Role of Helicobacter pylori and p53 in regulation of gastric epithelial cell cycle phase progression

Helicobacter pylori Infection Activates the Akt-Mdm2-p53 Signaling Pathway in Gastric Epithelial Cells

BACKGROUNDS AND AIMS

Although Helicobacter pylori is widely accepted as a causative factor of many gastric diseases, the signaling pathways affected by H. pylori and subsequent effects on cell apoptosis and proliferation remain unclear. Here, we investigated the molecular mechanisms mediating H. pylori infection in gastric epithelial cells.

METHODS

Tissues from 160 patients with various gastric diseases with or without H. pylori infection were obtained and analyzed by immunohistochemistry for Akt, pAkt, Mdm2, p53, and Bax expression. In vitro, human gastric epithelial cells, GES-1, were incubated with H. pylori culture filtrates. Cell viability was measured by MTT assay. Apoptosis was evaluated by Annexin V/PI double staining followed by flow cytometry, DNA electrophoresis, and comet assay. mRNA and protein expression was assessed by RT-PCR and Western blot analysis.

RESULTS

In patient tissues, H. pylori infection was associated with significantly elevated levels of pAkt in chronic nonatrophic gastritis (CNAG), Mdm2 in dysplasia, p53 in metaplastic atrophy (MA), and Bax in CNAG and MA. In vitro, H. pylori culture filtrates reduced GES-1 cell viability in a time- and dose-dependent manner, induced G0/G1 arrest, triggered apoptosis, and increased DNA fragmentation. Mdm2 and Bax mRNA expression and pAkt, Mdm2, p53, and Bax protein expression were significantly upregulated when treated with H. pylori culture filtrates. Akt inhibition by LY294002 decreased Mdm2 expression, upregulated p53, and enhanced H. pylori-induced growth inhibition of GES-1 cells.

CONCLUSIONS

These findings suggest that Akt-Mdm2-p53 signaling is involved in the molecular response of GES-1 cells to H. pylori infection.

Role of cagA-positive Helicobacter pylori on cell proliferation, apoptosis, and inflammation in biliary cells

BACKGROUND AND AIMS

The pathogenesis of Helicobacter pylori in the human hepatobiliary system has not been clearly elucidated. We compared the effects of H. pylori cagA(+) and cagA(-) mutant strains on cell proliferation, apoptosis, and inflammation in a cholangiocarcinoma (CCA) cell line (KKU-100).

METHODS

MTT and BrdU were used to determine cell viability and DNA synthesis, respectively. The results were further investigated by RT-PCR and Western-blot analysis. The production of interleukin-8 (IL-8) was measured by ELISA assay.

RESULTS

At low H. pylori inocula (cell-bacteria ratio of 1:1), the H. pylori cagA(+) strain showed a significant stimulation in KKU-100 cell growth (109 ± 1.79%) and DNA synthesis (131 ± 3.39%) than did the H. pylori cagA(-) strain (95 ± 3.06% and 120 ± 2.32%, respectively), through activation of the anti-apoptotic bcl-2 gene, MAP kinase and NF- κB cascade. By contrast, at high H. pylori inocula (cell-bacteria ratio of 1:200), the H. pylori cagA(+) strain showed a significant reduction in KKU-100 cell survival (49 ± 2.47%) and DNA synthesis (49 ± 1.14%) than did the H. pylori cagA(-) strain (60 ± 1.30% and 75 ± 4.00%, respectively), by increased iNOS, p53 and bax, while decreased bcl-2. Additionally, caspase-8 and -3 protein were activated. The H. pylori cagA (+) strain had significantly stronger effect on IL-8 production than did the cagA(-) strain.

CONCLUSIONS

These results suggest that the H. pylori cagA(+) strain may play an important role in the development of biliary cancer by disturbing cell proliferation, apoptosis, and promoting cell inflammation in the CCA cell line.

