Herpes Simplex Virus 1 E3 Ubiquitin Ligase ICP0 Protein Inhibits Tumor Necrosis Factor Alpha-Induced NF-κB Activation by Interacting with p65/RelA and p50/NF-κB1

Self Cite

During viral infection, accumulation of viral proteins can cause stress in the endoplasmic reticulum (ER) and trigger the unfolded protein response (UPR) to restore ER homeostasis. The inositol-requiring enzyme 1 (IRE1)-dependent pathway is the most conserved of the three UPR signal pathways. Upon activation, IRE1 splices out an intron from the unspliced inactive form of X box binding protein 1 [XBP1(u)] mRNA and produces a transcriptionally potent spliced form [XBP1(s)]. Previous studies have reported that the IRE1/XBP1 pathway is inhibited upon herpes simplex virus 1 (HSV-1) infection; however, the underlying molecular mechanism is still elusive. Here, we uncovered a role of the HSV-1 UL41 protein in inhibiting the IRE1/XBP1 signal pathway. Ectopic expression of UL41 decreased the expression of XBP1 and blocked XBP1 splicing activation induced by the ER stress inducer thapsigargin. Wild-type (WT) HSV-1, but not the UL41-null mutant HSV-1 (R2621), decreased XBP1 mRNA induced by thapsigargin. Nevertheless, infection with both WT HSV-1 and R2621 without drug pretreatment could reduce the mRNA and protein levels of XBP1(s), and additional mechanisms might contribute to this inhibition of XBP1(s) during R2621 infection. Taking these findings together, our results reveal XBP1 as a novel target of UL41 and provide insights into the mechanism by which HSV-1 modulates the IRE1/XBP1 pathway.IMPORTANCE During viral infection, viruses hijack the host translation apparatus to produce large amounts of viral proteins, which leads to ER stress. To restore ER homeostasis, cells initiate the UPR to alleviate the effects of ER stress. The IRE1/XBP1 pathway is the most conserved UPR branch, and it activates ER-associated protein degradation (ERAD) to reduce the ER load. The IRE1/XBP1 branch is repressed during HSV-1 infection, but little is known about the underlying molecular mechanism. Our results show for the first time that UL41 suppresses the IRE1/XBP1 signal pathway by reducing the accumulation of XBP1 mRNA, and characterization of the underlying molecular mechanism provides new insight into the modulation of UPR by HSV-1.KEYWORDS HSV-1, UL41, XBP1, UPR T he endoplasmic reticulum (ER) is an important cellular organelle that controls several critical aspects of cellular processes, such as biosynthesis, assembly, glycosylation, folding, and transport of proteins. Under conditions such as lipid metabolism, differentiation of secretory cells, DNA damage, and chemical insult, as well as viral infection, some misfolded or unfolded proteins accumulate in the lumen of the ER and cause ER stress (1). The ER plays a vital role in the process of viral replication. During viral infection, massive amounts of viral proteins are transported into the ER to induce ER stress. To reduce the protein load, cells activate the unfolded protein response (UPR) signal pathways to restore the homeostasis of the ER (2, 3). The goal of the UPR is to

Section: Resultsmentioning

confidence: 99%

Herpes Simplex Virus 1 UL41 Protein Suppresses the IRE1/XBP1 Signal Pathway of the Unfolded Protein Response via Its RNase Activity

Zhang

Jiang

et al. 2017

Self Cite

“…Studies have reported that HSV-1 uses a variety of proteins, mostly tegument proteins, to maintain effective infection (34). ICP0, an E3 ubiquitin ligase, disrupts NF-B activation by abrogating p65 nuclear translocation and promoting p50 to proteasomal degradation (35). US3 hyperphosphorylates p65 to inhibit NF-B activation and inflammatory chemokine expression (36).…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2017

