Masakyo Asahara

Gene expression of keratinocyte and hepatocyte growth factors during the healing of rat gastric mucosal lesions

BACKGROUND & AIMS The factors that stimulate the growth of gastric mucosal cells during gastric mucosal healing are not completely understood. This study was designed to investigate the gene expression of keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF) in the healing of gastric mucosal lesions. METHODS Northern blot analysis and reverse-transcription polymerase chain reaction were used to show HGF and KGF messenger RNA. RESULTS Transcripts of HGF and KGF were not shown in rat gastric mucosal epithelium but were found in submucosal and muscular layers under normal conditions. When acute gastric mucosal lesions were induced by indomethacin treatment, expression of HGF messenger RNA was augmented in submucosal, muscular, or serosal layers, whereas the transcript of KGF was not influenced. When rat gastric mucosal epithelial cell line RGM1 and rat gastric mucosal primary culture cells were incubated with HGF or KGF, their proliferation was enhanced. CONCLUSIONS The results showed increased gene expression of HGF together with constant production of KGF during gastric mucosal healing.

Presence of Prostaglandin EP4 Receptor Gene Expression in a Rat Gastric Mucosal Cell Line

RGM-1 is an epithelial cell line established from gastric mucosa of adult Wistar rats. In this study, we characterized this newly established cell line by Northern blot analysis. We also investigated deoxyribonucleic acid (DNA) synthesis and hexosamine production in RGM-1 by PGE2. Northern blot analysis did not detect any transcript of proton pump, gastrin receptor, histidine decarboxylase, somatostatin and pepsinogen 1, indicating the absence of characteristics of parietal, ECL, D and chief cells in RGM-1 cells. However, this periodic acid-Schiff (PAS)-positive cell line expressed prostaglandin EP4 receptor mRNA but not EP1 and EP3 receptor mRNAs. [3H]-thymidine incorporation into DNA of the cells was not increased by PGE2. In contrast, PGE2 increased hexosamine content in RGM-1 cells. These results suggest that RGM-1 may be a useful model of gastric mucosal cells and that PGE2 plays a role on mucin synthesis in RGM-1 cells possibly via EP4 receptors.

GASTRIN RECEPTOR GENES ARE EXPRESSED IN GASTRIC PARIETAL AND ENTEROCHROMAFFIN-LIKE CELLS OF MASTOMYS NATALENSIS

Although gastric enterochromaffin-like (ECL) carcinoid tumors are known to develop in patients with long-standing hypergastrinemia, the expression of the gastrin receptor gene in ECL cells has not yet been demonstrated. Therefore, this study was designed to examine gastrin receptor gene expression in ECL cells.Mastomys gastric mucosal cells isolated by enzyme dispersion were separated into 10 fractions (F1–10) by centrifugal elutriation. Each fraction was examined histologically to determine whether they contained ECL and/or parietal cells and Northern blot analysis was used to confirm the presence of histidine decarboxylase and H+, K+-ATPase gene expression. ECL cells were found only in fractions 1 and 2, whereas parietal cells were detected in fractions 6–10. Gastrin receptor gene expression was demonstrated in both parietal cell-rich and ECL cell-rich fractions. In addition, the gastrin receptor cDNA sequences obtained from the two of the fractions (F1 and 8) were identical. These results suggest that gastrin receptor genes are expressed in ECL cells as well as in parietal cells and that these receptors are identical.

Erythropoietin Stimulates Proliferation of Rat-Cultured Gastric Mucosal Cells

Most anemic patients with chronic renal failure have gastric mucosal lesions. However, these gastric lesions are often improved after the administration of recombinant human erythropoietin (rHuEPO). We have used the rat gastric mucosal cell line RGM-1, to examine the possibility that rHuEPO might directly stimulate the growth of gastric mucosal cells in vitro. Our results show that rHuEPO dose-dependently increased [3H]thymidine incorporation into RGM-1 cells and their expression of c-myc gene. In addition, 125I-rHuEPO specifically bound to RGM-1 cells, and moreover, erythropoietin receptor gene expression was detected by RT-PCR. We conclude that rHuEPO has a direct growth-promoting effect on RGM-1 cells, suggesting possible usefulness of rHuEPO administration for the treatment of gastric mucosal damage in patients with chronic renal failure.

Establishment of primary epithelial cell culture from elutriated rat gastric mucosal cells

Proliferating cells in the gastric mucosal epithelium were successfully enriched by counterflow elutriation in a medium-sized cell fraction. When inoculated on culture plates coated with E-C-L cell attachment matrix, these cells differentiated into mucus-producing cells after reaching confluence. Northern blot analysis did not detect any transcript of the proton pump, histidine decarboxylase, somatostatin, or pepsinogen I, indicating the absence of parietal, ECL, D, and chief cells in the confluent monolayer. These mucus-producing cell monolayers that respond to various growth factors may be a suitable model with which to investigate the function of gastric mucus cells in vitro.

