Leukotriene D(4) activates MAPK through a Ras-independent but PKCepsilon-dependent pathway in intestinal epithelial cells

Prostaglandin E2 attenuates lung fibroblast differentiation via inactivation of yes-associated protein signaling

Prostaglandin E2 (PGE2 ) has been implicated in counteracting fibroblast differentiation by TGFβ1 during pulmonary fibrosis. However, the precise mechanism is not well understood. We show here that PGE2 via EP2 R and EP4 R inhibits the expression of mechanosensory molecules Lysyl Oxidase Like 2 (LOXL2), myocardin-related transcription factor A (MRTF-A), ECM proteins, plasminogen activation inhibitor 1 (PAI-1), fibronectin (FN), α-smooth muscle actin (α-SMA), and redox sensor (nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4)) required for TGFβ1-mediated fibroblast differentiation. We further demonstrate that PGE2 inhibits fibrotic signaling via Yes-associated protein (YAP) but does so independently from its actions on SMAD phosphorylation and conserved cylindromatosis (CYLD; deubiquitinase) expression. Mechanistically, PGE2 phosphorylates/inactivates YAP downstream of EP2 R/Gαs and restrains its translocation to the nucleus, thus inhibiting its interaction with TEA domain family members (TEADs) and transcription of fibrotic genes. Importantly, pharmacological or siRNA-mediated inhibition of YAP significantly downregulates TGFβ1-mediated fibrotic gene expression and myofibroblast formation. Notably, YAP expression is upregulated in the lungs of D. farinae-treated wild type (WT) mice relative to saline-treated WT mice. Our results unravel a unique role for PGE2 -YAP interactions in fibroblast differentiation, and that PGE2 /YAP inhibition can be used as a novel therapeutic target in the treatment of pathological conditions associated with myofibroblasts like asthma.

1,4-dihydroxy quininib modulates the secretome of uveal melanoma tumour explants and a marker of oxidative phosphorylation in a metastatic xenograft model

Uveal melanoma (UM) is an intraocular cancer with propensity for liver metastases. The median overall survival (OS) for metastatic UM (MUM) is 1.07 years, with a reported range of 0.84-1.34. In primary UM, high cysteinyl leukotriene receptor 1 (CysLT₁) expression associates with poor outcomes. CysLT₁ antagonists, quininib and 1,4-dihydroxy quininib, alter cancer hallmarks of primary and metastatic UM cell lines in vitro. Here, the clinical relevance of CysLT receptors and therapeutic potential of quininib analogs is elaborated in UM using preclinical in vivo orthotopic xenograft models and ex vivo patient samples. Immunohistochemical staining of an independent cohort (n = 64) of primary UM patients confirmed high CysLT₁ expression significantly associates with death from metastatic disease (p = 0.02; HR 2.28; 95% CI 1.08-4.78), solidifying the disease relevance of CysLT₁ in UM. In primary UM samples (n = 11) cultured as ex vivo explants, 1,4-dihydroxy quininib significantly alters the secretion of IL-13, IL-2, and TNF-α. In an orthotopic, cell line-derived xenograft model of MUM, 1,4-dihydroxy quininib administered intraperitoneally at 25 mg/kg significantly decreases ATP5B expression (p = 0.03), a marker of oxidative phosphorylation. In UM, high ATP5F1B is a poor prognostic indicator, whereas low ATP5F1B, in combination with disomy 3, correlates with an absence of metastatic disease in the TCGA-UM dataset. These preclinical data highlight the diagnostic potential of CysLT₁ and ATP5F1B in UM, and the therapeutic potential of 1,4-dihydroxy quininib with ATP5F1B as a companion diagnostic to treat MUM.

Transcriptome-metabolome-wide association study (TMWAS) in rats revealed a potential carcinogenic effect of DEHP in thyroid associated with eicosanoids

The incidence of thyroid cancer (TC) has increased considerably in the last few decades. Environmental factors, including plasticizers, are recognized as potential risks leading to thyroid cancer in humans. In this study, we used a transcriptome-metabolome-wide association study to find the unidentified carcinogenic mechanism of di-2-ethylhexyl phthalate (DEHP) in thyroid and biomarkers for non-invasive diagnosis. Rats were treated with different doses of DEHP (0, 0.3, 3, 30, 150 mg DEHP/kg bw/day) for 13 weeks. Then, the thyroids were processed for Ki67 staining and RNA-seq. Also, 17-h urine samples were collected for high-resolution metabolomics analysis. After a high dose of DEHP exposure, the terminal body weights and the thyroid and parathyroid glands weights were not altered. However, the liver weights and numbers of Ki67-positive cells were increased. Further, multivariate statistical analysis revealed that metabolic shifts were considerably altered above 30 mg DEHP/kg bw/day. In RNA-seq analysis, some cancer-related genes were altered, including 18 upregulated and 9 downregulated transcripts. These cancer transcripts and whole metabolome data were integrated to uncover thyroid cancer-related metabolic pathways, which revealed that cancer-related transcripts had a network structure linked to eicosanoids such as leukotriene D4 and prostaglandin. In brief, our study demonstrated that DEHP can induce thyroid hyperplasia through the eicosanoid-associated pathway, providing further insight into the mechanism of DEHP-associated thyroid cancer.

Protein Kinase C α and β compensate for each other to promote stem cell factor-mediated KIT phosphorylation, mast cell viability and proliferation

Mast cells (MCs) develop from hematopoietic progenitors and differentiate into mature MCs that reside within connective or mucosal tissues. Though the number of MCs in tissues usually remains constant, inflammation and asthma disturb this homeostasis, leading to proliferation of MCs. Understanding the signaling events behind this proliferative response could lead to the development of novel strategies for better management of allergic diseases. MC survival, proliferation, differentiation, and migration are all maintained by a MC growth factor, stem cell factor (SCF) via its receptor, KIT. Here, we explored how protein kinase C (PKC) redundancy influences MC proliferation in bone marrow‐derived MC (BMMC). We found that SCF activates PKCα and PKCβ isoforms, which in turn modulates KIT phosphorylation and internalization. Further, PKCα and PKCβ activate p38 mitogen activated protein kinase (MAPK), and this axis subsequently regulates SCF‐induced MC cell proliferation. To ascertain the individual roles of PKCα and PKCβ, we knocked down either PKCα or PKCβ or both via short hairpin RNA (shRNA) and analyzed KIT phosphorylation, p38 MAPK phosphorylation, and MC viability and proliferation. To our surprise, downregulation of neither PKCα nor PKCβ affected MC viability and proliferation. In contrast, blocking both PKCα and PKCβ significantly attenuated SCF‐induced cell viability and proliferation, suggesting that PKCα and PKCβ compensate for each other downstream of SCF signaling to enhance MC viability and proliferation. Our results not only suggest that PKC classical isoforms are novel therapeutic targets for SCF/MC‐mediated inflammatory and allergic diseases, but they also emphasize the importance of inhibiting both PKCα and β isoforms simultaneously to prevent MC proliferation.

Two untargeted metabolomics reveals yogurt-associated metabolic alterations in women with multiple metabolic disorders from a randomized controlled study

The beneficial role of yogurt on metabolic profile has been widely reported. Yet, few studies have intended to describe the integrated metabolic alterations in response to yogurt. Yogurt and milk (220 g/d) were given to 48 and 44 obese women with metabolic syndrome and nonalcoholic fatty liver disease for 24 weeks in a randomized controlled trial (registered at http://www.chictr.org.cn as ChiCTR-IPR-15006801). Fasting serum samples were collected before and after intervention for global, untargeted metabolomics based on ¹H nuclear magnetic resonance (NMR) and ultra-high-performance liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry (UPLC-Q-TOF-MS) (in positive and negative ion modes). Multivariable statistical analysis and pathway analysis were conducted. In both ¹H NMR and UPLC-Q-TOF-MS metabolomics, no clustering was observed between the two groups at baseline. While, a clear clustering was shown after intervention, and the yogurt group had significantly different metabolic status from the milk. The metabolites that contributed mostly to class separation were identified, and involved into pathway analysis. Pathways on amino acids metabolism, fatty acid oxidation, cholesterol catabolism and choline metabolism significantly changed after yogurt intervention. The study revealed the integrated metabolic alterations in response to yogurt via two metabolomics approaches, suggesting the potential mechanisms of yogurt against metabolic disorders. TRIAL REGISTRATION: Chinese Clinical Trial Registry, ChiCTR-IPR-15006801. Registered 20 July 2015, http://www.chictr.org.cn/ ChiCTR-IPR-15006801. SIGNIFICANCE: Both review from prospective studies and our randomized clinical trial showed the protective role of yogurt against multiple metabolic disorders. However, they were focus on targeted glucose, lipid, and other metabolic indicators, which were only part of human metabolism, failing to show an integrated metabolic feature on yogurt. Therefore, two global, untargeted metabolomics were applied in our current randomized clinical trial, trying to uncover the significant metabolic alterations characterizing the effects of yogurt on obese women with multiple metabolic disorders, and to explore the potential biological mechanisms of yogurt. The finding will shed light on a more comprehensive picture of how yogurt affects host metabolism, and provide theoretical foundation for dietary prevention of chronic diseases.

