Endophilin-A2 functions in membrane scission in clathrin-independent endocytosis

摘要

During endocytosis, energy is invested to narrow the necks of cargo-containing plasma membrane invaginations to radii at which the opposing segments spontaneously coalesce, thereby leading to the detachment by scission of endocytic uptake carriers. In the clathrin pathway, dynamin uses mechanical energy from GTP hydrolysis to this effect, assisted by the BIN/amphiphysin/Rvs (BAR) domain-containing protein endophilin. Clathrin-independent endocytic events are often less reliant on dynamin, and whether in these cases BAR domain proteins such as endophilin contribute to scission has remained unexplored. Here we show, in human and other mammalian cell lines, that endophilin-A2 (endoA2) specifically and functionally associates with very early uptake structures that are induced by the bacterial Shiga and cholera toxins, which are both clathrin-independent endocytic cargoes. In controlled in vitro systems, endoA2 reshapes membranes before scission. Furthermore, we demonstrate that endoA2, dynamin and actin contribute in parallel to the scission of Shiga-toxin-induced tubules. Our results establish a novel function of endoA2 in clathrin-independent endocytosis. They document that distinct scission factors operate in an additive manner, and predict that specificity within a given uptake process arises from defined combinations of universal modules. Our findings highlight a previously unnoticed link between membrane scaffolding by endoA2 and pulling-force-driven dynamic scission.%细胞通过内吞过程来内化养分和周转膜成分，该过程在大多数情况下都涉及名为"网格蛋白"的蛋白。"内吞蛋白"一直被认为是由"网格蛋白"介导的内吞过程的一个成分，但本期Nature上发表的两篇研究论文显示，这种蛋白介导快速作用的、独立于"网格蛋白"的一种形式的内吞，后者涉及"管囊"的形成。Emmanuel Boucrot等人报告说，这一通道是由配体与运货受体的结合触发的，并且需要"发动蛋白"和"肌动蛋白"这两种蛋白的参与。"内吞蛋白"介导的内吞似乎还有截然不同的"细胞家"(cellular homes),出现在细胞的前缘上，在那里脂质PtdIns(3,4)P_2确保"内吞蛋白"的参与。这种形式的内吞被发现介导几种有生理功能和与疾病相关的受体的吸收，其中包括"G-蛋白耦合受体"和"酪氨酸激酶"受体。在第二篇论文中，Henri-Francois Renard等人提供的证据表明细菌毒素利用相同通道进入细胞，同时他们还发现，"内吞蛋白-A2"与"发动蛋白"和"肌动蛋白"一起发挥作用。