HGF triggers activation of the COX-2 gene in rat gastric epithelial cells: action mediated through the ERK2 signaling pathway

Induction of cyclooxygenase-2 synthesis by ligation of the macrophage alpha(2)-macroglobulin signalling receptor

We have studied the induction of cyclooxygenase-2 (COX-2) in macrophages consequent to ligating the alpha(2)-macroglobulin (alpha(2)M) signalling receptor (alpha(2)MSR) with receptor-recognized forms of alpha(2)M (alpha(2)M*). Macrophage stimulation with alpha(2)M* increased total cellular and nuclear COX-2 two- to threefold. The maximal increase in COX-2 occurred at a ligand concentration of 50-100 pM and after 2 h. Modulation of intracellular Ca(2+) levels or incubation of [35S] methionine-labelled macrophages with actinomycin D, prior to treatment with alpha(2)M*, markedly reduced the induction of total cellular and nuclear COX-2. Protein kinase C (PKC) or phospholipase A(2) (PLA(2)) inhibition in alpha(2)M*-stimulated macrophages or inhibition of the p21(ras)-dependent mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI 3-kinase) signalling pathways also significantly reduced alpha(2)M*-induced total cellular and nuclear COX-2 expression. Thus, COX-2 induction is dependent on cPLA(2) activity, Ca(2+) mobilization, and PKC activity and requires participation of both the p21(ras)-dependent MAPK and PI 3-kinase signalling pathways. COX-2 activation may mediate alpha(2)M*-induced mitogenesis, which we have previously observed in this and other cell types.

Expression of cyclooxygenase-2 in human neutrophils activated by Helicobacter pylori water-soluble proteins: possible involvement of NF-kappaB and MAP kinase signaling pathway

Helicobacter pylori infection elicits persistent neutrophil infiltration in gastric mucosa. The expression of cyclooxygenase (COX) -2 by the neutrophils results in prostaglandin (PG) E2 synthesis, which may account for alterations in tissue homeostasis. In this study, we found that COX-2 mRNA was up-regulated in the neutrophils when stimulated with both H. pylori water extract (HPWE) and live H. pylori in a transwell model and determined by quantitative RT-PCR. PGE2 synthesis was also enhanced in the neutrophils activated by both the HPWE and live H. pylori. A specific COX-2 inhibitor (NS-398) blocked PGE2 synthesis, and an anti-ulcer agent (rebamipide) suppressed it dose dependently. An NF-kappaB inhibitor (pyrrolidine dithiocarbamate), a MAP kinase (MEK) inhibitor (PD98059), and a p38 MAP kinase inhibitor (SB203580) significantly suppressed the COX-2 gene transcription and PGE2 synthesis in the neutrophils. In conclusion, H. pylori water-soluble proteins may enhance the COX-2 expression, and this action could be mediated through the NF-kappaB and MAP kinase signaling pathways. The increased section of PGE2 by the neutrophils may play a proinflammatory role in the gastric mucosal response to H. pylori.

Interleukin-1beta induces cyclo-oxygenase-2 expression in gastric cancer cells by the p38 and p44/42 mitogen-activated protein kinase signaling pathways

BACKGROUND AND AIMS

Cyclo-oxygenase-2 (COX-2) is the inducible enzyme in the gastric mucosa responsible for prostaglandin production during inflammation and ulcer healing. The regulation of COX-2 gene expression in gastric epithelial cells is not well understood. In this study, we investigated the effect of interleukin (IL)-1beta on COX-2 expression in the human gastric cancer cell, and explored the signaling pathways involved.

METHODS

Gastric cancer cell line AGS was treated with IL-1beta or the inhibitors of mitogen-activated protein-Erk kinase (MEK) and p38 mitogen-activated protein (MAP) kinase prior to the addition of IL-1beta. The COX-2 mRNA or protein levels were measured by using RT-PCR or western blot analysis, respectively. Prostaglandin E2 (PGE2) production/secretion was determined by using the prostaglandin E2 EIA assay. The phosphorylation/activation of p44/42 and p38 MAP kinases were determined by using western blot analysis and using phospho-specific antibodies.

