Expression of serum response factor in normal rat gastric mucosa

Serum response factor (SRF) is a transcription factor that is involved in cell proliferation, muscle and neuron development and maintenance. Its expression in gastric mucosa remains unknown. In this study we demonstrated that SRF is expressed in normal rat gastric tissue as two isoforms and localized mainly to smooth muscle cells of muscularis mucosae and its extensions into the lamina propria, to muscularis propria, and musculature of the vascular system. To a lesser extent, SRF is also expressed in the gastric epithelium of the mucosal neck area (proliferative zone) and in the endothelial cells of microvessels. These data suggest that the main role of SRF in normal gastric tissue is to maintain muscular support and contraction and possibly epithelial regeneration.

Indomethacin delays gastric restitution: association with the inhibition of focal adhesion kinase and tensin phosphorylation and reduced actin stress fibers

Repair of superficial gastric mucosal injury is accomplished by the process of restitution-migration of epithelial cells to restore continuity of the mucosal surface. Actin filaments, focal adhesions, and focal adhesion kinase (FAK) play crucial roles in cell motility essential for restitution. We studied whether epidermal growth factor (EGF) and/or indomethacin (IND) affect cell migration, actin stress fiber formation, and/or phosphorylation of FAK and tensin in wounded gastric monolayers. Human gastric epithelial monolayers (MKN 28 cells) were wounded and treated with either vehicle or 0.5 mM IND for 16 hr followed by EGF. EGF treatment significantly stimulated cell migration and actin stress fiber formation, and increased FAK localization to focal adhesions, and phosphorylation of FAK and tensin, whereas IND inhibited all these at the baseline and EGF-stimulated conditions. IND-induced inhibition of FAK phosphorylation preceded changes in actin polymerization, indicating that actin depolymerization might be the consequence of decreased FAK activity. In in vivo experiments, rats received either vehicle or IND (5 mg/kg i.g.), and 3 min later, they received water or 5% hypertonic NaCl; gastric mucosa was obtained at 1, 4, and 8 hr after injury. Four and 8 hr after hypertonic injury, FAK phosphorylation was induced in gastric mucosa compared with controls. IND pretreatment significantly delayed epithelial restitution in vivo, and reduced FAK phosphorylation and recruitment to adhesion points, as well as actin stress fiber formation in migrating surface epithelial cells. Our study indicates that FAK, tensin, and actin stress fibers are likely mediators of EGF-stimulated cell migration in wounded human gastric monolayers and potential targets for IND-induced inhibition of restitution.

Serum response factor: discovery, biochemistry, biological roles and implications for tissue injury healing

Serum response factor (SRF) is a transcription factor, which binds to a serum response element (SRE) associated with a variety of genes including immediate early genes such as c-fos, fosB, junB, egr-1 and -2, neuronal genes such as nurr1 and nur77 and muscle genes such as actins and myosins. By regulating expression of these genes, SRF controls cell growth and differentiation, neuronal transmission as well as muscle development and function. SRF can be activated by a variety of agents, including serum, lysophosphatidic acid (LPA), lipopolysaccharide (LPS), 12-O-tetradecanoylphorbol-13-acetate (TPA), cytokines, tumor necrosis factor-alpha (TNFalpha), agents that increase intracellular Ca2+, T-cell virus1 activator protein, hepatitis B virus activator proteins pX, activated oncogenes and protooncogenes as well as extracellular stimuli such as antioxidant and UV light. SRF itself is regulated by both cellular signal transduction pathways and interaction with other transcription factors e.g. Sp1, ATF6 and myogenic regulatory factors. Its biological function is best elucidated for myocardium. Specific cardiac SRF transgenesis demonstrated that overexpression of SRF caused hypertrophic cardiomyopathy in mouse and the mouse died of heart failure within 6 months after birth. Other transgenic data suggested that sufficient SRF was needed for embryogenesis and early development. Since SRF is important regulator of numerous genes involved in cell growth and differentiation, including muscle and neural components, SRF may also play a crucial role in tissue injury and ulcer healing, e.g. healing of gastrointestinal ulcers.

