Leukotriene D4 mediates survival and proliferation via separate but parallel pathways in the human intestinal epithelial cell line Int 407

Epigenetic histone modification by butyrate downregulates KIT and attenuates mast cell function

Short-chain fatty acid butyrate is produced from the bacterial fermentation of indigestible fiber in the intestinal lumen, and it has been shown to attenuate lung inflammation in murine asthma models. Mast cells (MCs) are initiators of inflammatory response to allergens, and they play an important role in asthma. MC survival and proliferation is regulated by its growth factor stem cell factor (SCF), which acts through the receptor, KIT. It has previously been shown that butyrate attenuates the activation of MCs by allergen stimulation. However, how butyrate mechanistically influences SCF signalling to impact MC function remains unknown. Here, we report that butyrate treatment triggered the modification of MC histones via butyrylation and acetylation, and inhibition of histone deacetylase (HDAC) activity. Further, butyrate treatment caused downregulation of SCF receptor KIT and associated phosphorylation, leading to significant attenuation of SCF-mediated MC proliferation, and pro-inflammatory cytokine secretion. Mechanistically, butyrate inhibited MC function by suppressing KIT and downstream p38 and Erk phosphorylation, and it mediated these effects via modification of histones, acting as an HDAC inhibitor and not via its traditional GPR41 (FFAR3) or GPR43 (FFAR2) butyrate receptors. In agreement, the pharmacological inhibition of Class I HDAC (HDAC1/3) mirrored butyrate's effects, suggesting that butyrate impacts MC function by HDAC1/3 inhibition. Taken together, butyrate epigenetically modifies histones and downregulates the SCF/KIT/p38/Erk signalling axis, leading to the attenuation of MC function, validating its ability to suppress MC-mediated inflammation. Therefore, butyrate supplementations could offer a potential treatment strategy for allergy and asthma via epigenetic alterations in MCs.

Regulation of inflammation in cancer by dietary eicosanoids

BACKGROUND

Cancer is a major burden of disease worldwide and increasing evidence shows that inflammation contributes to cancer development and progression. Eicosanoids are derived from dietary polyunsaturated fatty acids, such as arachidonic acid (AA), and are mainly produced by a series of enzymatic pathways that include cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P-450 epoxygenase (CYP). Eicosanoids consist of at least several hundred individual molecules and play important roles in the inflammatory response and inflammation-related cancers.

SCOPE AND APPROACH

Dietary sources of AA and biosynthesis of eicosanoids from AA through different metabolic pathways are summarized. The bioactivities of eicosanoids and their potential molecular mechanisms on inflammation and cancer are revealed. Additionally, current challenges and limitations in eicosanoid research on inflammation-related cancer are discussed.

KEY FINDINGS AND CONCLUSIONS

Dietary AA generates a large variety of eicosanoids, including prostaglandins, thromboxane A2, leukotrienes, cysteinyl leukotrienes, lipoxins, hydroxyeicosatetraenoic acids (HETEs), and epoxyeicosatrienoic acids (EETs). Eicosanoids exert different bioactivities and mechanisms involved in the inflammation and related cancer developments. A deeper understanding of eicosanoid biology may be advantageous in cancer treatment and help to define cellular targets for further therapeutic development.

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.

Montelukast, an Antagonist of Cysteinyl Leukotriene Signaling, Impairs Burn Wound Healing

BACKGROUND

Burns are severe injuries often associated with impaired wound healing. Impaired healing is caused by multiple factors, including dysregulated inflammatory responses at the wound site. Interestingly, montelukast, an antagonist for cysteinyl leukotrienes and U.S. Food and Drug Administration approved for treatment of asthma and allergy, was previously shown to enhance healing in excision wounds and to modulate local inflammation.

METHODS

In this study, the authors examined the effect of montelukast on wound healing in a mouse model of scald burn injury. Burn wound tissues isolated from montelukast- and vehicle-treated mice at various times after burn injury were analyzed for wound areas ( n = 34 to 36), reepithelialization ( n = 14), inflammation ( n = 8 to 9), and immune cell infiltration ( n = 3 to 6) and proliferation ( n = 7 to 8).

RESULTS

In contrast to previously described beneficial effects in excision wounds, this study shows that montelukast delays burn wound healing by impairing the proliferation of keratinocytes and endothelial cells. This occurs largely independently of inflammatory responses at the wound site, suggesting that montelukast impairs specifically the proliferative phase of wound healing in burns. Wound healing rates in mice in which leukotrienes are not produced were not affected by montelukast.

CONCLUSION

Montelukast delays wound healing mainly by reducing the proliferation of local cells after burn injury.

CLINICAL RELEVANCE STATEMENT

Although additional and clinical studies are necessary, our study suggests that burn patients who are on montelukast may exhibit delayed healing, necessitating extra observation.

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.

Blocking 5-LO pathway alleviates renal fibrosis by inhibiting the epithelial-mesenchymal transition

The enzyme 5-lipoxygenase (5-LO) converts arachidonic acid to leukotrienes, which mediate inflammation. The enzyme is known to contribute to organ fibrosis, but how it contributes to renal fibrosis is unclear. Here, we reported that fibrotic kidneys expressed high levels of 5-LO, and deleting the 5-LO gene mitigated renal fibrosis in mice subjected to unilateral ureteral obstruction (UUO), based on assays of collagen deposition, injury and inflammation. Mechanistically, the exogenous leukotrienes B4 and C4, the downstream products of 5-LO, could induce the epithelial-mesenchymal transition (EMT) in kidney epithelial cell cultures, based on assays of E-cadherin, vimentin and snail expression. Studies in UUO mice confirmed that 5-LO deletion inhibited the EMT in the obstructed kidney. More importantly, 5-LO inhibitor zileuton loaded in CREKA-Lip, which could target to fibrotic kidney, markedly attenuated UUO-induced renal fibrosis and injury by inhibiting the EMT in the obstructed kidney. Our results suggested that 5-LO activity may contribute to renal fibrosis by promoting renal EMT, implying that the enzyme may be a useful therapeutic target.