Concurrent overexpression of serum p53 mutation related with Helicobacter pylori infection

Background & Aims

In the province of Cadiz (Spain), the adjusted mortality rate for gastric cancer in the coastal town of Barbate is 10/100.000 inhabitants, whereas in the inland town of Ubrique, the rate is twice as high. The rate of Helicobacter pylori (H. pylori) infection (H. pylori antibodies) in the normal population was 54% in Ubrique, but only 32% in Barbate. In the two decades since its original discovery, p53 has found a singularly prominent place in our understanding of human gastric cancer and H. pylori cause accumulation of reactive oxygen species in the mucosa compartment. This study was designed to compare serum levels of p53 in a population characterized by high mortality due to stomach cancer and a high prevalence of H. pylori infection and another population in which mortality from this cause and the prevalence of H. pylori infection are low.

Materials and methods

319 subjects from the low mortality population and 308 from the high mortality population were studied, as were 71 patients with stomach cancer. We measured serum immunoglobulin G antibody to H. pylori and serum mutant p53 protein and ceruloplasmin.

Results

The difference between the two populations in the prevalence of H. pylori infection was significant (p < 0.001). Of the seropositive, 81% had elevated values of mutant p53, in comparison with 11% of the seronegative (p < 0.0001). Serum concentration of ceruloplasmin was significantly higher in seropositive with elevated mutant p53 protein than in seronegative with normal levels of p53 (p < 0.05).

Conclusions

There is a significant association between infection with H. pylori, elevated titers of H. pylori antibodies, and positivity for serum mutant p53 protein. Such information can significantly increase our basic knowledge in molecular pathology of gastric cancer and protection against H. pylori infection.

Helicobacter pylori and mitogen-activated protein kinases regulate the cell cycle, proliferation and apoptosis in gastric epithelial cells

BACKGROUND AND AIMS

Helicobacter pylori infection activates mitogen-activated protein kinases (MAPK) and modulates cell proliferation and apoptosis. However, the relationship between H. pylori infection and MAPK signaling in controlling cell proliferation and apoptosis is not clear, nor has the role of MAPK on the gastric epithelial cell cycle and proliferation been established. Therefore, we investigated the effects of H. pylori infection and MAPK inhibition on these processes.

METHODS

Gastric epithelial cell lines (AGS and MKN45) were infected with H. pylori and/or treated with MAPK inhibitors. Cell cycle and apoptosis were measured by flow cytometry. Cell cycle proteins and proliferation were monitored by western blot and cell count, respectively.

RESULTS

Infection with H. pylori resulted in dose-dependent MAPK activation, cell cycle arrest, reduced proliferation and increased apoptosis. The effect of H. pylori and MAPK at various cell cycle checkpoints was noted: MEK1/2 and p38 inhibition increased H. pylori-induced cell cycle G(1) arrest, while JNK inhibition reduced G(1) arrest. MEK1/2 inhibition increased p21, p27 and cyclin E and JNK inhibition additionally increased cyclin D1 expression. Both inhibitors decreased cell proliferation. All inhibitors enhanced apoptosis after H. pylori infection. We also detected MAPK cross-talk in AGS cells: p38 and JNK inhibitors increased ERK activation. The p38 inhibitor increased JNK and the MEK1/2 inhibitor decreased JNK activation only during H. pylori infection.

CONCLUSIONS

These results suggest H. pylori and MAPK differentially regulate the cell cycle, proliferation and apoptosis in gastric epithelial cells. The imbalance between H. pylori infection and MAPK activation likely contributes to the H. pylori-induced pathogenesis.

Relationship among oxidative DNA damage, gastric mucosal density and the relevance of cagA, vacA and iceA genotypes of Helicobacter pylori

The aim of this study was to evaluate the relationship among oxidative DNA damage, density of Helicobacter pylori and the relevance of cagA, vacA and iceA genotypes of H. pylori. Gastric epithelial cells were isolated from 24 uninfected patients, 42 H. pylori infected patients with gastritis, and 61 patients with gastric cancer. Oxidative DNA damage was analyzed by the Comet assay, the density of H. pylori was measured by real-time polymerase chain reaction (PCR), and allelic variants of cagA, vacA and iceA were identified using the PCR. Infected patients by Helicobacter pylori cagA(+), vacAs1 m1 and iceA1 genotype showed higher levels of oxidative DNA damage than infected patients with H. pylori cagA(-), vacAs2 m2 and iceA2 genotypes and uninfected patients. Density of H. pylori did not influence oxidative DNA damage. Our results indicate that H. pylori genotype is more relevant than density for oxidative DNA damage.