Low dose ethanol potentiates indomethacin induced inhibition of wound re-epithelialization in duodenal monolayers

Nonsteroidal anti-inflammatory drugs (NSAIDs) induce gastroduodenal mucosal injury and ulceration, and delay ulcer healing. In contrast, the effects of low dose ethanol in induction of gastroduodenal mucosal injury, and the subsequent wound repair remains unclear. The aim of this study was to determine, using an in-vitro duodenal epithelial wound model, whether low clinically relevant doses of ethanol or indomethacin interfere with the wound re-epithelialization of duodenal epithelial monolayers. The possible potentiating effect of ethanol on indomethacin modulation of duodenal re-epithelialization was also examined. In-vitro epithelial wounds were created in confluent IEC-6 duodenal epithelial monolayers by a razor blade scrape. Ethanol at low concentrations (0.25, 0.5, 0.75%) did not have significant effect on duodenal wound re-epithelialization. Similarly, low doses of indomethacin (.01,.05, 0.1 mM) also did not have a significant effect on wound re-epithelialization. However, the combination of ethanol (0.5 or 0.75%) and indomethacin (0.1mM) produced a marked inhibition of IEC-6 re-epithelialization. At the low doses used, ethanol and indomethacin (individually or in combination) did not have direct cytotoxic effect on IEC-6 cells. Ethanol or indomethacin (at the studied concentrations) had only minimal effect on the actin stress fibers in the cells at the migration front. However, in combination, they almost completely abolished the actin stress fibers at the migration front. These findings demonstrate that while low clinically relevant doses of ethanol and indomethacin individually do not affect re-epithelialization of wounded duodenal epithelial monolayers, in combination they produce a significant inhibition.

NSAID inhibition of RGM1 gastric monolayer wound re-epithelialization: comparison of selective Cox-2 versus non-selective Cox inhibitors

Clinical studies indicate that specific cyclooxygenase-2 (Cox-2) inhibitors are less ulcerogenic than their non-selective predecessors (e.g. indomethacin). However, Cox-2 inhibitors may also interfere with ulcer healing. Re-epithelialization is a crucial factor in both gastrointestinal mucosal injury and ulcer healing. This study was aimed to compare the effects of selective Cox-2 inhibitor (NS398) versus non-selective Cox inhibitor (indomethacin) on basal and basic fibroblast growth factor (bFGF) - stimulated gastric wound re-epithelialization. In-vitro epithelial wounds were created in confluent monolayers of RGM1 rat gastric epithelial cells by a razor blade scrape. Following wounding there was a significant re-epithelialization by 24 hrs. Indomethacin (0.25 mM and 0.5 mM) significantly inhibited basal wound re-epithelialization in a dose dependent manner. In contrast, selective Cox-2 inhibitor NS398 did not inhibit the basal re-epithelialization process. Basic FGF treatment produced significant enhancement of wound re-epitheliazation at the various concentrations [10, 20, 30, 40, 50 and 70 ng/ml] studied. Both indomethacin and NS398 inhibited bFGF stimulated wound re-epithelialization, with indomethacin having a greater inhibitory effect. The extent of NS398 inhibition was limited to the bFGF-stimulated component, whereas indomethacin inhibition extended to both the bFGF-stimulated and the basal re-epithelialization components. These findings indicate that specific Cox-2 inhibitor (NS398) does not interfere with the basal re-epithelialization but significantly inhibits the bFGF - stimulated re-epithelialization, whereas indomethacin interferes with both the basal as well as the bFGF-stimulated wound re-epithelialization.

Biological role of phosphatase PTEN in cancer and tissue injury healing

PTEN (phosphatase and tensin homolog deleted on chromosome ten) also referred to as MMAC (mutated in multiple advanced cancers) was discovered as a tumor suppressor gene and later found to be a phospholipid phosphatase. PTEN negatively regulates Akt activation by preventing its phosphorylation. PTEN therefore inhibits the PI 3-kinase/Akt signaling pathway which is important for cell growth and survival. Overexpression or enhanced activation of PTEN can potentially impair injury healing by at least 4 mechanisms. PTEN can: 1) inhibit entry into the cell cycle by inhibiting G1 to S phase progression and arrest cell proliferation required for tissue reconstruction during injury healing; 2) increase apoptosis by blocking Akt activation leading to increased Bad and Caspase-9 activities; 3) inhibit hypoxia-induced angiogenesis required for injury healing by blocking Akt-mediated VEGF gene transcription; 4) inhibit Akt-mediated cell migration, i.e. re-epithelialization, which is also required for injury healing. The same mechanisms can also suppress cancer growth and metastases. Therefore, elucidating the role of the PTEN/PI 3-kinase/Akt pathway will likely advance our knowledge of the mechanisms controlling the processes of injury healing and cancer growth.

