Chaudhary Anu, Fresquez Theresa M, Naranjo Michele J
Biosciences Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Immunol Cell Biol. 2007 Apr-May;85(3):249-56. doi: 10.1038/sj.icb7100030. Epub 2007 Jan 16.
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.
Toll样受体4（TLR4）通过识别脂多糖（LPS，革兰氏阴性菌细胞壁的一种成分）在哺乳动物中诱导先天免疫反应。在本研究中，我们发现酪氨酸激酶Syk在THP-1细胞中与TLR4组成性结合。如先前在外周血单核细胞中所报道的，在THP-1细胞中，LPS结合后TLR4可诱导性地发生酪氨酸磷酸化。白杨素，一种酪氨酸激酶Syk的药理学抑制剂，在低剂量时可消除TLR4的酪氨酸磷酸化。THP-1细胞中TLR4酪氨酸磷酸化的动力学与Syk酪氨酸磷酸化的早期波峰一致。此外，丝氨酸苏氨酸激酶白细胞介素-1（IL1）受体相关激酶1（IRAK-1）在LPS结合后1分钟内被短暂招募到包含衔接分子MyD88、TLR4和Syk的复合物中，并在30分钟时解离。最后，用白杨素抑制Syk对LPS介导的细胞因子IL6、IL1β、肿瘤坏死因子-α的释放没有影响，对趋化因子巨噬细胞抑制蛋白（MIP）1α、MIP1β、单核细胞趋化蛋白-1、IL8、Groα和RANTES也没有影响。然而，IL10和IL12p40的释放受到显著抑制。我们的研究结果表明Syk是人类单核细胞中LPS介导的TLR4反应的一种新型调节因子，并深入了解了LPS结合后早期复合物形成的动力学。
