Viral Infectious Diseases Unit, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
BMC Genomics. 2012 Mar 28;13:121. doi: 10.1186/1471-2164-13-121.
Bovine leukemia virus (BLV) is associated with enzootic bovine leukosis and is closely related to human T-cell leukemia virus type I. The Tax protein of BLV is a transcriptional activator of viral replication and a key contributor to oncogenic potential. We previously identified interesting mutant forms of Tax with elevated (TaxD247G) or reduced (TaxS240P) transactivation effects on BLV replication and propagation. However, the effects of these mutations on functions other than transcriptional activation are unknown. In this study, to identify genes that play a role in the cascade of signal events regulated by wild-type and mutant Tax proteins, we used a large-scale host cell gene-profiling approach.
Using a microarray containing approximately 18,400 human mRNA transcripts, we found several alterations after the expression of Tax proteins in genes involved in many cellular functions such as transcription, signal transduction, cell growth, apoptosis, stress response, and immune response, indicating that Tax protein has multiple biological effects on various cellular environments. We also found that TaxD247G strongly regulated more genes involved in transcription, signal transduction, and cell growth functions, contrary to TaxS240P, which regulated fewer genes. In addition, the expression of genes related to stress response significantly increased in the presence of TaxS240P as compared to wild-type Tax and TaxD247G. By contrast, the largest group of downregulated genes was related to immune response, and the majority of these genes belonged to the interferon family. However, no significant difference in the expression level of downregulated genes was observed among the Tax proteins. Finally, the expression of important cellular factors obtained from the human microarray results were validated at the RNA and protein levels by real-time quantitative reverse transcription-polymerase chain reaction and western blotting, respectively, after transfecting Tax proteins into bovine cells and human HeLa cells.
A comparative analysis of wild-type and mutant Tax proteins indicates that Tax protein exerts a significant impact on cellular functions as diverse as transcription, signal transduction, cell growth, stress response and immune response. Importantly, our study is the first report that shows the extent to which BLV Tax regulates the innate immune response.
牛白血病病毒（BLV）与地方性牛白血病有关，与人类 T 细胞白血病病毒 I 型密切相关。BLV 的 Tax 蛋白是病毒复制的转录激活因子，也是致癌潜力的关键贡献者。我们之前发现了具有增强（TaxD247G）或降低（TaxS240P）BLV 复制和传播转录激活作用的有趣突变形式的 Tax。然而，这些突变除了转录激活以外对其他功能的影响尚不清楚。在这项研究中，为了确定在野生型和突变型 Tax 蛋白调节的信号事件级联中起作用的基因，我们使用了大规模的宿主细胞基因谱分析方法。
使用包含大约 18400 个人类 mRNA 转录物的微阵列，我们在参与许多细胞功能（如转录、信号转导、细胞生长、凋亡、应激反应和免疫反应）的基因中发现了 Tax 蛋白表达后的几种改变，这表明 Tax 蛋白对各种细胞环境具有多种生物学效应。我们还发现，TaxD247G 强烈调节更多参与转录、信号转导和细胞生长功能的基因，而 TaxS240P 则调节较少的基因。此外，与野生型 Tax 和 TaxD247G 相比，TaxS240P 存在时与应激反应相关的基因表达显著增加。相比之下，下调基因中最大的一组与免疫反应有关，其中大多数基因属于干扰素家族。然而，在 Tax 蛋白之间，下调基因的表达水平没有观察到显著差异。最后，通过实时定量逆转录聚合酶链反应和 Western blot 分别在转染 Tax 蛋白到牛细胞和人 HeLa 细胞后，从人类微阵列结果获得的重要细胞因子的表达在 RNA 和蛋白质水平上进行了验证。
野生型和突变型 Tax 蛋白的比较分析表明，Tax 蛋白对转录、信号转导、细胞生长、应激反应和免疫反应等多种细胞功能都有显著影响。重要的是，我们的研究首次表明 BLV Tax 调节固有免疫反应的程度。
