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室中组装的蛋白质。从那里，这些新的蛋白质被定位到细胞内的不同位置来执行它们的任务。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，已经确定了各种信号，核导入是通过穿过核膜的小孔和复杂的机制来介导的，其中涉及称为重要蛋白和RAN的蛋白质。相反，去往细胞核的膜蛋白通过一条鲜为人知的途径到达那个隔室，这意味着一个定义松散的靶向信号。确定这种机制的特征是很重要的，因为不适当的核靶向这些蛋白质会阻碍它们的功能。 病毒是细胞内的寄生虫，依赖细胞机制进行传播。这使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，I型单纯疱疹病毒(绰号HSV-1)通常与唇疱疹有关，但也可导致几种更严重的情况。它编码几种以核膜为靶点的蛋白质。至于细胞蛋白质，目前还不清楚它们是如何到达那个隔间的，但人们推测它们使用的是细胞分选机器。有趣的是，这些蛋白质在整个感染过程中被动态地重新定位，这增加了病毒能够精细地调节这种运输装置的有趣的可能性。这使得它成为一个令人兴奋的模型，以更好地理解针对核膜的蛋白质。其中，HSV-1糖蛋白M(GM)具有潜在的核膜分离基序，是第一个在核膜上检测到的病毒蛋白。后来，随着感染的进行，它转移到其他细胞间隔，目前的证据表明，细胞和/或其他病毒成分调节其定位。因此，病毒转基因蛋白构成了研究核靶向机制和确定其调控方式的极佳候选者。 我们研究计划的长期目标是了解蛋白质对核膜的靶向，阐明这些蛋白质在核膜上的作用，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)研究细胞重要蛋白在GM核定位中的作用；3)表征哺乳动物的E-Syt1，我们最近发现的一个新的GM相互作用伙伴。这项工作具有很高的创新性，因为它依赖于最先进的技术，并研究了新的宿主与病原体的相互作用，这在细胞生物学和病毒学中具有潜在的广泛意义。

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.