Enteroaggregative Escherichia coli flagellin-induced interleukin-8 secretion requires Toll-like receptor 5-dependent p38 MAP kinase activation.
Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen that causes acute and chronic diarrhoea in a number of clinical settings. EAEC diarrhoea involves bacterial aggregation, adherence to intestinal epithelial cells and elaboration of several toxigenic bacterial mediators. Flagellin (FliC-EAEC), a major bacterial surface protein of EAEC, causes interleukin (IL)-8 release from several epithelial cell lines. The host response to flagellins from E. coli and several other bacteria is mediated by Toll-like receptor 5 (TLR5), which signals through nuclear factor kappa B (NF-kappaB) to induce transcription of pro-inflammatory cytokines. p38 mitogen-activating protein (MAP) kinase (MAPK) is a member of a family of stress-related kinases that influences a diverse range of cellular functions including host inflammatory responses to microbial products. We studied the role of p38 MAPK in FliC-EAEC-induced IL-8 secretion from Caco-2 human intestinal epithelial cells and THP-1 human monocytic cells. We found that IL-8 secretion from both cell types is dependent on p38 MAPK, which is phospho-activated in response to FliC-EAEC. The role of TLR5 in p38 MAPK-dependent IL-8 secretion was verified in HEp-2 cells transiently transfected with a TLR5 expression construct. Activation of interleukin-1 receptor-associated kinase (IRAK) was also observed in Caco-2 and TLR5-transfected HEp-2 cells after exposure to FliC-EAEC. Finally, we demonstrated that pharmacological inhibition of p38 MAPK reduced IL-8 transcription and mRNA levels, but did not affect NF-kappaB activation. Collectively, our results suggest that TLR5 mediates p38 MAPK-dependent IL-8 secretion from epithelial and monocytic cells incubated with FliC-EAEC, and that this effect requires IL-8 promoter activation independent of NF-kappaB nuclear migration.
Division of Infectious Diseases, University of British Columbia, Vancouver Hospital and Health Sciences Centre, 2733 Heather Street, Vancouver, BC V5Z 3J5 Canada.
Mohammed A S
MA
Khan
Jian
J
Kang
Theodore S
TS
Steiner
D018938:Caco-2 Cells; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000276:immunology*; D005408:Flagellin / Q000037:antagonists & inhibitors / Q000276:immunology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000276:immunology*; D016328:NF-kappa B / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D007093:Imidazoles; D016209:Interleukin-8; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D011725:Pyridines; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495346:TLR5 protein, human; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors; D005408:Flagellin; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580