Regulation of leukotriene-dependent induction of cyclooxygenase-2 and Bcl-2

Cysteinyl Leukotriene Receptor Antagonism by Montelukast to Treat Visual Deficits

Montelukast, a Food and Drug Administration-approved drug for asthma and allergic rhinitis modulates leukotriene (LT) receptors and serves as a critical anti-inflammatory agent. Recent research suggests that the LT signaling pathway targeted by montelukast has broader implications for diseases such as fibrosis, cardiovascular diseases, cancer, cerebrovascular disease, and immune defense. This expanded understanding highlights montelukast's potential for repurposing in conditions involving aberrant stress mechanisms, including ocular diseases marked by inflammation, oxidative stress, ER stress, and apoptosis, among several others. This review delves into montelukast's therapeutic mechanisms across various diseases, draws parallels to ocular conditions, and examines clinical trials and associated adverse effects to underscore the unmet need for cysteinyl LT receptor antagonism by montelukast as an effective therapy for visual deficits.

Potential of Anti-Leukotriene Drugs as New Therapeutic Agents for Inhibiting Cholangiocarcinoma Progression

Cholangiocarcinoma (CCA) is a cancer with a poor prognosis due to difficulties in diagnosis and limited treatment options, highlighting the urgent need for new targeted therapies. In a clinical setting, we found that leukotriene levels in bile were higher than in serum. Immunohistochemical analysis of surgically resected samples also revealed that CysLT receptor 1 (CysLTR1) was more highly expressed in CCA than in normal bile duct tissue, prompting us to investigate leukotriene as a potential therapeutic target in CCA. In vitro studies using CCA cell lines expressing CysLTR1 showed that leukotriene D4, a major ligand of CysLTR1, promoted cell proliferation, with increased phosphorylation of AKT and extracellular signal-regulated kinase 1/2 (ERK1/2). Additionally, treatment with two clinically available anti-allergic drugs-zileuton, an inhibitor of CysLT formation, and montelukast, a CysLTR1 inhibitor-had inhibitory effects on cell proliferation and migratory capacity, accompanied by the reduced phosphorylation of AKT and ERK1/2. Furthermore, the simultaneous administration of both drugs synergistically enhanced the inhibitory effect on cell proliferation. Our study suggests that use of these drugs may represent a novel approach to treat CCA through drug repositioning.

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.

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.

Focus on cutaneous and uveal melanoma specificities

Cutaneous melanoma (CM) and uveal melanoma (UM) derive from cutaneous and uveal melanocytes that share the same embryonic origin and display the same cellular function. However, the etiopathogenesis and biological behaviors of these melanomas are very different. CM and UM display distinct landscapes of genetic alterations and show different metastatic routes and tropisms. Hence, therapeutic improvements achieved in the last few years for the treatment of CM have failed to ameliorate the clinical outcomes of patients with UM. The scope of this review is to discuss the differences in tumorigenic processes (etiologic factors and genetic alterations) and tumor biology (gene expression and signaling pathways) between CM and UM. We develop hypotheses to explain these differences, which might provide important clues for research avenues and the identification of actionable vulnerabilities suitable for the development of new therapeutic strategies for metastatic UM.

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.

Assessment of Cyclooxygenase-2 Expression in Canine Hemangiosarcoma, Histiocytic Sarcoma, and Mast Cell Tumor

To determine whether cyclooxygenase-2 (COX-2) is expressed in canine hemangiosarcoma (HsA), histiocytic sarcoma (Hs), and grade-II mast cell tumor (MCT), we performed immunohistochemistry using COX-2 antibodies in the aforementioned tumors. Twenty cases of each tumor type were selected initially from the Laboratory of Pathology archives of cases submitted through the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania. Immunohistochemistry was performed, using a polyclonal antiprostaglandin endoperoxide synthase immunoglobulin G COX-2 antibody. Sections from the kidneys of young dogs, in which the macula densa stains positive for COX-2, served as positive controls. Slides were reviewed by a single pathologist (M. H. Goldschmidt) and graded for COX-2 expression according to previously established scales.18 Descriptive data is given for each tumor type. COX-2 expression was identified in 0 of 19 HSA, 1 of 20 HS, and 1 of 17 grade-II MCT. Although COX-2 has been shown to be overexpressed in selected human sarcomas and hematopoeitic tumors, these results indicate that canine HSA, HS, and MCT do not express COX-2 in any appreciable fashion.

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.

