Lipopolysaccharide-binding protein critically regulates lipopolysaccharide-induced IFN-beta signaling pathway in human monocytes.
LPS binding to Toll-like receptor 4 induces a large number of genes through activation of NF-kappaB and IFN-regulatory factor-3 (IRF-3). However, no previous reports have tested the role of serum proteins in LPS-induced gene expression profiles. To investigate how serum proteins affect LPS-induced signaling, we investigated LPS-inducible genes in PBMC using an oligonucleotide probe-array system. Approximately 120 genes up-regulated by LPS were hierarchically divided into two clusters. Induction of one cluster, containing only IFN-inducible genes, was serum dependent. Real-time PCR analysis confirmed that IFN-inducible genes were induced only in the presence of serum, whereas inflammatory genes were induced both in the presence and absence of serum. Further analysis demonstrated that addition of LPS-binding protein (LBP), but not of soluble CD14 to the serum-free medium enabled the induction of IFN-inducible genes and IFN-beta itself by LPS in human monocytes. The mRNAs for IFN-beta and IFN-inducible genes were induced by LPS only in the presence of serum from LBP(+/+) mice, and not in the presence of serum from LBP(-/-) mice. Blocking experiments also confirmed the involvement of LBP in this phenomenon. Immunoblotting analysis showed that phosphorylation of c-Jun N-terminal kinase, p38, IRF-3, tyrosine kinase 2, and STAT1 by LPS, but not of NF-kappaB and extracellular signal-regulated kinase was abrogated in the absence of LBP. This critical role for LBP implies the presence of possible mechanisms linking LBP to the intracellular signaling between Toll-like receptor 4 and IRF-3, leading to the induction of IFN-beta by LPS.
Kato
Atsushi
A
Department of Allergy and Immunology, National Research Institute for Child Health and Development, Tokyo, Japan.
Ogasawara
Takahisa
T
Homma
Toshiki
T
Saito
Hirohisa
H
Matsumoto
Kenji
K
D000209:Acute-Phase Proteins; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000276:immunology; D020869:Gene Expression Profiling; D006801:Humans; D050838:Interferon Regulatory Factor-3; D016899:Interferon-beta / Q000235:genetics / Q000502:physiology*; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology*; D008562:Membrane Glycoproteins; D051379:Mice; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009000:Monocytes / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D044967:Serum / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D014157:Transcription Factors / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D050838:Interferon Regulatory Factor-3; D016899:Interferon-beta; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D020928:Mitogen-Activated Protein Kinases; D014157:Transcription Factors; D048051:p38 Mitogen-Activated Protein Kinases; D000099231:Lipopolysaccharide-Binding Protein; C494232:IRF3 protein, human; C494233:Irf3 protein, mouse