Growth regulation of rabbit gastric epithelial cells and protooncogene expression

In vivo evidence for the role of RegI in gastric regeneration: transgenic overexpression of RegI accelerates the healing of experimental gastric ulcers

On the basis of its temporal and spatial pattern of expression during the healing of gastric ulcers, RegI is implied to be a key growth factor governing the gastric progenitor cell proliferation, which is fundamental for reconstruction of the gastric tissue; however, there is no direct in vivo evidence. The aim of this study was to use RegI-transgenic (Tg) mice to test the role of RegI protein in the healing of experimentally induced gastric ulcers. The stomachs from 48 pairs of wild-type (Wt) and Tg littermates were examined for gastric erosions after 24 h of water-immersion stress, or, 6, 12, 18 and 24 h after oral administration of HCl/ethanol. Expression levels of c-fos and c-myc proto-oncogenes were examined over time by real-time reverse transcriptase PCR to assess gastric cell proliferation. Almost all the littermate pairs tested showed superiority of Tg mice over Wt mice in the ability of decreasing ulcer index (UI) (cumulative length of erosion). The time-course study revealed that the UIs of Tg were lower in the healing phase, and not in the injury phase. The fraction of proliferating cells was higher in Tg mice than in Wt mice throughout the time course as assessed by c-fos expression levels. This is the first in vivo evidence that RegI has a role in gastric ulcer healing. We suggest that RegI exerts its effects by promoting growth and not by cytoprotection.

Characterization of integrin beta6 and thrombospondin-1 double-null mice

To identify overlapping and non-overlapping functions for TSP-1 and alphavbeta6, we crossed TSP-1-null and beta6-null mice and compared the phenotype of the double-null mice with those of wild-type and single-null mice. The double-null mice exhibited focal acute and organizing pneumonia that was more severe than the wild-type and single-null mice as well as a significantly higher incidence of inflammation in tissues other than the lung. The TSP-1-null and beta6-null mice exhibited a five to eight-fold increase in granulocyte recruitment to the lung three days after exposure to lipopolysaccharide. They also had abnormalities that were infrequently observed in the wild-type and single-null mice, including heart degeneration (8.35% in wild-type and 28.1% in double-null mice), hyperplasia of the glandular of the stomach (2.8% in wild-type and 21.1% in double-null mice) and endometrial hyperplasia (0% in wild-type and 38.5% in double-null females). Furthermore, the beta6-null and double-null mice displayed a significant elevation in benign and malignant cancers. Stomach papillomas, squamous cell carcinomas of the ear and stomach, and adenocarcinomas of the lungs, vagina/cervix and colon were observed with the highest frequency. These data demonstrate that TSP-1 and alphavbeta6 are involved in regulation of the immune system and epithelial homeostasis. They also indicate that alphavbeta6 functions as a tumor suppressor gene and that activation of TGFbeta by TSP-1 and alphavbeta6 contributes to normal tissue architecture and function.

Transgenic overexpression of Reg protein caused gastric cell proliferation and differentiation along parietal cell and chief cell lineages

Reg (regenerating gene product) was originally identified as a growth factor involved in pancreatic regeneration. During the healing course of gastric erosion, Reg expression is highly increased in the enterochromaffin-like (ECL) cells surrounding the ulcer crater, suggesting its role as a regulator of gastric mucosal regeneration. However, there has been no direct in vivo evidence of a growth-promoting role of Reg for the gastric mucosal cells. In the current study, Reg-transgenic mice were created and gastric mucosa were analysed for histological changes. Transgenic mice showed a marked increase in the thickness of the fundic mucosa. Anti-proliferating cell nuclear antigen (PCNA) staining of the fundic mucosa demonstrated the enlargement of the proliferating neck zone and the lower PCNA-negative zone. Histological analysis employing antibodies against cell-type markers revealed expansion of the chief cell and parietal cell populations and no change in the number of surface mucus-producing cells, ECL cells, or G cells. In conclusion, Reg has a growth-promoting effect on gastric progenitor cells and an activity to direct the differentiation of the cells into chief cell and parietal cell lineages. This was in contrast to other factors, all of which had been shown to drive differentiation towards mucus producing cells in vivo. In the injured gastric mucosa, Reg may play a unique and important part in the reconstruction of the properly organized mucosal architecture.

