Cyclooxygenase-2 is an independent prognostic factor in gastric cancer and its expression is regulated by the messenger RNA stability factor HuR

Aurothiomalate inhibits COX-2 expression in chondrocytes and in human cartilage possibly through its effects on COX-2 mRNA stability

Cyclooxygenase-2 (COX-2) is expressed in rheumatoid and osteoarthritic cartilage and produces pro-inflammatory prostanoids in the joint. In the present study, we investigated the effects of disease modifying anti-rheumatic drugs on COX-2 expression in chondrocytes. Unlike the other tested drugs, aurothiomalate was found to inhibit COX-2 expression in chondrocytes. In the further studies, effects and mechanisms of action of aurothiomalate were investigated in more detail. Aurothiomalate inhibited IL-1beta-induced COX-2 protein expression and PGE(2) production in chondrocytes in a dose-dependent manner. Because aurothiomalate did not alter IL-1beta-induced mRNA levels when measured 0-3 h after addition of IL-1beta, its effects on COX-2 mRNA degradation were tested by Actinomycin D assay. The half-life of COX-2 mRNA was reduced from 3 h to less than 1.5 h in aurothiomalate-treated cells. The 3'-untranslated region (3'-UTR) of COX-2 mRNA contains an ARE element which has been shown to bind mRNA stabilizing factor HuR. Interestingly, aurothiomalate inhibited HuR expression which may explain its destabilizing effect on COX-2 mRNA. Aurothiomalate reduced COX-2 expression and PGE(2) production also in human cartilage at drug concentrations which have been measured in serum and synovial fluid during treatment with aurothiomalate. The results show that aurothiomalate reduces COX-2 expression and PGE(2) production in chondrocyte cultures and in human cartilage. The action is likely mediated by enhanced COX-2 mRNA degradation possibly through a mechanism related to reduced expression of HuR. The results provide a novel mechanism of action for aurothiomalate which may be important in the treatment of arthritis.

Expression of HuR in Merkel cell carcinoma and in normal skin

BACKGROUND

HuR is a ubiquitously expressed member of the Elav/Hu family of mRNA-binding proteins, and its cytoplasmic expression has been recognised to participate in carcinogenesis. The aims of this study were to explore the expression pattern of HuR in primary Merkel cell carcinoma (MCC), lymph node metastases and non-neoplastic skin.

METHODS

Twenty-two primary MCC samples and five lymph node metastases were evaluated for HuR expression by immunohistochemistry. The data were compared with clinical parameters.

RESULTS

Nuclear and cytoplasmic HuR-staining patterns were observed. Nuclear immunoreactivity was observed in 91% of the primary tumors and in 80% of the lymph node metastases. Cytoplasm was positive in 27% of the primary tumors and in 60% of the lymph node metastases. No cytoplasmic HuR immunoreactivity was detected in non-neoplastic skin. However, moderate to strong nuclear staining was found in normal epidermis and in the epithelium of hair follicles and sebaceous glands. Expression of HuR in MCC did not associate with clinicopathological parameters.

CONCLUSIONS

Primary MCCs and their lymph node metastases as well as non-neoplastic skin show nuclear expression of HuR protein. In contrast to non-neoplastic skin, a subset of MCC tumors show cytoplasmic HuR staining, which may contribute to carcinogenesis in MCC.

Posttranslational modification of the AU-rich element binding protein HuR by protein kinase Cdelta elicits angiotensin II-induced stabilization and nuclear export of cyclooxygenase 2 mRNA

