Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario K7L 3N6, Canada.
J Biol Chem. 2011 Oct 21;286(42):36532-49. doi: 10.1074/jbc.M111.237578. Epub 2011 Aug 26.
The signaling pathways of mammalian Toll-like receptors (TLRs) are well characterized, but the precise mechanism(s) by which TLRs are activated upon ligand binding remains poorly defined. Recently, we reported a novel membrane sialidase-controlling mechanism that depends on ligand binding to its TLR to induce mammalian neuraminidase-1 (Neu1) activity, to influence receptor desialylation, and subsequently to induce TLR receptor activation and the production of nitric oxide and proinflammatory cytokines in dendritic and macrophage cells. The α-2,3-sialyl residue of TLR was identified as the specific target for hydrolysis by Neu1. Here, we report a membrane signaling paradigm initiated by endotoxin lipopolysaccharide (LPS) binding to TLR4 to potentiate G protein-coupled receptor (GPCR) signaling via membrane Gα(i) subunit proteins and matrix metalloproteinase-9 (MMP9) activation to induce Neu1. Central to this process is that a Neu1-MMP9 complex is bound to TLR4 on the cell surface of naive macrophage cells. Specific inhibition of MMP9 and GPCR Gα(i)-signaling proteins blocks LPS-induced Neu1 activity and NFκB activation. Silencing MMP9 mRNA using lentivirus MMP9 shRNA transduction or siRNA transfection of macrophage cells and MMP9 knock-out primary macrophage cells significantly reduced Neu1 activity and NFκB activation associated with LPS-treated cells. These findings uncover a molecular organizational signaling platform of a novel Neu1 and MMP9 cross-talk in alliance with TLR4 on the cell surface that is essential for ligand activation of TLRs and subsequent cellular signaling.
哺乳动物 Toll 样受体 (TLR) 的信号通路已经得到很好的描述,但是 TLR 在外源配体结合后被激活的确切机制仍未完全阐明。最近,我们报道了一种新的膜唾液酸酶调控机制,该机制依赖于配体与 TLR 的结合,诱导哺乳动物神经氨酸酶-1 (Neu1) 的活性,影响受体去唾液酸化,随后诱导 TLR 受体激活以及树突状细胞和巨噬细胞中一氧化氮和促炎细胞因子的产生。TLR 的α-2,3-唾液酸残基被确定为 Neu1 水解的特异性靶标。在这里,我们报告了一种由内毒素脂多糖 (LPS) 与 TLR4 结合引发的膜信号转导范例,通过膜 G 蛋白偶联受体 (GPCR) 信号通路增强 G 蛋白α(i)亚基蛋白和基质金属蛋白酶-9 (MMP9) 的激活,诱导 Neu1。这一过程的核心是 Neu1-MMP9 复合物结合到幼稚巨噬细胞表面 TLR4 上。特异性抑制 MMP9 和 GPCR Gα(i)信号蛋白可阻断 LPS 诱导的 Neu1 活性和 NFκB 激活。使用慢病毒 MMP9 shRNA 转导或巨噬细胞 siRNA 转染沉默 MMP9 mRNA 以及 MMP9 敲除原代巨噬细胞显著降低了与 LPS 处理细胞相关的 Neu1 活性和 NFκB 激活。这些发现揭示了一种新的 Neu1 和 MMP9 相互作用的分子组织信号平台,与细胞表面 TLR4 联合,对于 TLR 配体激活和随后的细胞信号转导至关重要。