Song-Ze Ding

Helicobacter pylori Infection Induces Oxidative Stress and Programmed Cell Death in Human Gastric Epithelial Cells

ABSTRACT Helicobacter pylori infection is associated with altered gastric epithelial cell turnover. To evaluate the role of oxidative stress in cell death, gastric epithelial cells were exposed to various strains of H. pylori, inflammatory cytokines, and hydrogen peroxide in the absence or presence of antioxidant agents. Increased intracellular reactive oxygen species (ROS) were detected using a redox-sensitive fluorescent dye, a cytochrome c reduction assay, and measurements of glutathione. Apoptosis was evaluated by detecting DNA fragmentation and caspase activation. Infection with H. pylori or exposure of epithelial cells to hydrogen peroxide resulted in apoptosis and a dose-dependent increase in ROS generation that was enhanced by pretreatment with inflammatory cytokines. Basal levels of ROS were greater in epithelial cells isolated from gastric mucosal biopsy specimens from H. pylori-infected subjects than in cells from uninfected individuals. H. pylori strains bearing the cag pathogenicity island (PAI) induced higher levels of intracellular oxygen metabolites than isogenic cag PAI-deficient mutants. H. pylori infection and hydrogen peroxide exposure resulted in similar patterns of caspase 3 and 8 activation. Antioxidants inhibited both ROS generation and DNA fragmentation by H. pylori. These results indicate that bacterial factors and the host inflammatory response confer oxidative stress to the gastric epithelium during H. pylori infection that may lead to apoptosis.

Helicobacter pylori infection, oncogenic pathways and epigenetic mechanisms in gastric carcinogenesis

Chronic colonization of the human stomach by Helicobacter pylori, a Gram-negative bacterium, is the major cause of chronic gastritis, peptic ulcers and gastric cancer. Recent progress has elucidated important bacterial and host factors that are responsible for H. pylori-induced gastric inflammation and gastric malignancy. H. pylori cytotoxin-associated antigen A is the major oncogenic factor injected into host cells from bacteria and it disrupts epithelial cell functions. Together with H. pylori cag pathogenicity island, it causes general inflammatory stress within gastric mucosa and activates multiple oncogenic pathways in epithelial cells. A growing list of these pathways includes NF-kappaB, activator protein-1, PI3K, signal transducers and activators of transcription 3, Wnt/beta-catenin and cyclooxygenase 2. H. pylori induces epigenetic alterations, such as DNA methylation and histone modification, which play critical roles in oncogenic transformation. In addition, investigations into gastric stem cell or progenitor cell biology have shed light on the mechanisms through which gastric cancer may originate. Continued investigation in these areas will yield novel insights and help to elucidate the mechanisms of bacteria-induced carcinogenesis.

Helicobacter pylori-Induced Histone Modification, Associated Gene Expression in Gastric Epithelial Cells, and Its Implication in Pathogenesis

Histone modifications are critical in regulating gene expression, cell cycle, cell proliferation, and development. Relatively few studies have investigated whether Helicobacter pylori, the major cause of human gastric diseases, affects histone modification. We therefore investigated the effects of H. pylori infection on histone modifications in a global and promoter-specific manner in gastric epithelial cells. Infection of gastric epithelial cells by wild-type H. pylori induced time- and dose-dependent dephosphorylation of histone H3 at serine 10 (H3 Ser10) and decreased acetylation of H3 lysine 23, but had no effects on seven other specific modifications. Different cag pathogenicity island (PAI)-containing-clinical isolates showed similar abilities to induce H3 Ser10 dephosphorylation. Mutation of cagA, vacA, nonphosphorylateable CagA mutant cagAEPISA, or disruption of the flagella showed no effects, while deletion of the entire cagPAI restored the H3 Ser10 phosphorylation to control levels. Analysis of 27 cagPAI mutants indicated that the genes that caused H3 Ser10 dephosphorylation were similar to those that were previously found to induce interleukin-8, irrespective of CagA translocation. This effect was independent of ERK or p38 pathways and type I interferon signaling. Additionally, c-Jun and hsp70 gene expression was associated with this histone modification. These results demonstrate that H. pylori alters histone modification and host response via a cagA-, vacA-independent, but cagPAI-dependent mechanisms, which contribute to its persistent infection and pathogenesis.

Toll‐like Receptor 2‐Mediated Gene Expression in Epithelial Cells During Helicobacter pylori Infection

Background.  Helicobacter pylori is the major pathogen causing chronic gastritis and peptic ulcer disease and is closely linked to gastric malignancy. We have previously shown that H. pylori‐induced NF‐κB activation and interleukin (IL)‐8 secretion are mediated by Toll‐like receptor (TLR) 2 in epithelial cells. However, the TLR2‐mediated global gene expression profile of the epithelial cell during H. pylori infection is still unknown. The goal of this study was to identify TLR2‐regulated genes in epithelial cells induced by H. pylori.

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.

Helicobacter pylori and mitogen-activated protein kinases mediate activator protein-1 (AP-1) subcomponent protein expression and DNA-binding activity in gastric epithelial cells

Emerging evidence has suggested a critical role for activator protein-1 (AP)-1 in regulating various cellular functions. The goal of this study was to investigate the effects of Helicobacter pylori and mitogen-activated protein kinases (MAPK) on AP-1 subcomponents expression and AP-1 DNA-binding activity in gastric epithelial cells. We found that H. pylori infection resulted in a time- and dose-dependent increase in the expression of the proteins c-Jun, JunB, JunD, Fra-1, and c-Fos, which make up the major AP-1 DNA-binding proteins in AGS and MKN45 cells, while the expression levels of Fra-2 and FosB remained unchanged. Helicobacter pylori infection and MAPK inhibition altered AP-1 subcomponent protein expression and AP-1 DNA-binding activity, but did not change the overall subcomponent composition. Different clinical isolates of H. pylori showed various abilities to induce AP-1 DNA binding. Mutation of cagA, cagPAI, or vacA, and the nonphosphorylateable CagA mutant (cagA(EPISA)) resulted in less H. pylori-induced AP-1 DNA-binding activity, while mutation of the H. pylori flagella had no effect. extracellular signal-related kinase (ERK), p38, and c-Jun N-terminal kinase (JNK) each selectively regulated AP-1 subcomponent expression and DNA-binding activity. These results provide more insight into how H. pylori and MAPK modulate AP-1 subcomponents in gastric epithelial cells to alter the expression of downstream target genes and affect cellular functions.