TLR5-mediated activation of p38 MAPK regulates epithelial IL-8 expression via posttranscriptional mechanism.
Toll-like receptors (TLRs) activate antimicrobial gene expression in response to detection of specific bacterial products. Relatively little is known about TLR5, the only TLR thought to be preferentially expressed by epithelial cells, beyond that it confers activation of the transcription factor NF-kappaB in a MyD-88 dependent manner in response to flagellin. Because TLRs, in general, are also thought to signal through members of the MAPK family, we examined flagellin-induced MAPK activation (via examining its phosphorylation status) and its subsequent role in expression of the chemokine IL-8 in polarized intestinal epithelia. Flagellin, like other proinflammatory stimuli (TNF-alpha, Salmonella typhimurium), activated p38 MAPK in a TLR5-dependent manner, whereas aflagellate bacteria or EGF did not activate this kinase. Although ERK1 and -2 were also observed to be activated in response to flagellin, their activation was not restricted to proinflammatory stimuli because they were also potently activated by aflagellate bacteria (S. typhimurium or Escherichia coli) and EGF (neither of which activate NF-kappaB in these cells). Pharmacological inhibition of p38 MAPK (by SB-203580) potently (IC50 = 10 nM) reduced expression of IL-8 protein (maximal inhibition, 75%) but had no effect on NF-kappaB activation, only slightly attenuated upregulation of IL-8 mRNA levels in response to flagellin, and did not effect IL-8 mRNA stability. Together, these results indicate that epithelial TLR5 mediates p38 activation and subsequently regulates flagellin-induced IL-8 expression independently of NF-kappaB, probably by influencing IL-8 mRNA translation.
Yu
Yimin
Y
Department of Pathology, Emory University, Atlanta, Georgia 30322, USA.
Zeng
Hui
H
Lyons
Sean
S
Carlson
Adam
A
Merlin
Didier
D
Neish
Andrew S
AS
Gewirtz
Andrew T
AT
D000818:Animals; D002460:Cell Line; D004285:Dogs; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism; D004926:Escherichia coli; D005408:Flagellin / Q000494:pharmacology; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D016209:Interleukin-8 / Q000235:genetics* / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides / Q000494:pharmacology; D048670:MAP Kinase Kinase 4; D008562:Membrane Glycoproteins / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011994:Recombinant Proteins; D012475:Salmonella; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors; D014158:Transcription, Genetic; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases
D016209:Interleukin-8; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C495346:TLR5 protein, human; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D005408:Flagellin; D004815:Epidermal Growth Factor; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases