Department of Integrative Biotechnology, Sungkyunkwan University, Suwon, South Korea.
Department of Life Sciences, Kyonggi University, Suwon, South Korea.
Front Immunol. 2021 Dec 23;12:767366. doi: 10.3389/fimmu.2021.767366. eCollection 2021.
Inflammation, a vital immune response to infection and injury, is mediated by macrophage activation. While spleen tyrosine kinase (Syk) and myeloid differentiation primary response 88 (MyD88) are reportedly involved in inflammatory responses in macrophages, their roles and underlying mechanisms are largely unknown.
Here, the role of the MyD88-Syk axis and the mechanism by which Syk and MyD88 cooperate during macrophage-mediated inflammatory responses are explored using knockout conditions of these proteins and mutation strategy as well as flowcytometric and immunoblotting analyses.
Syk rapidly activates the nuclear factor-kappa B (NF-κB) signaling pathway in lipopolysaccharide (LPS)-stimulated RAW264.7 cells, and the activation of the NF-κB signaling pathway is abolished in Syk RAW264.7 cells. MyD88 activates Syk and Syk-induced activation of NF-κB signaling pathway in LPS-stimulated RAW264.7 cells but Syk-induced inflammatory responses are significantly inhibited in MyD88 RAW264.7 cells. MyD88 interacts with Syk through the tyrosine 58 residue (Y58) in the hemi-immunoreceptor tyrosine-based activation motif (ITAM) of MyD88, leading to Syk activation and Syk-induced activation of the NF-κB signaling pathway. Src activates MyD88 by phosphorylation at Y58 the Src kinase domain. In addition, Ras-related C3 botulinum toxin substrate 1 (Rac1) activation and Rac1-induced formation of filamentous actin (F actin) activate Src in LPS-stimulated RAW264.7 cells.
These results suggest that the MyD88-Syk axis is a critical player in macrophage-mediated inflammatory responses, and its function is promoted by an upstream Src kinase activated by Rac1-generated filamentous actin (F-actin).
炎症是一种对感染和损伤的重要免疫反应，由巨噬细胞激活介导。虽然脾酪氨酸激酶（Syk）和髓样分化初级反应 88（MyD88）据报道参与巨噬细胞中的炎症反应，但它们的作用和潜在机制在很大程度上尚不清楚。
在这里，使用这些蛋白质的敲除条件和突变策略以及流式细胞术和免疫印迹分析，研究了 MyD88-Syk 轴的作用以及 Syk 和 MyD88 在巨噬细胞介导的炎症反应中合作的机制。
Syk 在脂多糖（LPS）刺激的 RAW264.7 细胞中迅速激活核因子-κB（NF-κB）信号通路，并且在 Syk RAW264.7 细胞中NF-κB 信号通路的激活被消除。MyD88 在 LPS 刺激的 RAW264.7 细胞中激活 Syk 和 Syk 诱导的 NF-κB 信号通路，但在 MyD88 RAW264.7 细胞中，Syk 诱导的炎症反应受到显著抑制。MyD88 通过 MyD88 半免疫受体酪氨酸基激活基序（ITAM）中的酪氨酸 58 残基（Y58）与 Syk 相互作用，导致 Syk 激活和 Syk 诱导的 NF-κB 信号通路激活。Src 通过磷酸化 Y58 激活 MyD88，Syk 激酶结构域。此外，Ras 相关 C3 肉毒梭菌毒素底物 1（Rac1）的激活和 Rac1 诱导的丝状肌动蛋白（F-actin）的形成在 LPS 刺激的 RAW264.7 细胞中激活 Src。
这些结果表明，MyD88-Syk 轴是巨噬细胞介导的炎症反应的关键参与者，其功能由 Rac1 产生的丝状肌动蛋白（F-actin）激活的上游 Src 激酶促进。
