. Tissue was stained with primary anti-EP3-antibodies. Immunoreactivity was quantified by the immunoreactivity-score (IRS); samples with an IRS ≥ 2 scored as EP3 positive. Chi-squared and Mann-Whitney-U test were used for comparison of data; Kaplan-Meier estimates and Cox-regression were used for survival analyses.

Results

EP3 receptor was expressed in 205 of 289 samples analyzed (70.9%). EP3 receptor expression was not associated with clinicopathological parameters (e. g. tumor size, hormone receptors, lymph node status). Kaplan-Meier estimates showed a significant association of EP3 positivity with improved progression-free survival (p = 0.002) and improved overall survival (p = 0.001) after up to 10 years. Cox regression analysis confirmed EP3 positivity as a significant prognostic factor even when other known prognosticators were accounted for.

Conclusions

In sporadic breast cancer, EP3 receptor expression is not significantly associated with clinicopathological parameters but is a significant prognostic factor for improved progression-free and overall survival. However, the functional aspects of EP3 receptor in breast cancer and the way how EP3 may oppose the pro-tumorigenic effects of PGE2 elevation and COX-2 overexpression are not fully understood so far. Further studies aiming at identification of the factors regulated by EP3 are necessary to evaluate the possibility of targeting EP3 in future anti-tumor therapy in breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4286-9) contains supplementary material, which is available to authorized users.

Lipidome in colorectal cancer

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths. Understanding its pathophysiology is essential for developing efficient strategies to treat this disease. Lipidome, the sum of total lipids, related enzymes, receptors and signaling pathways, plays crucial roles in multiple cellular processes, such as metabolism, energy storage, proliferation and apoptosis. Dysregulation of lipid metabolism and function contributes to the development of CRC, and can be used towards the evaluation of prognosis. The strategies targeting lipidome have been applied in clinical trails and showed promising results. Here we discuss recent advances in abnormal lipid metabolism in CRC, the mechanisms by which the lipidome regulates tumorigenesis and tumor progression, and suggest potential therapeutic targets for clinical trials.

Prostaglandin receptor EP3 regulates cell proliferation and migration with impact on survival of endometrial cancer patients

Background

Prostaglandin E2 (PGE2) receptor 3 (EP3) regulates tumor cell proliferation, migration, and invasion in numerous cancers. The role of EP3 as a prognostic biomarker in endometrial cancer remains unclear. The primary aim of this study was to analyze the prognostic significance of EP3 expression in endometrial cancer.

Methods

We analyzed the EP3 expression of 140 endometrial carcinoma patients by immunohistochemistry. RL95-2 endometrial cancer cell line was chosen from four endometrial cancer cell lines (RL95-2, Ishikawa, HEC-1-A, and HEC-1-B) according to EP3 expression level. Treated with PGE2 and EP3 antagonist, RL95-2 cells were investigated by MTT, BrdU, and wound healing assay for functional assessment of EP3.

Results

EP3 staining differed significantly according to WHO tumor grading in both whole cohort (p = 0.01) and the subgroup of endometrioid carcinoma (p = 0.01). Patients with high EP3 expression in their respective tumors had impaired progression-free survival as well as overall survival in both cohorts above. EP3 expression in the overall cohort was identified as an independent prognostic marker for progression-free survival (HR 1.014, 95%CI 1.003-1.024, p = 0.01) when adjusted for age, stage, grading, and recurrence. Treatment with EP3 antagonists induced upregulation of estrogen receptor β and decreased activity of Ras and led to attenuated proliferation and migration of RL95-2 cells.

Conclusions

EP3 seems to play a crucial role in endometrial cancer progression. In the context of limited systemic treatment options for endometrial cancer, this explorative analysis identifies EP3 as a potential target for diagnostic workup and therapy.

