Pseudolipasin A Is a Specific Inhibitor for Phospholipase A2 Activity of Pseudomonas aeruginosa Cytotoxin ExoU

A number of bacterial pathogens utilize the type III secretion pathway to deliver effector proteins directly into the host cell cytoplasm. Certain strains of Pseudomonas aeruginosa associated with acute infections express a potent cytotoxin, exoenzyme U (ExoU), that is delivered via the type III secretion pathway directly into contacting host cells. Once inside the mammalian cell, ExoU rapidly lyses the intoxicated cells via its phospholipase A2 (PLA2) activity. A high-throughput cell-based assay was developed to screen libraries of compounds for those capable of protecting cells against the cytotoxic effects of ExoU. A number of compounds were identified in this screen, including one group that blocks the intracellular activity of ExoU. In addition, these compounds specifically inhibited the PLA2 activity of ExoU in vitro, whereas eukaryotic secreted PLA2 and cytosolic PLA2 were not inhibited. This novel inhibitor of ExoU-specific PLA2 activity, named pseudolipasin A, may provide a new lead for virulence factor-based therapeutic design.