Endosomal proteolysis precedes ricin A-chain toxicity in macrophages.
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.
Fiani
M L
ML
Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Blum
J S
JS
Stahl
P D
PD
D000818:Animals; D001853:Bone Marrow / Q000378:metabolism; D001854:Bone Marrow Cells; D002401:Cathepsin B / Q000378:metabolism*; D002402:Cathepsin D / Q000378:metabolism*; D002478:Cells, Cultured; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D011480:Protease Inhibitors / Q000494:pharmacology; D012276:Ricin / Q000378:metabolism* / Q000633:toxicity*
D007976:Leupeptins; D011480:Protease Inhibitors; C063261:acetylleucyl-leucyl-norleucinal; D012276:Ricin; D002401:Cathepsin B; D002402:Cathepsin D