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Comparison of diphtheria intoxication in human and nonhuman cell lines and their resistant variants
Abstract:
Differences in sensitivity to diphtheria toxin of several toxin-sensitive and toxin-resistant human and non-human cell lines were compared. A method is described whereby it is possible to compare the sensitivity of one cell line with another and obtain meaningful quantitative results. Based on the concentration of toxin required to produce 50% inhibition of protein synthesis after 24 h of exposure the ID50 (24) value toxin-resistant cells were found to be 105 to 106 times more resistant to toxin than toxin-sensitive cells. There was little variation in the ID50 (24) values for cells in each of the two groups. The toxin-resistant cells used in this study, naturally resistant as well as selected variants, possess elongation factor 2 which is susceptible to inactivation by toxin. It is suggested that they are capable of activation of toxin but either cannot bind toxin or are unable to transport toxin across the plasma membrane. Protein synthesis is inhibited when these resistant cells are exposed to high concentrations of toxin. Under these conditions it is likely that enough toxin is able to bypass the block in toxin-specific entry and reach the cytosol by a second, less efficient, nonspecific mechanism to catalyze the inactivation of elongation factor 2 and inhibit protein synthesis.
Insights
Toxin-resistant cells are 105-106 times more resistant to diphtheria toxin than sensitive cells. This resistance may stem from an inability to bind or transport toxin, despite possessing susceptible elongation factor 2.
Area of Science:
- Cell Biology
- Toxicology
- Molecular Biology
Background:
- Diphtheria toxin inhibits protein synthesis by inactivating elongation factor 2 (EF-2).
- Cellular sensitivity to diphtheria toxin varies, but the mechanisms underlying resistance are not fully understood.
Purpose of the Study:
- To quantitatively compare the sensitivity of various human and non-human cell lines to diphtheria toxin.
- To investigate the mechanisms of diphtheria toxin resistance in cell lines.
Main Methods:
- Developed a quantitative method to compare cell line sensitivity.
- Determined the ID50 (24) values (concentration of toxin causing 50% inhibition of protein synthesis after 24 hours) for toxin-sensitive and toxin-resistant cell lines.
Main Results:
- Toxin-resistant cells exhibited ID50 (24) values 10^5 to 10^6 times higher than toxin-sensitive cells.
- Resistant cell lines, including natural and selected variants, possess functional EF-2.
- High toxin concentrations can inhibit protein synthesis in resistant cells, suggesting a less efficient, non-specific entry mechanism.
Conclusions:
- Diphtheria toxin resistance in these cell lines is not due to an inability to activate EF-2.
- Resistance likely arises from impaired toxin binding or translocation across the plasma membrane.
- A non-specific entry pathway may allow toxin to reach the cytosol at high concentrations, leading to EF-2 inactivation and protein synthesis inhibition.