Ihrke G, Martin G V, Shanks M R, Schrader M, Schroer T A, Hubbard A L
Department of Cell Biology and Anatomy, The Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
J Cell Biol. 1998 Apr 6;141(1):115-33. doi: 10.1083/jcb.141.1.115.
We studied basolateral-to-apical transcytosis of three classes of apical plasma membrane (PM) proteins in polarized hepatic WIF-B cells and then compared it to the endocytic trafficking of basolaterally recycling membrane proteins. We used antibodies to label the basolateral cohort of proteins at the surface of living cells and then followed their trafficking at 37 degreesC by indirect immunofluorescence. The apical PM proteins aminopeptidase N, 5'nucleotidase, and the polymeric IgA receptor were efficiently transcytosed. Delivery to the apical PM was confirmed by microinjection of secondary antibodies into the bile canalicular-like space and by EM studies. Before acquiring their apical steady-state distribution, the trafficked antibodies accumulated in a subapical compartment, which had a unique tubulovesicular appearance by EM. In contrast, antibodies to the receptors for asialoglycoproteins and mannose-6-phosphate or to the lysosomal membrane protein, lgp120, distributed to endosomes or lysosomes, respectively, without accumulating in the subapical area. However, the route taken by the endosomal/lysosomal protein endolyn-78 partially resembled the transcytotic pathway, since anti-endolyn-78 antibodies were found in a subapical compartment before delivery to lysosomes. Our results suggest that in WIF-B cells, transcytotic molecules pass through a subapical compartment that functions as a second sorting site for a subset of basolaterally endocytosed membrane proteins reaching this compartment.
我们研究了极化的肝WIF - B细胞中三类顶端质膜（PM）蛋白从基底外侧到顶端的转胞吞作用，然后将其与基底外侧循环膜蛋白的内吞运输进行比较。我们使用抗体标记活细胞表面的基底外侧蛋白群体，然后通过间接免疫荧光在37℃下追踪它们的运输。顶端PM蛋白氨肽酶N、5'核苷酸酶和聚合IgA受体被有效地转胞吞。通过向胆小管样空间显微注射二抗以及电子显微镜研究证实了向顶端PM的递送。在获得其顶端稳态分布之前，运输的抗体在顶端下隔室中积累，通过电子显微镜观察该隔室具有独特的小管泡状外观。相比之下，抗去唾液酸糖蛋白受体、甘露糖-6-磷酸受体或溶酶体膜蛋白lgp120的抗体分别分布到内体或溶酶体，而不会在顶端下区域积累。然而，内体/溶酶体蛋白endolyn - 78所采取的途径部分类似于转胞吞途径，因为在递送至溶酶体之前，在顶端下隔室中发现了抗endolyn - 78抗体。我们的结果表明，在WIF - B细胞中，转胞吞分子通过一个顶端下隔室，该隔室作为到达该隔室的一部分基底外侧内吞膜蛋白的第二个分选位点。