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.

Potential for a localized immune response by the ruminal epithelium in nonpregnant heifers following a short-term subacute ruminal acidosis challenge

The aim of this study was to investigate whether the ruminal epithelium activates a local inflammatory response following a short-term subacute ruminal acidosis (SARA) challenge. Seven ruminally cannulated, nonpregnant, nonlactating beef heifers, fed a baseline total mixed ration (TMR) with 50:50 forage-to-concentrate ratio, were used in a crossover design with 2 periods and 2 treatments: SARA and control (CON). Induction of SARA included feed restriction (25% of dry matter intake [DMI] for 24 h) followed by a grain overload (30% of baseline DMI) and provision of the full TMR; whereas, the CON group received the TMR ad libitum. Ruminal pH was recorded using indwelling probes, and ruminal lipopolysaccharide (LPS) concentration was measured daily following the challenge until d 6. Biopsies of ruminal papillae from the ventral sac were collected on d 2 and 6 after the grain overload. Transcript abundance of genes associated with acute inflammation was measured by quantitative real-time PCR, normalized to the geometric mean of 3 stable housekeeping genes. Target genes included toll-like receptor-2 (TLR2), TLR4, TLR9, tumor necrosis factor-α (TNFA), prostaglandin endoperoxide synthase-1 (PTGS1), PTGS2 transforming growth factor β-1 (TGFB1), and 4 intermediate enzymes of leukotriene synthesis (ALOX5, ALOX5AP, LTA4H, and LTC4S). Protein localization and expression of TLR4 were quantified by image analysis of fluorescence intensity. Statistical analysis was performed using as a crossover design with fixed effects of treatment, day, and the treatment × day interaction with the random effect of day within period. Ruminal pH was below 5.6 for 4.5 h/d and below 5.8 for 6.9 h/d in the SARA group compared with 22 and 72 min/d, respectively, for CON. Ruminal LPS concentration peaked on d 2 in SARA heifers at 51,481 endotoxin units (EU)/mL compared with 13,331 EU/mL in CON. Following grain overload, small but statistically significant decreases in the transcriptional abundance of TLR2, TLR4, TNF, PTGS2, ALOX5, and ALOX5AP were seen in SARA versus CON heifers. A functionally relevant decrease in TLR4 expression in SARA heifers compared with CON was confirmed by a decrease in fluorescence intensity of the corresponding protein following immunohistofluorescent staining of papillae. The study results indicate a suppression of the inflammatory response in the ruminal epithelium and suggest that the response is tightly regulated, allowing for tissue recovery and return to homeostasis following SARA.

Inhibition of 5-lipoxygenase decreases renal fibrosis and progression of chronic kidney disease

In inflammatory diseases, the 5-lipoxygenase (5-LO) pathway contributes to epithelial damage and fibrosis by catalyzing the production of leukotrienes (LTs). Antagonists of the 5-LO pathway are currently approved for use in patients and are well tolerated. We found that expression of 5-LO is strongly induced in three models of chronic kidney disease: unilateral ureteral obstruction (UUO), folate nephropathy, and an orthologous mouse model of polycystic kidney disease. Immunohistochemistry showed that macrophages are the dominant source of 5-LO. Zileuton, a US Food and Drug Administration-approved antagonist of 5-LO, significantly reduced fibrosis at 7 and 14 days after UUO; these findings were confirmed using a genetically modified [5-LO-associated protein-knockout ( Alox5ap^-/-)] mouse strain. Inhibition of 5-LO did not appear to change infiltration of leukocytes after UUO as measured by flow cytometry. However, fluorescence-lifetime imaging microscopy showed that 5-LO inhibitors reversed the glycolytic switch in renal tubular epithelial cells after UUO. Two downstream enzymes of 5-LO, LTA₄ hydrolase (LTA₄H) and LTC₄ synthase (LTC₄S), are responsible for the synthesis of LTB₄ and cysteinyl LTs, respectively. Fibrosis was reduced after UUO in Ltc4s^-/-, but not Lta4h^-/-, mice. In contrast, using the folate nephropathy model, we found reduced fibrosis and improved renal function in both Ltc4s^-/- and Lta4h^-/- mice. In summary, our studies suggest that manipulation of the 5-LO pathway may represent a novel treatment approach for chronic kidney disease.

