Phosphatidylserine Receptors in Flavivirus Infection

描述（由申请人提供）：磷脂酰丝氨酸（PS）定位于大多数细胞脂质双分子层的内小叶。当细胞凋亡时，PS暴露在其外小叶上。暴露的PS被吞噬细胞上的PS受体识别，并通过吞噬凋亡细胞作出反应。具有脂质包膜的病毒缺乏维持双层不对称的酶，因此暴露了PS。我们已经证明，许多（但不是全部）包膜病毒利用PS受体进入细胞。例如，甲型流感病毒感染的效率不受靶细胞上PS受体表达的影响。相反，当细胞表达PS受体时，登革热病毒或西尼罗河病毒感染细胞的能力显著增强。这一观察结果有些令人惊讶，因为在所谓的成熟状态下，黄病毒的磷脂双分子层在很大程度上被蛋白质外骨骼所封闭。这表明，PS受体主要在病毒粒子膜暴露较好的情况下与病毒粒子结合，例如，当病毒粒子处于部分未成熟的“马赛克”状态，在融合前的“颠簸”状态或在短暂的低ph诱导的融合状态时。这些构象状态中的每一种都对PS受体结合施加了不同的空间限制，这也许解释了为什么黄病毒只利用PS受体的一个子集，而其他病毒的选择性较低。这种选择性以及一些PS受体促进黄病毒感染的效力表明，少量PS受体可能有效地靶向治疗登革热或西尼罗河病毒感染。因此，我们的建议有两个具体目标。在特异性目的1中，我们将确定哪些PS受体在体内最有助于黄病毒感染，以及这些受体的缺失或阻断是否可以减缓黄病毒感染。在特异性目标2中，我们将通过回答几个问题来探讨黄病毒如何利用PS受体：病毒粒子的哪些构象状态参与？黄病毒是否主动增加PS与病毒粒子脂质膜的结合？PS受体连接的下游后果是什么？PS受体的利用如何影响从媒介到宿主的传播？总的来说，这些研究将确定哪些PS受体可能是控制登革热和西尼罗河病毒感染的治疗方法的良好靶点，并为开发这些治疗方法提供有用的机制见解。

DESCRIPTION (provided by applicant): Phosphatidylserine (PS) is localized on the inner leaflet of the lipid bilayer of most cells. As a cell apoptoses, PS becomes exposed on its outer leaflet. Exposed PS is recognized by PS receptors on phagocytes, which respond by engulfing the apoptotic cell. Viruses with lipid envelopes lack enzymes that maintain bilayer asymmetry and thus have exposed PS. We have shown that many - but not all - enveloped viruses exploit PS receptors to enter cells. For example, the efficiency of influenza A virus infection is not affected by PS receptors expression on the target cells. In contrast, infection of cells by dengue or West Nile viruses is markedly enhanced when cells express PS receptors. This observation is somewhat surprising, because, in their so-called mature states, the phospholipid bilayer of flaviviruses is largely occluded by a proteinaceous exoskeleton. This suggests that PS receptors primarily engage viral particles when the virion membrane is better exposed, for example when the virion particle is in its partially immature "mosaic" state, in its pre-fusogenic "bumpy" state or in a transient low-pH induced fusogenic state. Each of these conformational states imposes distinct steric restraints on PS receptor association, perhaps explaining why flaviviruses only utilize a subset of PS receptors, whereas other viruses are less selective. This selectivity, and the potency with which some PS receptors promote flavivirus infection, suggest that a small number of PS receptors might be effectively targeted to treat dengue or West Nile virus infections. Accordingly, our proposal has two specific aims. In Specific Aim 1 we will determine which PS receptors most contribute to flavivirus infections in vivo, and whether the absence or blockade of these receptors can slow a flavivirus infection. In Specific Aim 2 we will explore how flaviviruses utilize PS receptors by answering several questions: Which conformational states of the virion are involved? Do flaviviruses actively increase PS incorporation into the lipid membrane of the virion? What are the downstream consequences of PS receptor ligation? How does PS receptor utilization impact transmission from vector to host? Collectively, these studies will determine which PS receptors might be good targets for therapies that control dengue and West Nile virus infections, and provide mechanistic insight useful for developing these therapies.