Cysteinyl Leukotriene Pathway and Cancer

Cancer remains a leading cause of death worldwide, despite many advances being made in recent decades. Changes in the tumor microenvironment, including dysregulated immunity, may contribute to carcinogenesis and cancer progression. The cysteinyl leukotriene (CysLT) pathway is involved in several signal pathways, having various functions in different tissues. We summarized major findings of studies about the roles of the CysLT pathway in cancer. Many in vitro studies suggested the roles of CysLTs in cell survival/proliferation via CysLT₁ receptor (CysLT₁R). CysLT₁R antagonism decreased cell vitality and induced cell death in several types of cancer cells, such as colorectal, urological, breast, lung and neurological malignancies. CysLTs were also associated with multidrug resistance of cancer, and CysLT₁R antagonism might reverse chemoresistance. Some animal studies demonstrated the beneficial effects of CysLT₁R antagonist in inhibiting tumorigenesis and progression of some cancer types, particularly colorectal cancer and lung cancer. The expression of CysLT₁R was shown in various cancer tissues, particularly colorectal cancer and urological malignancies, and higher expression was associated with a poorer prognosis. The chemo-preventive effects of CysLT₁R antagonists were demonstrated in two large retrospective cohort studies. In summary, the roles of the CysLT pathway in cancer have been delineated, whereas further studies are still warranted.

Anti-Allergic Drug Suppressed Pancreatic Carcinogenesis via Down-Regulation of Cellular Proliferation

Pancreatic cancer is a fatal disease, and thus its chemoprevention is an important issue. Based on the recent report that patients with allergic diseases have a low risk for pancreatic cancer, we examined the potential chemopreventive effect of anti-allergic agents using a hamster pancreatic carcinogenesis model. Among the three anti-allergic drugs administered, montelukast showed a tendency to suppress the incidence of pancreatic cancer. Further animal study revealed a significantly decreased incidence of pancreatic cancer in the high-dose montelukast group compared with controls. The development of the pancreatic intraepithelial neoplasia lesions was also significantly suppressed. The Ki-67 labeling index was significantly lower in pancreatic carcinomas in the high-dose montelukast group than in controls. In vitro experiments revealed that montelukast suppressed proliferation of pancreatic cancer cells in a dose-dependent manner with decreased expression of phospho-ERK1/2. Montelukast induced G1 phase arrest. Conversely, leukotriene D₄ (LTD₄), an agonist of CYSLTR1, increased cellular proliferation of pancreatic cancer cells with an accumulation of phospho-ERK1/2. In our cohort, pancreatic ductal adenocarcinoma patients with high CYSLTR1 expression showed a significantly unfavorable clinical outcome compared with those with low expression. Our results indicate that montelukast exerts a chemopreventive effect on pancreatic cancer via the LTD₄–CYSLTR1 axis and has potential for treatment of pancreatic carcinogenesis.

Emerging role of cysteinyl LTs in cancer

Cysteinyl leukotrienes (CysLTs) are inflammatory lipid mediators that play a central role in the pathophysiology of several inflammatory diseases. Recently, there has been an increased interest in determining how these lipid mediators orchestrate tumour development and metastasis through promoting a pro-tumour micro-environment. Up-regulation of CysLTs receptors and CysLTs production is found in a number of cancers and has been associated with increased tumorigenesis. Understanding the molecular mechanisms underlying the role of CysLTs and their receptors in cancer progression will help investigate the potential of targeting CysLTs signalling for anti-cancer therapy. This review gives an overview of the biological effects of CysLTs and their receptors, along with current knowledge of their regulation and expression. It also provides a recent update on the molecular mechanisms that have been postulated to explain their role in tumorigenesis and on the potential of anti-CysLTs in the treatment of cancer.

Transient Receptor Potential Vanilloid channel regulates fibroblast differentiation and airway remodeling by modulating redox signals through NADPH Oxidase 4

Asthma is characterized by pathological airway remodeling resulting from persistent myofibroblast activation. Although transforming growth factor beta 1 (TGFβ1), mechanical signals, and reactive oxygen species (ROS) are implicated in fibroblast differentiation, their integration is still elusive. We identified that Transient Receptor Potential Vanilloid 4 (TRPV4), a mechanosensitive ion channel mediates lung fibroblast (LF) differentiation and D. farinae-induced airway remodeling via a novel TRPV4-NADPH Oxidase 4 (NOX4) interaction. NOX4-mediated ROS production is essential for TGFβ1-induced LF differentiation via myocardin-related transcription factor-A (MRTF-A) and plasminogen activator inhibitor 1 (PAI-1). Importantly, TRPV4 inhibition prevented TGFβ1-induced NOX4 expression and ROS production. Both TRPV4 and NOX4 are activated by phosphatidylinositol 3-kinase (PI3K) downstream of TGFβ1, and signals from both TRPV4 and Rac are necessary for NOX4 upregulation. Notably, NOX4 expression is higher in fibroblasts derived from asthmatic patients (disease human LF; DHLF) in comparison to non-asthmatics (normal human LF; NHLF). Further, NOX4 expression is up-regulated in the lungs of D.farinae-treated wild type mice (WT) relative to saline-treated WT, which was attenuated in TRPV4 knockout (KO) mice. Our findings suggest that TRPV4 integrates TGFβ1 and ROS signaling through NOX4 and, TRPV4-NOX4 interaction is amenable to target lung remodeling during asthma.

Eicosanoids and HB-EGF/EGFR in cancer

Eicosanoids are bioactive lipids that play crucial roles in various pathophysiological conditions, including inflammation and cancer. They include both the COX-derived prostaglandins and the LOX-derived leukotrienes. Furthermore, the epidermal growth factor receptor (EGFR) pathways family of receptor tyrosine kinases also are known to play a central role in the tumorigenesis. Various antitumor modalities have been approved cancer treatments that target therapeutically the COX-2 and EGFR pathways; these include selective COX-2 inhibitors and EGFR monoclonal antibodies. Research has shown that the COX-2 and epidermal growth factor receptor pathways actively interact with each other in order to orchestrate carcinogenesis. This has been used to justify a targeted combinatorial approach aimed at these two pathways. Although combined therapies have been found to have a greater antitumor effect than the administration of single agent, this does not exempt them from the possible fatal cardiac effects that are associated with COX-2 inhibition. In this review, we delineate the contribution of HB-EGF, an important EGFR ligand, to the cardiac dysfunction related to decreased shedding of HB-EGF after COX-2/PGE2 inhibition. A better understanding of the molecular mechanisms underlying these cardiac side effects will make possible more effective regimens that use the dual-targeting approach.

Lipid mediator Leukotriene D4-induces airway epithelial cells proliferation through EGFR/ERK1/2 pathway

BACKGROUND

Cysteinyl leukotrienes (CysLTs), the potent lipid inflammatory mediators, are elevated in many pathological conditions and implicated in various inflammatory diseases including asthma, however their role in airway epithelial cells modulation is not clearly understood. We have investigated the effects of a CysLT, Leukotriene D₄ (LTD₄) on human airway epithelial cells, and assessed its role and mode of action in these cells.

METHODOLOGY

Human small airway epithelial cells (SAECs) and A549 cells were incubated with different concentrations of LTD₄ for different time intervals. Subsequently trypan blue dye exclusion assay, MTT assay, Western blotting, RT-PCR and immunofluorescence experiments were performed to examine the effects of LTD₄ on proliferation and related molecular changes in the airway epithelial cells.

RESULTS

The treatment of human airway epithelial cells with LTD₄ resulted in a significant increase in cell proliferation and modulation in the expression of receptors, CysLT₁R and CysLT₂R in SAECs as well as A549 cells. In both types of cells, LTD₄ increased the expression levels of PCNA and c-myc, and trans-activated EGF receptor and increased the activation of ERK1/2. When treated along with epidermal growth factor (EGF), LTD₄ showed a marginal additive effect in ERK1/2 and EGFR phosphorylation compared to LTD₄ alone in both types of airway epithelial cells.

CONCLUSION

In conclusion, these results suggest that sustained presence of lipid inflammatory mediator LTD₄ could induce human airway epithelial cell proliferation through ERK1/2 phosphorylation, either directly via CysLT₁ receptor or by transactivating EGFR.

