Gastric carcinogenesis and Helicobacter pylori infection

Intersections between innate immune response and gastric cancer development

Worldwide, gastric cancer (GC) is the fifth most commonly diagnosed malignancy. It has a reduced prevalence but has maintained its poor prognosis being the fourth leading cause of deaths related to cancer. The highest mortality rates occur in Asian and Latin American countries, where cases are usually diagnosed at advanced stages. Overall, GC is viewed as the consequence of a multifactorial process, involving the virulence of the Helicobacter pylori (H. pylori) strains, as well as some environmental factors, dietary habits, and host intrinsic factors. The tumor microenvironment in GC appears to be chronically inflamed which promotes tumor progression and reduces the therapeutic opportunities. It has been suggested that inflammation assessment needs to be measured qualitatively and quantitatively, considering cell-infiltration types, availability of receptors to detect damage and pathogens, and presence or absence of aggressive H. pylori strains. Gastrointestinal epithelial cells express several Toll-like receptors and determine the first defensive line against pathogens, and have been also described as mediators of tumorigenesis. However, other molecules, such as cytokines related to inflammation and innate immunity, including immune checkpoint molecules, interferon-gamma pathway and NETosis have been associated with an increased risk of GC. Therefore, this review will explore innate immune activation in the context of premalignant lesions of the gastric epithelium and established gastric tumors.

Helicobacter pylori induces somatic mutations in TP53 via overexpression of CHAC1 in infected gastric epithelial cells

Infection with Helicobacter pylori is known to decrease the level of glutathione in gastric epithelial cells and increase the production of reactive oxygen species (ROS), which can lead to DNA damage and the development of gastric cancer. Cation transport regulator 1 (CHAC1) has γ‐glutamylcyclotransferase activity that degrades glutathione. We found that cagA‐positive H. pylori infection triggered CHAC1 overexpression in human gastric epithelial (AGS) cells leading to glutathione degradation and the accumulation of ROS. Nucleotide alterations in the TP53 tumour suppressor gene were induced in AGS cells overexpressing CHAC1, whereas no mutations were detected in cells overexpressing a catalytically inactive mutant of CHAC1. A high frequency of TP53 mutations occurred in H. pylori‐infected AGS cells, but this was prevented in cells transfected with CHAC1 siRNA. These findings indicate that H. pylori‐mediated CHAC1 overexpression degrades intracellular glutathione, allowing the accumulation of ROS which subsequently causes mutations that could contribute to the development of gastric cancer.

Association between Helicobacter pylori genotypes and severity of chronic gastritis, peptic ulcer disease and gastric mucosal interleukin-8 levels: Evidence from a study in the Middle East

Background

The varied clinical presentations of Helicobacter pylori (H. pylori) infection are most likely due to differences in the virulence of individual strains, which determines its ability to induce production of interleukin-8 (IL-8) in the gastric mucosa. The aim of this study was to examine association between cagA, vacA-s1 and vacA-s2 genotypes of H. pylori and severity of chronic gastritis and presence of peptic ulcer disease (PUD), and to correlate these with IL-8 levels in the gastric mucosa.

Methods

Gastric mucosal biopsies were obtained from patients during esophagogastroduodenoscopy. The severity of chronic gastritis was documented using the updated Sydney system. H. pylori cagA and vacA genotypes were detected by PCR. The IL-8 levels in the gastric mucosa were measured by ELISA.

Results

H. pylori cagA and/or vacA genotypes were detected in 99 patients (mean age 38.4±12.9; 72 males), of whom 52.5% were positive for cagA, 44.4% for vacA-s1 and 39.4% for vacA-s2; and 70.7% patients had PUD. The severity of inflammation in gastric mucosa was increased with vacA-s1 (p=0.017) and decreased with vacA-s2 (p=0.025), while cagA had no association. The degree of neutrophil activity was not associated with either cagA or vacA-s1, while vacA-s2 was significantly associated with decreased neutrophil activity (p=0.027). PUD was significantly increased in patients with cagA (p=0.002) and vacA-s1 (p=0.031), and decreased in those with vacA-s2 (p=0.011). The level of IL-8 was significantly increased in patients with cagA (p=0.011) and vacA-s1 (p=0.024), and lower with vacA-s2 (p=0.004). Higher levels of IL-8 were also found in patients with a more severe chronic inflammation (p=0.001), neutrophil activity (p=0.007) and those with PUD (p=0.001).

Conclusions

Presence of vacA-s1 genotype of H. pylori is associated with more severe chronic inflammation and higher levels of IL-8 in the gastric mucosa, as well as higher frequency of PUD. Patients with vacA-s2 have less severe gastritis, lower levels of IL-8, and lower rates of PUD. The presence of cagA genotype is not associated with the severity of gastritis or IL-8 induction in the gastric mucosa. The association of cagA with PUD may be a reflection of its presence with vacA-s1 genotype.

