Department of Biochemistry 2, Faculty of Medicine, University of Yamanashi, Chuo, Yamanashi 409-3898, Japan.
J Biochem. 2009 Nov;146(5):705-12. doi: 10.1093/jb/mvp116. Epub 2009 Jul 24.
The actin cytoskeleton of the yeast Saccharomyces cerevisiae can be altered rapidly in response to external cues. We reported previously that S. cerevisiae responds to low-pH stress by transiently depolarizing its actin cytoskeleton, and that this step requires a mitogen-activated protein kinase, high osmolarity glycerol 1 (Hog1p). This study further investigated the components involved in this actin reorganization at pH 3.0. Gene deletions on the Sln1p branch of the HOG pathway completely blocked actin depolarization, suggesting that Hog1p activation depends mainly on the osmosensor Sln1p. The protein-synthesis inhibitor cycloheximide did not influence the time course of actin depolarization, suggesting that the depolarization is a direct effect of the HOG pathway. Deletion of the scaffolding protein, Spa2p, or the Spa2p-interacting protein Pea2p, markedly inhibited the depolarization, and further deletion of the formin protein, Bni1p, notably delayed actin repolarization. Our results suggest the involvement of polarisome proteins, such as Spa2p, Pea2p and Bni1p, but not Bud6p, in Hog1p-dependent reorganization of the yeast actin cytoskeleton at low pH.
酵母酿酒酵母的肌动蛋白细胞骨架可以对外界刺激迅速改变。我们之前报道过，酿酒酵母通过短暂去极化其肌动蛋白细胞骨架来响应低 pH 应激，而这一步骤需要一个有丝分裂原激活的蛋白激酶，高渗透压甘油 1（Hog1p）。本研究进一步研究了在 pH 3.0 时参与这种肌动蛋白重排的成分。HOG 途径中 Sln1p 分支上的基因缺失完全阻断了肌动蛋白去极化，表明 Hog1p 的激活主要依赖于渗透压感受器 Sln1p。蛋白质合成抑制剂环己亚胺不影响肌动蛋白去极化的时间进程，表明去极化是 HOG 途径的直接作用。支架蛋白 Spa2p 或与 Spa2p 相互作用的蛋白 Pea2p 的缺失显著抑制了去极化，而formin 蛋白 Bni1p 的进一步缺失显著延迟了肌动蛋白再极化。我们的结果表明，在低 pH 下，Hog1p 依赖的酵母肌动蛋白细胞骨架重排涉及极体蛋白，如 Spa2p、Pea2p 和 Bni1p，但不涉及 Bud6p。
