Key Laboratory of Regenerative Biology, Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, 510530 China.
School of Life Sciences, Guangxi Normal University, Guilin, 541004 China ; Lab for Stem Cell and Pharmaceutical Biotechnology of Guangxi Normal University, Guilin, 541004 China.
Cell Biosci. 2014 Oct 2;4(1):60. doi: 10.1186/2045-3701-4-60. eCollection 2014.
The adapter proteins Appl1 (adaptor protein containing pleckstrin homology domain, phosphotyrosine domain, and leucine zipper motif 1) and Appl2 are highly homologous and involved in several signaling pathways. While previous studies have shown that Appl1 plays a pivotal role in adiponectin signaling and insulin secretion, the physiological functions of Appl2 are largely unknown.
In the present study, the role of Appl2 in sepsis shock was investigated by using Appl2 knockout (KO) mice. When challenged with lipopolysaccharides (LPS), Appl2 KO mice exhibited more severe symptoms of endotoxin shock, accompanied by increased production of proinflammatory cytokines. In comparison with the wild-type control, deletion of Appl2 led to higher levels of TNF-α and IL-1β in primary macrophages. In addition, phosphorylation of Akt and its downstream effector NF-κB was significantly enhanced. By co-immunoprecipitation, we found that Appl2 and Appl1 interacted with each other and formed a complex with PI3K regulatory subunit p85α, which is an upstream regulator of Akt. Consistent with these results, deletion of Appl1 in macrophages exhibited characteristics of reduced Akt activation and decreased the production of TNFα and IL-1β when challenged by LPS.
Results of the present study demonstrated that Appl2 is a critical negative regulator of innate immune response via inhibition of PI3K/Akt/NF-κB signaling pathway by forming a complex with Appl1 and PI3K.
衔接蛋白 Appl1（衔接蛋白，含有 PH 结构域、磷酸酪氨酸结构域和亮氨酸拉链基序 1）和 Appl2 高度同源，参与多种信号通路。虽然先前的研究表明 Appl1 在脂联素信号和胰岛素分泌中发挥关键作用，但 Appl2 的生理功能在很大程度上尚不清楚。
本研究通过应用 Appl2 敲除（KO）小鼠研究了 Appl2 在脓毒症休克中的作用。当用脂多糖（LPS）刺激时，Appl2 KO 小鼠表现出更严重的内毒素休克症状，伴有促炎细胞因子产生增加。与野生型对照相比，Appl2 的缺失导致原代巨噬细胞中 TNF-α 和 IL-1β 的水平升高。此外，Akt 的磷酸化及其下游效应因子 NF-κB 的活性显著增强。通过共免疫沉淀，我们发现 Appl2 与 Appl1 相互作用，并与 Akt 的上游调节因子 PI3K 调节亚基 p85α 形成复合物。与这些结果一致，当用 LPS 刺激时，巨噬细胞中 Appl1 的缺失表现出 Akt 激活减少和 TNFα 和 IL-1β 产生减少的特征。
本研究结果表明，Appl2 通过与 Appl1 和 PI3K 形成复合物来抑制 PI3K/Akt/NF-κB 信号通路，从而成为先天免疫反应的关键负调控因子。