RESULTS

Interleukin-1beta treatment dose- and time-dependently increased COX-2 mRNA and protein expression levels, and enhanced PGE2 production/secretion in AGS cells. In contrast, IL-1beta had no effect on the level of the constitutively expressed COX-1. In parallel to the increase of COX-2, we showed that p44/42 and p38 MAP kinase activities were also upregulated by IL-1beta treatment. To demonstrate the cause-effect relationship, we showed that inhibition of MEK and p38 MAP kinase with specific inhibitors suppressed IL-1beta-mediated increases in COX-2 mRNA and protein levels, and the PGE2 production.

CONCLUSIONS

Our results demonstrated that in human gastric cancer cells, IL-1beta upregulates the COX-2 gene expression through the activation of MEK/p44/42 and p38 MAP kinases pathway.

Nonsteroidal anti-inflammatory drugs for treatment of advanced gastric cancer: cyclooxygenase-2 is involved in hepatocyte growth factor mediated tumor development and progression

Surgical treatment of gastric cancer patients is dismal because advanced tumor is often noted at diagnosis. In order to obtain better adjuvant therapy for gastric cancer patients after operation, it is important to understand the mechanism of invasion and metastasis. It is well known that binding of hepatocyte growth factor (HGF) to its receptor (c-Met) regulates gastric cancer progression and metastasis. Recently, HGF was found to up-regulate the expression of cyclooxygenase-2 (COX-2) gene and increase prostaglandin (PG)synthesis in gastric mucosa cells. Over-expression of COX-2 and increased PG secretion have also been found to be involved in the growth and metastasis of gastric cancer. These results together suggest that the signaling pathway of HGF and c-Met may be mediated through ERK2 activation, up-regulation of COX-2 and increased production of PGE(2)in gastric cancer cells. In view of the fact that c-Met is over-expressed in the majority of gastric cancer patients with poor prognosis, COX-2 specific inhibitors may provide beneficial effects in these patients.

Expression of COX-2 and PGE synthase and synthesis of PGE(2)in endometrial adenocarcinoma: a possible autocrine/paracrine regulation of neoplastic cell function via EP2/EP4 receptors

This study was designed to investigate the possible role of cyclo-oxygenase-2 (COX-2) and prostaglandin E(2)(PGE(2)) in endometrial adenocarcinoma. COX-2 RNA expression was confirmed in various grades of adenocarcinoma by ribonuclease protection assay. COX-2 and microsomal glutathione-dependent prostaglandin E synthase (mPGES) expression and PGE(2)synthesis were localised to the neoplastic epithelial cells and endothelial cells. In order to establish whether PGE(2)has an autocrine/paracrine effect in adenocarcinomas, we investigated the expression of 2 subtypes of PGE(2)receptors, namely EP2 and EP4, by real time quantitative PCR. Expression of EP2 and EP4 receptors was detected in adenocarcinomas from all grades of differentiation and was significantly higher than that detected in normal secretory phase endometrium (P< 0.01). The fold induction of expression in adenocarcinoma compared with normal secretory phase endometrium was 28.0 +/- 7.4 and 52.5 +/- 10.1 for EP2 and EP4 receptors respectively. Immunohistochemistry localised the site of expression of EP4 receptor in neoplastic epithelial cells and in the endothelium of carcinomas of all grades of differentiation. Finally, the functionality of the EP2/EP4 receptors was assessed by investigating cAMP generation following in vitro culture of adenocarcinoma tissue in the presence or absence of 300 nM PGE(2). cAMP production in response to PGE(2)was significantly higher in carcinoma tissue than that detected in normal secretory phase endometrium (3.42 +/- 0.46 vs 1.15 +/- 0.05 respectively; P< 0.001). In conclusion, these data suggest that PGE(2)may regulate neoplastic cell function in an autocrine/paracrine manner via the EP2/EP4 receptors.