A mechanistic study of proliferation induced by Angelica sinensis in a normal gastric epithelial cell line

It has been reported that an extract from Angelica sinensis mainly consisting of polysaccharides (95%) prevented ethanol- or indomethacin-induced gastric mucosal damage (Cho CH et al. Planta Med 2000;66:348-51). However, it is not known whether Angelica sinensis has a direct stimulatory effect on the healing of gastric mucosal lesions. To study the hypothesis that Angelica sinensis has a direct mucosal healing effect in rats and in isolated gastric epithelial cells, we assessed the wound repair in both animals and normal cell culture (RGM-1), as well as [3H]thymidine incorporation, ornithine decarboxylase (ODC) activity, and ODC protein and c-Myc protein expression after different treatments in RGM-1 cells. We found that Angelica sinensis crude extract (ASCE) dose-dependently enhanced gastric ulcer healing in rats and promoted wound repair in RGM-1 cells. It also significantly stimulated [3H]thymidine incorporation and ODC activity in RGM-1 cells in a concentration-dependent manner. ODC and c-Myc protein expression was also increased as a result of this process. DL-alpha-difluoromethyl-ornithine repressed the [3H]thymidine incorporation and ODC activity induced by ASCE. Pretreatment with c-Myc antisense oligodeoxynucleotides blocked the stimulatory action of ASCE on [3H]thymidine incorporation and ODC protein expression. These data suggest that ASCE has a direct mucosal healing effect on gastric epithelial cells, while ODC and c-Myc are closely associated with this effect.

Inhibitory effect of macrophage-derived factors on the recovery of wounds induced in rat gastric epithelial monolayers

The effect of macrophage supernatant on the recovery of wounds induced in rat gastric epithelial RGM1 monolayers was investigated. The repair of wounds induced in the monolayers of RGM1 cells was accelerated time-dependently by 10 ng/mL of transforming growth factor-alpha (TGF-alpha). TGF-alpha also significantly stimulated DNA synthesis in RGM1 cells for 24 hr. Upon treatment of the cells with the macrophage supernatant, spontaneous and TGF-alpha-stimulated restoration was inhibited in a time- and concentration-dependent manner. After 24 hr, TGF-alpha-enhanced restoration was eliminated completely by the supernatant at 10(6) cells/mL. Similarly, the macrophage supernatant suppressed the spontaneous and TGF-alpha-stimulated DNA syntheses in a concentration-dependent manner. The macrophage supernatant at 10(6) cells/mL contained 0.4 ng/mL of interleukin-1beta (IL-1beta). Interleukin-1 receptor antagonist (IL-1RA) reversed the inhibition induced by the macrophage supernatant in a concentration-dependent manner. Nonetheless, pretreatment with IL-1RA had no effects on the spontaneous and TGF-alpha-stimulated DNA syntheses. Reverse transcription-polymerase chain reaction analysis revealed that RGM1 cells express mRNA for IL-1 receptor type 1, but not for type 2. These results indicate that macrophages can inhibit the spontaneous and TGF-alpha-stimulated recovery of wounds induced in gastric epithelial monolayers. The inhibitory effects of the supernatant are suggested to be partially mediated through a IL-1beta/IL-1 receptor type 1 pathway.

Effects of EGF and TGFbeta1 on c-myc gene expression and DNA synthesis in embryonic hamster palate mesenchymal cells

