Induction of IL-8 expression by bacterial flagellin is mediated through lipid raft formation and intracellular TLR5 activation in A549 cells.
We investigated the mechanism for the induction of a chemokine, IL-8, by bacterial flagellins in the human alveolar type II epithelial cell line, A549. Bacterial flagellin induced expression of IL-8 mRNA and protein in dose- and time-dependent manners. IL-8 expression was inhibited by nystatin (a lipid rafts inhibitor) but not by chlorpromazine (a clathrin-coated pits inhibitor). Interestingly, Toll-like receptor 5 (TLR5) recognizing flagellins was found in the intracellular compartment of A549 but rarely on the cell surface. Flagellin-induced IL-8 expression appears to be mediated through TLR5 as determined by in vitro transient transfection experiment in HEK-293 cells expressing TLR5 using a reporter gene construct containing IL-8 promoter. IL-8 expression was attenuated by inhibitors for protein kinase C (PKC) and mitogen-activated protein (MAP) kinases. Furthermore, NF-kappaB and NF-IL6 transcription factors played an important role in the flagellin-induced IL-8 gene expression in A549 cells. Collectively, these results suggest that flagellin-induced IL-8 expression requires formation of lipid rafts, intracellular TLR activation, and subsequent activation of PKC and MAP kinases leading to the activation of the transcription factors NF-kappaB and NF-IL6 in human alveolar type II epithelial cells.
Department of Oral Microbiology & Immunology, Dental Research Institute, and BK21 Program, School of Dentistry, Seoul National University, Seoul 110-749, Republic of Korea.
Jintaek
J
Im
Jun Ho
JH
Jeon
Min Kyung
MK
Cho
Sang Su
SS
Woo
Seok-Seong
SS
Kang
Cheol-Heui
CH
Yun
Kangseok
K
Lee
Dae Kyun
DK
Chung
Seung Hyun
SH
Han
D001412:Bacillus subtilis / Q000276:immunology*; D001980:Bronchi / Q000166:cytology; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000276:immunology / Q000382:microbiology; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000276:immunology / Q000382:microbiology; D005408:Flagellin / Q000276:immunology*; D005786:Gene Expression Regulation; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D042541:Intracellular Space / Q000382:microbiology*; D021962:Membrane Microdomains / Q000276:immunology / Q000382:microbiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012486:Salmonella typhimurium / Q000276:immunology*; D013997:Time Factors; D051198:Toll-Like Receptor 5 / Q000276:immunology*; D014158:Transcription, Genetic
D022782:CCAAT-Enhancer-Binding Protein-beta; D016209:Interleukin-8; D016328:NF-kappa B; D012333:RNA, Messenger; D051198:Toll-Like Receptor 5; D005408:Flagellin; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases