Wiedemann Agnès, Patel Jayesh C, Lim Jenson, Tsun Andy, van Kooyk Yvette, Caron Emmanuelle
Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, England, UK.
J Cell Biol. 2006 Mar 27;172(7):1069-79. doi: 10.1083/jcb.200508075.
AlphaMbeta2 integrins mediate phagocytosis of opsonized particles in a process controlled by RhoA, Rho kinase, myosin II, Arp2/3, and actin polymerization. AlphaMbeta2, Rho, Arp2/3, and F-actin accumulate underneath bound particles; however, the mechanism regulating Rho function during alphaMbeta2-mediated phagocytosis is poorly understood. We report that the binding of C3bi-opsonized sheep red blood cells (RBCs) to alphaMbeta2 increases Rho-GTP, but not Rac-GTP, levels. Deletion of the cytoplasmic domain of beta2, but not of alphaM, abolished Rho recruitment and activation, as well as phagocytic uptake. Interestingly, a 16-amino acid (aa) region in the membrane-proximal half of the beta2 cytoplasmic domain was necessary for activating Rho. Three COOH-terminal residues (aa 758-760) were essential for beta2-induced accumulation of Rho at complement receptor 3 (CR3) phagosomes. Activation of Rho was necessary, but not sufficient, for its stable recruitment underneath bound particles or for uptake. However, recruitment of active Rho was sufficient for phagocytosis. Our data shed light on the mechanism of outside-in signaling, from ligated integrins to the activation of Rho GTPase signaling.
αMβ2整合素在由RhoA、Rho激酶、肌球蛋白II、Arp2/3和肌动蛋白聚合作用控制的过程中介导调理素化颗粒的吞噬作用。αMβ2、Rho、Arp2/3和F-肌动蛋白在结合颗粒下方聚集；然而，在αMβ2介导的吞噬作用过程中调节Rho功能的机制尚不清楚。我们报告，C3bi调理的绵羊红细胞（RBCs）与αMβ2的结合增加了Rho-GTP水平，但不增加Rac-GTP水平。β2胞质结构域的缺失，而不是αM的缺失，消除了Rho的募集和激活以及吞噬摄取。有趣的是，β2胞质结构域膜近端一半中的一个16个氨基酸（aa）区域对于激活Rho是必需的。三个COOH末端残基（aa 758-760）对于β2诱导Rho在补体受体3（CR3）吞噬体处的积累至关重要。Rho的激活对于其在结合颗粒下方的稳定募集或摄取是必要的，但不是充分的。然而，活性Rho的募集对于吞噬作用是足够的。我们的数据揭示了从连接的整合素到Rho GTPase信号激活的外向内信号传导机制。
