Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
J Gen Virol. 2011 Mar;92(Pt 3):699-705. doi: 10.1099/vir.0.027573-0. Epub 2010 Nov 17.
The ubiquitin-proteasome system plays a central role in the degradation of intracellular proteins and is often required for efficient virus infection. Homologues of ubiquitin are found in all group I nucleopolyhedroviruses (NPVs), but their roles in NPV infection are still unclear. This study found that the specific proteasome inhibitor MG-132 markedly reduced budded virus (BV) production and polyhedrin expression in Bombyx mori NPV (BmNPV)-infected BmN-4 cells. Western blot analysis revealed that treatment of cells with MG-132 resulted in delayed and/or dysregulated viral gene product expression. Application of MG-132 significantly reduced BV production when applied up to 12 h post-infection (p.i.), whereas suppression of polyhedrin expression was almost abolished when applied after 6 h p.i. These results suggested that proteosomal degradation of viral and/or host proteins is required at an early stage of infection for efficient polyhedrin expression. To examine further the possible roles of ubiquitin signalling in BmNPV infection, the baculoviral ubiquitin gene (v-ubi) was deleted from the BmNPV genome. Deletion of v-ubi affected neither BV production nor polyhedrin expression. Furthermore, Western blots also showed that v-UBI was not required for degradation of IE2, which is known as a target viral protein of the ubiquitin-proteasome system.
泛素-蛋白酶体系统在细胞内蛋白质的降解中发挥着核心作用，通常是病毒有效感染所必需的。泛素的同源物存在于所有 I 组核多角体病毒（NPV）中，但它们在 NPV 感染中的作用仍不清楚。本研究发现，特异性蛋白酶体抑制剂 MG-132 显著降低了家蚕核型多角体病毒（BmNPV）感染的 BmN-4 细胞中的出芽病毒（BV）产量和多角体蛋白的表达。Western blot 分析显示，用 MG-132 处理细胞导致病毒基因产物表达的延迟和/或失调。MG-132 的应用显著降低了感染后 12 小时内的 BV 产量，而在感染后 6 小时应用时，对多角体蛋白表达的抑制几乎被消除。这些结果表明，病毒和/或宿主蛋白的蛋白酶体降解在感染的早期阶段对于高效多角体蛋白表达是必需的。为了进一步研究泛素信号在 BmNPV 感染中的可能作用，从 BmNPV 基因组中删除了杆状病毒泛素基因（v-ubi）。v-ubi 的缺失既不影响 BV 的产生，也不影响多角体蛋白的表达。此外，Western blot 还表明 v-UBI 也不参与已知是泛素-蛋白酶体系统靶病毒蛋白的 IE2 的降解。