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) activation contributes to the pathogenesis of experimental colitis via inhibition of intestinal epithelial cell proliferation

The incidence and prevalence of inflammatory bowel disease (IBD) are increasing worldwide. IBD is known to be multifactorial, but inflammatory signaling within the intestinal epithelium and a subsequent failure of the intestinal epithelial barrier have been shown to play essential roles in disease pathogenesis. CaMKIV is a multifunctional protein kinase associated with inflammation and cell cycle regulation. CaMKIV has been extensively studied in autoimmune diseases, but a role in idiopathic intestinal inflammation has not been described. In this study, active CaMKIV was highly expressed within the intestinal epithelium of humans with ulcerative colitis and wild-type (WT) mice with experimental induced colitis. Clinical disease severity directly correlates with CaMKIV activation, as does expression of proinflammatory cytokines and histologic features of colitis. In WT mice, CaMKIV activation is associated with increases in expression of 2 cell cycle proarrest signals: p53 and p21. Cell cycle arrest inhibits proliferation of the intestinal epithelium and ultimately results in compromised intestinal epithelial barrier integrity, further perpetuating intestinal inflammation during experimental colitis. Using a CaMKIV null mutant mouse, we demonstrate that a loss of CaMKIV protects against murine DSS colitis. Small molecules targeting CaMKIV activation may provide therapeutic benefit for patients with IBD.-Cunningham, K. E., Novak, E. A., Vincent, G., Siow, V. S., Griffith, B. D., Ranganathan, S., Rosengart, M. R., Piganelli, J. D., Mollen, K. P. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) activation contributes to the pathogenesis of experimental colitis via inhibition of intestinal epithelial cell proliferation.

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

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

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.

Expression of cysteinyl leukotriene receptor 1 and 2 (CysLTR1 and CysLTR2) in the lymphocytes of hyperplastic tonsils: comparison between allergic and nonallergic snoring children

BACKGROUND

Cysteinyl leukotriene receptor 1 and 2 (CysLTR1 and CysLTR2) are involved in allergic processes and play a role in adenotonsillar hyperplasia (AH). Clinically, only CysLTR1 may be blocked by montelukast. Our objective was to compare the expression of CysLTR1 and CysLTR2 in the B and T cells of hyperplasic tonsils of sensitized (SE) and control (NS) snoring children.

METHODS

Sixty children, 5 to 10 years of age, referred for adenotonsillectomy, were divided into SE and NS groups, according to their responses to the skin-prick test. Cells from the removed tissues were stained for CysLTR1, CysLTR2, CD19, and CD3 and counted via flow cytometry. messenger RNA (mRNA) expression of the CysLTRs genes was measured real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR).

RESULTS

The SE group showed reduced expression of the small CD3+/CysLTR1+ lymphocytes (4.6 ± 2.2 vs 6.5 ± 5.0; p = 0.04). Regarding the large lymphocytes, the SE group showed lower expression of CD3+/CysLTR1+ (40.9 ± 14.5 vs 47.6 ± 11.7; p = 0.05), CD19+/CysLTR1+ (44.6 ± 16.9 vs 54.1 ± 12.4; p = 0.01), and CD19+/CysLTR2+ (55.3 ± 11.3 vs 61.5 ± 12.6; p = 0.05) lymphocytes. Considering the total number of lymphocytes, the SE group had fewer CD3+/CysLTR1+ lymphocytes (11.1 ± 5.5 vs 13.7 ± 6.2; p = 0.04). All other cell populations exhibited reduced expression in the SE group without statistical significance. The expression of CysLTR2 was significantly higher (p < 0.05) than CysLTR1 in most studied cell populations. The mRNA expression did not show significant differences between the groups.

CONCLUSION

The expression of CysLTR is higher in the lymphocytes of the NS children, and CysLTR2 shows greater expression than CysLTR1 Respiratory allergies do not appear to be a stimulus for AH occurrence. Newer drugs capable of blocking both CysLTRs warrant further study.

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.

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

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

Cysteinyl leukotrienes and their receptors: Bridging inflammation and colorectal cancer

Long-standing inflammation has emerged as a hallmark of neoplastic transformation of epithelial cells and may be a limiting factor of successful conventional tumor therapies. A complex milieu composed of distinct stromal and immune cells, soluble factors and inflammatory mediators plays a crucial role in supporting and promoting various types of cancers. An augmented inflammatory response can predispose a patient to colorectal cancer (CRC). Common risk factors associated with CRC development include diet and lifestyle, altered intestinal microbiota and commensals, and chronic inflammatory bowel diseases. Cysteinyl leukotrienes are potent inflammatory metabolites synthesized from arachidonic acid and have a broad range of functions involved in the etiology of various pathologies. This review discusses the important role of cysteinyl leukotriene signaling in linking inflammation and CRC.

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.

CysLT(1)R antagonists inhibit tumor growth in a xenograft model of colon cancer

The expression of the inflammatory G-protein coupled receptor CysLT₁R has been shown to be upregulated in colon cancer patients and associated with poor prognosis. The present study investigated the correlation between CysLT₁R and colon cancer development in vivo using CysLT₁R antagonists (ZM198,615 or Montelukast) and the nude mouse xenograft model. Two drug administration regimens were established. The first regimen was established to investigate the importance of CysLT₁R in tumor initiation. Nude mice were inoculated with 50 µM CysLT₁R antagonist-pretreated HCT-116 colon cancer cells and received continued treatment (5 mg/kg/day, intraperitoneally). The second regimen aimed to address the role of CysLT₁R in tumor progression. Nude mice were inoculated with non-pretreated HCT-116 cells and did not receive CysLT₁R antagonist treatment until recordable tumor appearance. Both regimens resulted in significantly reduced tumor size, attributed to changes in proliferation and apoptosis as determined by reduced Ki-67 levels and increased levels of p21^WAF/Cip1 (P<0.01), cleaved caspase 3, and the caspase-cleaved product of cytokeratin 18. Decreased levels of VEGF (P<0.01) and reduced vessel size (P<0.05) were also observed, the latter only in the ZM198,615-pretreatment group. Furthermore, we performed a series of in vitro studies using the colon cancer cell line HCT-116 and CysLT₁R antagonists. In addition to significant reductions in cell proliferation, adhesion and colony formation, we observed induction of cell cycle arrest and apoptosis in a dose-dependent manner. The ability of Montelukast to inhibit growth of human colon cancer xenograft was further validated by using two additional colon cancer cell lines, SW-480 and HT-29. Our results demonstrate that CysLT₁R antagonists inhibit growth of colon cancer xenografts primarily by reducing proliferation and inducing apoptosis of the tumor cells.

