Evidence for distinct cellular internalization pathways of ricin and nigrin b.
Nigrin b and ricin are type 2 (two chain) ribosome-inactivating proteins that exhibited nearly the same strong inhibitory activity on cell-free protein synthesis. Incubation of HeLa cells for 6 hr with ricin at 37 degrees C promoted protein synthesis inhibition with an IC50 of 0.2 ng/ml. Incubation of the cells for 6 hr at 18 degrees C abolished completely the inhibition. Incubation of HeLa cells with nigrin b for 6 hr at 37 degrees C was nearly 10(5) times less inhibitory than ricin. In contrast to the effects observed with ricin, incubation of HeLa cells with nigrin b at 18 degrees C slightly increased the inhibitory action on protein synthesis as compared with incubation at 37 degrees C. These results strongly support the hypothesis that the internalization of ricin and nigrin b could involve different receptors and therefore they could follow different intracellular pathways.
Citores
L
L
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid, Spain.
Muñoz
R
R
Rojo
M A
MA
Jiménez
P
P
Ferreras
J M
JM
Girbés
T
T
D002474:Cell-Free System; D004705:Endocytosis; D006367:HeLa Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D014176:Protein Biosynthesis / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000378:metabolism / Q000494:pharmacology; D021381:Protein Transport; D012276:Ricin / Q000378:metabolism* / Q000494:pharmacology; D013308:Streptonigrin / Q000378:metabolism* / Q000494:pharmacology
D011500:Protein Synthesis Inhibitors; D013308:Streptonigrin; D012276:Ricin