Previous work has shown that cell proliferation is a major contributor to the early palate morphogenesis in mammals. The present study was undertaken to examine the effect of EGF, TGFbeta1 and their combination on proliferation (measured by DNA synthesis) and on the expression of a growth related proto-oncogene, c-myc, in embryonic hamster palate mesenchymal cells (HPMC). Vertically developing hamster palatal shelves were dissected on day 11 of gestation, and trypsinized, and primary cultures were grown in DMEM + 10% serum at 37 degrees C and 5% CO2. Following appropriate growth factor treatment of HPMC, DNA synthesis was measured by scintillation counting and extracted RNA was subjected to Northern blot analysis. In serum-starved, pre-confuent cultures treated with EGF (20 ng/ml), DNA synthesis was stimulated in the presence of 2.5% serum. In contrast, treatment of HPMC with TGFbeta1 (10 ng/ml) in the presence or absence of EGF/serum for 24 hr, or HPMC pre-treatment with TGFbeta1 (30 min) followed by EGF/serum (24 hr), resulted in an arrest of DNA synthesis. Northern blot analysis of RNA extracted from HPMC showed that as serum-starved, growth-arrested cells progressed through G0 to G1 phase of the cell cycle, following EGF treatment, c-myc was expressed by 1 hr and declined thereafter. In contrast, TGFbeta1 did not support expression of c-myc. Following pre- or co-treatment with TGFbeta1, the EGF +/- serum-induced expression of c-myc was seen between 1 and 6 hr. It appears that EGF-induced expression of c-myc may be involved in advancing the HPMC in G1, and thus may contribute to the onset of DNA synthesis in HPMC. Since co- or pre-treatment with TGFbeta1 did not inhibit EGF/serum induced expression of c-myc, it is possible that growth arresting effect of TGFbeta1 may not be exerted directly through inhibition or blockage of c-myc expression.

Transforming growth factor-beta inhibits proliferation and maturation of cultured guinea pig gastric pit cells

We studied the effects of transforming growth factor-beta1 (TGF-beta1) on guinea pig gastric mucous cells, cultured in serum-free conditions. Electron microscopy showed that most cells were pre-pit cells, characterized by the presence of a few secretory granules scattered in the cytoplasm. Epidermal growth factor (EGF) stimulated cell growth, [3H]glucosamine uptake, and accumulation of mucus granules positive for galactose oxidase-Schiff reaction. This EGF-induced maturation into pit cells was confirmed morphologically by the appearance of uniformly dense ovoid or spherical mucus granules packed in the ectoplasm. Western blotting with an antiphosphotyrosine antibody showed that TGF-beta1 did not inhibit the EGF-initiated tyrosine phosphorylation of the EGF receptor. Northern blotting with cDNA probes for c-fos and c-myc demonstrated that TGF-beta1 did not affect the EGF-induced expression of the transcripts. However, TGF-beta1-treated cells did not replicate and remained in an immature stage, even in the presence of EGF, suggesting a potential role of TGF-beta1 in the regulation of proliferation and differentiation of a pit cell lineage in vivo.

Water immersion-restraint stress induces expression of immediate-early genes in gastrointestinal tract of rats

The aims of this study were to determine 1) which cells are involved in stress-induced acute gastric mucosal lesion and 2) what kinds of molecular alterations are induced by stress, using immediate-early genes (IEG) as tools for detection of cellular activation. Male Wistar rats were exposed to acute water immersion-restraint stress. Protein and mRNA for IEG were detected by immunohistochemistry and in situ hybridization, respectively. This stress induced the expression of c-fos and nerve growth factor-induced gene (NGFI-A) mRNA in gastric epithelial cells, the smooth muscle layer of small blood vessels, and the stomach wall. Stress upregulated the mRNA levels of these IEG in the duodenal epithelial cells and induced de novo expression of IEG in the smooth muscle layer of small blood vessels and the duodenal wall. These findings indicate that these cells are activated in response to stress. Expression of these IEG and/or transcriptional factors may reflect an initiation of mechanisms for repairing the lesions induced by stress as well as an adaptation to the stress.

Helicobacter pylori culture supernatant interferes with epidermal growth factor-activated signal transduction in human gastric KATO III cells

The mechanisms by which Helicobacter pylori infection leads to gastroduodenal ulceration remain poorly understood. Previous studies have shown that H. pylori vacuolating cytotoxin (VacA) inhibits proliferation of gastric epithelial cells, which suggests that H pylori may interfere with gastric mucosal repair mechanisms. In this study, we investigated the effects of H. pylori broth culture supernatants on epidermal growth factor (EGF)-mediated signal transduction pathways in a gastric carcinoma cell line (KATO III). Exposure of these cells to EGF resulted in increased expression and phosphorylation of the EGF receptor (EGF-R), increased ERK2 activity and phosphorylation, and increased c-fos protein levels. Preincubation of cells with broth culture supernatant from VacA (+) H. pylori strain 60190 inhibited the capacity of EGF to induce each of these effects. In contrast, preincubation of cells with broth culture supernatant from an isogenic VacA-mutant strain (H. pylori 60190-v1) failed to inhibit the effects of EGF. These results suggest that the H. pylori vacuolating cytotoxin interferes with EGF-activated signal transduction pathways, which are known to be essential for cell proliferation and ulcer healing.

