Restriction of DNA viruses by TRIM5a and ZAP / TRIM25 / KHNYN: mechanisms of restriction and viral evasion

我们身体的细胞含有介导防御病毒感染的蛋白质。这种蛋白质被称为限制因子，因为它们的作用限制病毒复制。限制因子的例子是称为TRIM 5 α、ZAP、TRIM 25和KHNYN的蛋白质。然而，人们认为这些限制因子的作用主要针对具有RNA而不是DNA基因组的病毒。例如，TRIM 5 α作为逆转录病毒如HIV的限制因子是众所周知的，而ZAP、TRIM 25和KHNYN对具有富含核糖核苷酸（RNA结构单元）C和G的基因组的RNA病毒具有活性。然而，我们已经发现这些限制因子对牛痘病毒也有活性，牛痘病毒是一种大的DNA病毒，被用作根除天花的疫苗。此外，我们发现这4种细胞蛋白在牛痘病毒感染期间全部降解，从而使病毒能够逃避它们的抗病毒作用。最后，与HIV一样，另一种称为亲环素A的细胞蛋白质被整合到牛痘病毒颗粒中，它有助于保护免受TRIM 5 α的抗病毒作用。亲环素A的这种保护作用可以被药物环孢素A所抑制，环孢素A可以保护TRIM 5 α的抗病毒活性。本项目将研究这些限制因子如何对抗牛痘病毒，以及牛痘病毒如何采取对策来减少它们的影响。该项目有两个部分。首先，我们将确定这些宿主蛋白如何限制牛痘病毒复制，以及在病毒感染过程中的哪个阶段它们会这样做。该项目还将调查这些限制因素是否影响其他大型DNA病毒的复制，如单纯疱疹病毒，唇疱疹的原因，以及人类巨细胞病毒，妊娠期间和免疫抑制期间的疾病原因，如移植手术后。在第二部分，平行运行，该项目将调查牛痘病毒进化的对策，以逃避或中和这些限制因子的抗病毒活性。例如，牛痘病毒如何使亲环蛋白A包装到病毒颗粒中以保护免受TRIM 5 α，以及牛痘病毒如何诱导这些宿主限制因子的降解。这需要哪些牛痘病毒蛋白，它们与哪些细胞蛋白相互作用以介导这种靶向破坏？总的来说，这个项目将提高我们对病毒和它们感染的细胞之间相互作用的理解，最终可能导致更安全的减毒疫苗的开发和/或治疗病毒感染的药物的开发。

The cells of our body contain proteins that mediate defense against virus infection. Such proteins are called restriction factors, because their actions restrict virus replication. Examples of restriction factors are proteins called TRIM5alpha, ZAP, TRIM25 and KHNYN. Hitherto, it was thought that the action of these restriction factors was directed against mostly viruses that have RNA, rather than DNA, genomes. For instance, TRIM5alpha is well known as a restriction factor for retroviruses, such as HIV, and ZAP, TRIM25 and KHNYN are active against RNA viruses that have genomes rich in the ribonucleotides (RNA building blocks) C followed by G. However, we have discovered that these restriction factors are also active against vaccinia virus, a large DNA virus that was used as the vaccine to eradicate smallpox. Furthermore, we have found that these 4 cellular proteins are all degraded during vaccinia virus infection so enabling the virus to escape their anti-viral action. Lastly, as found with HIV, another cellular protein, called cyclophilin A, is incorporated into vaccinia virus particles where it helps protect against the anti-viral effect of TRIM5alpha. This protective role of cyclophilin A can be inhibited by a drug, cyclosporine A, which provides protection against the antiviral activity of TRIM5alpha.This project will study how these restriction factors work against vaccinia virus, and the countermeasures that vaccinia virus deploys to diminish their impact. The project has two parts. In the first, we will determine how these host proteins restrict vaccinia virus replication and at what stage during virus infection they do this. The project will also investigate if these restriction factors affect the replication of other large DNA viruses such as herpes simplex virus, the cause of cold sores, and human cytomegalovirus, a cause of disease during pregnancy and during immunosuppression, such as following transplant surgery. In the second part, to run in parallel, the project will investigate the countermeasures that vaccinia virus has evolved to escape or neutralise the antiviral activity of these restriction factors. For instance, how does vaccinia virus enable the packaging of cyclophilin A into virus particles to protect against TRIM5alpha, and how does vaccinia virus induce the degradation of these host restriction factors. Which vaccinia virus proteins are needed for this and which cellular proteins do they interact with to mediate this targeted destruction?Overall, this project will enhance our understanding of the interactions between viruses and the cells they infection that ultimately may lead to the development of safer attenuated vaccines and / or the development of drugs to treat virus infections.