The mRNA stabilizing factor HuR is involved in the posttranscriptional regulation of many genes, including that coding for cyclooxygenase 2 (COX-2). Employing RNA interference technology and actinomycin D experiments, we demonstrate that in human mesangial cells (hMC) the amplification of cytokine-induced COX-2 by angiotensin II (AngII) occurs via a HuR-mediated increase of mRNA stability. Using COX-2 promoter constructs with different portions of the 3' untranslated region of COX-2, we found that the increase in COX-2 mRNA stability is attributable to a distal class III type of AU-rich element (ARE). Likewise, the RNA immunoprecipitation assay showed AngII-induced binding of HuR to this ARE. Using the RNA pulldown assay, we demonstrate that the AngII-caused HuR assembly with COX-2 mRNA is found in free and cytoskeleton-bound polysomes indicative of an active RNP complex. Mechanistically, the increased HuR binding to COX-2-ARE by AngII is accompanied by increased nucleocytoplasmic HuR shuttling and depends on protein kinase Cdelta (PKCdelta), which physically interacts with nuclear HuR, thereby promoting its phosphorylation. Mapping of phosphorylation sites identified serines 221 and 318 as critical target sites for PKCdelta-triggered HuR phosphorylation and AngII-induced HuR export to the cytoplasm. Posttranslational modification of HuR by PKCdelta represents an important novel mode of HuR activation implied in renal COX-2 regulation.

Dietary supplementation with carbonate increases expression of ornithine decarboxylase and proliferation in gastric mucosa in a rat model of gastric cancer

Dietary factors play essential roles in gastric carcinogenesis. We recently found that dietary supplementation with NaHCO(3) significantly increased the development of gastric cancer in a rat gastric stump model. Here, we analysed nontransformed gastric mucosa for expression of the cancer-related proteins cyclooxygenase-2 (COX-2) and ornithine decarboxylase (ODC), and we examined the relationship between expression levels of those proteins and mucosal proliferation. Research has shown that COX-2 is upregulated in gastric mucosal inflammation and is strongly associated with gastrointestinal cancer. ODC is the key enzyme in polyamine synthesis and a regulator of cell proliferation. We performed gastric resections on 48 Wistar rats to induce spontaneous gastric cancer; half of these animals were given a normal diet, and the other half received a diet supplemented with NaHCO(3). Twenty-four unoperated rats served as a control group. The surgical procedure per se led to a significant rise in mucosal expression of COX-2 and an associated increase in cell proliferation. However, the COX-2 level in gastric mucosa was not further affected by dietary supplementation of carbonate. Interestingly, nontransformed gastric mucosa in the operated rats receiving a carbonate-supplemented diet showed a pronounced increase in ODC expression that was strongly correlated with a further enhanced cell proliferation. These results indicate that carbonate ions, which represent a major constituent of intestinal reflux into the stomach, increase the expression of ODC and thereby enhance cell proliferation in nontransformed mucosa, and consequently elevate the risk of gastric cancer.

Epigenetic silencing of cyclooxygenase-2 affects clinical outcome in gastric cancer

PURPOSE

Overexpression of cyclooxygenase-2 (COX-2) in gastric cancer has been shown to enhance tumor progression. We investigated whether silencing by promoter region hypermethylation of the COX-2 gene contributes to disease outcome in gastric cancer.

MATERIALS AND METHODS

COX-2 methylation status was initially assessed by capillary array electrophoresis methylation-specific polymerase chain reaction (CAE-MSP) and COX-2 protein expression by immunohistochemistry (IHC) in 40 primary gastric cancer tissues in a pilot study. Prognostic end points of correlative studies of COX-2 methylation status were time to recurrence, overall survival, and standard clinicopathologic features. CAE-MSP analysis was then validated in a second independent gastric cancer population (n = 137).

RESULTS

COX-2 methylation was detected in 23% and 28% of the pilot and validation patient groups, respectively. COX-2 expression (IHC) in gastric tumors inversely correlated with COX-2 gene methylation status in the pilot study (P = .02). COX-2 methylation in tumors was significantly associated with lower T, N, and TNM stage in the validation patient group (P = .02, P = .006, and P = .008, respectively). Patients with COX-2 methylated tumors had significantly longer time to recurrence and improved overall survival in a multivariate analysis in the validation patient group (hazard ratio[HR], 0.49; 95% CI, 0.24% to 0.99%; HR, 0.62; 95% CI, 0.38% to 0.99%, respectively).

CONCLUSION

Hypermethylation of COX-2 gene promoter was identified as an independent prognostic factor in gastric cancer patients. The results suggest promoter hypermethylation to be an important regulatory mechanism of COX-2 expression in gastric cancer and an important prognostic biomarker.

