BACTEROIDES-FRAGILIS ENTEROTOXIN INDUCES CYTOSKELETAL CHANGES AND SURFACE BLEBBING IN HT-29 CELLS

Certain strains of the anaerobic bacterium Bacteroides fragilis are kn own to produce an enterotoxin of about 20 kDa which is able to induce a fluid response in ligated intestinal loops and a cytotoxic response in HT-29 cells, It presents protease activity, belonging to a family o f metalloproteases termed metzincins. In order to investigate the mode of action of the enterotoxin in cultured cells, we performed a study with HT-29 cells, using both fluorescence and electron microscopy, Tre ated cells underwent morphological changes, mainly consisting of the r etraction of the cell body and the formation of numerous blebs on the cell surface, The microfilament system was reorganized, the F-actin be ing condensed as a ring at the cell periphery, whereas other cell orga nelles appeared to be unaffected, All these changes, clearly visible a fter 3 h of exposure to the toxin, were reversed within 24 h of treatm ent, By inhibiting the protease activity of the toxin with specific me tal chelators, the cytoskeletal effects were also prevented. Thus, B. fragilis enterotoxin appears to act on cells by reversibly modifying t he actin cytoskeleton, an effect probably dependent on its proteolytic activity.