Characterization of novel Bovine Leukemia Virus (BLV) antisense transcripts by deep sequencing reveals constitutive expression in tumors and transcriptional interaction with viral microRNAs.
Characterization of novel Bovine Leukemia Virus (BLV) antisense transcripts by deep sequencing reveals constitutive expression in tumors and transcriptional interaction with viral microRNAs.
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DOI：
10.1186/s12977-016-0267-8
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发表时间：
2016-05-03
期刊：
影响因子：
3.3
通讯作者：
Van den Broeke A
中科院分区：
文献类型：
--
作者：
Durkin K;Rosewick N;Artesi M;Hahaut V;Griebel P;Arsic N;Burny A;Georges M;Van den Broeke A
牛白血病病毒（BLV）是一种与人类T细胞白血病病毒1型（HTLV - 1）密切相关的δ反转录病毒。牛是BLV的自然宿主，该病毒整合到B细胞中，导致终身感染。大多数感染动物无症状，但在漫长的潜伏期后，约5%的动物会发展为侵袭性白血病/淋巴瘤，这与HTLV - 1的疾病进程相似。这些病毒引发细胞转化的机制仍不清楚。在这两种病毒中，在肿瘤中从5′长末端重复序列（5′LTR）观察到很少或没有转录，但前病毒并非转录沉默。就BLV而言，一组由RNA聚合酶III转录的微小RNA高度表达，而在所有检测的肿瘤中都能持续发现HTLV - 1的反义转录本HBZ。
在此，我们利用RNA测序证明，在所有检测的白血病和无症状样本中，BLV前病毒也组成性地表达反义转录本。第一种转录本（AS1）可以选择性地进行多聚腺苷酸化，产生约600bp的转录本（AS1 - S）以及一种含量较少的约2200bp的转录本（AS1 - L）。选择性剪接产生了约400bp的第二种转录本（AS2）。AS1 - S/L的编码潜能不明确，有一个264bp的小开放阅读框，但这些转录本主要保留在细胞核内，暗示其具有类似长链非编码RNA（lncRNA）的作用。AS1 - L转录本与BLV微小RNA重叠，并且通过对RNA连接酶介导的（RLM）5′快速扩增cDNA末端（5′RACE）进行高通量测序，我们发现RNA诱导沉默复合体（RISC）会切割AS1 - L。此外，使用微小RNA缺失或倒置的改变的BLV前病毒进行的实验表明，两种病毒RNA种类之间存在额外的转录干扰。
新型病毒反义转录本的鉴定表明，BLV前病毒在肿瘤中远非沉默。此外，这些转录本在白血病和非恶性克隆中的持续表达表明它们在病毒生命周期及其致瘤潜能中起着至关重要的作用。此外，BLV编码的微小RNA对AS1 - L转录本的切割以及两种病毒RNA种类之间的转录干扰表明它们在BLV的调控中具有共同作用。
本文的网络版（doi:10.1186/s12977 - 016 - 0267 - 8）包含补充材料，授权用户可获取。
Bovine Leukemia Virus (BLV) is a deltaretrovirus closely related to the Human T cell leukemia virus-1 (HTLV-1). Cattle are the natural host of BLV where it integrates into B-cells, producing a lifelong infection. Most infected animals remain asymptomatic but following a protracted latency period about 5 % develop an aggressive leukemia/lymphoma, mirroring the disease trajectory of HTLV-1. The mechanisms by which these viruses provoke cellular transformation remain opaque. In both viruses little or no transcription is observed from the 5′LTR in tumors, however the proviruses are not transcriptionally silent. In the case of BLV a cluster of RNA polymerase III transcribed microRNAs are highly expressed, while the HTLV-1 antisense transcript HBZ is consistently found in all tumors examined. Here, using RNA-seq, we demonstrate that the BLV provirus also constitutively expresses antisense transcripts in all leukemic and asymptomatic samples examined. The first transcript (AS1) can be alternately polyadenylated, generating a transcript of ~600 bp (AS1-S) and a less abundant transcript of ~2200 bp (AS1-L). Alternative splicing creates a second transcript of ~400 bp (AS2). The coding potential of AS1-S/L is ambiguous, with a small open reading frame of 264 bp, however the transcripts are primarily retained in the nucleus, hinting at a lncRNA-like role. The AS1-L transcript overlaps the BLV microRNAs and using high throughput sequencing of RNA-ligase-mediated (RLM) 5′RACE, we show that the RNA-induced silencing complex (RISC) cleaves AS1-L. Furthermore, experiments using altered BLV proviruses with the microRNAs either deleted or inverted point to additional transcriptional interference between the two viral RNA species. The identification of novel viral antisense transcripts shows the BLV provirus to be far from silent in tumors. Furthermore, the consistent expression of these transcripts in both leukemic and nonmalignant clones points to a vital role in the life cycle of the virus and its tumorigenic potential. Additionally, the cleavage of the AS1-L transcript by the BLV encoded microRNAs and the transcriptional interference between the two viral RNA species suggest a shared role in the regulation of BLV. The online version of this article (doi:10.1186/s12977-016-0267-8) contains supplementary material, which is available to authorized users.