NSAID inhibition of GI cancer growth: clinical implications and molecular mechanisms of action

Epidemiological studies suggest that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) reduce the incidence of and mortality from colorectal, gastric, and esophageal cancers. The precise mechanisms by which NSAIDs exert their chemopreventive effects are not fully explained, but likely involve inhibition of cyclo-oxygenase, the enzyme that converts arachidonic acid to prostaglandins. Two isoforms of this enzyme, cyclo-oxygenase 1 (COX-1) and COX-2, have been identified. COX-2 is absent in normal mucosa but is overexpressed in colonic, gastric, and esophageal cancers, as well as their precursor lesions. The inhibition of COX-2 through either pharmacological agents or gene deletion results in suppression of colonic polyp formation. NSAIDs reduce colonic, gastric, and esophageal cancer cell growth, in part, by inducing apoptosis. However, the antineoplastic effects of NSAIDs may be partly independent of their ability to inhibit COX-2. The mechanisms involved in the antineoplastic actions of NSAIDs include inhibition of angiogenesis (essential for delivery of oxygen and nutrients to a growing tumor), induction of apoptosis (which is usually reduced in cancer cells) by stimulation of proapoptotic genes, and direct inhibition of cancer cell growth by blocking signal transduction pathways responsible for cell proliferation.

Selective cyclooxygenase-2 blocker delays healing of esophageal ulcers in rats and inhibits ulceration-triggered c-Met/hepatocyte growth factor receptor induction and extracellular signal-regulated kinase 2 activation

Nonsteroidal anti-inflammatory drugs, both nonselective and cyclooxygenase-2 (COX-2) selective, delay gastric ulcer healing. Whether they affect esophageal ulcer healing remains unexplored. We studied the effects of the COX-2 selective inhibitor, celecoxib, on esophageal ulcer healing as well as on the cellular and molecular events involved in the healing process. Esophageal ulcers were induced in rats by focal application of acetic acid. Rats with esophageal ulcers were treated intragastrically with either celecoxib (10 mg/kg, once daily) or vehicle for 2 or 4 days. Esophageal ulceration triggered increases in: esophageal epithelial cell proliferation; expression of COX-2 (but not COX-1); hepatocyte growth factor (HGF) and its receptor, c-Met; and activation of extracellular signal-regulated kinase 2 (ERK2). Treatment with celecoxib significantly delayed esophageal ulcer healing and suppressed ulceration-triggered increases in esophageal epithelial cell proliferation, c-Met mRNA and protein expression, and ERK2 activity. In an ex vivo organ-culture system, exogenous HGF significantly increased ERK2 phosphorylation levels in esophageal mucosa. A structural analog of celecoxib, SC-236, completely prevented this effect. These findings indicate that celecoxib delays esophageal ulcer healing by reducing ulceration-induced esophageal epithelial cell proliferation. These actions are associated with, and likely mediated by, down-regulation of the HGF/c-Met-ERK2 signaling pathway.

Prostaglandin E2 transactivates EGF receptor: a novel mechanism for promoting colon cancer growth and gastrointestinal hypertrophy

Prostaglandins (PGs), bioactive lipid molecules produced by cyclooxygenase enzymes (COX-1 and COX-2), have diverse biological activities, including growth-promoting actions on gastrointestinal mucosa. They are also implicated in the growth of colonic polyps and cancers. However, the precise mechanisms of these trophic actions of PGs remain unclear. As activation of the epidermal growth factor receptor (EGFR) triggers mitogenic signaling in gastrointestinal mucosa, and its expression is also upregulated in colonic cancers and most neoplasms, we investigated whether PGs transactivate EGFR. Here we provide evidence that prostaglandin E2 (PGE2) rapidly phosphorylates EGFR and triggers the extracellular signal-regulated kinase 2 (ERK2)--mitogenic signaling pathway in normal gastric epithelial (RGM1) and colon cancer (Caco-2, LoVo and HT-29) cell lines. Inactivation of EGFR kinase with selective inhibitors significantly reduces PGE2-induced ERK2 activation, c-fos mRNA expression and cell proliferation. Inhibition of matrix metalloproteinases (MMPs), transforming growth factor-alpha (TGF-alpha) or c-Src blocked PGE2-mediated EGFR transactivation and downstream signaling indicating that PGE2-induced EGFR transactivation involves signaling transduced via TGF-alpha, an EGFR ligand, likely released by c-Src-activated MMP(s). Our findings that PGE2 transactivates EGFR reveal a previously unknown mechanism by which PGE2 mediates trophic actions resulting in gastric and intestinal hypertrophy as well as growth of colonic polyps and cancers.

