German Cancer Research Center, ATV-F100, Heidelberg, Germany.
J Virol. 2011 Oct;85(19):9801-10. doi: 10.1128/JVI.05100-11. Epub 2011 Jul 13.
Epstein-Barr virus (EBV) transforms B lymphocytes through the expression of the latent viral proteins EBNA and latent membrane protein (LMP). Recently, it has become apparent that microRNAs (miRNAs) also contribute to EBV's oncogenic properties; recombinant EBVs that lack the BHRF1 miRNA cluster display a reduced ability to transform B lymphocytes in vitro. Furthermore, infected cells evince a marked upregulation of the EBNA genes. Using recombinant viruses that lack only one member of the cluster, we now show that all three BHRF1 miRNAs contribute to B-cell transformation. Recombinants that lacked miR-BHRF1-2 or miR-BHRF1-3 displayed enhanced EBNA expression initiated at the Cp and Wp promoters. Interestingly, we find that the deletion of miR-BHRF1-2 reduced the expression level of miR-BHRF1-3 and possibly that of miR-BHRF1-1, demonstrating that the expression of one miRNA can potentiate the expression of other miRNAs located in the same cluster. Therefore, the phenotypic traits of the miR-BHRF1-2 null mutant could result partly from reduced miR-BHRF1-1 and miR-BHRF1-3 expression levels. Nevertheless, using an miR-BHRF1-1 and miR-BHRF1-3 double mutant, we could directly assess and confirm the contribution of miR-BHRF1-2 to B-cell transformation. Furthermore, we found that the potentiating effect of miR-BHRF1-2 on miR-BHRF1-3 synthesis can be reproduced with simple expression plasmids, provided that both miRNAs are processed from the same transcript. Therefore, this enhancing effect does not result from an idiosyncrasy of the EBV genome but rather reflects a general property of these miRNAs. This study highlights the advantages of arranging the BHRF1 miRNAs in clusters: it allows the synchronous and synergistic expression of genetic elements that cooperate to transform their target cells.
EB 病毒（EBV）通过表达潜伏病毒蛋白 EBNA 和潜伏膜蛋白（LMP）来转化 B 淋巴细胞。最近，微 RNA（miRNA）也有助于 EBV 的致癌特性变得明显；缺乏 BHRF1 miRNA 簇的重组 EBV 在体外转化 B 淋巴细胞的能力降低。此外，受感染的细胞表现出 EBNA 基因的显著上调。使用仅缺乏簇中一个成员的重组病毒，我们现在表明，BHRF1 三个 miRNA 都有助于 B 细胞转化。缺乏 miR-BHRF1-2 或 miR-BHRF1-3 的重组体显示出在 Cp 和 Wp 启动子起始的增强的 EBNA 表达。有趣的是，我们发现 miR-BHRF1-2 的缺失降低了 miR-BHRF1-3 的表达水平，可能还有 miR-BHRF1-1 的表达水平，表明一个 miRNA 的表达可以增强位于同一簇中的其他 miRNA 的表达。因此，miR-BHRF1-2 缺失突变体的表型特征可能部分是由于 miR-BHRF1-1 和 miR-BHRF1-3 表达水平降低所致。尽管如此，使用 miR-BHRF1-1 和 miR-BHRF1-3 双突变体，我们可以直接评估和确认 miR-BHRF1-2 对 B 细胞转化的贡献。此外，我们发现 miR-BHRF1-2 对 miR-BHRF1-3 合成的增强作用可以用简单的表达质粒来重现，只要这两个 miRNA 都来自同一转录本。因此，这种增强作用不是 EBV 基因组的特殊性造成的，而是反映了这些 miRNA 的一般特性。这项研究突出了将 BHRF1 miRNA 排列在簇中的优势：它允许遗传元件的同步和协同表达，这些元件协同作用转化它们的靶细胞。
