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对病毒感染起中介防御作用的蛋白质。这种蛋白质被称为限制因子，因为它们的作用限制了病毒的复制。限制因子的例子是称为TRIM5pha、ZAP、TRIM25和KHNYN的蛋白质。到目前为止，人们认为这些限制因子的作用主要针对的是具有RNA而不是DNA基因组的病毒。例如，众所周知，TRIM5pha是逆转录病毒(如HIV)的限制因子，ZAP、TRIM25和KHNYN对基因组中富含核糖核苷酸(RNA构建块)C和G的RNA病毒具有活性。然而，我们发现这些限制因子对牛痘病毒也有活性，牛痘病毒是一种大型DNA病毒，被用作根除天花的疫苗。此外，我们还发现，在痘苗病毒感染期间，这4种细胞蛋白都会被降解，从而使病毒能够逃避它们的抗病毒作用。最后，正如在HIV中发现的那样，另一种细胞蛋白，称为亲环素A，被结合到痘苗病毒颗粒中，在那里它有助于防止TRIM5pha的抗病毒作用。亲环素A的这种保护作用可以被一种药物环孢素A抑制，环孢菌素A提供了对TRIM5α的抗病毒活性的保护。本项目将研究这些限制因素如何对牛痘病毒起作用，以及牛痘病毒采取的对策来减少它们的影响。该项目包括两个部分。首先，我们将确定这些宿主蛋白是如何限制痘苗病毒复制的，以及在病毒感染的哪个阶段这样做。该项目还将调查这些限制因素是否会影响其他大型DNA病毒的复制，如单纯疱疹病毒和人类巨细胞病毒，人类巨细胞病毒是怀孕期间和免疫抑制期间(如移植手术后)的疾病原因。在第二部分中，为了同时进行，该项目将调查牛痘病毒进化为逃避或中和这些限制因素的抗病毒活性的对策。例如，痘苗病毒如何使亲环素A包装成病毒颗粒以保护其免受TRIM5α的攻击，以及痘苗病毒如何诱导这些宿主限制因子的降解。这需要哪些痘苗病毒蛋白，以及它们与哪些细胞蛋白相互作用来介导这种靶向破坏？总的来说，这个项目将增强我们对病毒与它们感染的细胞之间的相互作用的理解，最终可能导致开发更安全的减毒疫苗和/或开发治疗病毒感染的药物。

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.