Vps4 and the MVB sorting pathway.

描述（由申请人提供）：膜蛋白通过多泡体（MVB）途径降解，在调节细胞表面蛋白中起重要作用。因此，许多细胞功能，如营养摄取、细胞间通讯和免疫应答都依赖于MVBs。MVBs的形成是由一组高度保守的蛋白质复合物ESCRTs（运输所需的内体分选复合物）执行的。escrt执行一种独特的膜出芽事件，其结果是在MVB的管腔中形成囊泡。逆转录病毒，如HIV，在病毒感染期间利用ESCRT机制，通过类似的质膜出芽事件完成病毒颗粒的形成。此外，胞质分裂需要escrt依赖的质膜融合，以形成两个独立的细胞。我们最近的研究表明，ESCRT功能与蛋白质翻译密切相关。一方面，MVB途径降解蛋白质并循环氨基酸以进一步用于蛋白质翻译。另一方面，我们观察到翻译效率通过增加或减少ESCRT调控蛋白Ist1的细胞水平来调节ESCRT功能。细胞中的高氨基酸水平增加了翻译，从而增加了Ist1的细胞浓度，这反过来又降低了ESCRT活性和通过MVB途径的蛋白质降解。相反，饥饿通过降低Ist1水平和增加许多质膜蛋白的内吞作用，通过MVB途径诱导蛋白质降解。此外，我们观察到氨基酸饥饿导致一些ESCRT成分和翻译起始因子重新定位为丝状结构，我们将其称为“饥饿诱导的细胞质结构”（STICS）。我们认为，在饥饿过程中，tics的形成可能促进了从一般翻译到特殊蛋白质翻译的转变。总之，我们的初步实验揭示了一个复杂的调控系统，该系统协调MVB途径中翻译、内吞作用和蛋白质周转活动的必要变化，以确保在饥饿条件下存活。本研究的目标是描述这一调控系统的特征，并确定这一系统的故障如何影响细胞的生长和适应。

DESCRIPTION (provided by applicant): The degradation of membrane proteins via the multivesicular body (MVB) pathway plays an essential role in regulating cell-surface proteins. As a consequence, numerous cellular functions, such as nutrient uptake, cell- cell communication and immune response are dependent on MVBs. The formation of MVBs is executed by a group of highly conserved protein complexes called ESCRTs (Endosomal Sorting Complex Required for Transport). ESCRTs perform a unique membrane budding event, which results in vesicle formation in the lumen of the MVB. Retroviruses, such as HIV, co-opt the ESCRT machinery during viral infection to complete formation of viral particles via a similar membrane budding event at the plasma membrane. Furthermore, cytokinesis requires the ESCRT-dependent fusion of the plasma membrane in order to form two separate cells. Our recent studies indicate that ESCRT function and protein translation are tightly connected. On one hand, the MVB pathway degrades proteins and recycles amino acids for further use in protein translation. On the other hand, we observed that translation efficiency regulates ESCRT function by increasing or decreasing the cellular levels of the ESCRT regulatory protein Ist1. High amino acid levels in the cell increase translation and thus the cellular concentration of Ist1, which in turn decreases ESCRT activity and protein degradation via the MVB pathway. In contrast, starvation induces protein degradation via the MVB pathway by lowering Ist1 levels and by increasing endocytosis of numerous plasma membrane proteins. In addition, we observed that amino acid starvation resulted in the relocalization of some ESCRT components and translation-initiation factors to a filamentous structure, which we termed STICS (STarvation Induced Cytoplasmic Structure). We propose that STICS formation might facilitate the switch from general translation to the specialized protein translation occurring during starvation. Together, our preliminary experiments uncovered a complex regulatory system that coordinates the necessary changes in the activity of translation, endocytosis and protein turnover in the MVB pathway to ensure survival under starvation conditions. The goal of the proposed research is to characterize this regulatory system and to determine how malfunction of this system affects cellular growth and adaptation. PUBLIC HEALTH RELEVANCE: The proposed project studies how cellular metabolism regulates the function of a set of proteins, called ESCRTs, that are involved in protein turnover, cell division and formation of retroviruses. This knowledge has the potential to help us understand on a cellular level how nutrients might affect the pathology of human diseases such as HIV and cancer.