Cytotoxic effects by microinjection of ADP-ribosylated skeletal muscle G-actin in PtK2 cells in the absence of Clostridium perfringens iota toxin.

The ADP-ribosylating toxins Clostridium botulinum C2 toxin and C. perfringens iota toxin, which ADP-ribosylate monomeric G-actin at Arg-177 but not the polymeric F-actin, induce depolymerization of the actin cytoskeleton in cultured cells. Since ADP-ribosylated G-actin has properties of a barbed-end-capping protein, we studied whether the ADP-ribosylated actin affects the actin cytoskeleton of PtK2 cells even in the absence of ADP-ribosylating toxin. Skeletal muscle actin was ADP-ribosylated by C. perfringens iota toxin and the toxin was removed using an anti-iota toxin antibody. Microinjection of ADP-ribosylated actin caused retraction of the cell body, redistribution and depolymerization of the actin cytoskeleton in a concentration- and time-dependent manner. The finding that ADP-ribosylated actin affects per se the actin cytoskeleton explains the cytopathic effects of ADP-ribosylating toxins on microfilaments, although F-actin is not directly modified by the toxins.