Role of growth factors and their receptors in gastric ulcer healing

The repair of gastric ulcers requires the reconstitution of epithelial structures and the underlying connective tissue, including vessels and muscle layers. Several growth factors have been implicated in this process, since they are able to regulate important cell functions, such as cell proliferation, migration, differentiation, secretion, and degradation of extracellular matrix, all of which are essential during tissue healing. Epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), hepatocyte growth factor (HGF), and trefoil factors (TFFs) are mainly involved in the reconstitution of the epithelial structures. Platelet derived growth factor (PDGF), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and transforming growth factor-beta (TGF-beta) play a major role in the reconstitution of connective tissue, including vessels and smooth muscle cells, and provide the extracellular matrix substrate for cell migration and differentiation. The expression of these growth factors and their receptors is increased during ulcer healing and, in some cases, intracellular signaling related to receptor binding and transduction has been demonstrated. EGF, TGF-alpha and TFFs are normally present either in the gastric juice or in the mucosa, and may exert their effects immediately after damage, before newly synthesized EGF and TFFs are released from the ulcer margin. The inhibition of their effects by neutralizing antibodies may result in delayed ulcer healing, while the administration of recombinant or natural analogues may improve ulcer repair. In this review, we will summarize the basic molecular characteristics of some of these growth factors, and will discuss available evidence supporting their role in the ulcer repair process.

Activation of cellular invasion by trefoil peptides and src is mediated by cyclooxygenase- and thromboxane A2 receptor-dependent signaling pathways

We have investigated the possible functional relationships between cellular invasion pathways induced by trefoil factors (TFFs), src, and the cyclooxygenases COX-1 and COX-2. Pharmacological inhibitors of the Rho small GTPase (C3 exoenzyme), phospholipase C (U-73122), cyclooxygenases (SC-560, NS-398), and the thromboxane A2 receptor (TXA2-R) antagonist SQ-295 completely abolished invasion induced by intestinal trefoil factor, pS2, and src in kidney and colonic epithelial cells MDCKts.src and PCmsrc. In contrast, invasion was induced by the TXA2-R mimetic U-46619, constitutively activated forms of the heterotrimeric G-proteins Galphaq (AGalphaq), Galpha12, Galpha13 (AGalpha12/13), which are signaling elements downstream of TXA2-R. Ectopic overexpression of pS2 cDNA and protein in MDCKts.src-pS2 cells and human colorectal cancer cells HCT8/S11-pS2 initiate distinct invasion signals that are Rho independent and COX and TXA2-R dependent. We detected a marked induction of COX-2 protein and accumulation of the stable PGH2/TXA2 metabolite TXB2 in the conditioned medium from cells transformed by src. This led to activation of the TXA2-R-dependent invasion pathway, which is monitored via a Rho- and Galpha12/Galpha13-independent mechanism using the Galphaq/PKC signaling cascade. These findings identify a new intracrine/paracrine loop that can be monitored by TFFs and src in inflammatory diseases and progression of colorectal cancers.

Secretory phospholipase A2 mediates cooperative prostaglandin generation by growth factor and cytokine independently of preceding cytosolic phospholipase A2 expression in rat gastric epithelial cells

Transforming growth factor (TGF)-alpha and interleukin (IL)-1beta are responsible for the healing of gastric lesions through, in part, prostaglandin (PG) generation. We examined the contribution of cytosolic and secretory phospholipase A(2)s (cPLA(2) and sPLA(2)) to the PG generation by rat gastric epithelial cells in response to both stimuli. Stimulation with TGF-alpha for 24 h increased cPLA(2) and cyclooxygenase (COX)-2 markedly, PGE(2) slightly, and type IIA sPLA(2) and COX-1 not at all, whereas IL-1beta increased sPLA(2) only. Both stimuli synergistically increased PGE(2), sPLA(2), and the two COXs but not cPLA(2). The onset of the PGE(2) generation paralleled the sPLA(2) release but was apparently preceded by increases in cPLA(2) and the two COXs. The increase in PGE(2) was impaired by inhibitors for sPLA(2) and COX-2 but not COX-1. cPLA(2) inhibitors suppressed PGE(2) generation by TGF-alpha alone but not augmentation of PGE(2) generation or sPLA(2) release by IL-1beta in combination with TGF-alpha. Furthermore, despite an increase in cPLA(2) including its phosphorylated form (phosphoserine), -induced arachidonic acid liberation was impaired in the TGF-alpha/IL-1beta-stimulated cells, in which p11, a putative cPLA(2) inhibitory molecule, was also increased and co-immunoprecipitated with cPLA(2). These results suggest that synergistic stimulation of sPLA(2) and COX-2 expression by TGF-alpha and IL-1beta results in an increase in PGE(2). Presumably, the preceding cPLA(2) expression is not involved in the PGE(2) generation, because of impairment of its hydrolytic activity in the stimulated cells.