NSAID inhibition of GI cancer growth: clinical implications and molecular mechanisms of action

Epidemiological studies suggest that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) reduce the incidence of and mortality from colorectal, gastric, and esophageal cancers. The precise mechanisms by which NSAIDs exert their chemopreventive effects are not fully explained, but likely involve inhibition of cyclo-oxygenase, the enzyme that converts arachidonic acid to prostaglandins. Two isoforms of this enzyme, cyclo-oxygenase 1 (COX-1) and COX-2, have been identified. COX-2 is absent in normal mucosa but is overexpressed in colonic, gastric, and esophageal cancers, as well as their precursor lesions. The inhibition of COX-2 through either pharmacological agents or gene deletion results in suppression of colonic polyp formation. NSAIDs reduce colonic, gastric, and esophageal cancer cell growth, in part, by inducing apoptosis. However, the antineoplastic effects of NSAIDs may be partly independent of their ability to inhibit COX-2. The mechanisms involved in the antineoplastic actions of NSAIDs include inhibition of angiogenesis (essential for delivery of oxygen and nutrients to a growing tumor), induction of apoptosis (which is usually reduced in cancer cells) by stimulation of proapoptotic genes, and direct inhibition of cancer cell growth by blocking signal transduction pathways responsible for cell proliferation.

von Hippel Lindau tumor suppressor and HIF-1alpha: new targets of NSAIDs inhibition of hypoxia-induced angiogenesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) block prostaglandin synthesis and impair healing of gastrointestinal ulcers and growth of colonic tumors, in part, by inhibiting angiogenesis. The mechanisms of this inhibition are incompletely explained. Here we demonstrate that both nonselective (indomethacin) and COX-2-selective (NS-398) NSAIDs inhibit hypoxia-induced in vitro angiogenesis in gastric microvascular endothelial cells via coordinated sequential events: 1) increased expression of the von Hippel-Lindau (VHL) tumor suppressor, which targets proteins for ubiquitination leading to 2) reduced accumulation of hypoxia-inducible factor-1alpha (HIF-1alpha) and, as a result, 3) reduced expression of vascular endothelial growth factor (VEGF) and its specific receptor Flt-1. Because HIF-1alpha is the major trigger for hypoxia-induced activation of the VEGF and Flt-1 genes, this could explain how NSAIDs inhibit hypoxia-induced angiogenesis. Exogenous VEGF and, to a lesser extent, exogenous prostaglandins partly reversed the NSAIDs inhibition of hypoxia-induced angiogenesis. Taken together, these results indicate that NSAIDs inhibit hypoxia-induced angiogenesis in endothelial cells by inhibiting VEGF and Flt-1 expression through increased VHL expression and the resulting ubiquitination and degradation of HIF-1alpha. This action of NSAIDs has both prostaglandin-dependent and prostaglandin-independent components.

Esophageal ulceration activates keratinocyte growth factor and its receptor in rats: implications for ulcer healing

BACKGROUND & AIMS

Cellular and molecular mechanisms of esophageal ulcer healing remain unexplored. We studied the sequential cellular events and the expression of keratinocyte growth factor (KGF) and its receptor (KGF-R) during the healing of experimental esophageal ulcers.

METHODS

Esophageal ulcers were produced in rats by local application of acetic acid. Studies included (1) ulcer size, (2) quantitative histology, and (3) KGF and KGF-R messenger RNA and protein expression by reverse-transcription polymerase chain reaction, Western blotting, and immunostaining. In separate groups, ulcer size and esophageal epithelial proliferation were evaluated after a single injection of recombinant human KGF (1 mg/kg) around the ulcer.

RESULTS

Ulcers were fully developed 3 days after induction, and 58% of ulcers were re-epithelialized by 9 days. At 3 days, in esophageal tissue bordering the ulcers, KGF messenger RNA and protein were increased by 191% and 151%, respectively, and KGF-R messenger RNA and protein were increased by 357% and 237%, respectively. KGF was expressed in stromal cells, whereas KGF-R was expressed in epithelial cells. At 6 days, epithelial proliferation at the ulcer margin was increased by 216%, and treatment with KGF further enhanced cell proliferation and accelerated ulcer healing.

CONCLUSIONS

KGF is a likely mediator of esophageal epithelial proliferation and ulcer healing.

Activation of eNOS in rat portal hypertensive gastric mucosa is mediated by TNF-alpha via the PI 3-kinase-Akt signaling pathway