HETEs enhance IL-1-mediated COX-2 expression via augmentation of message stability in human colonic myofibroblasts

Proinflammatory cytokines and eicosanoids are central players in intestinal inflammation. IL-1, a key cytokine associated with intestinal mucosal inflammation, induces COX-2 expression in human colonic myofibroblasts (CMF) and increased prostaglandin E(2) secretion is associated with inflammatory bowel disease (IBD) and colorectal cancer (CRC). We have previously demonstrated that IL-1alpha-induced cyclooxygenase-2 (COX-2) expression is the result of NF-kappaB- and ERK-mediated transcription, as well as COX-2 message stabilization, which depends on p38, MAPKAPK-2 (MK-2) and human antigen R (HuR) RNA binding protein activation. Lipoxygenase (LOX)-derived hydroxyeicosatetraenoic acids (HETEs) are elevated in IBD and colonic adenomas and "cross talk" has been observed between the COX and LOX pathways. Since COX-2 expression is primarily in CMFs in colonic adenomas, we examined the impact of LOX metabolites, particularly HETEs, on IL-1alpha-induced COX-2 expression in human CMFs. Although 5(S)-, 12(R)-, and 15(S)-HETEs alone had little to no effect on COX-2 expression, they enhanced IL-1-mediated COX-2 expression 3.6 +/- 0.5-fold. Studies utilizing heterogeneous nuclear RNA amplification and 5,6-dichloro-beta-d-ribofuranosylbenzimidazole treatment were undertaken to measure COX-2 transcription and message stabilization, respectively. We found that HETEs enhanced IL-1-induced COX-2 mRNA levels in CMF as the result of increased p38, MK-2, and HuR activity, increasing message stability greater than that observed with IL-1 alone. Thus HETEs can act synergistically with IL-1alpha to induce COX-2 expression in human CMFs. HETEs may play a role in both colonic inflammation and in increasing the risk of CRC in IBD independently and via induction of COX-2-mediated prostaglandin secretion.

Expression of HuR is associated with increased cyclooxygenase-2 expression in uterine cervical carcinoma

The human family embryonic-lethal abnormal vision-like protein Hu antigen R (HuR) serves as a messenger RNA (mRNA)-binding protein and stabilizes a certain group of cellular mRNAs that contain adenylate/uridylate-rich elements in their 3-untranslated region. The HuR is predominantly located in the nucleus, but it shuttles between the nucleus and the cytoplasm. In the cytoplasm, it can stabilize certain transcripts. Reportedly, the mRNA of cyclooxygenase-2 (COX-2) can be stabilized by HuR in breast, ovary, colon, stomach, lung, and brain cancers. We investigated the expression of HuR and COX-2 in 308 primary uterine cervical carcinomas using immunohistochemistry. Nuclear HuR expression was seen in 280 (90.9%) of the cases, and cytoplasmic HuR expression was observed in 61 (19.8%) of the cases. The expression of nuclear HuR was significantly associated with stage (P = 0.031). We found that 135 patients (43.8%) showed positive reaction for the COX-2 protein. In the COX-2 positive cases, nuclear HuR expression was higher, but the difference was not statistically significant. Cytoplasmic HuR expression was significantly associated with tumor size (P = 0.029), stage (P = 0.005), and lymphatic/vascular invasion (P < 0.001). Considering only squamous cell lesions (carcinoma in situ, microinvasive squamous cell carcinoma [SCC], and invasive SCC), the cytoplasmic expression of HuR significantly increased in invasive SCC compared with microinvasive SCC or carcinoma in situ (P = 0.005). Cytoplasm HuR expression correlated with COX-2 (P < 0.001). There was no significant correlation between HuR (nuclear or cytoplasmic) expression and patient survival. Our results suggest that the cytoplasmic overexpression of HuR is associated with uterine cervical carcinomas with aggressive clinicopathologic features and that HuR might contribute to the stabilization of COX-2 mRNA in some uterine cervical carcinomas.

