Alternate COX-2 transcripts are differentially regulated: implications for post-transcriptional control

Intestinal Explant Cultures from Gilthead Seabream (Sparus aurata, L.) Allowed the Determination of Mucosal Sensitivity to Bacterial Pathogens and the Impact of a Plant Protein Diet

The interaction between diet and intestinal health has been widely discussed, although in vivo approaches have reported limitations. The intestine explant culture system developed provides an advantage since it reduces the number of experimental fish and increases the time of incubation compared to similar methods, becoming a valuable tool in the study of the interactions between pathogenic bacteria, rearing conditions, or dietary components and fish gut immune response. The objective of this study was to determine the influence of the total substitution of fish meal by plants on the immune intestinal status of seabream using an ex vivo bacterial challenge. For this aim, two growth stages of fish were assayed (12 g): phase I (90 days), up to 68 g, and phase II (305 days), up to 250 g. Additionally, in phase II, the effects of long term and short term exposure (15 days) to a plant protein (PP) diet were determined. PP diet altered the mucosal immune homeostasis, the younger fish being more sensitive, and the intestine from fish fed short-term plant diets showed a higher immune response than with long-term feeding. Vibrio alginolyticus (V. alginolyticus) triggered the highest immune and inflammatory response, while COX-2 expression was significantly induced by Photobacterium damselae subsp. Piscicida (P. damselae subsp. Piscicida), showing a positive high correlation between the pro-inflammatory genes encoding interleukin 1β (IL1-β), interleukin 6 (IL-6) and cyclooxygenase 2(COX-2).

Glucocorticoid-transactivated TSC22D3 attenuates hypoxia- and diabetes-induced Müller glial galectin-1 expression via HIF-1α destabilization

Galectin‐1/LGALS1, a newly recognized angiogenic factor, contributes to the pathogenesis of diabetic retinopathy (DR). Recently, we demonstrated that glucocorticoids suppressed an interleukin‐1β‐driven inflammatory pathway for galectin‐1 expression in vitro and in vivo. Here, we show glucocorticoid‐mediated inhibitory mechanism against hypoxia‐inducible factor (HIF)‐1α‐involved galectin‐1 expression in human Müller glial cells and the retina of diabetic mice. Hypoxia‐induced increases in galectin‐1/LGALS1 expression and promoter activity were attenuated by dexamethasone and triamcinolone acetonide in vitro. Glucocorticoid application to hypoxia‐stimulated cells decreased HIF‐1α protein, but not mRNA, together with its DNA‐binding activity, while transactivating TSC22 domain family member (TSC22D)3 mRNA and protein expression. Co‐immunoprecipitation revealed that glucocorticoid‐transactivated TSC22D3 interacted with HIF‐1α, leading to degradation of hypoxia‐stabilized HIF‐1α via the ubiquitin‐proteasome pathway. Silencing TSC22D3 reversed glucocorticoid‐mediated ubiquitination of HIF‐1α and subsequent down‐regulation of HIF‐1α and galectin‐1/LGALS1 levels. Glucocorticoid treatment to mice significantly alleviated diabetes‐induced retinal HIF‐1α and galectin‐1/Lgals1 levels, while increasing TSC22D3 expression. Fibrovascular tissues from patients with proliferative DR demonstrated co‐localization of galectin‐1 and HIF‐1α in glial cells partially positive for TSC22D3. These results indicate that glucocorticoid‐transactivated TSC22D3 attenuates hypoxia‐ and diabetes‐induced retinal glial galectin‐1/LGALS1 expression via HIF‐1α destabilization, highlighting therapeutic implications for DR in the era of anti‐vascular endothelial growth factor treatment.

Cyclooxygenase 2: its regulation, role and impact in airway inflammation

Cyclooxygenase 2 (COX-2: official gene symbol - PTGS2) has long been regarded as playing a pivotal role in the pathogenesis of airway inflammation in respiratory diseases including asthma. COX-2 can be rapidly and robustly expressed in response to a diverse range of pro-inflammatory cytokines and mediators. Thus, increased levels of COX-2 protein and prostanoid metabolites serve as key contributors to pathobiology in respiratory diseases typified by dysregulated inflammation. But COX-2 products may not be all bad: prostanoids can exert anti-inflammatory/bronchoprotective functions in airways in addition to their pro-inflammatory actions. Herein, we outline COX-2 regulation and review the diverse stimuli known to induce COX-2 in the context of airway inflammation. We discuss some of the positive and negative effects that COX-2/prostanoids can exert in in vitro and in vivo models of airway inflammation, and suggest that inhibiting COX-2 expression to repress airway inflammation may be too blunt an approach; because although it might reduce the unwanted effects of COX-2 activation, it may also negate the positive effects. Evidence suggests that prostanoids produced via COX-2 upregulation show diverse actions (and herein we focus on prostaglandin E2 as a key example); these can be either beneficial or deleterious and their impact on respiratory disease can be dictated by local concentration and specific interaction with individual receptors. We propose that understanding the regulation of COX-2 expression and associated receptor-mediated functional outcomes may reveal number of critical steps amenable to pharmacological intervention. These may prove invaluable in our quest towards future development of novel anti-inflammatory pharmacotherapeutic strategies for the treatment of airway diseases.

Regulation of COX-2 expression by miR-146a in lung cancer cells

Prostaglandins are a class of molecules that mediate cellular inflammatory responses and control cell growth. The oxidative conversion of arachidonic acid to prostaglandin H2 is carried out by two isozymes of cyclooxygenase, COX-1 and COX-2. COX-1 is constitutively expressed, while COX-2 can be transiently induced by external stimuli, such as pro-inflammatory cytokines. Interestingly, COX-2 is overexpressed in numerous cancers, including lung cancer. MicroRNAs (miRNAs) are small RNA molecules that function to regulate gene expression. Previous studies have implicated an important role for miRNAs in human cancer. We demonstrate here that miR-146a expression levels are significantly lower in lung cancer cells as compared with normal lung cells. Conversely, lung cancer cells have higher levels of COX-2 protein and mRNA expression. Introduction of miR-146a can specifically ablate COX-2 protein and the biological activity of COX-2 as measured by prostaglandin production. The regulation of COX-2 by miR-146a is mediated through a single miRNA-binding site present in the 3' UTR. Therefore, we propose that decreased miR-146a expression contributes to the up-regulation and overexpression of COX-2 in lung cancer cells. Since potential miRNA-mediated regulation is a functional consequence of alternative polyadenylation site choice, understanding the molecular mechanisms that regulate COX-2 mRNA alternative polyadenylation and miRNA targeting will give us key insights into how COX-2 expression is involved in the development of a metastatic condition.

Targeting COX-2 expression by natural compounds: a promising alternative strategy to synthetic COX-2 inhibitors for cancer chemoprevention and therapy

Cyclooxygenase (COX)-2 is a pro-inflammatory immediate early response protein, chronically up-regulated in many pathological conditions. In autoimmune diseases, it is responsible for degenerative effects whereas in cancer, it correlates with poor prognosis. A constitutive expression of COX-2 is triggered since the earliest steps of carcinogenesis. Consequently, strategies aimed at inhibiting COX-2 enzymatic activity have been clinically applied for the treatment of autoimmune disorders; in addition, the same approaches are currently investigated for anti-cancer purposes. However, COX-2 protein inhibitors (i.e., NSAIDs and COXIBs) are not amenable to prolonged administration since they may cause severe side effects, and efforts are underway to identify alternative approaches for chemoprevention/therapy. COX-2 expression is a multi-step process, highly regulated at transcriptional and post-transcriptional levels. Defects in the modulation of one or both of these steps may be found in pathological conditions. Targeting COX-2 expression may therefore represent a promising strategy, by which the same preventive and therapeutic benefits may be gained while avoiding the severe side effects of COX-2 enzymatic inhibition. Naturally occurring compounds derived from plants/organisms represent a huge source of biologically active molecules, that remains largely unexplored. Derived from plants/organisms used in traditional forms of medicine or as dietary supplements, these compounds have been experimentally investigated for their anti-inflammatory and anti-cancer potential. In this review, we will analyze how natural compounds may modulate the multistep regulation of COX-2 gene expression and discuss their potential as a new generation of COX-2 targeting agents alternative to the synthetic COX-2 inhibitors.

