INVOLVEMENT OF RAS-RELATED RHO-PROTEINS IN THE MECHANISMS OF ACTION OF CLOSTRIDIUM-DIFFICILE TOXIN-A AND TOXIN-B

Toxins A and B of Clostridium difficile are responsible for pseudomemb ranous colitis, a disease that afflicts a substantial number of hospit alized patients treated with antibiotics, A major effect of these prot eins is the disruption of the actin cytoskeleton. Recently, I. Just, G . Fritz, K. Aktories, M. Giry, M. R. Popoff, P. Boquet, S. Hegenbarth, and C. von Eichel-Streiber (J. Biol. Chem. 269:10706-10712, 1994) imp licated Rho proteins as cellular targets of C. difficile toxin B, sinc e pretreatment of cells or purified Rho with toxin prevented subsequen t ADP-ribosylation of Rho by exoenzyme C3. Moreover, they showed that overexpression of Rho proteins in cells suppressed cell rounding norma lly associated with exposure of cells to C. difficile toxin B, Here we expand these findings by showing directly that Rho proteins are coval ently modified by both C. difficile toxins A and B. In addition, we de monstrate that the stability of toxin-modified Rho in NIH 3T3 cells is dramatically reduced. Finally, we show that C. difficile toxins A and Il do not have similar effects on the closely related Rac and CDC42 G TP-binding proteins.