Cyclooxygenase-2 (cox-2) and the inflammogenesis of cancer

Cohesive scientific evidence from molecular, animal, and human investigations supports the hypothesis that aberrant induction of COX-2 and up-regulation of the prostaglandin cascade play a significant role in carcinogenesis, and reciprocally, blockade of the process has strong potential for cancer prevention and therapy. Supporting evidence includes the following: [1] expression of constitutive COX-2-catalyzed prostaglandin biosynthesis is induced by most cancer-causing agents including tobacco smoke and its components (polycylic aromatic amines, heterocyclic amines, nitrosamines), essential polyunsaturated fatty acids (unconjugated linoleic acid), mitogens, growth factors, proinflammatory cytokines, microbial agents, tumor promoters, and other epigenetic factors, [2] COX-2 expression is a characteristic feature of all premalignant neoplasms, [3] COX-2 expression is a characteristic feature of all malignant neoplasms, and expression intensifies with stage at detection and cancer progression and metastasis, [4] all essential features of carcinogenesis (mutagenesis, mitogenesis, angiogenesis, reduced apoptosis, metastasis, and immunosuppression) are linked to COX-2-driven prostaglandin (PGE-2) biosynthesis, [5] animal studies show that COX-2 up-regulation (in the absence of genetic mutations) is sufficient to stimulate the transformation of normal cells to invasive cancer and metastatic disease, [6] non-selective COX-2 inhibitors, such as aspirin and ibuprofen, reduce the risk of human cancer and precancerous lesions, and [7] selective COX-2 inhibitors, such as celecoxib, reduce the risk of human cancer and precancerous lesions at all anatomic sites thus far investigated. Results confirming that COX-2 blockade is effective for both cancer prevention and therapy have been tempered by observations that some COX2 inhibitors pose a risk to the cardiovascular system, and more studies are needed in order to determine if certain of these drugs can be taken at dosages that prevent cancer without increasing cardiovascular risk. It is emphasized that the "inflammogenesis model of cancer" is not mutually exclusive and may in fact be synergistic with the accumulation of somatic mutations in tumor suppressor genes and oncogenes or epigenetic factors in the development of cancer.

Cyclo-oxygenase-2 and its inhibition in cancer: is there a role?

Despite recent improvements in chemotherapy and radiation therapy in cancer management with the addition of biological agents, novel treatment approaches are needed to further benefit patients. Cyclo-oxygenase (COX)-2 inhibition represents one such possibility. COX-2 is an enzyme induced in pathological states such as inflammatory disorders and cancer, where it mediates production of prostanoids. The enzyme is commonly expressed in both premalignant lesions and malignant tumours of different types. A growing body of evidence suggests an association of COX-2 with tumour development, aggressive biological tumour behaviour, resistance to standard cancer treatment, and adverse patient outcome. COX-2 may be related to cancer development and propagation through multiple mechanisms, including stimulation of growth, migration, invasiveness, resistance to apoptosis, suppression of the immunosurveillance system, and enhancement of angiogenesis. Epidemiological data suggest that NSAIDs and selective COX-2 inhibitors might prevent the development of cancers, including colorectal, oesophageal and lung cancer. Preclinical investigations have demonstrated that inhibition of this enzyme with selective COX-2 inhibitors enhances tumour response to radiation and chemotherapeutic agents. These preclinical findings have been rapidly advanced to clinical oncology. Clinical trials of the combination of selective COX-2 inhibitors with radiotherapy, chemotherapy or both in patients with a number of cancers have been initiated, and preliminary results are encouraging. This review discusses the role of COX-2, its products (prostaglandins) and its inhibitors in tumour growth and treatment.

Overexpression of cyclooxygenase-2 correlates with cytoplasmic HuR expression in salivary mucoepidermoid carcinoma but not in pleomorphic adenoma

BACKGROUND

The overexpression of cyclooxygenase (COX)-2 in several human carcinomas suggests that COX-2 is related to carcinogenesis. Although COX-2 expression has been shown to be up-regulated in carcinomas of the salivary gland, its mechanisms are not completely understood. HuR is an mRNA-binding protein that controls the stability of certain transcripts including COX-2.

METHODS

The expression of COX-2 and HuR was determined by immunohistochemistry in 28 cases of salivary pleomorphic adenoma and 18 cases of salivary mucoepidermoid carcinoma.