Gastric epithelial cell proliferation and ras oncogene p21 expression in first-degree relatives of gastric cancer patients: a case-control study

OBJECTIVES

Individuals with a family history of gastric cancer have an increased risk of developing such neoplasia. This study aimed to assess epithelial cell proliferation and ras oncogene mutation in such individuals.

METHODS

Twenty dyspeptic, first-degree relatives of patients with gastric cancer and 20 matched controls were enrolled. Endoscopy with biopsies was performed in all cases. Gastric specimens were used to look for Helicobacter pylori infection and to assess both epithelial cell proliferation and ras oncogene expression by immunohistochemistry.

RESULTS

Cell proliferation values were not significantly different between the patient and control groups (18.1 +/- 7.1 versus 18.9 +/- 7.4; P = 0.7). Overall, ras mutation was detected in five out of 40 cases, and its distribution was similar between patients and controls (20 versus 10%; P = 0.9), as well as between H. pylori-positive and negative patients (22 versus 9%; P = 0.2). Cell proliferation values tended to be higher in cases with ras mutation than in those without (25.2 +/- 9.4 versus 16.8 +/- 5.8; P = 0.08). Cell proliferation values were significantly higher in H. pylori-positive cases compared with uninfected cases, in both patient (24.7 +/- 4.7 versus 12.5 +/- 2.4; P = 0.0003) and control (25.9 +/- 4.8 versus 13.3 +/- 2.8; P = 0.0003) groups.

CONCLUSIONS

Both gastric cell proliferation values and ras mutation prevalence did not differ between first-degree relatives of gastric cancer patients and controls. H. pylori infection similarly increased the proliferation index of gastric mucosa in both groups.

Helicobacter pylori induces apoptosis of rat gastric epithelial cells in vitro

AIM: To investigate the effect of Helicobacter pylori (H. pylori) sonicated extract on the apoptosis of rat gastric epithelial cells as well as the expression of apoptosis-related genes in vitro.

METHODS: H. pylori sonicated extract from strain Sydney SS-1 was cultured with OUMS-37, a kind of immortalized rat gastric cell lines. Apoptosis of the cells was confirmed according to specific changes of morphology and DNA ladder 24-48 h after co-incubation. The expression of P53 protein was detected by Western blotting and the expression of bax and bcl-2 mRNA were observed by Northern blotting.

RESULTS: The specific morphology of the cells such as shrinkage, condensation, margination of nuclear chromatin and apoptotic bodies were observed under light microscope. DNA ladder was manifested by fragment analysis. Western blotting showed a dose-dependent increased expression of wild-type P53 protein and Northern blotting showed a dose-pendent increased expression of bax mRNA and reduced expression of bcl-2 mRNA in the treated cells.

CONCLUSION: H. pylori sonicated extract induces the apoptosis in vitro through up-regulation of wild-type P53 protein and bax mRNA expression, and down-regulation of bcl-2 mRNA expression, suggesting that H. pylori infection may interrupt the balance between proliferation and apoptosis of the gastric epithelial cells, which plays a key role in gastric carcinogenesis.

Polymorphisms of DNA repair genes XRCC1 and XRCC3, interaction with environmental exposure and risk of chronic gastritis and gastric cancer

AIM

To evaluate the association between polymorphisms XRCC1 Arg194Trp and Arg399Gln and XRCC3 Thr241Met and the risk for chronic gastritis and gastric cancer, in a Southeastern Brazilian population.

METHODS

Genotyping by PCR-RFLP was carried out on 202 patients with chronic gastritis (CG) and 160 patients with gastric cancer (GC), matched to 202 (C1) and 150 (C2) controls, respectively.

RESULTS

No differences were observed among the studied groups with regard to the genotype distribution of XRCC1 codons 194 and 399 and of XRCC3 codon 241. However, the combined analyses of the three variant alleles (194Trp, 399Gln and 241Met) showed an increased risk for chronic gastritis when compared to the GC group. Moreover, an interaction between the polymorphic alleles and demographic and environmental factors was observed in the CG and GC groups. XRCC1 194Trp was associated with smoking in the CG group, while the variant alleles XRCC1 399Gln and XRCC3 241Met were related with gender, smoking, drinking and H pylori infection in the CG and GC groups.