The Prostaglandin EP3 Receptor Is an Independent Negative Prognostic Factor for Cervical Cancer Patients

We know that one of the main risk factors for cervical cancer is an infection with high-risk human papillomavirus (HR-HPV). Prostaglandins and their receptors are very important for the tumour growth and tumour-associated angiogenesis. Little is known about the expression of the Prostaglandin E receptor type 3 (EP3) or the Prostaglandin (PG)E₂-EP3 signalling in cervical cancer, so the aim of the study was to analyse the expression of the EP3 receptor in cervical cancer and find prognostic factors in relation to survival; EP3 immunohistological staining of 250 cervical cancer slides was performed and analysed with a semi-quantitative score. The statistical evaluation was performed with Statistical Package for the Social Sciences (SPSS) to evaluate the staining results and the survival analyses of the cervical cancer cases. A significant difference was observed in EP3 expression in Fédération Internationale de Gynécologie et d’Obstétrique (FIGO) stadium I versus FIGO stadium II–IV cases. High expression of EP3 (IRS ≥ 1.5) in cervical cancer patients was correlated with poor prognosis in overall survival rates. Survival in adenocarcinoma (AC) of the cervix was lower than in squamous cell carcinoma (SCC). Cox regression analysis shows that EP3 is an independent prognosticator. In this study we could show that the membrane-bound prostaglandin receptor EP3 is an independent prognosticator for cervical cancer patient survival. Targeting the EP3 receptor seems to be an interesting candidate for endocrine therapy. Therefore, more research is needed on the influence of the receptor system and its influence on cervical cancer growth.

The EP4 antagonist, L-161,982, induces apoptosis, cell cycle arrest, and inhibits prostaglandin E2-induced proliferation in oral squamous carcinoma Tca8113 cells

BACKGROUND

Recent studies suggest that cyclooxygenase 2 (COX-2) inhibitors may enhance the toxic effects of anticancer drugs on tumor cells, including oral squamous cell carcinoma (OSCC), but its long-term use can cause side effects such as stomach ulcers and myocardial infarction. Our aim was to investigate proliferative effects of a downstream product of COX-2, prostaglandin E2 (PGE2), in human oral squamous carcinoma cell line Tca8113 and explore the effects of PGE2 receptors, especially EP4 receptor, on the growth of Tca8113 cells.

METHODS

To evaluate the effects of PGE2 and EP receptors on Tca8113 cells, CCK8 assay, Western blotting, cell cycle analysis, and apoptosis assay were performed.

RESULTS

We found that the EP4 receptor agonist, PGE1-OH, could mimick PGE2 rescued the inhibitory effect of celecoxib and induced cell growth via ERK phosphorylation, and the EP4 receptor antagonist, L-161,982, completely blocked PGE2-stimulated ERK phosphorylation and proliferation of Tca8113 cells. Furthermore, L-161,982 may induce apoptosis and block cell cycle progression at s phase by upregulating Bax and p21 protein levels and by downregulating Bcl-2, CDK2, and cyclin A2 protein levels.

CONCLUSIONS

Our results indicate that EP4 receptor mediates PGE2-induced cell proliferation through ERK signaling, and inhibition of EP4 receptor may represent an alternative therapeutic strategy for the prevention and treatment of OSCC.

Eicosanoid receptors: Targets for the treatment of disrupted intestinal epithelial homeostasis

The importance of cyclooxygenase and lipoxygenase pathways and the consequent eicosanoid synthesis in the physiology and pathophysiology of the intestinal epithelium is currently being established. Each eicosanoid (prostanoid, leukotriene, hydroxyeicosatetraenoic acid) preferentially recognizes one or more receptors coupled to one or more signal-transduction processes. This overview focuses on the role of eicosanoid receptors in the maintenance of intestinal epithelium physiology through the control of proliferation/differentiation/apoptosis processes. Furthermore, it is reported that the role of these receptors on the regulation of the barrier function of the intestinal epithelium have arisen through the regulation of absorption/secretion processes, tight-junction state and the control of the intestinal immune response. Also, this review considers the implication of AA cascade in the disruption of epithelial homeostasis during inflammatory bowel diseases and colorectal cancer as well as the therapeutic values and potential of the eicosanoid receptors as novel targets for the treatments of the pathologies above mentioned.