RESULTS

28.6% and 72.2% of the pleomorphic adenomas and mucoepidermoid carcinomas showed high COX-2 expression respectively. 35.7% of pleomorphic adenomas and 72.2% of mucoepidermoid carcinomas were tested positive for HuR in the cytoplasm of tumor cells. There was a correlation between a high COX-2 immunoreactivity and cytoplasmic HuR expression in mucoepidermoid carcinomas but not in pleomorphic adenomas.

CONCLUSION

This study suggests that cytoplasmic HuR is correlated with COX-2 expression in salivary mucoepidermoid carcinomas. In addition, the immunoreactivity of COX-2 and cytoplasmic HuR might be used to evaluate the nature of a borderline malignancy in the salivary glands.

mRNA stability control: a clandestine force in normal and malignant hematopoiesis

This review addresses the scope of influence of mRNA decay on cellular functions and its potential role in normal and malignant hematopoiesis. Evidence is emerging that leukemic oncogenes and hematopoietic cytokines interact with mRNA decay pathways. These pathways can co-regulate functionally related genes through specific motifs in the 3'-untranslated region of targeted transcripts. The steps that link external stimuli to transcript turnover are not fully understood, but include subcellular relocalization or post-transcriptional modification of specific transcript-stabilizing or -destabilizing proteins. Improper functioning of these regulators of mRNA turnover can impede normal cellular differentiation or promote cancers. By delineating how subsets of transcripts decay in synchrony during normal hematopoiesis, it may be possible to determine whether this post-transcriptional regulatory pathway is hijacked in leukemogenesis.

Cyclo-oxygenase-2 over-expression is associated with human esophageal squamous cell carcinoma

Cyclo-oxygenase (COX)-2 is not usually detectable in normal tissues but is induced in inflammation and carcinogenesis. The level of COX-2 is elevated in cancer tissues of the colon, bladder, and skin. In the esophagus, squamous cell carcinoma and adenocarcinoma are known to express COX-2. The purpose of this study was to clarify the association of COX-2 expression with clinicopathological factors of squamous cell carcinoma. The immunohistochemical expression of COX-2 was examined in 48 surgical specimens of esophageal squamous cell carcinoma. Although COX-2 over-expression was more frequently observed in tumors invading the submucosa (T1b, 76.4%), muscularis propria (T2, 57.1%), adventitia, or adjacent organs (T3 approximately 4, 83.3%), even 33.3% of mucosal cancers, such as T1a, showed COX-2 over-expression. COX-2 over-expression was present in 82.3% of lymph node-negative patients but in only 54.8% of lymph node positive patients. There was no difference in COX-2 over-expression between the earlier stages (0 and I, 60%) and more advanced stages (II approximately IV, 69.6%). COX-2 over-expression did not correlate with survival during 3 years of follow-up. These findings suggest that COX-2 is associated with the phenotype of the esophageal squamous cell carcinoma cells, including superficial cancer cells, and may be related to tumor growth in esophageal squamous cell carcinoma.

Selective cyclooxygenase-2 inhibitor downregulates the paracrine epithelial-mesenchymal interactions of growth in scirrhous gastric carcinoma

The importance of cancer-mesenchymal interactions in the aggressive behavior of scirrhous gastric cancer is supported by experimental and clinical evidences. We have previously reported that gastric fibroblasts secretion of keratinocyte growth factor (KGF) underline the remarkable proliferation of scirrhous gastric cancer cells. Cyclooxygenase-2 (COX-2) is not only expressed in cancer cells, but also in interstitial fibroblasts in gastric carcinoma. To clarify the mechanisms responsible for the antiproliferation effect of COX-2 inhibitors, effect of COX-2 inhibitor on the paracrine epithelial-mesenchymal interactions of growth was examined. Scirrhous gastric cancer cell line, OCUM-2M, gastric fibroblasts, NF-21, and COX-2 inhibitor, JTE-522, were used. Growth-interaction was examined by calculating the number of cancer cells or by measuring [(3)H] thymidine incorporation of cancer cells. Effect of JTE-522 on KGF expression from NF-21 cells and OCUM-2M cells was analyzed by ELISA and RT-PCR. The conditioned medium from gastric fibroblasts significantly stimulated the growth of scirrhous gastric cancer cells. JTE-522 at the concentrations of 10(-5) and 10(-6) M significantly decreased the growth-stimulating activity of gastric fibroblasts. JTE-522 reduced the expression of KGF mRNA and the production of KGF from gastric fibroblasts. Oral administration of JTE-522 significantly decreased the size of xenografted tumor coinoculated with OCUM-2M cells and NF-21 cells in nude mice. JTE-522 decreased COX-2 expression and Ki67 labeling index within the coinoculated tumor. These findings suggested that a selective COX-2 inhibitor, JTE-522, downregulates KGF production from gastric fibroblasts, resulting in the inhibition of paracrine epithelial-mesenchymal interactions of proliferation between scirrhous gastric cancer cells and gastric fibroblasts.

