Phosphatidylserine Receptors in Flavivirus Infection

描述(申请人提供)：磷脂酰丝氨酸(PS)定位于大多数细胞的脂质双层的内叶上。随着细胞的凋亡，PS暴露在其外层小叶上。暴露的PS是由吞噬细胞上的PS受体识别的，后者通过吞噬凋亡的细胞来做出反应。有脂膜的病毒缺乏维持双层不对称性的酶，因此暴露了PS。我们已经证明，许多--但不是全部--包膜的病毒利用PS受体进入细胞。例如，甲型流感病毒的感染效率不受靶细胞上PS受体表达的影响。相反，当细胞表达PS受体时，登革热或西尼罗河病毒对细胞的感染显著增加。这一观察结果有些令人惊讶，因为在它们所谓的成熟状态下，黄病毒的磷脂双层主要被蛋白质类外骨骼所遮挡。这表明当病毒粒子膜暴露较好时，PS受体主要与病毒粒子结合，例如，当病毒粒子处于部分未成熟的“马赛克”状态时，处于融合前的“凹凸不平”状态，或处于短暂的低pH诱导融合状态。这些构象状态中的每一种都对PS受体的结合施加了不同的空间限制，这可能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受体可能被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。在特定的目标1中，我们将确定哪些PS受体对体内黄病毒感染最有贡献，以及这些受体的缺失或阻断是否可以减缓黄病毒的感染。在特定的目标2中，我们将通过回答几个问题来探索黄病毒如何利用PS受体：涉及病毒粒子的哪些构象状态？黄病毒是否主动增加PS掺入病毒粒子的脂膜？PS受体结扎的下游后果是什么？PS受体的利用如何影响从载体到宿主的传播？总而言之，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的良好靶点，并提供有助于开发这些治疗方法的机械性见解。

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.