Proximal signaling responses in peripheral T cells from colorectal cancer patients are affected by high concentrations of circulating prostaglandin E2

Patients with colorectal cancer (CRC) have been shown to have elevated levels of circulating prostaglandin E₂ (PGE₂) which promotes cancer progression and suppresses T cell immune responses. In this study we evaluated whether signaling responses in T lymphocytes obtained from peripheral blood of CRC patients were affected by the sustained exposure to increased levels of PGE₂. The phosphorylation status of an extended panel of proteins involved in downstream signaling cascades in T cells was profiled at a single cell level both in naïve and antigen-experienced cells after triggering T cell-, prostaglandin- and interleukin-2 receptors. Peripheral T cells from patients with elevated PGE₂ levels displayed aberrant T cell signaling responses downstream of the T cell receptor (assessed by reduced phosphorylation of CD3ζ and SLP76), and after triggering the IL-2 receptor (assessed by reduced phosphorylation of STAT5) when compared to T cells from CRC patients with lower levels of PGE₂ and T cells from healthy blood donors. This signaling study of circulating T cells from CRC patients indicates that increased systemic PGE₂ levels affect proximal T cell responses and confirms phospho-specific flow cytometry to be a valuable tool for revealing signaling signatures in immunological disorders.

PGE2 maintains self-renewal of human adult stem cells via EP2-mediated autocrine signaling and its production is regulated by cell-to-cell contact

Mesenchymal stem cells (MSCs) possess unique immunomodulatory abilities. Many studies have elucidated the clinical efficacy and underlying mechanisms of MSCs in immune disorders. Although immunoregulatory factors, such as Prostaglandin E₂ (PGE₂), and their mechanisms of action on immune cells have been revealed, their effects on MSCs and regulation of their production by the culture environment are less clear. Therefore, we investigated the autocrine effect of PGE₂ on human adult stem cells from cord blood or adipose tissue, and the regulation of its production by cell-to-cell contact, followed by the determination of its immunomodulatory properties. MSCs were treated with specific inhibitors to suppress PGE₂ secretion, and proliferation was assessed. PGE₂ exerted an autocrine regulatory function in MSCs by triggering E-Prostanoid (EP) 2 receptor. Inhibiting PGE₂ production led to growth arrest, whereas addition of MSC-derived PGE₂ restored proliferation. The level of PGE₂ production from an equivalent number of MSCs was down-regulated via gap junctional intercellular communication. This cell contact-mediated decrease in PGE₂ secretion down-regulated the suppressive effect of MSCs on immune cells. In conclusion, PGE₂ produced by MSCs contributes to maintenance of self-renewal capacity through EP2 in an autocrine manner, and PGE₂ secretion is down-regulated by cell-to-cell contact, attenuating its immunomodulatory potency.

Prostaglandin E2 Promotes Colorectal Cancer Stem Cell Expansion and Metastasis in Mice

BACKGROUND & AIMS

Inflammation may contribute to the formation, maintenance, and expansion of cancer stem cells (CSCs), which have the capacity for self-renewal, differentiation, and resistance to cytotoxic agents. We investigated the effects of the inflammatory mediator prostaglandin E2 (PGE2) on colorectal CSC development and metastasis in mice and the correlation between levels of PGE2 and CSC markers in human colorectal cancer (CRC) specimens.

METHODS

Colorectal carcinoma specimens and matched normal tissues were collected from patients at the Mayo Clinic (Scottsdale, AZ) and analyzed by mass spectrometry and quantitative polymerase chain reaction. Human primary CRC cells and mouse tumor cells were isolated using microbeads or flow cytometry and analyzed for sphere-formation and by flow cytometry assays. LS-174T cells were sorted by flow cytometry (for CD133(+)CD44(+) and CD133(-)CD44(-) cells) and also used in these assays. NOD-scidIL-2Rγ(-/-) (NSG) mice were given cecal or subcutaneous injections of LS-174T or human primary CRC cells. Apc(Min/+) mice and NSG mice with orthotopic cecal tumors were given vehicle (controls), PGE2, celecoxib, and/or Ono-AE3-208. PGE2 downstream signaling pathways were knocked down with small hairpin RNAs, expressed from lentiviral vectors in LS-174T cells, or blocked with inhibitors in human primary CRC cells.

