In vivo covalent cross-linking of cellular actin by the Vibrio cholerae RTX toxin

Enteric pathogens often export toxins that elicit diarrhea as a part of the etiology of disease, including toxins that affect cytoskeletal structure, Recently, we discovered that the intestinal pathogen Vibrio cholerae elicit s rounding of epithelial cells that is dependent upon a gene we designated rtxA. Here we investigate the association of rtxA with the cell-rounding ef fect, We find that V.cholerae exports a large toxin, RTX (repeats-in-toxin) toxin, to culture supernatant fluids and that this toxin is responsible fo r cell rounding. Furthermore, we find that cell rounding is not due to necr osis, suggesting that RTX toxin is not a typical member of the RTX family o f pore-forming toxins, Rather, RTX toxin causes depolymerization of actin s tress fibers and covalent cross-linking of cellular actin into dimers, trim ers and higher multimers. This RTX toxin-specific cross-linking occurs in c ells previously rounded with cytochalasin D, indicating that G-actin is the toxin target. Although several models explain our observations, our simult aneous detection of actin cross-linking and depolymerization points toward a novel mechanism of action for RTX toxin, distinguishing it from all other known toxins.