Montelukast Induces Apoptosis-Inducing Factor-Mediated Cell Death of Lung Cancer Cells

Developing novel chemo-prevention techniques and advancing treatment are key elements to beating lung cancer, the most common cause of cancer mortality worldwide. Our previous cohort study showed that cysteinyl leukotriene receptor antagonists, mainly montelukast, decreased the lung cancer risk in asthma patients. In the current study, we conducted in vivo and in vitro experiments to demonstrate the inhibiting effect of montelukast on lung cancer and to investigate the underlying mechanisms. Using Lewis lung carcinoma-bearing mice, we showed that feeding montelukast significantly delayed the tumor growth in mice (p < 0.0001). Montelukast inhibited cell proliferation and colony formation and induced the cell death of lung cancer cells. Further investigation showed the down-regulation of B-cell lymphoma 2 (Bcl-2), up-regulation of Bcl-2 homologous antagonist/killer (Bak), and nuclear translocation of apoptosis-inducing factor (AIF) in montelukast-treated lung cancer cells. Montelukast also markedly decreased the phosphorylation of several proteins, such as with no lysine 1 (WNK1), protein kinase B (Akt), extracellular signal-regulated kinase 1/2 (Erk1/2), MAPK/Erk kinase (MEK), and proline-rich Akt substrate of 40-kDa (PRAS40), which might contribute to cell death. In conclusion, montelukast induced lung cancer cell death via the nuclear translocation of AIF. This study confirmed the chemo-preventive effect of montelukast shown in our previous cohort study. The utility of montelukast in cancer prevention and treatment thus deserves further studies.

Mechanosensitive transient receptor potential vanilloid 4 regulates Dermatophagoides farinae-induced airway remodeling via 2 distinct pathways modulating matrix synthesis and degradation

Contributions of mechanical signals to airway remodeling during asthma are poorly understood. Transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel, has been implicated in cardiac and pulmonary fibrosis; however, its role in asthma remains elusive. Employing a Dermatophagoides farinae-induced asthma model, we report here that TRPV4-knockout mice were protected from D. farinae-induced airway remodeling. Furthermore, lung fibroblasts that were isolated from TRPV4-knockout mice showed diminished differentiation potential compared with wild-type mice. Fibroblasts from asthmatic lung exhibited increased TRPV4 activity and enhanced differentiation potential compared with normal human lung fibroblasts. Of interest, TGF-β1 treatment enhanced TRPV4 activation in a PI3K-dependent manner in normal human lung fibroblasts in vitro Mechanistically, TRPV4 modulated matrix remodeling in the lung via 2 distinct but dependent pathways: one enhances matrix deposition by fibrotic gene activation, whereas the other slows down matrix degradation by increased plasminogen activator inhibitor 1. Of importance, both pathways are regulated by Rho/myocardin-related transcription factor-A and contribute to fibroblast differentiation and matrix remodeling in the lung. Thus, our results support a unique role for TRPV4 in D. farinae-induced airway remodeling and warrant further studies in humans for it to be used as a novel therapeutic target in the treatment of asthma.-Gombedza, F., Kondeti, V., Al-Azzam, N., Koppes, S., Duah, E., Patil, P., Hexter, M., Phillips, D., Thodeti, C. K., Paruchuri, S. Mechanosensitive transient receptor potential vanilloid 4 regulates Dermatophagoides farinae-induced airway remodeling via 2 distinct pathways modulating matrix synthesis and degradation.

Targeting arachidonic acid pathway by natural products for cancer prevention and therapy

Arachidonic acid (AA) pathway, a metabolic process, plays a key role in carcinogenesis. Hence, AA pathway metabolic enzymes phospholipase A₂s (PLA₂s), cyclooxygenases (COXs) and lipoxygenases (LOXs) and their metabolic products, such as prostaglandins and leukotrienes, have been considered novel preventive and therapeutic targets in cancer. Bioactive natural products are a good source for development of novel cancer preventive and therapeutic drugs, which have been widely used in clinical practice due to their safety profiles. AA pathway inhibitory natural products have been developed as chemopreventive and therapeutic agents against several cancers. Curcumin, resveratrol, apigenin, anthocyans, berberine, ellagic acid, eugenol, fisetin, ursolic acid, [6]-gingerol, guggulsteone, lycopene and genistein are well known cancer chemopreventive agents which act by targeting multiple pathways, including COX-2. Nordihydroguaiaretic acid and baicalein can be chemopreventive molecules against various cancers by inhibiting LOXs. Several PLA₂s inhibitory natural products have been identified with chemopreventive and therapeutic potentials against various cancers. In this review, we critically discuss the possible utility of natural products as preventive and therapeutic agents against various oncologic diseases, including prostate, pancreatic, lung, skin, gastric, oral, blood, head and neck, colorectal, liver, cervical and breast cancers, by targeting AA pathway. Further, the current status of clinical studies evaluating AA pathway inhibitory natural products in cancer is reviewed. In addition, various emerging issues, including bioavailability, toxicity and explorability of combination therapy, for the development of AA pathway inhibitory natural products as chemopreventive and therapeutic agents against human malignancy are also discussed.

Evaluation of Cysteinyl Leukotriene Signaling as a Therapeutic Target for Colorectal Cancer

Colorectal cancer is the third most common cancer worldwide and is associated with significant morbidity and mortality. Current pharmacotherapy options include cytotoxic chemotherapy, anti-VEGF, and anti-EGFR targeting drugs, but these are limited by toxic side effects, limited responses and ultimately resistance. Cysteinyl leukotriene (CysLT) signaling regulates intestinal homeostasis with mounting evidence suggesting that CysLT signaling also plays a role in the pathogenesis of colorectal cancer. Therefore, CysLT signaling represents a novel target for this malignancy. This review evaluates reported links between CysLT signaling and established hallmarks of cancer in addition to its pharmacological potential as a new therapeutic target.

Cellular signalling of cysteinyl leukotriene type 1 receptor variants CysLT₁-G300S and CysLT₁-I206S

Cysteinyl-leukotrienes are pro-inflammatory lipid mediators, involved in allergic asthma, that bind the G-protein-coupled receptors CysLT1, CysLT2 and GPR99. A polymorphism in one of these receptors, CysLT1-G300S was strongly associated with atopy, whereas the CysLT1-I206S polymorphism was not. In the present work, our aim was to characterize these two variants by studying their cellular signalling. Cell surface expression of mutant receptors in transfected HEK-293 cells was comparable to that of the wild-type receptor. Compared to CysLT1-WT, production of inositol phosphates as well as IL-8 and IL-13 promoter transactivation in response to either LTD4 or LTC4 was significantly increased in CysLT1-G300S-transfected cells. Moreover, LTD4-induced phosphorylation of the signalling effector Erk, but not p38, p65 or c-Jun was higher in CysLT1-G300S-transfected cells. On the other hand, the variant CysLT1-I206S did not show a significant difference in its signal transduction compared to the wild-type receptor. Taken together, our results indicate that the variant CysLT1-G300S can induce a greater signal than the CysLT1-WT receptor, a feature that may be relevant to its association with atopy.

Leukotriene D4 and prostaglandin E2 signals synergize and potentiate vascular inflammation in a mast cell-dependent manner through cysteinyl leukotriene receptor 1 and E-prostanoid receptor 3

BACKGROUND

Although arachidonic acid metabolites, cysteinyl leukotrienes (cys-LTs; leukotriene [LT] C4, LTD4, and LTE4), and prostaglandin (PG) E2 are generated at the site of inflammation, it is not known whether crosstalk exists between these 2 classes of inflammatory mediators.

OBJECTIVE

We sought to determine the role of LTD4-PGE2 crosstalk in inducing vascular inflammation in vivo, identify effector cells, and ascertain specific receptors and pathways involved in vitro.

METHODS

Vascular (ear) inflammation was assessed by injecting agonists into mouse ears, followed by measuring ear thickness and histology, calcium influx with Fura-2, phosphorylation and expression of signaling molecules by means of immunoblotting, PGD2 and macrophage inflammatory protein 1β generation by using ELISA, and expression of transcripts by using RT-PCR. Candidate receptors and signaling molecules were identified by using antagonists and inhibitors and confirmed by using small interfering RNA.