RESULTS

Levels of PGE2 correlated with colonic CSC markers (CD133, CD44, LRG5, and SOX2 messenger RNAs) in human colorectal carcinoma samples. Administration of PGE2 to Apc(Min/+) mice increased tumor stem cells and tumor burden, compared with controls. NSG mice given PGE2 had increased numbers of cecal CSCs and liver metastases compared with controls after intracecal injection of LS-174T or human primary CRC cells. Alternatively, celecoxib, an inhibitor of prostaglandin-endoperoxide synthase 2, reduced polyp numbers in Apc(Min/+) mice, liver metastasis in NSG mice with orthotopic tumors, and numbers of CSCs in Apc(Min/+) and NSG mice. Inhibitors or knockdown of PGE2 receptor 4 (EP4), phosphoinositide 3-kinase (PI3K) p85α, extracellular signal-regulated kinase 1 (ERK1), or nuclear factor (NF)-κB reduced PGE2-induced sphere formation and expansion of LS-174T and/or human primary CRC cells. Knockdown of ERK1 or PI3K p85α also attenuated PGE2-induced activation of NF-κB in LS-174T cells. An EP4 antagonist reduced the ability of PGE2 to induce CSC expansion in orthotopic tumors and to accelerate the formation of liver metastases. Knockdown experiments showed that NF-κB was required for PGE2 induction of CSCs and metastasis in mice.

CONCLUSIONS

PGE2 induces CSC expansion by activating NF-κB, via EP4-PI3K and EP4-mitogen-activated protein kinase signaling, and promotes the formation of liver metastases in mice. The PGE2 signaling pathway therefore might be targeted therapeutically to slow CSC expansion and colorectal cancer progression.

Prostaglandin E2 and the EP receptors in malignancy: possible therapeutic targets?

Elevated expression of COX-2 and increased levels of PGE2 are found in numerous cancers and are associated with tumour development and progression. Although epidemiological, clinical and preclinical studies have shown that the inhibition of PGE2 synthesis through the use of either non-steroidal anti-inflammatory drugs (NSAIDs) or specific COX-2 inhibitors (COXibs) has the potential to prevent and treat malignant disease, toxicities due to inhibition of COX-2 have limited their use. Thus, there is an urgent need for the development of strategies whereby COX-2 activity may be reduced without inducing any side effects. The biological effects of PGE2 are mediated by signalling through four distinct E-type prostanoid (EP) receptors - EP1 , EP2 , EP3 and EP4 . In recent years, extensive effort has gone into elucidating the function of PGE2 and the EP receptors in health and disease, with the goal of creating selective inhibitors as a means of therapy. In this review, we focus on PGE2 , and in particular on the role of the individual EP receptors and their signalling pathways in neoplastic disease. As knowledge concerning the role of the EP receptors in cancer grows, so does the potential for exploiting the EP receptors as therapeutic targets for the treatment of cancer and metastatic disease.

Epigenetic regulations of inflammatory cyclooxygenase-derived prostanoids: molecular basis and pathophysiological consequences

The potential relevance of prostanoid signaling in immunity and immunological disorders, or disease susceptibility and individual variations in drug responses, is an important area for investigation. The deregulation of Cyclooxygenase- (COX-) derived prostanoids has been reported in several immunoinflammatory disorders such as asthma, rheumatoid arthritis, cancer, and autoimmune diseases. In addition to the environmental factors and the genetic background to diseases, epigenetic mechanisms involved in the fine regulation of prostanoid biosynthesis and/or receptor signaling appeared to be an additional level of complexity in the understanding of prostanoid biology and crucial in controlling the different components of the COX pathways. Epigenetic alterations targeting inflammatory components of prostanoid biosynthesis and signaling pathways may be important in the process of neoplasia, depending on the tissue microenvironment and target genes. Here, we focused on the epigenetic modifications of inflammatory prostanoids in physiological immune response and immunological disorders. We described how major prostanoids and their receptors can be functionally regulated epigenetically and consequently the impact of these processes in the pathogenesis inflammatory diseases and the development of therapeutic approaches that may have important clinical applications.

Epigenetics override pro-inflammatory PTGS transcriptomic signature towards selective hyperactivation of PGE2 in colorectal cancer

BACKGROUND

Misregulation of the PTGS (prostaglandin endoperoxide synthase, also known as cyclooxygenase or COX) pathway may lead to the accumulation of pro-inflammatory signals, which constitutes a hallmark of cancer. To get insight into the role of this signaling pathway in colorectal cancer (CRC), we have characterized the transcriptional and epigenetic landscapes of the PTGS pathway genes in normal and cancer cells.

