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Query: UMLS:C0023241 (Legionella)
 6,990 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Legionnaires' disease bacterium, Legionella pneumophila, is a facultative intracellular pathogen that invades and replicates within two evolutionarily distant hosts, free living protozoa and mammalian cells. Invasion and intracellular replication within protozoa are thought to be major factors in the transmission of Legionnaires' disease. We have recently reported the identification of a galactose/N-acetyl-D-galactosamine (Gal/GalNAc) lectin in the protozoan host Hartmannella vermiformis as a receptor for attachment and invasion by L. pneumophila (Venkataraman, C., B.J. Haack, S. Bondada, and Y.A. Kwaik. 1997. J. Exp. Med. 186:537-547). In this report, we extended our studies to the effects of bacterial attachment and invasion on the cytoskeletal proteins of H. vermiformis. We first identified the presence of many protozoan cytoskeletal proteins that were putative homologues to their mammalian counterparts, including actin, pp125(FAK), paxillin, and vinculin, all of which were basally tyrosine phosphorylated in resting H. vermiformis. In addition to L. pneumophila-induced tyrosine dephosphorylation of the lectin, bacterial attachment and invasion was associated with tyrosine dephosphorylation of paxillin, pp125(FAK), and vinculin, whereas actin was minimally affected. Inhibition of bacterial attachment to H. vermiformis by Gal or GalNAc monomers blocked bacteria-induced tyrosine dephosphorylation of detergent-insoluble proteins. In contrast, inhibition of bacterial invasion but not attachment failed to block bacteria-induced tyrosine dephosphorylation of H. vermiformis proteins. This was further supported by the observation that 10 mutants of L. pneumophila that were defective in invasion of H. vermiformis were capable of inducing tyrosine dephosphorylation of H. vermiformis proteins. Entry of L. pneumophila into H. vermiformis was predominantly mediated by noncoated receptor-mediated endocytosis (93%) but coiling phagocytosis was infrequently observed (7%). We conclude that attachment but not invasion by L. pneumophila into H. vermiformis was sufficient and essential to induce protein tyrosine dephosphorylation in H. vermiformis. These manipulations of host cell processes were associated with, or followed by, entry of the bacteria by a noncoated receptor-mediated endocytosis. A model for attachment and entry of L. pneumophila into H. vermiformis is proposed.
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PMID:Identification of putative cytoskeletal protein homologues in the protozoan host Hartmannella vermiformis as substrates for induced tyrosine phosphatase activity upon attachment to the Legionnaires' disease bacterium, Legionella pneumophila. 968 28

Intracellular replication of the Legionnaires' disease bacterium, Legionella pneumophila, within protozoa plays a major role in bacterial ecology and pathogenesis. Invasion of the protozoan host Hartmannella vermiformis by L. pneumophila is mediated by attachment to the Gal/GalNAc lectin receptor, which is similar to the beta(2) integrin transmembrane receptors of mammalian cells. Bacterial invasion is associated with induction of a protein tyrosine phosphatase (PTPase) activity in H. vermiformis that results in tyrosine dephosphorylation of the lectin receptor and several cytoskeletal proteins. In this report, we show that entry of L. pneumophila into H. vermiformis is not required to induce tyrosine dephosphorylation of one of the cytoskeletal proteins, paxillin. Tyrosine dephosphorylation of paxillin is mediated at the level of bacterial attachment to the lectin receptor, and is blocked by inhibiting bacterial attachment to the lectin receptor. Attachment of L. pneumophila to the lectin receptor is not mediated by the type IV pilus, which is one of the bacterial ligands involved in attachment to protozoa. Interestingly, the lectin receptor in resting H. vermiformis is associated with several phosphorylated proteins that are dissociated upon bacterial attachment and invasion. We show that the L. pneumophila-induced PTPase activity in H. vermiformis and the associated tyrosine dephosphorylation of host proteins can be mimicked by the cytoskeletal disrupting agent, cytochalasin D. Taken together, our data indicate that attachment of L. pneumophila to the lectin receptor of H. vermiformis induces a PTPase activity, tyrosine dephosphorylation of the lectin and cytoskeletal proteins, dissociation of the lectin from its associated phosphorylated proteins, and most probably disassembly of the cytoskeleton. This novel L. pneumophila-protozoa interaction may be a bacterial strategy to invade protozoa and to be trafficked into a replicative 'niche', or to block differentiation of the protozoan host into a cyst in which L. pneumophila cannot replicate.
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PMID:Signal transduction in the protozoan host Hartmannella vermiformis upon attachment to Legionella pneumophila. 1096 69