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.

Crosstalk between colon cancer cells and macrophages via inflammatory mediators and CD47 promotes tumour cell migration

Tumour-associated macrophages (TAMs) of the M2 phenotype are present in the stroma of many tumours and are frequently associated with the progression of several types of cancer. We investigated the role of M2 macrophages in colon cancer progression and found that human colon cancer tissue had elevated numbers of CD68(+) (macrophage marker) cells and CD206(+) (M2 macrophage marker) cells and increased CD47 expression. To explore potential interplay between colon cancer cells and M2 macrophages, we differentiated the monocyte cell line THP-1 into M1 and M2 macrophages (CD206(high) and Th2 cytokine-secreting cells), respectively. M2 macrophages migrated faster than M1 macrophages towards SW480-conditioned medium. Similarly, M2 macrophage-conditioned medium induced SW480 cell migration and CD47 expression. Factors released by macrophages were involved in this induction. In addition, SW480 cells migrated faster when co-cultured with M2 macrophages. Inhibition of CD47 with blocking antibodies or siRNA significantly reduced the migration of SW480 cells in the presence of M2 macrophages. This effect was further decreased via blocking antibodies against the CD47 ligand signal-regulatory protein α (SIRPα). Additionally, cancer cells also secreted significant levels of IL-10, thereby promoting M2 macrophage differentiation. These findings indicate that a TAM-enriched tumour microenvironment promotes colon cancer cell migration and metastasis.

Regulation of cysteinyl leukotriene receptor 2 expression--a potential anti-tumor mechanism

Background

The cysteinyl leukotrienes receptors (CysLTRs) are implicated in many different pathological conditions, such as inflammation and cancer. We have previously shown that colon cancer patients with high CysLT₁R and low CysLT₂R expression demonstrate poor prognosis. Therefore, we wanted to investigate ways for the transcriptional regulation of CysLT₂R, which still remains to be poorly understood.

Methodology/Principal Findings

We investigated the potential role of the anti-tumorigenic interferon α (IFN-α) and the mitogenic epidermal growth factor (EGF) on CysLT₂R regulation using non-transformed intestinal epithelial cell lines and colon cancer cells to elucidate the effects on the CysLT₂R expression and regulation. This was done using Western blot, qPCR, luciferase reporter assay and a colon cancer patient array. We found a binding site for the transcription factor IRF-7 in the putative promoter region of CysLT₂R. This site was involved in the IFN-α induced activity of the CysLT₂R luciferase reporter assay. In addition, IFN-α induced the activity of the differentiation marker alkaline phosphatase along with the expression of mucin-2, which protects the epithelial layer from damage. Interestingly, EGF suppressed both the expression and promoter activity of the CysLT₂R. E-boxes present in the CysLT₂R putative promoter region were involved in the suppressing effect. CysLT₂R signaling was able to suppress cell migration that was induced by EGF signaling.

Conclusions/Significance

The patient array showed that aggressive tumors generally expressed less IFN-α receptor and more EGFR. Interestingly, there was a negative correlation between CysLT₂R and EGFR expression. Our data strengthens the idea that there is a protective role against tumor progression for CysLT₂R and that it highlights new possibilities to regulate the CysLT₂R.

International Union of Basic and Clinical Pharmacology. LXXXIV: leukotriene receptor nomenclature, distribution, and pathophysiological functions

The seven-transmembrane G protein-coupled receptors activated by leukotrienes are divided into two subclasses based on their ligand specificity for either leukotriene B(4) or the cysteinyl leukotrienes (LTC(4), LTD(4), and LTE(4)). These receptors have been designated BLT and CysLT receptors, respectively, and a subdivision into BLT(1) and BLT(2) receptors and CysLT(1) and CysLT(2) receptors has been established. However, recent findings have also indicated the existence of putative additional leukotriene receptor subtypes. Furthermore, other ligands interact with the leukotriene receptors. Finally, leukotrienes may also activate other receptor classes, such as purinergic receptors. The aim of this review is to provide an update on the pharmacology, expression patterns, and pathophysiological roles of the leukotriene receptors as well as the therapeutic developments in this area of research.

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.

Cysteinyl leukotriene receptor expression pattern affects migration of breast cancer cells and survival of breast cancer patients

The fact that breast cancer patients with local or distal dissemination exhibit decreased survival, promotes a search for novel mechanisms to suppress such tumor progression. Here, we have determined the expression of proinflammatory cysteinyl leukotriene receptors (CysLTRs) in breast tumor tissue and their signaling effect on breast cancer cell functions related to tumor progression. Patients with breast tumors characterized by high CysLT(1)R and low CysLT(2)R expression levels exhibited increased risk of cancer-induced death in univariate analysis for both the total patient group (hazard ratio [HR] = 2.88, 95% confidence interval [CI] = 1.11-7.41), as well as patients with large (>20 mm) tumors (HR = 5.08, 95% CI = 1.39-18.5). Multivariate analysis revealed that patients with large tumors exhibiting high CysLT(1)R and low CysLT(2)R expression levels had a significantly reduced survival, also when adjusted for established prognostic parameters (HR = 7.51, 95% CI = 1.83-30.8). In patients with large (>20 mm) tumors, elevated CysLT(2)R expression predicted an improved 5-year survival (log-rank test p = 0.04). Surprisingly, for longer time periods, this prognostic value was lost. This disappearance coincided with the termination of hormonal treatment. Tamoxifen preserved and even induced transcription of CysLT(2)R, but not CysLT(1)R, in estrogene receptor-positive MCF-7 breast cancer cells. This elevated CysLT(2)R expression decreased, even below the level of untreated cells, when tamoxifen was withdrawn. CysLT(2)R signaling reduced MCF-7 cell migration, but had no effect on either proliferation or apoptosis. Our data indicate that low CysLT(1)R together with high CysLT(2)R expression levels might be useful parameters in prognostication and treatment stratification of breast cancer patients.

