The role of phosphorylation of a COPII coat protein, Sec31 in molecular export

描述（由申请人提供）：随着年龄的增长，内质网新生蛋白的输出减少可能通过两种机制缩短细胞寿命：1)内质网应激反应的启动，导致细胞凋亡的增强，以及2)细胞生长和分化所需的蛋白质（如细胞因子及其受体）的分泌和运输。衰老过程的一个标志是已被细胞降解系统清除的非活性蛋白质的积累。这个池子是由错误折叠的蛋白质和那些失去活性并达到生物半衰期的蛋白质组成的。三种一般机制可以解释这些蛋白质的积累：1)增加错误折叠，2)增强蛋白质变性和3)降解途径中的功能下降。我们认为，衰老过程中内质网蛋白质输出功能障碍导致内质网蛋白质积累、蛋白质错误折叠、内质网应激反应刺激和凋亡细胞死亡增加。该提案将研究COPII外壳蛋白在非活性细胞蛋白的年龄依赖性积累中的作用。内质网的分子输出被认为是由COPII囊泡介导的。研究表明，酵母中必不可少的COPII外壳成分Sec31被磷酸化，其磷酸化与COPII囊泡出芽有关。然而，分子机制，包括磷酸化位点和磷酸化的激酶，是未知的。假设COPII囊泡外壳组分的磷酸化-去磷酸化循环可能调节内质网的分子输出，我们最近发现了哺乳动物Sec31的磷酸化。在本提案中，我们将确定：1)哺乳动物Sec31的磷酸化-去磷酸化循环是否调节内质膜的蛋白质输出，2)klotho蛋白以及其他货物的运输是否受到Sec31去磷酸化的影响，以及3)Sec31的磷酸化是否存在与年龄相关的变化，这可能与早期分泌途径的潜在年龄相关损伤有关。这项研究的成功将导致对衰老分子机制的进一步了解，这可能有助于治疗与年龄有关的疾病。

DESCRIPTION (provided by applicant): A decrease in the export of nascent proteins from the endoplasmic reticulum with aging may shorten cell life by two mechanisms: 1) initiation of ER stress responses, leading to enhanced apoptosis, and 2) secretion and trafficking of proteins, such as cytokines and their receptors that are required for cell growth and differentiation. A hallmark of the aging processing is the accumulation of inactive proteins that have cleared by cellular degradation systems. This pool is formed by both proteins that have been misfolded and those that have been inactivated and reached the end of their biologic half-lives. Three general mechanisms could account for the accumulation of such proteins: 1) increased misfolding, 2) enhanced protein denaturation and 3) decreased function in degradation pathways. We propose that dysfunction of protein export from the endoplasmic reticulum during aging leads to protein accumulation in the ER, protein misfolding, stimulation of ER stress responses, and enhanced apoptotic cell death. This proposal will examine the role of COPII coat proteins in the age-dependent accumulation of inactive cellular proteins. Molecular export from the ER is thought to be mediated by COPII vesicles. It has been shown that an essential COPII coat component, Sec31 in yeast, is phosphorylated and its phosphorylation has been implicated in COPII vesicle budding. However, the molecular mechanisms, including the phosphorylation sites and the kinases for this phosphorylation, are unknown. Hypothesizing that the phosphorylation-dephosphorylation cycle of the coat components of COPII vesicles may regulate molecular export from the ER, we recently discovered the phosphorylation of mammalian Sec31. In this proposal, we will determine: 1) whether the cycle of phosphorylation-dephosphorylation of mammalian Sec31 regulates protein export from the ER, 2) whether trafficking of the klotho protein, as well as other cargoes, are affected by dephosphorylation of Sec31, and 3) whether there are age-associated changes in the phosphorylation of Sec31, which may correlate with potential age-related impairment of the early secretory pathway. The success of this study will lead to a further understanding of the molecular mechanisms of aging, which may contribute to cures for age-related diseases.