Two-Step Engulfment of Apoptotic Cells
Two-Step Engulfment of Apoptotic Cells
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DOI：
10.1128/mcb.05993-11
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发表时间：
2012-01-01
影响因子：
5.3
通讯作者：
Nagata, Shigekazu
中科院分区：
文献类型：
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作者：
Toda, Satoshi;Hanayama, Rikinari;Nagata, Shigekazu
凋亡细胞在其表面暴露磷脂酰丝氨酸作为“吃我”的信号，巨噬细胞通过吞噬它们做出反应。虽然已经确定了几种特异性结合磷脂酰丝氨酸的分子，但触发吞噬的分子机制仍然难以捉摸。在这里，我们使用悬浮生长的小鼠pro-B细胞系Ba/F3，重建了凋亡细胞的吞噬。亲本Ba/F3细胞不吞噬凋亡细胞。Ba/F3转化子表达T细胞免疫球蛋白和粘蛋白结构域分子4 (Tim4)，一种特异性结合磷脂酰丝氨酸的I型膜蛋白，以依赖磷脂酰丝氨酸的方式有效结合凋亡细胞，但不吞噬细胞。然而，同时表达Tim4和整合素α (v) β(3)复合物的Ba/F3转化子在乳脂球表皮生长因子VIII （MFG-E8）存在的情况下结合并吞噬凋亡细胞，MFG-E8是一种可以结合磷脂酰丝氨酸和整合素α (v) β的分泌蛋白(3)。这些结果表明，凋亡细胞的吞噬分两个步骤进行：Tim4捆绑凋亡细胞，整合素α (v) β(3)复合物与MFG-E8协同介导吞噬。在小鼠腹膜巨噬细胞中观察到类似的两步吞噬凋亡细胞。此外，在表达Rac1和Rab5的细胞中，Tim4/整合素介导的Ba/F3细胞吞噬增强，表明该系统很好地复制了巨噬细胞对凋亡细胞的吞噬。
Apoptotic cells expose phosphatidylserine on their surface as an "eat me" signal, and macrophages respond by engulfing them. Although several molecules that specifically bind phosphatidylserine have been identified, the molecular mechanism that triggers engulfment remains elusive. Here, using a mouse pro-B cell line, Ba/F3, that grows in suspension, we reconstituted the engulfment of apoptotic cells. The parental Ba/F3 cells did not engulf apoptotic cells. Ba/F3 transformants expressing T cell immunoglobulin-and mucin-domain-containing molecule 4 (Tim4), a type I membrane protein that specifically binds phosphatidylserine, efficiently bound apoptotic cells in a phosphatidylserine-dependent manner but did not engulf them. However, Ba/F3 transformants expressing both Tim4 and the integrin alpha(v)beta(3) complex bound to and engulfed apoptotic cells in the presence of milk fat globule epidermal growth factor factor VIII (MFG-E8), a secreted protein that can bind phosphatidylserine and integrin alpha(v)beta(3). These results indicate that the engulfment of apoptotic cells proceeds in two steps: Tim4 tethers apoptotic cells, and the integrin alpha(v)beta(3) complex mediates engulfment in coordination with MFG-E8. A similar two-step engulfment of apoptotic cells was observed with mouse resident peritoneal macrophages. Furthermore, the Tim4/integrin-mediated engulfment by the Ba/F3 cells was enhanced in cells expressing Rac1 and Rab5, suggesting that this system well reproduces the engulfment of apoptotic cells by macrophages.