CONCLUSION

Our results showed no evidence of a relationship between the polymorphisms XRCC1 Arg194Trp and Arg399Gln and XRCC3 Thr241Met and the risk of chronic gastritis and gastric cancer in the Brazilian population, but the combined effect of these variants may interact to increase the risk for chronic gastritis, considered a premalignant lesion. Our data also indicate a gene-environment interaction in the susceptibility to chronic gastritis and gastric cancer.

Effect of Helicobacter pylori on DNA synthesis of human epithelial cells

The effect of Helicobacter pylori on DNA synthesis of human cultured cells was examined. Viable H. pylori strains were able to stimulate DNA synthesis by gastric cancer MKN45 cells (eight of eight strains) and laryngeal cancer HEp-2 cells (seven of eight strains) but not by lung cancer A549 cells or fetal intestine Int407 cells. In contrast, neither heat-killed H. pylori nor culture supernatants of H. pylori other than SS-1 strain affected DNA synthesis of MKN45 and HEp-2 cells. In contrast, water extracts of H. pylori strains inhibited DNA synthesis. Soluble outer membrane protein (OMP) of the SS-1 strain stimulated DNA synthesis of MKN45 cells but produced no alteration in cell cycle or apoptosis induction of MKN45 cells. To identify those proteins in the soluble OMP that were capable of stimulating DNA synthesis, the OMP was fractionated by fast performance liquid chromatography with a Mono Q column. The results suggest that two proteins with molecular weights of 18 and 45 kDa, respectively, are associated with stimulation of DNA synthesis by MKN45 cells.

Antralization of gastric incisura is topographically associated with increased gastric epithelial apoptosis and proliferation, but not with CagA seropositivity

BACKGROUND AND AIMS

Helicobacter pylori infection is linked with increased antralization at the gastric incisura. The present study aimed to determine if antralization is associated with altered gastric epithelial apoptosis and proliferation and with seropositivity of the cytotoxin-associated gene product A (CagA) of H. pylori.

METHODS

Gastric biopsies taken from the antrum, incisura, body and fundus of 75 patients (34 male, 41 female; mean age 59.5 years) were used for diagnosis of H. pylori infection and assessments of histological changes. Apoptosis and Ki-67 expression in epithelial cells were determined for the antral, incisura and body biopsies by immunohistochemistry. Serum samples were tested by enzyme-linked immunosorbent assays for anti-H. pylori and anti-CagA IgG antibodies.

RESULTS

Apoptotic index (AI) and Ki-67 proliferation index (PI) were greater in the presence (vs absence) of H. pylori infection at the antrum, incisura and body (all P < 0.001), and topographically associated with chronic gastritis and gastric atrophy/intestinal metaplasia at the antrum and incisura (all P < 0.001). Moreover, AI and PI were greater in the presence (vs absence) of antralization at the incisura (20.2 +/- 0.9 vs 11.4 +/- 0.1.1 and 48.9 +/- 2.5 vs 29.9 +/- 2.5, both P < 0.001). CagA seroprevalence was 41% in the 39 infected patients. CagA seropositivity was associated with gastric atrophy/intestinal metaplasia at the antrum (chi(2) = 4.67, P = 0.03) and incisura (chi(2) = 4.88, P = 0.03), but not associated with gastric epithelial apoptosis and Ki-67 expression, nor with antralization at the incisura.

CONCLUSIONS

Antralization of gastric incisura is topographically associated with increased gastric epithelial apoptosis and proliferation, but not with CagA seropositivity.

Microbial-gut interactions in health and disease. Gastrointestinal cancer

A combination of both environmental and genetic factors contributes to the vast majority of human cancers and in particular cancers of the gastrointestinal tract, including the stomach, colon and rectum. The mechanisms associated with cancer causation or prevention are largely unknown and the subject of much research. Many of these mechanisms implicate the metabolic activities of the bacterial flora normally resident in the gastrointestinal tract. This paper examines both the detrimental and beneficial consequences of bacterial activity of the gastrointestinal tract, focusing in particular on the stomach and large intestine.