Role of cAMP in the promotion of colorectal cancer cell growth by prostaglandin E2

Current Understanding of the Role of Adenosine Receptors in Cancer

Cancer, a complex array of diseases, involves the unbridled proliferation and dissemination of aberrant cells in the body, forming tumors that can infiltrate neighboring tissues and metastasize to distant sites. With over 200 types, each cancer has unique attributes, risks, and treatment avenues. Therapeutic options encompass surgery, chemotherapy, radiation therapy, hormone therapy, immunotherapy, targeted therapy, or a blend of these methods. Yet, these treatments face challenges like late-stage diagnoses, tumor diversity, severe side effects, drug resistance, targeted drug delivery hurdles, and cost barriers. Despite these hurdles, advancements in cancer research, encompassing biology, genetics, and treatment, have enhanced early detection methods, treatment options, and survival rates. Adenosine receptors (ARs), including A1, A2A, A2B, and A3 subtypes, exhibit diverse roles in cancer progression, sometimes promoting or inhibiting tumor growth depending on the receptor subtype, cancer type, and tumor microenvironment. Research on AR ligands has revealed promising anticancer effects in lab studies and animal models, hinting at their potential as cancer therapeutics. Understanding the intricate signaling pathways and interactions of adenosine receptors in cancer is pivotal for crafting targeted therapies that optimize benefits while mitigating drawbacks. This review delves into each adenosine receptor subtype's distinct roles and signaling pathways in cancer, shedding light on their potential as targets for improving cancer treatment outcomes.

Isoproterenol Alters Metabolism, Promotes Survival and Migration in 5-Fluorouracil-Treated SW480 Cells with and without Beta-hydroxybutyrate

People with cancer often experience long-term physical and psychological stress, which can have a significant impact on tumor metabolism and treatment. The effects of adrenergic signaling on metabolic pathways are well known, but only a few studies have looked into the connection between this signaling and tumor metabolism. This study examined the effects of treatment with isoproterenol (Iso) alone and in combination with β-hydroxybutyrate (βHB), a mitochondrial fuel, on the metabolism, survival, and migration of SW480 colon cancer cells treated with 5-fluorouracil (5FU). The researchers measured the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) to determine the metabolic profile of these cells. They also analyzed the gene expression of PGC-1α, c-MYC, and NANOG to investigate the relationship between metabolic phenotype and stemness status. Scratch assays were used to assess cell migration. The results showed that Iso treatment increased cell viability in both SW480 and 5FU-treated SW480 cells. There was a significant decrease in ECAR and an increase in OCR after Iso treatment in both cell types. The expression of c-MYC and NANOG, genes associated with stemness, increased, while the expression of PGC-1α, a gene related to oxidative phosphorylation, decreased following Iso treatment. Iso treatment also increased the migration potential of both SW480 and 5FU-treated SW480 cells. These findings suggest that under stressful conditions, 5FU-treated colon cancer cells can utilize the oxidative phosphorylation pathway for growth and migration.

Inhibition of Prostaglandin E2 Receptor EP3 Attenuates Oxidative Stress and Neuronal Apoptosis Partially by Modulating p38MAPK/FOXO3/Mul1/Mfn2 Pathway after Subarachnoid Hemorrhage in Rats

Oxidative stress and neuronal apoptosis contribute to pathological processes of early brain injury (EBI) after subarachnoid hemorrhage (SAH). Previous studies demonstrated that the inhibition of prostaglandin E2 receptor EP3 suppressed oxidative stress and apoptotic effects after Alzheimer's disease and intracerebral hemorrhage. This study is aimed at investigating the antioxidative stress and antiapoptotic effect of EP3 inhibition and the underlying mechanisms in a rat mode of SAH. A total of 263 Sprague-Dawley male rats were used. SAH was induced by endovascular perforation. Selective EP3 antagonist L798106 was administered intranasally at 1 h, 25 h, and 49 h after SAH induction. EP3 knockout CRISPR and FOXO3 activation CRISPR were administered intracerebroventricularly at 48 h prior to SAH, while selective EP3 agonist sulprostone was administered at 1 h prior to SAH. SAH grade, neurological deficits, western blots, immunofluorescence staining, Fluoro-Jade C staining, TUNEL staining, 8-OHdG staining, and Nissl staining were conducted after SAH. The expression of endogenous PGES2 increased and peaked at 12 h while the expression of EP1, EP2, EP3, EP4, and Mul1 increased and peaked at 24 h in the ipsilateral brain after SAH. EP3 was expressed mainly in neurons. The inhibition of EP3 with L798106 or EP3 KO CRISPR ameliorated the neurological impairments, brain tissue oxidative stress, and neuronal apoptosis after SAH. To examine potential downstream mediators of EP3, we examined the effect of the increased expression of activated FOXO3 following the administration of FOXO3 activation CRISPR. Mechanism studies demonstrated that L798106 treatment significantly decreased the expression of EP3, p-p38, p-FOXO3, Mul1, 4-HNE, Bax, and cleaved caspase-3 but upregulated the expression of Mfn2 and Bcl-2 in SAH rats. EP3 agonist sulprostone or FOXO3 activation CRISPR abolished the neuroprotective effects of L798106 and its regulation on expression of p38MAPK/FOXO3/Mul1/Mfn2 in the ipsilateral brain after SAH. In conclusion, the inhibition of EP3 by L798106 attenuated oxidative stress and neuronal apoptosis partly through p38MAPK/FOXO3/Mul1/Mfn2 pathway post-SAH in rats. EP3 may serve as a potential therapeutic target for SAH patients.

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.

RPP30 is a novel diagnostic and prognostic biomarker for gastric cancer

Objective: This study aimed to identify the hub gene in gastric cancer (GC) tumorigenesis. A biomarker prediction model was constructed and analyzed, and protein expression in histopathological samples was verified in a validation cohort. Methods: Differentially expressed genes (DEGs) were identified from GC projects in The Cancer Genome Atlas (TCGA) database. Functional enrichment analysis of DEGs was performed between the high- and low- Ribonuclease P protein subunit p30 (RPP30) expression groups. ROC analysis was performed to assess RPP30 expression to discriminate GC from normal tissues. Functional enrichment pathways and immune infiltration of DEGs were analyzed using GSEA and ssGSEA. Survival analysis and nomogram construction were performed to predict patient survival. Immunohistochemical staining of GC tissues was performed to validate RPP30 expression in GC and paracancerous samples. Results: Gene expression data and clinical information of 380 cases (375 GC samples and 32 para-cancerous tissues) were collected from TCGA database. The AUC for RPP30 expression was found to be 0.785. The G alpha S signaling pathway was the most significantly enriched signaling pathway. Primary therapy outcome (p < 0.001, HR = 0.243, 95% CI = 0.156-0.379), age (p = 0.012, HR = 1.748, 95% CI = 1.133-2.698), and RPP30 expression (p < 0.001, HR = 2.069, 95% CI = 1.346-3.181) were identified as independent prognostic factors. As a quantitative approach, a nomogram constructed based on RPP30 expression, age, and primary therapy outcome performed well in predicting patient survival. Nineteen of the 25 tissue samples from the validation cohort showed positive RPP30 expression in GC tissues, whereas 16 cases showed negative RPP30 staining in normal tissues. The difference between the two was statistically significant. Conclusion: High RPP30 expression was significantly correlated with disease progression and poor survival in GC, promoting tumorigenesis and angiogenesis via tRNA dysregulation. This study provides new and promising insights into the molecular pathogenesis of tRNA in GC.

