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Entry of protein toxins in polarized epithelial cells
E L Melby1, J Jacobsen, S Olsnes
1Institute for Cancer Research, Norwegian Radium Hospital, Montebello, Oslo.
Abstract:
The action of a number of toxins used in the formation of immunotoxins was studied in polarized cells. Diphtheria toxin inhibited protein synthesis most efficiently when added to the basolateral side of the kidney cells, MDCK-I, MDBK and Pt K2, and the colon carcinoma cell Caco-2. Similar findings were made with Pseudomonas aeruginosa exotoxin A in MDCK-I, Pt K2, and Caco-2 cells, and with modeccin and volkensin in MDCK-I cells. In accordance with the toxicity data, diphtheria toxin bound specifically to the basolateral side of MDCK-I cells but not to the apical side. On the other hand, in the trophoblastic BeWo cell line there was little or no difference in the toxic effect of P. aeruginosa exotoxin A and modeccin added to the two sides. The plant toxins ricin and abrin and the bacterial Shigella toxin inhibited protein synthesis approximately equally well in all cell lines tested whether they were added apically or basolaterally. The results indicate that protein toxins are able to enter cells from both the apical and basolateral sides provided receptors are present. The consequences for the preparation of immunotoxins are discussed.
Insights
Toxins like diphtheria toxin target specific cell sides, impacting immunotoxin development. Understanding toxin entry points is crucial for effective targeted therapies.
Area of Science:
- Cell Biology
- Toxicology
- Immunology
Background:
- Polarized cells present distinct apical and basolateral membrane domains.
- Immunotoxins require efficient cellular entry for therapeutic efficacy.
- The differential action of toxins on polarized cells is not fully understood.
Purpose of the Study:
- To investigate the polarized cell entry and action of various protein toxins.
- To determine how toxin entry influences protein synthesis inhibition in different cell lines.
- To assess the implications for immunotoxin design and application.
Main Methods:
- Exposure of polarized cell lines (MDCK-I, MDBK, Pt K2, Caco-2, BeWo) to toxins.
- Assessment of protein synthesis inhibition following apical or basolateral toxin administration.
- Specific binding studies for diphtheria toxin on MDCK-I cells.
Main Results:
- Diphtheria toxin, Pseudomonas aeruginosa exotoxin A, modeccin, and volkensin showed preferential basolateral inhibition of protein synthesis in most cell lines.
- Diphtheria toxin specifically bound to the basolateral side of MDCK-I cells.
- Ricin, abrin, and Shigella toxin exhibited similar efficacy from both apical and basolateral sides.
- BeWo cells showed less polarized toxin action for P. aeruginosa exotoxin A and modeccin.
Conclusions:
- Protein toxins can enter polarized cells from both apical and basolateral sides if appropriate receptors are present.
- Toxin entry polarity significantly influences cytotoxic effects and immunotoxin efficacy.
- Targeting basolateral entry may be key for certain immunotoxins, while others are less dependent on entry side.