Secretory phospholipase A2 inhibition attenuates intercellular adhesion molecule-1 expression in human esophageal adenocarcinoma cells. Ann Thorac Surg. 2011;91:1539-1545. [PMID: 21396625 DOI: 10.1016/j.athoracsur.2011.01.017]

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.

Phospholipase A2 Drives Tumorigenesis and Cancer Aggressiveness through Its Interaction with Annexin A1

Phospholipids are suggested to drive tumorigenesis through their essential role in inflammation. Phospholipase A₂ (PLA₂) is a phospholipid metabolizing enzyme that releases free fatty acids, mostly arachidonic acid, and lysophospholipids, which contribute to the development of the tumor microenvironment (TME), promoting immune evasion, angiogenesis, tumor growth, and invasiveness. The mechanisms mediated by PLA₂ are not fully understood, especially because an important inhibitory molecule, Annexin A1, is present in the TME but does not exert its action. Here, we will discuss how Annexin A1 in cancer does not inhibit PLA₂ leading to both pro-inflammatory and pro-tumoral signaling pathways. Moreover, Annexin A1 promotes the release of cancer-derived exosomes, which also lead to the enrichment of PLA₂ and COX-1 and COX-2 enzymes, contributing to TME formation. In this review, we aim to describe the role of PLA₂ in the establishment of TME, focusing on cancer-derived exosomes, and modulatory activities of Annexin A1. Unraveling how these proteins interact in the cancer context can reveal new strategies for the treatment of different tumors. We will also describe the possible strategies to inhibit PLA₂ and the approaches that could be used in order to resume the anti-PLA₂ function of Annexin A1.

Expression of Adhesion Molecules in a Gastroduodenal Reflux Murine Model

BACKGROUND

Various adhesion molecules including intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) have been shown to play a role in inflammation as well as contribute to tumor progression and prognosis. We hypothesized that gastroduodenal reflux upregulates ICAM-1 and VCAM-1 expression in the distal esophagus, serving as possible early markers of pathologic esophageal disease.

METHODS

Normal human esophageal epithelial cells (HET1A), Barrett's cells (CPB), and esophageal adenocarcinoma cells (FLO1 and OE33) were treated with deoxycholic acid (DCA) at increasing concentrations for 24 hours. Adhesion molecule expression was assessed using immunoblotting. A surgical mouse reflux model was generated by performing a side-to-side anastomosis between the gastroesophageal junction and the first portion of the duodenum (duodeno-gastroesophageal anastomosis, DGEA). Esophageal sections were evaluated using H&E staining, immunohistochemistry, and immunofluorescence.

RESULTS

DCA induced a significant increase in ICAM-1 and VCAM-1 expression in HET1A, CPB, FLO1, and OE33 cells. Animals undergoing DGEA demonstrated a significant increase in mucosal hyperplasia (p<0.0001) and cellular proliferation (p<0.0001) compared to control animals. Immunofluorescence and western blot analysis of the lower esophagus demonstrated significant upregulation of ICAM-1 (p=0.005), with no change in VCAM-1 expression (p=0.82).

CONCLUSIONS

Our results reveal that ICAM-1 and VCAM-1 are upregulated in response to in vitro reflux treatment of normal esophageal epithelial cells. However, upon investigation using a mouse reflux model, ICAM-1 is noticeably upregulated without a concomitant increase in VCAM-1. These findings identify ICAM-1, but not VCAM-1, as a potential player in early esophageal disease developing from chronic reflux exposure.

Secretory Phospholipase A2 IIa Mediates Expression of Growth Factor Receptors in Esophageal Adenocarcinoma

BACKGROUND

Receptor tyrosine kinases of the epidermal growth factor receptor (EGFR) family such as human epidermal receptor-2 (HER2) are involved in the development and progression of esophageal adenocarcinoma (EAC). Prior studies have demonstrated that group IIa secretory phospholipase A2 (sPLA2 IIa) can function as a ligand for the EGFR family of receptors and lead to an increase in receptor signaling.

