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Endosomal proteolysis precedes ricin A-chain toxicity in macrophages
M L Fiani1, J S Blum, P D Stahl
1Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Abstract:
Ricin A-chain is delivered into macrophages via receptor-mediated endocytosis. We have found that following uptake via the mannose receptor, ricin A-chain is rapidly cleaved by endosomal proteases. Inhibition of endosomal proteases such as cathepsin D and B leads to the accumulation of toxin inside the cell. Inhibition of cathepsin D reduces ricin A-chain cytotoxicity, while blocking cathepsin B enhances cytotoxicity. Similar results were obtained using fibroblasts transfected with the mannose receptor. Our data strongly suggest that the activation or membrane translocation of ricin A-chain is dependent upon the action of specific proteases.
Insights
Ricin A-chain enters macrophages through the mannose receptor. Protease activity within endosomes is crucial for ricin A-chain activation and toxicity, with specific proteases influencing its cytotoxic effects.
Area of Science:
- Cell Biology
- Toxicology
- Molecular Biology
Background:
- Ricin A-chain is a potent toxin delivered into cells via endocytosis.
- The mannose receptor facilitates the uptake of ricin A-chain into macrophages.
- Endosomal processing is critical for the activation of many toxins.
Purpose of the Study:
- To investigate the role of endosomal proteases in ricin A-chain activation and cytotoxicity.
- To determine the specific proteases involved in ricin A-chain processing after mannose receptor-mediated endocytosis.
- To elucidate the mechanism by which ricin A-chain gains its toxic potential within the cell.
Main Methods:
- Utilizing macrophages and fibroblasts transfected with the mannose receptor.
- Employing receptor-mediated endocytosis for ricin A-chain uptake.
- Inhibiting specific endosomal proteases (cathepsin D and B) to observe effects on ricin A-chain.
- Assessing ricin A-chain accumulation and cytotoxicity.
Main Results:
- Ricin A-chain is rapidly cleaved by endosomal proteases after uptake via the mannose receptor.
- Inhibition of endosomal proteases leads to ricin A-chain accumulation within cells.
- Inhibition of cathepsin D decreased ricin A-chain cytotoxicity.
- Inhibition of cathepsin B enhanced ricin A-chain cytotoxicity.
Conclusions:
- Specific endosomal proteases, including cathepsin D and B, are essential for ricin A-chain activation.
- The differential effects of cathepsin D and B inhibition highlight distinct roles in ricin A-chain processing.
- Proteolytic cleavage within the endosome is a critical step for ricin A-chain membrane translocation and cytotoxicity.