Action of Viscumin, a toxic lectin from mistletoe on cells in culture

Journal/Book: J. Biol. Chem. 257 (22), 13271-13277. 1982;

Abstract: A toxin from mistletoe, viscumin, inhibited the incorporation of leucinein cells more rapidly than the incorporation of uridine and thymidine,indicating that the toxins act by inhibiting cellular protein synthesis.The presence of galactose, lactose, and melibiose in the mediumprotected cells against viscumin. The sensitivity to viscumin ofdifferent cell lines differed considerably. The cytotoxic properties ofviscumin were compared to those of the related toxins abrin, ricin, andmodeccin. The profile of the sensitivity of a panel of cell lines toviscumin was dissimilar from those obtained with abrin and modeccin.Cell lines selected for resistance to modeccin and ricin were fullysensitive to viscumin. Ca2+ was required for viscumin to express itstoxic effect. In contrast, the Ca2+ ionophore A23187 protected the cellsagainst viscumin. Whereas the sensitivity of cells to viscumin did notvary much between pH 7 and 9, the cells were much less sensitive at pH6. Also, cells treated with the two metabolic inhibitors, 2-deoxyglucoseand NaN3, were insensitive to the toxins. Viscumin taken up by cells inthe absence of Ca2+ or at pH 6 was able to intoxicate the cells whenCa2+ was added or when the pH was adjusted to neutrality. In contrast,cells exposed to viscumin in the presence of 2-deoxyglucose and NaN3,which inhibit endocytosis, were not intoxicated when the cells weretreated with antiviscumin and then transferred to normal medium. Theresults indicate that endocytosis is involved in the entry of viscumin.Author.

Keyword(s): ANIMAL

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