Molecular insights into the targeting of proteins to the inner nuclear membrane

我们的细胞由几种成分组成，包括我们在称为细胞质的细胞区室中组装的蛋白质。从那里，这些新蛋白质被靶向细胞内的不同位置以执行其任务。其中一个位置是细胞核，它包含我们的遗传信息，并由双层信封分隔。对于可溶性蛋白质，已经鉴定了多种信号，并且核输入由穿过核膜的小孔和涉及称为输入蛋白和Ran的蛋白质等的复杂机制介导。相比之下，膜蛋白的细胞核通过一个知之甚少的途径到达该隔室暗示一个松散定义的靶向信号。表征这种机制是重要的，因为这些蛋白质的不适当的核靶向会妨碍它们的功能。 病毒是细胞内的寄生虫，其繁殖依赖于细胞机制。这使得它们成为研究我们如何运作的理想工具，因为它们比我们简单得多。其中，单纯疱疹病毒I型（绰号HSV-1）通常与唇疱疹有关，但也可能导致几种更严重的疾病。它编码几种靶向核膜的蛋白质。至于细胞蛋白质，目前尚不清楚它们是如何到达该隔室的，但推测它们使用细胞分选机制。有趣的是，这些蛋白质在整个感染过程中动态地重新定位，这增加了病毒可以精细调节这种运输装置的有趣可能性。这使得它成为一个令人兴奋的模型，以更好地了解蛋白质靶向核膜。其中，HSV-1糖蛋白M（gM）具有潜在的核膜分选基序，并且是在核膜上检测到的几种病毒蛋白中的第一种。后来，随着感染的进行，它移动到其他细胞区室，目前的证据表明细胞和/或其他病毒成分调节其定位。因此，病毒gM蛋白构成了研究核靶向机制并确定其如何调节的极好候选物。 我们的长期研究目标是了解蛋白质靶向核膜，阐明这些蛋白质在核膜中的作用，探索这种分选机制的普遍性，并确定病毒如何调节它。我们未来5年的具体目标是：1）以HSV-1 gM为模型蛋白，阐明INM靶向的分子基础; 2）检查细胞输入蛋白对gM核定位的作用和3）表征哺乳动物E-Syt 1，我们最近鉴定的一种新的gM相互作用伴侣。这项工作具有高度创新性，因为它依赖于最先进的技术，并研究了新的宿主-病原体相互作用，在细胞生物学和病毒学中具有潜在的深远影响。

Our cells are made up of several constituents, including proteins that we assemble inside a cellular compartment called cytoplasm. From there, these new proteins are targeted to various locations within the cell to perform their tasks. One of those locations is the nucleus, which contains our genetic information and is delimited by a double layered envelope. For soluble proteins, a variety of signals have been identified and nuclear import is mediated by small pores traversing the nuclear envelopes and a complex machinery involving, among others, proteins called importins and Ran. In contrast, membrane proteins destined for the nucleus reach that compartment by a poorly understood route implicating a loosely defined targeting signal. Characterizing this machinery is important since improper nuclear targeting of these proteins would hamper their functions. Viruses are intracellular parasites that depend on cellular machineries for their propagation. This makes them ideal tools to study how we function, since much simpler than us. Among them, Herpes simplex virus type I (nicknamed HSV-1) is commonly associated with cold sores but can also cause several more severe conditions. It codes for several proteins that are targeted to nuclear membranes. As for cellular proteins, it is however not clear how they reach that compartment but are presumed to use the cellular sorting machinery. Interestingly, these proteins are dynamically re-localized throughout the infection, raising the intriguing possibility that the virus can finely regulate this transport apparatus. This makes it an exciting model to better understand protein targeting to the nuclear membranes. Among them, the HSV-1 glycoprotein M (gM) possesses a potential nuclear membrane sorting motif and is the first of several viral proteins detected on nuclear membranes. Later on, it moves to other cellular compartments as the infection proceeds and current evidence points to the implication of cellular and/or additional viral components modulating its localization. The viral gM protein thus constitutes an excellent candidate to study the nuclear targeting machinery and define how it is regulated. The long term goals of our research program are to understand the targeting of proteins to the nuclear membranes, clarify the role of these proteins there, probe the universality of this sorting machinery and define how viruses modulate it. Our specific Aims for the next 5 years are to 1) Elucidate the molecular basis of INM targeting, using HSV-1 gM as a model protein; 2) Examine the role of cellular importins for gM nuclear localization and 3) Characterize the mammalian E-Syt1, a novel gM interaction partner we recently identified. This work is highly innovative both because it relies on state-of-the-art technologies and investigates novel host-pathogen interactions with potentially far ranging implications in cell biology and virology.