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.

Activation of Gi induces mechanical hyperalgesia poststress or inflammation

In studies of the role of primary afferent nociceptor plasticity in the transition from acute to chronic pain we recently reported that exposure to unpredictable sound stress or a prior inflammatory response induces long-term changes in the second messenger signaling pathway, in nociceptors, mediating inflammatory hyperalgesia; this change involves a switch from a G(s)-cAMP-PKA to a G(i)-PKCepsilon signaling pathway. To more directly study the role of G(i) in mechanical hyperalgesia we evaluated the nociceptive effect of the G(i) activator, mastoparan. Intradermal injection of mastoparan in the rat hind paw induces dose-dependent (0.1 ng-1 microg) mechanical hyperalgesia. The highly selective inhibitors of G(i), pertussis toxin, and of protein kinase C epsilon (PKCepsilon), PKCepsilonV(1-2), both markedly attenuate mastoparan-induced hyperalgesia in stressed rats but had no effect on mastoparan-induced hyperalgesia in unstressed rats. Similar effects were observed, at the site of nociceptive testing, after recovery from carrageenan-induced inflammation. These studies provide further confirmation for a switch to a G(i)-activated and PKCepsilon-dependent signaling pathway in primary mechanical hyperalgesia, induced by stress or inflammation.

Regulation of the eicosanoid pathway by tumour necrosis factor alpha and leukotriene D4 in intestinal epithelial cells

In this study the mRNA and protein levels of the key enzymes involved in eicosanoid biosynthesis and the cysteinyl leukotriene receptors (CysLT1R and CysLT2R) have been analysed in non-transformed intestinal epithelial and colon cancer cell lines. Our results revealed that tumour necrosis factor alpha (TNF-alpha), and leukotriene D4 (LTD4), which are inflammatory mediators implicated in carcinogenesis, stimulated an increase of cyclooxygenase-2 (COX-2), in non-transformed epithelial cells, and 5-lipoxygenase (5-LO) in both non-transformed and cancer cell lines. Furthermore, these mediators also stimulated an up-regulation of LTC4 synthase in cancer cells as well as non-transformed cells. We also observed an endogenous production of CysLTs in these cells. TNF-alpha and LTD4, to a lesser extent, up-regulate the CysLT1R levels. Interestingly, TNF-alpha also reduced CysLT2R expression in cancer cells. Our results demonstrate that inflammatory mediators can cause intestinal epithelial cells to up-regulate the expression of enzymes needed for the biosynthesis of eicosanoids, including the cysteinyl leukotrienes, as well as the signal transducing proteins, the CysLT receptors, thus providing important mechanisms for both maintaining inflammation and for tumour progression.

Stress induces a switch of intracellular signaling in sensory neurons in a model of generalized pain

Stress dramatically exacerbates pain in diseases such as fibromyalgia and rheumatoid arthritis, but the underlying mechanisms are unknown. We tested the hypothesis that stress causes generalized hyperalgesia by enhancing pronociceptive effects of immune mediators. Rats exposed to nonhabituating sound stress exhibited no change in mechanical nociceptive threshold, but showed a marked increase in hyperalgesia evoked by local injections of prostaglandin E(2) or epinephrine. This enhancement, which developed more than a week after exposure to stress, required concerted action of glucocorticoids and catecholamines at receptors located in the periphery on sensory afferents. The altered response to pronociceptive mediators involved a switch in coupling of their receptors from predominantly stimulatory to inhibitory G-proteins (G(s) to G(i)), and for prostaglandin E(2), emergence of novel dependence on protein kinase C epsilon. Thus, an important mechanism in generalized pain syndromes may be stress-induced coactivation of the hypothalamo-pituitary-adrenal and sympathoadrenal axes, causing a long-lasting alteration in intracellular signaling pathways, enabling normally innocuous levels of immune mediators to produce chronic hyperalgesia.

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.

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.

Leukotriene D4 upregulates MUC2 gene transcription in human epithelial cells

BACKGROUND/AIMS

Leukotriene (LT) D(4) has been shown to induce mucus secretion in the airways. Excessive mucus secretion characterizes airway inflammatory disease such as asthma, allergic rhinitis. However, little is known about the effect of LTD(4) on mucin gene expression. The aim of this study was to investigate the effect of LTD(4) on MUC2 gene expression in cultured epithelial cells (HM3-MUC2 cells).

METHODS

HM3-MUC2 cells were treated with LTD(4) for 2 or 6 h. Reporter gene assay was mainly used for analysis.MUC2 protein levels were measured using an enzyme-linked immunosorbent assay.