RESULTS

Data from four independent series of CRC patients (502 tumors including adenomas and carcinomas and 222 adjacent normal tissues) and two series of colon mucosae from 69 healthy donors have been included in the study. Gene expression was analyzed by real-time PCR and Affymetrix U219 arrays. DNA methylation was analyzed by bisulfite sequencing, dissociation curves, and HumanMethylation450K arrays. Most CRC patients show selective transcriptional deregulation of the enzymes involved in the synthesis of prostanoids and their receptors in both tumor and its adjacent mucosa. DNA methylation alterations exclusively affect the tumor tissue (both adenomas and carcinomas), redirecting the transcriptional deregulation to activation of prostaglandin E2 (PGE2) function and blockade of other biologically active prostaglandins. In particular, PTGIS, PTGER3, PTGFR, and AKR1B1 were hypermethylated in more than 40 % of all analyzed tumors.

CONCLUSIONS

The transcriptional and epigenetic profiling of the PTGS pathway provides important clues on the biology of the tumor and its microenvironment. This analysis renders candidate markers with potential clinical applicability in risk assessment and early diagnosis and for the design of new therapeutic strategies.

Prostaglandin receptors EP1-4 as a potential marker for clinical outcome in urothelial bladder cancer

Prostaglandins, especially prostaglandin E2 (PGE2), and COX-2 play an important role in carcinogenesis of many tumors including bladder cancer (BCA). The PGE2 receptors EP1-4 regulate tumor cell growth, invasion and migration in different tumor entities but EP expression in BCA remains to be determined. In the present study we examined the expression of EP1-4 in non-muscle invasive bladder cancer (NMIBC), muscle invasive bladder cancer (MIBC) and normal urothelial tissue (NU) using immunohistochemistry. Nuclear and cytoplasmic EP1-4 expression was correlated with clinicopathological parameters and survival of BCA patients. EP1, EP2 and EP3 were significantly less expressed in the cytoplasm und nucleus of NMIBC and MIBC than in NU; EP4 cytoplasmic staining in MIBC was significantly higher compared to NU. The cytoplasmic staining was significantly more abundant in MIBC than in NMIBC in all investigated receptors except EP2. The level of EP staining in NMIBC was correlated with staging and grading, especially cytoplasmic EP1. Nuclear staining of EP1 was an independent predictor of BCA recurrence-free survival in NMIBC patients. EP receptors are dysregulated in BCA. The increase of EP1 may be used as prognostic parameter in NMIBC patients and its dysregulation could be targeted by specific EP1 inhibitors.

Loss of EP2 receptor subtype in colonic cells compromise epithelial barrier integrity by altering claudin-4

Prostaglandin E₂ (PGE₂) is a bioactive lipid mediator that exerts its biological function through interaction with four different subtypes of E-Prostanoid receptor namely EP1, EP2, EP3 and EP4. It has been known that EP2 receptor is differentially over-expressed in the epithelia of inflamed human colonic mucosa. However, the significance of the differential expression in altering epithelial barrier function is not known. In this study, we used Caco-2 cells expressing EP2 receptor, either high (EP2S) or low (EP2A), as a model epithelia and determined the barrier function of these cell monolayers by measuring the trans epithelial resistance (TER). Basal TER of EP2A (but not EP2S) monolayer was significantly lower suggesting a loss of colonic epithelial barrier integrity. In comparison, the TER of wild type Caco-2 was decreased in response to an EP2 receptor specific antagonist (AH-6809) indicating an important role for EP2 receptor in the maintenance of epithelial barrier function. The decrease TER in EP2A monolayer corresponded with a significant loss of the tight junction (TJ) protein claudin-4 without affecting other major TJ proteins. Similarly, EP2 receptor antagonism/siRNA based silencing significantly decreased claudin-4 expression in EP2S cells. Surprisingly, alteration in claudin-4 was not transcriptionally regulated in EP2A cells but rather undergoes increased proteosomal degradation. Moreover, among the TER compromising cytokines examined (IL-8, IL-1β, TNF-α, IFN-γ) only IFN-γ was significantly up regulated in EP2A cells. However, IFN-γ did not significantly decreased claudin-4 expression in Caco-2 cells indicating no role for IFN-γ in degrading claudin-4. We conclude that differential down-regulation of EP2 receptor play a major role in compromising colonic epithelial barrier function by selectively increasing proteosomal degradation of claudin-4.

