title: Flagellin-induced tolerance of the Toll-like receptor 5 signaling pathway in polarized intestinal epithelial cells.
abstract: Salmonella typhimurium is a gram-negative enteric pathogen that invades the mucosal epithelium and is associated with diarrheal illness in humans. Flagellin from S. typhimurium and other gram-negative bacteria has been shown to be the predominant proinflammatory mediator through activation of the basolateral Toll-like receptor 5 (TLR5). Recent evidence has shown that prior exposure can render immune cells tolerant to subsequent challenges by TLR ligands. Accordingly, we examined whether prior exposure to purified flagellin would render human intestinal epithelial cells insensitive to future contact. We found that flagellin-induced tolerance is common to polarized epithelial cells and prevents further activation of proinflammatory signaling cascades by both purified flagellin and Salmonella bacteria but does not affect TNF-alpha stimulation of the same pathways. Flagellin tolerance is a rapid process that does not require protein synthesis, and that occurs within 1 to 2 h of flagellin exposure. Prolonged flagellin exposure blocks activation of the NF-kappaB, MAPK, and phosphoinositol 3-kinase signaling pathways and results in the internalization of a fraction of the basolateral TLR5 without affecting the polarity or total expression of TLR5. After removal of flagellin, cells require more than 24 h to fully recover their ability to mount a normal proinflammatory response. We have found that activation of phosphoinositol 3-kinase and Akt by flagellin has a small damping effect in the early stages of flagellin signaling but is not responsible for tolerance. Our study indicates that inhibition of TLR5-associated IL-1 receptor-associated kinase-4 activity occurs during the development of flagellin tolerance and is likely to be the cause of tolerance.
authors.affiliation: Department of Pathology, The University of Chicago, Chicago, IL 60637, USA. jsun@bsd.uchicago.edu
authors.forename: Jun
authors.initials: J
authors.lastname: Sun
authors.forename: Pamela E
authors.initials: PE
authors.lastname: Fegan
authors.forename: Anjali S
authors.initials: AS
authors.lastname: Desai
authors.forename: James L
authors.initials: JL
authors.lastname: Madara
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hobert
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D016764:Cell Polarity; D003513:Cycloheximide / Q000494:pharmacology; D004285:Dogs; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005408:Flagellin / Q000494:pharmacology*; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D053592:Interleukin-1 Receptor-Associated Kinases / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D007413:Intestinal Mucosa / Q000166:cytology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D000072000:NF-KappaB Inhibitor alpha; D051058:Oncogene Protein v-akt / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D051198:Toll-Like Receptor 5 / Q000032:analysis / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D003513:Cycloheximide; D004815:Epidermal Growth Factor; D048049:Extracellular Signal-Regulated MAP Kinases; D005408:Flagellin; D020672:I-kappa B Proteins; D053592:Interleukin-1 Receptor-Associated Kinases; D016209:Interleukin-8; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides; D000072000:NF-KappaB Inhibitor alpha; D051058:Oncogene Protein v-akt; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051197:Toll-Like Receptor 4; D051198:Toll-Like Receptor 5; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases; C000606204:NFKBIA protein, human; C507773:IRAK4 protein, human