Oxidative DNA damage as a potential early biomarker of Helicobacter pylori associated carcinogenesis

Helicobacter pylori infection is an established risk factor for gastritis, gastric ulcer, peptic ulcer and gastric cancer. CagA +ve H. pylori has been associated with oxidative DNA damage of gastric mucosa but their combined role in the development of gastric cancer is still unknown. Here we compare the combined expression of cagA and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in normal, gastritis and gastric cancer tissues. Two hundred gastric biopsies from patients with dyspeptic symptoms, 70 gastric cancer tissue samples and 30 gastric biopsies from non-dyspeptic individuals (controls) were included in this study and 8-OHdG was detected by immunohistochemistry (IHC). Histological features and the presence of H. pylori infection were demonstrated by Hematoxylin and Eosin (HE), Giemsa and alcian blue-periodic acid-Schiff ± diastase (AB-PAS ± D) staining. DNA was extracted from tissues and polymerase chain reaction (PCR) performed to determine the presence of ureaseA and cagA genes of H. pylori. The results showed the presence of H. pylori in 106 (53 %) gastric biopsies out of 200 dyspeptic patients, including 70 (66 %) cases of cagA + ve H. pylori. The presence of cagA gene and high expression of 8-OHdG was highly correlated with severe gastric inflammation and gastric cancer particularly, in cases with infiltration of chronic inflammatory cells (36.8 % cagA + ve, 18 %), neutrophilic activity (47.2 %, 25.5 %), intestinal metaplasia (77.7 %, 35.7 %) and intestinal type gastric cancer (95 %, 95.4 %) (p ≤ 0.01). In conclusion, H. Pylori cagA gene expression and the detection of 8-OHdG adducts in gastric epithelium can serve as potential early biomarkers of H. Pylori-associated gastric carcinogenesis.

Helicobacter pylori CagA induces ornithine decarboxylase upregulation via Src/MEK/ERK/c-Myc pathway: implication for progression of gastric diseases

Helicobacter pylori (H. pylori) dysregulates the expression of various genes resulting in gastric precursor lesions and cancer. Meanwhile, ornithine decarboxylase (ODC) is a key enzyme that catalyzes the formation of polyamines which are critical for cell growth. So far, the possible regulation of ODC by H. pylori and its virulence factors, and the associated mechanism in gastric epithelial cells remains undefined. In the present study, we found that cellular ODC protein was upregulated by wild-type H. pylori infection and ectopic expression of a cytotoxin-associated gene A (CagA). As a negative control, there was no such effect by cagA-mutant H. pylori infection. Results of signal protein inhibitor treatment demonstrated that the Src, MEK (mitogen-activated protein kinase kinase) and ERK (extracellular signal-regulated kinase) pathway was involved. Moreover, when c-Myc was inhibited, the stimulatory effect of CagA on ODC expression was abolished. Clinically, a positive correlation between c-Myc and ODC expression was observed in patient-derived abnormal gastric tissues. These results implied that the Src/MEK/ERK/c-Myc pathway was required for CagA-mediated ODC induction. Finally, inhibition of ODC expression led to decreased foci formation of gastric epithelial cells before and after H. pylori infection, and ODC protein was over-expressed in precancerous gastric lesions and primary gastric cancer. Collectively, our findings provide new insights into the mechanism behind H. pylori-infection-associated gastric diseases.

Expression of Helicobacter pylori γ-glutamyltransferase in silkworm cells using a baculovirus expression system

AIM: To express the Helicobacter pylori (H. pylori) γ-glutamyltransferase (GGT) in silkworm cells using a baculovirus expression system and analyze its activity in vitro.

METHODS: The structure characteristics of the H. pylori ggt gene was analyzed using biological informatics software. The genomic DNA of H. pylori was extracted and used as template to amplify the ggt genes encoding proteins with and without signal peptide by polymerase chain reaction (PCR). After sequencing, the amplified ggt gene encoding protein without signal peptide was fused with a green fluorescent protein (GFP) sequence. Subsequently, the two amplicons and the fusion sequence were cloned into the baculovirus transfer vector pFastBac1, respectively. Bac-to-Bac baculovirus system was then used to generate recombinant virus DNA. Recombinant virus DNA was transfected into silkworm BmN cells to obtain recombinant viruses. The viruses were harvested and used to infect BmN cells again. After infection, BmN cells were harvested to detect protein expression and enzymatic activity. Fluorescence was observed in infected cells using a fluorescence microscope.

RESULTS: The ggt genes encoding proteins with and without signal peptide were successfully cloned by PCR. Sequencing results indicated that no mutations occurred. All the three recombinant viruses obtained could express GGT. The activity of GGT expressed by the recombinant viruses harboring the ggt genes encoding proteins with and without signal peptide and the fusion sequence was 3.61, 10.50 and 9.31 U/L, respectively. Western blot assay demonstrated the expression of GGT-GFP fusion protein. Fluorescent microscopy showed that the fluorescence was distributed throughout the whole cell, indicating that GGT expression is not confined to a certain organelle.

CONCLUSION: GGT with enzymatic activity can be expressed in silkworm cells using the baculovirus expression system.