Alteration of the cytoskeleton of mammalian cells cultured in vitro by Clostridium botulinum C2 toxin and C3 ADP-ribosyltransferase

The effects of Clostridium botulinum C3 ADP-ribosyltransferase and of Clostridium botulinum C2 toxin were studied on the cytoskeleton of rat hepatoma FAO and human glioma U333 cells. After treatment of these cells for 24 to 48 h with C3 (3-30 micrograms/ml), the actin microfilaments disappeared, and the intermediate filament network was found to collapse, while microtubules remained intact. Similar alterations of the cytoskeletal filaments without affecting microtubules were induced by the actin-ADP-ribosylating C2 toxin. In FAO cells, C3 caused the rounding up of cells. Concomitantly, cytosolic 22 to 24 kDa proteins were ADP-ribosylated in a guanine nucleotide-dependent manner. Rounding up of cells and ADP-ribosylation of proteins in intact cells were observed at similar concentration of the transferase. These data suggest a role of the protein substrates of C3 in the regulation of the cytoskeletal integrity.