The Saccharomyces cerevisiae AMPK, Snf1, Negatively Regulates the Hog1 MAPK Pathway in ER Stress Response.
The Saccharomyces cerevisiae AMPK, Snf1, Negatively Regulates the Hog1 MAPK Pathway in ER Stress Response.
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DOI：
10.1371/journal.pgen.1005491
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发表时间：
2015
期刊：
影响因子：
4.5
通讯作者：
Irie K
中科院分区：
文献类型：
--
作者：
Mizuno T;Masuda Y;Irie K
未折叠蛋白在内质网（ER）管腔内的积累引起内质网应激。Snf1是酿酒酵母amp活化蛋白激酶（AMPK）的同源物，在对各种环境胁迫的响应中起着至关重要的作用。然而，Snf1在内质网应激反应中的作用仍然知之甚少。在这项研究中，我们将Snf1描述为内质网应激反应中Hog1 MAPK的负调节因子。snf1突变细胞表现出内质网抗逆性表型。相反，snf1过度激活的细胞对内质网应激敏感。snf1突变增加了激活的Hog1水平，尽管snf1的过度激活干扰了Hog1的激活。Ssk1是在Hog1上游发挥作用的MAPKKK的特异性激活因子，可被内质网应激诱导，其诱导受到依赖于Snf1活性的抑制。此外，我们发现SSK1启动子不仅对snf1调控的SSK1表达很重要，而且对SSK1赋予内质网耐受性的功能也很重要。我们的数据表明，Snf1通过在转录水平上负调控其特异性激活子Ssk1的表达，下调由Hog1介导的内质网应激反应信号。我们还发现snf1突变上调未折叠蛋白反应（UPR）途径，而snf1超激活下调UPR活性。因此，Snf1通过负调控Hog1 MAPK通路和UPR通路，在内质网应激反应中发挥多效性作用。所有的生物总是暴露在各种环境压力下，包括紫外线、热量和化学化合物。因此，每个细胞都有防御机制来维持它们在应激条件下的生存。大量研究表明，一个蛋白激酶家族在对环境应激的适应性反应中起主要作用，其调控的扰动与多种人类病理，如癌症和神经退行性疾病有关。阐明控制其活性的分子机制不仅对了解生物体如何获得耐受性，而且对开发各种疾病的治疗方法仍然很重要。在酿酒酵母中，Hog1应激响应MAP激酶被内质网应激激活，并协调内质网应激的多效性反应。然而，在内质网应激反应中调控Hog1活性的机制仍然知之甚少。在本文中，我们证明了哺乳动物amp活化蛋白激酶（AMPK）的酿酒酵母同源物Snf1在内质网应激反应中负调控Hog1。内质网应激诱导Ssk1的表达，Ssk1是Hog1 MAPK级联的特异性激活因子。Snf1降低Ssk1的表达水平，从而下调从上游组分到Hog1 MAPK级联的信号。内质网应激也增强了Snf1的活性。因此，我们的数据表明Snf1在调控由Hog1介导的内质网应激反应信号中起重要作用。
Accumulation of unfolded proteins in the lumen of the endoplasmic reticulum (ER) causes ER stress. Snf1, the Saccharomyces cerevisiae ortholog of AMP–activated protein kinase (AMPK), plays a crucial role in the response to various environmental stresses. However, the role of Snf1 in ER stress response remains poorly understood. In this study, we characterize Snf1 as a negative regulator of Hog1 MAPK in ER stress response. The snf1 mutant cells showed the ER stress resistant phenotype. In contrast, Snf1-hyperactivated cells were sensitive to ER stress. Activated Hog1 levels were increased by snf1 mutation, although Snf1 hyperactivation interfered with Hog1 activation. Ssk1, a specific activator of MAPKKK functioning upstream of Hog1, was induced by ER stress, and its induction was inhibited in a manner dependent on Snf1 activity. Furthermore, we show that the SSK1 promoter is important not only for Snf1-modulated regulation of Ssk1 expression, but also for Ssk1 function in conferring ER stress tolerance. Our data suggest that Snf1 downregulates ER stress response signal mediated by Hog1 through negatively regulating expression of its specific activator Ssk1 at the transcriptional level. We also find that snf1 mutation upregulates the unfolded protein response (UPR) pathway, whereas Snf1 hyperactivation downregulates the UPR activity. Thus, Snf1 plays pleiotropic roles in ER stress response by negatively regulating the Hog1 MAPK pathway and the UPR pathway. All organisms are always exposed to several environmental stresses, including ultraviolet, heat, and chemical compounds. Therefore, every cell possesses defense mechanisms to maintain their survival under stressed conditions. Numerous studies have shown that a family of protein kinases plays a principal role in adaptive response to environmental stresses and perturbation of their regulation is implicated in a variety of human pathologies, such as cancer and neurodegenerative diseases. Elucidation of molecular mechanisms controlling their activities is still important not only for understanding how the organism acquires stress tolerance, but also for development of therapies for various diseases. In Saccharomyces cerevisiae, the Hog1 stress-responsive MAP kinase is activated by ER stress and coordinates a pleiotropic response to ER stress. However, the mechanisms for regulating Hog1 activity during ER stress response remain poorly understood. In this paper, we demonstrate that a Saccharomyces cerevisiae ortholog of mammalian AMP–activated protein kinase (AMPK), Snf1, negatively regulates Hog1 in ER stress response. ER stress induces expression of Ssk1, a specific activator of the Hog1 MAPK cascade. Snf1 lowers the expression level of Ssk1, thereby downregulating the signaling from upstream components to the Hog1 MAPK cascade. The activity of Snf1 is also enhanced by ER stress. Thus, our data suggest that Snf1 plays an important role in regulation of ER stress response signal mediated by Hog1.