AIMS

We hypothesized that sPLA2 IIa inhibition downregulates the expression of EGFR and HER-2 in EAC and through this mechanism decreases proliferation in EAC.

METHODS

Normal human esophageal epithelium, Barrett's esophagus (BE), and EAC tissue samples were assayed for baseline expression of EGFR, HER-2, and sPLA2 IIa. sPLA2 IIa was attenuated via inhibitor or lentiviral knockdown in esophageal cell lines, and cells were assayed for EGFR and HER2 expression as well as proliferation. FLO1 EAC cells were injected into the flank of nude mice. After randomization, mice received daily group IIA sPLA2 inhibitor or a control solution, and tumor volume was measured with calipers.

RESULTS

sPLA2 IIa, EGFR, and HER2 expression increased across the spectrum of normal esophageal epithelium to EAC. sPLA2 IIa inhibition and knockdown decreased the expression of HER-2 and EGFR and proliferation. Mice treated with sPLA2 IIa inhibitor had smaller tumors than controls.

CONCLUSIONS

sPLA2 IIa inhibition decreases EGFR and HER2 expression and lowers proliferation of human EAC. The discovery of sPLA2 IIa inhibition's ability to attenuate growth factor receptor signaling underscores the exciting potential of sPLA2 IIa inhibitors as therapeutics in the treatment of EAC.

Secretory Phospholipase A2 Inhibition Attenuates Adhesive Properties of Esophageal Barrett's Cells

BACKGROUND

Gastroesophageal reflux and Barrett's esophagus are significant risk factors for the development of esophageal adenocarcinoma. Group IIa secretory phospholipase A₂ (sPLA₂) catalyzes the production of various proinflammatory metabolites and plays a critical role in promoting reflux-induced inflammatory changes within the distal esophagus. We hypothesized that inhibition of sPLA₂ in human Barrett's cells would attenuate adhesion molecule expression via decreased activation of nuclear factor kappa B (NF-κB) and decrease cell proliferation, possibly mitigating the invasive potential of Barrett's esophagus.

MATERIALS AND METHODS

Normal human esophageal epithelial cells (HET1A) and Barrett's cells (CPB) were assayed for baseline sPLA₂ expression. CPB cells were treated with a specific inhibitor of sPLA₂ followed by tumor necrosis factor-α. Protein expression was evaluated using immunoblotting. Cell proliferation was assessed using an MTS cell proliferation assay kit. Statistical analysis was performed using the Student's t-test or analysis of variance, where appropriate.

RESULTS

CPB cells demonstrated higher baseline sPLA₂ expression than HET1A cells (P = 0.0005). Treatment with 30 μM sPLA₂ inhibitor significantly attenuated intercellular adhesion molecule-1 (P = 0.004) and vascular cell adhesion molecule-1 (P < 0.0001) expression as well as decreased NF-κB activation (P = 0.002). sPLA₂ inhibition decreased cell proliferation in a dose-dependent manner (P < 0.001 for 15, 20, and 30 μM doses).

CONCLUSIONS

sPLA₂ inhibition in human Barrett's cells decreases cellular adhesive properties and NF-κB activation as well as decreases cell proliferation, signifying downregulation of the inflammatory response and possible attenuation of cellular malignant potential. These findings identify sPLA₂ inhibition as a potential chemopreventive target for premalignant lesions of the esophagus.

