The low molecular mass GTP-binding protein Rho is affected by toxin A from Clostridium difficile

Enterotoxin A is one of the major virulence factors of Clos-tridium difficile, and the causative agent of antibiotic-associ-ated pseudomembranous colitis. In cell culture (NIH-3T3, rat basophilic leukemia cells) toxin A inhibits Clostridium botulinum ADP-ribosyltransferase C3 (C3)-catalyzed ADP-ribosylation of the low molecular mass GTP-binding Rho proteins. Rho participates in the regulation of the microfil-ament cytoskeleton. Decrease in ADP-ribosylation of Rho occurs in a time- and concentration-dependent manner and precedes the toxin A-induced destruction of the actin cy-toskeleton. Action of toxin A is not due to proteolytical deg-radation of Rho or to an inherent ADP-ribosyltransferase activity of toxin A. Toxin A-induced decrease in ADP-ribo-sylation is observed also in cell lysates and with recombinant RhoA protein. A heat stable low molecular mass cytosolic factor is essential for the toxin effect on Rho. Thus, the enterotoxin (toxin A) resembles the effects of the C. difficil