Functional interaction between acyl-CoA synthetase 4, lipooxygenases and cyclooxygenase-2 in the aggressive phenotype of breast cancer cells

The acyl-CoA synthetase 4 (ACSL4) is increased in breast cancer, colon and hepatocellular carcinoma. ACSL4 mainly esterifies arachidonic acid (AA) into arachidonoyl-CoA, reducing free AA intracellular levels, which is in contradiction with the need for AA metabolites in tumorigenesis. Therefore, the causal role of ACSL4 is still not established. This study was undertaken to determine the role of ACSL4 in AA metabolic pathway in breast cancer cells. The first novel finding is that ACSL4 regulates the expression of cyclooxygenase-2 (COX-2) and the production of prostaglandin in MDA-MB-231 cells. We also found that ACSL4 is significantly up-regulated in the highly aggressive MDA-MB-231 breast cancer cells. In terms of its overexpression and inhibition, ACSL4 plays a causal role in the control of the aggressive phenotype. These results were confirmed by the increase in the aggressive behaviour of MCF-7 cells stably transfected with a Tet-off ACSL4 vector. Concomitantly, another significant finding was that intramitochondrial AA levels are significantly higher in the aggressive cells. Thus, the esterification of AA by ACSL4 compartmentalizes the release of AA in mitochondria, a mechanism that serves to drive the specific lipooxygenase metabolization of the fatty acid. To our knowledge, this is the first report that ACSL4 expression controls both lipooxygenase and cyclooxygenase metabolism of AA. Thus, this functional interaction represents an integrated system that regulates the proliferating and metastatic potential of cancer cells. Therefore, the development of combinatory therapies that profit from the ACSL4, lipooxygenase and COX-2 synergistic action may allow for lower medication doses and avoidance of side effects.

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.

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.

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.

Up-regulation of prostaglandin biosynthesis by leukotriene C4in elicited mice peritoneal macrophages activated with lipopolysaccharide/interferon-γ

Leukotrienes (LT) and prostaglandins (PG) are proinflammatory mediators generated by the conversion of arachidonic acid via 5-lipoxygenase (5-LO) and cyclooxygenase (COX) pathways. It has long been proposed that the inhibition of the 5-LO could enhance the COX pathway leading to an increased PG generation. We have found that in in vitro models of inflammation, such as mice-elicited peritoneal macrophages activated with lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma), the deletion of the gene encoding for 5-LO or the enzyme activity inhibition corresponded to a negative modulation of the COX pathway. Moreover, exogenously added LTC(4), but not LTD(4), LTE(4), and LTB(4), was able to increase PG production in stimulated cells from 5-LO wild-type and knockout mice. LTC(4) was not able to induce COX-2 expression by itself but rather potentiated the action of LPS/IFN-gamma through the extracellular signal-regulated kinase-1/2 activation, as demonstrated by the use of a specific mitogen-activated protein kinase (MAPK) kinase inhibitor. The LT-induced increase in PG generation, as well as MAPK activation, was dependent by a specific ligand-receptor interaction, as demonstrated by the use of a cys-LT1 receptor antagonist, although also a direct action of the antagonist used, on PG generation, cannot be excluded. Thus, the balance between COX and 5-LO metabolites could be of great importance in controlling macrophage functions and consequently, inflammation and tumor promotion.

Cysteinyl leukotrienes are secretagogues in atrophic coeliac and in normal duodenal mucosa of children

OBJECTIVE

The pathophysiology of intestinal inflammation and diarrhoea is complex and involves the arachidonic acid cascade. Prostaglandins induce chloride secretion in healthy subjects and in patients with coeliac disease. Leukotrienes (LTs) are also known inflammatory mediators which have been shown to stimulate ion secretion in ileum and colon of rats and rabbits. The aim of this study was to determine the effects of leukotrienes C(4) (LTC(4)) and D(4) (LTD(4)) in normal and atrophic intestinal mucosa in children.

MATERIAL AND METHODS

Routine paediatric intestinal biopsies were obtained from 109 children. Sixty-seven control biopsies and 42 biopsies from children with different stages of coeliac disease were mounted in a modified Ussing chamber. Potential difference (Pd) was measured continuously and tissue resistance (R(t)) and the generated current (I(m)) were calculated.

RESULTS

In morphologically normal mucosa of duodenum, LTC(4) and LTD(4) increased Pd and I(m) in a dose-dependent manner. The increase was more pronounced in the distal than in the proximal part, similar to the response to prostaglandin E(2). The induced current was chloride-mediated, since replacement of Cl(-) with SO(4)(2-) in the bathing solution eliminated the response to the LTs. The LTC(4)-induced secretion was significantly decreased in atrophic mucosa, but the response was partially restored after preincubation with the cyclooxygenase inhibitor indomethacin.

CONCLUSIONS

The results showed that LTC(4) and LTD(4) are secretagogues in the duodenal mucosa from healthy children by inducing a net chloride secretion. Restoration of the response in coeliac disease by cyclooxygenase inhibition suggests interactions between the different pathways of the arachidonic cascade in the intestinal mucosa.

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.

