Valdivia Raphael H, Schekman Randy
Howard Hughes Medical Institute and Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 2003 Sep 2;100(18):10287-92. doi: 10.1073/pnas.1834246100. Epub 2003 Aug 19.
During cell stress, Saccharomyces cerevisiae increases the synthesis of chitin and glucans to strengthen and repair the cell wall. In this study, we show that under conditions of cell stress, the steady-state localization of chitin synthase III (Chs3p) shifts from internal stores (chitosomes) to the plasma membrane (PM). This redistribution occurs rapidly and requires the activators of the cell wall stress response signaling pathway, the G protein Rho1p, and the protein kinase Pkc1p, but not the cell integrity response mitogen-activated protein kinase cascade. Furthermore, expression of activated forms of Rho1p or Pkc1p, in the absence of cell stress, is sufficient to redistribute Chs3p to the PM. In cells deficient for both the clathrin adaptor complex 1 and Chs6p, where Chs3p is transported to the PM by an alternative bypass pathway, cell wall stress did not cause mobilization of Chs3p, suggesting that Rho1p/Pkc1p regulate Chs3p exit from the trans-Golgi network. The mobilization of an intracellular reservoir of Chs3p presents a novel opportunity to investigate the genetic basis of regulated vesicular traffic.
在细胞应激期间，酿酒酵母会增加几丁质和葡聚糖的合成，以强化和修复细胞壁。在本研究中，我们发现，在细胞应激条件下，几丁质合酶III（Chs3p）的稳态定位会从内部储存位点（几丁质体）转移至质膜（PM）。这种重新分布迅速发生，且需要细胞壁应激反应信号通路的激活剂、G蛋白Rho1p和蛋白激酶Pkc1p，但不需要细胞完整性反应丝裂原活化蛋白激酶级联反应。此外，在不存在细胞应激的情况下，Rho1p或Pkc1p的活化形式的表达足以将Chs3p重新分布至质膜。在网格蛋白衔接复合体1和Chs6p均缺失的细胞中，Chs3p通过一条替代旁路途径转运至质膜，细胞壁应激并未导致Chs3p的动员，这表明Rho1p/Pkc1p调节Chs3p从反式高尔基体网络的输出。Chs3p细胞内储存库的动员为研究受调控的囊泡运输的遗传基础提供了一个新机会。
