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The secreted Ipa complex of Shigella flexneri promotes entry into mammalian cells
R Ménard1, M C Prévost, P Gounon
1Unité de Pathogénic Microbienne Moléculaire, Paris, France.
Abstract:
The bacterial pathogen Shigella flexneri causes bacillary dysentery in humans by invading coloncytes. Upon contact with epithelial cells, S. flexneri elicits localized plasma membrane projections sustained by long actin filaments which engulf the microorganism. The products necessary for Shigella entry include three secretory proteins: IpaB, IpaC, and IpaD. Extracellular IpaB and IpaC associate in a soluble complex, the Ipa complex. We have immunopurified this Ipa complex on latex beads and found that they were efficiently internalized into HeLa cells. Like S. flexneri entry, uptake of the beads bearing the Ipa complex was associated with membrane projections and polymerization of actin at the site of cell-bead interaction and was dependent on small Rho GTPases. These results indicate that a secreted factor can promote S. flexneri entry into epithelial cells.
Insights
Shigella flexneri uses secreted proteins, IpaB and IpaC, to invade human colon cells. These proteins, forming an Ipa complex, trigger actin polymerization and membrane projections for bacterial entry.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Shigella flexneri is a bacterial pathogen causing bacillary dysentery.
- Invasion of host colonocytes is crucial for S. flexneri pathogenesis.
- Epithelial cell entry involves plasma membrane projections and actin polymerization.
Purpose of the Study:
- To investigate the role of secreted Shigella proteins in host cell invasion.
- To determine if a secreted factor can mediate bacterial entry.
Main Methods:
- Immunopurification of the Ipa complex (IpaB and IpaC) from S. flexneri.
- Internalization assays using latex beads coated with the Ipa complex in HeLa cells.
- Microscopic analysis of cell-bead interactions, including membrane projections and actin polymerization.
Main Results:
- The Ipa complex, when purified and coated on beads, was efficiently internalized by HeLa cells.
- Uptake of Ipa complex-coated beads mimicked S. flexneri entry, involving membrane projections and actin polymerization.
- The entry process mediated by the Ipa complex was dependent on small Rho GTPases.
Conclusions:
- Secreted factors, specifically the Ipa complex of IpaB and IpaC, are sufficient to promote Shigella entry into epithelial cells.
- The Ipa complex plays a direct role in initiating host cell invasion by S. flexneri.
- Understanding the mechanism of Ipa complex-mediated entry can inform strategies against Shigella infections.