INTERNALIZATION OF Sambucusnigra AGGLUTININS I AND II ININSECT MIDGUT CF-203 CELLS

摘要

In this project, the uptake mechanisms and localization of two lectinsfrom Sambucus nigra, further referred to as S. nigra agglutinin (SNA)-Iand SNA-II, into insect midgut CF-203 cells were studied. SNA-I is achimeric lectin belonging to the class of ribosome-inactivating proteins,whereas SNA-II is a hololectin devoid of enzymatic activity. Internalization of the fluorescein isothiocyanate-labeled lectin was investigated using confocal microscopy. Both lectins were internalized into thecytoplasm of CF-203 cells at similar rates. Preexposure of the insectmidgut cells to specific inhibitors of clathrin- and caveolae-mediatedendocytosis resulted in an inhibition of lectin uptake in CF-203 cells andcaspase-induced cytotoxicity caused by SNA-I and SNA-II, confirmingthe involvement of both endocytosis pathways. Further studies demonstrated that the uptake mechanism(s) for both lectins required phosphoinositide 3-kinases, but did not depend on the actin cytoskeleton.Since the hololectin SNA-II apparently uses a similar endocytosis pathway as the chimerolectin SNA-I, it can be concluded that theendocytosis process mainly relies on the carbohydrate-binding activity ofthe lectins under investigation.