Hong Nan Hyung, Qi Aidong, Weaver Alissa M
Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232.
Department of Biochemistry, Vanderbilt University Medical Center, Nashville, TN 37232.
J Cell Biol. 2015 Aug 31;210(5):753-69. doi: 10.1083/jcb.201412127.
Branched actin critically contributes to membrane trafficking by regulating membrane curvature, dynamics, fission, and transport. However, how actin dynamics are controlled at membranes is poorly understood. Here, we identify the branched actin regulator cortactin as a direct binding partner of phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) and demonstrate that their interaction promotes turnover of late endosomal actin. In vitro biochemical studies indicated that cortactin binds PI(3,5)P2 via its actin filament-binding region. Furthermore, PI(3,5)P2 competed with actin filaments for binding to cortactin, thereby antagonizing cortactin activity. These findings suggest that PI(3,5)P2 formation on endosomes may remove cortactin from endosome-associated branched actin. Indeed, inhibition of PI(3,5)P2 production led to cortactin accumulation and actin stabilization on Rab7(+) endosomes. Conversely, inhibition of Arp2/3 complex activity greatly reduced cortactin localization to late endosomes. Knockdown of cortactin reversed PI(3,5)P2-inhibitor-induced actin accumulation and stabilization on endosomes. These data suggest a model in which PI(3,5)P2 binding removes cortactin from late endosomal branched actin networks and thereby promotes net actin turnover.
分支状肌动蛋白通过调节膜曲率、动力学、裂变和运输，对膜运输起着关键作用。然而，目前人们对肌动蛋白动力学在膜上是如何被控制的了解甚少。在这里，我们确定分支状肌动蛋白调节因子皮层肌动蛋白是磷脂酰肌醇3,5-二磷酸（PI(3,5)P2）的直接结合伴侣，并证明它们的相互作用促进晚期内体肌动蛋白的周转。体外生化研究表明，皮层肌动蛋白通过其肌动蛋白丝结合区域与PI(3,5)P2结合。此外，PI(3,5)P2与肌动蛋白丝竞争与皮层肌动蛋白的结合，从而拮抗皮层肌动蛋白的活性。这些发现表明，内体上PI(3,5)P2的形成可能会将皮层肌动蛋白从与内体相关的分支状肌动蛋白中去除。事实上，抑制PI(3,5)P2的产生会导致皮层肌动蛋白在Rab7(+)内体上积累以及肌动蛋白稳定。相反，抑制Arp2/3复合物的活性会大大减少皮层肌动蛋白在晚期内体上的定位。敲低皮层肌动蛋白可逆转PI(3,5)P2抑制剂诱导的肌动蛋白在内体上的积累和稳定。这些数据提出了一个模型，即PI(3,5)P2结合将皮层肌动蛋白从晚期内体分支状肌动蛋白网络中去除，从而促进肌动蛋白的净周转。
