title: Isolated ricin B-chain-mediated apoptosis in U937 cells.
abstract: We have previously reported that ricin, a toxic lectin that inhibits protein synthesis induced apoptotic cell death. In this study, we have found that isolated ricin CM-B-chain, which has no effect on cellular protein synthesis, induced DNA fragmentation in U937 cells in a dose- and time-dependent manner, albeit it required a longer incubation time and higher concentration than those of holotoxin ricin. Z-Asp-CH2-DCB, a caspase family inhibitor and serine protease inhibitor, 3,4-dichloroisocoumarine (DCI) effectively inhibited the CM-B-chain-mediated DNA fragmentation as well as in ricin. Thus, like ricin, multiple proteases with different substrate specificity may also be involved in the CM-B-chain-mediated apoptotic pathway. Furthermore, BFA inhibited both ricin- and CM-B-chain-mediated DNA fragmentation, suggesting an intracellular vesicle transport system through the Golgi complex may be involved in the apoptotic induction by these proteins as a common feature. On the other hand, cycloheximide (CHA) strongly increased the CM-B-chain-mediated DNA fragmentation, but inhibited ricin-mediated DNA fragmentation. The opposite effects of CHA may reflect the difference in the apoptotic mechanism between ricin and CM-B-chain. In conclusion, our results suggest that ricin-B-chain can induce apoptosis through its lectin activity, but the underlying mechanism may be distinct from that of ricin in which the A-chain contributes profoundly to the apoptotic induction.
authors.affiliation: Division of Biochemistry, Faculty of Fisheries, Nagasaki University, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Hasegawa
authors.forename: Y
authors.initials: Y
authors.lastname: Kimura
authors.forename: T
authors.initials: T
authors.lastname: Oda
authors.forename: N
authors.initials: N
authors.lastname: Komatsu
authors.forename: T
authors.initials: T
authors.lastname: Muramatsu
mesh_terms: D017209:Apoptosis; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D020126:Brefeldin A / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects; D003374:Coumarins / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D053938:DNA Fragmentation / Q000187:drug effects; D006801:Humans; D049934:Isocoumarins; D009842:Oligopeptides / Q000494:pharmacology; D014176:Protein Biosynthesis; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D012276:Ricin / Q000031:analogs & derivatives*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D020298:U937 Cells
chemical_list: D003374:Coumarins; D015853:Cysteine Proteinase Inhibitors; D049934:Isocoumarins; D009842:Oligopeptides; D011500:Protein Synthesis Inhibitors; D015842:Serine Proteinase Inhibitors; C099158:acetyl-aspartyl-glutamyl-valyl-aspartal; C110923:acetyl-valyl-isoleucyl-aspartyl-aldehyde; C093260:benzyloxycarbonyl-Asp-CH2OC(O)-2,6-dichlorobenzene; C096429:L 709049; D020126:Brefeldin A; D001224:Aspartic Acid; C046235:3,4-dichloroisocoumarin; D012276:Ricin; D003513:Cycloheximide