Phospholipase A2 superfamily in cancer

Phospholipase A2 enzymes (PLA₂s) comprise a superfamily that is generally divided into six subfamilies known as cytosolic PLA₂s (cPLA₂s), calcium-independent PLA₂s (iPLA₂s), secreted PLA₂s (sPLA₂s), lysosomal PLA₂s, platelet-activating factor (PAF) acetylhydrolases, and adipose specific PLA₂s. Each subfamily consists of several isozymes that possess PLA₂ activity. The first three PLA₂ subfamilies play important roles in inflammation-related diseases and cancer. In this review, the roles of well-studied enzymes sPLA₂-IIA, cPLA₂α and iPLA₂β in carcinogenesis and cancer development were discussed. sPLA₂-IIA seems to play conflicting roles and can act as a tumor suppressor or a tumor promoter according to the cancer type, but cPLA₂α and iPLA₂β play protumorigenic role in most cancers. The mechanisms of PLA₂-mediated signal transduction and crosstalk between cancer cells and endothelial cells in the tumor microenvironment are described. Moreover, the mechanisms by which PLA₂s mediate lipid reprogramming and glycerophospholipid remodeling in cancer cells are illustrated. PLA₂s as the upstream regulators of the arachidonic acid cascade are generally high expressed and activated in various cancers. Therefore, they can be considered as potential pharmacological targets and biomarkers in cancer. The detailed information summarized in this review may aid in understanding the roles of PLA₂s in cancer, and provide new clues for the development of novel agents and strategies for tumor prevention and treatment.

Synergistic mechanisms of Sanghuang-Danshen phytochemicals on postprandial vascular dysfunction in healthy subjects: A network biology approach based on a clinical trial

With the increased risk of cardiovascular disease, the use of botanicals for vascular endothelial dysfunction has intensified. Here, we explored the synergistic mechanisms of Sanghuang–Danshen (SD) phytochemicals on the homeostatic protection against high-fat-induced vascular dysfunction in healthy subjects, using a network biology approach, based on a randomised crossover clinical trial. Seventeen differential markers identified in blood samples taken at 0, 3 and 6 h post-treatment, together with 12SD phytochemicals, were mapped onto the network platform, termed the context-oriented directed associations. The resulting vascular sub-networks illustrated associations between 10 phytochemicals with 32 targets implicated in 143 metabolic/signalling pathways. The three key events included adhesion molecule production (ellagic acid, fumaric acid and cryptotanshinone; VCAM-1, ICAM-1 and PLA2G2A; fatty acid metabolism), platelet activation (ellagic acid, protocatechuic acid and tanshinone IIA; VEGFA, APAF1 and ATF3; mTOR, p53, Rap1 and VEGF signalling pathways) and endothelial inflammation (all phytochemicals, except cryptotanshinone; 29 targets, including TP53 and CASP3; MAPK and PI3K-Akt signalling pathways, among others). Our collective findings demonstrate a potential of SD to protect unintended risks of vascular dysfunction in healthy subjects, providing a deeper understanding of the complicated synergistic mechanisms of signature phytochemicals in SD.

Overexpression of the phospholipase A2 group V gene in glioma tumors is associated with poor patient prognosis

Purpose: Gliomas are the most common primary malignant neoplasms of the central nervous system. Secreted phospholipases A2 (sPLA2s) are known to play an important role in various physiological processes, including bioactive lipid production, defense mechanisms, and cell signaling. However, their roles and clinical importance in gliomas remain unclear. Patients and methods: In this study, we analyzed the association between the expression of various sPLA2-encoding genes and the clinicopathology of gliomas, using the data of 1047 patients obtained from a public database. Immunohistochemical analysis of 82 glioma tissues was also carried out to assess the relationship between phospholipase A2 group V (PLA2G5) protein expression and the World Health Organization (WHO) glioma grades. Results: We found that high PLA2G5 gene expression was associated with unfavorable prognosis in both low-grade and high-grade gliomas. The immunohistochemistry of the 82 glioma tissues further confirmed that PLA2G5 protein expression was dependent on the WHO glioma grade. In addition, we found a correlation between PLA2G5 gene expression and both epithelial-mesenchymal transition and the isocitrate dehydrogenase 1 mutation status in these tumors. Conclusion: Our results indicate that PLA2G5 could be a potential biomarker for predicting poor prognosis in patients with gliomas.

