Roles of the Unfolded Protein Response in Cell Cycle

描述(由申请人提供)：内质网(ER)是几乎所有细胞分泌和膜蛋白的折叠和成熟的场所。细胞对分泌蛋白的需求随着发育或环境因素的变化而剧烈波动。在所有真核生物中都保守的未折叠蛋白反应信号通路(UPR)感受到对增加ER蛋白折叠能力的需求。UPR途径的激活导致ER伴侣和其他蛋白质折叠成分的表达增加，从而增加ER蛋白质的折叠能力。由于内质网不能从头产生，而必须由子代细胞继承，因此我们对确保遗传性内质网功能质量的机制感兴趣。最近，我们发现：(1)功能应激性内质网不能传递到子代细胞，(2)导致酿酒酵母胞质分裂受阻。我们证实，胞质分裂受阻不是由于内质网应激导致对细胞分裂至关重要的分泌途径组件定位的整体缺陷。此外，胞质分裂阻断不依赖于典型的UPR途径，即使在IRE1缺陷细胞中也会发生。(3)我们还发现了一种挑衅性的表型：内质网应激扰乱了隔素复合体的动态，该复合体通常聚集在母/子细胞的芽颈，并在细胞质分裂过程中介导细胞分离。最近，我们发现SLT2蛋白在协调ER功能和ER遗传方面发挥着重要作用。缺乏SLT2的细胞在受到内质网应激时，胞质分裂不再受阻，具有正常的隔膜环动力学，并将应激的内质网传递给子细胞。然而，这些细胞不能维持超过随后几轮的细胞分裂，这表明迫切需要有功能的内质网。综合这些结果，我们假设存在一种内质网应激监测机制，该机制确保内质网传递给子细胞的保真度，从而使有关内质网功能能力的信息直接或间接地传递给Septin复合体和在遗传过程中影响内质网运动的组件。在这一建议中，我们建议：(1)确定ER应激影响ER遗传过程的哪个阶段；(2)研究ER应激引起的异常Septin复合体行为的分子本质；(3)分析SLT2在细胞质分裂和CER遗传中的分子作用；(4)将我们现有的以及新的成分定位到构成ER应激监视机制的途径中。人们越来越认识到，未能调节内质网功能能力是导致包括某些癌症在内的许多人类疾病的病理生理学的原因。因此，对确保维持和传递具有功能能力的ER的细胞机制的了解，对于开发以前未被认识的治疗干预策略将是非常宝贵的。 与公共健康相关：内质网(ER)对膜蛋白和分泌蛋白的产生起着至关重要的作用。此外，内质网还执行多种额外的关键功能，包括脂质合成和细胞内钙调节。内质网的功能能力受到环境和发育信号的调节，每次细胞分裂时都必须传递给子细胞，因为没有内质网可以从头合成。ER功能的正确调节和维持失败越来越被认为是人类健康的病理生理学因素，因此，详细了解细胞如何在正常细胞周期中协调ER功能及其适当的遗传将有望为新的人类疗法奠定基础。

DESCRIPTION (provided by applicant): The endoplasmic reticulum (ER) is the site of folding and maturation for virtually all secreted and membrane proteins of the cell. The demand for secreted protein production fluctuates dramatically in cells in response to developmental or environmental cues. Demand for increased ER protein folding capacity is sensed by the Unfolded Protein Response signaling pathway (UPR), conserved in all eukaryotes. Activation of the UPR pathway results in increased expression of ER chaperones and other protein folding components in order to increase ER protein folding capacity. As ER cannot be generated de novo but must be inherited by daughter cells, we became interested in mechanisms that assure the functional quality of inherited ER. Recently, we have found that: (1) functionally stressed ER is not transmitted to daughter cells, and (2) results in block in cytokinesis in S. cerevisiae. We confirmed that blocked cytokinesis is not due to ER-stress induced global defects in the localization of secretory pathway components critical for cell division. Moreover, the cytokinesis block is not dependent on the canonical UPR pathway, occurring even in IRE1-defective cells. (3) We also find a provocative phenotype: ER stress disrupts the dynamics of the septin complex, which normally assembles at the mother/daughter cell bud neck and mediates cell separation during cytokinesis. Most recently, we have identified the SLT2 MAP kinase as playing an important role in coordinating ER function with ER inheritance. Cells lacking SLT2, when subjected to ER stress, are no longer blocked for cytokinesis, have normal septin ring dynamics, and transmit stressed ER to their daughter cells. However, such cells are unable to sustain more than a subsequent rounds of cell division, indicating a critical need for functional ER. Taking these results together, we hypothesize the existence of an ER- stress surveillance mechanism that ensures the fidelity of ER transmitted to daughter cells, such that information on ER functional capacity is communicated, either directly or indirectly, to the septin complex and to components that affect ER movement during inheritance. In this proposal we propose to: (1) determine which stage of the ER inheritance process is effected by ER stress, (2) investigate the molecular nature of the aberrant septin complex behavior caused by ER stress, (3) analyze the molecular role of SLT2 in cytokinesis and cER inheritance, and (4) map our existing as well as new components into the pathway that comprises the ER stress surveillance mechanism. The failure to regulate ER functional capacity is increasingly recognized as contributing to the pathophysiology of a number of human diseases, including certain cancers. Thus, knowledge of the cellular mechanisms assuring the maintenance and transmission of a functionally competent ER will be invaluable towards the development of previously unrecognized strategies for therapeutic intervention. PUBLIC HEALTH RELEVANCE: The endoplasmic reticulum (ER) plays a essential orgaqnelles for production of membrane and secretory proteins. In addition, the ER carries out a variety of additional critical functions including lipid synthesis and intracellular calcium regulation. Functional capacity of the ER is regulated in response to environmental and developmental cues and has to be transmitted to the daughter cell every time cells divide as no ER can be synthesized de novo. Failuare of proper regulation and mainteinance of ER functions is increasingly recognized as contributing element of the pathophysiology of human health and thus, a detail understanding of how cells coordinates ER functional capacity with its proper inheritance during normal cell cycle will hold promise to lay groundwork for novel human therapeutics.