Induction of epithelial-mesenchymal transition by flagellin in cultured lung epithelial cells.
Toll-like receptor 5 (TLR5) recognizes bacterial flagellin and activates host inflammatory responses, mainly through activation of the NF-κB pathway. Although pulmonary fibrosis occurs in some cases of lung infection by flagellated bacteria, the pathological roles of TLR5 stimulation in pulmonary fibrosis have yet to be elucidated. In the present study, we first confirmed that flagellin activated the NF-κB pathway in cultured A549 alveolar epithelial cells. Next, we examined the types of genes whose expression was modulated by flagellin in the cells. Microarray analysis of gene expression indicated that flagellin induced a change in gene expression that had a similar trend to transforming growth factor-β1 (TGF-β(1)), a key factor in the induction of epithelial-mesenchymal transition (EMT). Biochemical analysis revealed that TGF-β(1) and flagellin increased the level of fibronectin protein, while they reduced the level of E-cadherin protein after 30 h of treatment. Interestingly, simultaneous treatment with TGF-β(1) and flagellin significantly augmented these EMT-related changes. Flagellin strongly activated p38 MAP kinase, and the activation was sustained for longer than 30 h. SB203580, an inhibitor of p38 MAP kinase, inhibited the upregulation of fibronectin by both flagellin and TGF-β(1). Simultaneous treatment with TGF-β(1) and flagellin augmented the activation of p38 MAP kinase by TGF-β(1) or flagellin alone. These results strongly suggest that flagellin cooperates with TGF-β(1) in the induction of EMT in alveolar epithelial cells.
Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan.
Yutaka
Y
Kondo
Sayomi
S
Higa-Nakamine
Nobuhiro
N
Noguchi
Noriko
N
Maeda
Seikichi
S
Toku
Yoichiro
Y
Isohama
Kazuhiro
K
Sugahara
Ichiro
I
Kukita
Hideyuki
H
Yamamoto
D000818:Animals; D015820:Cadherins / Q000032:analysis; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects*; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects*; D005353:Fibronectins / Q000032:analysis; D005408:Flagellin / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008168:Lung / Q000187:drug effects*; D008297:Male; D016328:NF-kappa B / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D015820:Cadherins; D004791:Enzyme Inhibitors; D005353:Fibronectins; D007093:Imidazoles; D016328:NF-kappa B; D011725:Pyridines; D053773:Transforming Growth Factor beta1; D005408:Flagellin; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580