Department of Microbiology, College of Natural Sciences, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu, South Korea.
Virus Res. 2010 Sep;152(1-2):50-8. doi: 10.1016/j.virusres.2010.06.002. Epub 2010 Jun 9.
Viruses are known to develop the ability to manipulate a variety of host cell signal transduction pathways in order to facilitate successful virus survival. However, to date, little is known about the intracellular signaling mechanisms involved in porcine reproductive and respiratory syndrome virus (PRRSV) replication. The extracellular signal-regulated kinase (ERK) pathway that transduces signals to modulate a wide range of cellular functions has been shown to regulate a number of viral infections. The present study therefore aimed to determine the role of this pathway during PRRSV infection in porcine alveolar macrophages. We found that the PRRSV infection induces early robust but transient activation of ERK1/2 by 6h postinfection and thereafter the progressive decrease of its phosphorylation. However, the maximal induction of phosphorylated ERK1/2 seen at 6h postinfection was inconsistent with synthesis of a viral nucleocapsid protein that was first evident by 12h postinfection. These results indicate that ERK1/2 activation is mediated independently of viral gene expression during PRRSV replication. Notably, infection with UV-irradiated, inactivated virus, which is capable of receptor binding and internalization but prevents viral gene synthesis, was sufficient to trigger ERK1/2 phosphorylation, suggesting that the viral entry process may be responsible for early ERK activation. Treatment of cells with U0126, a selective ERK1/2 inhibitor, markedly diminished PRRSV infection and its inhibitory effect on PRRSV replication was exerted at the early stage in virus infection. Furthermore, inhibition of ERK activation resulted in significant suppression of subgenomic RNA transcription, viral protein translation, and progeny virus production. Taken together, the findings in this study suggest that the ERK signaling pathway plays an important role in postentry steps of the PRRSV replication cycle and beneficially contributes to viral infection.
病毒被认为能够操纵各种宿主细胞信号转导途径，以促进病毒的存活。然而，迄今为止，人们对猪繁殖与呼吸综合征病毒（PRRSV）复制所涉及的细胞内信号机制知之甚少。细胞外信号调节激酶（ERK）途径可传递信号，调节广泛的细胞功能，已被证明可调节多种病毒感染。因此，本研究旨在确定该途径在 PRRSV 感染猪肺泡巨噬细胞中的作用。我们发现，PRRSV 感染在感染后 6 小时诱导 ERK1/2 的早期强烈但短暂的激活，随后其磷酸化逐渐减少。然而，感染后 6 小时观察到的磷酸化 ERK1/2 的最大诱导与病毒核衣壳蛋白的合成不一致，该蛋白在感染后 12 小时首次出现。这些结果表明，在 PRRSV 复制过程中，ERK1/2 的激活是独立于病毒基因表达介导的。值得注意的是，感染经紫外线照射失活的病毒足以触发 ERK1/2 磷酸化，尽管这种病毒能够与受体结合并内化，但不能合成病毒基因，这表明病毒进入过程可能是早期 ERK 激活的原因。用 U0126（一种选择性 ERK1/2 抑制剂）处理细胞可显著降低 PRRSV 感染，并且对 PRRSV 复制的抑制作用在病毒感染的早期阶段发挥作用。此外，抑制 ERK 激活可显著抑制亚基因组 RNA 转录、病毒蛋白翻译和子代病毒产生。总之，本研究的结果表明，ERK 信号通路在 PRRSV 复制周期的进入后步骤中发挥重要作用，并有助于病毒感染。
