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Eukaryotic cell uptake of heparin-coated microspheres: a model of host cell invasion by Chlamydia trachomatis
R S Stephens1, F S Fawaz, K A Kennedy
1Program in Infectious Diseases, School of Public Health, University of California, Berkeley, California 94720, USA. rss@uclink4.berkeley.edu
Abstract:
Using polystyrene microspheres coated with heparin or heparan sulfate, it was shown that coated microspheres specifically bound eukaryotic cells and were endocytosed by nonprofessional phagocytic cells. Coated microspheres displayed properties of binding to eukaryotic cells that were similar to those of chlamydiae, and the microspheres were competitively inhibited by chlamydial organisms. Endocytosis of heparin-coated beads resulted in the tyrosine phosphorylation of a similar set of host proteins as did endocytosis of chlamydiae; however, unlike viable chlamydial organisms, which prevent phagolysosomal fusion, endocytosed beads were trafficked to a lysosomal compartment. These findings suggest that heparin-coated beads and Chlamydia trachomatis enter eukaryotic cells by similar pathways.
Insights
Heparin-coated microspheres and Chlamydia trachomatis use similar cellular entry pathways. While both bind eukaryotic cells, the microspheres traffic to lysosomes, unlike the bacteria which block phagolysosomal fusion.
Area of Science:
- Cell Biology
- Microbiology
- Biochemistry
Background:
- Eukaryotic cells internalize various particles and pathogens through endocytosis.
- Chlamydia trachomatis is an obligate intracellular bacterium known to manipulate host cell pathways for entry and survival.
- Heparan sulfate proteoglycans on cell surfaces are implicated in the binding and uptake of various molecules and microorganisms.
Purpose of the Study:
- To investigate whether heparin-coated microspheres mimic the cellular entry mechanisms of Chlamydia trachomatis.
- To compare the host protein interactions and intracellular trafficking of heparin-coated microspheres with Chlamydia trachomatis entry.
Main Methods:
- Polystyrene microspheres coated with heparin or heparan sulfate were used as model particles.
- Binding assays with eukaryotic cells were performed.
- Endocytosis and intracellular trafficking of microspheres were analyzed.
- Host protein tyrosine phosphorylation was assessed after microsphere or Chlamydia infection.
- Competitive inhibition assays using Chlamydia organisms were conducted.
Main Results:
- Heparin-coated microspheres specifically bound to eukaryotic cells and were endocytosed by nonprofessional phagocytic cells.
- The binding of coated microspheres was competitively inhibited by Chlamydia organisms, suggesting shared binding mechanisms.
- Endocytosis of heparin-coated microspheres induced tyrosine phosphorylation of host proteins similar to Chlamydia infection.
- Unlike Chlamydia, which prevents phagolysosomal fusion, endocytosed microspheres were trafficked to a lysosomal compartment.
Conclusions:
- Heparin-coated microspheres and Chlamydia trachomatis utilize similar initial pathways for entering eukaryotic cells.
- The data suggest that cell surface heparan sulfate plays a crucial role in the initial attachment and entry of Chlamydia.
- Differences in intracellular trafficking highlight distinct survival strategies of Chlamydia compared to inert particles.