Activation of endothelial nitric oxide synthase (eNOS) in portal hypertensive (PHT) gastric mucosa leads to hyperdynamic circulation and increased susceptibility to injury. However, the signaling mechanisms for eNOS activation in PHT gastric mucosa and the role of TNF-alpha in this signaling remain unknown. In PHT gastric mucosa we studied (1) eNOS phosphorylation (at serine 1177) required for its activation; (2) association of the phosphatidylinositol 3-kinase (PI 3-kinase), and its downstream effector Akt, with eNOS; and, (3) whether TNF-alpha neutralization affects eNOS phosphorylation and PI 3-kinase-Akt activation. To determine human relevance, we used human microvascular endothelial cells to examine directly whether TNF-alpha stimulates eNOS phosphorylation via PI 3-kinase. PHT gastric mucosa has significantly increased (1) eNOS phosphorylation at serine 1177 by 90% (P <.01); (2) membrane translocation (P <.05) and phosphorylation (P <.05) of p85 (regulatory subunit of PI 3-kinase) by 61% and 85%, respectively; (3) phosphorylation (P <.01) and activity (P <.01) of Akt by 40% and 52%, respectively; and (4) binding of Akt to eNOS by as much as 410% (P <.001). Neutralizing anti-TNF-alpha antibody significantly reduced p85 phosphorylation, phosphorylation and activity of Akt, and eNOS phosphorylation in PHT gastric mucosa to normal levels. Furthermore, TNF-alpha stimulated eNOS phosphorylation in human microvascular endothelial cells. In conclusion, these findings show that in PHT gastric mucosa, TNF-alpha stimulates eNOS phosphorylation at serine 1177 (required for its activation) via the PI 3-kinase-Akt signal transduction pathway.

Despite activation of EGF-receptor-ERK signaling pathway, epithelial proliferation is impaired in portal hypertensive gastric mucosa: relevance of MKP-1, c-fos, c-myc, and cyclin D1 expression

Portal hypertensive (PHT) gastric mucosa has increased susceptibility to injury and impaired mucosal healing. Our previous study demonstrated increased ERK activation and MAP kinase phosphatase-1 (MKP-1) overexpression in PHT gastric mucosa. However, it remains unknown which tyrosine kinase receptors are involved in ERK activation and whether ERK activation results in increased cell proliferation. We examined whether EGF receptor (EGF-R) is involved in ERK activation and whether ERK activation triggers epithelial proliferation in PHT gastric mucosa. In gastric mucosa of PHT and sham-operated (SO) rats we studied: (1) EGF-R mRNA and protein expression as well as phosphorylation and membrane protein tyrosine kinase (PTK) activity; (2) ERK2 phosphorylation and activity; (3) MKP-1 mRNA and protein; (4) c-fos, c-myc and cyclin D1 mRNAs, and gastric epithelial proliferation. In PHT gastric mucosa: (1) EGF-R mRNA, protein and phosphorylation and membrane PTK activity were all significantly increased by 38%, 49%, 43% and 49%, respectively; (2) ERK2 phosphorylation and activity were significantly increased by 40% and 50 %, respectively; (3) MKP-1 mRNA and protein expression were significantly increased by 27% and 34%, respectively. In contrast, (4) c-fos, c-myc, and cyclin D1 mRNAs expression were all significantly decreased in PHT gastric mucosa by 36%, 33%, and 49%, respectively, and cell proliferation was significantly lower that in SO rats (11% in PHT vs. 18% in SO). These results suggest that in PHT gastric mucosa, ERK activation is mediated through EGF-R upregulation, but the gastric epithelial proliferation is impaired, possibly by MKP-1 overexpression, leading to reduction of c-fos, c-myc and cyclin D1.

Nonsteroidal anti-inflammatory drugs inhibit re-epithelialization of wounded gastric monolayers by interfering with actin, Src, FAK, and tensin signaling

Re-epithelialization is essential for gastrointestinal ulcer and cutaneous wound healing. It requires epithelial cell migration and proliferation, processes that are stimulated by epidermal growth factor (EGF), and dependent on the cell cytoskeleton. Activation of Src and focal adhesion kinase (FAK) has been implicated in EGF-stimulated cell migration. Nonsteroidal anti-inflammatory drugs (NSAIDs) (both nonselective and Cox2-selective) interfere with ulcer healing and re-epithelialization in vitro and in vivo, but the cellular targets and mechanisms remain unexplored forming the basis of this study. Using a wounded gastric epithelial cell monolayer model, we demonstrated that NSAIDs reduce both basal and epidermal growth factor (EGF)-induced re-epithelialization, and that this action involves disruption of actin stress fiber formation, reduced c-Src activity, decreased phosphorylation of focal adhesion kinase (FAK), tensin and their cellular re-distribution. There was a strong correlation between NSAIDs-mediated inhibitory effect on re-epithelialization and loss of stress fibers and reduced tensin signal. Furthermore, NSAIDs significantly reduced EGF-stimulated c-Src association with FAK. These findings suggest that NSAIDs can directly affect the cell cytoskeleton and signaling pathways essential for re-epithelialization.

