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Binding and invasion of HeLa and MRC-5 cells by Streptococcus agalactiae
Gregory J Tyrrell1,2,3, Alexander Kennedy2,3, Sandra E Shokoples3
1Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, CanadaT6G 2J23.
Abstract:
The interactions of group B streptococci (GBS) with HeLa cells (an epithelial cell line) and MRC-5 cells (a fibroblastic cell line) were explored. A host-cell invasion assay using GBS strains from all serotypes revealed that GBS invaded HeLa cells to a greater extent than MRC-5 cells. One strain, a serotype V (NCS13), was highly invasive against HeLa cells. All strains were poorly invasive against MRC-5 cells. Further characterization of the binding of NCS13 to HeLa and MRC-5 cell surfaces showed that the lack of recoverable c.f.u. from MRC-5 cells was due to a lack of binding of NCS13 to the MRC-5 cell surface in comparison to HeLa cells. Although fibronectin had been reported to bind to GBS, fibronectin assays showed 2.7-fold more fibronectin on the MRC-5 cell surface in comparison to HeLa cells, suggesting that other extracellular matrix proteins besides fibronectin may be involved in GBS binding. Scanning electron microscopy of NCS13 and HeLa cells over a 6 h time period showed increased numbers of NCS13 on the HeLa cell surface over time until cell death at 6 h. Direct contact of the HeLa cell surface by NCS13 was found to be necessary for cell death to occur. Further scanning electron microscopy studies found that, once GBS are bound to the HeLa cell surface, HeLa cell microvilli entwine the bacteria, which then enter the HeLa cell in a polar fashion. Cytoskeletal actin is involved, as this process is disrupted by cytochalasin D, and recruitment of actin is visible at the site of adherent chains of GBS. Also, the host-cell signalling enzyme, PI 3-kinase, is involved in the GBS internalization process, since the PI 3-kinase inhibitor, wortmannin, inhibited NCS13 invasion of HeLa cells in a dose-dependent manner.
Insights
Group B streptococci (GBS) invade epithelial HeLa cells more effectively than fibroblastic MRC-5 cells, with a specific serotype V strain showing high invasiveness. GBS entry into HeLa cells involves microvilli, actin, and PI 3-kinase signaling.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Group B streptococci (GBS) are a significant human pathogen.
- Understanding GBS interactions with host cells is crucial for developing effective treatments.
- Epithelial and fibroblastic cell lines offer distinct models for studying host-pathogen dynamics.
Purpose of the Study:
- To investigate the differential interactions of GBS with epithelial (HeLa) and fibroblastic (MRC-5) cell lines.
- To characterize the mechanisms underlying GBS invasion and host cell damage.
- To identify host cell factors involved in GBS adherence and internalization.
Main Methods:
- Host-cell invasion assays using various GBS serotypes and cell lines.
- Scanning electron microscopy (SEM) to visualize GBS-host cell interactions over time.
- Fibronectin binding assays.
- Inhibition studies using cytochalasin D and wortmannin (PI 3-kinase inhibitor).
Main Results:
- GBS exhibited significantly higher invasion rates in HeLa cells compared to MRC-5 cells.
- A specific GBS serotype V strain (NCS13) demonstrated high invasiveness against HeLa cells.
- NCS13 binding to MRC-5 cells was poor, correlating with low invasiveness, despite higher fibronectin presence on MRC-5 cells.
- SEM revealed GBS-induced HeLa cell death, requiring direct contact and involving microvillar engulfment and polar entry.
- GBS internalization was dependent on cytoskeletal actin and host cell PI 3-kinase signaling.
Conclusions:
- GBS invasion tropism is cell-type dependent, favoring epithelial cells.
- Host cell surface components and signaling pathways, including actin and PI 3-kinase, are critical for GBS internalization.
- The study elucidates key molecular mechanisms of GBS pathogenesis at the host cell level.