Involvement of cyclooxygenase-2 in proliferation and morphogenesis induced by transforming growth factor alpha in gastric epithelial cells

Melatonin in Prevention of the Sequence from Reflux Esophagitis to Barrett's Esophagus and Esophageal Adenocarcinoma: Experimental and Clinical Perspectives

Melatonin is a tryptophan-derived molecule with pleiotropic activities which is produced in all living organisms. This "sleep" hormone is a free radical scavenger, which activates several anti-oxidative enzymes and mechanisms. Melatonin, a highly lipophilic hormone, can reach body target cells rapidly, acting as the circadian signal to alter numerous physiological functions in the body. This indoleamine can protect the organs against a variety of damaging agents via multiple signaling. This review focused on the role played by melatonin in the mechanism of esophagoprotection, starting with its short-term protection against acute reflux esophagitis and then investigating the long-term prevention of chronic inflammation that leads to gastroesophageal reflux disease (GERD) and Barrett's esophagus. Since both of these condition are also identified as major risk factors for esophageal carcinoma, we provide some experimental and clinical evidence that supplementation therapy with melatonin could be useful in esophageal injury by protecting various animal models and patients with GERD from erosions, Barrett's esophagus and neoplasia. The physiological aspects of the synthesis and release of this indoleamine in the gut, including its release into portal circulation and liver uptake is examined. The beneficial influence of melatonin in preventing esophageal injury from acid-pepsin and acid-pepsin-bile exposure in animals as well as the usefulness of melatonin and its precursor, L-tryptophan in prophylactic and supplementary therapy against esophageal disorders in humans, are also discussed.

Geranylgeranylacetone induces cyclooxygenase-2 expression in cultured rat gastric epithelial cells through NF-kappaB

Geranylgeranylacetone (GGA) effectively protects the gastric mucosa against noxious agents. The precise mechanisms underlying the gastroprotective actions of GGA are not known. To elucidate the precise mechanism of GGA, the effect of GGA treatment on COX-2 expression in rat gastric epithelial (RGM1) cells was investigated. We used a prostaglandin E2 (PGE2) enzyme-linked immunoassay kit and Western blot analysis to measure PGE2 production and COX-2 induction by GGA treatment in serum-starved RGM1 cells. Gel-shift assay, Western blot analysis, and a reporter assay were performed to determine which COX-2 promoter was involved in GGA-induced COX-2 expression. GGA treatment dose dependently increased COX-2 expression and PGE2 production. The nuclear factor (NF)-kappaB sites of the COX-2 gene promoter were critical for GGA-mediated COX-2 expression. GGA induces COX-2 expression and increases PGE2 production in serum-starved RGM1 cells via activation of the NF-kappaB sites of COX-2 gene promoters.

Regulation of apoptosis during homeostasis and disease in the intestinal epithelium

A single epithelial layer serves as the interface between the organism and the contents of the gastrointestinal tract, underlining the importance of regulating cellular viability despite an onslaught of pathogens, toxins, waste by-products, and cytokines. A balance between cellular proliferation and apoptosis is necessary to maintain this critical barrier. Recent findings have begun to explain the mechanisms by which intestinal epithelial cells are able to survive in such an environment and how loss of normal regulatory processes may lead to inflammatory bowel disease (IBD) and predispose to inflammation-associated neoplasia. This review focuses on the regulation of physiological apoptosis in development and homeostasis and on pathological apoptosis in intestinal disease, inflammation, and neoplasia, identifying remaining questions and areas of needed investigation.

Cyclooxygenase 2, pS2, inducible nitric oxide synthase and transforming growth factor alpha in gastric adaptation to stress

AIM

To determine the role of mucosal gene expression of cyclooxygenase 2 (COX-2), pS2 (belongs to trefoil peptides), inducible nitric oxide synthase (iNOS) and transforming growth factor alpha (TGFalpha) in gastric adaptation to water immersion and restraint stress (WRS) in rats.