The inhibitory effect of saPLIγ, a snake sourced PLA2 inhibitor on carrageenan-induced inflammation in mice

SaPLIγ is a natural phospholipase A₂ (PLA₂) inhibitor, isolated from Sinonatrix annularis, that has been demonstrated to protect against envenomation by other venomous snakes. As snake venom PLA₂s and mammalian secretory PLA₂s are similar, saPLIγ is thought to have potential to alleviate inflammatory reactions in which PLA₂s act as a key enzyme for arachidonic acid release. The aim of this study was to investigate the anti-inflammatory effects and mechanisms of action of saPLIγ in an animal model of carrageenan-induced acute inflammation. The results indicated that saPLIγ inhibited PLA₂ subtypes extensively, especially IIA-PLA₂, in a dose-dependent manner. Paw swelling in mice was reduced markedly by intraperitoneal saPLIγ 2.5 mg/kg, and the effect was significantly better than observed with dexamethasone at the same dose. Lower neutrophil infiltration and tissue edema was observed in the paws of saPLIγ-treated mice. Additionally, carrageenan-induced cyclooxygenase-2 (COX-2) and pro-inflammatory cytokines (TNFα and IL-1β) were also significantly down-regulated by saPLIγ in a dose-dependent manner. These results suggested that saPLIγ had effective anti-inflammatory effects in vivo, and these were produced by blocking mammalian IB, IIA, V and X sPLA2 subtypes.

sPLA2 -IIA Overexpression in Mice Epidermis Depletes Hair Follicle Stem Cells and Induces Differentiation Mediated Through Enhanced JNK/c-Jun Activation

Secretory phospholipase A2 Group-IIA (sPLA2 -IIA) catalyzes the hydrolysis of the sn-2 position of glycerophospholipids to yield fatty acids and lysophospholipids. sPLA2 -IIA is deregulated in various cancers; however, its role in hair follicle stem cell (HFSC) regulation is obscure. Here we report a transgenic mice overexpressing sPLA2 -IIA (K14-sPLA2 -IIA) showed depletion of HFSC pool. This was accompanied with increased differentiation, loss of ortho-parakeratotic organization and enlargement of sebaceous gland, infundibulum and junctional zone. The colony forming efficiency of keratinocytes was significantly reduced. Microarray profiling of HFSCs revealed enhanced level of epithelial mitogens and transcription factors, c-Jun and FosB that may be involved in proliferation and differentiation. Moreover, K14-sPLA2 -IIA keratinocytes showed enhanced activation of EGFR and JNK1/2 that led to c-Jun activation, which co-related with enhanced differentiation. Further, depletion of stem cells in bulge is associated with high levels of chromatin silencing mark, H3K27me3 and low levels of an activator mark, H3K9ac suggestive of alteration in gene expression contributing toward stem cells differentiation. Our results, first time uncovered that overexpression of sPLA2 -IIA lead to depletion of HFSCs and differentiation associated with altered histone modification. Thus involvement of sPLA2 -IIA in stem cells regulation and disease pathogenesis suggest its prospective clinical implications. Stem Cells 2016;34:2407-2417.

Knockdown of secretory phospholipase A2 IIa reduces lung cancer growth in vitro and in vivo

OBJECTIVE

Group IIa secretory phospholipase A2 (sPLA2 IIa) plays a role in the malignant potential of several epithelial cancers. Nuclear factor kappa B (NF-κB) regulates cancer cell growth and is modulated by phospholipase activity in many cancer cells. We hypothesized that knockdown of sPLA2 in lung cancer cells would reduce cell proliferation and NF-κB activity in vitro and attenuate tumor growth in vivo.

METHODS

Two human non-small cell lung cancer cell lines (A549 and H358) were transduced with short hairpin RNA targeting sPLA2 group IIa. Quantitative reverse transcriptase-polymerase chain reaction and immunoblotting confirmed knockdown of sPLA2 IIa messenger RNA and protein, respectively. Cell proliferation was evaluated by the 5-bromo-2'-deoxyuridine DNA labeling assay. NF-κB phosphorylation was assayed by western blot. 1 × 10(6) of A549 or A549 sPLA2 knockdown cells were injected into the left flanks of nude mice (aged 6 to 8 weeks). Tumors were followed for 23 days, then removed and stained with hematoxylin and eosin, stained with Ki-67, and analyzed for sPLA2 IIa messenger RNA expression.