Prostaglandin pathway gene therapy for sustained reduction of intraocular pressure

Cyclooxygenase-2 (COX-2) is a rate-limiting enzyme in prostaglandin (PG) biosynthesis. In the eye, loss of COX-2 expression in aqueous humor-secreting cells has been associated with primary open-angle glaucoma (POAG). Reduction of intraocular pressure (IOP) is the main treatment goal in this disease. We used lentiviral vectors to stably express COX-2 and other PG biosynthesis and response transgenes in the ciliary body epithelium and trabecular meshwork (TM), the ocular suborgans that produce aqueous humor and regulate its outflow, respectively. We show that robust ectopic COX-2 expression and PG production require COX-2 complementary DNA (cDNA) sequence optimization. When COX-2 expression was coupled with a similarly optimized synthetic PGF2alpha receptor transgene to enable downstream signaling, gene therapy produced substantial and sustained reductions in IOP in a large animal model, the domestic cat. This study provides the first gene therapy for correcting the main cause of glaucoma.

The p38 MAPK pathway inhibits tristetraprolin-directed decay of interleukin-10 and pro-inflammatory mediator mRNAs in murine macrophages

p38 mitogen-activated protein kinase (MAPK) stabilises pro-inflammatory mediator mRNAs by inhibiting AU-rich element (ARE)-mediated decay. We show that in bone-marrow derived murine macrophages tristetraprolin (TTP) is necessary for the p38 MAPK-sensitive decay of several pro-inflammatory mRNAs, including cyclooxygenase-2 and the novel targets interleukin (IL)-6, and IL-1alpha. TTP(-/-) macrophages also strongly overexpress IL-10, an anti-inflammatory cytokine that constrains the production of the IL-6 despite its disregulation at the post-transcriptional level. TTP directly controls IL-10 mRNA stability, which is increased and insensitive to inhibition of p38 MAPK in TTP(-/-) macrophages. Furthermore, TTP enhances deadenylation of an IL-10 3'-untranslated region RNA in vitro.

Chemosensitization of B-cell lymphomas by methylseleninic acid involves nuclear factor-kappaB inhibition and the rapid generation of other selenium species

Although recent reports suggest that selenium can modulate the activity of cytotoxic drugs, the mechanism underlying this activity remains unclear. This has been investigated using a panel of human B-cell lymphoma cell lines. The cytotoxic effects of chemotherapeutic agents (e.g., doxorubicin, etoposide, 4-hydroperoxycyclophosphamide, melphalan, and 1-beta-d-arabinofuranosylcytosine) were increased by up to 2.5-fold when combined with minimally toxic concentrations (EC(5-10)) of the organic selenium compound, methylseleninic acid (MSA). DNA strand breaks were identified using comet assays, but the measured genotoxic activity of the combinations did not explain the observed synergistic effects in cell death. However, minimally toxic (EC(10)) concentrations of MSA induced a 50% decrease in nuclear factor-kappaB (NF-kappaB) activity after an exposure of 5 h, similar to that obtained with the specific NF-kappaB inhibitor, BAY 11-7082. Combinations of BAY 11-7082 with these cytotoxic drugs also resulted in synergism, suggesting that the chemosensitizing activity of MSA is mediated, at least in part, by its effects on NF-kappaB. Basal intracellular selenium concentration was higher in a MSA-sensitive cell line. After exposure to MSA, methylselenocysteine and selenomethionine were identified as the main intracellular species generated. Volatile selenium species, trapped using solid-phase microextraction fibers, were identified as dimethylselenide and dimethyldiselenide. These volatile species are thought to be the most biologically active forms of selenium. Taken together, these results show that the NF-kappaB pathway is one target for MSA underlying the interaction between MSA and chemotherapy. These data encourage the further clinical development of selenium as a potential modulator of cytotoxic drug activity in B-cell lymphomas.

Specific trans-acting proteins interact with auxiliary RNA polyadenylation elements in the COX-2 3'-UTR

Two cyclooxygenase (COX) enzymes, COX-1 and COX-2, are present in human cells. While COX-1 is constitutively expressed, COX-2 is inducible and up-regulated in response to many signals. Since increased transcriptional activity accounts for only part of COX-2 up-regulation, we chose to explore other RNA processing mechanisms in the regulation of this gene. Previously, we showed that COX-2 is regulated by alternative polyadenylation, and that the COX-2 proximal polyadenylation signal contains auxiliary upstream sequence elements (USEs) that are very important in efficient polyadenylation. To explore trans-acting protein factors interacting with these cis-acting RNA elements, we performed pull-down assays with HeLa nuclear extract and biotinylated RNA oligonucleotides representing COX-2 USEs. We identified PSF, p54(nrb), PTB, and U1A as proteins specifically bound to the COX-2 USEs. We further explored their participation in polyadenylation using MS2 phage coat protein-MS2 RNA binding site tethering assays, and found that tethering any of these four proteins to the COX-2 USE mutant RNA can compensate for these cis-acting elements. Finally, we suggest that these proteins (p54(nrb), PTB, PSF, and U1A) may interact as a complex since immunoprecipitations of the transfected MS2 fusion proteins coprecipitate the other proteins.

cPGES/p23 is required for glucocorticoid receptor function and embryonic growth but not prostaglandin E2 synthesis

A number of studies have identified cytosolic prostaglandin E(2) synthase (cPGES)/p23 as a cytoplasmic protein capable of metabolism of prostaglandin E(2) (PGE(2)) from the cyclooxygenase metabolite prostaglandin endoperoxide (PGH(2)). However, this protein has also been implicated in a number of other pathways, including stabilization of the glucocorticoid receptor (GR) complex. To define the importance of the functions assigned to this protein, mice lacking detectible cPGES/p23 expression were generated. cPGES/p23(-/-) pups die during the perinatal period and display retarded lung development reminiscent of the phenotype of GR-deficient neonates. Furthermore, GR-sensitive gluconeogenic enzymes are not induced in the prenatal period. However, unlike GR-deficient embryos, cPGES/p23(-/-) embryos are small and a proliferation defect is observed in cPGES/p23(-/-) fibroblasts. Analysis of arachidonic acid metabolites in embryonic tissues and primary fibroblasts failed to support a function for this protein in PGE(2) biosynthesis. Thus, while the growth retardation of the cPGES/p23(-/-) pups and decreased proliferation of primary fibroblasts identify functions for this protein in addition to GR stabilization, it is unlikely that these functions include metabolism of PGH(2) to PGE(2).

Transforming growth factor beta regulates cyclooxygenase-2 in glomerular mesangial cells

This study examines the hypothesis that transforming growth factor beta (TGFbeta) regulates cyclooxygenase-2 (COX-2) and induces prostaglandin E synthase (mPGES-1) in rat mesangial cells. COX-2 expression was determined by Northern blot analysis after treatment with either TGFbeta1 or the selective COX-2 inhibitor, NS398. mPGES-1 expression was determined by real-time polymerase chain reaction. The effect of TGFbeta1 on COX-2 gene transcription was assessed using a luciferase reporter assay, and mRNA stability was also determined. To determine whether TGFbeta1 activates elements of the COX-2 promoter, we performed gel shift analyses to examine activation of activator protein-1 (AP-1) and nuclear factor kappaB (NF-kappaB). Prostaglandin E(2) (PGE(2)) and thromboxane B2 (TxB2) production was assayed by enzyme immunoassay. Finally, the pathophysiological relevance of COX-2 inhibition on the downstream effects of TGFbeta was assessed by examining collagen type I mRNA and net collagen production. COX-2 mRNA and mPGES-1 were induced after treatment with TGFbeta1 for 4 h, and this rise was accompanied by a three-fold increase in PGE(2) production that could be antagonized by selective inhibition of COX-2 with NS398. TGFbeta1 increased transcription by approximately 50% and activated both AP-1 and NF-kappaB. These effects were antagonized by co-treatment with NS398. Treatment with TGFbeta1 also doubled the half-life of COX-2 mRNA. Neither collagen type I mRNA nor net collagen production were altered by co-treatment with NS398. In conclusion, these results indicate that TGFbeta stimulates COX-2 and mPGES-1, with additional effects on transcription and stability of COX-2 mRNA.

