Herpes Simplex Virus 1 Counteracts Viperin via Its Virion Host Shutoff Protein UL41

Abstract

bThe interferon (IFN)-inducible viperin protein restricts a broad range of viruses. However, whether viperin plays a role during herpes simplex virus 1 (HSV-1) infection is poorly understood. In the present study, it was shown for the first time that wild-type (WT) HSV-1 infection couldn't induce viperin production, and ectopically expressed viperin inhibited the replication of UL41-null HSV-1 but not WT viruses. The underlying molecular mechanism is that UL41 counteracts viperin's antiviral activity by reducing its mRNA accumulation. Viperin is a highly conserved, 361-amino-acid protein. It was first identified as a gamma interferon (IFN-␥)-inducible protein which is directly induced by human cytomegalovirus (HCMV), and its constitutive expression is low (1). The viperin gene (also known as cig5 or RASD2) can also be categorized as an antiviral interferon-stimulated gene (ISG) which limits the replication of many DNA and RNA viruses (1-14). However, whether viperin plays a role during herpes simplex virus 1 (HSV-1) infection is unknown.To investigate whether HSV-1 could induce the expression of viperin, HEK293T cells were infected with wild-type (WT) HSV-1 at different multiplicities of infection (MOI) or with Sendai virus (SeV) (15). Infection with SeV induced a significant amount of viperin; however, infection with a low MOI (0.2) of HSV-1 induced only a trace amount of viperin, and infection with a moderate MOI (2) abrogated the expression of viperin (Fig. 1A).To further explore whether viperin could inhibit the replication of WT HSV-1, HEK293T cells with ectopic expression of viperin-Flag were infected with HSV-1 at an MOI of 0.2. Then cells were harvested at the time points indicated in the figures, and viral plaque assay was performed to determine viral replication (16). As a result, ectopically expressed viperin did not affect the replication of WT HSV-1 (Fig. 1B). The data from Western blot (WB) analysis also showed that viperin did not affect viral protein expression (Fig. 1C). These results demonstrated that ectopic expression of viperin failed to inhibit the replication of WT HSV-1.The aforementioned data led us to hypothesize that at least one of the HSV-1 proteins could counteract the expression of viperin. As a member of the ISGs, viperin was effectively induced by SeV ( Fig. 1) (15). With a high-throughput screen assay of all 84 proteins carried by HSV-1, dual-luciferase reporter gene assays were performed in HEK293T cells cotransfected with viperin-luciferase reporter plasmid and individual HSV-1 protein expression plasmid for 20 h and infected with SeV (17). As a result, ectopically expressed UL41 abrogated the expression of viperin; however, other HSV-1 proteins did not (data not shown). UL41 has been reported to degrade both viral and cellular mRNAs (18)(19)(20)(21)(22)(23)(24)(25)(26). Recently, mRNA of tetherin has been reported to be degraded by UL41 (27). Meanwhile, ICP0, an E3 ubiquitin ligase, promotes degradation of many cellular antiviral proteins, such as IRF3, IRF7, IFI16, and ATRX ...

Herpes Simplex Virus 1 Abrogates the cGAS/STING-Mediated Cytosolic DNA-Sensing Pathway via Its Virion Host Shutoff Protein, UL41

“…In this study, we found that UL41 targeted and reduced cGAS expression by degrading its mRNA. In addition, we and other researchers have demonstrated that UL41 is also involved in HSV-1-mediated immune evasion by targeting several IFN-stimulated genes (ISGs) (17,20,21). Therefore, UL41 is a broad innate immune inhibitor and can block cGAS/STING-mediated IFN signaling at multiple steps.…”

“…Samples were digested with DNase I and subjected to reverse transcription as previously described. The cDNA was used as the template for qRT-PCR to test the levels of IFN-␤ or cGAS mRNA, and 18S rRNA was used as an internal reference as previously described (17).…”

“…The aforementioned data lead us to hypothesize that UL41 might act directly on cGAS. We and others have shown that UL41 selectively degrades both viral and cellular mRNAs containing an AU-rich element (ARE) in its 3= untranslated region (UTR) (17,18,20,26). Meanwhile, ICP0, an HSV-1 immediate early protein, directs the proteasomal degradation of several cellular antiviral proteins (27,28).…”

“…HSV-1 tegument protein UL41, also known as the virion host shutoff protein, is an endoribonuclease with the activity of mRNA-specific RNase and plays a role in HSV-1-mediated evasion of host antiviral responses (16)(17)(18)(19)(20)(21). UL41 triggers selective degradation of host mRNAs to facilitate viral infection.…”

Herpes Simplex Virus 1 Ubiquitin-Specific Protease UL36 Abrogates NF-κB Activation in DNA Sensing Signal Pathway

“…VP16 suppresses NF-B by binding to p65 and blocks IRF3-mediated transactivation by interfering with the formation of the CREB binding protein-IRF3 complex (39). The virion host shutoff protein abrogates the antiviral activity of some IFN-stimulated genes, such as those for tetherin, viperin, and zinc finger antiviral protein, by targeting their mRNA for degradation (40)(41)(42). ␥ 1 34.5 targets TBK1 to prevent its interaction with IRF3 and therefore inhibits IFN production (43).…”