Post-transcriptional regulation of RNase-L expression is mediated by the 3'-untranslated region of its mRNA

RNase-L mediates critical cellular functions including antiviral, pro-apoptotic, and tumor suppressive activities; accordingly, its expression must be tightly regulated. Little is known about the control of RNASEL expression; therefore, we examined the potential regulatory role of a conserved 3'-untranslated region (3'-UTR) in its mRNA. The 3'-UTR mediated a potent decrease in the stability of RNase-L mRNA, and of a chimeric beta-globin-3'-UTR reporter mRNA. AU-rich elements (AREs) are cis-acting regulatory regions that modulate mRNA stability. Eight AREs were identified in the RNase-L 3'-UTR, and deletion analysis identified positive and negative regulatory regions associated with distinct AREs. In particular, AREs 7 and 8 served a strong positive regulatory function. HuR is an ARE-binding protein that stabilizes ARE-containing mRNAs, and a predicted HuR binding site was identified in the region comprising AREs 7 and 8. Co-transfection of HuR and RNase-L enhanced RNase-L expression and mRNA stability in a manner that was dependent on this 3'-UTR region. Immunoprecipitation demonstrated that RNase-L mRNA associates with a HuR containing complex in intact cells. Activation of endogenous HuR by cell stress, or during myoblast differentiation, increased RNase-L expression, suggesting that RNase-L mRNA is a physiologic target for HuR. HuR-dependent regulation of RNase-L enhanced its antiviral activity demonstrating the functional significance of this regulation. These findings identify a novel mechanism of RNase-L regulation mediated by its 3'-UTR.

Prognostic significance of cyclin A in gastric cancer

High level of cyclin A promotes carcinogenesis, and overexpression of cyclin A has been associated with poor prognosis of cancer patients. We validated the prognostic role of cyclin A in gastric cancer and evaluated its correlation with expression of an mRNA stability factor HuR. From 342 consecutive histologically confirmed gastric cancer patients were obtained 325 representative tissue specimens for cyclin A and 316 for HuR immunohistochemistry. Specimens were stained by cyclin A and HuR specific monoclonal antibodies. Nuclear immunostaining detected in > or =5% of the tumor cells was considered the cut-off for cyclin A positivity. Positive HuR immunoreactivity was scored as nuclear or cytoplasmic. Associations between scores, clinicopathological factors and survival were calculated by the chi2-test, Fisher's exact test, Kaplan-Meier test and Cox model. Cyclin A detected in the nuclei of cancer cells was positive in 55% (179 of 325) of the specimens; 40% (127 of 316) of the specimens had cytoplasmic and 88% (279 of 316) nuclear immunoreactivity of HuR. Cyclin A expression was an independent prognostic factor for poor survival. Cyclin A immunoreactivity was associated with old age, high stage, proximal location of the tumor, intestinal type, noncurative resection, advanced penetration depth and with nodal metastases but not distant metastases. Furthermore, cyclin A expression was associated with cytoplasmic HuR expression, whereas no association with nuclear HuR was evident. Cyclin A is an independent prognostic factor in gastric cancer, and one mechanism for its overexpression may depend on cytoplasmic localization of HuR.

