Department of Public Health - Microbiology - Virology, University of Milan, Via Carlo Pascal 36, 20133 Milan, Italy.
Virus Res. 2010 May;149(2):190-6. doi: 10.1016/j.virusres.2010.01.017. Epub 2010 Feb 4.
The major capsid protein, VP1, of the human polyomavirus BK (BKV) is structurally divided into five outer loops, referred to as BC, DE, EF, GH, and HI. The BC loop includes a short region, named the BKV subtyping region, spanning nucleotides 1744-1812 and characterized by non-synonymous nucleotide polymorphisms that have been used to classify different strains of BKV into four subtypes. The aim of this study was to determine if the nucleotide changes clustered within the BKV subtyping region may influence the in vitro growth efficiency of the virus. We therefore infected the African Green Monkey kidney cell line Vero with four different viral strains (named BKV I, II, III, and IV) that contained the nucleotide sequences of the BKV subtypes within the same genomic background. Infected cells were followed for 59 days and viral replication was assessed at different time points by quantitative real-time PCR (Q-PCR). BKV I, II, and IV were successfully propagated over time in Vero cells, whereas BKV III viral loads progressively decreased during the infection course, demonstrating that the non-synonymous nucleotide polymorphisms of subtype III confer a strong disadvantage for viral replication. Since subtype III differs from all the other subtypes at position 68 of the VP1, where Leu is replaced by Gln, we created viral strains bearing Gln at this position together with the polymorphisms of subtypes I, II, IV and tested their growth in Vero cells. Our results demonstrate that this amino acid substitution does not lower the replication efficiency of subtypes I, II, and IV. In conclusion, this study provides further insights to the importance of the BC loop of BKV in the virus life cycle. In addition, given the effect of the amino acid substitutions of the four BKV subtypes on infectious spread of the virus, our results suggest the need to investigate their potential association with BKV related complications.
人多瘤病毒 BK（BKV）的主要衣壳蛋白 VP1 在结构上分为五个外环，分别称为 BC、DE、EF、GH 和 HI。BC 环包含一个短区域，称为 BKV 亚型区域，跨度为核苷酸 1744-1812，其特征是非同义核苷酸多态性，这些多态性已被用于将不同株的 BKV 分为四个亚型。本研究的目的是确定 BKV 亚型区域内聚集的核苷酸变化是否会影响病毒的体外生长效率。因此，我们用含有相同基因组背景下的 BKV 亚型核苷酸序列的四种不同病毒株（命名为 BKV I、II、III 和 IV）感染非洲绿猴肾细胞系 Vero，感染细胞在 59 天内进行跟踪，并在不同时间点通过实时定量 PCR（Q-PCR）评估病毒复制。BKV I、II 和 IV 可在 Vero 细胞中随时间成功复制，而 BKV III 的病毒载量在感染过程中逐渐降低，表明 III 型的非同义核苷酸多态性对病毒复制有很强的不利影响。由于 III 型在 VP1 的位置 68 处与所有其他亚型不同，其中亮氨酸被谷氨酰胺取代，我们创建了在这个位置带有谷氨酰胺的病毒株，同时具有 I、II、IV 型的多态性，并在 Vero 细胞中测试了它们的生长。我们的结果表明，这种氨基酸取代不会降低 I、II 和 IV 型的复制效率。总之，本研究进一步证明了 BKV BC 环在病毒生命周期中的重要性。此外，鉴于四个 BKV 亚型的氨基酸取代对病毒传播的影响，我们的结果表明需要研究它们与 BKV 相关并发症之间的潜在关联。
