Inhibition of phagocyte signaling by the Yersinia virulence protein YopH

Abstract:

Yersinia pseudotuberculosis evades the immediate immune defense of a host organism by inhibiting bactericidal functions of phagocytes, including phagocytosis, cytokine release, and the oxidative burst. Consequently, this pathogen can survive and multiply in lymphatic tissues. An ensemble of proteins called Yops are involved in the virulence of Y. pseudotuberculosis. Through a polarized mechanism, certain Yops are translocated directly into the host cell, where they are assumed to exert their effects. The present studies were performed to gain further knowledge about the role of the tyrosine phosphatase YopH in Yersinia virulence, especially in regard to effects on the immediate functions and signals of phagocytes.

Y. pseudotuberculosis was found to resist phagocytic uptake by a mechanism involving translocation of bacterially synthesized YopH into the target cell. The antiphagocytic mechanism had an impact on ingestion of both non-opsonized and IgO-opsonized bacteria. Phagocytosis of a YopH-negative strain was accompanied by induction of tyrosinephosphorylated cellular proteins (among them paxillin), and this involved binding of the bacterial surface protein invasin to ß1 integrins of the eukaryotic cell, which also initiated an immediate Ca²⁺ signal in the target cell. The phosphotyrosine proteins Cas and FYB were recruited to the focal complex area during phagocytosis of the YopH-negative strain. Furthermore, we found that a phosphatase-inactive YopH eo-localized with focal adhesion to the periphery of a host cell. In phagocytes infected with wild-type bacteria, phosphatase-active YopH dephosphorylated Cas and FYB, which caused disruption of focal complex structures, and inhibition of the Ca2+ signal. The phosphorylation events as well as the Ca²⁺ signal were rapid responses to bacterial attachment, suggesting that the action of YopH is instantaneous.

Genetic studies revealed that the YopH protein contain an inherent sequence important for anchoring at focal complex structures. Specifically, deletion of the amino acids 223-226 disabled YopH to localize to the focal complexes and to inhibit phagocytosis and Ca²⁺-signaling. This indicates that Y opH must bind to a specific site in focal complexes to focus its activity on the appropriate substrates (i.e. Cas and FYB). Our results show that targeting such complexes is important for Y. pseudotuberculosis, not only as a means of avoiding ingestion by phagocytes, but also for its virulence in mice.