MMP-2 but not MMP-9 associated with COX-2 and survival in gastric cancer

BACKGROUND AND AIM

Matrix metalloproteinases (MMPs) MMP-2 and MMP-9 can degrade type IV collagen of extracellular matrix and basal membranes. As cyclo-oxygenase-2 (COX-2) has been shown to activate MMPs, creating one of the COX-2-promoted pathways of tumour growth and metastasis, the prognostic role of MMP-2 and MMP-9 in gastric cancer was assessed and their association with COX-2 expression was evaluated.

MATERIALS AND METHODS

Samples were collected from 342 consecutive patients operated on for gastric cancer, of which 315 were acceptable for MMP-2, MMP-9 and COX-2 immunohistochemistry. Specimens were stained with specific antibodies, evaluated and categorised by two interpreters, and then correlated with clinical data and survival.

RESULTS

Epithelial MMP-2 immunoreactivity was associated with male sex, high stage, advanced penetration depth, non-curative surgery, high COX-2 expression and poor survival. Stromal MMP-2 expression correlated with high stage, intestinal type and non-curative surgery whereas MMP-9 correlated only with intestinal type. Stage, intent of surgery and COX-2 were independent prognostic factors.

CONCLUSIONS

Epithelial MMP-2 expression in gastric cancer is associated with aggressive forms, COX-2 and poor survival, although MMP-2 was not an independent prognostic factor. In gastric cancer tumour growth is apparently induced by COX-2, and invasion is mediated by MMP-2.

What are cyclooxygenases and lipoxygenases doing in the driver's seat of carcinogenesis?

Substantial evidence supports a functional role for cyclooxygenase- and lipoxygenase-catalyzed arachidonic and linoleic acid metabolism in cancer development. Genetic intervention studies firmly established cause-effect relations for cyclooxygenase-2, but cyclooxygenase-1 may also be involved. In addition, pharmacologic cyclooxygenase inhibition was found to suppress carcinogenesis in both experimental mouse models and several cancers in humans. Arachidonic acid-derived eicosanoid or linoleic acid-derived hydro[peroxy]fatty acid signaling are likely to be involved impacting fundamental biologic phenomena as diverse as cell growth, cell survival, angiogenesis, cell invasion, metastatic potential and immunomodulation. However, long chain unsaturated fatty acid oxidation reactions indicate antipodal functions of distinct lipoxygenase isoforms in carcinogenesis, i.e., the 5- and platelet-type 12-lipoxygenase exhibit procarcinogenic activities, while 15-lipoxygenase-1 and 15-lipoxygenase-2 may suppress carcinogenesis.

Expression of Cyclooxygenase-2 Is Regulated by Glycogen Synthase Kinase-3β in Gastric Cancer Cells

Cyclooxygenase-2 (COX-2) expression is a marker of poor prognosis in gastric cancer patients, and its inhibition suppresses gastric tumorigenesis in experimental animal models. The mechanism that leads to COX-2 overexpression in this tumor type is unknown. We have now shown that inhibition of phosphatidylinositol 3-kinase by LY294002 suppresses both basal and phorbol myristate acetate-induced COX-2 expression in TMK-1 and MKN-28 gastric cancer cells. Furthermore, inhibition of glycogen synthase kinase-3beta (GSK-3beta) by SB415286 induced expression of COX-2 mRNA and protein as well as the enzyme activity in the gastric cancer cells. The effect of SB415286 was confirmed by the use of two additional GSK-3beta inhibitors, lithium chloride and SB216763. SB415286 had a modest 1.6-fold stimulatory effect on a 2-kb COX-2 promoter reporter construct, but more importantly, it was shown to block the decay of COX-2 mRNA. In contrast to modulation of phosphatidylinositol 3-kinase/Akt/GSK-3beta pathway, inhibitors of mitogen-activated protein kinases (MEK 1/2, p38, JNK) or the mammalian target of rapamycin did not alter COX-2 expression in gastric cancer cells. Our data show that inhibition of GSK-3beta stimulates COX-2 expression in gastric cancer cells, which seems to be primarily facilitated via an increase in mRNA stability and to a lesser extent through enhanced transcription.