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Interaction of Shigella shigae cytotoxin with receptors on sensitive and insensitive cells
Abstract:
The effect of a cytotoxin isolated from Shigella shigae has been tested on different cell lines. HeLa S3 cells, as well as some other human carcinoma cells, were killed by picomolar to femtomolar concentrations of the pure toxin, whereas certain other human carcinoma cells and a variety of non-epithelial cells from human tissue and from various animal tissues were resistant to-nanomolar concentrations of the toxin. Binding studies with 125 I-labelled Shigella shigae cytotoxin showed that the sensitive HeLa S3 cells contain 1.3 x 10(6) binding sites per cell, whereas in an insensitive HeLa cell line 2.6 x 10(5) sites per cell were measured. In all cases the apparent association constant, Ká was found to be about 10(10) M-1. The binding occurred fairly rapidly, whereas dissociation of bound toxin occurred at a very slow rate, even in the presence of excess unlabaled toxin. All toxin sensitive cell lines bound similar amounts of toxin as HeLa S3 cells, whereas some of the resistant cell lines did not contain measurable amounts of toxin receptors.
Insights
Shigella shigae cytotoxin selectively kills sensitive human carcinoma cells at low concentrations. Toxin binding studies reveal differences in receptor numbers on sensitive versus resistant cell lines.
Area of Science:
- Microbiology
- Cell Biology
- Toxicology
Background:
- Shigella shigae produces a potent cytotoxin.
- Differential cellular responses to toxins are common in biology.
- Understanding toxin-host interactions is crucial for medicine.
Purpose of the Study:
- To investigate the cytotoxic effects of Shigella shigae cytotoxin on various human and animal cell lines.
- To quantify the binding of the cytotoxin to sensitive and resistant cells.
- To determine the mechanism of selective cell killing by the toxin.
Main Methods:
- Exposure of diverse cell lines (HeLa S3, human carcinoma, non-epithelial) to purified Shigella shigae cytotoxin.
- Cytotoxicity assays to determine lethal concentrations (picomolar to nanomolar).
- Binding studies using 125I-labeled cytotoxin to measure receptor number and affinity (apparent association constant, Ká).
Main Results:
- HeLa S3 and some human carcinoma cells were sensitive (killed by picomolar to femtomolar concentrations).
- Other human carcinoma and non-epithelial cells were resistant (to nanomolar concentrations).
- Sensitive cells (HeLa S3) had significantly more binding sites (1.3 x 10^6/cell) than resistant cells (2.6 x 10^5/cell), with similar high affinity (Ká ≈ 10^10 M⁻¹).
- Dissociation of bound toxin was very slow.
Conclusions:
- Shigella shigae cytotoxin exhibits selective toxicity towards specific cell types, primarily sensitive human carcinoma cells.
- The differential sensitivity is directly correlated with the number of available toxin receptors on the cell surface.
- High-affinity binding and slow dissociation contribute to the toxin's potent and persistent effects on susceptible cells.