Simmen Thomas, Höning Stefan, Icking Ann, Tikkanen Ritva, Hunziker Walter
Institute of Biochemistry, University of Lausanne, CH-1066 Epalinges, Switzerland.
Nat Cell Biol. 2002 Feb;4(2):154-9. doi: 10.1038/ncb745.
Adaptors are heterotetrameric complexes that mediate the incorporation of cargo into transport vesicles by interacting with sorting signals present in the cytosolic domain of transmembrane proteins. Four adaptors, AP-1 (beta 1, gamma, mu 1A or mu 1B, sigma 1), AP-2 (beta 2, alpha, mu 2, sigma 2), AP-3 (beta 3 , delta, mu 3, sigma 3) or AP-4 (beta 4, epsilon, mu 4, sigma 4), have been characterized. AP-1 and AP-3 mediate sorting events at the level of the TGN and/or endosomes, whereas AP-2 functions in endocytic clathrin coated vesicle formation; no function is known so far for AP-4. Here, we show that AP-4 can bind different types of cytosolic signals known to mediate basolateral transport in epithelial cells. Furthermore, in MDCK cells with depleted mu 4 protein levels, several basolateral proteins are mis-sorted to the apical surface, showing that AP-4 participates in basolateral sorting in epithelial cells.
衔接蛋白是异源四聚体复合物，通过与跨膜蛋白胞质结构域中存在的分选信号相互作用，介导货物掺入运输小泡。已鉴定出四种衔接蛋白，即AP-1（β1、γ、μ1A或μ1B、σ1）、AP-2（β2、α、μ2、σ2）、AP-3（β3、δ、μ3、σ3）或AP-4（β4、ε、μ4、σ4）。AP-1和AP-3介导反式高尔基体网络和/或内体水平的分选事件，而AP-2在内吞网格蛋白包被小泡形成中起作用；目前尚不清楚AP-4的功能。在这里，我们表明AP-4可以结合已知介导上皮细胞基底外侧运输的不同类型的胞质信号。此外，在μ4蛋白水平耗尽的MDCK细胞中，几种基底外侧蛋白被错误分选到顶端表面，表明AP-4参与上皮细胞的基底外侧分选。
