The Adenovirus E4-ORF3 Protein Stimulates SUMOylation of General Transcription Factor TFII-I to Direct Proteasomal Degradation.
The Adenovirus E4-ORF3 Protein Stimulates SUMOylation of General Transcription Factor TFII-I to Direct Proteasomal Degradation.
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DOI：
10.1128/mbio.02184-15
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发表时间：
2016-01-26
期刊：
影响因子：
6.4
通讯作者：
Hearing P
中科院分区：
文献类型：
--
作者：
Bridges RG;Sohn SY;Wright J;Leppard KN;Hearing P
宿主细胞转录、翻译和翻译后修饰过程的调节对于许多病毒在宿主细胞内有效复制的能力至关重要。人腺病毒（Ad）早期4区开放阅读框3 （E4-ORF3）蛋白在感染细胞的细胞核中形成独特的内含物，并通过重定位抑制抗病毒的Mre11-Rad50-Nbs1 DNA修复复合体。E4-ORF3也能诱导Mre11和Nbs1的sumo化。我们最近发现了E4-ORF3的其他细胞靶点，并发现E4-ORF3刺激涉及多种过程的41种细胞蛋白的泛素样修饰。在以依赖e4 - orf3的方式进行最丰富修饰的蛋白质中，一般转录因子i - i - i （TFII-I）。对ad感染细胞的分析显示，E4-ORF3在感染早期诱导TFII-I重新定位和SUMOylation。在本研究中，我们探讨了E4-ORF3与TFII-I之间的关系。我们发现，Ad感染或E4-ORF3异位表达可导致TFII-I的sumo化，从而导致TFII-I蛋白水平迅速下降。我们还发现E4-ORF3是TFII-I泛素化和随后的蛋白酶体降解所必需的。这是E4-ORF3调控泛素化的第一个证据。有趣的是，我们发现E4-ORF3对TFII-I的调节发生在多种细胞类型中，但只有Ad物种C的E4-ORF3调节TFII-I，这为E4-ORF3靶向TFII-I的机制提供了重要的见解。最后，我们发现E4-ORF3在感染过程中刺激了tfii - i抑制的病毒启动子的活性。我们的研究结果描述了Ad调控TFII-I的新机制，并强调了病毒蛋白如何在感染期间调节关键的细胞转录因子。腺病毒已经进化出许多机制来靶向宿主信号通路，以优化感染期间的细胞环境。E4-ORF3是一种在感染早期产生的小病毒蛋白，对灭活宿主抗病毒反应至关重要。除了捕获和重组细胞蛋白的能力外，E4-ORF3还调节靶蛋白的翻译后修饰，但对这些修饰的功能后果知之甚少。我们最近发现TFII-I是E4-ORF3的一个新靶点，它被重新定位到E4-ORF3的动态核结构中，并受到E4-ORF3介导的SUMO修饰。在这里，我们发现TFII-I是E4-ORF3的泛素化和蛋白酶体降解目标，E4-ORF3通过TFII-I抑制的病毒启动子刺激基因表达。我们的研究结果表明，E4-ORF3特异性靶向TFII-I是一种灭活其抗病毒特性的机制。这些研究进一步揭示了E4-ORF3如何发挥作用来对抗宿主的抗病毒反应。
Modulation of host cell transcription, translation, and posttranslational modification processes is critical for the ability of many viruses to replicate efficiently within host cells. The human adenovirus (Ad) early region 4 open reading frame 3 (E4-ORF3) protein forms unique inclusions throughout the nuclei of infected cells and inhibits the antiviral Mre11-Rad50-Nbs1 DNA repair complex through relocalization. E4-ORF3 also induces SUMOylation of Mre11 and Nbs1. We recently identified additional cellular targets of E4-ORF3 and found that E4-ORF3 stimulates ubiquitin-like modification of 41 cellular proteins involved in a wide variety of processes. Among the proteins most abundantly modified in an E4-ORF3-dependent manner was the general transcription factor II–I (TFII-I). Analysis of Ad-infected cells revealed that E4-ORF3 induces TFII-I relocalization and SUMOylation early during infection. In the present study, we explored the relationship between E4-ORF3 and TFII-I. We found that Ad infection or ectopic E4-ORF3 expression leads to SUMOylation of TFII-I that precedes a rapid decline in TFII-I protein levels. We also show that E4-ORF3 is required for ubiquitination of TFII-I and subsequent proteasomal degradation. This is the first evidence that E4-ORF3 regulates ubiquitination. Interestingly, we found that E4-ORF3 modulation of TFII-I occurs in diverse cell types but only E4-ORF3 of Ad species C regulates TFII-I, providing critical insight into the mechanism by which E4-ORF3 targets TFII-I. Finally, we show that E4-ORF3 stimulates the activity of a TFII-I-repressed viral promoter during infection. Our results characterize a novel mechanism of TFII-I regulation by Ad and highlight how a viral protein can modulate a critical cellular transcription factor during infection. Adenovirus has evolved a number of mechanisms to target host signaling pathways in order to optimize the cellular environment during infection. E4-ORF3 is a small viral protein made early during infection, and it is critical for inactivating host antiviral responses. In addition to its ability to capture and reorganize cellular proteins, E4-ORF3 also regulates posttranslational modifications of target proteins, but little is known about the functional consequences of these modifications. We recently identified TFII-I as a novel target of E4-ORF3 that is relocalized into dynamic E4-ORF3 nuclear structures and subjected to E4-ORF3-mediated SUMO modification. Here, we show that TFII-I is targeted by E4-ORF3 for ubiquitination and proteasomal degradation and that E4-ORF3 stimulates gene expression from a TFII-I-repressed viral promoter. Our findings suggest that the specific targeting of TFII-I by E4-ORF3 is a mechanism to inactivate its antiviral properties. These studies provide further insight into how E4-ORF3 functions to counteract host antiviral responses.