MAPK (ERK2) kinase--a key target for NSAIDs-induced inhibition of gastric cancer cell proliferation and growth

Limited clinical and experimental studies indicate that nonsteroidal anti-inflammatory drugs (NSAIDs) may inhibit gastric cancer growth. However, the mechanisms involved are not completely understood and cannot be explained by COX-2 inhibition alone. MAPK signaling pathway is essential for cell proliferation, but the effect of NSAIDs on MAPK activity and phosphorylation in gastric cancer has never been studied. Since increased and unregulated cell proliferation and reduced cell apoptosis are important features of cancer growth, we studied whether NS-398, a selective COX-2 inhibitor and/ or indomethacin (IND), a non-selective NSAID: 1) inhibit gastric cancer cell proliferation, 2) whether this inhibition is mediated via MAPK (ERK2), and 3) whether NSAIDs enhance apoptosis in gastric cancer cells. Human gastric epithelial cells (MKN28) derived from gastric tubular adenocarcinoma were cultured and treated with either vehicle, IND (0.25-0.5mM) or NS-398 (50-100 microM) for 6, 16, 24 and 48h.

STUDIES

1) Cellular proliferation was determined by 3H-thymidine uptake. 2) MAPK activity was measured by incorporation of radiolabeled phosphate into myelin basic protein. 3) Apoptosis was evaluated using TUNEL assay. IND and NS-398 significantly inhibited the proliferation of MKN28 cells at 24h by 3.5 - 5 fold (p<0.002) and at 48h by 2.5 - 10 fold (p<0.02). Both NSAIDs also significantly inhibited ERK2 activity: IND >53% inhibition, NS-398, 100 microM >72% inhibition; all p<0.05. Both IND and NS-398 significantly increased apoptotic index. In conclusion, IND and NS-398 significantly inhibit proliferation and growth of human gastric cancer cell line MKN28. This effect is mediated by NSAID-induced inhibition of MAPK (ERK2) kinase signaling pathway, essential for cell proliferation. NSAIDs also increase apoptosis in MKN28 cells. In addition to inhibiting cyclooxygenase, NSAIDs inhibit phosphorylating enzymes--kinases essential for signaling cell proliferation.

Activation of hypoxia inducible factor-1alpha in gastric mucosa in response to ethanol injury: a trigger for angiogenesis?

Gastric mucosal injury triggers angiogenesis and activation of VEGF expression, but the mechanism(s) of VEGF gene activation are not known. In some tissues (e.g. myocardium), hypoxia triggers activation of hypoxia-inducible factor-1alpha (HIF-1alpha), a transcription factor known to activate VEGF gene expression. This study was aimed to determine whether hypoxia and/or alcohol injury may induces HIF-1alpha in gastric mucosa. Normal rat gastric tissue was incubated in organ culture under either hypoxic or normoxic conditions for 6hrs. Rats received, intragastrically, either saline or alcohol and gastric mucosa bordering necrosis was obtained at 1-24hrs. HIF-1alpha mRNA and protein were determined by RT-PCR and Western-blot analysis. HIF-1alpha and VEGF proteins were localized by immunostaining. Incubation of normal gastric mucosa under hypoxia caused a significant elevation of HIF-1alpha mRNA (20+/-2%, p<0.05) and protein (262+/-15%, p<0.005) vs. normoxia. Following alcohol injury, gastric mucosa bordering necrosis demonstrated a significant increase in HIF-1alpha mRNA at 3 and 6hrs (40+/-4%, 19+/-2%; p<0.05), and protein (>300+/-16%; p<0.02 at all time points; highest at 1-3hrs). HIF-1alpha signal was detected in regenerating mucosal microvessels, where it co-localized with VEGF. Since HIF-1alpha initiates transcription of VEGF mRNA, HIF-1alpha activation by ethanol-induced injury is likely responsible for activation of VEGF gene and induction of angiogenesis.

Effect of Helicobacter pylori culture supernatant on acute reflux esophagitis in a rat model

BACKGROUND/AIMS

Prevalence of Helicobacter pylori, especially cagA-positive strains is inversely related to gastroesophageal reflux disease. The aim of this study was to examine whether H. pylori culture supernatants affect acute esophagitis induced by acid or mixed reflux in rats.

METHODOLOGY

Three different H. pylori strains were used. Acute esophagitis was induced in 59 male Wistar rats by ligation of both the transitional regions between the forestomach and glandular portion, and the pylorus or the lower part of duodenum. After operation, the rats were either left untreated or treated with intragastric injection of either vehicle or H. pylori culture supernatants and were sacrificed 6 or 24 hours later. Esophagitis index, depth of esophageal lesions, esophageal epithelial degeneration, and infiltration of inflammatory cells were examined.

RESULTS

Gross esophageal erosions and ulcers were observed up to mid-esophagus in all animals. H. pylori culture supernatants did not affect esophageal mucosal injury and no histologically significant differences were found among rats.

CONCLUSIONS

H. pylori culture supernatants, regardless of cagA gene expression, did not affect acute esophagitis induced by acid or mixed reflux. This finding suggests that no powerful protective factors against reflux-induced mucosal injury were produced by H. pylori.