Biliary cancer growth factor pathways, cyclo-oxygenase-2 and potential therapeutic strategies

Cholangiocarcinoma is a hepatic biliary cancer of high morbidity and mortality, whose molecular pathogenesis is unknown. However, there is increasing evidence to suggest that alterations in selected growth factor pathways, including an overexpression of the growth factor receptor tyrosine kinases c-ErbB-2/c-Neu and c-Met, together with possible aberrant autocrine expression of hepatocyte growth factor/scatter factor, the ligand for c-Met, may be playing important roles associated with the development of cholangiocarcinoma in both the human liver and in the furan rat model of cholangiocarcinogenesis. Cyclo-oxygenase-2, whose regulation has been experimentally related to c-ErbB-2/c-Neu as well as to hepatocyte growth factor/scatter factor, and which has been demonstrated to be overexpressed in other cancers of the gastrointestinal tract, has also been observed in preliminary studies to be upregulated in human biliary cancers and in cholangiocarcinoma induced in the furan rat model. Moreover, new data from our laboratory have demonstrated the cyclo-oxygenase-2 inhibitor NS-398 to produce a significant dose-dependent growth inhibition of rat cholangiocarcinoma cells in vitro, as well as to suppress anchorage-independent growth of these cells in soft agar. Based on the data reviewed, we propose that the selective therapeutic targeting of aberrant growth factor receptor tyrosine kinase signaling and of cyclo-oxygenase-2, alone or in combination, has potential to become a useful new approach for the treatment and/or chemoprevention of cholangiocarcinoma. We further propose that the furan rat model may serve as a powerful preclinical model for testing therapeutic and chemopreventative strategies that selectively target c-ErbB-2/c-Neu, cyclo-oxygenase-2, and/or autocrine hepatocyte growth factor/c-Met, aberrantly expressed in cholangiocarcinogenesis.

Adenovirus-mediated hepatocyte growth factor gene transfer prevents lethal liver failure in rats

Hepatocyte growth factor (HGF) has a potent antiapoptotic effect on hepatocytes in D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-treated rats. Here, we report that adenovirus mediated HGF gene transfer into liver prevents liver failure and reduces mortality of rats treated with d-GalN/LPS. Fisher 344 rats, which were given intraperitoneal injections of pAxCAHGF 48 h before, were treated with D-GalN/LPS. Serum ALT in the HGF group at 6 and 12 h after D-GalN/LPS was decreased to 1/6 and 1/12 of the control group (P < 0.01, each). Concomitant reduction of apoptotic cells were also observed. The Kaplan-Meier analysis showed that a survival rate in the HGF group was improved, compared to that in the control group (P < 0.05). Caspase-3 activity in the HGF group decreased, compared to that in the control group, especially at 12 h (P < 0.05), although it maintained a high level in the control group. Expression of Bcl-xL and cyclooxygenase-2 (Cox-2) was induced in liver by HGF gene transfer. These data suggest that HGF exerts an antiapoptotic effect through dual induction of Bcl-xL and Cox-2, which suppresses caspase-3 activity.

Keratinocyte growth factor-2 (FGF-10) promotes healing of experimental small intestinal ulceration in rats

Keratinocyte growth factor-2 (KGF-2, repifermin) is a homolog of KGF-1 with epithelial mitogenic activities. We investigated the therapeutic role of KGF-2 in intestinal ulceration and its mechanisms of protection. KGF-2 (0.3-5 mg/kg) was administered before or after induction of small intestinal ulceration by indomethacin (Indo) in prevention and treatment protocols. In acute studies, KGF-2 was injected for up to 7 days before or daily for 5 days after Indo. In a 15-day chronic study, KGF-2 was injected intravenously daily beginning before or 7 days after Indo. Injury was evaluated by blinded macroscopic and microscopic inflammatory scores, epithelial BrdU staining, tissue IL-1beta, PGE(2), and hydroxyproline concentrations, and collagen type I RNA expression. In vitro effects of KGF-2 were evaluated by epithelial cellular proliferation, restitution of wounded monolayers, PGE(2) secretion, and expression of COX-2 and collagen mRNA. Intravenous KGF-2 significantly decreased acute intestinal injury by all parameters and significantly decreased chronic ulceration. Pretreatment, daily infusion, and delayed treatment were effective. KGF-2 promoted in vitro epithelial restitution with only modest effects on epithelial cell proliferation, stimulated COX-2 expression in cultured epithelial cells, and upregulated in vitro and in vivo PGE(2) production. KGF-2 did not affect in vivo fibrosis, although it induced collagen expression in cultured intestinal myofibroblasts. These results suggest that KGF-2 inhibits intestinal inflammation by stimulating epithelial restitution and protective PGs.

