Baculovirus infection induces disruption of the nuclear lamina

Xiaomei Zhang,Kai Yang,Denghui Wei,Meijin Yuan,Wenbi Wu,Kaiyan Xu

doi:10.1038/s41598-017-08437-5

Abstract

Baculovirus nucleocapsids egress from the nucleus primarily via budding at the nuclear membrane. The nuclear lamina underlying the nuclear membrane represents a substantial barrier to nuclear egress. Whether the nuclear lamina undergoes disruption during baculovirus infection remains unknown. In this report, we generated a clonal cell line, Sf9-L, that stably expresses GFP-tagged Drosophila lamin B. GFP autofluorescence colocalized with immunofluorescent anti-lamin B at the nuclear rim of Sf9-L cells, indicating GFP-lamin B was incorporated into the nuclear lamina. Meanwhile, virus was able to replicate normally in Sf9-L cells. Next, we investigated alterations to the nuclear lamina during baculovirus infection in Sf9-L cells. A portion of GFP-lamin B localized diffusely at the nuclear rim, and some GFP-lamin B was redistributed within the nucleus during the late phase of infection, suggesting the nuclear lamina was partially disrupted. Immunoelectron microscopy revealed associations between GFP-lamin B and the edges of the electron-dense stromal mattes of the virogenic stroma, intranuclear microvesicles, and ODV envelopes and nucleocapsids within the nucleus, indicating the release of some GFP-lamin B from the nuclear lamina. Additionally, GFP-lamin B phosphorylation increased upon infection. Based on these data, baculovirus infection induced lamin B phosphorylation and disruption of the nuclear lamina.

Highlights

The nuclear envelope (NE) consists of the inner nuclear membrane (INM) and outer nuclear membrane (ONM), which are separated by the perinuclear space and spanned by nuclear pore complexes (NPCs)[1]
To investigate whether any alterations to the nuclear lamina occur during baculovirus infection, we sought to generate an Sf21-AE clonal isolate 9 (Sf9) cell line stably expressing GFPtagged lamin B to analyze the nuclear lamina with respect to its major component, lamin B, in Autographa californica multiple nucleopolyhedrovirus (AcMNPV)-infected Sf9 cells
Confocal microscopy revealed a nuclear rim fluorescence pattern in stably expressing GFP-lamin B (Sf9-L) cells, and green fluorescent protein (GFP) autofluorescence colocalized with the immunofluorescence signal generated by the antibody ADL67, which recognized both native lamin B and chimeric GFP-lamin B (Fig. 1A)

Summary

Introduction

The nuclear envelope (NE) consists of the inner nuclear membrane (INM) and outer nuclear membrane (ONM), which are separated by the perinuclear space and spanned by nuclear pore complexes (NPCs)[1]. Herpesvirus nucleocapsids must cross the NE to access the final maturation compartment[10, 11] Because these nucleocapsids are too large to traverse nuclear pores or the crossover spacing of the nuclear lamina, herpesviruses dissolve the nuclear lamina through a kinase-mediated phosphorylation mechanism and bud at the INM for nuclear egress[4, 9]. Both viral and cellular kinases are involved in the phosphorylation of lamins, which mediate partial dismantling of the nuclear lamina. We provide the first evidence of baculovirus infection-induced lamin B phosphorylation and disruption of the nuclear lamina

Methods

Results

Conclusion