Bax translocation and mitochondrial fragmentation induced by Helicobacter pylori
H Ashktorab1, S Frank, A R Khaled
1Cancer Center and GI Division, Department of Medicine, Howard University, Washington, DC 20060, USA. hashktorab@howard.edu
Background And Aims:
Previous in vitro and in vivo studies have revealed an association between Helicobacter pylori infection and apoptosis in gastric epithelial cells. Although involvement of the Bcl-2 family of proteins as well as cytochrome c release has been demonstrated in H pylori induced cell death, the exact role of the mitochondria during this type of programmed cell death has not been fully elucidated. Therefore, we sought to determine whether or not Bax translocation and mitochondrial fragmentation occur on exposure of gastric epithelial cells to H pylori, resulting in cell death.
Methods:
Experiments were performed with human gastric adenocarcinoma (AGS) cells, AGS cells transfected with the HPV-E6 gene (which inactivates p53 function), AGS-neo cells (transfected with the backbone construct), mouse embryonic fibroblasts (MEFs), and p19(ARF) null (ARF(-/-)) MEFs. Cells were incubated with a cag positive H pylori strain for up to 24 hours, lysed, and cytoplasmic and mitochondrial membrane fractions were analysed by western blot for Bax translocation.
Results:
Bax translocation was detected in AGS, AGS-neo, and normal MEF cells after exposure to H pylori for three hours, but not in ARF(-/-) MEFs cells. Translocation of Bax after H pylori incubation was also detected in AGS-E6 cells (inactive p53 gene) but to a lesser degree than in AGS-neo cells. In parallel studies, the mitochondrial morphology of living cells infected with H pylori was assessed by confocal microscopy. Mitochondrial fragmentation was detectable after 10 hours of H pylori incubation with AGS cells and after seven hours with MEF cells. In wild-type MEFs, mitochondrial fragmentation was significantly increased in comparison with ARF null MEFs (43% v 10.4%, respectively). Furthermore, mitochondrial depolarisation and caspase-3 activity were initiated within four hours in cells incubated with H pylori, and these events were inhibited by forced expression of Bcl-2.
Conclusions:
These data suggest that during H pylori induced apoptosis, Bax translocates to the mitochondria which subsequently undergo depolarisation and profound fragmentation. Functional ARF and p53 proteins may play an important role in H pylori induced mitochondrial modification.
Insights
Helicobacter pylori infection triggers Bax translocation to mitochondria, leading to fragmentation and cell death. This process is influenced by functional ARF and p53 proteins.
Area of Science:
- Cell Biology
- Microbiology
- Pathology
Background:
- Helicobacter pylori infection is linked to gastric epithelial cell apoptosis.
- Mitochondrial involvement in H. pylori-induced cell death requires further elucidation.
- Bcl-2 family proteins and cytochrome c release are implicated in H. pylori-induced cell death.
Purpose of the Study:
- To investigate Bax translocation and mitochondrial fragmentation in gastric cells exposed to H. pylori.
- To determine the role of mitochondria in H. pylori-induced programmed cell death.
Main Methods:
- Utilized human gastric adenocarcinoma (AGS) cells, p53-deficient AGS cells, and mouse embryonic fibroblasts (MEFs).
- Exposed cells to a cag-positive H. pylori strain for up to 24 hours.
- Analyzed Bax translocation via western blot and mitochondrial morphology using confocal microscopy.
Main Results:
- Bax translocation to mitochondria occurred within 3 hours of H. pylori exposure in AGS and MEF cells.
- Mitochondrial fragmentation was observed after 7-10 hours of H. pylori infection.
- Mitochondrial depolarization and caspase-3 activation were inhibited by Bcl-2 expression.
Conclusions:
- H. pylori induces apoptosis via Bax translocation to mitochondria, leading to depolarization and fragmentation.
- Functional ARF and p53 proteins appear crucial in H. pylori-mediated mitochondrial changes.
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