Inhibition of DDX3 and COX-2 by forskolin and evaluation of anti-proliferative, pro-apoptotic effects on cervical cancer cells: molecular modelling and in vitro approaches

Several studies have reported up-regulation of both cyclooxygenase-2 (COX-2) and DEAD-box RNA helicase3 (DDX3) and have validated their oncogenic role in many cancers. Inhibition of COX-2 and DDX3 offers a potential pharmacological strategy for prevention of cancer progression. The COX-2 isoform is expressed in response to pro-inflammatory stimuli in premalignant lesions, including cervical tissues. This study elucidates the potential role of plant derived compound Forskolin (FSK) in plummeting the expression of COX-2 and DDX3 in cervical cancer. To establish this, the cervical cancer cells were treated with the FSK compound which induced a dose dependent significant inhibition of COX-2 and DDX3 expression. The FSK treatment also significantly induced apoptosis in cancer cells by modulating the expression of apoptotic markers like caspase-3, cleaved caspase-3, caspase-9, cleaved caspase-9, full length-poly ADP ribose polymerase (PARP), cleaved-poly ADP ribose polymerase (C-PARP) and Bcl2 in dose dependent manner. Further FSK significantly modulated the cell survival pathway Phosphatidylinositol 3-kinase (PI3-K)/Akt signalling pathway upon 24 h of incubation in cervical cancer cells. The molecular docking studies revealed that the FSK engaged the active sites of both the targets by interacting with key residues.

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.

Piclamilast mitigates 1,2-dimethylhydrazine induced colon cancer in rats through modulation of Ras/PI3K/Akt/mTOR and NF-κβ signaling

Colorectal cancer (CRC) is the third leading type of adult cancer in both genders with high morbidity and mortality worldwide. Even though the discovery of many antineoplastic drugs for CRC, the current therapy is not adequately efficient.This study was designed to investigate the effect and mechanism of Piclamilast (PIC), a selective PDE4 inhibitor, on a DMH-induced colorectal cancer (CRC) rat model. The rats were grouped (n = 10) into group 1 (control), group 2 (PIC 3 mg/kg, p.o.), groups 3-5 received DMH (20 mg/kg/week, S.C.), and groups 4 and 5 received PIC (1 and 3 mg/kg/day, p.o.) for 15 weeks. The DMH treatment increased aberrant crypt foci (ACF), Proliferating cell nuclear antigen (PCNA), and TBARS levels, along with decreased antioxidant defenses (GSH, GSH-Px, and catalase). Increased NF-κβ expression and inflammatory cytokines were also evident. PIC dose-dependently reduced ACF and restored oxidative stress and inflammatory markers favorably. Moreover, PIC in its large, tested dose only significantly increased the intracellular level of cAMP and suppressed the activation of Ras and PI3K and its downstream Akt/mTOR signaling. Furthermore, PIC promoted CRC apoptosis, and increased the gene expression of the apoptotic factors, caspase-3 and Bax, and decreased the anti-apoptotic factor Bcl-2. The results of this study show that PIC may be a promising therapeutic agent for the treatment of CRC. PIC might inhibit the proliferation of CRC cells and induce apoptosis via multiple mechanisms that involve its antioxidant effect and inhibition of NF-κβ and Ras/PI3K/Akt/mTOR signaling.

Expression Pattern of Purinergic Signaling Components in Colorectal Cancer Cells and Differential Cellular Outcomes Induced by Extracellular ATP and Adenosine

The purine nucleotide adenosine triphosphate (ATP) is known for its fundamental role in cellular bioenergetics. However, in the last decades, different works have described emerging functions for ATP, such as that of a danger signaling molecule acting in the extracellular space on both tumor and stromal compartments. Beside its role in immune cell signaling, several studies have shown that high concentrations of extracellular ATP can directly or indirectly act on cancer cells. Accordingly, it has been reported that purinergic receptors are widely expressed in tumor cells. However, their expression pattern is often associated with contradictory cellular outcomes. In this work, we first investigated gene expression profiles through "RNA-Sequencing" (RNA Seq) technology in four colorectal cancer (CRC) cell lines (HT29, LS513, LS174T, HCT116). Our results demonstrate that CRC cells mostly express the A2B, P2X4, P2Y1, P2Y2 and P2Y11 purinergic receptors. Among these, the P2Y1 and P2Y2 coding genes are markedly overexpressed in all CRC cells compared to the HCEC-1CT normal-like colonic cells. We then explored the cellular outcomes induced by extracellular ATP and adenosine. Our results show that in terms of cell death induction extracellular ATP is consistently more active than adenosine against CRC, while neither compound affected normal-like colonic cell survival. Intriguingly, while for the P2Y2 receptor pharmacological inhibition completely abolished the rise in cytoplasmic Ca²⁺ observed after ATP exposure in all CRC cell lines, Ca²⁺ mobilization only impacted the cellular outcome for HT29. In contrast, non-selective phosphodiesterase inhibition completely abolished the effects of extracellular ATP on CRC cells, suggesting that cAMP and/or cGMP levels might determine cellular outcome. Altogether, our study provides novel insights into the characterization of purinergic signaling in CRC.

Identification of PDE7B as a Potential Core Gene Involved in the Metastasis of Clear Cell Renal Cell Carcinoma

Background

Metastasis is the main cause of treatment failure in various cancer, including ccRCC. However, the key genes involved in ccRCC metastasis remain largely unknown.

Purpose

The identification of the aberrant gene expression patterns associated with metastatic traits is of great clinical significance. The aim of this study was to investigate the clinical significance and function of PDE7B in ccRCC.

Materials and Methods

Expression profiling data for patient-matched primary and metastatic ccRCC tumors were obtained from GEO Dataset. Limma package was used to identify differentially expressed genes (DEGs) between the metastatic and the primary groups. Gene Ontology, Kyoto Encyclopedia of Genes Genomes (KEGG), and PPI network analysis were used to study the interacting activities and the interconnection of the DEGs. CCK-8 assays and Transwell assays were performed to detect the proliferation and migration of renal cancer cells.

Results

We obtained 163 DEGs, including 132 that were upregulated and 31 that were downregulated in metastatic ccRCC tissues. Both Gene Ontology function and KEGG pathway analysis showed that DEGs were involved in extracellular matrix (ECM) organization and cell adhesion. After utilizing PPI network to explore the interconnection among the DEGs, 22 genes were selected as the hub genes. Subsequently, survival analysis revealed that seven hub genes (SFN, NKX2-1, HP, MAPT, EPHA4, KCNAB1, and PDE7B) were significantly associated with overall survival disease-specific survival, and progression-free interval in ccRCC. Moreover, the low expression of PDE7B was found in clinical ccRCC samples and correlated with TNM stage and histologic grade. We further showed that knockdown of PDE7B increased cell growth and migration of renal cancer cells.

Conclusion

Our results implicated that PDE7B may play a key role in the development of metastatic RCC.

pathfindR: An R Package for Comprehensive Identification of Enriched Pathways in Omics Data Through Active Subnetworks

Pathway analysis is often the first choice for studying the mechanisms underlying a phenotype. However, conventional methods for pathway analysis do not take into account complex protein-protein interaction information, resulting in incomplete conclusions. Previously, numerous approaches that utilize protein-protein interaction information to enhance pathway analysis yielded superior results compared to conventional methods. Hereby, we present pathfindR, another approach exploiting protein-protein interaction information and the first R package for active-subnetwork-oriented pathway enrichment analyses for class comparison omics experiments. Using the list of genes obtained from an omics experiment comparing two groups of samples, pathfindR identifies active subnetworks in a protein-protein interaction network. It then performs pathway enrichment analyses on these identified subnetworks. To further reduce the complexity, it provides functionality for clustering the resulting pathways. Moreover, through a scoring function, the overall activity of each pathway in each sample can be estimated. We illustrate the capabilities of our pathway analysis method on three gene expression datasets and compare our results with those obtained from three popular pathway analysis tools. The results demonstrate that literature-supported disease-related pathways ranked higher in our approach compared to the others. Moreover, pathfindR identified additional pathways relevant to the conditions that were not identified by other tools, including pathways named after the conditions.

