20618341

pubmed:Citation

11

Intracellular proliferation of Francisella tularensis is essential for manifestation of the fatal disease tularaemia, and is classified as a category A bioterrorism agent. The F. tularensis-containing phagosome (FCP) matures into a late endosome-like phagosome with limited fusion to lysosomes, followed by rapid bacterial escape into the cytosol. The Francisella pathogenicity island (FPI) encodes a type VI-like secretion system, and the FPI-encoded IglC is essential for evasion of lysosomal fusion and phagosomal escape. Many host signalling events are likely to be modulated by F. tularensis to render the cell permissive for intracellular proliferation but they are not fully understood. Here we show that within 15 min of infection, intracellular F. tularensis ssp. novicida triggers IglC-dependent temporal activation of Ras, but attached extracellular bacteria fail to trigger Ras activation, which has never been shown for other intracellular pathogens. Intracellular F. tularensis ssp. novicida triggers activation of Ras through recruitment of PKC? and PKC?I to the SOS2/GrB2 complex. Silencing of SOS2, GrB2 and PKC? and PKC?I by RNAi has no effect on evasion of lysosomal fusion and bacterial escape into the cytosol but renders the cytosol non-permissive for replication of F. tularensis ssp. novicida. Since Ras activation promotes cell survival, we show that silencing of SOS2, GrB2 and PKC? and ?I is associated with rapid early activation of caspase-3 within 8 h post infection. However, silencing of SOS2, GrB2 and PKC? and ?I does not affect phosphorylation of Akt or Erk, indicating that activation of the PI3K/Akt and the Erk signalling cascade are independent of the F. tularensis-triggered Ras activation. We conclude that intracellular F. tularensis ssp. novicida triggers temporal and early activation of Ras through the SOS2/GrB2/PKC?/PKC?I quaternary complex. Temporal and rapid trigger of Ras signalling by intracellular F. tularensis is essential for intracellular bacterial proliferation within the cytosol, and this is associated with downregulation of early caspase-3 activation.

eng

IM

MEDLINE

1462-5822

© 2010 Blackwell Publishing Ltd.

12

Y

pubmed-meshheading:20618341-Bacterial Proteins, pubmed-meshheading:20618341-Caspase 3, pubmed-meshheading:20618341-Cell Line, pubmed-meshheading:20618341-Cytosol, pubmed-meshheading:20618341-Down-Regulation, pubmed-meshheading:20618341-Extracellular Signal-Regulated MAP Kinases, pubmed-meshheading:20618341-Francisella tularensis, pubmed-meshheading:20618341-GRB2 Adaptor Protein, pubmed-meshheading:20618341-Genes, ras, pubmed-meshheading:20618341-Genomic Islands, pubmed-meshheading:20618341-Humans, pubmed-meshheading:20618341-Lysosomal-Associated Membrane Protein 2, pubmed-meshheading:20618341-Lysosomes, pubmed-meshheading:20618341-Phagosomes, pubmed-meshheading:20618341-Phosphorylation, pubmed-meshheading:20618341-Protein Kinase C, pubmed-meshheading:20618341-Protein Kinase C-alpha, pubmed-meshheading:20618341-Proto-Oncogene Proteins c-akt, pubmed-meshheading:20618341-Signal Transduction, pubmed-meshheading:20618341-Son of Sevenless Proteins, pubmed-meshheading:20618341-ras Proteins

Triggering Ras signalling by intracellular Francisella tularensis through recruitment of PKC? and ?I to the SOS2/GrB2 complex is essential for bacterial proliferation in the cytosol.

Journal Article, Research Support, Non-U.S. Gov't, Research Support, N.I.H., Extramural