RESULTS

LTD(4) significantly increased MUC2 gene transcriptional activity in a dose-dependent manner. Pranlukast, which is a selective antagonist of CysLT(1) receptor, inhibited LTD(4)-induced MUC2 gene transcriptional activity in a dose-dependent manner. LTD(4)-induced MUC2 gene transcriptional activity was also suppressed by a G-protein inhibitor (pertussis toxin),a protein kinase C (PKC) inhibitor (bisindolylmaleimide), a mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitor (PD98059), an extracellular signal regulated kinase-2 (ERK-2) inhibitor (AG126) and a nuclear factor kappaB (NF-kappaB) inhibitor. In addition, pranlukast inhibited LTD(4)-induced NF-kappaB activity.

CONCLUSION

These results suggest that LTD(4 )upregulates MUC2 gene transcription via a signaling pathway involving CysLT(1) receptor, G-protein, PKC, MEK, ERK and NF-kappaB.

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.

An increased expression of cysteinyl leukotriene 2 receptor in colorectal adenocarcinomas correlates with high differentiation

Increased levels of inflammatory mediators such as cysteinyl leukotrienes (CysLT) have been found in and around tumors. These data, along with our previous observation that the G-protein-coupled receptor CysLT(1)R, which signals survival and proliferation, is up-regulated in colon cancer, suggest an important role for CysLT(1)R in tumor development. The objective of this study was to examine the expression and function of the low-affinity CysLT2 receptor (CysLT2R) in colon cancer. We found lower expression levels of CysLT2R compared with CysLT(1)R in cancer cell lines as well as clinical tumor material. Interestingly, CysLT2R, like CysLT(1)R, was found to be one of few G-protein-coupled receptors that are located both at the plasma membrane and the nuclear membrane. No effect of CysLT2R signaling on cell proliferation was observed, nor was there a correlation between CysLT2R and different proliferation markers such as Ki-67 and cyclooxygenase-2 in the tumor material. Instead, we found that activation of this receptor in colon cancer cells led to cellular differentiation similar to the effects of butyrate treatment. In accordance with this finding, we found that reduced expression of CysLT2R in colon cancer was associated with poor prognosis. We report the novel finding that CysLT2R signaling leads to terminal differentiation of colon carcinoma cells and growth inhibition, and that its expression is relatively high in less malignant forms of colon cancer. These data suggest that the balance between these two receptors is important for tumor progression and disease outcome.

Mast cells and eicosanoid mediators: a system of reciprocal paracrine and autocrine regulation

When activated by specific antigen, complement, or other transmembrane stimuli, mast cells (MCs) generate three eicosanoids: prostaglandin (PG)D(2), leukotriene (LT)B(4), and LTC(4), the parent molecule of the cysteinyl leukotrienes (cysLTs). These diverse lipid mediators, which are generated from a single cell membrane-associated precursor, arachidonic acid, can initiate, amplify, or dampen inflammatory responses and influence the magnitude, duration, and nature of subsequent immune responses. PGD(2) and cysLTs, which were originally recognized for their bronchoconstricting and vasoactive properties, also serve diverse and pivotal functions in effector cell trafficking, antigen presentation, leukocyte activation, matrix deposition, and fibrosis. LTB(4) is a powerful chemoattractant for neutrophils and certain lymphocyte subsets. Thus, MCs can contribute to each of these processes through eicosanoid generation. Additionally, MCs express G-protein-coupled receptors specific for cysLTs, LTB(4), and another eicosanoid, PGE(2). Each of these receptors can regulate MC functions in vivo by autocrine and paracrine mechanisms. This review focuses on the biologic functions for MC-associated eicosanoids, the regulation of their production, and the mechanisms by which eicosanoids may regulate MC function in host defense and disease.

Alpha2beta1 integrin signalling enhances cyclooxygenase-2 expression in intestinal epithelial cells

Inflammatory bowel diseases (IBD) are linked to an increased risk of developing colon cancer, by inflammatory mediators and alterations to the extracellular matrix (ECM). The events induced by inflammatory mediators lead to dysregulated activation and induction of inflammatory genes such as cyclooxygenase-2 (COX-2). COX-2 is involved in the conversion of arachidonic acid to biologically active prostanoids and is highly upregulated in colon cancer. Since inflammation-induced changes to the extracellular matrix could affect integrin activities, we here investigated the effect of integrin signalling on the level of COX-2 expression in the non-transformed intestinal epithelial cell lines, Int 407 and IEC-6. Adhesion of these cells to a collagen I- or IV-coated surface, increased surface expression of alpha2beta1 integrin. Activation of integrins with collagen caused an increased cox-2 promoter activity, with a subsequent increase in COX-2 expression. The signalling cascade leading to this increased expression and promoter activity of cox-2, involves PKCalpha, the small GTPase Ras and NFkappaB but not Erk1/2 or Src activity. The integrin-induced increase in cellular COX-2 activity is responsible for an elevated generation of reactive oxygen species (ROS) and increased cell migration. This signalling pathway suggests a mechanism whereby inflammation-induced modulations of the ECM, can promote cancer transformation in the intestinal epithelial cells.

