Cavallari Ilaria, Rende Francesca, Bona Marion K, Sztuba-Solinska Joanna, Silic-Benussi Micol, Tognon Martina, LeGrice Stuart F J, Franchini Genoveffa, D'Agostino Donna M, Ciminale Vincenzo
Department of Surgery, Oncology and Gastroenterology, University of Padua, Padua, Italy.
Leidos Biomedical Research, Inc., Frederick National Laboratory, Frederick, Maryland, USA.
J Virol. 2015 Nov 18;90(3):1486-98. doi: 10.1128/JVI.02298-15. Print 2016 Feb 1.
Human T-cell leukemia virus type 1 (HTLV-1) expression depends on the concerted action of Tax, which drives transcription of the viral genome, and Rex, which favors expression of incompletely spliced mRNAs and determines a 2-phase temporal pattern of viral expression. In the present study, we investigated the Rex dependence of the complete set of alternatively spliced HTLV-1 mRNAs. Analyses of cells transfected with Rex-wild-type and Rex-knockout HTLV-1 molecular clones using splice site-specific quantitative reverse transcription (qRT)-PCR revealed that mRNAs encoding the p30Tof, p13, and p12/8 proteins were Rex dependent, while the p21rex mRNA was Rex independent. These findings provide a rational explanation for the intermediate-late temporal pattern of expression of the p30tof, p13, and p12/8 mRNAs described in previous studies. All the Rex-dependent mRNAs contained a 75-nucleotide intronic region that increased the nuclear retention and degradation of a reporter mRNA in the absence of other viral sequences. Selective 2'-hydroxyl acylation analyzed by primer extension (SHAPE) analysis revealed that this sequence formed a stable hairpin structure. Cell cycle synchronization experiments indicated that mitosis partially bypasses the requirement for Rex to export Rex-dependent HTLV-1 transcripts. These findings indicate a link between the cycling properties of the host cell and the temporal pattern of viral expression/latency that might influence the ability of the virus to spread and evade the immune system.
HTLV-1 is a complex retrovirus that causes two distinct pathologies termed adult T-cell leukemia/lymphoma and tropical spastic paraparesis/HTLV-1-associated myelopathy in about 5% of infected individuals. Expression of the virus depends on the concerted action of Tax, which drives transcription of the viral genome, and Rex, which favors expression of incompletely spliced mRNAs and determines a 2-phase temporal pattern of virus expression. The findings reported in this study revealed a novel cis-acting regulatory element and indicated that mitosis partially bypasses the requirement for Rex to export Rex-dependent HTLV-1 transcripts. Our results add a layer of complexity to the mechanisms controlling the expression of alternatively spliced HTLV-1 mRNAs and suggest a link between the cycling properties of the host cell and the temporal pattern of viral expression/latency that might influence the ability of the virus to spread and evade the immune system.
1型人类T细胞白血病病毒（HTLV-1）的表达依赖于Tax和Rex的协同作用，Tax驱动病毒基因组的转录，Rex则有利于不完全剪接的mRNA的表达，并决定病毒表达的两阶段时间模式。在本研究中，我们调查了HTLV-1全套可变剪接mRNA对Rex的依赖性。使用剪接位点特异性定量逆转录（qRT）-PCR对转染了Rex野生型和Rex敲除型HTLV-1分子克隆的细胞进行分析，结果显示，编码p30Tof、p13和p12/8蛋白的mRNA依赖于Rex，而p21rex mRNA不依赖于Rex。这些发现为先前研究中描述的p30tof、p13和p12/8 mRNA的中晚期时间表达模式提供了合理的解释。所有依赖Rex的mRNA都包含一个75个核苷酸的内含子区域，在没有其他病毒序列的情况下，该区域会增加报告基因mRNA的核滞留和降解。通过引物延伸（SHAPE）分析进行的选择性2'-羟基酰化显示，该序列形成了一个稳定的发夹结构。细胞周期同步实验表明，有丝分裂部分绕过了Rex输出依赖Rex的HTLV-1转录本的需求。这些发现表明宿主细胞的循环特性与病毒表达/潜伏的时间模式之间存在联系，这可能会影响病毒传播和逃避免疫系统的能力。
HTLV-1是一种复杂的逆转录病毒，在约5%的感染者中会导致两种不同的疾病，即成人T细胞白血病/淋巴瘤和热带痉挛性截瘫/HTLV-1相关脊髓病。病毒的表达依赖于Tax和Rex的协同作用，Tax驱动病毒基因组的转录，Rex则有利于不完全剪接的mRNA的表达，并决定病毒表达的两阶段时间模式。本研究报告的发现揭示了一种新的顺式作用调节元件，并表明有丝分裂部分绕过了Rex输出依赖Rex的HTLV-1转录本的需求。我们的结果为控制HTLV-1可变剪接mRNA表达的机制增加了一层复杂性，并表明宿主细胞的循环特性与病毒表达/潜伏的时间模式之间存在联系，这可能会影响病毒传播和逃避免疫系统的能力。