Generation of ROS by CAY10598 leads to inactivation of STAT3 signaling and induction of apoptosis in human colon cancer HCT116 cells

Prostaglandin E2 (PGE2) has been reported to play critical roles in cell fate decision by interacting with four types of prostanoid receptors such as EP1, EP2, EP3 and EP4. The present study was aimed at investigating the effect of the EP4-specific agonist CAY10598 in human colon cancer HCT116 cells. Our study revealed that treatment with CAY10598 significantly reduced the cell viability and induced apoptosis in HCT116 cells, as evidenced by the induction of p53 and Bax, release of cytochrome c, cleavage of caspase-9, -7, and -3, and PARP, and the inhibition of Bcl-2, Bcl-xL and survivin expression. Moreover, treatment with CAY10598 diminished the phosphorylation of JAK2, leading to the attenuation of STAT3 activation in HCT116 cells. CAY10598-induced apoptosis in cells which were transiently transfected with EP4 siRNA or treated with an EP4 antagonist prior to incubation with the compound remained unaffected, suggesting an EP4-independent mechanism of apoptosis induction by CAY10598. We found that treatment with CAY10598 generated reactive oxygen species (ROS) and pretreatment of cells with N-acetyl cysteine rescued cells from apoptosis by abrogating the inhibitory effect of CAY10598 on the activation of JAK2/STAT3 signaling. In conclusion, CAY10598 induced apoptosis in HCT116 cells in an EP4-independent manner, but through the generation of ROS and inactivation of JAK2/STAT3 signaling.

The impact of inflammatory lipid mediators on colon cancer-initiating cells

The role of inflammatory lipid-mediators in tumor progression is well recognized in colorectal cancer; however, if this includes promotion of cancer-initiating cells remains unclear. We show that the inflammatory lipid-mediators leukotriene D4 and prostaglandin E2 increased the Aldehyde dehydrogenase (ALDH(+) ) population, the colony formation capacity, and tumor growth in a xenograft model of colon cancer. The ALDH(+) cells showed significant resistance to irradiation and 5-fluorouracil treatment that could be further augmented by these lipid-mediators, occurring in parallel with increased target gene expression. Our data emphasize a role for tumor microenvironment derived inflammatory lipid-mediators to favor cancer stem cells-like characteristics and thus promote tumor progression.

PGE₂ promotes apoptosis induced by cytokine deprivation through EP3 receptor and induces Bim in mouse mast cells

Increased mast cell numbers are observed at sites of allergic inflammation and restoration of normal mast cell numbers is critical to the resolution of these responses. Early studies showed that cytokines protect mast cells from apoptosis, suggesting a simple model in which diminished cytokine levels during resolution leads to cell death. The report that prostaglandins can contribute both to recruitment and to the resolution of inflammation together with the demonstration that mast cells express all four PGE₂ receptors raises the question of whether a single PGE₂ receptor mediates the ability of PGE₂ to regulate mast cell survival and apoptosis. We report here that PGE₂ through the EP3 receptor promotes cell death of mast cells initiated by cytokine withdrawal. Furthermore, the ability of PGE₂ to limit reconstitution of tissues with cultured mast cells is lost in cell lacking the EP3 receptor. Apoptosis is accompanied by higher dissipation of mitochondrial potential (ΔΨ_m), increased caspase-3 activation, chromatin condensation, and low molecular weight DNA cleavage. PGE₂ augmented cell death is dependent on an increase in intracellular calcium release, calmodulin dependent kinase II and MAPK activation. Synergy between the EP3 pathway and the intrinsic mitochondrial apoptotic pathway results in increased Bim expression and higher sensitivity of mast cells to cytokine deprivation. This supports a model in which PGE₂ can contribute to the resolution of inflammation in part by augmenting the removal of inflammatory cells in this case, mast cells.

