The TLR4-associated phospholipase D1 activation is crucial for Der f 2-induced IL-13 production.
BACKGROUND
House dust mites (HDMs) are the most important source of indoor aeroallergens that contribute to the rising incidence of allergic diseases such as allergic asthma. The major HDM, Der f 2, induces inflammatory cytokine expression. Little is known about the signaling pathway involved.


OBJECTIVE
We wanted to define the Der f 2 signaling pathway from its receptor to the transcription factor responsible for IL-13 expression and production.


METHODS
Human bronchial epithelial cells were stimulated with Der f 2. The release and gene expression of IL-13 were measured by means of ELISA and RT-PCR, respectively. In the airway inflammation mouse model, airway responses were assessed using ELISA, histology, BAL fluid, and methacholine responsiveness.


RESULTS
Here, we show that Der f 2 binds to TLR4 and induces IL-13 expression and production. In the airway inflammation mouse model, Der f 2-induced IL-13 production significantly decreased with treatment of TAK-242, a novel TLR4 inhibitor. Activation of TLR4 by Der f 2 requires the recruitment and activation of Syk, which leads to phosphorylation of PLCγ and membrane translocation of PKCα. p38 MAPK is then activated by PKCα and stimulates PLD1 activity by phosphorylating the Thr147 residue of PLD1. PLD1 activation enhanced binding of ROCK1 to ATF-2 and leads to increased expression of IL-13.


CONCLUSIONS
Our data extend the knowledge for a variety of possible roles of PLD1 in allergic disorders including asthma pathogenesis and suggest possible candidacy of PLD1 as a molecular target for novel therapeutic approaches.
Biomedical Research Institute and Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul, Korea.
H-J
HJ
Choi
Biomedical Research Institute and Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul, Korea.
S-Y
SY
Park
Biomedical Research Institute and Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul, Korea.
J H
JH
Cho
Department of Internal Medicine and Institute of Allergy, College of Medicine, Yonsei University, Seoul, Korea.
J-W
JW
Park
Department of Internal Medicine and Institute of Allergy, College of Medicine, Yonsei University, Seoul, Korea.
J-H
JH
Sohn
Department of Internal Medicine and Institute of Allergy, College of Medicine, Yonsei University, Seoul, Korea.
Y-J
YJ
Kim
Department of Pediatrics, College of Medicine, Hanyang University, Seoul, Korea.
J-W
JW
Oh
Biomedical Research Institute and Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul, Korea.
J-S
JS
Han
D000818:Animals; D039741:Antigens, Dermatophagoides / Q000276:immunology* / Q000378:metabolism; D060829:Arthropod Proteins / Q000276:immunology* / Q000378:metabolism; D001249:Asthma / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D047468:Immunoprecipitation; D018793:Interleukin-13 / Q000096:biosynthesis*; D051379:Mice; D010739:Phospholipase D / Q000276:immunology* / Q000378:metabolism; D039981:Pyroglyphidae / Q000276:immunology; D012130:Respiratory Hypersensitivity / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism
D039741:Antigens, Dermatophagoides; D060829:Arthropod Proteins; C451160:Dermatophagoides farinae antigen f 2; D018793:Interleukin-13; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D010739:Phospholipase D; C106801:phospholipase D1
airway hyper-responsiveness; house dust mite; interleukin 13; phospholipase D; toll-like receptor 4