Interleukin-1beta inhibits growth factor-stimulated restoration of wounded rat gastric epithelial cell monolayers

We examined the effect of interleukin-1beta (IL-1beta) on spontaneous and enhanced restoration (cell migration and proliferation) using an in vitro wound model comprising a confluent monolayer of rat gastric epithelial RGM1 cells. Repair of an artificial wound in a cell monolayer was found to be time- and concentration-dependent when the cells were incubated with epidermal growth factor (EGF) or transforming growth factor (TGF) -alpha alone for up to 24 hr. The growth factors also stimulated DNA synthesis significantly for 24 hr in a concentration-related manner. IL-1beta had no effect on wound restoration in the absence of the growth factors. However, it markedly inhibited the restoration enhanced by EGF and TGF-alpha, the inhibition being about 60% and 70%, respectively. In addition, IL-1beta significantly reduced the DNA synthesis stimulated by the growth factors. The EGF- and TGF-alpha-enhanced restoration was reduced by about 30% by mitomycin C, which potently inhibited the stimulated DNA synthesis. Mitomycin C had no effect on the spontaneous restoration. Even when treated with mitomycin C, the inhibitory effect of IL-1beta on the enhanced wound repair was still observed; however, the extent of the inhibition was decreased. These results indicate that IL-1beta inhibits the migration as well as the proliferation of gastric epithelial cells enhanced by EGF and TGF-alpha, resulting in a failure of wound healing.

Effect of sofalcone on the expression of hepatocyte growth factor (HGF) and a brief review of HGF in the stomach

Previous studies of hepatocyte growth factor (HGF) in the stomach are briefly reviewed. Exogenous HGF has a strong effect on proliferation and migration of gastric epithelial cells. These effects of HGF are mediated by the specific receptor c-MET. Our previous immunohistochemical study revealed that the main source of endogenous HGF in human gastric ulcer is gastric fibroblasts. These findings suggest that HGF may play an important role in the repair of gastric ulcers through a paracrine mechanism. Therefore, regulation of HGF expression by gastric fibroblasts may be important. We have demonstrated that prostaglandins (PGs) E1 and E2 strongly stimulate HGF expression by gastric fibroblasts, indicating that the clinical efficacy of PGs is mediated by HGF, PGE1 actually facilitates restitution in an in vitro gastric mucosal model consisting of gastric epithelial cells and fibroblasts, which was completely inhibited by anti-HGF antibody. In this study we investigated the effect of an anti-ulcer drug, sofalcone, on PGE2 release and HGF expression by human gastric fibroblasts in primary culture. Sofalcone induced PGE2 release by human gastric fibroblasts in a dose-dependent manner. It also stimulated HGF expression by gastric fibroblasts, indicating that PGs induced by sofalcone increased HGF expression. These findings suggest that clinical efficacy of PGs and sofalcone might be mediated, at least in part, by HGF.

Epiregulin stimulates proliferation of rabbit gastric cells in primary culture through autophosphorylation of the epidermal growth factor receptor

Epiregulin, a growth factor of the epidermal growth factor (EGF) family, was recently purified from conditioned medium of a mouse fibroblast-derived tumor cell line. It was reported that epiregulin exhibited bifunctional properties in the regulation of cell growth. However, the effect of epiregulin on gastric cell proliferation is not known. The aims of this study were to determine whether: (1) epiregulin affects proliferation of rabbit cultured gastric cells, (2) epiregulin-induced stimulation of cell proliferation is mediated by the tyrosine kinase pathway, and (3) epiregulin stimulates autophosphorylation of EGF-receptors. Epiregulin stimulated cell proliferation to a significant extent. This effect was completely blocked by treatment with genistein. Epiregulin stimulated tyrosine phosphorylation of a 170 kDa protein, which represents the EGF receptor, in a dose-dependent fashion. These findings suggest that epiregulin has mitogenic effects on rabbit gastric cultured cells, possibly mediated via the tyrosine kinase pathway through autophosphorylation of EGF receptors.

