Culleton Sara P, Kanginakudru Sriramana, DeSmet Marsha, Gilson Timra, Xie Fang, Wu Shwu-Yuan, Chiang Cheng-Ming, Qi Guihong, Wang Mu, Androphy Elliot J
Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
Department of Dermatology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
J Virol. 2017 Jan 3;91(2). doi: 10.1128/JVI.01854-16. Print 2017 Jan 15.
Papillomaviruses are small, double-stranded DNA viruses that encode the E2 protein, which controls transcription, replication, and genome maintenance in infected cells. Posttranslational modifications (PTMs) affecting E2 function and stability have been demonstrated for multiple types of papillomaviruses. Here we describe the first phosphorylation event involving a conserved tyrosine (Y) in the bovine papillomavirus 1 (BPV-1) E2 protein at amino acid 102. While its phosphodeficient phenylalanine (F) mutant activated both transcription and replication in luciferase reporter assays, a mutant that may act as a phosphomimetic, with a Y102-to-glutamate (E) mutation, lost both activities. The E2 Y102F protein interacted with cellular E2-binding factors and the viral helicase E1; however, in contrast, the Y102E mutant associated with only a subset and was unable to bind to E1. While the Y102F mutant fully supported transient viral DNA replication, BPV genomes encoding this mutation as well as Y102E were not maintained as stable episomes in murine C127 cells. These data imply that phosphorylation at Y102 disrupts the helical fold of the N-terminal region of E2 and its interaction with key cellular and viral proteins. We hypothesize that the resulting inhibition of viral transcription and replication in basal epithelial cells prevents the development of a lytic infection.
Papillomaviruses (PVs) are small, double-stranded DNA viruses that are responsible for cervical, oropharyngeal, and various genitourinary cancers. Although vaccines against the major oncogenic human PVs are available, there is no effective treatment for existing infections. One approach to better understand the viral replicative cycle, and potential therapies to target it, is to examine the posttranslational modification of viral proteins and its effect on function. Here we have discovered that the bovine papillomavirus 1 (BPV-1) transcription and replication regulator E2 is phosphorylated at residue Y102. While a phosphodeficient mutant at this site was fully functional, a phosphomimetic mutant displayed impaired transcription and replication activity as well as a lack of an association with certain E2-binding proteins. This study highlights the influence of posttranslational modifications on viral protein function and provides additional insight into the complex interplay between papillomaviruses and their hosts.
乳头瘤病毒是小型双链DNA病毒，可编码E2蛋白，该蛋白控制受感染细胞中的转录、复制和基因组维持。多种乳头瘤病毒已证实存在影响E2功能和稳定性的翻译后修饰（PTM）。在此，我们描述了牛乳头瘤病毒1型（BPV-1）E2蛋白第102位氨基酸处保守酪氨酸（Y）的首次磷酸化事件。在荧光素酶报告基因检测中，其磷酸化缺陷型苯丙氨酸（F）突变体激活了转录和复制，而一个可能模拟磷酸化作用的Y102突变为谷氨酸（E）的突变体则失去了这两种活性。E2 Y102F蛋白与细胞E2结合因子和病毒解旋酶E1相互作用；然而，相比之下，Y102E突变体仅与一部分因子相关，且无法与E1结合。虽然Y102F突变体完全支持瞬时病毒DNA复制，但编码此突变以及Y102E的BPV基因组在鼠C127细胞中不能维持为稳定的附加体。这些数据表明，Y102处的磷酸化破坏了E2 N端区域的螺旋结构及其与关键细胞和病毒蛋白的相互作用。我们推测，由此导致的基础上皮细胞中病毒转录和复制的抑制可防止溶细胞性感染的发展。
乳头瘤病毒（PVs）是小型双链DNA病毒，可引发宫颈癌、口咽癌和各种泌尿生殖系统癌症。尽管有针对主要致癌性人乳头瘤病毒的疫苗，但现有感染尚无有效治疗方法。更好地理解病毒复制周期以及针对该周期的潜在治疗方法的一种途径是研究病毒蛋白的翻译后修饰及其对功能的影响。在此，我们发现牛乳头瘤病毒1型（BPV-1）转录和复制调节因子E2在Y102位点发生磷酸化。虽然该位点的磷酸化缺陷型突变体功能完全正常，但模拟磷酸化的突变体表现出转录和复制活性受损，以及与某些E2结合蛋白缺乏关联。这项研究突出了翻译后修饰对病毒蛋白功能的影响，并为乳头瘤病毒与其宿主之间复杂的相互作用提供了更多见解。