RESULTS

LTD4 plus PGE2 potentiated vascular permeability and edema, gearing the system toward proinflammation in wild-type mice but not in Kit(W-sh) mice. Furthermore, LTD4 plus PGE2, through cysteinyl leukotriene receptor 1 (CysLT1R) and E-prostanoid receptor (EP) 3, enhanced extracellular signal-regulated kinase (Erk) and c-fos phosphorylation, inflammatory gene expression, macrophage inflammatory protein 1β secretion, COX-2 upregulation, and PGD2 generation in mast cells. Additionally, we uncovered that this synergism is mediated through Gi, protein kinase G, and Erk signaling. LTD4 plus PGE2-potentiated effects are partially sensitive to CysLT1R or EP3 antagonists but completely abolished by simultaneous treatment both in vitro and in vivo.

CONCLUSIONS

Our results unravel a unique LTD4-PGE2 interaction affecting mast cells through CysLT1R and EP3 involving Gi, protein kinase G, and Erk and contributing to vascular inflammation in vivo. Furthermore, current results also suggest an advantage of targeting both CysLT1R and EP3 in attenuating inflammation.

Modulation of mast cell proliferative and inflammatory responses by leukotriene d4 and stem cell factor signaling interactions

Mast cells (MCs) are important effector cells in asthma and pulmonary inflammation, and their proliferation and maturation is maintained by stem cell factor (SCF) via its receptor, c-Kit. Cysteinyl leukotrienes (cys-LTs) are potent inflammatory mediators that signal through CysLT1 R and CysLT2 R located on the MC surface, and they enhance MC inflammatory responses. However, it is not known if SCF and cys-LTs cross-talk and influence MC hyperplasia and activation in inflammation. Here, we report the concerted effort of the growth factor SCF and the inflammatory mediator LTD4 in MC activation. Stimulation of MCs by LTD4 in the presence of SCF enhances c-Kit-mediated proliferative responses. Similarly, SCF synergistically enhances LTD4 -induced calcium, c-fos expression and phosphorylation, as well as MIP1β generation in MCs. These findings suggest that integration of SCF and LTD4 signals may contribute to MC hyperplasia and hyper-reactivity during airway hyper-response and inflammation.

Protein kinase C-mediated phosphorylation of RKIP regulates inhibition of Na-alanine cotransport by leukotriene D(4) in intestinal epithelial cells

Leukotriene D4 (LTD4) is an important immune inflammatory mediator that is known to be elevated in the mucosa of chronically inflamed intestine and alter nutrient absorption. LTD4 inhibits Na-alanine cotransport in intestinal epithelial cells by decreasing the affinity of the cotransporter ASCT1. LTD4 is known to increase intracellular Ca(++) and cAMP concentrations. However, the intracellular signaling mechanism of LTD4-mediated ASCT1 inhibition is unknown. In the present study, pretreatment with calcium chelator BAPTA-AM or inhibition of Ca(++)-dependent protein kinase C (PKC), specifically PKCα, resulted in the reversal of LTD4-mediated inhibition of ASCT1, revealing the involvement of the Ca(++)-activated PKC pathway. PKCα is known to phosphorylate Raf kinase inhibitor protein (RKIP), thus activating its downstream signaling pathway. Immunoblotting with anti-RKIP-Ser(153) antibody showed an increase in phosphorylation levels of RKIP in LTD4-treated cells. Downregulation of endogenous RKIP showed no decrease in ASCT1 activity by LTD4, thus confirming its involvement in ASCT1 regulation. Phosphorylation of RKIP by PKC is known to activate different signaling pathways, and in this study it was found to activate cAMP-activated protein kinase A (PKA) pathway. Although protein abundance of ASCT1 was not altered in any of the experimental conditions, there was an increase in the levels of phosphothreonine in ASCT1 protein, thus showing that phosphorylation changes were responsible for the altered affinity of ASCT1 by LTD4. In conclusion, LTD4 inhibits ASCT1 through PKC-mediated phosphorylation of RKIP, leading to the subsequent activation of PKA pathway, possibly through β2-andrenergic receptor activation.

Cysteinyl leukotrienes regulate endothelial cell inflammatory and proliferative signals through CysLT₂ and CysLT₁ receptors

Cysteinyl leukotrienes (cys-LTs), LTC₄, LTD₄, LTE₄ are potent inflammatory lipid mediators that act through two distinct G-protein-coupled receptors, CysLT₁R and CysLT₂R. Although cys-LTs are shown to induce vascular leakage and atherosclerosis, the molecular mechanism by which cys-LTs modulate endothelial function is not known. Here, we show that cys-LTs (LTC₄ and LTD₄) induce robust calcium influx in human umbilical vein endothelial cells (HUVECs) through CysLT₂R, but not CysLT₁R. Further, cys-LT treatment induced endothelial cell (EC) contraction leading to monolayer disruption via CysLT₂R/Rho kinase dependent pathway. Furthermore, stimulation with cys-LTs potentiated TNFα-induced VCAM-1 expression and leukocyte recruitment to ECs through CysLT₂R. In contrast, we found that both LTC₄ and LTD₄ stimulated EC proliferation through CysLT₁R. Taken together, these results suggest that cys-LTs induce endothelial inflammation and proliferation via CysLT₂R/Rho kinase and CysLT₁R/Erk dependent pathways, respectively, which play critical role in the etiology of cardiovascular diseases such as atherosclerosis and myocardial infarction.

The inflammatory mediator leukotriene D₄ induces subcellular β-catenin translocation and migration of colon cancer cells

The abnormal activation of the Wnt/β-catenin pathway frequently occurs in colorectal cancer. The nuclear translocation of β-catenin activates the transcription of target genes that promote cell proliferation, survival, and invasion. The pro-inflammatory mediator leukotriene D4 (LTD4) exerts its effects through the CysLT1 receptor. We previously reported an upregulation of CysLT1R in patients with colon cancer, suggesting the importance of leukotrienes in colon cancer. The aim of this study was to investigate the impact of LTD4 on Wnt/β-catenin signaling and its effects on proliferation and migration of colon cancer cells. LTD4 stimulation led to an increase in β-catenin expression, β-catenin nuclear translocation and the subsequent transcription of MYC and CCND1. Furthermore, LTD4 significantly reduced the expression of E-cadherin and β-catenin at the plasma membrane and increased the migration and proliferation of HCT116 colon cancer cells. The effects of LTD4 can be blocked by the inhibition of CysLT1R. Furthermore, LTD4 induced the inhibition of glycogen synthase kinase 3 (GSK)-3β activity, indicating a crosstalk between the G-protein-coupled receptor CysLT1 and the Wnt/β-catenin pathway. In conclusion, LTD4, which can be secreted from macrophages and leukocytes in the tumor microenvironment, induces β-catenin translocation and the activation of β-catenin target genes, resulting in the increased proliferation and migration of colon cancer cells.

Eicosanoid modulation by the short-chain fatty acid n-butyrate in human monocytes

n-Butyrate deriving from bacterial fermentation in the mammalian intestine is a key determinant in gastrointestinal homeostasis. We examined the effects of this short-chain fatty acid and Toll-like receptor 2 (TLR) and TLR4 engagement on inflammatory/immunity-associated genes, cyclo-oxygenases (COXs), prostaglandins (PGs) and leukotrienes (LTs) in human monocytes. Before RNA isolation, freshly isolated human monocytes were co-incubated for different time-points with 1 mm n-butyrate alone or in combination with bacterial stimuli. Based on a knowledge-driven approach, a signature of 180 immunity/inflammation-associated genes was picked and real-time PCR analysis was performed. Pathway analysis was carried out using a web-based database analysing program. Based on these gene expression studies the findings were evaluated at the protein/mediator level by Western blot analysis, FACS and ELISA. Following co-incubation with n-butyrate and lipopolysaccharide, key enzymes of the eicosanoid pathway, like PTGS2 (COX-2), TXS, ALOX5, LTA4H and LTC4S, were significantly up-regulated compared with stimulation with lipopolysaccharide alone. Furthermore, release of the lipid mediators PGE(2), 15d-PGJ(2), LTB(4) and thromboxane B(2) was increased by n-butyrate. Regarding signalling, n-butyrate had no additional effect on mitogen-activated protein kinase and interfered differently with early and late phases of nuclear factor-κB signalling. Our results suggest that among many other mediators of eicosanoid signalling n-butyrate massively induces PGE(2) production by increasing the expression of PTGS2 (COX-2) in monocytes following TLR4 and TLR2 activation and induces secretion of LTB(4) and thromboxane B(2). This underscores the role of n-butyrate as a crucial mediator of gut-specific immunity.