Different ratios of eicosapentaenoic and docosahexaenoic omega-3 fatty acids in commercial fish oils differentially alter pro-inflammatory cytokines in peritoneal macrophages from C57BL/6 female mice

The use of fish oil (FO) as a dietary supplement to prevent or reduce the severity of cardiovascular diseases and autoimmune disorders such as rheumatoid arthritis is receiving much attention. Several recent reports indicate that eating fish often or the use of small doses of FO capsules appears to have benefits against cardiovascular diseases. We have reported in the past that diets enriched with FO protect against renal diseases and prolong the life span of autoimmune-prone mice compared to corn oil (CO) diets. However, the optimum ratio of eicosapentaenoic acid (EPA) to docosahexaenoic acid (DHA) in commercially available FOs to reduce the production of various pro-inflammatory cytokines has not been well established. We, therefore, obtained deodorized FO from three sources containing different EPA/DHA contents, fed them to C57BL/6 mice for 8 weeks in a 10% (vol/wt) diet (oil A, 11/10; oil B, 14/9; oil C, 23/14) and compared them with (10%) CO-fed mice as control. TNF-alpha, IL-6 and IL-1beta were measured by enzyme-linked immunosorbent assay in thioglycollate-induced macrophages, 8 and 24 h after lipopolysaccharide treatment. The results showed a significant decrease in TNF-alpha after only 8 h in oil C. After 24 h, TNF-alpha, IL-6 and IL-1beta levels decreased only in mice fed oil C, although nonsignificant decreases were seen in mice fed oil A compared to mice fed CO. The antioxidant enzymes, catalase and glutathione transferase, were higher in kidneys of mice fed oil C compared to mice fed CO. The study suggests that anti-inflammatory activity may vary among different sources of FO due to variations in EPA/DHA content.

Elevated levels of the 64-kDa cleavage stimulatory factor (CstF-64) in lipopolysaccharide-stimulated macrophages influence gene expression and induce alternative poly(A) site selection

Lipopolysaccharide (LPS) activation of murine RAW 264.7 macrophages influences the expression of multiple genes through transcriptional and post-transcriptional mechanisms. We observed a 5-fold increase in CstF-64 expression following LPS treatment of RAW macrophages. The increase in CstF-64 protein was specific in that several other factors involved in 3'-end processing were not affected by LPS stimulation. Activation of RAW macrophages with LPS caused an increase in proximal poly(A) site selection within a reporter mini-gene containing two linked poly(A) sites that occurred concomitant with the increase in CstF-64 expression. Furthermore, forced overexpression of the CstF-64 protein also induced alternative poly(A) site selection on the reporter minigene. Microarray analysis performed on CstF-64 overexpressing RAW macrophages revealed that elevated levels of CstF-64 altered the expression of 51 genes, 14 of which showed similar changes in gene expression with LPS stimulation. Sequence analysis of the 3'-untranslated regions of these 51 genes revealed that over 45% possess multiple putative poly(A) sites. Two of these 51 genes demonstrated alternative polyadenylation under both LPS-stimulating and CstF-64-overexpressing conditions. We concluded that the physiologically increased levels of CstF-64 observed in LPS-stimulated RAW macrophages contribute to the changes in expression and alternative polyadenylation of a number of genes, thus identifying another level of gene regulation that occurs in macrophages activated with LPS.

Induced microsomal PGE synthase-1 is involved in cyclooxygenase-2-dependent PGE2 production in gastric fibroblasts

We have previously shown that the cyclooxygenase (COX)-2/PGE2 pathway plays a key role in VEGF production in gastric fibroblasts. Recent studies have identified three PGE synthase (PGES) isozymes: cytosolic PGES (cPGES) and microsomal PGES (mPGES)-1 and -2, but little is known regarding the expression and roles of these enzymes in gastric fibroblasts. Thus we examined IL-1beta-stimulated mPGES-1 and cPGES mRNA and protein expression in gastric fibroblasts by quantitative PCR and Western blot analysis, respectively, and studied both their relationship to COX-1 and -2 and their roles in PGE2 and VEGF production in vitro. IL-1beta stimulated increases in both COX-2 and mPGES-1 mRNA and protein expression levels. However, COX-2 mRNA and protein expression were more rapidly induced than mPGES-1 mRNA and protein expression. Furthermore, MK-886, a nonselective mPGES-1 inhibitor, failed to inhibit IL-1beta-induced PGE2 release at the 8-h time point, while totally inhibiting PGE2 at the later stage. However, MK-886 did inhibit IL-1beta-stimulated PGES activity in vitro by 86.8%. N-(2-cyclohexyloxy-4-nitrophenyl)-methanesulfonamide (NS-398), a selective COX-2 inhibitor, totally inhibited PGE2 production at both the 8-h and 24-h time points, suggesting that COX-2-dependent PGE2 generation does not depend on mPGES-1 activity at the early stage. In contrast, NS-398 did not inhibit VEGF production at 8 h, and only partially at 24 h, whereas MK-886 totally inhibited VEGF production at each time point. These results suggest that IL-1beta-induced mPGES-1 protein expression preferentially coupled with COX-2 protein at late stages of PGE2 production and that IL-1beta-stimulated VEGF production was totally dependent on membrane-associated proteins involved in eicosanoid and glutathione metabolism (MAPEG) superfamily proteins, which includes mPGES-1, but was partially dependent on the COX-2/PGE2 pathway.

Cyclooxygenase-2 and prostaglandins in articular tissues

OBJECTIVES

To provide an overview on: 1) the expression of cyclooxygenase (COX)-2 in articular tissues; 2) the role of prostaglandin E2 (PGE2) in these tissue functions; and 3) clinical trials with COX-2-selective nonsteroidal anti-inflammatory drugs (NSAIDs) (coxibs).

METHODS

MEDLINE search was performed using the key words "cyclooxygenase," "prostaglandin," "osteoarthritis" (OA), and "rheumatoid arthritis" (RA). Selected publications related to clinical trials with coxibs also are included.

RESULTS

COX-2 is upregulated in inflamed joint tissues and is responsible for elevated PGE2 production. The overexpression of COX-2 is likely induced by proinflammatory mediators such as interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF) alpha. However, the exact molecular mechanisms through which the expression of COX-2 is regulated remain to be elucidated. Several studies suggest that PGE2 is involved in inflammation, apoptosis, angiogenesis, and possibly structural changes that characterize arthritic diseases. NSAIDs are prescribed for the treatment of OA and RA and provide effective relief from symptoms; however, serious gastrointestinal complications occur with their use. The clinical efficacy of NSAIDs is primarily related to the inhibition of COX-2, whereas much of the toxicity is related to COX-1 inhibition. Selective COX-2 inhibitors (coxibs) that spare COX-1 at therapeutic doses are more effective than placebo and as effective as other NSAIDs for relief of symptoms of OA and RA, and have significantly improved gastrointestinal safety and tolerability. However, some studies showed that COX-2-selective inhibitors still have classic NSAID complications.

CONCLUSIONS

Overexpression of COX-2 protein in articular tissues is a characteristic feature of arthritic diseases. However, the molecular mechanisms involved in the regulation of COX-2 expression and activity are still unclear. Elucidating the mechanisms of COX-2 expression and PGE2 production and action will help identify novel and more selective potential drug targets in the treatment of arthritic diseases.

Inhibitors of p38 mitogen-activated protein kinase: potential as anti-inflammatory agents in asthma?

Asthma is an inflammatory disease of the airways, which in patients with mild to moderate symptoms is adequately controlled by either beta(2)-adrenoceptor agonists or corticosteroids, or a combination of both. Despite this, there are classes of patients that fail to respond to these treatments. In addition, there is a general trend towards increasing morbidity and mortality due to asthma, which suggests that there is a need for new and improved treatments. The p38 mitogen-activated protein kinases (MAPKs) represent a point of convergence for multiple signalling processes that are activated in inflammation and that impact on a diverse range of events that are important in inflammation. Small molecule pyridinyl imidazole inhibitors of p38 MAPK have proved to be highly effective in reducing various parameters of inflammation, in particular cytokine expression. Like corticosteroids, inhibitors of p38 MAPK appear to be able to repress gene expression at multiple levels, for example, by transcriptional, posttranscriptional and translational repression, and this raises the possibility of a similarly broad spectrum of anti-inflammatory activities. Indeed these molecules have proved to be effective in numerous in vitro and in vivo models of inflammation and septicaemia, which suggests that such compounds may be effective as therapeutic agents against inflammatory disorders. Despite these very promising indications of the possible therapeutic use of p38 MAPK inhibitors, a number of events that are p38-dependent are in fact also beneficial to the resolution or modulation of diseases such as asthma. We conclude that the overall effect of p38 MAPK inhibition would be beneficial in inflammatory diseases such as rheumatoid arthritis and asthma. However, these drugs may result in a complex phenotype that will require careful evaluation. Currently, a number of second or third generation inhibitors of p38 MAPK are being tested in phase I and phase II clinical trials.

