Large T Antigens of Polyomaviruses: Amazing Molecular Machines
ABSTRACT The large tumor antigen (T antigen) encoded by simian virus 40 is an amazing molecular machine because it orchestrates viral infection by modulating multiple fundamental viral and cellular processes. T antigen is required for viral DNA replication, transcription, and virion assembly. In addition, T antigen targets multiple cellular pathways, including those that regulate cell proliferation, cell death, and the inflammatory response. Ectopic T antigen expression results in the immortalization and transformation of many cell types in culture and T antigen induces neoplasia when expressed in rodents. The analysis of the mechanisms by which T antigen carries out its many functions has proved to be a powerful way of gaining insights into cell biology. The accelerating pace at which new polyomaviruses are being discovered provides a collection of novel T antigens that, like simian virus 40, can be used to discover and study key cellular regulatory systems.
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ABSTRACT: Progressive Multifocal Leukoencephalopathy (PML) is caused by lytic replication of JC virus (JCV) in specific cells of the central nervous system. Like other polyomaviruses, JCV encodes a large T-antigen helicase needed for replication of the viral DNA. Here, we report the development of a luciferase-based, quantitative and high-throughput assay of JCV DNA replication in C33A cells, which, unlike the glial cell lines Hs 683 and U87, accumulate high levels of nuclear T-ag needed for robust replication. Using this assay, we investigated the requirement for different domains of T-ag, and for specific sequences within and flanking the viral origin, in JCV DNA replication. Beyond providing validation of the assay, these studies revealed an important stimulatory role of the transcription factor NF1 in JCV DNA replication. Finally, we show that the assay can be used for inhibitor testing, highlighting its value for the identification of antiviral drugs targeting JCV DNA replication.Virology 11/2014; s 468–470:113–125. DOI:10.1016/j.virol.2014.07.042 · 3.28 Impact Factor
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ABSTRACT: Polyomaviruses have so far only been isolated from mammals and birds. Typical for all members of this family is their double-stranded genome of approximately 5,000 base-pairs which can be divided into an early region encoding at least two functional proteins, the large and small tumor antigens, and a late region encompassing genes for the capsid proteins VP1 and VP2. During the last 10 years several novel polyomaviruses have been described in non-human primates and man. This review compares the non-human primate polyomavirus genomes that have been completely sequenced with each other and with the genomes of human polyomaviruses. We predict the presence of protein- and microRNA-encoding sequences. Our analyses demonstrate that several genetically distinct groups of non-human primate polyomaviruses exist, that different polyomaviruses can infect the same non-human primate species but that most of their proteins display highly similar domains and motifs, indicating conservation of key functions.Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases 06/2014; 26. DOI:10.1016/j.meegid.2014.05.030 · 3.26 Impact Factor
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ABSTRACT: JC virus (JCV) lytically infects the oligodendrocytes in the central nervous system in a subset of immunocompromized patients and causes the demyelinating disease, progressive multifocal leukoencephalopathy. JCV replicates and assembles into infectious virions in the nucleus. However, understanding the molecular mechanisms of its virion biogenesis remains elusive. In this report, we have attempted to shed more light on this process by investigating molecular interactions between large T antigen (LT-Ag), Hsp70 and minor capsid proteins, VP2/VP3. We demonstrated that Hsp70 interacts with VP2/VP3 and LT-Ag; and accumulates heavily in the nucleus of the infected cells. We also showed that VP2/VP3 associates with LT-Ag through their DNA binding domains resulting in enhancement in LT-Ag DNA binding to Ori and induction in viral DNA replication. Altogether, our results suggest that VP2/VP3 and Hsp70 actively participate in JCV DNA replication and may play critical roles in coupling of viral DNA replication to virion encapsidation.Virology 01/2014; 449:1–16. DOI:10.1016/j.virol.2013.10.031 · 3.28 Impact Factor