Ras regulates the polarity of the yeast actin cytoskeleton through the stress response pathway
Ras regulates the polarity of the yeast actin cytoskeleton through the stress response pathway
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DOI：
10.1091/mbc.12.6.1541
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发表时间：
2001-06-01
影响因子：
3.3
通讯作者：
Bretscher, A
中科院分区：
文献类型：
--
作者：
Ho, J;Bretscher, A
在酵母中的极化生长需要极化肌动蛋白细胞骨架和高尔基体后分泌囊泡之间的合作。我们以前曾报道，损失的主要原肌球蛋白亚型，TPM 1 P，结果在细胞敏感的细胞极性扰动。为了鉴定桥接这些过程的组分，我们寻找具有分泌条件缺陷和极性部分缺陷的突变。因此，我们建立了一个基因筛选突变，赋予条件性生长缺陷，显示合成致死性与tpm 1 δ，并同时成为在限制性温度下，分泌缺陷细胞的标志密度。回收的10个互补组中，具有最多独立分离株的组是RAS 2的功能无效等位基因。与此一致，ras 2 Delta和tpm 1 Delta在35 ℃下是合成致死的。我们发现，ras 2三角洲赋予温度敏感的增长和温度依赖的去极化。肌动蛋白细胞骨架。此外，我们发现，在高温下，ras 2三角洲细胞是部分缺陷的内吞作用，并显示出两个关键的极性标记，Myo 2 p和Cdc 42 p的离域。然而，ras 2 δ细胞的条件性密度增强表型不是分泌缺陷。ras 2 Delta细胞的所有表型可以通过酵母RAS 1或RAS 2基因、人Ha-ras的表达或应激反应基因msn 2 Delta msn 4 Delta的双重破坏而被完全抑制。尽管酵母中Ras功能的最佳表征途径涉及cAMP依赖性蛋白激酶A途径的激活，但蛋白激酶A途径的激活并不能完全抑制肌动蛋白极性缺陷，这表明存在从Ras 2 p到Msn 2/4p的额外途径。因此，Ras 2 p调节酵母细胞骨架极性在温和的温度应激条件下，通过应激反应途径。
Polarized growth in yeast requires cooperation between the polarized actin cytoskeleton and delivery of post-Golgi secretory vesicles. We have previously reported that loss of the major tropomyosin isoform, Tpm1p, results in cells sensitive to perturbations in cell polarity. To identify components that bridge these processes, we sought mutations with both a conditional defect in secretion and a partial defect in polarity. Thus, we set up a genetic screen for mutations that conferred a conditional growth defect, showed synthetic lethality with tpm1 Delta, and simultaneously became denser at the restrictive temperature, a hallmark of secretion-defective cells. Of the 10 complementation groups recovered, the group with the largest number of independent isolates was functionally null alleles of RAS2. Consistent with this, ras2 Delta and tpm1 Delta are synthetically lethal at 35 degreesC. We show that ras2 Delta confers temperature-sensitive growth and temperature-dependent depolarization. of the actin cytoskeleton. Furthermore, we show that at elevated temperatures ras2 Delta cells are partially defective in endocytosis and show a delocalization of two key polarity markers, Myo2p and Cdc42p. However, the conditional enhanced density phenotype of ras2 Delta cells is not a defect in secretion. All the phenotypes of ras2 Delta cells can be fully suppressed by expression of yeast RAS1 or RAS2 genes, human Ha-ras, or the double disruption of the stress response genes msn2 Delta msn4 Delta. Although the best characterized pathway of Ras function in yeast involves activation of the cAMP-dependent protein kinase A pathway, activation of the protein kinase A pathway does not fully suppress the actin polarity defects, suggesting that there is an additional pathway from Ras2p to Msn2/4p. Thus, Ras2p regulates cytoskeletal polarity in yeast under conditions of mild temperature stress through the stress response pathway.