Relationship of trichothecene structure to COX-2 induction in the macrophage: selective action of type B (8-keto) trichothecenes

The trichothecene mycotoxin deoxynivalenol (DON, vomitoxin), when at partially cytotoxic concentrations, induces cyclooxygenase-2 (COX-2) expression by promoting transcriptional activity and mRNA stability via mitogen-activated protein kinase (MAPK) signaling pathways. The purpose of this study was to test the hypothesis that trichothecenes differentially affect COX-2 gene expression and that these effects were related to MAPK activation. Representative members of the three major trichothecene families (A, B, and D) were compared for their capacity to induce COX-2 in the RAW 264.7 murine macrophage cell line. When cells were treated with concentrations that inhibited the 3-(4,5-di-methylthizol-2-yl)-2,5 diphenyl tetrazolium bromide (MTT) viability response by 20% (IC20), Type B trichothecenes including DON, 15-acetyl-DON, 3-acetyl-DON, and fusarenon-X were found to be effective inducers of COX-2 mRNA expression, whereas equitoxic Type A and Type D trichothecenes had markedly less effects. To compare effects of COX-2 gene transactivation and mRNA stabilization, luciferase reporter vectors containing 5'-promoter or 3'-untranslated regions of the gene, respectively, were transfected into RAW 264.7 cells and the effects of various trichothecenes on luciferase activities were measured. Type B but not Type A or D toxins at concentrations up to the MTT IC50 enhanced luciferase activities, indicating preferential COX-2 transcriptional activation and mRNA stabilization by this trichothecene subset. At their respective IC20s, Type B trichothecenes also significantly activated the three major MAPK families, whereas Type A and D did not. Blocking ERK and p38 with chemical inhibitors significantly suppressed Type B-induced COX-2 expression. Although JNK reportedly contributes to COX-2 expression in the other signaling models, transfection with the dominant negative JNK vector did not diminish the COX-2 expression. Taken together, Type B trichothecenes selectively enhanced transcription and stabilization of the COX-2 gene, and this was mediated by the ERK 1/2 and p38 signaling pathways. Selective action on COX-2 might contribute to unique pathologic manifestations associated with Type B trichothecene-mediated immunotoxicity.

Myeloid differentiation factor 88-dependent post-transcriptional regulation of cyclooxygenase-2 expression by CpG DNA: tumor necrosis factor-alpha receptor-associated factor 6, a diverging point in the Toll-like receptor 9-signaling

The immune stimulatory unmethylated CpG motifs present in bacterial DNA (CpG DNA) induce expression of cyclooxygenase-2 (cox-2). The present study demonstrates that CpG DNA can up-regulate cox-2 expression by post-transcriptional mechanisms in RAW264.7 cells. To determine the CpG DNA-mediated signaling pathway that post-transcriptionally regulates cox-2 expression, a cox-2 translational reporter (COX2-3'-UTR-luciferase) was generated by inserting sequences within the 3'-untranslated region (UTR) of cox-2 to the 3' end of the luciferase gene under control of the SV40 promoter. CpG DNA-induced COX2-3'-UTR-luciferase activity was completely inhibited by an endosomal acidification inhibitor chloroquine, a Toll-like receptor 9 antagonist inhibitory CpG DNA, or overexpression of a dominant negative (DN) form of MyD88. However, overexpression of DN-IRAK-1 or DN-TRAF6 resulted in substantial, but not complete, inhibition of the CpG DNA-induced COX2-3'-UTR-luciferase activity. Activation of all three MAPKs (ERK, p38, and JNK) was required for optimal COX2-3'-UTR-luciferase activity induced by CpG DNA. Overexpression of DN-TRAF6 suppressed CpG DNA-mediated activation of p38 and JNK, but not ERK, explaining the partial inhibitory effects of DN-TRAF6 on CpG DNA-induced COX2-3'-UTR-luciferase activity. Co-expression of DN-TRAF6 and N17Ras completely inhibited CpG DNA-induced COX2-3'-UTR-luciferase activity, indicating the involvement of Ras in CpG DNA-mediated ERK and COX2-3'-UTR regulation. Collectively, our results suggest that MyD88 and MAPKs play a key regulatory role in CpG DNA-mediated cox-2 expression at the post-transcriptional level and that TRAF6 is a diverging point in the Toll-like receptor 9-signaling pathway for CpG DNA-mediated MAPK activation.

Up-regulation of cyclooxygenase-2 and apoptosis resistance by p38 MAPK in hypericin-mediated photodynamic therapy of human cancer cells

Photodynamic Therapy (PDT) is an approved anticancer therapy that kills cancer cells by the photochemical generation of reactive oxygen species following absorption of visible light by a photosensitizer, which selectively accumulates in tumors. We report that hypericin-mediated PDT of human cancer cells leads to up-regulation of the inducible cyclooxygenase-2 (COX-2) enzyme and the subsequent release of PGE2. Dissection of the signaling pathways involved revealed that the selective activation of p38 MAPK alpha and beta mediate COX-2 up-regulation at the protein and messenger levels. The p38 MAPK inhibitor, PD169316, abrogated COX-2 expression in PDT-treated cells, whereas overexpression of the drug-resistant PD169316-insensitive p38 MAPK alpha and beta isoforms restored COX-2 levels in the presence of the kinase inhibitor. Transcriptional regulation by nuclear factor-kappaB was not involved in COX-2 up-regulation by PDT. The half-life of the COX-2 messenger was drastically shortened by p38 MAPK inhibition in transcriptionally arrested cells, suggesting that p38 MAPK mainly acts by stabilizing the COX-2 transcript. Overexpression of WT-p38 MAPK increased cellular resistance to PDT-induced apoptosis, and inhibiting this pathway exacerbated cell death and prevented PGE2 secretion. Hence, the combination of PDT with pyridinyl imidazole inhibitors of p38 MAPK may improve the therapeutic efficacy of PDT by blocking COX-2 up-regulation, which contributes to tumor growth by the release of growth- and pro-angiogenic factors, as well as by sensitizing cancer cells to apoptosis.

T-cell-derived interleukin-17 regulates the level and stability of cyclooxygenase-2 (COX-2) mRNA through restricted activation of the p38 mitogen-activated protein kinase cascade: role of distal sequences in the 3'-untranslated region of COX-2 mRNA

Although interleukin-17 (IL-17) is the pre-eminent T-cell-derived pro-inflammatory cytokine, its cellular mechanism of action remains poorly understood. We explored novel signaling pathways mediating IL-17 induction of the cyclooxygenase-2 (COX-2) gene in human chondrocytes, synovial fibroblasts, and macrophages. In preliminary work, recombinant human (rh) IL-17 stimulated a rapid (5-15 min), substantial (>8-fold), and sustained (>24 h) increase in COX-2 mRNA, protein, and prostaglandin E2 release. Screening experiments with cell-permeable kinase inhibitors (e.g. SB202190 and p38 inhibitor), Western analysis using specific anti-phospho-antibodies to a variety of mitogen-activated protein kinase cascade intermediates, co-transfection studies using chimeric cytomegalovirus-driven constructs of GAL4 DNA-binding domains fused to the transactivation domains of transcription factors together with Gal-4 binding element-luciferase reporters, ectopic overexpression of activated protein kinase expression plasmids (e.g. MKK3/6), or transfection experiments with wild-type and mutant COX-2 promoter constructs revealed that rhIL-17 induction of the COX-2 gene was mediated exclusively by the stress-activated protein kinase 2/p38 cascade. A rhIL-17-dependent transcriptional pulse (1.76 +/- 0.11-fold induction) was initiated by ATF-2/CREB-1 transactivation through the ATF/CRE enhancer site in the proximal promoter. However, steady-state levels of rhIL-17-induced COX-2 mRNA declined rapidly (<2 h) to control levels under wash-out conditions. Adding rhIL-17 to transcriptionally arrested cells stabilized COX-2 mRNA for up to 6 h, a process compromised by SB202190. Deletion analysis using transfected chimeric luciferase-COX-2 mRNA 3'-untranslated region reporter constructs revealed that rhIL-17 increased reporter gene mRNA stability and protein synthesis via distal regions (-545 to -1414 bases) of the 3'-untranslated region. This response was mediated entirely by the stress-activated protein kinase 2/p38 cascade. As such, IL-17 can exert direct transcriptional and post-transcriptional control over target proinflammatory cytokines and oncogenes.

Robust induction of PGHS-2 by IL-1 in orbital fibroblasts results from low levels of IL-1 receptor antagonist expression

Human orbital fibroblasts are more susceptible to some actions of proinflammatory cytokines than are fibroblasts from other anatomic regions. These cells produce high levels of PGE(2) when activated by cytokines. Here we report that they express high levels of prostaglandin-endoperoxide H synthase (PGHS)-2, the inflammatory cyclooxygenase, when treated with IL-1beta. This induction results from enhanced PGHS-2 mRNA stability and small increases in gene promoter activity. The enhanced transcript stability is a result of actions of the cytokine on the 3'-untranslated region. Orbital fibroblasts, unlike those from skin, fail to express high levels of IL-1 receptor antagonist (IL-1ra) when treated with IL-1beta, leading to loss of modulation of IL-1 action. This can be overcome by transiently transfecting cells with IL-1ra. Thus a decreased level of IL-1ra expression in orbital fibroblasts may underlie the exaggerated responses to IL-1 observed in those cells and, therefore, the susceptibility of the orbit to inflammation.

