Zacchi P, Stenmark H, Parton R G, Orioli D, Lim F, Giner A, Mellman I, Zerial M, Murphy C
European Molecular Biology Laboratory, Postfach 10.2209, D-69012 Heidelberg, Germany.
J Cell Biol. 1998 Mar 9;140(5):1039-53. doi: 10.1083/jcb.140.5.1039.
A key feature of polarized epithelial cells is the ability to maintain the specific biochemical composition of the apical and basolateral plasma membrane domains while selectively allowing transport of proteins and lipids from one pole to the opposite by transcytosis. The small GTPase, rab17, a member of the rab family of regulators of intracellular transport, is specifically induced during cell polarization in the developing kidney. We here examined its intracellular distribution and function in both nonpolarized and polarized cells. By confocal immunofluorescence microscopy, rab17 colocalized with internalized transferrin in the perinuclear recycling endosome of BHK-21 cells. In polarized Eph4 cells, rab17 associated with the apical recycling endosome that has been implicated in recycling and transcytosis. The localization of rab17, therefore, strengthens the proposed homology between this compartment and the recycling endosome of nonpolarized cells. Basolateral to apical transport of two membrane-bound markers, the transferrin receptor and the FcLR 5-27 chimeric receptor, was specifically increased in Eph4 cells expressing rab17 mutants defective in either GTP binding or hydrolysis. Furthermore, the mutant proteins stimulated apical recycling of FcLR 5-27. These results support a role for rab17 in regulating traffic through the apical recycling endosome, suggesting a function in polarized sorting in epithelial cells.
极化上皮细胞的一个关键特征是能够维持顶端和基底外侧质膜结构域的特定生化组成，同时通过转胞吞作用选择性地允许蛋白质和脂质从一极运输到另一极。小GTP酶rab17是细胞内运输调节因子rab家族的成员，在发育中的肾脏细胞极化过程中被特异性诱导。我们在此研究了它在非极化和极化细胞中的细胞内分布及功能。通过共聚焦免疫荧光显微镜观察，rab17与内化的转铁蛋白在BHK - 21细胞的核周回收内体中共定位。在极化的Eph4细胞中，rab17与顶端回收内体相关，该内体与回收和转胞吞作用有关。因此，rab17的定位加强了该区室与非极化细胞回收内体之间推测的同源性。在表达GTP结合或水解缺陷的rab17突变体的Eph4细胞中，两种膜结合标记物转铁蛋白受体和FcLR 5 - 27嵌合受体从基底外侧到顶端的运输特异性增加。此外，突变蛋白刺激了FcLR 5 - 27的顶端回收。这些结果支持rab17在调节通过顶端回收内体的运输中起作用，提示其在上皮细胞极化分选中有功能。
