IFOM, Fondazione Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139 Milan, Italy.
IFOM, Fondazione Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139 Milan, Italy; Istituto Europeo di Oncologia IRCCS, Via Ripamonti 435, 20141 Milan, Italy.
Cell Rep. 2019 Jun 4;27(10):3049-3061.e6. doi: 10.1016/j.celrep.2019.05.017.
Adaptor protein 2 (AP2) is a major constituent of clathrin-coated pits (CCPs). Whether it is essential for all forms of clathrin-mediated endocytosis (CME) in mammalian cells is an open issue. Here, we demonstrate, by live TIRF microscopy, the existence of a subclass of relatively short-lived CCPs lacking AP2 under physiological, unperturbed conditions. This subclass is retained in AP2-knockout cells and is able to support the internalization of epidermal growth factor receptor (EGFR) but not of transferrin receptor (TfR). The AP2-independent internalization mechanism relies on the endocytic adaptors eps15, eps15L1, and epsin1. The absence of AP2 impairs the recycling of the EGFR to the cell surface, thereby augmenting its degradation. Accordingly, under conditions of AP2 ablation, we detected dampening of EGFR-dependent AKT signaling and cell migration, arguing that distinct classes of CCPs could provide specialized functions in regulating EGFR recycling and signaling.
衔接蛋白 2（AP2）是网格蛋白包被小窝（CCPs）的主要成分。它是否对哺乳动物细胞中所有形式的网格蛋白介导的胞吞作用（CME）都是必不可少的，这是一个悬而未决的问题。在这里，我们通过活 TIRF 显微镜证明，在生理、未受干扰的条件下，存在一类相对寿命较短的 CCPs，缺乏 AP2。这个亚类在 AP2 敲除细胞中被保留下来，并且能够支持表皮生长因子受体（EGFR）的内化，但不能支持转铁蛋白受体（TfR）的内化。AP2 不依赖的内化机制依赖于内吞作用衔接蛋白 eps15、eps15L1 和 epsin1。AP2 的缺失会损害 EGFR 向细胞表面的再循环，从而加速其降解。因此，在 AP2 缺失的条件下，我们检测到 EGFR 依赖性 AKT 信号和细胞迁移的减弱，这表明不同类别的 CCPs 可能在调节 EGFR 再循环和信号转导方面提供专门的功能。
