Identification of a lytic-cycle Epstein-Barr virus gene product that can regulate PKR activation
Identification of a lytic-cycle Epstein-Barr virus gene product that can regulate PKR activation
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DOI：
10.1128/jvi.77.1.228-236.2003
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发表时间：
2003-01-01
影响因子：
5.4
通讯作者：
Mohr, I
中科院分区：
文献类型：
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作者：
Poppers, J;Mulvey, M;Mohr, I
EB病毒(EBV)SM蛋白是病毒基因表达的转录后调节因子。像许多由疱疹病毒编码的反式激活剂一样，SM将主要未剪接的病毒mRNA货物从细胞核运输到胞浆，然后在胞浆中进行翻译。这一活性可能涉及与1型单纯疱疹病毒(HSV-1)ICP27基因产物同源的蛋白质区域，这是发现的第一个此类调节子成员。然而，SM也包含一个富含精氨酸和脯氨酸残基的重复片段，这对于它对RNA运输和剪接的影响是必不可少的。SM的这一部分由RXP三联体重复组成，与US11的羧基末端结构域同源，US11是一种由HSV-1编码的双链RNA(DsRNA)结合蛋白，可抑制细胞内PKR激酶的激活。为了评价SM调节PKR的内在能力，我们表达和纯化了几种SM蛋白衍生物，并用多种生化方法检测了它们的活性。全长SM蛋白与dsRNA结合，物理上与PKR结合，并阻止PKR激活。去除37个残基的RXP结构域显著损害了所有这些活性。此外，SM RXP结构域本身足以抑制PKR的激活并与该激酶相互作用。相对于US11，SM RXP片段与dsRNA结合的亲和力降低，并且对单链竞争对手多核苷酸的反应不同。因此，SM代表了第一个在裂解周期中表达的可以阻止PKR激活的EBV基因产物。此外，RXP重复片段似乎是一个保守的疱疹病毒基序，能够与dsRNA结合并调节PKR激酶的激活，PKR激酶是控制翻译和细胞抗病毒反应的重要分子。
The Epstein-Barr virus (EBV) SM protein is a posttranscriptional regulator of viral gene expression. Like many transactivators encoded by herpesviruses, SM transports predominantly unspliced viral mRNA cargo from the nucleus to the cytosol, where it is subsequently translated. This activity likely involves a region of the protein that has homology to the herpes simplex virus type 1 (HSV-1) ICP27 gene product, the first member of this class of regulators to be discovered. However, SM also contains a repetitive segment rich in arginine and proline residues that is dispensable for its effects on RNA transport and splicing. This portion of SM, comprised of RXP triplet repeats, shows homology to the carboxyl-terminal domain of Us11, a double-stranded RNA (dsRNA) binding protein encoded by HSV-1 that inhibits activation of the cellular PKR kinase. To evaluate the intrinsic ability of SM to regulate PKR, we expressed and purified several SM protein derivatives and examined their activity in a variety of biochemical assays. The full-length SM protein bound dsRNA, associated physically with PKR, and prevented PKR activation. Removal of the 37-residue RXP domain significantly compromised all of these activities. Furthermore, the SM RXP domain was itself sufficient to inhibit PKR activation and interact with the kinase. Relative to its Us11 counterpart, the SM RXP segment bound dsRNA with reduced affinity and responded differently to single-stranded competitor polynucleotides. Thus, SM represents the first EBV gene product expressed during the lytic cycle that can prevent PKR activation. In addition, the RXP repeat segment appears to be a conserved herpesvirus motif capable of associating with dsRNA and modulating activation of the PKR kinase, a molecule important for the control of translation and the cellular antiviral response.