Tristetraprolin binds to the 3'-untranslated region of cyclooxygenase-2 mRNA. A polyadenylation variant in a cancer cell line lacks the binding site

In human colorectal adenocarcinoma cell lines, we found two major transcripts of cyclooxygenase-2, the full-length mRNA and a short polyadenylation variant (2577 kb) lacking the distal segment of the 3'-untranslated region. Tristetraprolin, an mRNA-binding protein that promotes message instability, was shown to bind the cyclooxygenase-2 mRNA in the region of the 3'-untranslated region between nucleotides 3125 and 3432 and to reduce levels of the full-length mRNA. During cell growth and confluence, the expression of tristetraprolin mRNA was inversely correlated with that of the full-length cyclooxygenase-2 transcript, and transfection of tristetraprolin into HCA-7 cells reduced the level of full-length cyclooxygenase-2 mRNA. However, the truncated transcript escaped tristetraprolin binding and downregulation.

Cyclooxygenase-2 mediates interleukin-6 upregulation by vomitoxin (deoxynivalenol) in vitro and in vivo

Interleukin-6 (IL-6) is a central mediator of immunotoxicity that is associated with exposure to the trichothecene vomitoxin (VT). The purpose of this investigation was to test the hypothesis that the inducible cyclooxygenase-2 (COX-2) and its metabolites contribute to VT-induced IL-6 upregulation. VT at 100 to 250 ng/ml readily induced COX-2 protein expression in the RAW 264.7 murine macrophage cell line. Superinduction of lipopolysaccharide (LPS)-mediated IL-6 production by VT in these cells was significantly reduced by the COX inhibitors indomethacin and NS-398, whereas the inhibitors did not affect direct induction of IL-6 by LPS alone. Mice that had been gavaged orally with 5 and 25 mg/kg VT exhibited elevated COX-2 mRNA expression in Peyer's patches and spleen with peak induction occurring 2 h after VT exposure. IL-6 mRNA was also induced by VT in vivo, however, peak expression occurred from 2 to 4 h after toxin exposure, suggesting that maximal COX-2 gene upregulation preceded or was concurrent with that for IL-6. Also consistent with a putative contributory role for COX-2 was the finding that both induction of splenic IL-6 mRNA and serum IL-6 by VT were significantly reduced by pretreating mice with the COX inhibitors indomethacin or NS-398. Finally, COX-2 knockout mice showed significantly reduced splenic IL-6 mRNA and serum IL-6 responses to oral VT exposure compared to their parental wild type. Taken together, these in vitro and in vivo data suggest that VT-induced COX-2 gene expression and resultant COX-2 metabolites contributed, in part, to subsequent upregulation of IL-6 gene expression, which has been previously shown to be a hallmark of VT-mediated immunotoxicity.

The role of p38 in UVA-induced cyclooxygenase-2 expression in the human keratinocyte cell line, HaCaT

We examined the expression of cycloxygenase-2, the rate-limiting enzyme in the production of prostaglandins, in the UVA-irradiated human keratinocyte cell line, HaCaT. UVA induced a dose-dependent increase in COX-2 at the protein level at 2 and 4 h post-irradiation and at the mRNA level at 1 and 2 h post-irradiation. Experiments using semi-quantitative RT-PCR demonstrate that UVA increased the half-life of the COX-2 message by more than fourfold in the presence of Actinomycin D (with a half life between 4 and 8 h post-irradiation), suggesting that UVA induction of COX-2 is post-transcriptionally regulated. Through the use of the specific p38 inhibitor, SB202190, increases in COX-2 message and protein levels were abrogated in UVA-irradiated cells. In UVA-irradiated cells treated with SB202190, the half-life of the COX-2 message was decreased to basal levels (between 1 and 2 h post-irradiation), indicating that p38 was responsible for the stabilization of the message. Luciferase activity was increased in UVA-irradiated cells transfected with reporter constructs containing the 3' UTR of COX-2, a region containing AU-rich elements (AREs). These regulatory sequences of AUUUA have been proposed as one mechanism of post-transcriptional regulation. Increases observed in luciferase activity could be decreased using a p38 dominant-negative construct. We report for the first that UVA can induce COX-2 expression in the human keratinocyte cell line, HaCaT. Additionally, p38 appears to play a critical role in the UVA-induced expression of COX-2 in these keratinocytes and may serve as a potential drug target in the chemoprevention of skin cancer.

Transcriptional and posttranscriptional regulation of cyclooxygenase-2 expression by fluid shear stress in vascular endothelial cells

OBJECTIVE

Fluid shear stress induces cyclooxygenase (COX)-2 gene expression in vascular endothelial cells. We investigated the underlying mechanism of this induction.

METHODS AND RESULTS

Exposure of human umbilical vein endothelial cells to laminar shear stress in the physiological range (1 to 30 dyne/cm2) upregulated the expression of COX-2 but not COX-1, a constitutive isozyme of COX. The expression of COX-2 mRNA began to increase within 0.5 hour after the loading of shear stress and reached a maximal level at 4 hours. Roles of the promoter region and the 3'-untranslated region in the human COX-2 gene were evaluated by the transient transfection of luciferase reporter vectors into bovine arterial endothelial cells. Shear stress elevated luciferase activity via the region between -327 and 59 bp. Mutation analysis indicated that cAMP-responsive element (-59/-53 bp) was mainly involved in this response. On the other hand, shear stress selectively stabilized COX-2 mRNA. Moreover, shear stress elevated luciferase activity when a 3'-untranslated region of COX-2 gene containing 17 copies of the AUUUA mRNA instability motif was inserted into the vector.

CONCLUSIONS

Transcriptional activation and posttranscriptional mRNA stabilization contribute to the rapid and sustained expression of COX-2 in response to shear stress.

Cyclooxygenase isozymes and their gene structures and expression

The cyclooxygenase (COX, prostaglandin endoperoxide synthase) is a key enzyme in prostaglandin biosynthesis. Two isoforms of COX, COX-1 and COX-2, have been identified by molecular biological methods. The amino acid sequence homology between COX-1 and COX-2 is about 60% for the human enzymes. COX-1 is constitutively expressed in most tissues and cells in animal species. The COX-1 promoter region lacks a canonical TATA or CAAT box and is GC-rich. These features are consistent with those of a housekeeping gene. On the other hand, COX-2 is an inducible enzyme and is induced by various cytokines and mitogenic factors. The induction of COX-2 is suppressed by dexamethasone and PGJ2. There are many consensus cis-elements in the 5'-flanking region to regulate the expression of COX-2. Among them, a CRE, an NF-kappaB site, a NF-IL6 motif and an E-box, regulate transcription independently or synergistically. Most of the transcriptional signaling pathways require activation of the mitogen-activated protein kinase (MAPK) cascade. Moreover, MAPK signaling pathways are involved in regulating COX-2 gene expression at the post-transcriptional level.

Nimesulide, a preferential cyclooxygenase 2 inhibitor, suppresses peroxisome proliferator-activated receptor induction of cyclooxygenase 2 gene expression in human synovial fibroblasts: evidence for receptor antagonism

OBJECTIVE

To characterize the inhibitory effects of therapeutic concentrations of the nonsteroidal antiinflammatory drug nimesulide (NIM) on peroxisome proliferator-activated receptor (PPAR)-induced cyclooxygenase 2 (COX-2) gene expression in human synovial fibroblasts (HSFs) from patients with osteoarthritis (OA) and to define the intracellular mechanisms mediating the response.

