Roles of the Unfolded Protein Response in Cell Cycle

描述（由申请人提供）：内质网（ER）是细胞中几乎所有分泌蛋白和膜蛋白折叠和成熟的部位。细胞对分泌蛋白生产的需求随着发育或环境的变化而剧烈波动。增加内质网蛋白折叠能力的需求是由未折叠蛋白反应信号通路（UPR）感知的，在所有真核生物中都是保守的。UPR通路的激活导致内质网伴侣和其他蛋白质折叠成分的表达增加，从而增加内质网蛋白的折叠能力。由于内质网不能从头产生，而必须由子细胞遗传，因此我们对确保遗传内质网功能质量的机制产生了兴趣。最近，我们发现：(1)功能应激的内质网不会传递给子细胞，(2)导致酿酒葡萄球菌细胞分裂阻滞。我们证实细胞分裂阻断不是由于内质网应激引起的细胞分裂关键分泌通路成分定位的全局缺陷。此外，细胞分裂阻断并不依赖于典型的UPR通路，即使在ire1缺陷细胞中也会发生。(3)我们还发现了一个令人兴奋的表型：内质网应激破坏了间隔蛋白复合物的动力学，间隔蛋白复合物通常聚集在母/子细胞芽颈，并在细胞分裂过程中介导细胞分离。最近，我们发现SLT2 MAP激酶在协调内质网功能和内质网遗传中起着重要作用。缺乏SLT2的细胞在受到内质网应激时，不再被阻断细胞分裂，具有正常的隔素环动力学，并将应激的内质网传递给它们的子细胞。然而，这样的细胞不能维持超过后续的细胞分裂，这表明对功能性内质网的迫切需要。综合这些结果，我们假设存在一种内质网应激监测机制，确保内质网传递给子细胞的保真度，从而将内质网功能能力的信息直接或间接地传递给间隔蛋白复合体和遗传过程中影响内质网运动的成分。在本提案中，我们提出：(1)确定内质网应激影响内质网遗传过程的哪个阶段；(2)研究内质网应激导致的异常septin复合物行为的分子性质；(3)分析SLT2在细胞分裂和cER遗传中的分子作用；(4)将我们现有的和新的成分映射到构成内质网应激监测机制的途径中。越来越多的人认识到，内质网功能调节的失败导致了包括某些癌症在内的许多人类疾病的病理生理学。因此，了解确保维持和传递功能性内质网的细胞机制对于开发以前未被认识到的治疗干预策略将是非常宝贵的。

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.