Role of 5-lipoxygenase pathway in the regulation of RAW 264.7 macrophage proliferation

Arachidonic acid (AA) metabolites control cell proliferation, among other physiologic functions. RAW 264.7 macrophages can metabolise AA through the cyclooxygenase and lipoxygenase (LOX) pathways. We aimed to study the role of AA-metabolites derived from 5-LOX in the control of RAW 264.7 macrophage growth. Our results show that zileuton, a specific 5-LOX inhibitor, and nordihydroguaiaretic acid (NDGA), a non-specific LOX inhibitor, inhibit cell proliferation and [(3)H]-thymidine incorporation in a concentration-dependent fashion. Growth inhibition induced by NDGA can be explained by an apoptotic process, while zileuton does not seem to induce apoptosis. Moreover, these treatments delay the cell cycle, as analysed by flow cytometry. On the other hand, the leukotriene (LT) B(4) receptor antagonist U-75302, the LTD(4) receptor antagonists LY-171883 and MK-571, and the cysteinyl-LT receptor antagonist REV-5901 also inhibit cell proliferation and [(3)H]-thymidine incorporation in a concentration-dependent manner, and delay the RAW 264.7 cell cycle. However, these antagonists did not induce annexin V staining, caspase activation or DNA fragmentation. Furthermore, we demonstrated that exogenous addition of LTB(4) or LTD(4) revert the cell growth inhibition induced by zileuton or the leukotriene receptor antagonists mentioned above. Finally, we observed that LTB(4) and LTD(4), in the absence of growth factors, have pro-proliferative effects on macrophages, and we obtained preliminary evidences that this effect could be through mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways. In conclusion, our results show that the interaction between LTB(4) and LTD(4) with its respective receptor is involved in the control of RAW 264.7 macrophage growth.

Endogenous production of leukotriene D4 mediates autocrine survival and proliferation via CysLT1 receptor signalling in intestinal epithelial cells

The cysteinyl leukotriene1 (CysLT1) receptor (CysLT1R) enhances survival and proliferation of intestinal cells via distinct pathways. Here, we have demonstrated that there is significant endogenous production of CysLTs from both non-tumour- and tumour-derived intestinal epithelial cells. Treatment of two non-tumour cell lines, Int 407 and IEC-6, with CysLT1R antagonists led to shrinkage and detachment of cells, confirmed as apoptotic cell death, and a dose-dependent reduction in proliferation. However, in the tumour intestinal cell lines Caco-2, SW480, HCT-116 and HT-29, treatment with CysLT1R antagonists significantly reduced proliferation, but had no effect on apoptosis. A unique characteristic of intestinal cancer cells is the presence of nuclear CysLT1Rs, which are inaccessible to receptor antagonists. In these cells, inhibition of the endogenous production of CysLTs indirectly, by 5-lipoxygenase inhibition, impaired CysLT1R signalling throughout the cell, and resulted in apoptosis of the tumour cells. These data reveal the existence of constitutive CysLT1R signalling that mediates both survival and proliferation in intestinal cells. Importantly, we propose that tumour-derived intestinal cells are resistant to CysLT1R antagonist-induced apoptosis, a phenomena that could be explained by nuclear CysLT1R signalling.

The inflammatory mediator leukotriene D4 induces beta-catenin signaling and its association with antiapoptotic Bcl-2 in intestinal epithelial cells

Increased levels of the inflammatory mediator leukotriene D4 (LTD4) are present at sites of inflammatory bowel disease, and such areas also exhibit an increased risk for subsequent cancer development. It is known that LTD4 affects the expression of many proteins that influence survival and proliferation of intestinal epithelial cells. We demonstrate here that after LTD4 exposure, beta-catenin translocates to the nucleus where it signals activation of the TCF/LEF family of transcription factors. These events are mediated via a phosphatidylinositol 3-kinase-dependent phosphorylation of the inhibitory Ser-9 residue of glycogen synthase kinase 3beta. We also show that in the presence of LTD4, free beta-catenin translocates to the mitochondria where it associates with the cell survival protein Bcl-2. We hypothesize that LTD4 may enhance cell survival via activation of beta-catenin signaling, in particular, by promoting the association of beta-catenin with Bcl-2 in the mitochondria. Similar to Wnt-1 signaling, LTD4 signals an increased level of free beta-catenin and elevated TCF/LEF promotor activity. This work in intestinal epithelial cells further lends credence to the idea that inflammatory signaling pathways are intrinsically linked with potential oncogenic signals involved in cell survival and apoptosis.

Pro-inflammatory mediator leukotriene D4 induces transcriptional activity of potentially oncogenic genes

The inflammatory mediator LTD4 (leukotriene D4) is present at high levels in many inflammatory conditions, and areas of chronic inflammation have an increased risk for subsequent cancer development. We demonstrate here that following LTD4 stimulation, β-catenin is translocated to the nucleus, triggering the transcriptional activity of the TCF (T-cell factor)/LEF (lymphoid enhancer factor) family of transcription factors. These events are dependent on phosphoinositide-3 kinase activation and glycogen synthase kinase inhibition. Our data suggest that, similar to Wnt signalling, LTD4 increases free β-catenin and targets it to the nucleus.

Activation of cPLA 2 is required for leukotriene D 4 -induced proliferation in colon cancer cells

It is well documented that prolonged inflammatory conditions, particularly those relating to the colon, have been shown to induce cancer. We have previously demonstrated that the pro-inflammatory mediator leukotriene D(4) (LTD(4)) induces survival and proliferation in intestinal cells and that its receptor, CysLT(1), is upregulated in human colon cancer tissue. Here we demonstrate, for the first time that in both Int 407 (a non-transformed human intestinal epithelial cell line) and Caco-2 cells (a human colorectal carcinoma cell line), cytosolic phospholipase A(2)alpha (cPLA(2)alpha) is activated and translocates to the nucleus upon LTD(4) stimulation via a calcium-dependent mechanism that involves activation of protein kinase C (PKC), and the mitogen-activated protein kinases ERK1/2 and p38. We also show with a cPLA(2)alpha promoter luciferase assay, that LTD(4) induces an increase in the transcriptional activity of cPLA(2)alpha via activation of cPLA(2)alpha and the transcription factor NFkappaB. Interestingly we demonstrate here that both the basal and the LTD(4)-induced cPLA(2)alpha activity is elevated approximately 3-fold in Caco-2 colon cancer cells compared with Int 407 cells. The difference in basal activity was confirmed in human colon tumor samples by the finding of a similar increase in cPLA(2)alpha activity when compared with normal colon tissue. A functional role of the increased cPLA(2)alpha activity in tumor cells was revealed by our findings that inhibition of this enzyme reduced both basal and LTD(4)-induced proliferation, the effects being most pronounced in Caco-2 tumor cells. The present data reveal that cPLA(2)alpha, an important intracellular signal activated by inflammatory mediators, is an important regulator of colon tumor growth.