Sesamol suppresses cyclooxygenase-2 transcriptional activity in colon cancer cells and modifies intestinal polyp development in Apc (Min/+) mice

Excessive prostaglandin production by cyclooxygenase-2 in stromal and epithelial cells is a causative factor of colorectal carcinogenesis. Thus, compounds which inhibit cyclooxygenase-2 transcriptional activity in colon epithelial cells could be candidates for anti-carcinogenic agents. A cyclooxygenase-2 transcriptional activity in the human colon cancer cell line DLD-1 has been measured using a β-galactosidase reporter gene system. Using this system, we demonstrated that the decrease in basal cyclooxygenase-2 transcriptional activities at 100 µM sesamol, one of the lignans in sesame seeds, was 50%. Other compounds in sesame seeds such as sesamin, sesamolin, ferulic acid, and syringic acid did not exhibit significant suppression of cyclooxygenase-2 transcriptional activity at up to 100 µM. In a following experiment, 6-week-old male Min mice, Apc-deficient mice, were divided into a non-treated and 500 ppm sesamol groups. At the age of 15 weeks, it was found that treatment with sesamol decreased the number of polyps in the middle part of small intestine to 66.1% of the untreated value. Moreover, sesamol suppressed cyclooxygenase-2 and cytosolic prostaglandin E2 synthase mRNA in the polyp parts. The present findings may demonstrate the novel anti-carcinogenetic property of sesamol, and imply that agents that can suppress cyclooxygenase-2 expression may be useful cancer chemopreventive agents.

Oxidized low-density lipoprotein suppresses expression of prostaglandin E receptor subtype EP3 in human THP-1 macrophages

EP3, one of four prostaglandin E2 (PGE2) receptors, is significantly lower in atherosclerotic plaques than in normal arteries and is localized predominantly in macrophages of the plaque shoulder region. However, mechanisms behind this EP3 expression pattern are still unknown. We investigated the underlying mechanism of EP3 expression in phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 macrophages with oxidized low-density lipoprotein (oxLDL) treatment. We found that oxLDL decreased EP3 expression, in a dose-dependent manner, at both the mRNA and protein levels. Moreover, oxLDL inhibited nuclear factor-κB (NF-κB)-dependent transcription of the EP3 gene by the activation of peroxisome proliferator-activated receptor-γ (PPAR-γ). Finally, chromatin immunoprecipitation revealed decreased binding of NF-κB to the EP3 promoter with oxLDL and PPAR-γ agonist treatment. Our results show that oxLDL suppresses EP3 expression by activation of PPAR-γ and subsequent inhibition of NF-κB in macrophages. These results suggest that down-regulation of EP3 expression by oxLDL is associated with impairment of EP3-mediated anti-inflammatory effects, and that EP3 receptor activity may exert a beneficial effect on atherosclerosis.

Microvascular COX-2/mPGES-1/EP-4 axis in human abdominal aortic aneurysm

We investigated the prostaglandin (PG)E2 pathway in human abdominal aortic aneurysm (AAA) and its relationship with hypervascularization. We analyzed samples from patients undergoing AAA repair in comparison with those from healthy multiorgan donors. Patients were stratified according to maximum aortic diameter: low diameter (LD) (<55 mm), moderate diameter (MD) (55-69.9 mm), and high diameter (HD) (≥70 mm). AAA was characterized by abundant microvessels in the media and adventitia with perivascular infiltration of CD45-positive cells. Like endothelial cell markers, cyclooxygenase (COX)-2 and the microsomal isoform of prostaglandin E synthase (mPGES-1) transcripts were increased in AAA (4.4- and 1.4-fold, respectively). Both enzymes were localized in vascular cells and leukocytes, with maximal expression in the LD group, whereas leukocyte markers display a maximum in the MD group, suggesting that the upregulation of COX-2/mPGES-1 precedes maximal leukocyte infiltration. Plasma and in vitro tissue secreted levels of PGE2 metabolites were higher in AAA than in controls (plasma-controls, 19.9 ± 2.2; plasma-AAA, 38.8 ± 5.5 pg/ml; secretion-normal aorta, 16.5 ± 6.4; secretion-AAA, 72.9 ± 6.4 pg/mg; mean ± SEM). E-prostanoid receptor (EP)-2 and EP-4 were overexpressed in AAA, EP-4 being the only EP substantially expressed and colocalized with mPGES-1 in the microvasculature. Additionally, EP-4 mediated PGE2-induced angiogenesis in vitro. We provide new data concerning mPGES-1 expression in human AAA. Our findings suggest the potential relevance of the COX-2/mPGES-1/EP-4 axis in the AAA-associated hypervascularization.