Differential regulation of cysteinyl leukotriene receptor signaling by protein kinase C in human mast cells

Cysteinyl leukotrienes (cys-LTs) are a group of lipid mediators that are potent bronchoconstrictors, powerful inducers of vascular leakage and potentiators of airway hyperresponsiveness. Cys-LTs play an essential role in asthma and are synthesized as well as activated in mast cells (MCs). Cys-LTs relay their effects mainly through two known GPCRs, CysLT₁R and CysLT₂R. Although protein kinase C (PKC) isoforms are implicated in the regulation of CysLT₁R function, neither the role of PKCs in cys-LT-dependent MC inflammatory signaling nor the involvement of specific isoforms in MC function are known. Here, we show that PKC inhibition augmented LTD₄ and LTE₄-induced calcium influx through CysLT₁R in MCs. In contrast, inhibition of PKCs suppressed c-fos expression as well MIP1β generation by cys-LTs. Interestingly, cys-LTs activated both PKCα and PKCε isoforms in MC. However, knockdown of PKCα augmented cys-LT mediated calcium flux, while knockdown of PKCε attenuated cys-LT induced c-fos expression and MIP1β generation. Taken together, these results demonstrate for the first time that cys-LT signaling downstream of CysLT₁R in MCs is differentially regulated by two distinct PKCs which modulate inflammatory signals that have significant pathobiologic implications in allergic reactions and asthma pathology.

The cysteinyl leukotriene 2 receptor contributes to all-trans retinoic acid-induced differentiation of colon cancer cells

Background

Cysteinyl leukotrienes (CysLTs) are potent pro-inflammatory mediators that are increased in samples from patients with inflammatory bowel diseases (IBDs). Individuals with IBDs have enhanced susceptibility to colon carcinogenesis. In colorectal cancer, the balance between the pro-mitogenic cysteinyl leukotriene 1 receptor (CysLT₁R) and the differentiation-promoting cysteinyl leukotriene 2 receptor (CysLT₂R) is lost. Further, our previous data indicate that patients with high CysLT₁R and low CysLT₂R expression have a poor prognosis. In this study, we examined whether the balance between CysLT₁R and CysLT₂R could be restored by treatment with the cancer chemopreventive agent all-trans retinoic acid (ATRA).

Methods

To determine the effect of ATRA on CysLT₂R promoter activation, mRNA level, and protein level, we performed luciferase gene reporter assays, real-time polymerase chain reactions, and Western blots in colon cancer cell lines under various conditions.

Results

ATRA treatment induces CysLT₂R mRNA and protein expression without affecting CysLT₁R levels. Experiments using siRNA and mutant cell lines indicate that the up-regulation is retinoic acid receptor (RAR) dependent. Interestingly, ATRA also up-regulates mRNA expression of leukotriene C₄ synthase, the enzyme responsible for the production of the ligand for CysLT₂R. Importantly, ATRA-induced differentiation of colorectal cancer cells as shown by increased expression of MUC-2 and production of alkaline phosphatase, both of which could be reduced by a CysLT₂R-specific inhibitor.

Conclusions

This study identifies a novel mechanism of action for ATRA in colorectal cancer cell differentiation and demonstrates that retinoids can have anti-tumorigenic effects through their action on the cysteinyl leukotriene pathway.

Iron modulates cell survival in a Ras- and MAPK-dependent manner in ovarian cells

Ovarian cancer is a leading cause of cancer death in women in the United States. While the majority of ovarian cancers are serous, some rarer subtypes (i.e. clear cell) are often associated with endometriosis, a benign gynecological disease. Iron is rich in the cyst fluid of endometriosis-associated ovarian cancers and induces persistent oxidative stress. The role of iron, an essential nutrient involved in multiple cellular functions, in normal ovarian cell survival and ovarian cancer remains unclear. Iron, presented as ferric ammonium citrate (FAC), dramatically inhibits cell survival in ovarian cancer cell types associated with Ras mutations, while it is without effect in immortalized normal ovarian surface epithelial (T80) and endometriotic epithelial cells (lacking Ras mutations). Interestingly, FAC induced changes in cytoplasmic vacuolation concurrently with increases in LC3-II levels (an autophagy marker); these changes occurred in an ATG5/ATG7-dependent, beclin-1/hVps34-independent, and Ras-independent manner. Knockdown of autophagy mediators in HEY ovarian cancer cells reversed FAC-induced LC3-II levels, but there was little effect on reversing the cell death response. Intriguingly, transmission electron microscopy of FAC-treated T80 cells demonstrated abundant lysosomes (confirmed using Lysotracker) rich in iron particles, which occurred in a Ras-independent manner. Although the mitogen-activated protein kinase (MAPK) inhibitor, U0126, reversed FAC-induced LC3-II/autophagic punctae and lysosomes in a Ras-independent manner, it was remarkable that U0126 reversed cell death in malignant ovarian cells associated with Ras mutations. Moreover, FAC increased heme oxygenase-1 expression in H-Ras-overexpressing T80 cells, which was associated with increased cell death when overexpressed in T80 cells. Disruption of intracellular iron levels, via chelation of intracellular iron (deferoxamine), was also detrimental to malignant ovarian cell survival; thus, homeostatic intracellular iron levels are essential for cell survival. Collectively, our results implicate iron in modulating cell death in a Ras- and MAPK-dependent manner in ovarian cancer cells.

Interactions between prostaglandins, leukotrienes and HIV-1: possible implications for the central nervous system

In HIV-1-infected individuals, there is often discordance between viremia in peripheral blood and viral load found in the central nervous system (CNS). Although the viral burden is often lower in the CNS compartment than in the plasma, neuroinflammation is present in most infected individuals, albeit attenuated by the current combined antiretroviral therapy. The HIV-1-associated neurological complications are thought to result not only from direct viral replication, but also from the subsequent neuroinflammatory processes. The eicosanoids - prostanoids and leukotrienes - are known as potent inflammatory lipid mediators. They are often present in neuroinflammatory diseases, notably HIV-1 infection. Their exact modulatory role in HIV-1 infection is, however, still poorly understood, especially in the CNS compartment. Nonetheless, a handful of studies have provided evidence as to how these lipid mediators can modulate HIV-1 infection. This review summarizes findings indicating how eicosanoids may influence the progression of neuroAIDS.

Polysaccharides from Capsosiphon fulvescens stimulate the growth of gastrointestinal cells

Capsosiphon fulvescens is a green alga that is abundant along the southwest coast of South Korea. Although it is consumed for its purported health-enhancing properties, particularly as a treatment for stomach disorders and hangovers, the health effects of dietary C. fulvescens remain unclear. Polysaccharides extracted from C. fulvescens (Cf-PS) are investigated for their effects on the proliferation of rat small intestinal epithelial IEC-6 cells. Cf-PS stimulated IEC-6 cell proliferation in a dose-dependent manner. Further, Cf-PS treatment induced the translocation of β-catenin, an effector of the Wnt signaling pathway, from the cytosol to the nucleus and increased the expression of cyclinD1 and c-myc. Cf-PS also induced ERK1/2 phosphorylation, which is activated by mitogenic and proliferative stimuli such as growth factors, but the phosphorylation of JNK and p38 was not enhanced. Therefore, this chapter discusses the effect of Cf-PS on the growth of gastrointestinal cells.

Integrating signals from the T-cell receptor and the interleukin-2 receptor

T cells orchestrate the adaptive immune response, making them targets for immunotherapy. Although immunosuppressive therapies prevent disease progression, they also leave patients susceptible to opportunistic infections. To identify novel drug targets, we established a logical model describing T-cell receptor (TCR) signaling. However, to have a model that is able to predict new therapeutic approaches, the current drug targets must be included. Therefore, as a next step we generated the interleukin-2 receptor (IL-2R) signaling network and developed a tool to merge logical models. For IL-2R signaling, we show that STAT activation is independent of both Src- and PI3-kinases, while ERK activation depends upon both kinases and additionally requires novel PKCs. In addition, our merged model correctly predicted TCR-induced STAT activation. The combined network also allows information transfer from one receptor to add detail to another, thereby predicting that LAT mediates JNK activation in IL-2R signaling. In summary, the merged model not only enables us to unravel potential cross-talk, but it also suggests new experimental designs and provides a critical step towards designing strategies to reprogram T cells.

