PDF(Pubmed)
Abstract：
Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular behaviors, including the response to stress and cell differentiation, and are highly conserved across eukaryotes. MAPK pathways can be activated by the interaction between the small GTPase Cdc42p and the p21-activated kinase (Ste20p in yeast). By studying MAPK pathway regulation in yeast, we recently found that the active conformation of Cdc42p is regulated by turnover, which impacts the activity of the pathway that regulates filamentous growth (fMAPK). Here, we show that Ste20p is regulated in a similar manner and is turned over by the 26S proteasome. This turnover did not occur when Ste20p was bound to Cdc42p, which presumably stabilized the protein to sustain MAPK pathway signaling. Although Ste20p is a major component of the fMAPK pathway, genetic approaches here identified a Ste20p-independent branch of signaling. Ste20p-independent signaling partially required the fMAPK pathway scaffold and Cdc42p-interacting protein, Bem4p, while Ste20p-dependent signaling required the 14-3-3 proteins, Bmh1p and Bmh2p. Interestingly, Ste20p-independent signaling was inhibited by one of the GTPase-activating proteins for Cdc42p, Rga1p, which unexpectedly dampened basal but not active fMAPK pathway activity. These new regulatory features of the Rho GTPase and p21-activated kinase module may extend to related pathways in other systems.
摘要：
丝裂原活化蛋白激酶(MAPK)通路调节多种细胞行为,包括对压力和细胞分化的反应，并且在真核生物中高度保守。MAPK通路可以通过小GTP酶Cdc42p和p21激活的激酶（PAK，在酵母中步进20p）。通过研究酵母中MAPK通路的调控,我们最近发现Cdc42p的活性构象受周转调节，这会影响调节丝状生长（fMAPK）的途径的活性。这里,我们显示Ste20p以类似的方式调节，并由26S蛋白酶体翻转。当Ste20p绑定到Cdc42p时，这种周转没有发生，这可能稳定了蛋白质以维持MAPK途径信号传导。尽管Ste20p是fMAPK途径的主要组成部分，这里的遗传方法确定了一个不依赖Ste20p的信号分支。不依赖Ste20p的信号部分需要fMAPK通路支架和Cdc42p相互作用蛋白，Bem4p,而Ste20p依赖性信号需要14-3-3蛋白，Bmh1p和Bmh2p。有趣的是,Cdc42p的GTP酶激活蛋白之一抑制了不依赖Ste20p的信号传导，Rga1p,这出乎意料地抑制了基础但不活跃的fMAPK途径活性。RhoGTP酶和PAK模块的这些新的调节特征可以扩展到其他系统中的相关途径。