Cyclin-Dependent Kinase 5 (CDK5)-Mediated Phosphorylation of Upstream Stimulatory Factor 2 (USF2) Contributes to Carcinogenesis

The transcription factor USF2 is supposed to have an important role in tumor development. However, the regulatory mechanisms contributing to the function of USF2 are largely unknown. Cyclin-dependent kinase 5 (CDK5) seems to be of importance since high levels of CDK5 were found in different cancers associated with high USF2 expression. Here, we identified USF2 as a phosphorylation target of CDK5. USF2 is phosphorylated by CDK5 at two serine residues, serine 155 and serine 222. Further, phosphorylation of USF2 at these residues was shown to stabilize the protein and to regulate cellular growth and migration. Altogether, these results delineate the importance of the CDK5-USF2 interplay in cancer cells.

Alternariol induced proliferation in primary mouse keratinocytes and inflammation in mouse skin is regulated via PGE2/EP2/cAMP/p-CREB signaling pathway

Alternariol (AOH) is a mycotoxin that contaminates various food stuffs as well as animal feed and may cause toxicity after consumption. However, a dermal toxic potential of AOH has not been explored so far. In the present study, skin toxicity after topical exposure of AOH and the involved mechanism/s are revealed. Single topical application of different AOH doses (12.5, 25, 50 μg/animal) caused increased bi-fold thickness as well as hyperplasia and higher production of prostaglandin E2 (PGE₂) along with cAMP in the skin demonstrating its inflammatory potential. Western blot analysis showed that exposure of AOH lead to phosphorylation of CREB and increased the expression of COX-2, cyclin D1 as well as prostanoid EP2 receptor. Further studies on primary mouse keratinocytes (PMK) revealed that very low concentrations of AOH (50-500 nM) resulted in significant PMK proliferation. Additionally, using specific antagonist or agonist of prostanoid receptors, we delineated that EP2 receptor play a key role in AOH-induced PMKs proliferation. Collectively, our findings show that AOH can lead to dermal toxicity in mice by activating the EP2/cAMP/p-CREB signaling cascade.

Recurrence-Associated Long Non-coding RNA Signature for Determining the Risk of Recurrence in Patients with Colon Cancer

Patients with colon cancer are often faced a high risk of disease recurrence within 5 years of treatment that is the major cause of cancer mortality. Reliable molecular markers were required to improve the most effective personalized therapy. Here, we identified a recurrence-associated six-lncRNA (long non-coding RNA) signature (LINC0184, AC105243.1, LOC101928168, ILF3-AS1, MIR31HG, and AC006329.1) that can effectively distinguish between high and low risk of cancer recurrence from 389 patients of a discovery dataset, and validated its robust performance in four independent datasets comprising a total of 906 colon cancer patients. We found that the six-lncRNA signature was an independent predictive factor of disease recurrence in multivariate analysis and was superior to the performance of clinical factors and known gene signature. Furthermore, in silico functional analysis showed that the six-lncRNA-signature-associated coding genes are significantly enriched in proliferation and angiogenesis, cell death, as well as critical cancer pathways that could play important roles in colon cancer recurrence. Together, the six-lncRNA signature holds great potential for recurrence risk assessment and personalized management of colon cancer patients.

Preclinical Efficacy of [V4 Q5 ]dDAVP, a Second Generation Vasopressin Analog, on Metastatic Spread and Tumor-Associated Angiogenesis in Colorectal Cancer

Purpose

Control of metastatic spread of colorectal cancer (CRC) remains as a major therapeutic challenge. [V4 Q5 ]dDAVP is a vasopressin peptide analog with previously reported anticancer activity against carcinoma tumors. By acting as a selective agonist of arginine vasopressin type 2 membrane receptor (AVPR2) present in endothelial and tumor cells, [V⁴Q⁵]dDAVP is able to impair tumor aggressiveness and distant spread. Our aim was to evaluate the potential therapeutic benefits of [V⁴Q⁵]dDAVP on highly aggressive CRC disease using experimental models with translational relevance.

Materials and Methods

Murine CT-26 and human Colo-205 AVPR2-expressing CRC cell lines were used to test the preclinical efficacy of [V⁴Q⁵]dDAVP, both in vitro and in vivo.

Results

In syngeneic mice surgically implanted with CT-26 cells in the spleen, sustained intravenous treatment with [V⁴Q⁵]dDAVP (0.3 µg/kg) dramatically impaired metastatic progression to liver without overt signs of toxicity, and also reduced experimental lung colonization. The compound inhibited in vivo angiogenesis driven by Colo-205 cells in athymic mice, as well as in vitro endothelial cell migration and capillary tube formation. [V⁴Q⁵]dDAVP exerted AVPR2-dependent cytostatic activity in vitro (IC₅₀ 1.08 µM) and addition to 5-fluorouracil resulted in synergistic antiproliferative effects both in CT-26 and Colo-205 cells.

Conclusion

The present preclinical study establishes for the first time the efficacy of [V⁴Q⁵]dDAVP on CRC. These encouraging results suggest that the novel second generation vasopressin analog could be used for the management of aggressive CRC as an adjuvant agent during surgery or to complement standard chemotherapy, limiting tumor angiogenesis and metastasis and thus protecting the patient from CRC recurrence.

The prostaglandin E2 receptor PTGER2 and prostaglandin F2α receptor PTGFR mediate oviductal glycoprotein 1 expression in bovine oviductal epithelial cells

Oviductal glycoprotein 1 (OVGP1), an oviductin, is involved in the maintenance of sperm viability and motility and contributes to sperm capacitation in the oviduct. In this study, the regulatory effects exerted by prostaglandin E₂ (PGE₂) and F_2α (PGF_2α) on OVGP1 expression via their corresponding receptors in bovine oviductal epithelial cells (BOECs) were investigated. BOECs were cultured in vitro, and their expression of receptors of PGE₂ (PTGER1, PTGER2, PTGER3, and PTGER4) and PGF_2α (PTGFR) was measured using RT-qPCR. Ca²⁺ concentration was determined with a fluorescence-based method and cAMP was quantified by enzyme-linked immunosorbent assays to verify activation of PTGER2 and PTGFR by their corresponding agonists in these cells. OVGP1 mRNA and protein expression was measured using RT-qPCR and western blotting, respectively, following PTGER2 and PTGFR agonist-induced activation. PTGER1, PTGER2, PTGER4, and PTGFR were found to be present in BOECs; however, PTGER3 expression was not detected. OVGP1 expression was significantly promoted by 10^–6 M butaprost (a PTGER2 agonist) and decreased by 10^–6 M fluprostenol (a PTGFR agonist). In addition, 3 μM H-89 (a PKA inhibitor) and 3 μM U0126 (an ERK inhibitor) effectively inhibited PGE₂-induced upregulation of OVGP1, and 5 μM chelerythrine chloride (a PKC inhibitor) and 3 μM U0126 negated OVGP1 downregulation by PGF_2α. In conclusion, this study demonstrates that OVGP1 expression in BOECs is enhanced by PGE₂ via PTGER2-cAMP-PKA signaling, and reduced by PGF_2α through the PTGFR-Ca²⁺-PKC pathway.

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.

Phosphodiesterases in non-neoplastic appearing colonic mucosa from patients with colorectal neoplasia

Background

Intracellular signaling through cyclic nucleotides, both cyclic AMP and cyclic GMP, is altered in colorectal cancer. Accordingly, it is hypothesized that an underlying mechanism for colorectal neoplasia involves altered function of phosphodiesterases (PDEs), which affects cyclic nucleotide degradation. Here we present an approach to evaluate the function of selected cyclic nucleotide-PDEs in colonic endoscopic biopsies from non-neoplastic appearing mucosa.

