Höning S, Griffith J, Geuze H J, Hunziker W
Institute of Biochemistry, University of Lausanne, Epalinges, Switzerland.
EMBO J. 1996 Oct 1;15(19):5230-9.
Diversion of membrane proteins from the trans-Golgi network (TGN) or the plasma membrane into the endosomal system occurs via clathrin-coated vesicles (CCVs). These sorting events may require the interaction of cytosolic domain signals with clathrin adaptor proteins (APs) at the TGN (AP-1) or the plasma membrane (AP-2). While tyrosine- and di-leucine-based signals in several proteins mediate endocytosis via cell surface CCVs, segregation into Golgi-derived CCVs has so far only been documented for the mannose 6-phosphate receptors, where it is thought to require a casein kinase II phosphorylation site adjacent to a di-leucine motif. Although recently tyrosine-based signals have also been shown to interact with the mu chain of AP-1 in vitro, it is not clear if these signals also bind intact AP-1 adaptors, nor if they can mediate sorting of proteins into AP-1 CCVs. Here we show that the cytosolic domain of the lysosomal membrane glycoprotein lamp-1 binds AP-1 and AP-2. Furthermore, lamp-1 is present in AP-1-positive vesicles and tubules in the trans-region on the Golgi complex. AP-1 binding as well as localization to AP-1 CCVs require the presence of the functional tyrosine-based lysosomal targeting signal of lamp-1. These results indicate that lamp-1 can exit the TGN in CCVs and that tyrosine signals can mediate these sorting events.
膜蛋白从反式高尔基体网络（TGN）或质膜转运至内体系统是通过网格蛋白包被囊泡（CCV）实现的。这些分选事件可能需要胞质结构域信号与TGN处（AP-1）或质膜处（AP-2）的网格蛋白衔接蛋白（AP）相互作用。虽然几种蛋白质中基于酪氨酸和双亮氨酸的信号通过细胞表面CCV介导内吞作用，但到目前为止，只有甘露糖6-磷酸受体被证明可分选至源自高尔基体的CCV，据认为这需要一个与双亮氨酸基序相邻的酪蛋白激酶II磷酸化位点。尽管最近基于酪氨酸的信号在体外也被证明可与AP-1的μ链相互作用，但尚不清楚这些信号是否也能结合完整的AP-1衔接蛋白，以及它们是否能介导蛋白质分选至AP-1 CCV。在这里，我们表明溶酶体膜糖蛋白lamp-1的胞质结构域可结合AP-1和AP-2。此外，lamp-1存在于高尔基体复合体反式区域的AP-1阳性囊泡和小管中。AP-1结合以及定位于AP-1 CCV需要lamp- functional酪氨酸基溶酶体靶向信号的存在。这些结果表明lamp-1可以通过CCV从TGN中输出，并且酪氨酸信号可以介导这些分选事件。 1的功能性基于酪氨酸的溶酶体靶向信号的存在。这些结果表明lamp-1可以通过CCV从TGN中输出，并且酪氨酸信号可以介导这些分选事件。