METHODS

PPARalpha and PPARgamma messenger RNA (mRNA) expression and protein synthesis in OA HSFs were measured by reverse transcription-polymerase chain reaction and electrophoretic mobility shift assay, respectively. Experiments investigating endogenous and overexpressed PPARalpha and PPARgamma activation of COX-2 mRNA and protein were conducted by incubating nontransfected and transfected cells with increasing concentrations of cognate ligands WY-14,643 (alpha agonist), ciglitasone (gamma agonist), and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) in the absence or presence of NIM and NS-398 (1 microM). COX-2 mRNA and protein were measured by Northern and Western blotting procedures, respectively. Receptor activation studies were evaluated by cotransfecting pSG5-Gal 4 DNA binding domain (DBD)-PPARalpha ligand binding domain (LBD) or pSG5-Gal 4 DBD-PPARgamma LBD chimeric constructs with a 5x Gal 4 enhancer site tk-tataa-luciferase reporter under ligand stimulation in the presence or absence of increasing concentrations of NIM. Gene transactivation analyses were conducted by treating cells overexpressing cytomegalovirus (CMV)-PPARalpha or CMV-PPARgamma expression constructs with either a PPAR response element (PPRE)-luciferase construct containing 3 DR1 acyl-coenzyme A (acyl-CoA) oxidase gene response elements or human COX-2 promoter constructs with WY-14,643, ciglitasone, and 15d-PGJ(2) in the presence or absence of increasing concentrations of NIM.

RESULTS

Human synovial cells expressed functional PPAR isoforms, PPARalpha and PPARgamma. Neither receptor agonists nor antagonists modulated the intracellular protein levels of PPAR. PPARalpha and, especially, PPARgamma mediated the induction of COX-2 gene expression by receptor agonists. Stimulation of COX-2 mRNA expression and protein synthesis by 15d-PGJ(2) appeared to occur through a receptor-independent process. NIM inhibited PPAR agonist stimulation of COX-2 expression and synthesis in a dose-dependent manner in both nontransfected cells and cells overexpressing both receptor isoforms. NIM potently abrogated basal and ligand-stimulated PPRE(3X) DR1 acyl-CoA oxidase-driven luciferase activity and also human PPRE-containing COX-2 promoter activity.

CONCLUSION

PPAR-mediated induction of COX-2 expression and synthesis in human OA synovial fibroblasts is inhibited by therapeutic concentrations of NIM through the functional antagonism of ligand-dependent receptor activation, with the resultant suppression of PPAR-dependent transactivation of target genes (e.g., COX-2).

Mechanism of intramedullary high intensity area on T2-weighted magnetic resonance imaging in osteoid osteoma: a possible role of COX-2 expression

To study the mechanism and pathophysiology of the development of intramedullary high intensity areas on T2-weighted magnetic resonance images (MRI) in cases of osteoid osteoma, we examined the expression of cyclooxygenase-2 (COX-2) in the nidus and surrounding bone tissues. In all six cases showing a marked intramedullary high intensity area adjacent to the nidus before surgery, neoplastic osteoblasts inside the nidus showed strong and diffuse COX-2 immunoreactivity. On the other hand, the osteoblasts rimming the surrounding reactive bone were COX-2 negative. In two cases examined by reverse transcription-polymerase chain reaction (RT-PCR), COX-2 mRNA was detected in abundance in the nidus. Histologically, vascular dilatation together with intramedullary edema was observed in all cases, which was probably reflected as a high intensity area on T2-weighted MRI. From our study, a high level of COX-2 expression in neoplastic osteoblasts in the nidus of osteoid osteomas may cause the secondary changes depicted by MRI.

Prostaglandin E(2) regulates the level and stability of cyclooxygenase-2 mRNA through activation of p38 mitogen-activated protein kinase in interleukin-1 beta-treated human synovial fibroblasts

The p38 MAPK mediates transcriptional and post-transcriptional control of cyclooxygenase-2 (COX-2) mRNA following interleukin-1(IL-1)/lipopolysaccharide cellular activation. We explored a positive feedback, prostaglandin E(2) (PGE(2))-dependent stabilization of COX-2 mRNA mediated by the p38 MAPK cascade in IL-1 beta-stimulated human synovial fibroblasts. We observed a rapid (5 min), massive (>30-fold), and sustained (>48 h) increase in COX-2 mRNA, protein, and PGE(2) release following a recombinant human (rh) IL-1 beta signal that was inhibited by NS-398, a COX-2 inhibitor, and SB202190, a selective, cell-permeable p38 MAPK inhibitor. PGE(2) completely reversed NS-398-mediated inhibition but not SB202190-dependent inhibition. The eicosanoid didn't potentiate IL-1 beta-induced COX-2 expression nor did it activate COX-2 gene expression in quiescent cells. Transfection experiments with a human COX-2 promoter construct revealed a minor element of p38 MAPK-dependent transcriptional control after IL-1 beta stimulation. p38 MAPK synergized with the cAMP/cAMP-dependent protein kinase cascade to transactivate the COX-2 promoter. When human synovial fibroblasts were activated with rhIL-1 beta for 3-4 h (steady state) followed by washout, the elevated levels of COX-2 mRNA declined rapidly (<2 h) to control levels. If PGE(2), unlike EP2/3 agonists butaprost and sulprostone, was added to fresh medium, COX-2 mRNA levels remained elevated for up to 16 h. SB202190 or anti-PGE(2) monoclonal antibody compromised the stabilization of COX-2 mRNA by PGE(2). Deletion analysis using transfected chimeric luciferase-COX-2 mRNA 3'-untranslated region reporter constructs revealed that IL-1 beta increased reporter gene mRNA stability and translation via AU-containing distal regions of the untranslated region. This response was mediated entirely by a PGE(2)/p38 MAPK-dependent process. We conclude that the magnitude and duration of the induction of COX-2 mRNA, protein, and PGE(2) release by rhIL-1 beta is primarily the result of PGE(2)-dependent stabilization of COX-2 mRNA and stimulation of translation, a process involving a positive feedback loop mediated by the EP4 receptor and the downstream kinases p38 MAPK and, perhaps, cAMP-dependent protein kinase.

Dexamethasone destabilizes cyclooxygenase 2 mRNA by inhibiting mitogen-activated protein kinase p38

The stability of cyclooxygenase 2 (Cox-2) mRNA is regulated positively by proinflammatory stimuli acting through mitogen-activated protein kinase (MAPK) p38 and negatively by anti-inflammatory glucocorticoids such as dexamethasone. A tetracycline-regulated reporter system was used to investigate mechanisms of regulation of Cox-2 mRNA stability. Dexamethasone was found to destabilize beta-globin-Cox-2 reporter mRNAs by inhibiting p38. This inhibition occurred at the level of p38 itself: stabilization of reporter mRNA by a kinase upstream of p38 was blocked by dexamethasone, while stabilization by a kinase downstream of p38 was insensitive to dexamethasone. Inhibition of p38 activity by dexamethasone was observed in a variety of cell types treated with different activating stimuli. Furthermore, inhibition of p38 was antagonized by the anti-glucocorticoid RU486 and was delayed and actinomycin D sensitive, suggesting that ongoing glucocorticoid receptor-dependent transcription is required.

Posttranscriptional regulation of cyclooxygenase-2 in rat intestinal epithelial cells

Modulation of cyclooxygenase-2 (COX-2) mRNA stability plays an important role in the regulation of its expression by oncogenic Ras. Here, we evaluate COX-2 mRNA stability in response to treatment with two known endogenous promoters of gastrointestinal cancer, the bile acid (chenodeoxycholate; CD) and ceramide. Treatment with CD and ceramide resulted in a 10-fold increase in the level of COX-2 protein and a four-fold lengthening of the half-life of COX-2 mRNA. COX-2 mRNA stability was assessed by Northern blot analysis and by evaluating the AU-rich element located in the COX-2 3'-UTR. A known inhibitor of mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK), PD98059, reversed the effects of CD or ceramide to stabilize COX-2 mRNA. Overexpression of a dominant-negative ERK-1 or ERK-2 protein also led to destabilization of COX-2 mRNA. Treatment with a p38 MAPK inhibitor, PD169316, or transfection with a dominant-negative p38 MAPK construct reversed the effect of CD or ceramide to stabilize COX-2 mRNA. Expression of a dominant-negative c-Jun N-terminal kinase (JNK) had no effect on COX-2 mRNA stability in cells treated with CD or ceramide. We conclude that posttranscriptional mechanisms play an important role in the regulation of COX-2 expression during carcinogenesis.