Gastrin Receptor Gene Expression in Several Human Carcinomas

Gastrin has been shown to enhance the growth of various human tumors. The present study was designed to examine the gastrin receptor gene expression in various human carcinoma cell lines and in surgically resected carcinoma tissues. By Northern blot analysis, gastrin receptor mRNA was detected in 3 out of 7 small cell lung carcinoma cell lines. Gastrin receptor mRNA was also expressed in one out of 8 colon carcinoma cell lines and 2 out of 10 colon carcinoma tissues. Moreover, one of two small cell carcinoma cell lines of the stomach clearly expressed gastrin receptor mRNA. However, none of the gastric adenocarcinoma cell lines or surgically resected gastric adenocarcinomas tested had any detectable expression of gastrin receptor gene. These findings may suggest a role of gastrin receptor in the growth and differentiation of certain human carcinomas.

Regenerating gene expression in normal gastric mucosa and indomethacin-induced mucosal lesions of the rat

Regenerating (reg) gene expression was tested in rat gastrointestinal mucosa to investigate the role played by this gene in the healing of mucosal lesions. Expression ofreg mRNA was higher in the stomach than in any other region of the gastrointestinal tract. The gastric cells that expressedreg mRNA were located in the deepest mucosal layer and were small in diameter. In an injured state following indomethacin treatment,reg gene expression was markedly augmented, accompanied by an increase of c-fos expression and healing of the mucosal lesions. These results suggest a role of thereg gene in the healing of gastrointestinal mucosal lesions.

Production and Activation of Hepatocyte Growth Factor during the Healing of Rat Gastric Ulcers

The hepatocyte growth factor has been reported to be a potent mitogen of various epithelial cells, including gastric mucosal cells. Therefore, production and activation of hepatocyte growth factor in the gastric wall were investigated to speculate on the possible role of this factor in the healing of gastric ulcer in rats. Indomethacin-induced gastric mucosal lesions and acetic acid induced ulcers were employed as models of acute gastric lesions and chronic ulcer, respectively. Immunoblot and Northern blot analyses indicate that experimentally induced gastric mucosal lesions stimulate not only the production of hepatocyte growth factor, but also the conversion to its active form. This conversion was accompanied by increased gene expression of hepatocyte growth factor activator in the stomach. In rats with acute mucosal lesions, hepatocyte growth factor activator mRNA was most abundant 6 h after induction of mucosal lesions. On the other hand, hepatocyte growth factor and hepatocyte growth factor activator mRNA levels were elevated until 15 days after the induction of chronic ulcers. In summary, it has been clarified that not only production, but also activation of hepatocyte growth factor is stimulated during gastric ulcer healing.

Involvement of β-Adrenergic Receptor Kinase-1 in Homologous Desensitization of Histamine H2 Receptors in Human Gastric Carcinoma Cell Line MKN-45

The poorly differentiated human gastric carcinoma cell line MKN-45 possesses histamine H2 receptors which are homologously desensitized by histamine. In order to clone the cDNA of a receptor kinase specific for H2 receptors, we performed RT-PCR at a low annealing temperature using oligo-DNA primers bearing the conserved sequences of the kinase domain of the G protein-coupled receptor kinase (GRK) family. However, we were able to isolate only cDNAs for beta-adrenergic receptor kinase 1 (beta ARK1) and GRK6. Interestingly, treatment of MKN-45 cells with beta ARK1 antisense phosphorothioate oligo-DNA (PON) resulted in significant loss of desensitization of H2 receptors by histamine, whereas GRK6 antisense PON had no effect. Thus, beta ARK1 appears to be involved in the homologous desensitization of H2 receptors in MKN-45 cells.

Effect of aging on gastrin receptor gene expression in rat stomach

Gastrin is a pivotal humoral factor which regulates gastric acid secretion through its receptors. There is no report, however, concerning the age-related changes of gastrin receptor gene expression in the stomach. Northern blot analysis and in situ hybridization were performed to clarify the changes of gastrin receptor expression during the aging. In situ hybridization clarified that gastrin receptor mRNA was expressed mainly in enterochromaffin-like (ECL) cells in adult rat gastric mucosa. With aging, gastrin receptor gene expression in the stomach increased with the concomitant increase in histidine decarboxylase mRNA. Since histidine decarboxylase is a marker of gastric ECL cells, the augmented gastrin receptor mRNA in aged rats may be caused by the increased ECL cells in gastric mucosa during the aging.