PSEUDOMONAS-AERUGINOSA INVASION AND CYTOTOXICITY ARE INDEPENDENT EVENTS, BOTH OF WHICH INVOLVE PROTEIN-TYROSINE KINASE-ACTIVITY

Pseudomonas aeruginosa clinical isolates exhibit invasive or cytotoxic phenotypes. Cytotoxic strains acquire some of the characteristics of invasive strains when a regulatory gene, exsA, that controls the expre ssion of several extracellular proteins, is inactivated. exsA mutants are not cytotoxic and can be detected within epithelial cells by genta micin survival assays. The purpose of this study was to determine whet her epithelial cell invasion precedes and/or is essential for cytotoxi city. This was tested by measuring invasion (gentamicin survival) and cytotoxicity (trypan blue staining) of PA103 mutants deficient in spec ific exsA-regulated proteins and by testing the effect of drugs that i nhibit invasion for their effect on cytotoxicity. A transposon mutant in the exsA-regulated extracellular factor exoU was neither cytotoxic nor invasive. Furthermore, several of the drugs that inhibited invasio n did not prevent cytotoxicity. These results show that invasion and c ytotoxicity are mutually exclusive events, inversely regulated by an e xsA-encoded invasion inhibitor(s). Both involve host cell protein tyro sine kinase (PTK) activity, but they differ in that invasion requires Src family tyrosine kinases and calcium-calmodulin activity. PTK inhib itor drugs such as genistein may have therapeutic potential through th eir ability to block both invasive and cytotoxicity pathways via an ac tion on the host cell.