Methods

Biopsies were obtained from patients with and without colorectal neoplasia. Activities of PDEs were characterized functionally by measurements of transepithelial ion transport and their expression and localization by employing real-time qPCR and immunohistochemistry.

Results

In functional studies PDE subtype-4 displayed lower activity in colorectal neoplasia patients (p = 0.006). Furthermore, real-time qPCR analysis showed overexpression of subtype PDE4B (p = 0.002) and subtype PDE5A (p = 0.02) in colorectal neoplasia patients. Finally, immunohistochemistry for 7 PDE isozymes demonstrated the presence of all 7 isozymes, albeit with weak reactions, and with no differences in localization between colorectal neoplasia and control patients. Of note, quantification of PDE subtype immunostaining revealed a lower amount of PDE3A (p = 0.04) and a higher amount of PDE4B (p = 0.02) in samples from colorectal neoplasia patients.

Conclusion

In conclusion, functional data indicated lower activity of PDE4 subtypes while expressional and abundance data indicated a higher expression of PDE4B in patients with colorectal neoplasia. We suggest that cyclic nucleotide-PDE4B is overexpressed as a malfunctioning protein in non-neoplastic appearing colonic mucosa from patients with colorectal neoplasia. If a predisposition of reduced PDE4B activity in colonic mucosa from colorectal neoplasia patients is substantiated further, this subtype could be a potential novel early diagnostic risk marker and may even be a target for future medical preventive treatment of colorectal cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2980-z) contains supplementary material, which is available to authorized users.

Cytotoxic and pro-oxidative effects of Imperata cylindrica aerial part ethyl acetate extract in colorectal cancer in vitro

BACKGROUND

Colorectal cancer (CRC) is the third most common cancer. Its global incidence and mortality have been on the rise. Recent strategy of therapies has involved the use of non-steroid anti-inflammatory drugs and cyclooxygenase-selective inhibitors. Aerial parts of Imperata cylindrical L. Raeusch (IMP) have been used as an anti-inflammatory agent in traditional Chinese medicine.

HYPOTHESIS

Asarachidonate acid cascadeis often involved in inflammation-related malignancy and IMP is an anti-inflammatory agent, hence it is hypothesized that IMP aerial part ethyl acetate extract exerts cytotoxic effects on colorectal cancer cells in vitro.

STUDY DESIGN

The HT-29 adenocarcinoma cell line was used to elucidate its pro-apoptotic activities. Flow cytometry and fluorescent microscopy were performed to assess cell cycle arrest and the accumulation of reactive oxygen species (ROS). The mRNA and hormone levels of arachidonate acid pathways were studied via quantitative reverse transcription PCR (qRT-PCR) and ELISA.

RESULTS

The 50% growth inhibitory effect (GI50) of the IMP extract on HT-29 was measured with a value of 14.5 µg/ml. Immuno-blot and caspase-3/7 activity assay showed the pro-apoptotic effect of IMP on the activation of caspase cascade. G2/M arrest was observed via flow cytometry. The ROS activity was modulated by the IMP extraction a concentration-dependent manner in HT-29 cells. The IMP extract increased PGE2 and PGF2α levels qRT-PCR revealed that transcripts of rate-limiting PGE2- and PGF2α-biosynthetic enzymes - COX-1, mPGES1 and AKR1C3 were notably up-regulated. Among the prostanoid receptors, EP1 and FP transcripts were up-regulated while EP4 transcripts decreased. The findings suggest that the proliferative effect of PGE2, which is generally believed to associate with heightened DNA synthesis and cross-talk with MAPK pathways, is likely triggered by the pro-apoptotic or -oxidative effects exerted by IMP extract in HT-29 cells. Concurring with this notion, indomethacin (COX-1/2-inhibitor) was demonstrated to potentiate the cytotoxic effect of IMP extract (GI50 ≦ 10.8 µg/ml). The results show that the cytotoxic effect of IMP extract predominates over the influence of proliferative prostanoids released by challenged colorectal cancer cells, and may present a potential source for development of novel anti-cancer drugs.

Prostaglandin E2 promotes proliferation of skeletal muscle myoblasts via EP4 receptor activation

We recently demonstrated that conditioned media (CM) from osteocytes enhances myogenic differentiation of myoblasts, suggesting that signaling from bone may be important for skeletal muscle myogenesis. The effect of CM was closely mimicked by prostaglandin E₂ (PGE₂), a bioactive lipid mediator in various physiological or pathological conditions. PGE₂ is secreted at high levels by osteocytes and such secretion is further enhanced under loading conditions. Although four types of receptors, EP1 to EP4, mediate PGE₂ signaling, it is unknown whether these receptors play a role in myogenesis. Therefore, in this study, the expression of EPs in mouse primary myoblasts was characterized, followed by examination of their roles in myoblast proliferation by treating myoblasts with PGE₂ or specific agonists. All four PGE₂ receptor mRNAs were detectable by quantitative real-time PCR (qPCR), but only PGE₂ and EP4 agonist CAY 10598 significantly enhance myoblast proliferation. EP1/EP3 agonist 17-phenyl trinor PGE₂ (17-PT PGE₂) and EP2 agonist butaprost did not have any significant effects. Moreover, treatment with EP4 antagonist L161,982 dose-dependently inhibited myoblast proliferation. These results were confirmed by cell cycle analysis and the gene expression of cell cycle regulators. Concomitant with the inhibition of myoblast proliferation, treatment with L161,982 significantly increased intracellular reactive oxygen species (ROS) levels. Cotreatment with antioxidant N-acetyl cysteine (NAC) or sodium ascorbate (SA) successfully reversed the inhibition of myoblast proliferation and ROS overproduction caused by L161,982. Therefore, PGE₂ signaling via the EP4 receptor regulates myogenesis by promoting myoblast proliferation and blocking this receptor results in increased ROS production in myoblasts.

Nicotine-induced cellular stresses and autophagy in human cancer colon cells: A supportive effect on cell homeostasis via up-regulation of Cox-2 and PGE(2) production

Nicotine, one of the active components in cigarette smoke, has been described to contribute to the protective effect of smoking in ulcerative colitis (UC) patients. Furthermore, the nicotinic acetylcholine receptor α7 subunit (α7nAChR) expressed on immune cells, is an essential regulator of inflammation. As intestinal epithelial cells also express α7nAChR, we investigated how nicotine could participate in the homeostasis of intestinal epithelial cells. First, using the human adenocarcinoma cell line HT-29, we revealed that nicotine, which triggers an influx of extracellular Ca(2+) following α7nAChR stimulation, induces mitochondrial reactive oxygen species (ROS) production associated with a disruption of the mitochondrial membrane potential and endoplasmic reticulum stress. This results in caspase-3 activation, which in turn induces apoptosis. Additionally, we have shown that nicotine induces a PI3-K dependent up-regulation of cyclooxygenase-2 (Cox-2) expression and prostaglandin E2 (PGE2) production. In this context, we suggest that this key mediator participates in the cytoprotective effects of nicotine against apoptosis by stimulating autophagy in colon cancer cells. Our results provide new insight into one potential mechanism by which nicotine could protect from UC and suggest an anti-inflammatory role for the cholinergic pathway at the epithelial cell level.

Protein kinases as switches for the function of upstream stimulatory factors: implications for tissue injury and cancer

The upstream stimulatory factors (USFs) are regulators of important cellular processes. Both USF1 and USF2 are supposed to have major roles in metabolism, tissue protection and tumor development. However, the knowledge about the mechanisms that control the function of USFs, in particular in tissue protection and cancer, is limited. Phosphorylation is a versatile tool to regulate protein functions. Thereby, phosphorylation can positively or negatively affect different aspects of transcription factor function including protein stability, protein-protein interaction, cellular localization, or DNA binding. The present review aims to summarize the current knowledge about the regulation of USFs by direct phosphorylation and the consequences for USF functions in tissue protection and cancer.