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.

Transforming growth factor-alpha stimulates prostaglandin generation through cytosolic phospholipase A(2) under the control of p11 in rat gastric epithelial cells

The regulatory effects of transforming growth factor (TGF)-alpha on phospholipase A(2) (PLA(2)) isozymes contributing to prostaglandin generation in rat gastric epithelial RGM1 cells were examined. Stimulation with TGF-alpha for 24 h time-dependently induced prostaglandin E(2) generation with an increase in cyclo-oxygenase-2 protein. The TGF-alpha-induced prostaglandin E(2) generation was suppressed by NS-398, a cyclo-oxygenase-2 inhibitor. TGF-alpha stimulated the activity and the protein synthesis of cytosolic PLA(2) (cPLA(2)). A time-dependent increase in cPLA(2) protein occurred in parallel with PGE(2) generation, which was inhibited by methyl arachidonyl fluorophosphonate (MAFP), a cPLA(2) inhibitor. However, no change in activity of secretory PLA(2) or Ca(+2)-independent PLA(2) was observed in the TGF-alpha-stimulated cells. Stimulation with the Ca(2+) ionophore A23187 for 10 min induced MAFP-sensitive arachidonic acid liberation. Interestingly, preincubation with TGF-alpha for 24 h diminished A23187-stimulated arachidonic acid liberation despite the increase in cPLA(2) protein. Under the conditions, TGF-alpha was found to increase p11, an endogenous cPLA(2) suppressor, also known as annexin II light chain. The TGF-alpha-induced increase in p11 was suppressed by tyrphostin AG1478, an inhibitor of tyrosine kinase of epidermal growth factor receptor, which was also found to restore the inhibition by TGF-alpha of A23187-stimulated arachidonic acid liberation. However, TGF-alpha did not alter protein levels of annexin II heavy chain. These results suggest that TGF-alpha stimulates prostaglandin generation through an increase in cPLA(2), the hydrolytic action of which may be under the control of p11.

Hepatocyte growth factor promotes cell survival from fas-mediated cell death in hepatocellular carcinoma cells via Akt activation and Fas-death-inducing signaling complex suppression

The Akt/PI-3 kinase pathway is a system essential for cell survival. In the current study, we showed that hepatocyte growth factor (HGF) activates the Akt/PI-3 kinase pathway to suppress Fas-mediated cell death in human hepatocellular carcinoma (HCC; 3 lines; SK-Hep1, HLE, and Chang Liver cell lines), hepatoblastoma (1 line; HepG2), and embryonic hepatocyte (1 line; WRL). Five tested cell lines showed the resistance to Fas-mediated cell death by the pretreatment of HGF. This HGF-induced cell survival was suppressed by wortmannin (Akt/PI-3 kinase pathway inhibitor), suggesting an involvement of Akt. When cells were pretreated with HGF, Fas-mediated cell death was suppressed, followed by Akt phosphorylation at Ser473. Fas-death-inducing signaling complex (DISC) formation, especially FADD and caspase 8 interaction, was suppressed by HGF and the suppression of the Akt/PI-3 kinase pathway by transient expression of PTEN, resulting in acquisition of Fas-DISC formation and Fas-mediated cell death in HGF-treated cells. We suggest that HGF promotes cell survival in hepatocyte-derived cell lines (HCC, hepatoblastoma, and embryonic hepatocyte) from Fas-mediated cell death via Fas-DISC suppression as a result of Akt activation.

Eicosanoids and the stomach

Eicosanoids are arachidonic acid derivatives that include prostaglandins, thromboxanes, and leukotrienes. During the last three decades, it has become evident that these bioactive lipids play a pivotal role in gastric physiology. The goal of the present review is to describe their involvement in the normal regulation of gastric secretion and gastric motility, as well as in gastric mucosal defense. Their role in gastric mucosal mitogenesis, apoptosis, inflammation, and immune modulatory responses is also discussed.