Molecular Genetics and Microbiology, The University of Texas at Austin, 1 University Station A5000, Austin, TX 78712-0162, USA.
J Virol. 2011 May;85(9):4487-500. doi: 10.1128/JVI.02557-10. Epub 2011 Feb 23.
Several different members of the Polyomaviridae, including some human pathogens, encode microRNAs (miRNAs) that lie antisense with respect to the early gene products, the tumor (T) antigens. These miRNAs negatively regulate T antigen expression by directing small interfering RNA (siRNA)-like cleavage of the early transcripts. miRNA mutant viruses of some members of the Polyomaviridae express increased levels of early proteins during lytic infection. However, the importance of miRNA-mediated negative regulation of the T antigens remains uncertain. Bandicoot papillomatosis carcinomatosis virus type 1 (BPCV1) is associated with papillomas and carcinomas in the endangered marsupial the western barred bandicoot (Perameles bougainville). BPCV1 is the founding member of a new group of viruses that remarkably share distinct properties in common with both the polyomavirus and papillomavirus families. Here, we show that BPCV1 encodes, in the same orientation as the papillomavirus-like transcripts, a miRNA located within a long noncoding region (NCR) of the genome. Furthermore, this NCR serves the function of both promoter and template for the primary transcript that gives rise to the miRNA. Unlike the polyomavirus miRNAs, the BPCV1 miRNA is not encoded antisense to the T antigen transcripts but rather lies in a separate, proximal region of the genome. We have mapped the 3' untranslated region (UTR) of the BPCV1 large T antigen early transcript and identified a functional miRNA target site that is imperfectly complementary to the BPCV1 miRNA. Chimeric reporters containing the entire BPCV1 T antigen 3' UTR undergo negative regulation when coexpressed with the BPCV1 miRNA. Notably, the degree of negative regulation observed is equivalent to that of an identical reporter that is engineered to bind to the BPCV1 miRNA with perfect complementarity. We also show that this miRNA and this novel mode of early gene regulation are conserved with the related BPCV2. Finally, papillomatous lesions from a western barred bandicoot express readily detectable levels of this miRNA, stressing its likely importance in vivo. Combined, the alternative mechanisms of negative regulation of T antigen expression between the BPCVs and the polyomaviruses support the importance of miRNA-mediated autoregulation in the life cycles of some divergent polyomaviruses and polyomavirus-like viruses.
多瘤病毒科的几个不同成员，包括一些人类病原体，编码与早期基因产物（肿瘤（T）抗原）反义的 microRNA（miRNA）。这些 miRNA 通过指导早期转录物的小干扰 RNA（siRNA）样切割来负调控 T 抗原的表达。多瘤病毒科的一些成员的 miRNA 突变病毒在裂解感染期间表达更高水平的早期蛋白。然而，miRNA 介导的 T 抗原负调控的重要性仍不确定。袋狸乳头瘤病致癌病毒 1 型（BPCV1）与濒危有袋动物西部条纹袋狸中的乳头瘤和癌有关。BPCV1 是一个新病毒群的创始成员，该病毒群与多瘤病毒和乳头瘤病毒家族具有显著的共同特征。在这里，我们表明 BPCV1 在与乳头瘤病毒样转录物相同的方向上编码位于基因组长非编码区（NCR）内的 miRNA。此外，该 NCR 既作为初级转录物的启动子，又作为模板发挥作用，该初级转录物产生 miRNA。与多瘤病毒 miRNA 不同，BPCV1 miRNA 不是编码反义于 T 抗原转录物，而是位于基因组的单独、近端区域。我们已经绘制了 BPCV1 大 T 抗原早期转录物的 3'非翻译区（UTR），并鉴定了一个功能 miRNA 靶位点，该位点与 BPCV1 miRNA 不完全互补。当与 BPCV1 miRNA 共表达时，包含整个 BPCV1 T 抗原 3'UTR 的嵌合报告基因受到负调控。值得注意的是，观察到的负调控程度与经过工程改造以与 BPCV1 miRNA 具有完美互补性的相同报告基因相当。我们还表明，这种 miRNA 和这种新的早期基因调控模式与相关的 BPCV2 保守。最后，西部条纹袋狸的乳头瘤病变表达可检测到的这种 miRNA 水平，强调了其在体内的重要性。BPCV 和多瘤病毒之间 T 抗原表达负调控的替代机制支持 miRNA 介导的自动调节在一些不同的多瘤病毒和多瘤病毒样病毒的生命周期中的重要性。