METHODS

Wistar rats were exposed to single or repeated WRS for 4 h every other day for up to 6 d. Gastric mucosal blood flow (GMBF) was measured by laser Doppler flowmeter-3. The extent of gastric mucosal lesions were evaluated grossly and histologically and expressions of COX-2, pS2,iNOS and TGFalpha were determined by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot.

RESULTS

The damage to the surface of gastric epithelium with focal areas of deep haemorrhagic necrosis was induced by repeated WRS. The adaptative cytoprotection against stress was developed with activation of cell proliferation in the neck regions of gastric glands. The ulcer index (UI) in groups II, III and IV was markedly reduced as compared with group I (I: 47.23+/-1.20; IV: 10.39+/-1.18,P<0.01). GMBF significantly decreased after first exposure to WRS with an adaptive increasement of GMBF in experimental groups after repetitive challenges with WRS. After the 4th WRS, the value of GMBF almost restored to normal level (I: 321.87+/-8.85; IV: 455.95+/-11.81, P<0.01). First WRS significantly decreased the expression of pS2 and significantly increased the expressions of COX-2, iNOS and TGFalpha. After repeated WRS, pS2 and TGFalpha expressions gradually increased (pS2: I: 0.37+/-0.02; IV: 0.77+/-0.01; TGFalpha: I: 0.86+/-0.01; IV: 0.93+/-0.03, P<0.05) with a decrease in the expressions of COX-2 and iNOS (COX-2: I: 0.45+/-0.02; IV: 0.22+/-0.01; iNOS: I: 0.93+/-0.01; IV: 0.56+/-0.01, P<0.01). Expressions of pS2, COX-2, iNOS and TGFalpha showed regular changes with a good relationship among them.

CONCLUSION

Gastric adaptation to WRS injury involves enhanced cell proliferation, increased expression of pS2 and TGFalpha, and reduced expression of COX-2 and iNOS. These changes play an important role in adaptation of gastric mucosa after repeated WRS.

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.

Lansoprazole induces mucosal protection through gastrin receptor-dependent up-regulation of cyclooxygenase-2 in rats

Proton pump inhibitors (PPIs) are antiulcer agents that have both gastric antisecretory and mucosal protective actions. The mechanisms of PPI-induced gastric mucosal protection are not known. The present study was designed to examine the mechanism for lansoprazole-induced gastric mucosal protection in rats. Rats were given 0.5, 5, and 50 mg/kg/day lansoprazole alone or both lansoprazole (50 mg/kg/day) and a specific gastrin receptor antagonist 3R-1-(2,2-diethoxyethyl)-((4-methylphenyl)amino-carbonyl methyl)-3-((4-methylphenyl)ureidoindoline-2- one) (AG-041R) (3, 10, and 30 mg/kg/day) for 14 days. Serum gastrin concentrations were measured. The expression of cyclooxygenases (COX-1 and COX-2) in the gastric mucosa was analyzed using Western blotting and immunohistochemical staining. Another series of rats was used to examine the 1) levels of prostaglandin (PG) E2 in gastric mucosa, 2) influences of the drugs on gastric damage caused by absolute ethanol, and 3) effects of a COX-2-specific inhibitor on PGE2 in the gastric mucosa and the mucosal protection afforded by lansoprazole. Lansoprazole dose dependently increased the serum gastrin concentration and enhanced the mucosal expression of COX-2 but not that of COX-1. Lansoprazole increased gastric mucosal PGE2 and reduced gastric damage caused by ethanol. Concomitant administration of AG-041R abolished the lansoprazole-induced COX-2 expression, and increased mucosal PGE2 and mucosal protection. A specific COX-2 inhibitor blocked the lansoprazole-induced increase in mucosal PGE2 and mucosal protection. Activation of gastrin receptors by endogenous gastrin has a pivotal role in the effects of lansoprazole on COX-2 up-regulation and mucosal protection in the rat stomach.