Selective inhibitors of MEK1/ERK44/42 and p38 mitogen-activated protein kinases potentiate apoptosis induction by sulindac sulfide in human colon carcinoma cells

The nonsteroidal anti-inflammatory drug (NSAID) sulindac prevents experimental colon cancer and can regress precancerous polyps in humans. Sulindac sulfide inhibits cyclooxygenase (COX)-mediated prostaglandin synthesis and retards the growth of cultured colon cell lines primarily by inducing apoptosis. Given the known role of mitogen-activated protein kinase (MAPK) in signal transduction and the regulation of cell survival and death, we determined the effect of sulindac sulfide on MAPK activation, COX-2 expression, and apoptosis induction in HCA-7 human colon cancer cells. Sulindac sulfide treatment was associated with activation of ERKp44/42 and p38 MAPK in a dosage- and time-dependent manner, and also activated upstream MEK. Similar results were seen in HCT-15 cells and also with the selective COX-2 inhibitor NS398. ERKp44/42 and p38 activation were accompanied by an induction of COX-2 protein expression. Selective inhibitors of sulindac sulfide–induced ERKp44/42 (PD98059) and p38 MAPK (SB203580) activation also suppressed the induction of COX-2 by this NSAID. Furthermore, both MAPK inhibitors significantly augmented sulindac sulfide–induced apoptosis, as did suppression of constitutive COX-2 using antisense oligonucleotides. In conclusion, MEK/ERK and p38 MAPK activation mediate COX-2 induction by sulindac sulfide. Selective inhibitors of these MAPKs potentiate apoptosis induction by this NSAID, suggesting a novel strategy for the prevention or treatment of colorectal cancer.

The quest for new cysteinyl-leukotriene and lipoxin receptors: recent clues

The metabolism of arachidonic acid via the 5-lipoxygenase enzymatic pathway leads to the formation of the cysteinyl-leukotrienes and lipoxins, which have been implicated in several inflammatory reactions. While these lipid mediators are responsible for a variety of effects, their actions occur through the activation of 3 specific types of cloned receptors (i.e., CysLT(1), CysLT(2), and ALX). Although receptor activation can explain several biological actions associated with the mediators, there is some evidence to suggest that not all responses fit the well-known characteristics of these cloned receptors. Other receptor subtypes may also exist. Interestingly, the indirect evidence for support of this observation is principally derived from work performed on either blood elements and/or vascular smooth muscle. Because the initiating events associated with inflammation are essentially of vascular origin, further work at the molecular level may be necessary to confirm the data, which do not fit the well-known CysLT and ALX receptor profiles.

Significance of COX-2 expression in human renal cell carcinoma cell lines

Accumulating evidences indicate that cyclooxygenase (COX)-2 plays an important role in tumorigenesis in many human cancers. Yet the relationship between COX-2 and human renal cell carcinoma (RCC) remains unclear. The aim of our study was to evaluate COX-2 expression in human RCC cell lines and its role in tumorigenesis of human RCC. Among the human RCC cell lines (SMKT-R4, OS-RC-2, ACHN) and normal renal cell line RPTEC, COX-2 overexpression was found in OS-RC-2 cells both at mRNA and protein levels. COX-2 sense- and antisense-orientated vectors were constructed and transferred into RCC cells. Significant suppression of cellular proliferation was demonstrated in OS-RC-2 antisense transfectants, whereas promotion was found in SMKT-R4 sense transfectants by colony-forming assay despite the observation that COX-2 specific inhibitor NS398 exhibited similar IC50 among RCC cell lines by MTT assay. In comparison with parent cells and sense transfectants, significant suppression of COX-2 expression and PGE2 production and increase in butyrate-induced apoptosis were observed in OS-RC-2 antisense transfectants by Western blot, ELISA assay and FACS analysis, respectively. Furthermore, tumor growth and angiogenesis of OS-RC-2 antisense transfectants in nude mice was significantly suppressed and the survival time of these mice was significantly prolonged. Our study demonstrates that COX-2 is overexpressed in OS-RC-2 RCC cell line and plays an important role in tumorigenesis of the cells in vivo, which implies that COX-2 may be a therapeutic target for COX-2-expressing RCC, and that suppression of COX-2 expression by antisense-based strategy may have potential utility in treatment of COX-2-expressing RCC.

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

We demonstrated previously that leukotriene D4 (LTD4) regulates proliferation of intestinal epithelial cells through a CysLT receptor by protein kinase C (PKC)epsilon-dependent stimulation of the mitogen-activated protein kinase ERK1/2. Our current study provides the first evidence that LTD4 can activate 90-kDa ribosomal S6 kinase (p90RSK) and cAMP-responsive element-binding protein (CREB) via pertussis-toxin-sensitive Gi protein pathways. Transfection and inhibitor experiments revealed that activation of p90RSK, but not CREB, is a PKCepsilon/Raf-1/ERK1/2-dependent process. LTD4-mediated CREB activation was not affected by expression of kinase-dead p90RSK but was abolished by transfection with the regulatory domain of PKCalpha (a specific dominant-inhibitor of PKCalpha). Kinase-negative mutants of p90RSK and CREB (K-p90RSK and K-CREB) blocked the LTD4-induced increase in cell number and DNA synthesis (thymidine incorporation). Compatible with these results, flow cytometry showed that LTD4 caused transition from the G0/G1 to the S+G2/M cell cycle phase, indicating increased proliferation. Similar treatment of cells transfected with K-p90RSK resulted in cell cycle arrest in the G0/G1 phase, consistent with a role of p90RSK in LTD4-induced proliferation. On the other hand, expression of K-CREB caused a substantial buildup in the sub-G0/G1 phase, suggesting a role for CREB in mediating LTD4-mediated survival in intestinal epithelial cells. Our results show that LTD4 regulates proliferation and survival via distinct intracellular signaling pathways in intestinal epithelial cells.