Infected cell protein 0 (ICP0) of herpes simplex virus 1 (HSV-1) is a key regulator in both lytic and latent infections. In lytic infection, an important early event is the colocalization of ICP0 to nuclear domain 10 (ND10), the discrete nuclear bodies that impose restrictions on viral expression. ICP0 contains an E3 ubiquitin ligase that degrades promyelocytic leukemia protein (PML) and Sp100, two major components of ND10, and disperses ND10 to alleviate repression. We previously reported that the association between ICP0 and ND10 is a dynamic process that includes three steps: adhesion, fusion, and retention. ICP0 residues 245 to 474, defined as ND10 entry signal (ND10-ES), is a region required for the fusion step. Without ND10-ES, ICP0 adheres at the ND10 surface but fails to enter. In the present study, we focus on characterizing ND10-ES. Here we report the following.
IMPORTANCE
ND10 nuclear bodies are part of the cell-intrinsic antiviral defenses that restrict viral gene expression upon virus infection. As a countermeasure, infected cell protein 0 (ICP0) of herpes simplex virus 1 (HSV-1) localizes to ND10s, degrades the ND10 organizer, and disperses ND10 components in order to alleviate repression. We studied the ICP0-ND10 association to delineate elements important for this dynamic interaction and to understand its role in viral replication and host defense. In this work, we show that ICP0 contains three redundant segments to ensure an effective mergence of ICP0 with ND10 nuclear bodies. This is the first study to systematically investigate ICP0 elements that are important for ICP0-ND10 fusion.
Herpes simplex virus 1 (HSV-1) infected cell protein 0 (ICP0) is a multifunctional immediate early protein that plays a key role in both lytic and latent infections. The protein is essential at a low multiplicity of infection (MOI) in cultured cells (1). Its main functions are to counteract cell-intrinsic and innate defenses by targeting saturable cellular restrictive factors and consequently to enhance viral gene expression (1).The 775-amino-acid ICP0 contains a RING (really interesting new gene) type E3 ubiquitin ligase in its second exon (2, 3), which ubiquitinates various cellular proteins for proteasomal degradation. Known ICP0 substrates include promyelocytic leukemia protein (PML) (4), speckled protein Sp100 (4), DNA-dependent protein kinase (DNA-PK) (5), centromeric protein A (CENP-A) (6), and interferon (IFN)-inducible protein 16 (IFI16) (7). Some of these ICP0 substrates are restrictive for HSV-1 infection, inasmuch as small interfering RNA (siRNA) knockdown of PML, Sp100, or IFI16, individually or in combination, enhances viral replication in the absence of ICP0 (8, 9).A second tactic of ICP0 to overcome antiviral defenses is to regulate a diverse array of cell pathways via protein-protein interactions. For example, ICP0 interacts with corepressor of RE1-silencing transcription factor (CoREST). This interaction leads to the dissociation of histone deacetylases (HDACs) 1 and 2 from the REST/CoREST...