Gastrin enhances gastric mucosal integrity through cyclooxygenase-2 upregulation in rats

Gastrin, PGs, and growth factors have important roles in maintaining gastrointestinal mucosal integrity. Cyclooxygenases (COX-1 and COX-2) are the key enzymes involved in PG synthesis. This study aimed to clarify the mechanisms of gastric mucosal protection by gastrin. Fasted rats were administered subcutaneous gastrin 17 with or without gastrin receptor antagonist YM022 pretreatment. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) and COX-2 expression were examined using Western blot analysis. Another series of experiments investigated 1) PGE(2) levels in gastric mucosa, 2) the protective action of gastrin against gastric damage by acidified ethanol, 3) the effects of a specific HB-EGF-neutralizing antibody on gastrin-induced COX-2 expression, and 4) the effects of a specific COX-2 inhibitor NS-398 on PGE(2) synthesis and the mucosal protection afforded by gastrin. Gastrin dose-dependently increased HB-EGF, COX-2 expression, and PGE(2) levels and reduced gastric damage. However, pretreatment with YM022 dose-dependently abolished such effects of gastrin. A specific HB-EGF- neutralizing antibody and an EGF receptor inhibitor decreased gastrin-induced COX-2 expression. NS-398 blocked gastrin-induced PGE(2) synthesis and mucosal protection. In conclusion, this study demonstrates that gastrin enhances gastric mucosal integrity through COX-2, which is partially mediated by HB-EGF, and PGE(2) upregulation in rats.

Stimulation of the gastrin-cholecystokinin(B) receptor promotes branching morphogenesis in gastric AGS cells

Epithelial organization is maintained by cell proliferation, migration, and differentiation. In the case of the gastric epithelium, at least some of these events are regulated by the hormone gastrin. In addition, gastric epithelial cells are organized into characteristic tubular structures (the gastric glands), but the cellular mechanisms regulating the organization of tubular structures (sometimes called branching morphogenesis) are uncertain. In the present study, we examined the role of the gastrin-cholecystokinin(B) receptor in promoting branching morphogenesis of gastric epithelial cells. When gastric cancer AGS-G(R) cells were cultured on plastic, gastrin and PMA stimulated cell adhesion, formation of lamellipodia, and extension of long processes in part by activation of protein kinase C (PKC) and phosphatidylinositol (PI)-3 kinase. Branching morphogenesis was not observed in these circumstances. However, when cells were cultured on artificial basement membrane, the same stimuli increased the formation of organized multicellular arrays, exhibiting branching morphogenesis. These effects were reversed by inhibitors of PKC but not of PI-3 kinase. We conclude that, in the presence of basement membrane, activation of PKC by gastrin stimulates branching morphogenesis.

Cyclo-oxygenase 2 expression is associated with angiogenesis and lymph node metastasis in human breast cancer

AIMS

Cyclo-oxygenases 1 and 2 (COX-1 and COX-2) are key enzymes in prostaglandin biosynthesis. COX-2 is induced by a wide variety of stimuli, and present during inflammation. COX-2 overexpression has been observed in colon, head and neck, lung, prostate, stomach, and breast cancer. In colon and gastric cancer, COX-2 expression was associated with angiogenesis. The aim of this study was to determine the relation between COX-2 expression and angiogenesis in breast cancer, and to correlate the expression of this enzyme with classic clinicopathological parameters.

METHODS

COX-2 expression was investigated by immunohistochemistry and western blotting analysis. The expression of COX-2 was then related to age, histological grade, nodal status, oestrogen receptor status, p53 expression,c-erb-B2 overexpression, mitotic counts, MIB-1 labelling index, apoptotic index, sialyl-Tn expression, transforming growth factor alpha expression, microvessel density, and disease free survival in 46 patients with invasive ductal breast carcinoma.

RESULTS

By means of immunohistochemistry, COX-2 expression was detected in eight of the 46 carcinomas studied. Western blotting showed COX-2 protein expression in the same breast tumours, but not in normal adjacent tissues. The density of microvessels immunostained with anti-F-VIII related antigen was significantly higher in patients with COX-2 expression than in those without expression (p = 0.03). In addition, COX-2 was significantly associated with the presence of sialyl-Tn expression (p = 0.02), lymph node metastasis (p = 0.03), a high apoptotic index (p = 0.03), and a short disease free survival (p = 0.03) in univariate analyses.