Defective mitogen-activated protein kinase (ERK2) signaling in gastric mucosa of portal hypertensive rats: potential therapeutic implications

Portal hypertensive (PHT) gastropathy is a frequent, serious complication of liver cirrhosis. PHT gastric mucosa has numerous abnormalities such as reduced mucosal potential differences, reduced surface oxygenation, and increased susceptibility to injury caused by alcohol, aspirin, and other noxious factors. Because such mucosal injury is initially mediated by oxygen free radicals, and because mitogen-activated protein (MAP) kinase (ERK2) protects against cellular stress and induces cell proliferation, we postulated that oxidative stress-induced ERK2 activation is defective in PHT gastric mucosa. Here we show that in PHT gastric mucosa, ERK2 activation by oxidative stress is impaired. This impairment is mediated by overexpression of MAP kinase phosphatase-1 (MKP-1), which results from the underlying and continual oxidative state associated with portal hypertension, and is ameliorated by inhibiting MKP-1. Furthermore, we found that supplementing vitamin E, a free radical scavenger, reduces the oxidative state in PHT gastric mucosa, normalizes MKP-1 expression, and thereby reverses impairment of oxidative stress-induced ERK2 activation. Finally, we show that orally administered vitamin E completely reverses the increased susceptibility of PHT gastric mucosa to alcohol injury. Our findings point to a new molecular and mechanistic basis for PHT gastropathy and provide a new therapeutic modality for protection of PHT gastric mucosa.

Gene therapy for gastric ulcers with single local injection of naked DNA encoding VEGF and angiopoietin-1

BACKGROUND & AIMS

Angiogenesis, formation of new capillary blood vessels, is crucial for gastroduodenal ulcer healing because it enables delivery of oxygen and nutrients to the healing site. Because angiogenesis is stimulated by vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1), we studied whether local gene therapy with nonviral DNA encoding VEGF and/or Ang1 into the ulcer base could accelerate ulcer healing through enhanced angiogenesis.

METHODS

Gastric ulcers were induced in rats by acetic acid applied to the serosal surface of the stomach, and the site around the ulcer was injected with nonviral plasmid-encoding full-length complementary DNA (cDNA) of human recombinant (rh) VEGF165, rhAng1, or their combination. For some studies, neutralizing anti-VEGF antibody was administered.

RESULTS

Single local injection of plasmids encoding VEGF165 and Ang1 significantly increased neovascularization and accelerated ulcer healing. A neutralizing anti-VEGF antibody significantly reduced the acceleration of ulcer healing resulting from the treatment. Coinjection of both plasmids encoding rhVEGF165 and rhAng1 resulted in formation of more mature vessels and to more complete restoration of gastric glandular structures within the ulcer scar. However, this did not result in further reduction of ulcer size.

CONCLUSIONS

VEGF and Ang1 gene therapy, with limited duration of target gene expression, significantly accelerates gastric ulcer healing. Coinjection of both plasmids leads to more complete structural restoration. Inhibition of accelerated healing by a neutralizing anti-VEGF antibody indicates an essential role for VEGF and enhanced angiogenesis in ulcer healing.

Inhibition of human colon cancer cell growth by antisense oligodeoxynucleotides targeted at basic fibroblast growth factor

BACKGROUND

Basic fibroblast growth factor has been shown to be mitogenic in colon cancer cell lines. In human malignant melanoma cells, antisense oligodeoxynucleotides targeted against basic fibroblast growth factor messenger RNA significantly inhibit cell growth. However, the efficacy of such an antisense oligodeoxynucleotide strategy has not been evaluated for colon cancer cells.

AIM

To investigate whether basic fibroblast growth factor can stimulate the growth of HT-29 human colon cancer cells and whether antisense oligodeoxynucleotides can inhibit growth of these cells at baseline.

METHODS

Western blotting analyses were used to confirm the presence of basic fibroblast growth factor protein in this cell line. Cell growth was assessed after 2, 4 and 6 days of treatment by cell counting using the trypan blue exclusion method. Phosphorothioate-modified oligodeoxynucleotides (10 microM) were used, complementary to codon 60 of the basic fibroblast growth factor messenger RNA. Cationic liposomes (DOTAP) were used to enhance the cellular uptake of the oligodeoxynucleotides.

RESULTS

Western blotting demonstrated the presence of basic fibroblast growth factor protein in this cell line. Basic fibroblast growth factor (1-40 ng/mL) dose-dependently stimulated cell growth and peak values were obtained at a dose of 20 ng/mL. By contrast, antisense oligodeoxynucleotide treatment significantly inhibited cell growth compared with the sense oligodeoxynucleotide-treated cells (P=0.007). This inhibition was reversed by the addition of basic fibroblast growth factor, 20 ng/mL.

