Regulation of Extracellular Chaperone Capacity by the Unfolded Protein Response

描述(申请人提供)：细胞外蛋白质聚集与人类神经退行性疾病如阿尔茨海默病、克雅氏病和转甲状腺蛋白淀粉样变性有着千丝万缕的联系。蛋白质聚集在这些疾病中的重要性导致了大量的实验工作，重点是描述调节细胞外蛋白质稳态(或蛋白质稳态)的细胞通路。通过这些努力确定的两个主要决定因素是内质网(ER)质量控制途径的效率和细胞外伴侣蛋白的光谱和活性。内质网的一个主要功能是促进蛋白质的正确折叠，以便运输到分泌途径的下游环境，如细胞外环境，同时防止不稳定的、易错折叠的蛋白质的分泌。通过这种所谓的质量控制机制，内质网通过减少细胞外可用于浓度依赖聚集的易错折叠蛋白的数量来间接影响细胞外蛋白平衡。或者，像Clusterin这样的细胞外伴侣通过结合容易错误折叠的蛋白来直接影响细胞外蛋白平衡，阻止它们的聚集。虽然在正常情况下，内质网质量控制通路和胞外伴侣蛋白的结合活性有效地调节细胞外的蛋白平衡，但环境、遗传或衰老相关的损伤导致内质网质量控制效率的失衡可导致聚集倾向蛋白的分泌增加，从而挑战细胞外伴侣能力。为了应对这一挑战，细胞激活未折叠蛋白反应(UPR)--一种应激反应信号通路，在翻译和转录上重塑内质网质量控制通路。因此，UPR的激活恢复了ER的功能，并减弱了易于聚集的蛋白的分泌。尽管UPR在调节内质网和分泌途径下游环境中的蛋白平衡方面很重要，但UPR的激活与细胞外伴侣能力之间的联系尚未建立。我们假设，UPR的激活，作为对应激的反应，增加了细胞外伴侣的分泌，以防止容易错误折叠的蛋白质在细胞外的异常聚集。在这里，我们确定ERdj3(DNAJB11)是一个以前未知的，受UPR调控的胞外伴侣蛋白。我们建议评估ERdj3在细胞外环境中减弱病理性蛋白聚集的能力，表征导致应激诱导ERdj3分泌的生物途径，并确定在正常生理过程中和应激反应中与ERdj3相互作用的分泌蛋白的亚群。本实验的成功将为UPR在调节细胞外蛋白稳定能力中的直接、功能作用提供原理证明，催化研究以确定其他UPR调节的细胞外蛋白稳定因子，并探索诱导UPR依赖的细胞外伴侣能力增加以治疗聚集相关退行性疾病的可能性。

DESCRIPTION (provided by applicant): Extracellular protein aggregation is inextricably linked to human neurodegenerative diseases such as Alzheimer's disease, Creutzfeldt-Jakob disease and the transthyretin amyloidoses. The importance of protein aggregation in these disorders has led to significant experimental effort focused on characterizing the cellular pathways that regulate extracellular protein homeostasis (or proteostasis). Two primary determinants in defining extracellular proteostasis identified through these efforts are the efficiency of endoplasmic reticulum (ER) quality control pathways and the spectrum and activity of extracellular chaperones. A primary function of the ER is to facilitate the proper folding of proteins for trafficking to downstream environments of the secretory pathway such as the extracellular environment, while preventing the secretion of destabilized, misfolding-prone proteins. Through this so-called quality control mechanism, the ER indirectly influences extracellular proteostasis by reducing the extracellular population of misfolding prone proteins available for concentration- dependent aggregation. Alternatively, extracellular chaperones such as clusterin directly influence extracellular proteostasis by binding misfolding prone proteins, preventing their aggregation. While the combined activity of ER quality control pathways and extracellular chaperones efficiently regulate extracellular proteostasis under normal conditions, imbalances in ER quality control efficiency induced by environmental, genetic or aging- related insults can lead to increased secretion of aggregation-prone proteins that challenge extracellular chaperoning capacity. To confront this challenge, cells activate the unfolded protein response (UPR) - a stress-responsive signaling pathway that translationally and transcriptionally remodels ER quality control pathways. Thus, UPR activation restores ER function and attenuates the secretion of aggregation-prone proteins. Despite the importance of the UPR in regulating proteostasis in the ER and downstream environments of the secretory pathway, no link between UPR activation and extracellular chaperoning capacity has been established. We hypothesize that UPR activation, in response to stress, increases secretion of extracellular chaperones to prevent the aberrant, extracellular aggregation of misfolding prone proteins. Herein, we identify ERdj3 (DNAJB11) as a previously uncharacterized, UPR-regulated extracellular chaperone. We propose to evaluate the capacity for ERdj3 to attenuate pathologic protein aggregation in the extracellular environment, characterize the biological pathways responsible for stress-induced ERdj3 secretion, and identify the subset of secreted proteins that interacts with ERdj3 during normal physiology and in response to stress. Experimental success herein will provide proof-of-principle of a direct, functional role for the UPR in regulating extracellular proteostasis capacit, catalyzing research to both identify other UPR-regulated extracellular proteostasis factors and explore the potential for inducing the UPR-dependent increase in extracellular chaperone capacity to treat aggregation-associated degenerative disorders.