PKCα mediates acetylcholine-induced activation of TRPV4-dependent calcium influx in endothelial cells

Transient receptor potential vanilloid channel 4 (TRPV4) is a polymodally activated nonselective cationic channel implicated in the regulation of vasodilation and hypertension. We and others have recently shown that cyclic stretch and shear stress activate TRPV4-mediated calcium influx in endothelial cells (EC). In addition to the mechanical forces, acetylcholine (ACh) was shown to activate TRPV4-mediated calcium influx in endothelial cells, which is important for nitric oxide-dependent vasodilation. However, the molecular mechanism through which ACh activates TRPV4 is not known. Here, we show that ACh-induced calcium influx and endothelial nitric oxide synthase (eNOS) phosphorylation but not calcium release from intracellular stores is inhibited by a specific TRPV4 antagonist, AB-159908. Importantly, activation of store-operated calcium influx was not altered in the TRPV4 null EC, suggesting that TRPV4-dependent calcium influx is mediated through a receptor-operated pathway. Furthermore, we found that ACh treatment activated protein kinase C (PKC) α, and inhibition of PKCα activity by the specific inhibitor Go-6976, or expression of a kinase-dead mutant of PKCα but not PKCε or downregulation of PKCα expression by chronic 12-O-tetradecanoylphorbol-13-acetate treatment, completely abolished ACh-induced calcium influx. Finally, we found that ACh-induced vasodilation was inhibited by the PKCα inhibitor Go-6976 in small mesenteric arteries from wild-type mice, but not in TRPV4 null mice. Taken together, these findings demonstrate, for the first time, that a specific isoform of PKC, PKCα, mediates agonist-induced receptor-mediated TRPV4 activation in endothelial cells.

Polysaccharides from Capsosiphon fulvescens stimulate the growth of IEC-6 Cells by activating the MAPK signaling pathway

Seaweed extracts show diverse bioactivities, such as antioxidant and antitumor activity. Capsosiphon fulvescens is a green alga that is abundant along the southwest coast of South Korea. Although it is consumed for its purported health-enhancing properties, particularly as a treatment for stomach disorders and hangovers, the health effects of dietary C. fulvescens remain unclear. We extracted polysaccharides from C. fulvescens (Cf-PS), investigated their effects on the proliferation of rat small intestinal epithelial IEC-6 cells, and determined the signaling cascade involved. We cultured IEC-6 cells in the presence of Cf-PS, which stimulated cell proliferation in a dose-dependent manner, and analyzed the Wnt and MAPK signaling pathways, which are related to cell proliferation. Cf-PS treatment induced the translocation of β-catenin, an effector of the Wnt signaling pathway, from the cytosol to the nucleus and increased the expression of cyclinD1 and c-myc. Cf-PS also induced ERK1/2 phosphorylation, which is activated by mitogenic and proliferative stimuli such as growth factors, but the phosphorylation of JNK and p38 was not enhanced. Our results show that Cf-PS regulates proliferation via stimulating the nuclear translocation of β-catenin and ERK1/2 activation in intestinal epithelial cells.

Effect of leukotriene D4 on mouse embryonic stem cell migration and proliferation: involvement of PI3K/Akt as well as GSK-3β/β-catenin signaling pathways

The actual leukotriene D(4) (LTD(4)) signaling pathways that regulate cell proliferation have not been elucidated thoroughly although fatty acid and its metabolites play a key role in regulations of embryonic functions. Thus, this study investigated the response of mouse embryonic stem (ES) cells exposed to LTD(4) and elucidated the signaling pathways as well. LTD(4) increased DNA synthesis in concentration-dependent (≥10(-7) M) and time-dependent (≥12 h) manners, as determined by [(3)H] thymidine incorporation and increased cell number. LTD(4) induced the phosphorylation of signal transducer and activator of transcription-3 (STAT3) and the increase of intracellular Ca(2+) levels via cysteinyl leukotriene (CysLT) 1 and 2 receptors. LTD(4) increased Akt activation and calcineurin expression, which were blocked by STAT3 inhibitor and calcium chelators. LTD(4)-induced glycogen synthase kinase (GSK)-3β phosphorylation was decreased by LY294002, Akt inhibitor, and cyclosporine A. LTD(4) inhibited the phosphorylation of β-catenin. In addition, LTD(4)-stimulated migration through increased activation of focal adhesion kinase (FAK) and paxillin which were blocked by Akt inhibitor and cyclosporine A. LTD(4)-induced increases in protooncogene and cell cycle regulatory proteins were blocked by cyclosporine A, FAK siRNA, and β-catenin siRNA. In conclusion, LTD(4)-stimulated mouse ES cell proliferation and migration via STAT3, phosphoinositide 3-kinases (PI3K)/Akt, Ca(2+)-calcineurin, and GSK-3β/β-catenin pathway.

Ligand-induced tyrosine phosphorylation of cysteinyl leukotriene receptor 1 triggers internalization and signaling in intestinal epithelial cells

Background

Leukotriene D₄ (LTD₄) belongs to the bioactive lipid group known as eicosanoids and has implications in pathological processes such as inflammation and cancer. Leukotriene D₄ exerts its effects mainly through two different G-protein-coupled receptors, CysLT₁ and CysLT₂. The high affinity LTD₄ receptor CysLT₁R exhibits tumor-promoting properties by triggering cell proliferation, survival, and migration in intestinal epithelial cells. In addition, increased expression and nuclear localization of CysLT₁R correlates with a poorer prognosis for patients with colon cancer.

Methodology/Principal Findings

Using a proximity ligation assay and immunoprecipitation, this study showed that endogenous CysLT₁R formed heterodimers with its counter-receptor CysLT₂R under basal conditions and that LTD₄ triggers reduced dimerization of CysLTRs in intestinal epithelial cells. This effect was dependent upon a parallel LTD₄-induced increase in CysLT₁R tyrosine phosphorylation. Leukotriene D₄ also led to elevated internalization of CysLT₁Rs from the plasma membrane and a simultaneous increase at the nucleus. Using sucrose, a clathrin endocytic inhibitor, dominant-negative constructs, and siRNA against arrestin-3, we suggest that a clathrin-, arrestin-3, and Rab-5-dependent process mediated the internalization of CysLT₁R. Altering the CysLT₁R internalization process at either the clathrin or the arrestin-3 stage led to disruption of LTD₄-induced Erk1/2 activation and up-regulation of COX-2 mRNA levels.

Conclusions/Significance

Our data suggests that upon ligand activation, CysLT₁R is tyrosine-phosphorylated and released from heterodimers with CysLT₂R and, subsequently, internalizes from the plasma membrane to the nuclear membrane in a clathrin-, arrestin-3-, and Rab-5-dependent manner, thus, enabling Erk1/2 signaling and downstream transcription of the COX-2 gene.

Eicosanoids and cancer

Eicosanoids, including prostaglandins and leukotrienes, are biologically active lipids that have been implicated in various pathological processes, such as inflammation and cancer. This Review highlights our understanding of the intricate roles of eicosanoids in epithelial-derived tumours and their microenvironment. The knowledge of how these lipids orchestrate the complex interactions between transformed epithelial cells and the surrounding stromal cells is crucial for understanding tumour evolution, progression and metastasis. Understanding the molecular mechanisms underlying the role of prostaglandins and other eicosanoids in cancer progression will help to develop more effective cancer chemopreventive and/or therapeutic agents.

Low expression of CysLT1R and high expression of CysLT2R mediate good prognosis in colorectal cancer

Colorectal cancer is the third most common cancer type in the Western world. In search of new treatment possibilities, the inflammation mediators, know as cysteinyl leukotrienes (CysLTs), have been shown to regulate intestinal epithelial cell survival and proliferation via the CysLT(1)R, and cell differentiation via the CysLT(2)R. These results prompted us to investigate the significance of CysLT(1)R and CysLT(2)R expression in colorectal cancer tissue for patient survival. The CysLT(1)R, CysLT(2)R, beta-catenin and Bcl-xL protein expression levels were evaluated by immunohistochemistry in a tissue microarray of 329 colorectal patients. We found that high nuclear expression of CysLT(1)R is associated with a poor prognosis, whereas high nuclear expression of CysLT(2)R is associated with a good prognosis. We also observed that patients with colorectal tumours characterised by high CysLT(1)R but low CysLT(2)R nuclear expression had the lowest survival expectancy, whereas patients with colorectal tumours characterised by low CysLT(1)R but high CysLT(2)R nuclear expression had the best survival expectancy. Interestingly, beta-catenin as a single prognostic marker did not exhibit any prognostic value. However, in patients with tumours characterised by a high CysLT(1)R nuclear expression, an elevated beta-catenin nuclear expression had a significantly prognostic value. In conclusion these data indicate that nuclear expressions of CysLTRs are potential prognostic indicators of colorectal cancer.

Beta-catenin is involved in alterations in mitochondrial activity in non-transformed intestinal epithelial and colon cancer cells

BACKGROUND

Alteration in respiratory activity and mitochondrial DNA (mtDNA) transcription seems to be an important feature of cancer cells. Leukotriene D(4) (LTD(4)) is a proinflammatory mediator implicated in the pathology of chronic inflammation and cancer. We have shown earlier that LTD(4) causes translocation of beta-catenin both to the mitochondria, in which it associates with the survival protein Bcl-2 identifying a novel role for beta-catenin in cell survival, and to the nucleus in which it activates the TCF/LEF transcription machinery.