Potential targets for colorectal cancer prevention

The step-wise development of colorectal neoplasia from adenoma to carcinoma suggests that specific interventions could delay or prevent the development of invasive cancer. Several key factors involved in colorectal cancer pathogenesis have already been identified including cyclooxygenase 2 (COX-2), nuclear factor kappa B (NF-κB), survivin and insulin-like growth factor-I (IGF-I). Clinical trials of COX-2 inhibitors have provided the “proof of principle” that inhibition of this enzyme can prevent the formation of colonic adenomas and potentially carcinomas, however concerns regarding the potential toxicity of these drugs have limited their use as a chemopreventative strategy. Curcumin, resveratrol and quercetin are chemopreventive agents that are able to suppress multiple signaling pathways involved in carcinogenesis and hence are attractive candidates for further research.

Prostaglandin receptor EP3 mediates growth inhibitory effect of aspirin through androgen receptor and contributes to castration resistance in prostate cancer cells

Although numerous epidemiological studies show aspirin to reduce risk of prostate cancer, the mechanism of this effect is unclear. Here, we first confirmed that aspirin downregulated androgen receptor (AR) and prostate-specific antigen in prostate cancer cells. We also found that aspirin upregulated prostaglandin receptor subtype EP3 but not EP2 or EP4. The EP3 antagonist L798106 and EP3 knockdown increased AR expression and cell proliferation, whereas the EP3 agonist sulprostone decreased them, indicating that EP3 affects AR expression. Additionally, EP3 (PTGER3) transcript levels were significantly decreased in human prostate cancer tissues compared with those in normal human prostate tissues, suggesting that EP3 is important to prostate carcinogenesis. Decreased EP3 expression was also seen in castration-resistant subtype CxR cells compared with parental LNCaP cells. Finally, we found that aspirin and EP3 modulators affected prostate cancer cell growth. Taken together, aspirin suppressed LNCaP cell proliferation via EP3 signaling activation; EP3 downregulation contributed to prostate carcinogenesis and to progression from androgen-dependent prostate cancer to castration-resistant prostate cancer by regulating AR expression. In conclusion, cyclooxygenases and EP3 may represent attractive therapeutic molecular targets in androgen-dependent prostate cancer.

Effect of sphingosine kinase 1 inhibition on blood pressure

Accumulating evidence suggests that sphingosine kinase 1 (SphK1) plays a key role in carcinogenesis by regulating cyclooxygenase-2 (COX-2) expression. Recent clinical studies have revealed that COX-2 inhibitors cause adverse cardiovascular side effects, likely due to inhibition of prostacyclin (PGI(2)). In this work, we investigated the roles of SphK1 inhibition on blood pressure (BP). The results show that lack of SphK1 expression did not exacerbate angiotensin II (Ang II)-induced acute hypertension, whereas celecoxib, a COX-2 inhibitor, augmented and sustained higher BP in mice. Interestingly, SphK1-knockout mice inhibited prostaglandin E(2) (PGE(2)) but not PGI(2) production in response to Ang II, whereas celecoxib blocked both PGE(2) and PGI(2) production. Mechanistically, SphK1 down-regulation by siRNA in human umbilical vein endothelial cells decreased cytokine-induced PGE(2) production primarily through inhibition of microsomal PGE synthase-1 (mPGES-1), not COX-2. SphK1 down-regulation also decreased MKK6 expression, which phosphorylates and activates P38 MAPK, which, in turn, regulates early growth response-1 (Egr-1), a transcription factor of mPGES-1. Together, these data indicate that SphK1 regulates PGE(2) production by mPGES-1 expression via the p38 MAPK pathway, independent of COX-2 signaling, in endothelial cells, suggesting that SphK1 inhibition may be a promising strategy for cancer chemoprevention with lack of the adverse cardiovascular side effects associated with coxibs.