Novel link between prostaglandin E2 (PGE2) and cholinergic signaling in lung cancer: The role of c-Jun in PGE2-induced α7 nicotinic acetylcholine receptor expression and tumor cell proliferation

BACKGROUND

Cyclooxygenase-2-derived prostaglandin E2 (PGE2) stimulates tumor cell growth and progression. α7 nicotinic acetylcholine receptor (nAChR) is a major mediator of cholinergic signaling in tumor cells. In the present study, we investigated the mechanisms by which PGE2 increases non-small cell lung cancer (NSCLC) proliferation via α7 nAChR induction.

METHODS

The effects of PGE2 on α7 nAChR expression, promoter activity, and cell signaling pathways were detected by Western blot analysis, real time reverse transcriptase polymerase chain reaction, and transient transfection assay. The effect of PGE2 on cell growth was determined by cell viability assay.

RESULTS

We found that PGE2 induced α7 nAChR expression and its promoter activity in NSCLC cells. The stimulatory role of PGE2 on cell proliferation was attenuated by α7 nAChR small interfering ribonucleic acids (siRNA) or acetylcholinesterase. PGE2-induced α7 nAChR expression was blocked by an antagonist of the PGE2 receptor subtype EP4 and by EP4 siRNA. Furthermore, PGE2 enhanced α7 nAChR expression via activation of c-Jun N-terminal kinase (JNK), phosphatidylinositol 3-kinase (PI3-K), and protein kinase A (PKA) pathways followed by increased c-Jun expression, a critical transcription factor. Blockade of c-Jun diminished the effects of PGE2 on α7 nAChR promoter activity and protein expression, and cell growth.

CONCLUSION

Our results demonstrate that PGE2 promotes NSCLC cell growth through increased α7 nAChR expression. This effect is dependent on EP4-mediated activation of JNK, PI3K, and PKA signals that induce c-Jun protein expression and α7 nAChR gene promoter activity. Our findings unveil a novel link between prostanoids and cholinergic signaling.

Upregulation of adenylate cyclase 3 (ADCY3) increases the tumorigenic potential of cells by activating the CREB pathway

Adenylate cyclase 3 (ADCY3) is a widely expressed membrane-associated protein in human tissues, which catalyzes the formation of cyclic adenosine-3′,5′-monophosphate (cAMP). However, our transcriptome analysis of gastric cancer tissue samples (NCBI GEO GSE30727) revealed that ADCY3 expression was specifically altered in cancer samples. Here we investigated the tumor-promoting effects of ADCY3 overexpression and confirmed a significant correlation between the upregulation of ADCY3 and Lauren's intestinal-type gastric cancers. ADCY3 overexpression increased cell migration, invasion, proliferation, and clonogenicity in HEK293 cells; conversely, silencing ADCY3 expression in SNU-216 cells reduced these phenotypes. Interestingly, ADCY3 overexpression increased both the mRNA level and activity of matrix metalloproteinase 2 (MMP2) and MMP9 by increasing the levels of cAMP and phosphorylated cAMP-responsive element-binding protein (CREB). Consistent with these findings, treatment with a protein kinase A (PKA) inhibitor decreased MMP2 and MMP9 expression levels in ADCY3-overexpressing cells. Knockdown of ADCY3 expression by stable shRNA in human gastric cancer cells suppressed tumor growth in a tumor xenograft model. Thus, ADCY3 overexpression may exert its tumor-promoting effects via the cAMP/PKA/CREB pathway. Additionally, bisulfite sequencing of the ADCY3 promoter region revealed that gene expression was reduced by hypermethylation of CpG sites, and increased by 5-Aza-2′-deoxycytidine (5-Aza-dC)-induced demethylation. Our study is the first to report an association of ADCY3 with gastric cancer as well as its tumorigenic potentials. In addition, we demonstrate that the expression of ADCY3 is regulated through an epigenetic mechanism. Further study on the mechanism of ADCY3 in tumorigenesis will provide the basis as a new molecular target of gastric cancer.

The hidden switches underlying RORα-mediated circuits that critically regulate uncontrolled cell proliferation

Prostaglandin E2 (PGE2) is known to have a key role in the development of colorectal cancer, but previous experiments showed its contrasting (i.e. tumor-promoting or tumor-suppressive) roles depending on experimental conditions. To elucidate the mechanisms underlying such contrasting roles of PGE2 in tumorigenesis, we investigated all the previous experiments and found a new signal transduction pathway mediated by retinoic acid receptor-related orphan receptor (ROR)α, in which PGE2/PKCα-dependent phosphorylation of RORα attenuates Wnt target gene expression in colon cancer cells. From mathematical simulations combined with biochemical experimentation, we revealed that RORα induces a biphasic response of Wnt target genes to PGE2 stimulation through a regulatory switch formed by an incoherent feedforward loop, which provides a mechanistic explanation on the contrasting roles of PGE2 observed in previous experiments. More interestingly, we found that RORα constitutes another regulatory switch formed by coupled positive and negative feedback loops, which regulates the hysteretic response of Wnt signaling and eventually converts a proliferative cellular state into an anti-proliferative state in a very delicate way. Our results indicate that RORα is the key regulator at the center of these hidden switches that critically regulate cancer cell proliferation and thereby being a promising anti-cancer therapeutic target.

Effects of catecholamines on thymocyte apoptosis and proliferation depend on thymocyte microenvironment

The present study, through quantification of tyrosine hydroxylase (TH) expression and catecholamine (CA) content in the presence and in the absence of α-methyl-p-tyrosine (AMPT), a TH inhibitor, in adult thymic organ (ATOC) and thymocyte culture, demonstrated that thymic cells produce CAs. In addition, in ATOC an increase in β2-adrenoceptor (AR) mRNA expression and β2-AR thymocyte surface density was registered. Furthermore, AMPT (10(-4)M), as propranolol (10(-4)M), augmented thymocyte apoptosis and diminished thymocyte proliferation in ATOC. Propranolol exerted these effects acting on CD3(high) thymocytes. However, in thymocyte cultures, propranolol (10(-6)M) acting on the same thymocyte subset exerted the opposing effect on thymocyte apoptosis and ConA-stimulated proliferation. This suggested that, depending on thymocyte microenvironment, differential effects can be induced through the same type of AR. Additionally, arterenol (10(-8) to 10(-6)M), similar to propranolol, diminished apoptosis, but increased ConA-stimulated thymocyte proliferation in thymocyte culture. However, differently from propranolol, arterenol affected manly CD3- thymocyte subset, which harbors majority of α1-AR+thymocytes. Additionally, arterenol showed a dose-dependent decrease in efficiency of thymocyte apoptosis and proliferation modulation with the rise in its concentration. Considering greater affinity of arterenol for α1-ARs than for β2-ARs, the previous findings could be attributable to increased engagement of β2-ARs with the rise of arterenol concentration. Consistently, in the presence of propranolol (10(-6)M), a β-AR blocker, the arterenol (10(-8)M) effects on thymocytes were augmented. In conclusion, thymic endogenous CAs, acting through distinct AR types and, possible, the same AR type (but in different cell microenvironment) may exert the opposing effects on thymocyte apoptosis/proliferation.

