Massachusetts Biologic Laboratories
Adaptor Proteins, Signal Transducing; Antigens, Differentiation; Bacterial Proteins; Cell Line, Tumor; Cells, Cultured; Central Nervous System Neoplasms; DNA; Enzyme Activation; Epithelial Cells; Flagellin; Glioblastoma; HT29 Cells; HeLa Cells; Humans; I-kappa B Kinase; Inflammation; Intestines; Kidney; Lung Neoplasms; Membrane Glycoproteins; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Myeloid Differentiation Factor 88; NF-kappa B; Protein Binding; Protein-Serine-Threonine Kinases; Receptors, Cell Surface; Receptors, Immunologic; Salmonella; Salmonella Infections; Signal Transduction; Solubility; Toll-Like Receptor 5; Toll-Like Receptors
Life Sciences | Medicine and Health Sciences | Microbiology
BACKGROUND: Infection of intestinal epithelial cells by pathogenic Salmonella leads to activation of signaling cascades that ultimately initiate the proinflammatory gene program. The transcription factor NF-kappa B is a key regulator/activator of this gene program and is potently activated. We explored the mechanism by which Salmonella activates NF-kappa B during infection of cultured intestinal epithelial cells and found that flagellin produced by the bacteria and contained on them leads to NF-kappa B activation in all the cells; invasion of cells by the bacteria is not required to activate NF-kappa B.
RESULTS: Purified flagellin activated the mitogen activated protein kinase (MAPK), stress-activated protein kinase (SAPK) and I kappa B kinase (IKK) signaling pathways that lead to expression of the proinflammatory gene program in a temporal fashion nearly identical to that of infection of intestinal epithelial cells by Salmonella. Flagellin expression was required for Salmonella invasion of host cells and it activated NF-kappa B via toll-like receptor 5 (TLR5). Surprisingly, a number of cell lines found to be unresponsive to flagellin express TLR5 and expression of exogenous TLR5 in these cells induces NF-kappa B activity in response to flagellin challenge although not robustly. Conversely, overexpression of dominant-negative TLR5 alleles only partially blocks NF-kappa B activation by flagellin. These observations are consistent with the possibility of either a very stable TLR5 signaling complex, the existence of a low abundance flagellin co-receptor or required adapter, or both.
CONCLUSION: These collective results provide the evidence that flagellin acts as the main determinant of Salmonella mediated NF-kappa B and proinflammatory signaling and gene activation by this flagellated pathogen. In addition, expression of the fli C gene appears to play an important role in the proper functioning of the TTSS since mutants that fail to express fli C are defective in expressing a subset of Sip proteins and fail to invade host cells. Flagellin added in trans cannot restore the ability of the fli C mutant bacteria to invade intestinal epithelial cells. Lastly, TLR5 expression in weak and non-responding cells indicates that additional factors may be required for efficient signal propagation in response to flagellin recognition.
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© 2004 Tallant et al; licensee BioMed Central Ltd. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
DOI of Published Version
BMC Microbiol. 2004 Aug 23;4:33. Link to article on publisher's site
Tallant, Thomas; Deb, Amitabha; Kar, Niladri; Lupica, Joseph; de Veer, Michael J.; and DiDonato, Joseph A., "Flagellin Acting Via TLR5 is the Major Activator of Key Signaling Pathways Leading to NF-kappa B and Proinflammatory Gene Program activation in intestinal epithelial cells" (2004). Open Access Articles. 2291.