Wan J, Taub M E, Shah D, Shen W C
Department of Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles 90033.
J Biol Chem. 1992 Jul 5;267(19):13446-50.
The effects of brefeldin A (BFA) on transferrin (Tf) transcellular transport, Tf receptor (TfR) distribution, and TfR-mediated endocytosis in filter-grown Madin-Darby canine kidney (MDCK) cells were studied. BFA (1.6 micrograms/ml) markedly enhanced the transcytosis of 125I-labeled Tf (125I-Tf) in both apical-to-basal and basal-to-apical directions; yet, BFA did not enhance the transcytosis of either native horseradish peroxidase (HRP) or membrane-bound HRP-poly(L-lysine) conjugates. Furthermore, this enhanced transcytosis of 125I-Tf was abolished either by competition with excess unlabeled Tf or by incubation at temperatures less than or equal to 25 degrees C. In addition, BFA treatment to MDCK cells: (a) increased 125I-Tf specific binding to the apical membrane and decreased 125I-Tf specific binding to the basal membrane; (b) decreased TfR recycling at the basolateral membrane; (c) altered the apical/basolateral distribution of TfRs in favor of the apical side; and (d) markedly increased 59Fe extraction, but not transcytosis, from apically endocytosed 59Fe-loaded Tf. These effects are consistent with a model in which BFA alters the traffic pattern of internalized Tf by decreasing basolateral TfR recycling, while diverting the nonrecycled fraction to the apical side of the cell. Our results indicate that, unlike the reported inhibition of polymeric IgA transcytosis (Hunziker, W., Whitney, J. A., and Mellman, I. (1991) Cell 67, 617-627), BFA can enhance the transcytosis of Tf in MDCK cells. Thus, by altering the intracellular traffic of ligand-receptor complexes, BFA can elicit either a decrease or an increase in transcytosis depending on the nature of the intracellular receptor processing.
研究了布雷菲德菌素A（BFA）对滤膜生长的犬肾上皮细胞（MDCK）中转铁蛋白（Tf）跨细胞转运、Tf受体（TfR）分布以及TfR介导的内吞作用的影响。BFA（1.6微克/毫升）显著增强了125I标记的Tf（125I-Tf）在从顶侧向基底以及从基底向顶侧两个方向的转胞吞作用；然而，BFA并未增强天然辣根过氧化物酶（HRP）或膜结合的HRP-聚（L-赖氨酸）缀合物的转胞吞作用。此外，125I-Tf这种增强的转胞吞作用可通过与过量未标记的Tf竞争或在小于或等于25℃的温度下孵育而被消除。另外，用BFA处理MDCK细胞：（a）增加了125I-Tf与顶膜的特异性结合，减少了125I-Tf与基底膜的特异性结合；（b）减少了基底外侧膜上TfR的再循环；（c）改变了TfR在顶侧/基底外侧的分布，使其更倾向于顶侧；（d）显著增加了从顶侧内吞的59Fe负载的Tf中59Fe的摄取，但未增加其转胞吞作用。这些效应与一个模型相符，即BFA通过减少基底外侧TfR的再循环来改变内化Tf的运输模式，同时将未再循环的部分转向细胞的顶侧。我们的结果表明，与报道的对聚合IgA转胞吞作用的抑制（洪齐克，W.，惠特尼，J. A.，和梅尔曼，I.（1991年）《细胞》67卷，617 - 627页）不同，BFA可增强MDCK细胞中Tf的转胞吞作用。因此，通过改变配体-受体复合物的细胞内运输，BFA可根据细胞内受体加工的性质引发转胞吞作用的减少或增加。
