ADP-ribosylation in cultured cells treated with Clostridium difficile toxin B

In cultured fibroblasts intoxicated with Clostridium difficile toxin B, a radioactive moiety was transferred from [14C-adenosine]NAD, but not from [14C-nicotinamide] NAD, into a cellular protein (MW 90,000). No labeling was detected in toxin-treated cultures not yet showing any toxin-induced cytopathogenic effect, whereas maximal labeling was obtained in cultures with about half of the cells showing a cytopathogenic effect. The radioactivity was removed from the substrate by treatment with snake venom phosphodiesterase. The results suggest that ADP-ribosylation of a cellular protein occurs in toxin B-treated cells and that this reaction may be responsible for development of the cytopathogenic effect.