Cao T T, Deacon H W, Reczek D, Bretscher A, von Zastrow M
Department of Biochemistry and Biophysics, University of California, San Francisco 94143, USA.
Nature. 1999 Sep 16;401(6750):286-90. doi: 10.1038/45816.
A fundamental question in cell biology is how membrane proteins are sorted in the endocytic pathway. The sorting of internalized beta2-adrenergic receptors between recycling endosomes and lysosomes is responsible for opposite effects on signal transduction and is regulated by physiological stimuli. Here we describe a mechanism that controls this sorting operation, which is mediated by a family of conserved protein-interaction modules called PDZ domains. The phosphoprotein EBP50 (for ezrinradixin-moesin(ERM)-binding phosphoprotein-50) binds to the cytoplasmic tail of the beta2-adrenergic receptor through a PDZ domain and to the cortical actin cytoskeleton through an ERM-binding domain. Disrupting the interaction of EBP50 with either domain or depolymerization of the actin cytoskeleton itself causes missorting of endocytosed beta2-adrenergic receptors but does not affect the recycling of transferrin receptors. A serine residue at position 411 in the tail of the beta2-adrenergic receptor is a substrate for phosphorylation by GRK-5 (for G-protein-coupled-receptor kinase-5) and is required for interaction with EBP50 and for proper recycling of the receptor. Our results identify a new role for PDZ-domain-mediated protein interactions and for the actin cytoskeleton in endocytic sorting, and suggest a mechanism by which GRK-mediated phosphorylation could regulate membrane trafficking of G-protein-coupled receptors after endocytosis.
细胞生物学中的一个基本问题是膜蛋白如何在内吞途径中进行分选。内化的β2-肾上腺素能受体在回收型内体和溶酶体之间的分选对信号转导具有相反的影响，并受生理刺激的调节。在此，我们描述了一种控制这种分选操作的机制，该机制由一类称为PDZ结构域的保守蛋白质相互作用模块介导。磷蛋白EBP50（即埃兹蛋白-根蛋白-膜突蛋白（ERM）结合磷蛋白50）通过一个PDZ结构域与β2-肾上腺素能受体的胞质尾结合，并通过一个ERM结合结构域与皮质肌动蛋白细胞骨架结合。破坏EBP50与任一结构域的相互作用或肌动蛋白细胞骨架本身的解聚都会导致内吞的β2-肾上腺素能受体分选错误，但不影响转铁蛋白受体的循环利用。β2-肾上腺素能受体尾端第411位的丝氨酸残基是GRK-5（即G蛋白偶联受体激酶-5）磷酸化的底物，是与EBP50相互作用及受体正常循环利用所必需的。我们的结果确定了PDZ结构域介导的蛋白质相互作用和肌动蛋白细胞骨架在内吞分选中的新作用，并提出了一种GRK介导的磷酸化可能调节内吞后G蛋白偶联受体膜转运的机制。