CONCLUSION

Treatment targeted against basic fibroblast growth factor messenger RNA inhibits growth of HT-29 human colon cancer cells. This finding may provide a rationale for the therapeutic use of antisense oligodeoxynucleotides targeted at basic fibroblast growth factor for the treatment of colon cancer.

PGE(2) stimulates VEGF expression in endothelial cells via ERK2/JNK1 signaling pathways

Vascular endothelial growth factor (VEGF) plays an essential role in the initiation and regulation of angiogenesis-a crucial component of wound healing and cancer growth. Prostaglandins (PGs) stimulate angiogenesis but the precise mechanisms of their pro-angiogenic actions remain unexplained. We investigated whether prostaglandin E(2) (PGE(2)) can induce VEGF expression in rat gastric microvascular endothelial cells (RGMEC) and the signaling pathway(s) involved. We demonstrated that PGE(2) significantly increased ERK2 and JNK1 activation and VEGF mRNA and protein expression. Incubation of RGMEC with PD 98059 (MEK kinase inhibitor) significantly reduced PGE(2)-induced ERK2 activity, VEGF mRNA and protein expression. Furthermore, PD 98059 treatment almost completely abolished JNK1 activation. Our data suggest that PGE(2)-stimulates VEGF expression in RGMEC via transactivation of JNK1 by ERK2. One potential implication of this finding is that increased PG levels in cancers could facilitate tumor growth by stimulating VEGF synthesis and angiogenesis.

Cyclooxygenase 2-implications on maintenance of gastric mucosal integrity and ulcer healing: controversial issues and perspectives

Cyclooxygenase (COX), the key enzyme for synthesis of prostaglandins, exists in two isoforms (COX-1 and COX-2). COX-1 is constitutively expressed in the gastrointestinal tract in large quantities and has been suggested to maintain mucosal integrity through continuous generation of prostaglandins. COX-2 is induced predominantly during inflammation. On this premise selective COX-2 inhibitors not affecting COX-1 in the gastrointestinal tract mucosa have been developed as gastrointestinal sparing anti-inflammatory drugs. They appear to be well tolerated by experimental animals and humans following acute and chronic (three or more months) administration. However, there is increasing evidence that COX-2 has a greater physiological role than merely mediating pain and inflammation. Thus gastric and intestinal lesions do not develop when COX-1 is inhibited but only when the activity of both COX-1 and COX-2 is suppressed. Selective COX-2 inhibitors delay the healing of experimental gastric ulcers to the same extent as non-COX-2 specific non-steroidal anti-inflammatory drugs (NSAIDs). Moreover, when given chronically to experimental animals, they can activate experimental colitis and cause intestinal perforation. The direct involvement of COX-2 in ulcer healing has been supported by observations that expression of COX-2 mRNA and protein is upregulated at the ulcer margin in a temporal and spatial relation to enhanced epithelial cell proliferation and increased expression of growth factors. Moreover, there is increasing evidence that upregulation of COX-2 mRNA and protein occurs during exposure of the gastric mucosa to noxious agents or to ischaemia-reperfusion. These observations support the concept that COX-2 represents (in addition to COX-1) a further line of defence for the gastrointestinal mucosa necessary for maintenance of mucosal integrity and ulcer healing.

Portal hypertensive gastric mucosa has reduced activation of MAP kinase (ERK2) in response to alcohol injury: a key to impaired healing?

Portal hypertensive (PHT) gastric mucosa has increased susceptibility to injury and impaired mucosal healing. Because our previous study showed that ulcer-induced activation of mitogen-activated protein (MAP) kinase (ERK) plays a pivotal role in gastric mucosal healing, we investigated whether ERK activation is altered in PHT gastric mucosa following alcohol injury. We studied ERK2 phosphorylation and activity and expression of MAP kinase phosphatase-1 (MKP-1) in gastric mucosa of PHT and sham-operated (SO) normal rats both at baseline and following alcohol injury. In SO gastric mucosa, ERK2 phosphorylation and activity were significantly increased time-dependently following alcohol injury: by 221% and 137%, respectively at 24 h vs. baseline. In contrast, in PHT gastric mucosa following alcohol injury, neither ERK2 phosphorylation nor activity was increased versus baseline. In PHT gastric mucosa, MKP-1 mRNA and protein expression were increased at baseline versus SO rats and were increased further following alcohol injury with values higher by 20%-40% at each study time versus SO rats. Because ERK2 is crucial for mucosal healing, reduced ERK2 activation resulting from the overexpression of MKP-1 might be the basis for the impaired mucosal healing in PHT gastric mucosa.