Tatebayashi Kazuo, Yamamoto Katsuyoshi, Tanaka Keiichiro, Tomida Taichiro, Maruoka Takashi, Kasukawa Eri, Saito Haruo
Division of Molecular Cell Signaling, Institute of Medical Sciences, University of Tokyo, Tokyo, Japan.
EMBO J. 2006 Jul 12;25(13):3033-44. doi: 10.1038/sj.emboj.7601192. Epub 2006 Jun 15.
The yeast high osmolarity glycerol (HOG) signaling pathway can be activated by either of the two upstream pathways, termed the SHO1 and SLN1 branches. When stimulated by high osmolarity, the SHO1 branch activates an MAP kinase module composed of the Ste11 MAPKKK, the Pbs2 MAPKK, and the Hog1 MAPK. To investigate how osmostress activates this MAPK module, we isolated both gain-of-function and loss-of-function alleles in four key genes involved in the SHO1 branch, namely SHO1, CDC42, STE50, and STE11. These mutants were characterized using an HOG-dependent reporter gene, 8xCRE-lacZ. We found that Cdc42, in addition to binding and activating the PAK-like kinases Ste20 and Cla4, binds to the Ste11-Ste50 complex to bring activated Ste20/Cla4 to their substrate Ste11. Activated Ste11 and its HOG pathway-specific substrate, Pbs2, are brought together by Sho1; the Ste11-Ste50 complex binds to the cytoplasmic domain of Sho1, to which Pbs2 also binds. Thus, Cdc42, Ste50, and Sho1 act as adaptor proteins that control the flow of the osmostress signal from Ste20/Cla4 to Ste11, then to Pbs2.
酵母高渗甘油（HOG）信号通路可被两条上游通路中的任意一条激活，这两条通路分别称为SHO1分支和SLN1分支。当受到高渗刺激时，SHO1分支会激活一个由Ste11 MAPKKK、Pbs2 MAPKK和Hog1 MAPK组成的MAP激酶模块。为了研究渗透压应激如何激活这个MAPK模块，我们在参与SHO1分支的四个关键基因（即SHO1、CDC42、STE50和STE11）中分离出了功能获得性和功能丧失性等位基因。这些突变体通过一个依赖HOG的报告基因8xCRE - lacZ进行表征。我们发现，Cdc42除了结合并激活PAK样激酶Ste20和Cla4外，还与Ste11 - Ste50复合物结合，从而将激活的Ste20/Cla4带到其底物Ste11处。激活的Ste11及其HOG通路特异性底物Pbs2通过Sho1聚集在一起；Ste11 - Ste50复合物与Sho1的胞质结构域结合，Pbs2也结合在该结构域上。因此，Cdc42、Ste50和Sho1作为衔接蛋白，控制着渗透压应激信号从Ste20/Cla4到Ste11，再到Pbs2的传递。