Differential localization of transforming growth factor-beta isoforms in human gastric mucosa and overexpression in gastric carcinoma

Transforming growth factor beta (TGF-beta) isoforms comprise a family of multifunctional polypeptide growth factors that either inhibit or stimulate cell proliferation. We examined TGF-beta expression in normal human gastric mucosa and carcinoma. The distribution and expression of TGF-beta isoforms in 4 normal mucosa samples from organ donors, in 12 normal mucosa samples adjacent to gastric cancer and in 12 gastric carcinomas were examined using immunohistochemistry and Northern blot analysis. Because TGF-beta s regulate collagen expression, collagen type I alpha1 mRNA amounts were also examined. Immunohistochemical analysis of normal human gastric tissue samples indicated that TGF-beta1 localized principally in parietal cells but also in some surface mucus cells, TGF-beta2 was present exclusively in chief cells and TGF-beta3 was present in parietal, chief and mucus cells. In the gastric cancers, strong colocalization of TGF-beta1, -beta2 and -beta3 was evident in the cancer cells. Northern blot analysis indicated that, compared to normal gastric tissue, gastric cancers showed a 4.8- and 6-fold increase in mRNA amounts encoding TGF-beta1 and TGF-beta3, respectively. In contrast, TGF-beta2 mRNA amounts were comparable in both groups. Northern blot analysis showed a 10-fold increase in human collagen type I alpha1 mRNA amounts compared to normal gastric tissue. These findings imply a role forTGF-beta s in normal human gastric mucosa function, and raise the possibility that the aberrant colocalization and overexpression of all 3 TGF-beta isoforms in human gastric cancer cells in vivo may contribute to the pathobiology of gastric carcinoma.

Keratinocyte growth factor is an endogenous stimulant of rabbit gastric epithelial cell proliferation and migration in primary culture

Mesenchymal-epithelial interactions are important in the gastric mucosal repair. However, specific factors responsible for such interactions have not been established. In the present study, keratinocyte growth factor (KGF) significantly stimulated proliferation of gastric epithelial cells dose dependently and synergistically with hepatocyte growth factor (HGF), epidermal growth factor (EGF) and insulin. Restitution of gastric epithelial monolayers was also assessed, using a round wound restitution model. Keratinocyte growth factor facilitated the restitution of gastric epithelial cells significantly but did not have any effects on gastric fibroblasts. Keratinocyte growth factor receptor mRNA was expressed by gastric epithelial cells, indicating that these effects were elicited by the specific receptor mediated pathway. Northern blot analysis revealed the expression of KGF mRNA in gastric fibroblasts but not in gastric epithelial cells, indicating the production of KGF. These results suggest that KGF might be involved in gastric mucosal repair, through mesenchymal-epithelial interaction.

Hepatocyte growth factor is the most potent endogenous stimulant of rabbit gastric epithelial cell proliferation and migration in primary culture

Various growth factors are suggested to be involved in gastric mucosal repair. Our previous studies have shown that exogenous hepatocyte growth factor (HGF) has a proliferative effect on gastric epithelial cells. In the present study, comparison of the maximum proliferative effects and the optimum concentrations of several growth factors revealed that HGF was the most potent mitogen for gastric epithelial cells, as is the case for hepatocytes. Restitution of gastric epithelial cell monolayers was assessed using a round wound restitution model. HGF was the most effective agent for facilitating gastric epithelial restitution among those tested. A binding assay revealed specific binding of HGF to its receptor on gastric epithelial cells. Northern blot analysis confirmed the expression of specific HGF receptor mRNA (c-met) by gastric epithelial cells but not by gastric fibroblasts. To investigate endogenous HGF production, we determined the effect of gastric fibroblast-conditioned medium on epithelial proliferation and restitution. The conditioned medium produced similar effects to HGF and its activity was neutralized by an anti-HGF antibody. In addition, expression of HGF mRNA was detected in gastric fibroblasts but not in gastric epithelial cells. Our immunohistochemical study confirmed these in vitro data by means of demonstrating the existence and localization of HGF at human native gastric mucosa. HGF was localized at fibroblasts under the epithelial cell layer around gastric ulcers. These results suggest that HGF may be a potent endogenous promotor of gastric epithelial cell proliferation and migration, and may contribute to gastric mucosal repair through a paracrine mechanism.