Bannykh Serguei I, Plutner Helen, Matteson Jeanne, Balch William E
Department of Pathology, Yale University Medical School, 310 Cedar Street, New Haven, CT 06520, USA.
Traffic. 2005 Sep;6(9):803-19. doi: 10.1111/j.1600-0854.2005.00319.x.
The organization and sorting of proteins within the Golgi stack to establish and maintain its cis to trans polarization remains an enigma. The function of Golgi compartments involves coat assemblages that facilitate vesicle traffic, Rab-tether-SNAP receptor (SNARE) machineries that dictate membrane identity, as well as matrix components that maintain structure. We have investigated how the Golgi complex achieves compartmentalization in response to a key component of the coat complex I (COPI) coat assembly pathway, the ARF1 GTPase, in relationship to GTPases-regulating endoplasmic reticulum (ER) exit (Sar1) and targeting fusion (Rab1). Following collapse of the Golgi into the ER in response to inhibition of activation of ARF1 by Brefeldin A, we found that Sar1- and Rab1-dependent Golgi reformation took place at multiple peripheral and perinuclear ER exit sites. These rapidly converged into immature Golgi that appeared as onion-like structures composed of multiple concentrically arrayed cisternae of mixed enzyme composition. During clustering to the perinuclear region, Golgi enzymes were sorted to achieve the degree of polarization within the stack found in mature Golgi. Surprisingly, we found that sorting of Golgi enzymes into their subcompartments was insensitive to the dominant negative GTP-restricted ARF1 mutant, a potent inhibitor of COPI coat disassembly and vesicular traffic. We suggest that a COPI-independent, Rab-dependent mechanism is involved in the rapid reorganization of resident enzymes within the Golgi stack following synchronized release from the ER, suggesting an important role for Rab hubs in directing Golgi polarization.
高尔基体堆叠中蛋白质的组织和分类以建立并维持其从顺面到反面的极化状态仍是一个谜。高尔基体各间隔的功能涉及促进囊泡运输的衣被组装、决定膜身份的Rab连接蛋白-SNAP受体（SNARE）机制，以及维持结构的基质成分。我们研究了高尔基体复合体如何响应衣被复合体I（COPI）衣被组装途径的关键成分ARF1 GTP酶实现区室化，以及与调节内质网（ER）出口（Sar1）和靶向融合（Rab1）的GTP酶的关系。在用布雷菲德菌素A抑制ARF1激活导致高尔基体坍塌进入内质网后，我们发现依赖Sar1和Rab1的高尔基体重新形成发生在多个外周和核周内质网出口位点。这些位点迅速汇聚形成不成熟的高尔基体，其呈现为由多个混合酶组成的同心排列的扁平囊组成的洋葱状结构。在向核周区域聚集的过程中，高尔基体酶被分类以达到成熟高尔基体堆叠中发现的极化程度。令人惊讶的是，我们发现将高尔基体酶分类到其亚间隔对显性负性GTP限制的ARF1突变体不敏感，该突变体是COPI衣被解体和囊泡运输的有效抑制剂。我们认为，一种不依赖COPI、依赖Rab的机制参与了高尔基体堆叠中驻留酶从内质网同步释放后的快速重组，这表明Rab中心在指导高尔基体极化中起重要作用。
