Structure-function relationships of the influenza virus RNA polymerase: influence on virulence, host restriction and innate immune responses

季节性流感病毒每年在人类中造成300万至500万例严重感染，导致全世界25万至50万人死亡。甲型流感病毒还可以通过从野鸟和猪中出现新的病毒株而引起大流行，对社会造成潜在的灾难性后果。目前，H5N1和H7N9“禽流感”亚型被认为是最大的威胁，因为它们在鸟类中流行，可以直接感染人类，导致严重的疾病和死亡。令人担忧的是，这些病毒或其他“禽流感”亚型，通过适应或与人类或猪流感病毒混合，可能获得在人类之间轻松传播的能力，并导致新的大流行。目前的抗病毒方法仅限于需要每年更新的疫苗，不太可能对新出现的新型大流行病毒有用，以及一些病毒耐药性可能发展的抗病毒药物。我们的研究重点是流感病毒的RNA聚合酶。RNA聚合酶是一种关键的多亚单位酶复合物，含有多个功能域，被认为是开发新型抗病毒药物的主要病毒靶点。病毒RNA聚合酶负责复制储存在八段RNA中的流感病毒遗传信息。它直接负责将RNA片段转录成宿主细胞的指令以产生病毒蛋白（信使mRNA，mRNA）以及通过互补RNA中间体复制RNA片段。病毒蛋白与复制的RNA片段一起组装成新的病毒颗粒，从宿主细胞中释放出来。禽流感病毒的RNA聚合酶在哺乳动物细胞中的功能很差，除非它们经历适应性变化。因此，RNA聚合酶可以确定病毒感染的宿主（例如人类、鸟类或猪），还可以确定所引起疾病的严重程度和结果。然而，我们并不了解这些活动的分子基础。我们的研究计划旨在揭示RNA聚合酶如何工作，并利用受感染细胞中的宿主辅助因子。通过了解这些过程，我们将发现抑制聚合酶的新方法，从而防止病毒繁殖，传播和引起疾病。我们还将了解聚合酶的遗传变化如何使流感病毒从鸟类跳到人类并引起疾病。我们的身体通过产生保护我们免受病毒感染的物质来应对病毒感染。然而，感染“禽流感”会导致我们的身体过度反应，产生太多的这些物质，实际上导致更严重的疾病。我们发现，“禽流感”病毒的聚合酶在哺乳动物细胞中不能最佳地工作，并产生异常的短RNA，我们称之为迷你病毒RNA（mvRNA）。这些mvRNA是非常强的抗病毒物质诱导剂，可能是H5N1和H7N9“禽流感”病毒在人类中高毒力的基础。通过阐明这些mvRNA是如何产生的以及它们的作用是什么，我们将能够理解是什么使“禽流感”在人类中如此致命。与工业伙伴合作，这一知识还可以帮助设计改进的流感疫苗，这些疫苗经过微调，可以诱导精确水平的抗病毒物质，并为接种疫苗的人提供最高水平的保护。

Seasonal influenza viruses cause 3 to 5 million cases of severe infections in humans each year, leading to between 250,000 to 500,000 deaths worldwide. Influenza A viruses can also cause pandemics, through the emergence of new viral strains from wild birds and pigs, with potentially catastrophic consequences for society. Currently the H5N1 and H7N9 'bird flu' subtypes are considered the biggest threats as these are prevalent in birds and can infect humans directly, leading to severe disease and death. The concern is that these viruses, or other 'bird flu' subtypes, through adaptation or by mixing with human or swine influenza viruses, could gain the ability to easily transmit between humans and lead to a new pandemic. Current antiviral approaches are limited to vaccines that require annual updating and are unlikely to be useful against an emerging novel pandemic virus, and a few antiviral drugs against which viral resistance can develop. The focus of our research programme is the RNA polymerase of influenza viruses, a key multi-subunit enzyme complex containing multiple functional domains, considered to be a prime viral target for the development of novel antiviral drugs.The viral RNA polymerase is responsible for copying the genetic information of influenza virus that is stored in eight segments of RNA. It is directly responsible for transcribing the RNA segments into instructions to the host cell to produce viral proteins (messenger mRNA, mRNA) as well as replicating the RNA segments through complementary RNA intermediates. The viral proteins together with the replicated RNA segments assemble into new virus particles to be released from the host cell. RNA polymerases of avian influenza viruses function poorly in mammalian cells unless they undergo adaptive changes. Therefore the RNA polymerase can determine which hosts the virus infects (e.g. humans, birds or swine) and can also determine the severity and the outcome of the disease caused. However, we do not understand the molecular basis of these activities.Our research programme aims to uncover how the RNA polymerase works and takes advantage of host co-factors in the infected cell. By understanding these processes we will uncover new ways of inhibiting the polymerase, and thus preventing the virus from multiplying, spreading and causing disease. We will also learn how genetic changes in the polymerase allow an influenza virus to jump from birds to humans and cause disease. Our bodies react to viral infection by producing substances that protect us from the virus. However, infection with 'bird flu' can cause our bodies to overreact by producing far too much of these substances, actually resulting in more severe disease. We found that the polymerases of 'bird flu' viruses do not work optimally in mammalian cells and produce aberrant short RNAs that we call mini viral RNAs (mvRNAs). These mvRNAs are very strong inducers of antiviral substances and could underlie the high virulence of H5N1 and H7N9 'bird flu' viruses in humans. By elucidating how these mvRNAs are made and what their effects are, we will be able to understand what makes 'bird flu' so deadly in humans. Working with industrial partners, this knowledge could also help with the design of improved influenza vaccines that are fine-tuned to induce a precise level of antiviral substances and to give the highest level of protection to those vaccinated.