Laird V, Spiess M
Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland.
Exp Cell Res. 2000 Nov 1;260(2):340-5. doi: 10.1006/excr.2000.5006.
The mechanism of transport of membrane proteins from the trans-Golgi to the cell surface is still poorly understood. Previous studies suggested that basolateral membrane proteins, such as the transferrin receptor and the asialoglycoprotein receptor H1, take an indirect route to the plasma membrane via an intracellular, most likely endosomal intermediate. To define this compartment we developed a biochemical assay based on the very definition of endosomes. The assay is based on internalizing anti-H1 antibodies via the endocytic cycle of the receptor itself. Internalized antibody formed immune complexes with newly synthesized H1, which had been pulse-labeled with [(35)S]sulfate and chased out of the trans-Golgi for a period of time that was insufficient for H1 to reach the surface. Hence, antibody capture occurred intracellularly. Double-immunofluorescence labeling demonstrated that antibody-containing compartments also contained transferrin and thus corresponded to early and recycling endosomes. The results therefore demonstrate an intracellular intersection of the exocytic and endocytic pathways with implications for basolateral sorting.
膜蛋白从反式高尔基体转运至细胞表面的机制仍知之甚少。先前的研究表明，基底外侧膜蛋白，如转铁蛋白受体和去唾液酸糖蛋白受体H1，通过细胞内（很可能是内体中间体）的间接途径到达质膜。为了定义这个区室，我们基于内体的定义开发了一种生化分析方法。该分析方法基于通过受体自身的内吞循环内化抗H1抗体。内化的抗体与新合成的H1形成免疫复合物，新合成的H1已用[（35）S]硫酸盐进行脉冲标记，并从反式高尔基体中追踪一段时间，这段时间不足以使H1到达表面。因此，抗体捕获发生在细胞内。双重免疫荧光标记表明，含有抗体的区室也含有转铁蛋白，因此对应于早期和再循环内体。因此，结果表明胞吐和内吞途径在细胞内有交叉，这对基底外侧分选有影响。
