Pathogenic Yersinia resist uptake by eukaryotic cells by a mechanism involving the virulence protein YopH, a protein tyrosine phosphatase. We show that p130Cas and FAK are phosphorylated and recruited to peripheral focal complexes during bacterial uptake in HeLa cells. The inactive form of YopH interacts with the tyrosine phosphorylated forms of FAK and p130Cas and co-localizes with these proteins in focal adhesions. On the other hand, the presence of active YopH results in inhibition of uptake, dephosphorylation of p130Cas and FAK, and disruption of peripheral focal complexes. We suggest that p130Cas and FAK are substrates for YopH and that the dephosphorylation of these proteins impairs the uptake of Yersinia pseudotuberculosis into HeLa cells.

The PTPase YopH of Yersinia is essential to the ability of these bacteria to block phagocytosis. Wild-type Yersinia pseudotuberculosis, but not the yopH mutant strain, resisted phagocytosis by J774 cells. Ingestion of a yopH mutant was dependent on tyrosine kinase activity. Transcomplementation with wild-type yopH restored the anti-phagocytic effect, whereas introduction of the gene encoding the catalytically inactive yopHC403A was without effect. The PTPase inhibitor orthovanadate impaired the anti-phagocytic effect of the wild-type strain, further demonstrating the importance of bacteria-derived PTPase activity for this event. The ability to resist phagocytosis indicates that the effect of the bacterium is immediately exerted when it becomes associated with the phagocyte. Within 30 s after the onset of infection, wild-type Y. pseudotuberculosis caused a YopH-dependent dephosphorylation of phosphotyrosine proteins in J774 cells. Furthermore, interaction of the cells with phagocytosable strains led to a rapid and transient increase in tyrosine phosphorylation of paxillin and some other proteins, an event dependent on the presence of the bacterial surface-located protein invasin. Co-infection with the phagocytosable strain and the wild-type strain abolished the induction of tyrosine phosphorylation. Taken together, the present findings demonstrate an immediate YopH-mediated dephosphorylation of macrophage phosphotyrosine proteins, suggesting that this PTPase acts by preventing early phagocytosis-linked signalling in the phagocyte.

The Yersinia pseudotuberculosis cell surface-located protein invasin was found to promote binding between the pathogen and resting peripheral B cells via ␤ 1 integrin receptors (CD29). B cells responded by expressing several activation markers and by growing. In contrast, T cells did not react, although these cells express CD29. An isogenic invA mutant failed to activate B cells. The mutation could be complemented by providing the invA ؉ gene in trans. Purified invasin alone did not activate B cells, although it was able to block the binding of bacteria to the cells.