RESULTS

sPLA2 knockdown reduced NF-κB phosphorylation and tumor growth in vivo. A549 wild-type tumors grew twice as fast as knockdown tumors. Ki-67 staining was more prominent throughout the wild-type tumors compared with knockdown tumors. Explanted knockdown tumors maintained lower sPLA2 levels compared with wild-type, confirmed by reverse transcriptase-polymerase chain reaction.

CONCLUSIONS

Knockdown of sPLA2 IIa suppresses lung cancer growth in part by attenuating NF-κB activity. These findings justify further investigation into the cellular mechanisms of sPLA2 in lung cancer and its potential role as a therapeutic target.

Group IIa secretory phospholipase expression correlates with group IIa secretory phospholipase inhibition-mediated cell death in K-ras mutant lung cancer cells

OBJECTIVE

There are currently no targeted therapies against lung tumors with oncogenic K-ras mutations that are found in 25% to -40% of lung cancers and are characterized by their resistance to epidermal growth factor receptor inhibitors. The isozyme group IIa secretory phospholipase A(2) (sPLA(2)IIa) is a potential biomarker and regulator of lung cancer cell invasion; however, the relationship between K-ras mutations and sPLA(2)IIa has yet to be investigated. We hypothesize that sPLA(2)IIa modulates lung cancer cell growth in K-ras mutant cells and that sPLA(2)IIa expression in human lung tumors is increased in K-ras mutant tumors.

METHODS

Baseline sPLA(2)IIa expression in K-ras mutant lung cancer cell lines (A549, SW1573, H358, H2009) was assessed. Cells were treated with a specific sPLA(2)IIa inhibitor and evaluated for apoptosis and cell viability. Nuclear factor kappa-b (NF-κB) and extracellular signal-regulated kinase 1/2 activity were detected by Western blot. Human tumor samples were evaluated for sPLA(2)IIa mRNA expression by quantitative reverse-transcription polymerase chain reaction.

RESULTS

Cytotoxicity of sPLA(2)IIa inhibition correlates with sPLA(2)IIa expression. Apoptosis in response to sPLA(2) inhibition parallels attenuation in NF-κB activity. In addition, sPLA(2)IIa expression in human tumors correlates with squamous cell pathology and increasing stage of K-ras mutant lung tumors.

CONCLUSIONS

Baseline sPLA(2)IIa expression predicts response to sPLA(2)IIa inhibition in some K-ras mutant lung cancer cells. This finding is independent of p53 mutation status. Furthermore, squamous tumors and advanced-stage K-ras mutant tumors express more sPLA(2)IIa. These data support a role for sPLA(2)IIa as a potential global therapeutic target in the treatment of lung cancer.

Lung cancer cell invasion and expression of intercellular adhesion molecule-1 (ICAM-1) are attenuated by secretory phospholipase A₂ inhibition

OBJECTIVE

Invasive lung tumors are associated with intercellular adhesion molecule-1 (ICAM-1) expression. Secretory phospholipase A(2) (sPLA(2)) enzymes produce inflammatory mediators that stimulate ICAM-1 expression, and upregulation of PLA(2) activity can enhance metastasis. We hypothesize a link between sPLA(2) activity, ICAM-1 expression, and tumor cell invasion. We propose that inhibition of sPLA(2) modulates ICAM-1 expression in cancer cells and attenuates their invasiveness.

METHODS

Human lung adenocarcinoma cells (A549) were treated with an ICAM-1 blocking antibody and assayed for invasion. Lung cancer cells (A549 and H358) were then treated with an sPLA(2) inhibitor and evaluated by immunoblotting for ICAM-1 expression. Next cells (A549) treated with sPLA(2) inhibitor were assayed for invasion. Finally, sPLA(2) messenger RNA and protein expression were evaluated by quantitative reverse-transcriptase polymerase chain reaction and immunofluorescence microscopy, respectively. Statistical analysis was performed by the Student t test or analysis of variance, as appropriate.

RESULTS

Antibody blockade of ICAM-1 decreased lung cancer cell invasion. sPLA(2) inhibition significantly reduced ICAM-1 expression and invasion. sPLA(2) inhibition also significantly decreased sPLA(2) mRNA expression and immunofluorescent staining of sPLA(2).

