SIGNAL-TRANSDUCTION PATHWAYS AND CELLULAR INTOXICATION WITH CLOSTRIDIUM-DIFFICILE TOXINS

In cultured cells the cytopathic effects (CPE) of Clostridium difficil e toxins A and B are superficially similar. The irreversible CPEs invo lve a reorganization of the cytoskeleton, but the molecular details of the mechanism(s) of action are unknown. As part of the work to elucid ate the events leading to the CPE, cultured cells were preincubated wi th agents known to either stimulate or inhibit some major signal trans duction pathways, whereupon toxin was added and the development of the CPE was followed. Both toxin-induced CPEs were enhanced by phorbol es ters and mezerein, which stimulate protein kinase C, while they were i nhibited by the phospholipase A2 inhibitors quinacrine and 4-bromophen acylbromide. Agents affecting certain G-proteins, cGMP and cAMP levels , phosphatases, prostacyclin, lipoxygenase, and phospholipase C did no t affect the development of the CPE of either toxin. Thus, the cytoske letal effect induced by toxins A or B appears to require PLA2 activity and involves at least part of a protein kinase C-dependent pathway, b ut not pertussis toxin-sensitive G-proteins, cyclic nucleotides, eicos anoid metabolites, or phospholipase C activity. In addition, both toxi ns were shown to activate phospholipase A2.