Tumor Virus RNA Biology Laboratory, HIV and AIDS Malignancy Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
J Virol. 2013 Jan;87(1):243-56. doi: 10.1128/JVI.01693-12. Epub 2012 Oct 17.
Polyadenylate-binding protein cytoplasmic 1 (PABPC1) is a cytoplasmic-nuclear shuttling protein important for protein translation initiation and both RNA processing and stability. We report that PABPC1 forms a complex with the Kaposi's sarcoma-associated herpesvirus (KSHV) ORF57 protein, which allows ORF57 to interact with a 9-nucleotide (nt) core element of KSHV polyadenylated nuclear (PAN) RNA, a viral long noncoding RNA (lncRNA), and increase PAN stability. The N-terminal RNA recognition motifs (RRMs) of PABPC1 are necessary for the direct interaction with ORF57. During KSHV lytic infection, the expression of viral ORF57 leads to a substantial decrease in overall PABPC1 expression, along with a shift in the cellular distribution of the remaining PABPC1 to the nucleus. Interestingly, PABPC1 and ORF57 have opposing functions in modulating PAN steady-state accumulation. The suppressive effect of PABPC1 specific to PAN expression is alleviated by small interfering RNA knockdown of PABPC1 or by overexpression of ORF57. Conversely, ectopic PABPC1 reduces ORF57 steady-state protein levels and induces aberrant polyadenylation of PAN and thereby indirectly inhibits ORF57-mediated PAN accumulation. However, E1B-AP5 (heterogeneous nuclear ribonucleoprotein U-like 1), which interacts with a region outside the 9-nt core to stimulate PAN expression, does not interact or even colocalize with ORF57. Unlike PABPC1, the nuclear distribution of E1B-AP5 remains unchanged by viral lytic infection or overexpression of ORF57. Together, these data indicate that PABPC1 is an important cellular target of viral ORF57 to directly upregulate PAN accumulation during viral lytic infection, and the ability of host PABPC1 to disrupt ORF57 expression is a strategic host counterbalancing mechanism.
多聚腺苷酸结合蛋白细胞质 1（PABPC1）是一种重要的细胞质-核穿梭蛋白，对于蛋白质翻译起始以及 RNA 加工和稳定性都有重要作用。我们报告称，PABPC1 与卡波济肉瘤相关疱疹病毒（KSHV）ORF57 蛋白形成复合物，使 ORF57 能够与 KSHV 多聚腺苷酸化核（PAN）RNA 的 9 个核苷酸（nt）核心元件相互作用，该元件是一种病毒长非编码 RNA（lncRNA），并增加 PAN 的稳定性。PABPC1 的 N 端 RNA 识别基序（RRMs）对于与 ORF57 的直接相互作用是必需的。在 KSHV 裂解感染期间，病毒 ORF57 的表达导致总 PABPC1 表达量显著下降，同时剩余 PABPC1 的细胞分布向核内转移。有趣的是，PABPC1 和 ORF57 在调节 PAN 稳态积累方面具有相反的功能。通过 PABPC1 的 siRNA 敲低或 ORF57 的过表达，减轻了 PABPC1 对 PAN 表达的抑制作用。相反，异位 PABPC1 降低了 ORF57 的稳态蛋白水平，并诱导 PAN 的异常多聚腺苷酸化，从而间接抑制 ORF57 介导的 PAN 积累。然而，E1B-AP5（异质核核糖核蛋白 U 样 1）与 9-nt 核心之外的区域相互作用以刺激 PAN 表达，不与 ORF57 相互作用甚至共定位。与 PABPC1 不同，E1B-AP5 的核分布在病毒裂解感染或 ORF57 过表达时保持不变。总之，这些数据表明，PABPC1 是病毒 ORF57 在病毒裂解感染期间直接上调 PAN 积累的重要细胞靶标，宿主 PABPC1 破坏 ORF57 表达的能力是宿主的一种战略平衡机制。
