Mechanisms of Legionella pneumophila-induced interleukin-8 expression in human lung epithelial cells.
BACKGROUND
Legionella pneumophila is a facultative intracellular bacterium, capable of replicating within the phagosomes of macrophages and monocytes, but little is known about its interaction with human lung epithelial cells. We investigated the effect of L. pneumophila on the expression of interleukin-8 (IL-8) in human A549 alveolar and NCI-H292 tracheal epithelial cell lines.


RESULTS
Infection of L. pneumophila strain, but not heat-killed strain, resulted in upregulation of IL-8. IL-8 mRNA expression was induced immediately after the infection and its signal became gradually stronger until 24 h after infection. On the other hand, IL-8 expression in A549 cells infected with L. pneumophila lacking a functional type IV secretion system was transient. The IL-8 expression was slightly induced at 16 h and increased at 24 h after infection with flagellin-deficient Legionella. Activation of the IL-8 promoter by L. pneumophila infection occurred through the action of nuclear factor-kappaB (NF-kappaB). Transfection of dominant negative mutants of NF-kappaB-inducing kinase, IkappaB kinase and IkappaB inhibited L. pneumophila-mediated activation of IL-8 promoter. Treatment with hsp90 inhibitor suppressed L. pneumophila-induced IL-8 mRNA due to deactivation of NF-kappaB.


CONCLUSIONS
Collectively, these results suggest that L. pneumophila induces activation of NF-kappaB through an intracellular signaling pathway that involves NF-kappaB-inducing kinase and IkappaB kinase, leading to IL-8 gene transcription, and that hsp90 acts as a crucial regulator in L. pneumophila-induced IL-8 expression, presumably contributing to immune response in L. pneumophila. The presence of flagellin and a type IV secretion system are critical for Legionella to induce IL-8 expression in lung epithelial cells.
Division of Molecular Virology and Oncology, Graduate School of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa 903-0215, Japan. hiromitsu20@hotmail.com
Hiromitsu
H
Teruya
Futoshi
F
Higa
Morikazu
M
Akamine
Chie
C
Ishikawa
Taeko
T
Okudaira
Koh
K
Tomimori
Naofumi
N
Mukaida
Masao
M
Tateyama
Klaus
K
Heuner
Jiro
J
Fujita
Naoki
N
Mori
D016227:Benzoquinones / Q000494:pharmacology; D045744:Cell Line, Tumor; D024202:Electrophoretic Mobility Shift Assay; D004847:Epithelial Cells / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D005786:Gene Expression Regulation; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors; D006801:Humans; D016209:Interleukin-8 / Q000235:genetics* / Q000276:immunology*; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D016952:Legionella pneumophila / Q000254:growth & development / Q000276:immunology*; D008168:Lung / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D000097782:NF-kappaB-Inducing Kinase
D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D016209:Interleukin-8; D047029:Lactams, Macrocyclic; D016328:NF-kappa B; D017346:Protein Serine-Threonine Kinases; D000097782:NF-kappaB-Inducing Kinase; C112765:tanespimycin