Parnas Oren, Corcoran David L, Cullen Bryan R
mBio. 2014 Jan 21;5(1):e01060-13. doi: 10.1128/mBio.01060-13.
Marek's disease virus 1 (MDV-1), an oncogenic α-herpesvirus that induces T-cell lymphomas in chickens, serves as model system to study transformation by lymphotropic herpesviruses. Like the oncogenic human γ-herpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), MDV-1 encodes several viral microRNAs (miRNAs). One MDV-1 miRNA, miR-M4, shares the same "seed" targeting sequence with both a KSHV miRNA, miR-K11, and cellular miR-155. Importantly, miR-M4 plays a critical role in T-cell transformation by MDV-1, while miR-K11 and cellular miR-155 are thought to play key roles in B-cell transformation by KSHV and EBV, respectively. Here, we present an analysis of the mRNAs targeted by viral miRNAs expressed in the chicken T-cell line MSB1, which is naturally coinfected with MDV-1 and the related nonpathogenic virus MDV-2. Our analysis identified >1,000 endogenous mRNAs targeted by miRNAs encoded by each virus, many of which are targeted by both MDV-1 and MDV-2 miRNAs. We present a functional analysis of an MDV-1 gene, RLORF8, targeted by four MDV-1 miRNAs and a cellular gene, encoding interleukin-18 (IL-18) and targeted by both MDV-1 and MDV-2 miRNAs, and show that ectopic expression of either protein in a form resistant to miRNA inhibition results in inhibition of cell proliferation. Finally, we present a restricted list of 9 genes targeted by not only MDV-1 miR-M4 but also KSHV miR-K11 and human miR-155. Given the critical role played by miR-155 seed family members in lymphomagenesis in humans and chickens, these mRNA targets may contain genes whose inhibition plays a conserved role in herpesvirus transformation.
Herpesviruses cause lymphomas in both humans and chickens, and in both cases, evidence indicates that virally encoded miRNAs, or virally subverted cellular miRNAs, belonging to the miR-155 seed family, play a critical role in this process. However, because each miRNA regulates numerous cellular mRNAs species, it has been difficult to elucidate which miRNA targets are important. Given the evolutionary distance between chickens and humans and the observation that miR-155 is nevertheless highly conserved in both species, we reasoned that the identification of shared miR-155 targets might shed light on this process. Here, we present an analysis of the mRNAs targeted by miRNAs encoded by the oncogenic avian herpesvirus MDV-1 in transformed chicken T cells, including a short list of mRNAs that are also targeted by miR-155 seed family miRNAs in EBV- or KSHV-transformed human B cells, and present an initial functional analysis of some of these miRNA targets.
马立克氏病病毒1型（MDV-1）是一种致癌性α疱疹病毒，可在鸡体内诱发T细胞淋巴瘤，是研究嗜淋巴细胞疱疹病毒转化作用的模型系统。与致癌性人类γ疱疹病毒卡波西肉瘤相关疱疹病毒（KSHV）和爱泼斯坦-巴尔病毒（EBV）一样，MDV-1编码多种病毒微小RNA（miRNA）。一种MDV-1 miRNA，即miR-M4，与一种KSHV miRNA（miR-K11）和细胞miR-155具有相同的“种子”靶向序列。重要的是，miR-M4在MDV-1诱导的T细胞转化中起关键作用，而miR-K11和细胞miR-155分别被认为在KSHV和EBV诱导的B细胞转化中起关键作用。在此，我们对鸡T细胞系MSB1中表达的病毒miRNA靶向的mRNA进行了分析，该细胞系自然感染了MDV-1和相关的非致病性病毒MDV-2。我们的分析确定了每种病毒编码的miRNA靶向的1000多个内源性mRNA，其中许多同时被MDV-1和MDV-2 miRNA靶向。我们对一个被四种MDV-1 miRNA靶向的MDV-1基因RLORF8和一个编码白细胞介素-18（IL-18）且被MDV-1和MDV-2 miRNA共同靶向的细胞基因进行了功能分析，结果表明以对miRNA抑制具有抗性的形式异位表达这两种蛋白中的任何一种都会导致细胞增殖受到抑制。最后，我们列出了一份仅9个基因的受限清单，这些基因不仅被MDV-1的miR-M4靶向，也被KSHV的miR-K11和人类miR-155靶向。鉴于miR-155种子家族成员在人类和鸡的淋巴瘤发生中起关键作用，这些mRNA靶点可能包含其抑制在疱疹病毒转化中起保守作用的基因。
疱疹病毒在人类和鸡体内都会引发淋巴瘤，在这两种情况下，证据都表明属于miR-155种子家族的病毒编码miRNA或被病毒颠覆的细胞miRNA在这一过程中起关键作用。然而，由于每种miRNA调控众多细胞mRNA种类，很难阐明哪些miRNA靶点是重要的。考虑到鸡和人类之间的进化距离以及miR-155在这两个物种中仍然高度保守这一观察结果，我们推断鉴定共享的miR-155靶点可能会揭示这一过程。在此，我们对致癌性禽疱疹病毒MDV-1在转化的鸡T细胞中编码的miRNA靶向的mRNA进行了分析，包括一份在EBV或KSHV转化的人类B细胞中也被miR-155种子家族miRNA靶向的mRNA简短清单，并对其中一些miRNA靶点进行了初步功能分析。