A Novel Localization of the G-Protein-Coupled CysLT1 Receptor in the Nucleus of Colorectal Adenocarcinoma Cells

Searching for a link between inflammation and colon cancer, we have found that the inflammatory mediator leukotriene D4 (LTD4), via its receptor CysLT1, induces cyclooxygenase-2 expression, survival, and proliferation in intestinal epithelial cells. In conjunction with our previous observation that CysLT1 receptor expression is increased in colorectal adenocarcinomas, we here found an increased nuclear localization of the CysLT1 receptor in colorectal adenocarcinomas. This novel discovery of CysLT1 receptors in the nucleus was further analyzed. It was found to be located in the outer nuclear membrane in colon cancer cells and in the nontransformed epithelial cell line Int 407 cells by Western blot and electron microscopy. Cancer cells displayed higher amounts of the nuclear CysLT1 receptor, but prolonged LTD4 exposure induced its nuclear translocation in nontransformed cells. Truncation of a nuclear localization sequence abrogated this translocation as well as the LTD4-induced proliferative response. In accordance, nuclear CysLT1 receptors exhibited proliferative extracellular signal-regulated kinase 1/2 signaling. The significance of these experimental findings is supported by the observed correlation between the proliferative marker Ki-67 and nuclear CysLT1 receptor localization in colorectal adenocarcinomas. The present findings indicate that LTD4 cannot only be synthesized but also signal proliferation through nuclear CysLT1 receptors, stressing the importance of leukotrienes in inflammation-induced colon carcinogenesis.

The pro-inflammatory mediator leukotriene D4 induces phosphatidylinositol 3-kinase and Rac-dependent migration of intestinal epithelial cells

Inflammatory bowel diseases are associated with increased risk of developing colon cancer. A possible role of the pro-inflammatory leukotriene D4 (LTD4) in this process has been implicated by the findings that LTD4 can signal increased proliferation and survival, both hallmarks of a cancer cell, in non-transformed intestinal epithelial cells. Here we make the novel finding that LTD4 can also signal increased motility in these cells. In parallel, we found that LTD4 induced a simultaneous transient 10-fold increase in Rac but not Cdc42 activity. These data were also supported by the ability of LTD4 to activate the Rac GDP/GTP exchange factor Vav2. Further, LTD4 triggered a 3-fold transient increase in phosphatidylinositol 3-kinase (PI3K) phosphorylation, a possible upstream activator of the Vav2/Rac signaling pathway. The activation of Rac was blocked by the PI3K inhibitors LY294002 and wortmannin and by transfection of a kinase-negative mutant of PI3K or a dominant-negative form of Vav2. Furthermore, Rac was found to co-localize with actin in LTD4-generated membrane ruffles that were formed by a PI3K-dependent mechanism. In accordance, the inhibition of the PI3K and Rac signaling pathway also blocked the LTD4-induced migration of the intestinal cells. The present data reveal that an inflammatory mediator such as LTD4 cannot only increase proliferation and survival of non-transformed intestinal epithelial cells but also, via a PI3K/Rac signaling pathway, trigger a motile response in such cells. These data demonstrate the capacity of inflammatory mediators to participate in the process by which inflammatory bowel conditions increase the risk for colon cancer development.

Leukotriene D4 activates distinct G-proteins in intestinal epithelial cells to regulate stress fibre formation and to generate intracellular Ca2+ mobilisation and ERK1/2 activation

We have shown that the pro-inflammatory mediator LTD4, via its G-protein-coupled receptor CysLT1, signals through both pertussis-toxin-sensitive and -insensitive G-proteins to induce various cellular responses. To further characterise the initial step of the different signalling pathways emanating from the CysLT1 receptor, we transfected intestinal epithelial cells, Int 407, with different mini vectors that each express a specific inhibitory peptide directed against a unique alpha subunit of a specific heterotrimeric G-protein. Our results revealed that LTD4-induced stress fibre formation is inhibited approximately 80% by a vector expressing an inhibitory peptide against the pertussis-toxin-insensitive Galpha12-protein in intestinal epithelial Int 407 cells. Control experiments revealed that the LPA-induced stress fibre formation, mediated via the Galpha12-protein in other cell types, was blocked by the same peptide in intestinal Int 407 cells. Furthermore, the CysLT1-receptor-mediated calcium signal and activation of the proliferative ERK1/2 kinase are blocked in cells transfected with a vector expressing an inhibitory peptide against the Galphai3-protein, whereas in cells transfected with an empty ECFP-vector or vectors expressing inhibitory peptides against the Galphai1-2-, Galpha12-, GalphaR-proteins these signals are not significantly affected. Consequently, the CysLT1 receptor has the capacity to activate at least two distinctly different heterotrimeric G-proteins that transduce activation of unique downstream cellular events.