The prostanoid EP4 receptor and its signaling pathway

The EP4 prostanoid receptor is one of four receptor subtypes for prostaglandin E2. It belongs to the family of G protein-coupled receptors. It was originally identified, similar to the EP2 receptor as a G(s)α-coupled, adenylyl cyclase-stimulating receptor. EP4 signaling plays a variety of roles through cAMP effectors, i.e., protein kinase A and exchange protein activated by cAMP. However, emerging evidence from studies using pharmacological approaches and genetically modified mice suggests that EP4, unlike EP2, can also be coupled to G(i)α, phosphatidylinositol 3-kinase, β-arrestin, or β-catenin. These signaling pathways constitute unique roles for the EP4 receptor. EP4 is widely distributed in the body and thus plays various physiologic and pathophysiologic roles. In particular, EP4 signaling is closely related to carcinogenesis, cardiac hypertrophy, vasodilation, vascular remodeling, bone remodeling, gastrointestinal homeostasis, renal function, and female reproductive function. In addition to the classic anti-inflammatory action of EP4 on mononuclear cells and T cells, recent evidence has shown that EP4 signaling contributes to proinflammatory action as well. The aim of this review is to present current findings on the biologic functions of the EP4 receptor. In particular, we will discuss its diversity from the standpoint of EP4-mediated signaling.

Nuclear orphan receptor NR4A2 confers chemoresistance and predicts unfavorable prognosis of colorectal carcinoma patients who received postoperative chemotherapy

BACKGROUND

NR4A2, an orphan nuclear receptor essential in neuron generation, has been recently linked to inflammatory and metabolic pathways of colorectal carcinoma (CRC). However, the effects of NR4A2 on chemo-resistance and postoperative prognosis of CRC remain unknown.

METHODS

NR4A2 was transfected into CRC cells to investigate its effects on chemo-resistance to 5-fluorouracil and oxaliplatin and chemotherapeutics-induced apoptosis. We also investigated prostaglandin E2 (PGE2)-induced NR4A2 expression and its effect on chemo-resistance. Tissue microarrays including 51 adenoma, 14 familial adenomatous polyposis with CRC, 17 stage IV CRC with adjacent mucosa and 682 stage I-III CRC specimens were examined immunohistochemically for NR4A2 expression. Median follow-up time for stage I-III CRC patients was 53 months.

RESULTS

Ectopic expression of NR4A2 increased the chemo-resistance, and attenuated the chemotherapeutics-induced apoptosis. Transient treatment of PGE2 significantly up-regulated NR4A2 expression via protein kinase A pathway and increased the chemo-resistance. NR4A2 expression in epithelials consecutively increased from adenoma, adjacent mucosa to CRC (P(trend)<0.001). In multivariate Cox regression analyses, high NR4A2 expression in cancer nuclei (immunoreactive score ≥ 4) significantly predicted a shorter disease-specific survival (DSS) of CRC patients (hazard ratio [HR]=1.88, P=0.024). High NR4A2 expression specifically predicted a shorter DSS of colon cancer patients (dichotomisation, HR=2.55, log-rank test P=0.011), especially for those who received postoperative 5-fluorouracil/leucovorin plus oxaliplatin (FOLFOX) chemotherapy (3-score range, HR=1.86, log-rank test P=0.020).

CONCLUSION

High expression of NR4A2 in CRC cells confers chemo-resistance, attenuates chemotherapeutics-induced apoptosis, and predicts unfavorable prognosis of colon cancer patients, especially for those who received postoperative chemotherapy. NR4A2 may be prognostic and predictive for colon cancer.

Cyclic nucleotide signaling in intestinal epithelia: getting to the gut of the matter

The intestine is the primary site of nutrient absorption, fluid-ion secretion, and home to trillions of symbiotic microbiota. The high turnover of the intestinal epithelia also renders it susceptible to neoplastic growth. These diverse processes are carefully regulated by an intricate signaling network. Among the myriad molecules involved in intestinal epithelial cell homeostasis are the second messengers, cyclic AMP (cAMP) and cyclic GMP (cGMP). These cyclic nucleotides are synthesized by nucleotidyl cyclases whose activities are regulated by extrinsic and intrinsic cues. Downstream effectors of cAMP and cGMP include protein kinases, cyclic nucleotide gated ion channels, and transcription factors, which modulate key processes such as ion-balance, immune response, and cell proliferation. The web of interaction involving the major signaling pathways of cAMP and cGMP in the intestinal epithelial cell, and possible cross-talk among the pathways, are highlighted in this review. Deregulation of these pathways occurs during infection by pathogens, intestinal inflammation, and cancer. Thus, an appreciation of the importance of cyclic nucleotide signaling in the intestine furthers our understanding of bowel disease, thereby aiding in the development of therapeutic approaches.

Fluorescent Human EP3 Receptor Antagonists

Exchange of the lipophilc part of ortho-substituted cinnamic acid lead structures with different small molecule fluorophoric moieties via a dimethylene spacer resulted in hEP3R ligands with affinities in the nanomolar concentration range. Synthesized compounds emit fluorescence in the blue, green, and red range of light and have been tested concerning their potential as a pharmacological tool. hEP3Rs were visualized by confocal laser scanning microscopy on HT-29 cells, on murine kidney tissues, and on human brain tissues and functionally were characterized as antagonists on human platelets. Inhibition of PGE2 and collagen-induced platelet aggregation was measured after preincubation with novel hEP3R ligands. The pyryllium-labeled ligand 8 has been shown as one of the most promising structures, displaying a useful fluorescence and highly affine hEP3R antagonists.

HT-29 human colon cancer cell proliferation is regulated by cytosolic phospholipase A(2)α dependent PGE(2)via both PKA and PKB pathways

Cytosolic phospholipase A(2)α (cPLA(2)α) up-regulation has been reported in human colorectal cancer cells, thus we aimed to elucidate its role in the proliferation of the human colorectal cancer cell line, HT-29. EGF caused a rapid activation of cPLA(2)α which coincided with a significant increase in cell proliferation. The inhibition of cPLA(2)α activity by pyrrophenone or by antisense oligonucleotide against cPLA(2)α (AS) or inhibition of prostaglandin E(2) (PGE(2)) production by indomethacin resulted with inhibition of cell proliferation, that was restored by addition of PGE(2). The secreted PGE(2) activated both protein kinase A (PKA) and PKB/Akt pathways via the EP2 and EP4 receptors. Either, the PKA inhibitor (H-89) or the PKB/Akt inhibitor (Ly294002) caused a partial inhibition of cell proliferation which was restored by PGE(2). But, inhibited proliferation in the presence of both inhibitors could not be restored by addition of PGE(2). AS or H-89, but not Ly294002, inhibited CREB activation, suggesting that CREB activation is mediated by PKA. AS or Ly294002, but not H-89, decreased PKB/Akt activation as well as the nuclear localization of β-catenin and cyclin D1 and increased the plasma membrane localization of β-catenin with E-cadherin, suggesting that these processes are regulated by the PKB pathway. Similarly, Caco-2 cells exhibited cPLA(2)α dependent proliferation via activation of both PKA and PKB/Akt pathways. In conclusion, our findings suggest that the regulation of HT-29 proliferation is mediated by cPLA(2)α-dependent PGE(2) production. PGE(2)via EP induces CREB phosphorylation by the PKA pathway and regulates β-catenin and cyclin D1 cellular localization by PKB/Akt pathway.

A study of prostaglandin pathway genes and interactions with current nonsteroidal anti-inflammatory drug use in colorectal adenoma

Colorectal cancer (CRC) is the second leading cause of cancer-related death and usually arises from colorectal polyps. Screening and removal of polyps reduce mortality from CRC. Colorectal polyps are known to aggregate in families; however the genetic determinants for risk of polyps are unknown. In addition, it has been shown that nonsteroidal anti-inflammatory drug (NSAID) use decreases the risk of CRC and the incidence and size of polyps. In this study, we used data from the Tennessee Colorectal Polyp Study and the Tennessee-Indiana Adenoma Recurrence Study to evaluate selected genes from the prostaglandin (PG) metabolism and signaling pathways for association with risk of polyps and for interactions with NSAIDs. Our design consisted of discovery and replication phases for a total of 2,551 Caucasian polyp cases and 3,285 Caucasian controls. We carried out multivariable logistic regression to test for association in both the discovery and replication phase and further examined the results with meta-analysis. We detected association signals in the genes PGE receptor 3 (PTGER3) and 15-hydroxyprostaglandin dehydrogenase (HPGD), both strong biologic candidates for influence on polyp risk. We did not observe the previously reported effects and effect modification in PG-endoperoxide synthase 2 (PTGS2), PGE receptor 2 (PTGER2), or PGE receptor 4 (PTGER4), although we did observe a single nucleotide polymorphism in PTGER2 associated with risk of multiple adenomas. We also observed effect modification of the HPGD signal by NSAID exposure.