CONCLUSIONS

These data suggest that COX-2 expression is associated with angiogenesis, lymph node metastasis, and apoptosis in human breast cancer. Moreover, these results warrant further studies with larger series of patients to confirm the association with short disease free survival in patients with breast cancer.

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.

Growth Factors Influence Growth and Differentiation of the Middle Ear Mucosa

OBJECTIVE

Otitis media is a major cause of morbidity in pediatric and adult patients. This inflammatory condition is characterized by mucosal hyperplasia that is thought to be mediated by the complex actions of growth factors and their respective receptors. It was the purpose of this study to determine which growth factors might be responsible for the growth and differentiation of the middle ear epithelium during otitis media.

STUDY DESIGN

The effect of several growth factors on the expansion and differentiation of normal middle ear mucosa was evaluated in tissue culture.

MATERIALS AND METHODS

Explants of normal rat middle ear mucosa were exposed in vitro to six different growth factors known to influence epithelial cells in other tissues: epidermal growth factor, amphiregulin, betacellulin, heregulin-alpha, keratinocyte growth factor, and hepatocyte growth factor.

RESULTS

After 12 days, the growth and level of cytokeratin expression were analyzed for each of the explant outgrowths. Each factor appeared to have a significant, concentration-dependent effect on either the growth or differentiation of the cultured middle ear epithelial cells.

CONCLUSION

The results suggest that several of the tested growth factors may play a significant role in controlling hyperplasia of the middle ear mucosa during otitis media.

Nuclear factor-kappaB regulates cyclooxygenase-2 expression and cell proliferation in human gastric cancer cells

Nuclear factor-kappaB (NF-kappaB) is a transcriptional regulator of inducible expression of genes including cyclooxygenase-2 (COX-2), regulating cell proliferation. NF-kappaB is kept silent in the cytoplasm via interaction with the inhibitory protein IkappaBalpha and transmigrated into the nucleus upon activation. However, constitutive NF-kappaB has been found in the nucleus of some cancer cells. We investigated the role of NF-kappaB in COX-2 expression and cell proliferation in human gastric cancer AGS cells. AGS cells were treated with antisense oligodeoxynucleotide (AS ODN) or sense oligodeoxynucleotide (S ODN) for the NF-kappaB subunit p50, or they were transfected with a mutated IkappaBalpha gene (MAD-3 mutant) or a control vector, pcDNA-3. AGS cells were treated with COX-2 inhibitors such as indomethacine and NS-398 or prostaglandin E2. mRNA expression for COX-2, and protein levels for p50, IkappaBalpha, and COX-2 were determined by reverse transcription polymerase chain reaction and Western blot analysis. The NF-kappaB levels were examined by electrophoretic mobility shift assay. Thromboxane B2 (TXB2) and 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) levels were determined by enzyme-linked immunosorbent assay. Cell proliferation was assessed by viable cell counting, [3H] thymidine incorporation, and colony formation. The nuclear level of p50 decreased in AGS cells treated with AS ODN. The IkappaBa mutant was observed in cells transfected with the mutated IkappaBa gene. NF-kappaB was inhibited in cells treated with AS ODN or transfected with the mutated IkappaBalpha gene, compared with the cells treated with S ODN or transfected with control vector. Cell proliferation, mRNA expression and protein level of COX-2, and production of TXB2 and 6-keto-PGF1alpha were inhibited in cells treated with AS ODN or transfected with the mutated IkappaBalpha gene, which had lower NF-kappaB levels than cells treated with S ODN or transfected with control vector. COX-2 inhibitors suppressed cell proliferation and production of TXB2 and 6-keto-PGF1alpha, in a dose-dependant manner. Prostaglandin E2 prevented the inhibition of proliferation in cells treated with AS ODN or transfected with the mutated IkappaBalpha gene. In conclusion, NF-kappaB mediates COX-2 expression, which may be related to cell proliferation, in human gastric cancer cells.

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.