Biochemistry of cyclooxygenase (COX)-2 inhibitors and molecular pathology of COX-2 in neoplasia

Several types of human tumors overexpress cyclooxygenase (COX) -2 but not COX-1, and gene knockout transfection experiments demonstrate a central role of COX-2 in experimental tumorigenesis. COX-2 produces prostaglandins that inhibit apoptosis and stimulate angiogenesis and invasiveness. Selective COX-2 inhibitors reduce prostaglandin synthesis, restore apoptosis, and inhibit cancer cell proliferation. In animal studies they limit carcinogen-induced tumorigenesis. In contrast, aspirin-like nonselective NSAIDs such as sulindac and indomethacin inhibit not only the enzymatic action of the highly inducible, proinflammatory COX-2 but the constitutively expressed, cytoprotective COX-1 as well. Consequently, nonselective NSAIDs can cause platelet dysfunction, gastrointestinal ulceration, and kidney damage. For that reason, selective inhibition of COX-2 to treat neoplastic proliferation is preferable to nonselective inhibition. Selective COX-2 inhibitors, such as meloxicam, celecoxib (SC-58635), and rofecoxib (MK-0966), are NSAIDs that have been modified chemically to preferentially inhibit COX-2 but not COX-1. For instance, meloxicam inhibits the growth of cultured colon cancer cells (HCA-7 and Moser-S) that express COX-2 but has no effect on HCT-116 tumor cells that do not express COX-2. NS-398 induces apoptosis in COX-2 expressing LNCaP prostate cancer cells and, surprisingly, in colon cancer S/KS cells that does not express COX-2. This effect may due to induction of apoptosis through uncoupling of oxidative phosphorylation and down-regulation of Bcl-2, as has been demonstrated for some nonselective NSAIDs, for instance, flurbiprofen. COX-2 mRNA and COX-2 protein is constitutively expressed in the kidney, brain, spinal cord, and ductus deferens, and in the uterus during implantation. In addition, COX-2 is constitutively and dominantly expressed in the pancreatic islet cells. These findings might somewhat limit the use of presently available selective COX-2 inhibitors in cancer prevention but will probably not deter their successful application for the treatment of human cancers.

Intraarticular osteoid osteoma associated with synovitis: a possible role of cyclooxygenase-2 expression by osteoblasts in the nidus

To clarify the condition of development of synovitis associated with intraarticular osteoid osteoma (OO), expressions of cyclooxygenase-2 (COX-2) protein and its messenger ribonucleic acid were investigated both in the nidus and the synovial tissue using immunohistochemical and reverse transcription-polymerase chain reaction analyses. Diffuse and strong COX-2 immunoreactivity was found in osteoblast-like tumor cells in the nidus of all six cases of OO (three of six cases were intraarticular OO associated with synovitis) and one case of osteoblastoma associated with synovitis. Expression of COX-2 messenger ribonucleic acid was demonstrated in one case of OO associated with synovitis, and was higher in the nidus than that in the inflamed synovial tissue. However, there were no significant difference between the nidus and synovium in the expression of cytosolic phospholipase A2, one of the enzymes involved in arachidonic acid metabolism, and inflammatory cytokines such as interleukin-1beta and tumor necrosis factor alpha. Finally, as there was only one case in which the examinations of gene expression were performed, no definitive overall conclusions could be reached; rather it is suggested that COX-2 expressed primarily by osteoblasts in the nidus of intraarticular OO may play a role in activating the pathway of arachidonic acid metabolism, resulting in synovitis of the involved joint.

Regulation of cyclooxygenase 2 mRNA stability by the mitogen-activated protein kinase p38 signaling cascade

A tetracycline-regulated reporter system was used to investigate the regulation of cyclooxygenase 2 (Cox-2) mRNA stability by the mitogen-activated protein kinase (MAPK) p38 signaling cascade. The stable beta-globin mRNA was rendered unstable by insertion of the 2, 500-nucleotide Cox-2 3' untranslated region (3' UTR). The chimeric transcript was stabilized by a constitutively active form of MAPK kinase 6, an activator of p38. This stabilization was blocked by SB203580, an inhibitor of p38, and by two different dominant negative forms of MAPK-activated protein kinase 2 (MAPKAPK-2), a kinase lying downstream of p38. Constitutively active MAPKAPK-2 was also able to stabilize chimeric beta-globin-Cox-2 transcripts. The MAPKAPK-2 substrate hsp27 may be involved in stabilization, as beta-globin-Cox-2 transcripts were partially stabilized by phosphomimetic mutant forms of hsp27. A short (123-nucleotide) fragment of the Cox-2 3' UTR was necessary and sufficient for the regulation of mRNA stability by the p38 cascade and interacted with a HeLa protein immunologically related to AU-rich element/poly(U) binding factor 1.

Complement C5b-9-mediated arachidonic acid metabolism in glomerular epithelial cells : role of cyclooxygenase-1 and -2

In the passive Heymann nephritis (PHN) model of membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which is partially mediated by eicosanoids. This study addresses the role of cyclooxygenase (COX)-1 and -2 in C5b-9-mediated eicosanoid production in GEC. Unstimulated rat GEC in culture primarily express COX-1. When stimulated with sublytic C5b-9, COX-2 was significantly up-regulated, whereas COX-1 was not affected. Compared with control, complement-treated GEC produced 32% more prostaglandin (PG) E(2) in the presence of exogenous substrate, and the increase was abolished with the COX-2-selective inhibitor, NS-398. Release of arachidonic acid from GEC phospholipids via C5b-9-induced activation of cytosolic phospholipase A(2) was associated with a marked stimulation of PGE(2) production, which was inhibited by 60% with NS-398. The results in cultured GEC were extended to GEC injury in vivo by examining COX-1 and -2 expression in PHN. Glomeruli from rats with PHN expressed significantly more COX-1 and COX-2, as compared with normal rats. PGE(2) production in glomeruli of rats with PHN was about twofold greater than in control glomeruli, and the increase was partially inhibited with NS-398. Thus, in GEC in culture and in vivo, C5b-9-induced eicosanoid production is regulated by both isoforms of COX. The inducible COX-2 may be an important novel mediator of C5b-9-induced glomerular injury.

Post-transcriptional control of cyclooxygenase-2 gene expression. The role of the 3'-untranslated region

The cyclooxygenase (COX)-2 enzyme is responsible for increased prostaglandin formation in inflammatory states and is the major target of nonsteroidal anti-inflammatory drugs. Normally COX-2 expression is tightly regulated, however, constitutive overexpression plays a key role in colon carcinogenesis. To understand the mechanisms controlling COX-2 expression, we examined the ability of the 3'-untranslated region of the COX-2 mRNA to regulate post-transcriptional events. When fused to a reporter gene, the 3'-untranslated region mediated rapid mRNA decay (t(1/2) = 30 min), which was comparable to endogenous COX-2 mRNA turnover in serum-induced fibroblasts treated with actinomycin D or dexamethasone. Deletion analysis demonstrated that a conserved 116-nucleotide AU-rich sequence element (ARE) mediated mRNA degradation. In transiently transfected cells, this region inhibited protein synthesis approximately 3-fold. However, this inhibition did not occur through changes in mRNA stability since mRNA half-life and steady-state mRNA levels were unchanged. RNA mobility shift assays demonstrated a complex of cytoplasmic proteins that bound specifically to the ARE, and UV cross-linking studies identified proteins ranging from 90 to 35 kDa. Fractionation of the cytosol showed differential association of ARE-binding proteins to polysomes and S130 fractions. We propose that these factors influence expression at a post-transcriptional step and, if dysregulated, may increase COX-2 protein as detected in colon cancer.

Regulation of cyclooxygenase-2 by interferon gamma and transforming growth factor alpha in normal human epidermal keratinocytes and squamous carcinoma cells. Role of mitogen-activated protein kinases

Treatment of normal human epidermal keratinocytes (NHEK) with interferon-gamma (IFN-gamma) causes a 9-fold increase in the level of cyclooxygenase-2 (COX-2) mRNA expression. Nuclear run-off assays indicate that this induction is at least partly due to increased transcription. Activation of the epidermal growth factor receptor (EGFR) signaling pathway due to the enhanced transforming growth factor alpha (TGFalpha) expression plays an important role in the induction of COX-2 by IFN-gamma. This is supported by the ability of TGFalpha to rapidly induce COX-2 and the inhibition of the IFN-gamma-mediated COX-2 mRNA induction by an EGFR antibody and EGFR-selective kinase inhibitors. Deletion and mutation analysis indicates the importance of the proximal cAMP-response element/ATF site in the transcriptional control of this gene by TGFalpha. The increase in COX-2 mRNA by TGFalpha requires activation of both the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) pathways. Inhibition of p38 MAPK decreases the stability of COX-2 mRNA, while inhibition of MAPK/ERK kinase (MEK) does not. These results suggest that the p38 MAPK signaling pathway controls COX-2 at the level of mRNA stability, while the ERK signaling pathway regulates COX-2 at the level of transcription. In contrast to NHEK, IFN-gamma and TGFalpha are not very effective in inducing TGFalpha or COX-2 expression in several squamous carcinoma cell lines, indicating alterations in both IFN-gamma and TGFalpha response pathways.

