How flaviviruses hijack a host transmembrane protein chaperone to promote viral infection

登革热病毒（DENV）感染是全球最常见的虫媒病毒性疾病，每年有多达4亿人感染，2.5万人死亡。与之相关的黄病毒寨卡病毒（ZIKV）也在热带和亚热带地区迅速传播，DENV和ZIKV感染的暴发现已到达美国大陆。目前还没有针对这两种病毒的有效抗病毒药物，美国还没有批准使用DENV疫苗，也没有寨卡病毒疫苗。我们的长期目标是全面识别和表征黄病毒感染所需的细胞途径，因为这些途径可能代表抗病毒治疗的新靶点。我们和其他人已经确定宿主内质网膜蛋白复合体（EMC）是多种黄病毒（包括DENV和ZIKV）感染所必需的。EMC似乎作为分子伴侣起作用，促进内质网中多通道膜蛋白的生物发生。然而，EMC如何支持黄病毒感染尚不清楚。引人注目的是，我们发表的研究结果表明，在感染过程中，通过在早期翻译后步骤促进黄病毒NS4A和NS4B的生物发生，EMC是黄病毒复制所必需的。这两种蛋白都是病毒复制所必需的非结构性多通跨膜蛋白。本提案的目的是定义EMC如何支持DENV和ZIKV复制。基于强有力的初步数据，我们的中心假设是，EMC作为分子伴侣，对选择的黄病毒编码的多通跨膜蛋白的适当生物发生起作用。该提案利用了一位在黄病毒-宿主生物学方面具有丰富经验的研究者（Tai）和另一位在病毒感染期间劫持er质量控制机制方面的研究者（Tsai）的互补优势。该项目的具体目标是：(1)定义和验证EMC依赖性的病毒决定因素；(2)确定EMC在黄病毒复制中的具体作用；(3)对绕过EMC依赖性的DENV和ZIKV突变体进行表征。该项目的成功完成将阐明EMC支持黄病毒感染的机制，从而深入了解这些医学上重要的病毒共有的一个新漏洞。它还将增加我们对需要EMC的其他病毒的了解。

Dengue virus (DENV) infection is the most common arboviral disease globally, with up to 400 million infections and 25,000 deaths annually. The related flavivirus Zika virus (ZIKV) has also spread rapidly across the tropics and subtropics, and outbreaks of both DENV and ZIKV infection have now reached the continental United States. There are currently no effective antiviral agents against either virus, no DENV vaccine approved for use in the United States, and no ZIKV vaccine. Our long-term goal is to comprehensively identify and characterize the cellular pathways required for flavivirus infection, as these may represent novel targets for antiviral treatment. We and others have identified the host Endoplasmic Reticulum Membrane Protein Complex (EMC) as required for infection by multiple flaviviruses, including DENV and ZIKV. The EMC appears to function as a molecular chaperone, promoting the biogenesis of multipass membrane proteins in the endoplasmic reticulum. However, how the EMC supports flavivirus infection is unknown. Strikingly, our published findings reveal that during infection, the EMC is required by flavivirus replication by promoting the biogenesis of flavivirus NS4A and NS4B at an early post-translational step. Both proteins are non-structural multipass transmembrane proteins essential for viral replication. The objective of this proposal is to define how the EMC supports DENV and ZIKV replication. Our central hypothesis, based on strong preliminary data, is that the EMC functions as a molecular chaperone for the proper biogenesis of select flavivirus-encoded multipass transmembrane proteins. This proposal leverages the complementary strengths of an investigator with extensive experience in flavivirus-host biology (Tai), and another in ER-quality control mechanisms hijacked during viral infection (Tsai). The specific aims of the project are to (1) Define and validate the viral determinants of EMC dependence; (2) Determine the specific role of the EMC in flaviviral replication; and (3) Characterize DENV and ZIKV mutants that bypass EMC dependency. Successful completion of this project will illuminate the mechanism by which the EMC supports flavivirus infection, thereby providing insights into a novel vulnerability shared by these medically important viruses. It will also increase our understanding of other viruses that require the EMC.