Multifunctional viral protein γ34.5 manipulates nucleolar protein NOP53 for optimal viral replication of HSV-1

Abstract

To ensure efficient virus replication, herpes simplex virus type 1 (HSV-1) encodes several viral proteins to counter host defense response upon infection. Among these proteins, the multifunctional viral protein γ34.5 crucially interferes with or disrupts several antiviral pathways at multiple levels. The current study shows that γ34.5 utilizes nucleolar protein NOP53 to facilitate the dephosphorylation of eukaryotic initiation factor eIF2α for efficient viral translation. Our study shows that: (1) ectopic expression of NOP53 greatly increases the intracellular and extracellular viral yields of HSV-1 (wild strain F) in type I interferon-deficient Vero cells, and more subtly promotes viral replication of γ34.5 deletion mutant virus HSV-1/Δγ34.5. (2) NOP53 is migrated from nuclei in HSV-1/F infected cells, but is redistributed incompletely after infection by either HSV-1/Δγ34.5 or ICP4 deletion mutant virus HSV-1/d120 (replication inadequate). Ectopic expression of γ34.5, consequently, induces cytoplasmic translocation of NOP53 in response to HSV-1/Δγ34.5 infection. (3) Increase of NOP53, in two forms of transient transfection and in vitro expression, attenuates the phosphorylation level of eIF2α in HSV-1/F infected cells, but fails to affect eIF2α phosphorylation induced by HSV-1/Δγ34.5 infection. (4) Knockdown of NOP53, which impairs the specific interaction between γ34.5 and protein phosphatase PP1α, disrupts the ability of γ34.5 to maintain HSV-1 virulence. (5) NOP53 knockdown also significantly reduces tissue damage and decreases viral yield in livers of HSV-1 infected mice. Our findings expand the understanding of the underlying mechanism by which viral protein γ34.5 induces NOP53 redistribution; cytoplasmic NOP53 facilitates γ34.5 recruitment of PP1α to dephosphorylate eIF2α, for optimal viral replication. This paper also demonstrates that blocking the specific interaction between γ34.5 and PP1α would be a useful approach for the development of antiviral agents.

Selective regulation in ribosome biogenesis and protein production for efficient viral translation

“…NOP53 (GLTSCR2/PICT-1), for example, shares homology with the yeast 60S ribosomal protein Nop53p, which acts as an essential ribosome biogenesis factor (Sydorskyy et al 2005 ; Thomson et al 2005 ). A previous study by the present author showed that NOP53, expressed as a set of discrete globular structures within the nucleolus, is migrated to the cytoplasm upon infection by herpes simplex virus 1 (HSV-1) (Meng et al 2018 ). Furthermore, the cytoplasmic translocation of NOP53 is required for efficient viral replication, which occurs via depression of the activity of innate immune receptor RIG-I and decrease of the phosphorylation level of eIF2α to facilitate the production of viral proteins without affecting global protein synthesis (Meng et al 2018 , 2019 ).…”

“…A previous study by the present author showed that NOP53, expressed as a set of discrete globular structures within the nucleolus, is migrated to the cytoplasm upon infection by herpes simplex virus 1 (HSV-1) (Meng et al 2018 ). Furthermore, the cytoplasmic translocation of NOP53 is required for efficient viral replication, which occurs via depression of the activity of innate immune receptor RIG-I and decrease of the phosphorylation level of eIF2α to facilitate the production of viral proteins without affecting global protein synthesis (Meng et al 2018 , 2019 ). Similarly, both nucleolar proteins of ribosomal RNA processing 1 homolog B (RRP1B) and nucleolin are involved in ribosomal biogenesis (Chamousset et al 2010 ).…”

Cytoplasmic Translocation of Nucleolar Protein NOP53 Promotes Viral Replication by Suppressing Host Defense

“…All cells were cultured at 37 °C in a humidified incubator with 5% CO 2 . Herpes simplex virus 1 (HSV-1) strain F, mutant viruses d120 [ 26 ] and Δγ34.5 [ 25 ], vesicular stomatitis virus (VSV) strain Indiana [ 24 ], canine distemper virus (CDV) strain MD77 [ 27 ], enterovirus A71 (EV-A71) strain BC08 [ 28 ], pseudorabies virus (PRV) strain Fa [ 29 ], foot-and-mouth disease virus (FMDV) strain O [ 30 ], and porcine epidemic diarrhea virus (PEDV) strain CV777 [ 31 ] were reproduced in Vero, HEK293T, Vero, RD, Vero, PK-15, and Vero cells, respectively, according to the reports indicated above.…”

“…Cytoplasmic NOP53 negatively regulates RIG-I via K63-linked ubiquitination, leading to inactivation of RIG-I and blockage of IFN-β induction [ 24 ]. We also found that NOP53 migrates from the nucleus of HSV-1 infected cells and that ectopic expression of viral protein γ34.5 facilitates the redistribution of NOP53 in response to infection by γ34.5 deleted HSV-1 (Δγ34.5) [ 25 ].…”

Targeting nuclear proteins for control of viral replication

“…K63-ubiquitination of TRAF6 and IKKe is required for activation of MAPK and NF-jB in TLR-mediated cytokine response. HSV-1 c34.5 protein induces cytoplasmic translocation of the nucleolar ribosome biogenesis factor NOP53 (also the glioma tumor suppressor candidate region gene 2 protein, GLTSCR2) to facilitates the interaction of c34.5 with protein phosphatase 1a (PP1a) leading to dephosphorylation of eIF2a and synthesis of viral proteins for viral replication (Meng et al 2018). VSV infection induces cytoplasmic translocation of NOP53 to deactivate RIG-I and block type I IFN induction (Wang et al 2016).…”