Posttranscriptional destabilization of the bradykinin B1 receptor messenger RNA: cloning and functional characterization of the 3'-untranslated region

We showed previously that the inducible bradykinin B1 receptor (BKB1R) gene expression is regulated, in part, through mRNA stabilization. Here we clone the 3'-untranslated region (3'-UTR) of the BKB1R. This region proves to be very short, containing only 14 bases with an alternative polyadenylation signal (AUUAAA) which overlaps with the stop codon. Reverse transcription confirms the presence of this alternative polyadenylation signal. Northern blot shows a single species of BKB1R mRNA of approximately 1.4 kb in agreement with its calculated length. The BKB1R mRNA induced by TNFalpha, phorbol ester, bradykinin, and desArg10-kallidin contain the same 3'-UTR species. To test the role of this region in the regulation of mRNA stability, we generated a chimeric luciferase construct containing the BKB1R 3'-UTR. The mRNA transcribed from the wild-type luciferase gene displayed a half-life of approximately 6 h. The mRNA transcribed from the chimeric construct displayed a half-life of only 1 h. This decrease was also reflected at the level of enzyme activity. Luciferase activity from cells transfected with the chimeric construct was 10 times less than from cells transfected with wild-type luciferase. The data presented provide compelling evidence that the 3'-UTR is participating in the regulation of BKB1R mRNA stability and its ultimate expression.

Repression of cyclooxygenase-2 and prostaglandin E2 release by dexamethasone occurs by transcriptional and post-transcriptional mechanisms involving loss of polyadenylated mRNA

The two cyclooxygenase (COX) isoforms convert arachidonic acid to precursor prostaglandins (PGs). Up-regulation of COX-2 is responsible for increased PG production in inflammation and is antagonized by corticosteriods such as dexamethasone. In human pulmonary A549 cells, interleukin-1beta (IL-1beta) increases prostaglandin E2 (PGE2) synthesis via dexamethasone-sensitive induction of COX-2. Nuclear run-off assays showed that COX-2 transcription rate was repressed 25-40% by dexamethasone, while PGE2 release, COX activity, and COX-2 protein were totally repressed. At the mRNA level, complete repression of COX-2 was only observed at later (6 h) time points. Preinduced COX-2 mRNA was also potently repressed by dexamethasone, yet suppression of transcription by actinomycin D showed little effect. This dexamethasone-dependent repression involved a reduced COX-2 mRNA half-life, was blocked by actinomycin D or cycloheximide, and was antagonized by the steroid antagonist RU38486. Repression of IL-1beta-induced PGE2 release, COX activity, and COX-2 protein by actinomycin D was only effective within the first hour following IL-1beta treatment, while dexamethasone was effective when added up to 10 h later, suggesting a functional role for post-transcriptional mechanisms of repression. Following dexamethasone treatment, shortening of the average length of COX-2 mRNA poly(A) tails was observed. Finally, ligation of the COX-2 3'-UTR to a heterologous reporter failed to confer dexamethasone sensitivity. In conclusion, these data indicate a major role for post-transcriptional mechanisms in the dexamethasone-dependent repression of COX-2 that require de novo glucocorticoid receptor-dependent transcription and translation. This mechanism involves shortening of the COX-2 poly(A) tail and requires determinants other than just the 3'-UTR for specificity.

A p38 MAP kinase inhibitor regulates stability of interleukin-1-induced cyclooxygenase-2 mRNA

The mechanism by which p38 mitogen-activated protein kinase (MAPK) regulates the induction of cyclooxygenase (COX)-2 by interleukin-1 (IL-1) has been investigated in HeLa cells. SB 203580, an inhibitor of p38 MAPK, in the range 0.1-1 microM inhibited IL-1-stimulated PGE2 (but not arachidonic acid) release and this was associated with inhibition of induction of COX-2 protein and mRNA. IL-1 stimulated COX-2 transcription in HeLa cells about 2-fold as judged by both reporter gene and nuclear run-on assays. The inhibitor had no significant effect on this. However, in cells previously stimulated with IL-1 it caused rapid destabilisation of COX-2 mRNA independently of on-going transcription. The results suggest a novel function for p38 MAPK in the regulation of mRNA stability.

Cyclooxygenases as the principal targets for the actions of NSAIDs

The recent identification, cloning, and characterization of two cyclooxygenases has provided insight into how nonsteroidal anti-inflammatory drugs can beneficially inhibit prostaglandin production in inflammation but also produce side-effects in the gut and kidney. The subtle differences in the sites in which these drugs bind the enzymes has allowed development of inhibitors that exhibit selectivity for the inflammatory cyclooxygenase and spare the housekeeping enzyme. This selectivity in theory should enhance the therapeutic potential of these new drugs.

zALK-8, a novel type I serine/threonine kinase receptor, is expressed throughout early zebrafish development

Here, we report the isolation and characterization of zebrafish activin receptor-like kinase-8 (zALK-8), a novel type I serine/threonine (ser/thr) kinase receptor of the transforming growth factor beta (TGF-beta) family. zALK-8 is novel, in that it contains an extracellular domain that is quite distinct from that of previously identified ALK receptors 1 through 7. Analysis of the predicted amino acid sequence of the 506 amino acid zALK-8 receptor reveals an ser/thr kinase domain characteristic of type I TGF-beta family member receptors. zALK-8, therefore, is a traditional type I ser/thr kinase receptor of the TGF-beta family, but it may exhibit novel ligand-binding activities. The developmental expression of zALK-8 mRNA was examined by wholemount in situ hybridization analysis using a probe from the 3'-untranslated sequence of zALK-8, which does not cross react with other members of the highly conserved TGF-beta receptor family. zALK-8 mRNA is present as a maternal message that is expressed ubiquitously before the start of zygotic transcription. By 16 hr postfertilization (hpf), zALK-8 mRNA is still expressed fairly evenly throughout the embryo. In 24-hpf embryos, zALK-8 mRNA is expressed predominantly in the developing eye and neural structures. By 48 hpf, zALK-8 mRNA is faintly detectable as a diffuse signal throughout the head. zALK-8 mRNA is not detectable by this method in 72-hpf or 96-hpf embryos. Northern analysis of zALK-8 mRNA in poly(A+) mRNA isolated from 6-9 hpf embryos detects a major transcript of 3.6 kb and a minor transcript of 4.3 kb. zALK-8 mRNA expression correlates well with known functions of TGF-beta family members as early axial patterning and mesoderm-inducing growth factors and as potent growth and differentiation factors in craniofacial development.

Superinduction of COX-2 mRNA by cycloheximide and interleukin-1beta involves increased transcription and correlates with increased NF-kappaB and JNK activation

Many primary response genes, including cyclooxygenase-2 (COX-2), exhibit mRNA superinduction following agonist stimulation in the presence of translational blockers such as cycloheximide. This is widely assumed to result from mRNA stabilisation. However, superinduction of IL-1beta-induced COX-2 mRNA levels by cycloheximide in pulmonary type II A549 cells occurred by increased transcription and not by mRNA stabilisation. Furthermore, equivalent effects were observed on NF-kappaB binding to COX-2 promoter kappaB sites and activation of the Jun N-terminal kinases (JNK), p54 and p46. These signalling pathways play important roles in COX-2 induction and may therefore account for the observed increases in COX-2 transcription. These data are consistent with negative feed-back involving down-regulation of NF-kappaB by de novo IkappaB alpha synthesis and suggest that JNK activation may also be down-regulated by a cycloheximide sensitive process.

Evidence for involvement of NF-kappaB in the transcriptional control of COX-2 gene expression by IL-1beta

The cyclooxygenase (COX) isoforms COX-1 and COX-2 convert arachidonic acid to prostaglandin (PG) precursors and are a limiting step in PG production. Interleukin-1beta (IL-1beta) treatment of type II A549 cells increases PGE2 synthesis via transcription- and translation-dependent induction of COX-2. IL-1beta produces a 10-fold induction of COX-2 mRNA and an 8-fold increase in COX-2 transcription that was temporally preceded by activation of the transcription factor nuclear factor-kappaB (NF-kappaB). The protein-tyrosine phosphatase inhibitor phenylarsine oxide (PAO) prevented both NF-kappaB activation and induction of COX-2 mRNA. We show that two putative NF-kappaB motifs, kappaBu (-447/-438) and kappaBd (-224/-214), from the COX-2 promoter bind p50/p65 NF-kappaB heterodimers in an IL-1beta-dependent manner and that the upstream element has the greater affinity. Finally, we demonstrate that the two NF-kappaB subunits, p50 and p65, synergistically activate a -917/+49 COX-2 promoter construct. We conclude that IL-1beta stimulates PG production via transcriptional activation of COX-2 and provide evidence that this may involve NF-kappaB.