Arf GTP-binding proteins and membrane traffic

Arf6 GTP结合蛋白已被证明在质膜上发挥作用，以协调内体膜运输途径，并维持皮质肌动蛋白细胞骨架。最近，我们将注意力转向研究其他Arf蛋白(特别是Arf1)是否也可以在细胞表面发挥功能，这些蛋白通常被认为在高尔基复合体中起作用。我们先前证明了Arf6在PM的激活可以通过Arno鸟嘌呤核苷酸交换因子的招募而导致Arf1的激活，从而激活Arf1(Cohen等人，2007 Mol Biol Cell 18：2244)。现在，我们已经证明，像Arf1这样的高尔基体相关ARF需要在质膜上启动特定的皮质肌动蛋白重排(Caviston等人，2014年)。我们发现Arf1是产生腹侧肌动蛋白结构所必需的，而腹侧肌动蛋白结构是佛波酯处理后形成的。佛波酯，如PMA，是肿瘤的促进剂，并导致蛋白激酶C和Src家族的激活。这些腹侧肌动蛋白结构代表了皮质肌动蛋白细胞骨架和局灶性粘连的主要重组。这增加了越来越多发生在质膜上的细胞活动，现在被认为与Arf1有关。虽然所有Arf蛋白都有共同的效应因子(磷脂酶D和磷脂酰肌醇4-磷酸5-激酶的刺激)，但它们被不同的鸟核苷酸交换因子(GEF)激活，并被不同的GTP-ase激活蛋白(GAP)失活。此外，这些GEF和GAP本身可能具有独特的信号和脚手架功能，从而产生不同的信号输出。我们的发现证实了细胞表面Arf功能级联的存在，并为细胞内Arf功能的协调提供了新的见解。

The Arf6 GTP-binding protein has been shown to function at the plasma membrane to coordinate an endosomal membrane trafficking pathway and maintain the cortical actin cytoskeleton. More recently, we turned our attention to examining whether other Arf proteins (especially Arf1), typically thought to function at the Golgi complex, could also serve a function at the cell surface. We previously showed that activation of Arf6 at the PM could lead to activation of Arf1 by the recruitment of the ARNO guanine nucleotide exchange factor, which activates Arf1 (Cohen et al., 2007 Mol Biol Cell 18:2244). Now we have shown that Golgi-associated Arfs like Arf1 are required at the plasma membrane to initiate specific cortical actin rearrangements (Caviston et al., 2014). We found that Arf1 is required for the generation of ventral actin structures formed in response to phorbol ester treatment. Phorbol esters like PMA are tumor promoters and lead to the activation of protein kinase C and Src family kinases. These ventral actin structures represent a major re-organization of the cortical actin cytoskeleton and focal adhesions. This adds to the growing list of cellular activities occurring at the plasma membrane that now are thought to involve Arf1. Athough all Arf protein share common effectors (stimulation of phospholipase D, and phosphatidylinositol 4-phosphate 5-kinase), they are activated by different guanine nucleotide exchange factors (GEFs) and inactivated by different GTP-ase activating proteins (GAPs). Furthermore these GEFs and GAPs themselves may have unique signaling and scaffolding functions giving rise to distinct signaling outputs. Our findings confirm the presence of a cascade of Arf functioning at the cell surface and open up new insights into the coordination of Arf functioning in the cell.