Tosello-Trampont A C, Brugnera E, Ravichandran K S
Beirne B. Carter Center for Immunology Research and the Department of Microbiology, University of Virginia, Charlottesville 22908, USA.
J Biol Chem. 2001 Apr 27;276(17):13797-802. doi: 10.1074/jbc.M011238200. Epub 2001 Jan 31.
Apoptosis or programmed cell death occurs in multicellular organisms throughout life. The removal of apoptotic cells by phagocytes prevents secondary necrosis and inflammation and also plays a key role in tissue remodeling and regulating immune responses. The molecular mechanisms that regulate the engulfment of apoptotic cells are just beginning to be elucidated. Recent genetic studies in the nematode Caenorhabditis elegans have implicated at least six genes in the removal of apoptotic cell corpses. The gene products of ced-2, ced-5, and ced-10 are thought to be part of a pathway that regulates the reorganization of the cytoskeleton during engulfment. The adapter proteins CrkII and Dock180 and the small GTPase Rac represent the mammalian orthologues of the ced-2, ced-5 and ced-10 gene products, respectively. It is not known whether CrkII, Dock180, or Rac proteins have any role during engulfment in mammalian cells. Here we show, using stable cell lines and transient transfections, that overexpression of wild-type CrkII or an activated form of Rac1 enhances engulfment. Mutants of CrkII failed to mediate this increased engulfment. The higher CrkII-mediated uptake was inhibited by coexpression of a dominant negative form of Rac1 but not by a dominant a negative Rho protein; this suggested that Rac functions downstream of CrkII in this process, which is consistent with genetic studies in the worm that place ced-10 (rac) downstream of ced-2 (crk) in cell corpse removal. Taken together, these data suggest that CED-2/CrkII and CED-10/Rac are part of an evolutionarily conserved pathway in engulfment of apoptotic cells.
凋亡或程序性细胞死亡在多细胞生物的整个生命过程中都会发生。吞噬细胞清除凋亡细胞可防止继发性坏死和炎症，并且在组织重塑和调节免疫反应中也起着关键作用。调节凋亡细胞吞噬的分子机制才刚刚开始被阐明。最近对线虫秀丽隐杆线虫的遗传学研究表明，至少有六个基因参与凋亡细胞尸体的清除。ced-2、ced-5和ced-10的基因产物被认为是在吞噬过程中调节细胞骨架重组的一条途径的一部分。衔接蛋白CrkII和Dock180以及小GTP酶Rac分别代表ced-2、ced-5和ced-10基因产物的哺乳动物直系同源物。目前尚不清楚CrkII、Dock180或Rac蛋白在哺乳动物细胞吞噬过程中是否发挥任何作用。在这里，我们使用稳定细胞系和瞬时转染表明，野生型CrkII或激活形式的Rac1的过表达增强了吞噬作用。CrkII的突变体未能介导这种增加的吞噬作用。CrkII介导的较高摄取被显性负性形式的Rac1的共表达所抑制，但不被显性负性Rho蛋白所抑制；这表明在这个过程中Rac在CrkII的下游发挥作用，这与在蠕虫中的遗传学研究一致，即在细胞尸体清除中ced-10（rac）位于ced-2（crk）的下游。综上所述，这些数据表明CED-2/CrkII和CED-10/Rac是凋亡细胞吞噬过程中进化保守途径的一部分。
