Expression of functional leukotriene B4 receptors on human airway smooth muscle cells.
BACKGROUND
Leukotriene B4 (LTB4) increases in induced sputum and exhaled breath condensate in people with asthma. Furthermore, the T(H)2-type immune response and airway hyperresponsiveness induced by ovalbumin sensitization is markedly suppressed in LTB4 receptor (BLT) 1 null mice. These studies suggest that LTB4 may contribute to asthma pathophysiology. However, the direct effects of LTB4 on human airway smooth muscle (ASM) have not been studied.


OBJECTIVE
We sought to determine the expression of LTB4 receptors on human ASM and its functional role in mediating responses of human ASM cells, and the effect of LTB4 on these cells.


METHODS
Immunohistochemistry, RT-PCR, Western blotting, and flow cytometry were used to determine the expression of LTB4 receptors. To determine the effect of LTB4 on human ASM cells, cell proliferation was assessed by counting cells, and chemokinesis was assessed by gold particle phagokinesis assay.


RESULTS
We confirmed expression of both BLT1 and BLT2 in human ASM cells in bronchial tissue and in cell culture. LTB4 markedly induced cyclin D1 expression, proliferation, and chemokinesis of human ASM cells. LTB4 also induced phosphorylation of both p42/p44 mitogen-activated protein kinase (MAPK) and downstream PI3 kinase effector, Akt1. However, we observed no induction of c-Jun N-terminal kinase or p38 MAPK. Notably, LTB4-induced migration and proliferation of ASM cells were inhibited by the BLT1 specific antagonist, U75302, and by inhibitors of p42/p44 MAPK phosphorylation (U1026), and PI3 kinase (LY294002).


CONCLUSIONS
These observations are the first to suggest a role for a LTB4-BLT1 signaling axis in ASM responses that may contribute to the pathogenesis of airway remodeling in asthma.
Watanabe
Satoko
S
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, Faculty of Medicine, Tottori University, Tottori, Japan.
Yamasaki
Akira
A
Hashimoto
Kiyoshi
K
Shigeoka
Yasushi
Y
Chikumi
Hiroki
H
Hasegawa
Yasuyuki
Y
Sumikawa
Takashi
T
Takata
Miyako
M
Okazaki
Ryota
R
Watanabe
Masanari
M
Yokogawa
Tsuyoshi
T
Yamamura
Miki
M
Hayabuchi
Tatsuya
T
Gerthoffer
William T
WT
Halayko
Andrew J
AJ
Shimizu
Eiji
E
D015153:Blotting, Western; D001980:Bronchi / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D002465:Cell Movement; D049109:Cell Proliferation; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000276:immunology / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D018102:Receptors, Leukotriene B4 / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D000095043:Cyclin-Dependent Kinase-Activating Kinase
C513240:LTB4R protein, human; D012333:RNA, Messenger; D018102:Receptors, Leukotriene B4; D018844:Cyclin-Dependent Kinases; D048052:Mitogen-Activated Protein Kinase 3; D000095043:Cyclin-Dependent Kinase-Activating Kinase