METHODS

Here we have used non-transformed intestinal epithelial Int 407 cells and Caco-2 colon cancer cells, transfected or not with wild type and mutated (S33Y) beta-catenin to analyse its effect on mitochondria activity. We have measured the ATP/ADP ratio, and transcription of the mtDNA genes ND2, ND6 and 16 s in these cells stimulated or not with LTD(4).

RESULTS

We have shown for the first time that LTD(4) triggers a cellular increase in NADPH dehydrogenase activity and ATP/ADP ratio. In addition, LTD(4) significantly increased the transcription of mtDNA genes. Overexpression of wild-type beta-catenin or a constitutively active beta-catenin mutant mimicked the effect of LTD(4) on ATP/ADP ratio and mtDNA transcription. These elevations in mitochondrial activity resulted in increased reactive oxygen species levels and subsequent activations of the p65 subunit of NF-kappaB.

CONCLUSIONS

The present novel data show that LTD(4), presumably through beta-catenin accumulation in the mitochondria, affects mitochondrial activity, lending further credence to the idea that inflammatory signalling pathways are intrinsically linked with potential oncogenic signals.

Mechanical control of cAMP signaling through integrins is mediated by the heterotrimeric Galphas protein

Mechanical stresses that are preferentially transmitted across the cell surface via transmembrane integrin receptors activate gene transcription by triggering production of intracellular chemical second messengers, such as cAMP. Here we show that the sensitivity of the cAMP signaling pathway to mechanical stresses transferred across beta1 integrins is mediated by force-dependent activation of the heterotrimeric G protein subunit Galphas within focal adhesions at the site of stress application. Galphas is recruited to focal adhesions that form within minutes following clustering of beta1 integrins induced by cell binding to magnetic microbeads coated with activating integrin ligands, and beta1 integrin and Galphas co-precipitate when analyzed biochemically. Stress application to activated beta1 integrins using magnetic twisting cytometry increases Galphas recruitment and activates these large G proteins within focal adhesions, as measured by binding of biotinylated azido-anilido-GTP, whereas application of similar stresses to inactivated integrins or control histocompatibility antigens has little effect. This response is relevant physiologically as application of mechanical strain to cells bound to flexible extracellular matrix-coated substrates induce translocation of phospho-CREB to the nucleus, which can be attenuated by inhibiting Galphas activity, either using the inhibitor melittin or suppressing its expression using siRNA. Although integrins are not typical G protein-coupled receptors, these results show that integrins focus mechanical stresses locally on heterotrimeric G proteins within focal adhesions at the site of force application, and transduce mechanical stimuli into an intracellular cAMP signaling response by activating Galphas at these membrane signaling sites.

PKC isoenzymes differentially modulate the effect of thrombin on MAPK-dependent RPE proliferation

Thrombin signalling through PAR (protease-activated receptor)-1 is involved in cellular processes, such as proliferation, differentiation and cell survival. Following traumatic injury to the eye, thrombin signalling may participate in disorders, such as PVR (proliferative vitreoretinopathy), a human eye disease characterized by the uncontrolled proliferation, transdifferentiation and migration of otherwise quiescent RPE (retinal pigment epithelium) cells. PARs activate the Ras/Raf/MEK/ERK MAPK pathway (where ERK is extracellular-signal-regulated kinase, MAPK is mitogen-activated protein kinase and MEK is MAPK/ERK kinase) through the activation of G(alpha) and G(betagamma) heterotrimeric G-proteins, and the downstream stimulation of the PLC (phospholipase C)-beta/PKC (protein kinase C) and PI3K (phosphoinositide 3-kinase) signalling axis. In the present study, we examined the molecular signalling involved in thrombin-induced RPE cell proliferation, using rat RPE cells in culture as a model system for PVR pathogenesis. Our results showed that thrombin activation of PAR-1 induces RPE cell proliferation through Ras-independent activation of the Raf/MEK/ERK1/2 MAPK signalling cascade. Pharmacological analysis revealed that the activation of 'conventional' PKC isoforms is essential for proliferation, although thrombin-induced phosphorylation of ERK1/2 requires the activation of atypical PKCzeta by PI3K. Consistently, thrombin-induced ERK1/2 activation and RPE cell proliferation were prevented completely by PI3K or PKCzeta inhibition. These results suggest that thrombin induces RPE cell proliferation by joint activation of PLC-dependent and atypical PKC isoforms and the Ras-independent downstream stimulation of the Raf/MEK/ERK1/2 MAPK cascade. The present study is the first report demonstrating directly thrombin-induced ERK phosphorylation in the RPE, and the involvement of atypical PKCzeta in this process.

Differential kinase requirement for enhancement of Fc gammaR-mediated phagocytosis in alveolar macrophages by leukotriene B4 vs. D4

In alveolar macrophages, leukotriene (LT) B(4) and cysteinyl LTs (LTC(4), LTD(4) and LTE(4)) both enhance Fc gamma receptor (Fc gammaR)-mediated phagocytosis. In the present study we investigated the role of specific PKC isoforms (PKC-alpha and -delta), the MAP kinases p38 and ERK 1/2, and PI3K in mediating the potentiation of Fc gammaR-mediated phagocytosis induced by addition of leukotrienes to the AMs. It was found that exogenously added LTB(4) and LTD(4) both enhanced PKC-delta and -alpha phosphorylation during Fc gammaR engagement. Studies with isoform-selective inhibitors indicated that exogenous LTB(4) effects were dependent on both PKC-alpha and -delta, while LTD(4) effects were exclusively due to PKC-delta activation. Although both exogenous LTB(4) and LTD(4) enhanced p38 and ERK 1/2 activation, LTB(4) required only ERK 1/2, while LTD(4) required only p38 activation. Activation by both LTs was dependent on PI3K activation. Effects of endogenous LTs on kinase activation were also investigated using selective LT receptor antagonists. Endogenous LTB(4) contributed to Fc gammaR-mediated activation of PKC-alpha, ERK 1/2 and PI3K, while endogenous cysLTs contributes to activation of PKC-delta, p38 and PI3K. Taken together, our data show that the capacities of LTB(4) and LTD(4) to enhance Fc gammaR-mediated phagocytosis reflect their differential activation of specific kinase programs.

BLT2 is expressed in PanINs, IPMNs, pancreatic cancer and stimulates tumour cell proliferation

Pancreatic cancer has an abysmal prognosis. Targets for early detection, prevention and therapy are desperately needed. Inflammatory pathways have an important impact on tumour growth and progression. Expression of BLT2 (the second leukotriene B(4) receptor) was investigated by real-time RT-PCR and immunohistochemistry. Cell proliferation was studied after stable transfection with BLT2, after treatment with siRNA and Compound A as an agonist. BLT2 is expressed in all pancreatic cancer cell lines. Results from real-time RT-PCR revealed significant overexpression of BLT2 in malignant intraductal papillary mucinous neoplasias (IPMNs) and pancreatic adenocarcinoma. Intense staining was evident in IPMNs, infiltrating tumour cells and advanced pancreatic intraepithelial neoplasias (PanINs) but not in normal ductal cells. Overexpression of BLT2 as well as stimulation of Colo357, Panc-1 and AsPC1 cells with Compound A caused a significant increase in tumour cell proliferation, an effect reversed after siRNA treatment. This study demonstrates for the first time the expression of BLT2 in the pancreas and overexpression in pancreatic cancers and malignant IPMNs in particular. Upregulation of BLT2 is already evident in precursor lesions (PanINs, IPMNs). Overexpression of this receptor leads to significant growth stimulation. Therefore, we suggest BLT2 as a new target for chemoprevention and therapy for pancreatic cancer.

Expression of enzymes and receptors of the leukotriene pathway in human neuroblastoma promotes tumor survival and provides a target for therapy

The metabolism of arachidonic acid by the cyclooxygenase (COX) or lipoxygenase (LO) pathways generates eicosanoids that have been implicated in the pathogenesis of a variety of human diseases, including cancer. In this study, we examined the expression and significance of components within the 5-LO pathway in human neuroblastoma, an embryonal tumor of the sympathetic nervous system. High expression of 5-LO, 5-LO-activating protein (FLAP), leukotriene A(4) hydrolase, leukotriene C(4) synthase, and leukotriene receptors was detected in a majority of primary neuroblastoma tumors and all cell lines investigated. Expression of 5-LO and FLAP was evident in tumor cells but not in nonmalignant adrenal medulla where neuroblastomas typically arise. Moreover, neuroblastoma cells produce leukotrienes, and stimulation of neuroblastoma cells with leukotrienes increased neuroblastoma cell viability. Inhibitors of 5-LO (AA-861), FLAP (MK-886), or the leukotriene receptor antagonist montelukast inhibited neuroblastoma cell growth by induction of G(1)-cell cycle arrest and apoptosis. Similarly, specific 5-LO and leukotriene receptor silencing by small interfering RNA decreased neuroblastoma cell growth. These findings provide new insights into the pathobiology of neuroblastoma, and the use of leukotriene pathway inhibitors as a novel adjuvant therapy for children with neuroblastoma warrants further consideration.