CONCLUSIONS

sPLA(2) plays a significant role in mediating the inflammatory signals that induce ICAM-1 expression in lung cancer cells. Inhibition of the enzyme can significantly decrease ICAM-1 expression and subsequent cancer cell invasion. This lays the groundwork for further investigation into the cellular mechanisms of sPLA(2) and its role in lung cancer.

Polymorphisms of ICAM-1 are associated with gastric cancer risk and prognosis

AIM: To investigate the association between single nucleotide polymorphisms (SNPs) in intercellular adhesion molecule-1 (ICAM-1) and the risk, biological behavior and prognosis of gastric cancer (GC) in Chinese population.

METHODS: The study group consisted of 332 GC patients and 380 healthy controls. Genotyping was performed using polymerase chain reaction and the results were confirmed by sequencing. The association of ICAM-1 K469E polymorphisms and the risk of GC were studied, and the correlation of ICAM-1 K469E polymorphisms with the clinicopathological parameters and prognosis of the patients with complete clinical and follow-up data was analyzed.

RESULTS: Carriers of AA genotype had a significantly increased risk of GC compared with carriers of AG and GG genotypes [odds ratios: 1.36; 95% confidence interval (CI): 1.01-1.84; P = 0.041]. GC patients with AA genotype were more prone to distant metastasis than those carrying AG and GG genotypes (18.9% vs 7.0%, respectively; P = 0.002). In addition, patients at stage IV had significantly more carriers of AA genotype than those of AG and GG genotype (27.4% vs 16.9%, respectively; P = 0.046). Follow-up study showed that the overall cumulative survival rate was 23.7% in AA genotype group and 42.9% in AG and GG genotypes group. In univariate analysis, AA genotype was correlated with the overall cumulative survival (P = 0.034). But in multivariate analysis, ICAM-1 polymorphism was not an independent prognostic factor for the overall survival (relative risk, 1.145; 95% CI: 0.851-1.540; P = 0.370).

CONCLUSION: Polymorphisms of ICAM-1 K469E can be a useful biomarker for identifying individuals with higher risk of GC, predicting disease progression, and guiding individualized treatment.

Statin therapy attenuates growth and malignant potential of human esophageal adenocarcinoma cells

OBJECTIVES

Esophageal adenocarcinoma is an aggressive malignancy generally diagnosed after metastatic spread and currently lacks effective medical therapy. Expression of intracellular adhesion molecule-1 (ICAM-1) is an adverse prognostic indicator in various human tumor cells and contributes significantly to their metastatic potential. Statin therapy reduces circulating ICAM-1 levels in patients with coronary heart disease and is associated with reduction in progression from Barrett esophagus to esophageal adenocarcinoma. We hypothesize that statin therapy may attenuate growth and malignant potential via ICAM-1 expression and nuclear factor-kappa beta activation in human esophageal adenocarcinoma cells.

METHODS

Verified human esophageal adenocarcinoma cells (FLO-1) were treated with simvastatin, atorvastatin, or pravastatin (10-, 30-, and 50-μmol/L concentrations). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide viability, 5-bromo-2'-deoxyuridine proliferation, or annexin V apoptosis assays were performed, or cells were stimulated with tumor necrosis factor-alpha and collected for immunoblotting and flow cytometry.

RESULTS

Simvastatin decreased cell viability and proliferation while increasing apoptosis in a dose-dependent manner (P < .05). Simvastatin attenuated total cellular and cell-surface ICAM-1 expression as well as nuclear factor-kappa beta activation (P < .05). Atorvastatin had mild effects and pravastatin had essentially no effect on growth and metastatic potential of these cells.

CONCLUSIONS

We demonstrate that treatment of human esophageal adenocarcinoma cells with simvastatin attenuates growth, by decreasing cell viability, decreasing cell proliferation, and increasing apoptosis, and attenuates metastatic potential, by decreasing expression of key metastatic markers. These findings identify simvastatin as a potential therapeutic and chemopreventive modality to thwart the progression of esophageal adenocarcinoma.