Brefeldin-A enhancement of ricin A-chain immunotoxins and blockade of intact ricin, modeccin, and abrin.
After binding, the protein toxins ricin, abrin, and modeccin are endocytosed and processed through the cell's vesicular system in a poorly understood fashion, prior to translocation to the cytosol. The role of the Golgi apparatus in toxin processing was studied using brefeldin-A (BFA), a fungal metabolite which blocks Golgi function. At concentrations that inhibit secretion of interleukin-2 (IL-2), BFA blocks ricin, modeccin, and abrin intoxication of a lymphocyte derived cell line (Jurkat). Paradoxically, BFA enhances the toxicity of two ricin A-chain immunotoxins targeted against distinct cell surface determinants. BFA concentrations which are optimal for immunotoxin enhancement are below those needed to affect ricin intoxication or IL-2 secretion. BFA blockade of ricin does not involve effects on ricin endocytosis, toxin translocation to the cytosol, or the enzymatic activity of toxin A-chain. In contrast, BFA has no effect on immunotoxin processing but does enhance the immunotoxin translocation step. It is concluded that: 1) intact Golgi function is required for holotoxin processing. 2) Intact Golgi function is not required for holotoxin translocation. 3) Golgi function is tightly linked to immunotoxin translocation. 4) BFA has effects on vesicular routing in addition to the block of Golgi function in secretion which has been reported.
Department of Biology, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D. C. 20307-5100.
T H
TH
Hudson
F G
FG
Grillo
D000036:Abrin / Q000378:metabolism*; D000992:Antitoxins; D001692:Biological Transport / Q000187:drug effects; D020126:Brefeldin A; D003517:Cyclopentanes / Q000494:pharmacology*; D004347:Drug Interactions; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D000922:Immunotoxins / Q000378:metabolism* / Q000633:toxicity; D007376:Interleukin-2 / Q000378:metabolism; D007700:Kinetics; D037102:Lectins / Q000378:metabolism*; D008223:Lymphoma; D037121:Plant Lectins; D054790:Ribosome Inactivating Proteins, Type 2; D012276:Ricin / Q000378:metabolism*; D014118:Toxins, Biological / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D000992:Antitoxins; D003517:Cyclopentanes; D000922:Immunotoxins; D007376:Interleukin-2; D037102:Lectins; D037121:Plant Lectins; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; D000036:Abrin; D020126:Brefeldin A; C016004:modeccin; D012276:Ricin