Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC, Canada V6T 1Z4.
J Virol. 2011 May;85(10):4863-74. doi: 10.1128/JVI.01999-10. Epub 2011 Mar 2.
Parvoviruses are small, nonenveloped, single-stranded DNA viruses which replicate in the nucleus of the host cell. We have previously found that early during infection the parvovirus minute virus of mice (MVM) causes small, transient disruptions of the nuclear envelope (NE). We have now investigated the mechanism used by MVM to disrupt the NE. Here we show that the viral phospholipase A2, the only known enzymatic domain on the parvovirus capsid, is not involved in causing NE disruption. Instead, the virus utilizes host cell caspases, which are proteases involved in causing NE breakdown during apoptosis, to facilitate these nuclear membrane disruptions. Studies with pharmacological inhibitors indicate that caspase-3 in particular is involved. A caspase-3 inhibitor prevents nuclear lamin cleavage and NE disruption in MVM-infected mouse fibroblast cells and reduces nuclear entry of MVM capsids and viral gene expression. Caspase-3 is, however, not activated above basal levels in MVM-infected cells, and other aspects of apoptosis are not triggered during early MVM infection. Instead, basally active caspase-3 is relocalized to the nuclei of infected cells. We propose that NE disruption involving caspases plays a role in (i) parvovirus entry into the nucleus and (ii) alteration of the compartmentalization of host proteins in a way that is favorable for the virus.
细小病毒是一种小型、无包膜、单链 DNA 病毒，在宿主细胞的核内复制。我们之前发现，在感染早期，小鼠微小病毒（MVM）会导致核膜（NE）的短暂、微小的破坏。现在我们研究了 MVM 破坏 NE 所使用的机制。我们发现病毒的磷脂酶 A2，即衣壳上唯一已知的酶结构域，不参与导致 NE 破坏。相反，病毒利用宿主细胞半胱天冬酶（参与凋亡过程中导致 NE 破裂的蛋白酶）来促进这些核膜破坏。用药理学抑制剂进行的研究表明，半胱天冬酶-3 特别参与其中。半胱天冬酶-3 抑制剂可防止 MVM 感染的鼠成纤维细胞中的核层粘连蛋白裂解和 NE 破坏，并减少 MVM 衣壳和病毒基因表达的核内进入。然而，在 MVM 感染的细胞中，半胱天冬酶-3 没有被激活到基础水平以上，并且在早期 MVM 感染期间不会触发凋亡的其他方面。相反，基础活性的半胱天冬酶-3 被重新定位到感染细胞的核内。我们提出，涉及半胱天冬酶的 NE 破坏在（i）细小病毒进入细胞核和（ii）改变宿主蛋白的区室化方面发挥作用，这对病毒有利。
