Interaction Between BGLF2 and BBLF1 Is Required for the Efficient Production of Infectious Epstein-Barr Virus Particles.

Chien-Hui Hung,Lee-Wen Chen,Wan-Ju Tsai,Wen-Hung Wang,Tsung-Yu Huang,Pey-Jium Chang,Ya-Fang Chiu,Ying-Ju Lin,Chia-Ching Yang

doi:10.3389/fmicb.2019.03021

Abstract

BGLF2 is a tegument protein of the Epstein–Barr virus (EBV). This study finds that BGLF2 is expressed in the late stage of the EBV lytic cycle. Microscopic investigations reveal that BGLF2 is present in both the nucleus and the cytoplasm and colocalized with BBLF1 and gp350 at juxtanuclear regions in the cytoplasm. This study also finds that the basic KKK69 motif of BGLF2 and acidic DYEE31 motif of BBLF1 are crucial for the interaction between BGLF2 and BBLF1, which is required for the recruitment of BGLF2 to the BBLF1 that is anchored on the trans-Golgi-network (TGN). In addition, BGLF2 in a density gradient is co-sedimented with un-enveloped capsids, revealing that BGLF2 associates with the EBV capsid before the final envelopment. The knockout of BGLF2 expression is demonstrated to reduce the numbers of infectious virions that are released into the culture medium, but they do not affect the expression of lytic proteins and viral DNA replication. The production of infectious viral particles by a BGLF2-knockout mutant can be rescued by exogenously expressed BGLF2 but only partially rescued by BGLF2-3KA, which is a mutant with reduced ability to interact with BBLF1 but does not affect its ability to activate the MAPK pathway and the expression of the EBV lytic proteins, suggesting that the interaction of BGLF2 with BBLF1 is important to the efficient production of infectious viral particles during the maturation. The results of this study improve our understanding of how BGLF2 promotes EBV viral production.

Highlights

Epstein–Barr virus (EBV) causes infectious mononucleosis and is associated with Burkitt’s lymphoma, nasopharyngeal carcinoma, Hodgkin’s lymphoma, and gastric cancer (Epstein and Barr, 1964; Diehl et al, 1968; Klein et al, 1970; Takada, 2000)
The expression of BBLF1 and BGLF2 was unobserved when the cells were treated with phosphonoacetic acid (PAA), which is an EBV DNA polymerase inhibitor (Figures 1A,B), at the time of lytic induction, indicating that the expression of BBLF1 and BGLF2 depends on lytic DNA replication and that BBLF1 and BGLF2 are EBV late proteins
This study shows that BGLF2, a tegument protein (Johannsen et al, 2004), associates with the EBV capsid before final envelopment, is recruited to TGN via the interaction with BBLF, and is important for the efficient production of infectious virion

Summary

Introduction

Epstein–Barr virus (EBV) causes infectious mononucleosis and is associated with Burkitt’s lymphoma, nasopharyngeal carcinoma, Hodgkin’s lymphoma, and gastric cancer (Epstein and Barr, 1964; Diehl et al, 1968; Klein et al, 1970; Takada, 2000). The assembled capsids are recruited to the nuclear egress complex (NEC) at the nuclear inner membrane and bud into the perinuclear space to acquire an envelope during primary envelopment. This envelope is removed by fusion with the outer nuclear membrane, releasing the capsid into the cytoplasm (Farina et al, 2005; Granato et al, 2008). The enveloped virion exits the cell by exocytosis (Mettenleiter, 2004; Guo et al, 2010)

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