Eicosanoid signalling pathways in the development and progression of colorectal cancer: novel approaches for prevention/intervention

Arachidonic acid metabolism through cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P-450 epoxygenase (EPOX) pathways leads to the generation of biologically active eicosanoids, including prostanoids, leukotrienes, hydroxyeicosatetraenoic acid, epoxyeicosatrienoic acid and hydroperoxyeicosatetraenoic acids. Eicosanoid expression levels vary during tumor development and progression of a range of malignancies, including colorectal cancer. The actions of these autocoids are also directly influenced by diet, as demonstrated by recent evidence for omega-3 fatty acids in colorectal cancer (CRC) prevention and/or treatment. Eicosanoids regulate CRC development and progression, while inhibition of these pathways has generally been shown to inhibit tumor growth/progression. A progressive sequence of colorectal cancer development has been identified, ranging from normal colon, to colitis, dysplasia, and carcinoma. While both COX and LOX inhibition are both promising candidates for colorectal cancer prevention and/or treatment, there is an urgent need to understand the mechanisms through which these signalling pathways mediate their effects on tumorigenesis. This will allow identification of safer, more effective strategies for colorectal cancer prevention and/or treatment. In particular, binding to/signalling through prostanoid receptors have recently been the subject of considerable interest in this area. In this review, we discuss the role of the eicosanoid signalling pathways in the development and progression of colorectal cancer. We discuss the effects of the eicosanoids on tumor cell proliferation, their roles in cell death induction, effects on angiogenesis, migration, invasion and their regulation of the immune response. Signal transduction pathways involved in these processes are also discussed. Finally, novel approaches targeting these arachidonic acid-derived eicosanoids (using pharmacological or natural agents) for chemoprevention and/or treatment of colorectal cancer are outlined.

Cyclic AMP is both a pro-apoptotic and anti-apoptotic second messenger

The second messenger cyclic AMP (cAMP) can either stimulate or inhibit programmed cell death (apoptosis). Here, we review examples of cell types that show pro-apoptotic or anti-apoptotic responses to increases in cAMP. We also show that cells can have both such responses, although predominantly having one or the other. Protein kinase A (PKA)-promoted changes in phosphorylation and gene expression can mediate pro-apoptotic responses, such as in murine S49 lymphoma cells, based on evidence that mutants lacking PKA fail to undergo cAMP-promoted, mitochondria-dependent apoptosis. Mechanisms for the anti-apoptotic response to cAMP likely involve Epac (Exchange protein activated by cAMP), a cAMP-regulated effector that is a guanine nucleotide exchange factor (GEF) for the low molecular weight G-protein, Rap1. Therapeutic approaches that activate PKA-mediated pro-apoptosis or block Epac-mediated anti-apoptotisis may provide a means to enhance cell killing, such as in certain cancers. In contrast, efforts to block PKA or stimulate Epac have the potential to be useful in diseases settings (such as heart failure) associated with cAMP-promoted apoptosis.

Increase in intracellular PGE2 induces apoptosis in Bax-expressing colon cancer cell

BACKGROUND

NSAIDs exhibit protective properties towards some cancers, especially colon cancer. Yet, it is not clear how they play their protective role. PGE2 is generally shown as the only target of the NSAIDs anticancerous activity. However, PGE2 known targets become more and more manifold, considering both the molecular pathways involved and the target cells in the tumour. The role of PGE2 in tumour progression thus appears complex and multipurpose.

METHODS

To gain understanding into the role of PGE2 in colon cancer, we focused on the activity of PGE2 in apoptosis in colon cancer cell lines.

RESULTS

We observed that an increase in intracellular PGE2 induced an apoptotic cell death, which was dependent on the expression of the proapoptotic protein Bax. This increase was induced by increasing PGE2 intracellular concentration, either by PGE2 microinjection or by the pharmacological inhibition of PGE2 exportation and enzymatic degradation.

CONCLUSIONS

We present here a new sight onto PGE2 in colon cancer cells opening the way to a new prospective therapeutic strategy in cancer, alternative to NSAIDs.

Protein kinase a in cancer

In the past, many chromosomal and genetic alterations have been examined as possible causes of cancer. However, some tumors do not display a clear molecular and/or genetic signature. Therefore, other cellular processes may be involved in carcinogenesis. Genetic alterations of proteins involved in signal transduction have been extensively studied, for example oncogenes, while modifications in intracellular compartmentalization of these molecules, or changes in the expression of unmodified genes have received less attention. Yet, epigenetic modulation of second messenger systems can deeply modify cellular functioning and in the end may cause instability of many processes, including cell mitosis. It is important to understand the functional meaning of modifications in second messenger intracellular pathways and unravel the role of downstream proteins in the initiation and growth of tumors. Within this framework, the cAMP system has been examined. cAMP is a second messenger involved in regulation of a variety of cellular functions. It acts mainly through its binding to cAMP-activated protein kinases (PKA), that were suggested to participate in the onset and progression of various tumors. PKA may represent a biomarker for tumor detection, identification and staging, and may be a potential target for pharmacological treatment of tumors.

Effect of eicosapentaenoic acid on E-type prostaglandin synthesis and EP4 receptor signaling in human colorectal cancer cells

The omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA), in the free fatty acid (FFA) form, has been demonstrated to reduce adenoma number and size in patients with familial adenomatous polyposis. However, the mechanistic basis of the antineoplastic activity of EPA in the colorectum remains unclear. We tested the hypothesis that EPA-FFA negatively modulates synthesis of and signaling by prostaglandin (PG) E(2) in human colorectal cancer (CRC) cells. EPA-FFA induced apoptosis of cyclooxygenase (COX)-2-positive human HCA-7 CRC cells in vitro. EPA-FFA in cell culture medium was incorporated rapidly into phospholipid membranes of HCA-7 human CRC cells and acted as a substrate for COX-2, leading to reduced synthesis of PGE(2) and generation of PGE(3). Alone, PGE(3) bound and activated the PGE(2) EP4 receptor but with reduced affinity and efficacy compared with its "natural" ligand PGE(2). However, in the presence of PGE(2), PGE(3) acted as an antagonist of EP4 receptor-dependent 3',5' cyclic adenosine monophosphate induction in naturally EP4 receptor-positive LoVo human CRC cells and of resistance to apoptosis in HT-29-EP4 human CRC cells overexpressing the EP4 receptor. We conclude that EPA-FFA drives a COX-2-dependent "PGE(2)-to-PGE(3) switch" in human CRC cells and that PGE(3) acts as a partial agonist at the PGE(2) EP4 receptor.

