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Partial characterization of a cell proliferation-inhibiting protein produced by Helicobacter pylori
1Department of Medical Microbiology and Immunology, Ruhr-University Bochum, Federal Republic of Germany.
Abstract:
Despite the induction of an immunological reaction, Helicobacter pylori-associated gastritis is a chronic disease, suggesting that this microbe can evade the host immune defense. Previous studies by our group showed that H. pylori suppresses the in vitro proliferative response of human mononuclear cells to mitogens and antigens. Here we demonstrate that the antiproliferative activity of H. pylori also affects the proliferation of various mammalian cell lines (U937, Jurkat, AGS, Kato-3, HEP-2, and P388D1). This effect is detectable in the first 16 h of incubation and maximal between 24 and 48 h. In addition, the presence of H. pylori significantly diminished the protein synthesis of cells in the first 6 h of incubation, comparable to the results with cycloheximide and diphtheria toxin. The urease enzyme, the cagA gene product, and the vacuolizing cytotoxin of H. pylori were excluded as causative agents of the antiproliferative effect by using isogenic knockout mutant strains. The inhibitory effect was not due to a lytic activity of this bacterium. The results reported here indicate that the responsible factor is a protein with an apparent native molecular mass of 100 +/- 10 kDa. Our work implicates the presence of a protein factor in H. pylori (termed PIP [for proliferation-inhibiting protein]) with antiproliferative activity for mammalian cells, including immunocompetent and epithelial cells. Thus, it is reasonable to presume that this property may contribute to the pathogenesis of H. pylori-induced diseases. It may be involved on the one hand in immune response evasion and on the other hand in the suppression of epithelial repair mechanisms.
Insights
Helicobacter pylori infection causes chronic gastritis by suppressing mammalian cell proliferation and protein synthesis. A novel proliferation-inhibiting protein (PIP) is identified as the causative factor, aiding immune evasion and hindering epithelial repair.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Helicobacter pylori infection leads to chronic gastritis, indicating immune evasion mechanisms.
- Previous research demonstrated H. pylori suppresses human mononuclear cell proliferation.
- The bacterium's role in chronic disease pathogenesis warrants investigation into its cellular effects.
Purpose of the Study:
- To investigate the antiproliferative activity of H. pylori on various mammalian cell lines.
- To identify the specific H. pylori factor responsible for inhibiting cell proliferation and protein synthesis.
- To explore the potential role of this factor in H. pylori pathogenesis and immune evasion.
Main Methods:
- Incubation of mammalian cell lines (U937, Jurkat, AGS, Kato-3, HEP-2, P388D1) with H. pylori.
- Assessment of cell proliferation and protein synthesis over time.
- Utilized isogenic knockout mutant strains to exclude urease, CagA, and vacuolating cytotoxin as causative agents.
- Protein identification via molecular mass estimation.
Main Results:
- H. pylori significantly inhibited proliferation and protein synthesis in multiple mammalian cell lines.
- The antiproliferative effect was observed within 16 hours and maximal by 24-48 hours.
- Urease, CagA, and vacuolating cytotoxin were ruled out; the effect was not due to lysis.
- A protein factor, named proliferation-inhibiting protein (PIP), with a molecular mass of 100 ± 10 kDa was identified.
Conclusions:
- H. pylori possesses a proliferation-inhibiting protein (PIP) that affects mammalian cell proliferation and protein synthesis.
- PIP likely contributes to H. pylori pathogenesis by enabling immune evasion and suppressing epithelial repair.
- This finding provides a molecular mechanism for the chronic nature of H. pylori-associated gastritis.