McCaffrey M W, Bielli A, Cantalupo G, Mora S, Roberti V, Santillo M, Drummond F, Bucci C
Cell and Molecular Biology Laboratory, Biochemistry Department, UCC, Cork, Ireland.
FEBS Lett. 2001 Apr 20;495(1-2):21-30. doi: 10.1016/s0014-5793(01)02359-6.
The small GTPases Rab4, Rab5 and Rab7 are endosomal proteins which play important roles in the regulation of various stages of endosomal trafficking. Rab4 and Rab5 have both been localized to early endosomes and have been shown to control recycling and endosomal fusion, respectively. Rab7, a marker of the late endosomal compartment, is involved in the regulation of the late endocytic pathway. Here, we compare the role of Rab4, Rab5 and Rab7 in early and late endosomal trafficking in HeLa cells monitoring ligand uptake, recycling and degradation. Expression of the Rab4 dominant negative mutant (Rab4AS22N) leads to a significant reduction in both recycling and degradation while, as expected, Rab7 mutants exclusively affect epidermal growth factor (EGF) and low density lipoprotein degradation. As also expected, expression of the dominant negative Rab5 mutant perturbs internalization kinetics and affects both recycling and degradation. Expression of Rab4WT and dominant positive mutant (Rab4AQ67L) changes dramatically the morphology of the transferrin compartment leading to the formation of membrane tubules. These transferrin positive tubules display swellings (varicosities) some of which are positive for early endosomal antigen-1 and contain EGF. We propose that the Rab4GTPase is important for the function of the early sorting endosomal compartment, affecting trafficking along both recycling and degradative pathways.
小GTP酶Rab4、Rab5和Rab7是内体蛋白，在调节内体运输的各个阶段中发挥重要作用。Rab4和Rab5都定位于早期内体，分别被证明可控制再循环和内体融合。Rab7是晚期内体区室的标志物，参与晚期内吞途径的调节。在此，我们通过监测配体摄取、再循环和降解，比较Rab4、Rab5和Rab7在HeLa细胞早期和晚期内体运输中的作用。Rab4显性负性突变体（Rab4AS22N）的表达导致再循环和降解均显著减少，而正如预期的那样，Rab7突变体仅影响表皮生长因子（EGF）和低密度脂蛋白的降解。同样如预期的那样，显性负性Rab5突变体的表达扰乱内化动力学，并影响再循环和降解。Rab4WT和显性正性突变体（Rab4AQ67L）的表达显著改变转铁蛋白区室的形态，导致形成膜小管。这些转铁蛋白阳性小管显示出肿胀（静脉曲张），其中一些对早期内体抗原-1呈阳性，并含有EGF。我们认为Rab4 GTP酶对早期分拣内体区室的功能很重要，影响再循环和降解途径的运输。
