Schlam Daniel, Bagshaw Richard D, Freeman Spencer A, Collins Richard F, Pawson Tony, Fairn Gregory D, Grinstein Sergio
Division of Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G1X8.
Institute of Medical Science, University of Toronto, Faculty of Medicine, 1 King's College Circle, Toronto, Ontario, Canada M5S1A8.
Nat Commun. 2015 Oct 14;6:8623. doi: 10.1038/ncomms9623.
Phagocytosis is responsible for the elimination of particles of widely disparate sizes, from large fungi or effete cells to small bacteria. Though superficially similar, the molecular mechanisms involved differ: engulfment of large targets requires phosphoinositide 3-kinase (PI3K), while that of small ones does not. Here, we report that inactivation of Rac and Cdc42 at phagocytic cups is essential to complete internalization of large particles. Through a screen of 62 RhoGAP-family members, we demonstrate that ARHGAP12, ARHGAP25 and SH3BP1 are responsible for GTPase inactivation. Silencing these RhoGAPs impairs phagocytosis of large targets. The GAPs are recruited to large--but not small--phagocytic cups by products of PI3K, where they synergistically inactivate Rac and Cdc42. Remarkably, the prominent accumulation of phosphatidylinositol 3,4,5-trisphosphate characteristic of large-phagosome formation is less evident during phagocytosis of small targets, accounting for the contrasting RhoGAP distribution and the differential requirement for PI3K during phagocytosis of dissimilarly sized particles.
吞噬作用负责清除大小差异很大的颗粒，从大型真菌或衰老细胞到小细菌。尽管表面上相似，但涉及的分子机制不同：吞噬大型靶标需要磷酸肌醇3激酶（PI3K），而吞噬小型靶标则不需要。在这里，我们报告说，吞噬杯处Rac和Cdc42的失活对于大型颗粒的完全内化至关重要。通过对62个RhoGAP家族成员的筛选，我们证明ARHGAP12、ARHGAP25和SH3BP1负责GTP酶的失活。沉默这些RhoGAP会损害大型靶标的吞噬作用。这些GAP被PI3K的产物募集到大型吞噬杯而非小型吞噬杯，在那里它们协同使Rac和Cdc42失活。值得注意的是，大型吞噬体形成过程中典型的磷脂酰肌醇3,4,5-三磷酸的显著积累在吞噬小型靶标的过程中不太明显，这解释了不同大小颗粒吞噬过程中RhoGAP分布的差异以及对PI3K的不同需求。