Effects of osmotic stress on the activity of MAPKs and PDGFR-β-mediated signal transduction in NIH-3T3 fibroblasts

Signaling in cell proliferation, cell migration, and apoptosis is highly affected by osmotic stress and changes in cell volume, although the mechanisms underlying the significance of cell volume as a signal in cell growth and death are poorly understood. In this study, we used NIH-3T3 fibroblasts in a serum- and nutrient-free inorganic medium (300 mosM) to analyze the effects of osmotic stress on MAPK activity and PDGF receptor (PDGFR)-β-mediated signal transduction. We found that hypoosmolarity (cell swelling at 211 mosM) induced the phosphorylation and nuclear translocation of ERK1/2, most likely via a pathway independent of PDGFR-β and MEK1/2. Conversely, hyperosmolarity (cell shrinkage at 582 mosM) moved nuclear and phosphorylated ERK1/2 to the cytoplasm and induced the phosphorylation and nuclear translocation of p38 and phosphorylation of JNK1/2. In a series of parallel experiments, hypoosmolarity did not affect PDGF-BB-induced activation of PDGFR-β, whereas hyperosmolarity strongly inhibited ligand-dependent PDGFR-β activation as well as downstream mitogenic signal components of the receptor, including Akt and the MEK1/2-ERK1/2 pathway. Based on these results, we conclude that ligand-dependent activation of PDGFR-β and its downstream effectors Akt, MEK1/2, and ERK1/2 is strongly modulated (inhibited) by hyperosmotic cell shrinkage, whereas cell swelling does not seem to affect the activation of the receptor but rather to activate ERK1/2 via a different mechanism. It is thus likely that cell swelling via activation of ERK1/2 and cell shrinkage via activation of the p38 and JNK pathway and inhibition of the PDGFR signaling pathway may act as key players in the regulation of tissue homeostasis.

Cysteinyl leukotriene-1 receptor activation in a human bronchial epithelial cell line leads to signal transducer and activator of transcription 1-mediated eosinophil adhesion

We studied the effect of leukotriene D(4) (LTD(4)) on a human bronchial epithelial cell line (16HBE) overexpressing the cysteinyl leukotriene (CysLT) (1) receptor (HBECysLT(1)R), looking at the associated signal transduction mechanisms as well as at effects on inflammatory cell adhesion. The results obtained showed that LTD(4) increases the phosphorylation of extracellular signal-regulated protein kinase (ERK) 1/2 and of the signal transducer and activator of transcription 1 (STAT-1) in serine 727 (STAT-1Ser727), resulting in increased eosinophil adhesion to HBECysLT(1)R, associated with enhanced surface expression of intercellular adhesion molecule (ICAM) 1. Pretreatment with a CysLT(1)R-selective antagonist or with a selective inhibitor of protein kinase C (PKC) or with a selective inhibitor of the mitogen-activated protein kinase kinase (MEK) successfully suppressed both LTD(4)-induced STAT-1Ser727 phosphorylation and the associated increase in eosinophil adhesion. The use of the MEK inhibitor and of the selective CysLT(1)R antagonist in electrophoretic mobility shift assay experiments showed that LTD(4) promotes the nuclear translocation of STAT-1 through the activation of ERK1/2 pathway. The key role of STAT-1 in leukotriene D(4) transduction signaling was confirmed by RNA interference experiments, where silencing of STAT-1 expression abolished the effect of leukotriene D(4) on eosinophil adhesion. In conclusion, for the first time, we provide evidence of the involvement of STAT-1 in the signal transduction mechanism of the CysLT(1) receptor; phosphorylation of STAT-1, through PKC and ERK1/2 activation, causes enhanced ICAM-1 surface expression and eosinophil adhesion. Effective CysLT(1)R antagonism may therefore contribute to the control of the chronic inflammatory condition that characterizes human airways in asthma.

Ras/PI3kinase/cofilin-independent activation of human CD45RA+ and CD45RO+ T cells by superagonistic CD28 stimulation

T cell activation requires costimulation of TCR/CD3 plus accessory receptors (e.g. CD28). A hallmark of costimulation is the dynamic reorganization of the actin cytoskeleton, important for receptor polarization in the immunological synapse. The classical model of T cell costimulation was challenged by the detection of superagonistic anti-CD28 antibodies. These induce T cell proliferation and--as demonstrated here--production of IFN-gamma, CD25 and CD69 even in the absence of TCR/CD3 coligation. Here, we analyzed whether superagonistic CD28 stimulation induces costimulatory signaling events. Costimulation leads to phosphorylation of the actin-bundling protein L-plastin and dephosphorylation of the actin-reorganizing protein cofilin. Cofilin binds to F-actin only in its dephosphorylated form. Binding of cofilin to F-actin leads to depolymerization or severing of F-actin. The latter ends up in smaller F-actin fragments, which can be elongated at the free barbed ends. This results in enhanced actin polymerization. Dephosphorylation of cofilin requires activation of Ras and PI3Kinase. Interestingly, superagonistic CD28 stimulation activates human peripheral blood T cells independently of Ras and PI3Kinase. Accordingly, it does not lead to cofilin dephosphorylation and receptor polarization. Likewise, L-plastin is not phosphorylated. Thus, superagonistic CD28 stimulation does not mimic costimulation. Instead, it leads to a Ras/PI3Kinase/cofilin-independent state of "unpolarized T cell activation".

Leukotriene D(4) induces AP-1 but not NFkappaB signaling in intestinal epithelial cells

We have previously shown that leukotriene D(4) (LTD(4)), a known pro-inflammatory mediator, induces increased survival and proliferation of intestinal epithelial cells. In this study we examined whether LTD(4) functions via activation of the transcription factors NFkappaB and AP-1, which are potent inducers of mitogenesis. We found that the NFkappaB inhibitory protein IkappaBalpha was not degraded upon LTD(4) stimulation. Furthermore, nuclear translocation of the classical p65 or alternative p52 subunits of NFkappaB was not observed. Accordingly, LTD(4) stimulation failed to induce NFkappaB transcriptional activity. Instead we found that LTD(4) induced phosphorylation of c-Jun-N-terminal kinase (JNK) and transcriptional activity of AP-1, which could be reduced by a JNK inhibitor. Moreover, LTD(4) induced cell proliferation, and this effect was also blocked upon addition of a JNK inhibitor. Our findings show for the first time that JNK/AP-1 but not NFkappaB is a downstream target of LTD(4) in intestinal epithelial cells, suggesting that AP-1 is an important mediator of LTD(4)-induced mitogenic effects.

The effect of propofol on actin, ERK-1/2 and GABAA receptor content in neurones

AIM

Interaction with the gamma-aminobutyric acid receptor (GABA(A)R) complex is recognized as an important component of the mechanism of many anaesthetic agents, including propofol. The aims of this study were to investigate the effect of propofol on GABA(A)R, to determine whether exposure of neurones to propofol influences the localization of GABA(A)R within the cell and to look for cytoskeletal changes that may be connected with activation, such as the mitogen-activated protein kinase (MAPK) pathway.

METHODS

Primary cortical cell cultures from rat, with and without pre-incubation with the GABA(A)R antagonist bicuculline, were exposed to propofol. The cells were lysed and separated into membrane and cytosolic fractions. Immunoblot analyses of filamentous actin (F-actin), the GABA(A)beta(2)-subunit receptor and extracellular signal-regulated kinase-1/2 (ERK-1/2) were performed.

RESULTS

Propofol triggers an increase in GABA(A)R, actin content and ERK-1/2 phosphorylation in the cytosolic fraction. In the membrane fraction, there is a decrease in GABA(A)beta(2)-subunit content and an increase in both actin content and ERK-1/2 phosphorylation. The GABA(A)R antagonist bicuculline blocks the propofol-induced changes in F-actin, ERK and GABA(A)beta(2)-subunit content, and ERK-1/2 phosphorylation.

CONCLUSION

We believe that propofol triggers a dose-dependent internalization of the GABA(A)beta(2)-subunit. The increase in internal GABA(A)beta(2)-subunit content exhibits a close relationship to actin polymerization and to an increase in ERK-1/2 activation. Actin contributes to the internalization sequestering of the GABA(A)beta(2)-subunit.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.