Tyrosine kinase Syk associates with toll-like receptor 4 and regulates signaling in human monocytic cells.
Toll-like receptor 4 (TLR4) induces an innate immune response in mammals by recognizing lipopolysaccharide (LPS), a component of the cell wall of Gram-negative bacteria. In this study, we show that tyrosine kinase Syk constitutively associates with TLR4 in THP-1 cells. As previously reported in peripheral blood mononuclear cells, TLR4 gets inducibly tyrosine phosphorylated upon LPS engagement in THP-1 cells. Piceatannol, a pharmacological inhibitor of the tyrosine kinase Syk, abrogates TLR4 tyrosine phosphorylation at low doses. The kinetics of TLR4 tyrosine phosphorylation in THP-1 cells coincides with an early wave of Syk tyrosine phosphorylation. Additionally, serine threonine kinase interleukin-1 (IL1) receptor-associated kinase 1 (IRAK-1) is transiently recruited to the complex containing adaptor molecule MyD88, TLR4 and Syk within 1 min of LPS engagement and dissociates by 30 min. Finally, the inhibition of Syk with piceatannol has no effect on LPS-mediated release of cytokines IL6, IL1beta, tumor necrosis factor-alpha, neither on chemokines macrophage inhibitory protein (MIP)1alpha, MIP1beta, monocyte chemoattractant protein -1, IL8, Groalpha and RANTES. However, IL10 and IL12p40 releases are significantly inhibited. Our findings implicate Syk as a novel modulator of LPS-mediated TLR4 responses in human monocytic cells and shed insight into the kinetics of early complex formation upon LPS engagement.
Chaudhary
Anu
A
Biosciences Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. anu@lanl.gov
Fresquez
Theresa M
TM
Naranjo
Michele J
MJ
D045744:Cell Line, Tumor; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases / Q000378:metabolism; D016753:Interleukin-10 / Q000378:metabolism; D018664:Interleukin-12 / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology; D009000:Monocytes / Q000276:immunology / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D013267:Stilbenes / Q000494:pharmacology; D000072377:Syk Kinase; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; D013267:Stilbenes; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D016753:Interleukin-10; D018664:Interleukin-12; C041525:3,3',4,5'-tetrahydroxystilbene; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D053592:Interleukin-1 Receptor-Associated Kinases