The serine/threonine kinase Akt promotes Fcγ receptor-mediated phagocytosis in murine macrophages through the activation of p70S6 kinase
The serine/threonine kinase Akt promotes Fcγ receptor-mediated phagocytosis in murine macrophages through the activation of p70S6 kinase
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DOI：
10.1074/jbc.m408188200
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发表时间：
2004-12-24
影响因子：
4.8
通讯作者：
Tridandapani, S
中科院分区：
文献类型：
--
作者：
Ganesan, LP;Wei, G;Tridandapani, S
通过免疫复合物聚集的Fc γ受体（Fc γ R）激活导致吞噬作用的多种信号传导途径。我们和其他人以前曾报道Akt是磷酸化的FcgammaR聚类反应。然而，FcgammaR激活Akt的功能后果尚不清楚。使用Raw 264.7巨噬细胞转染过表达组成型活性肉豆蔻酰化（Myr）-Akt或显性阴性CAAX-Akt和骨髓巨噬细胞（BTH）从野生型和转基因小鼠表达巨噬细胞特异性Myr-Akt，我们分析了Akt的功能在吞噬作用。我们报道Myr-Akt的过表达导致吞噬效率的显著增加，而CAAX-Akt下调Raw 264.7细胞的吞噬作用。同样地，表达Myr-Akt的Bacteria显示增强的吞噬能力。通过分析Akt的下游效应子，我们证明了p70 S6激酶在Myr-Akt表达的Bp 53中是组成性磷酸化的。p70 S6激酶被报道影响肌动蛋白细胞骨架和细胞迁移，这表明Akt可能通过激活p70 S6激酶来影响吞噬作用。与此一致，野生型或组成型活性，但不是激酶失活的p70 S6激酶在Raw 264.7细胞中的过度表达显着增强吞噬作用。同样，用雷帕霉素抑制p70 S6激酶下调了由组成型活性Akt表达所赋予的吞噬效率。这些发现证明了Akt通过激活p70 S6激酶在吞噬作用中的新作用。
Fcgamma receptor (FcgammaR) clustering by immune complexes activates multiple signaling pathways leading to phagocytosis. We and others have previously reported that Akt is phosphorylated in response to FcgammaR clustering. However, the functional consequence of Akt activation by FcgammaR is not known. Using Raw 264.7 macrophage cells transfected to overexpress either constitutively active myristoylated (Myr)-Akt or a dominant-negative CAAX-Akt and bone marrow macrophages (BMMs) from wild-type and transgenic mice expressing macrophage-specific Myr-Akt, we analyzed the function of Akt in phagocytosis. We report that overexpression of Myr-Akt resulted in significant increase in phagocytic efficiency, whereas CAAX-Akt down-regulated phagocytosis in Raw 264.7 cells. Likewise BMMs expressing Myr-Akt displayed enhanced phagocytic ability. Analyzing the downstream effectors of Akt, we demonstrate that p70S6 kinase is constitutively phosphorylated in Myr-Akt-expressing BMMs. p70S6 kinase is reported to influence actin cytoskeleton and cell migration, suggesting that Akt may influence phagocytosis through the activation of p70S6 kinase. Consistent with this, overexpression of either wild-type or constitutively active but not a kinase-inactive p70S6 kinase in Raw 264.7 cells significantly enhanced phagocytosis. Likewise suppression of p70S6 kinase with rapamycin down-regulated phagocytic efficiency conferred by the expression of constitutively active Akt. These findings demonstrate a novel role for Akt in phagocytosis through the activation of p70S6 kinase.