Content area
Full text
Introduction
Varicella-zoster virus (VZV) is the causative agent of chicken pox and herpes zoster, which is also known as shingles. VZV is a member of the human herpesvirus family and has a 125 kb double-stranded DNA genome that encodes 70 open reading frames (ORFs), including 44 essential and 26 non-essential ORFs for viral replication (1–7).
In 1974, chickenpox blister fluid was inoculated into primary human embryonic lung cells, and the VZV Oka strain, parent Oka, was isolated by Takahashi et al (8). Subsequently, a live attenuated Oka vaccine (vOka) was successfully obtained following numerous passages in human embryonic lung fibroblasts. While the pathogenicity of vOka was significantly decreased, its immunogenicity remained. The vOka strain is used in VZV vaccines worldwide and is recommended by the World Health Organization; however, it is still likely to cause delayed infection (9,10).
The incidence of chicken pox has decreased since the chicken pox vaccine (vOka strain) was introduced in 1995 (11–13). However, VZV outbreaks still occasionally occur (14,15), and herpes zoster can cause serious harm to patient health. In particular, VZV remains an important pathogenic factor since the current herpes zoster vaccine only reduces the risk of infection by 50% (16).
Viral proliferation has been analyzed using highly unstable FK506 binding protein (FKBP)12 protein mutants, which rapidly degrade when they are expressed in mammalian cells (17–19). Specifically, recombinant viruses containing the destabilization domain of FKBP tagged to ORFs of interest have been constructed using an FKBP tagged mutant method (20). A synthetic ligand of FKBP, Shield1, can penetrate the cell and stabilize the domain of the FKBP fusion protein. As a result, the recombinant virus can replicate in mammalian cells if Shield1 is added to the mammalian cell culture medium. Conversely, if Shield1 is not added to the mammalian cell culture medium, the FKBP-tagged fusion protein is rapidly degraded, and the recombinant virus does not grow. Accordingly, the FKBP-tagged fusion protein is a powerful genetic tool for studying the role of viral genes and vaccines.
VZV ORF4 encodes transcription factors, whereas VZV ORF48 encodes deoxyribonuclease, which is essential for the formation of infectious virus particles (4). In the present study, recombinant VZV containing FKBP-tagged ORF4 and 48 was constructed. The results of the present study indicated that Shield1 can...