Toll-like receptor 2-mediated sequential activation of MyD88 and MAPKs contributes to lipopolysaccharide-induced sp-a gene expression in human alveolar epithelial cells.
Surfactant proteins (SPs) produced by pulmonary epithelial cells participate in the regulation of sepsis-induced acute lung injury. Our previous study has shown that lipopolysaccharide (LPS), a Gram-negative bacterial outer membrane component, can regulate sp-a gene expression in human lung carcinoma type II epithelial A549 cells. This study was further designed to evaluate the signal-transducing mechanisms of LPS-induced sp-a gene expression. Exposure of A549 cells to LPS induced SP-A mRNA and protein production in time-dependent manners. Application of toll-like receptor 2 (TLR2) siRNA into A549 cells decreased the levels of this receptor and simultaneously inhibited LPS-induced SP-A mRNA expression. Sequentially, LPS enhanced phosphorylation of mitogen-activated protein kinase (MEK) 4 and c-Jun NH(2) terminal kinase 1 (JNK1) in time-dependent manners. Application of TLR2 siRNA decreased LPS-enhanced phosphorylation of MEK4 and JNK1. After knocking-down the translation of MyD88 by RNA interference, the LPS-triggered MEK4 phosphorylation was attenuated. Consequently, LPS augmented the translocation of c-Jun from the cytoplasm to nuclei without affecting c-Fos. Pretreatment of A549 cells with SP600125, an inhibitor of JNK1, significantly lowered LPS-induced SP-A mRNA production. Analyses of an electrophoretic mobility shift assay and a reporter gene further showed that LPS increased the transactivation activity of AP-1 in A549 cells. Therefore, the present study demonstrates that LPS can induce sp-a gene expression in human type II epithelial A549 cells through TLR2-mediated sequential activation of MyD88-MEK4-JNK1-AP-1.
Graduate Institute of Clinical Medicine, Taipei Medical University, Taipei, Taiwan.
Chi-Yuan
CY
Chuang
Tyng-Guey
TG
Chen
Yu-Tyng
YT
Tai
Ta-Liang
TL
Chen
Yu-Hua
YH
Lin
Cheng Hsiu
CH
Tsai
Ruei-Ming
RM
Chen
D056809:Alveolar Epithelial Cells / Q000378:metabolism*; D045744:Cell Line, Tumor; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism
D008070:Lipopolysaccharides; D053594:Myeloid Differentiation Factor 88; D037662:Pulmonary Surfactant-Associated Protein A; D012333:RNA, Messenger; D051195:Toll-Like Receptor 2; D018808:Transcription Factor AP-1; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4