H-ras but not K-ras traffics to the plasma membrane through the exocytic pathway
H-ras but not K-ras traffics to the plasma membrane through the exocytic pathway
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DOI：
10.1128/mcb.20.7.2475-2487.2000
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发表时间：
2000-04-01
影响因子：
5.3
通讯作者：
Hancock, JF
中科院分区：
文献类型：
--
作者：
Apolloni, A;Prior, IA;Hancock, JF
Ras蛋白必须定位到质膜内表面才能具有生物活性。影响Ras质膜靶向的基序由一个C末端的CAAX基序以及第二个信号组成，第二个信号包括相邻半胱氨酸残基的棕榈酰化或多碱性结构域的存在。在这项研究中，我们研究了在内质网（ER）中CAAX基序加工完成后Ras蛋白如何到达细胞表面。我们发现，棕榈酰化的CAAX蛋白除了定位在质膜上，还存在于整个胞吐途径中，并且当细胞在15℃下孵育时会在高尔基体区域积聚。相比之下，多碱性CAAX蛋白仅在细胞表面被发现，而不在胞吐途径中。缺乏质膜靶向第二个信号的CAAX蛋白积聚在内质网和高尔基体中。布雷菲德菌素A（BFA）显著抑制新合成的棕榈酰化CAAX蛋白在质膜的积聚，但不抑制它们的棕榈酰化。BFA对多碱性CAAX蛋白的运输没有影响。我们得出结论，H - ras和K - ras通过不同的途径运输到细胞表面，并且多碱性结构域是一个分选信号，它使K - Ras偏离靠近高尔基体的经典胞吐途径。缺乏多碱性结构域的法尼基化Ras蛋白能够到达高尔基体，但需要棕榈酰化才能进一步运输到细胞表面。这些数据还表明，一种Ras棕榈酰转移酶存在于胞吐途径的早期区室中。
Ras proteins must be localized to the inner surface of the plasma membrane to be biologically active. The motifs that effect Ras plasma membrane targeting consist of a C-terminal CAAX motif plus a second signal comprising palmitoylation of adjacent cysteine residues or the presence of a polybasic domain. In this study, we examined how Ras proteins access the cell surface after processing of the CAAX motif is completed in the endoplasmic reticulum (ER). We show that palmitoylated CAAX proteins, in addition to being localized at the plasma membrane, are found throughout the exocytic pathway and accumulate in the Golgi region when cells are incubated at 15 degrees C. In contrast, polybasic CAAX proteins are found only at the cell surface and not in the exocytic pathway. CAAX proteins which lack a second signal for plasma membrane targeting accumulate in the ER and Golgi. Brefeldin A (BFA) significantly inhibits the plasma membrane accumulation of newly synthesized, palmitoylated CAAX proteins without inhibiting their palmitoylation. BFA has no effect on the trafficking of polybasic CAAX proteins. We conclude that H-ras and K-ras traffic to the cell surface through different routes and that the polybasic domain is a sorting signal diverting K-Ras out of the classical exocytic pathway proximal to the Golgi. Farnesylated Ras proteins that lack a polybasic domain reach the Golgi but require palmitoylation in order to traffic further to the cell surface. These data also indicate that a Ras palmitoyltransferase is present in an early compartment of the exocytic pathway.