The {omega}-3 fatty acid eicosapentaenoic acid elicits cAMP generation in colonic epithelial cells via a "store-operated" mechanism

Eicosapentaenoic acid (EPA) is an omega-3 polyunsaturated fatty acid abundant in fish oil that exerts a wide spectrum of documented beneficial health effects in humans. Because dietary interventions are relatively inexpensive and are widely assumed to be safe, they have broad public appeal. Their endorsement can potentially have a major impact on human health, but hard mechanistic evidence that specifies how these derivatives work at the cellular level is limited. EPA (50 microM) caused a small elevation of cytoplasmic Ca(2+) concentration ([Ca(2+)]) in intact NCM460 human colonic epithelial cells as measured by fura 2 and a profound drop of [Ca(2+)] within the endoplasmic reticulum (ER) of permeabilized cells as monitored by compartmentalized mag-fura 2. Total internal reflection fluorescence microscopy showed that this loss of ER store [Ca(2+)] led to translocation of the ER-resident transmembrane Ca(2+) sensor STIM1. Using sensitive FRET-based sensors for cAMP in single cells, we further found that EPA caused a substantial increase in cellular cAMP concentration, a large fraction of which was dependent on the drop in ER [Ca(2+)], but independent of cytosolic Ca(2+). An additional component of the EPA-induced cAMP signal was sensitive to the phosphodiesterase inhibitor isobutyl methylxanthine. We conclude that EPA slowly releases ER Ca(2+) stores, resulting in the generation of cAMP. The elevated cAMP is apparently independent of classical G protein-coupled receptor activation and is likely the consequence of a newly described "store-operated" cAMP signaling pathway that is mediated by STIM1.

PGE2 promotes Ca2+-mediated epithelial barrier disruption through EP1 and EP4 receptors in Caco-2 cell monolayers

We recently demonstrated that PGE(2) induces the disruption of the intestinal epithelial barrier function. In the present study, our objectives were to study the role of PGE(2) receptors (EP(1)-EP(4)) and the signaling pathways involved in this event. Paracellular permeability (PP) was assessed in differentiated Caco-2 cell cultures from d-mannitol fluxes and transepithelial electrical resistance (TER) in the presence of different PGE(2) receptor agonists (carbacyclin, sulprostone, butaprost, ONO-AE1-259, ONO-AE-248, GR63799, and ONO-AE1-329) and antagonists (ONO-8711, SC-19220, AH-6809, ONO-AE3-240, ONO-AE3-208, and AH-23848). The results indicate that EP(1) and EP(4) but not EP(2) and EP(3) might be involved in PP regulation. These effects were mediated through PLC-inositol trisphosphate (IP(3))-Ca(2+) and cAMP-PKA signaling pathways, respectively. We also observed an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) strengthened by cAMP formation indicating a cross talk interaction of these two pathways. Moreover, the participation of a conventional PKC isoform was shown. The results also indicate that the increase in PP may be correlated with the redistribution of occludin, zona occludens 1 (ZO-1), and the perijunctional actin ring together with an increase in myosin light chain kinase activity. Although the disruption of epithelial barrier function observed in inflammatory bowel disease (IBD) patients has been traditionally attributed to cytokines, the present study focused on the role of PGE(2) in PP regulation, as mucosal levels of this eicosanoid are also increased in these inflammatory processes.

Prostaglandin E2 promotes lung cancer cell migration via EP4-betaArrestin1-c-Src signalsome

Many human cancers express elevated levels of cyclooxygenase-2 (COX-2), an enzyme responsible for the biosynthesis of prostaglandins. Available clinical data establish the protective effect of COX-2 inhibition on human cancer progression. However, despite these encouraging outcomes, the appearance of unwanted side effects remains a major hurdle for the general application of COX-2 inhibitors as effective cancer drugs. Hence, a better understanding of the molecular signals downstream of COX-2 is needed for the elucidation of drug targets that may improve cancer therapy. Here, we show that the COX-2 product prostaglandin E(2) (PGE(2)) acts on cognate receptor EP4 to promote the migration of A549 lung cancer cells. Treatment with PGE(2) enhances tyrosine kinase c-Src activation, and blockade of c-Src activity represses the PGE(2)-mediated lung cancer cell migration. PGE(2) affects target cells by activating four receptors named EP1 to EP4. Use of EP subtype-selective ligand agonists suggested that EP4 mediates prostaglandin-induced A549 lung cancer cell migration, and this conclusion was confirmed using a short hairpin RNA approach to specifically knock down EP4 expression. Proximal EP4 effectors include heterotrimeric Gs and betaArrestin proteins. Knockdown of betaArrestin1 expression with shRNA significantly impaired the PGE(2)-induced c-Src activation and cell migration. Together, these results support the idea that increased expression of the COX-2 product PGE(2) in the lung tumor microenvironment may initiate a mitogenic signaling cascade composed of EP4, betaArrestin1, and c-Src which mediates cancer cell migration. Selective targeting of EP4 with a ligand antagonist may provide an efficient approach to better manage patients with advanced lung cancer.

Regulation of renal proximal tubule Na-K-ATPase by prostaglandins

Prostaglandins (PGs) play a number of roles in the kidney, including regulation of salt and water reabsorption. In this report, evidence was obtained for stimulatory effects of PGs on Na-K-ATPase in primary cultures of rabbit renal proximal tubule (RPT) cells. The results of our real-time PCR studies indicate that in primary RPTs the effects of PGE(2), the major renal PG, are mediated by four classes of PGE (EP) receptors. The role of these EP receptors in the regulation of Na-K-ATPase was examined at the transcriptional level. Na-K-ATPase consists of a catalytic α-subunit encoded by the ATP1A1 gene, as well as a β-subunit encoded by the ATP1B1 gene. Transient transfection studies conducted with pHβ1-1141 Luc, a human ATP1B1 promoter/luciferase construct, indicate that both PGE(1) and PGE(2) are stimulatory. The evidence for the involvement of both the cAMP and Ca(2+) signaling pathways includes the inhibitory effects of the myristolylated PKA inhibitor PKI, the adenylate cyclase (AC) inhibitor SQ22536, and the PKC inhibitors Gö 6976 and Ro-32-0432 on the PGE(1) stimulation. Other effectors that similarly act through cAMP and PKC were also stimulatory to transcription, including norepinephrine and dopamine. In addition to its effects on transcription, a chronic incubation with PGE(1) was observed to result in an increase in Na-K-ATPase mRNA levels as well as an increase in Na-K-ATPase activity. An acute stimulatory effect of PGE(1) on Na-K-ATPase was observed and was associated with an increase in the level of Na-K-ATPase in the basolateral membrane.

Differential effects of NOD2 polymorphisms on colorectal cancer risk: a meta-analysis

INTRODUCTION

Since Kurzawski et al. described an association between the 3020insC NOD2 single nucleotide polymorphism and the risk of colorectal cancer(CRC) in 2004, reports published in the past several years have controversial results regarding the relationship between the development of CRC and NOD2 gene polymorphisms. To clarify the potential role of NOD2 P286S, R702W, G908R, and 3020insC polymorphisms in CRC patients, we have undertaken a systematic review and meta-analysis of published articles.

MATERIALS AND METHODS

Studies reporting on NOD2 polymorphisms and CRC were searched in the PubMed, EMBASE, and the Science Citation Index from the inception of each database to May, 2009. The search strategy included the keywords "CRC", "colon cancer", "rectal cancer", "polymorphism", and "NOD2/CARD15".

RESULT

Eight eligible case-control studies about Caucasians from four countries contributed data on 5,888 subjects (cases: 3,524; controls: 2,364). Compared to the wild genotype, the R702W, G908R, and 3020insC polymorphisms were associated with an increased risk of CRC (odds ratio (OR): 1.59, 1.98, 1.44; 95% confidence interval (CI): 1.09-2.32, 1.14-3.44, 1.13-1.84; P = 0.02, 0.01, 0.003). However, P268S polymorphism did not influence CRC risk (OR: 1.27; CI: 0.32-5.00; P = 0.73).

CONCLUSIONS

These findings indicate that NOD2 R702W, G908R, and 3020insC polymorphisms contribute to CRC susceptibility in Caucasians. Meta-analysis of these polymorphisms in NOD2 gene will help determine their role in CRC carcinogenesis.