Self Cite

The DNA sensing pathway triggers innate immune responses against DNA virus infection, and NF-B signaling plays a critical role in establishing innate immunity. We report here that the herpes simplex virus 1 (HSV-1) ubiquitinspecific protease (UL36USP), which is a deubiquitinase (DUB), antagonizes NF-B activation, depending on its DUB activity. In this study, ectopically expressed UL36USP blocked promoter activation of beta interferon (IFN-␤) and NF-B induced by cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING). UL36USP restricted NF-B activation mediated by overexpression of STING, TANKbinding kinase 1, IB kinase ␣ (IKK␣), and IKK␤, but not p65. UL36USP was also shown to inhibit IFN-stimulatory DNA-induced IFN-␤ and NF-B activation under conditions of HSV-1 infection. Furthermore, UL36USP was demonstrated to deubiquitinate IB␣ and restrict its degradation and, finally, abrogate NF-B activation. More importantly, the recombinant HSV-1 lacking UL36USP DUB activity, denoted as C40A mutant HSV-1, failed to cleave polyubiquitin chains on IB␣. For the first time, UL36USP was shown to dampen NF-B activation in the DNA sensing signal pathway to evade host antiviral innate immunity.IMPORTANCE It has been reported that double-stranded-DNA-mediated NF-B activation is critical for host antiviral responses. Viruses have established various strategies to evade the innate immune system. The N terminus of the HSV-1 UL36 geneencoded protein contains the DUB domain and is conserved across all herpesviruses. This study demonstrates that UL36USP abrogates NF-B activation by cleaving polyubiquitin chains from IB␣ and therefore restricts proteasome-dependent degradation of IB␣ and that DUB activity is indispensable for this process. This study expands our understanding of the mechanisms utilized by HSV-1 to evade the host antiviral innate immune defense induced by NF-B signaling.KEYWORDS HSV-1, DNA sensor, UL36, NF-B, IB␣ C ells have developed plenty of ways to govern their homeostasis, and the recognition of double-stranded DNA (dsDNA) by DNA sensors is a central host cellular defense against DNA virus infection. Among these DNA sensors, cyclic GMP-AMP synthase (cGAS), which is a nucleotidyltransferase, has been demonstrated to be the predominant cytosolic DNA sensor. Upon binding to DNA fragments, cGAS utilizes GTP and ATP to produce cyclic-GMP-AMP (cGAMP) through its enzymatic activity, and cGAMP activates an endoplasmic reticulum (ER)-resident receptor, stimulator of interferon genes (STING) (1). Activated STING then recruits TANK-binding kinase 1 (TBK1) and traffics from the ER to a perinuclear endosomal compartment, leading to the activation of transcription factors NF-B and interferon (IFN) regulatory factor 3 (IRF3), which induce IFN-␤ production (1-4).

“…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). To determine whether ectopic expression of UL41 or ICP0 could decrease the expression of cGAS, HEK293T cells were cotransfected with cGAS-Flag and UL41-HA or ICP0-Myc plasmids, and then cells were harvested and subjected to Western blot (WB) analysis.…”

Section: Ul41 Inhibits the Ifn Signaling Pathway At The Level Upstreamentioning

confidence: 99%

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

Zheng

2017

Self Cite

140

106

Cyclic GMP-AMP synthase (cGAS) is a key DNA sensor capable of detecting microbial DNA and activating the adaptor protein stimulator of interferon genes (STING), leading to interferon (IFN) production and host antiviral responses. Cells exhibited reduced type I IFN production in response to cytosolic DNA in the absence of cGAS. Although the cGAS/STING-mediated DNA-sensing signal is crucial for host defense against many viruses, especially for DNA viruses, few viral components have been identified to specifically target this signaling pathway. Herpes simplex virus 1 (HSV-1) is a DNA virus that has evolved multiple strategies to evade host immune responses. In the present study, we found that HSV-1 tegument protein UL41 was involved in counteracting the cGAS/STING-mediated DNA-sensing pathway. Our results showed that wild-type (WT) HSV-1 infection could inhibit immunostimulatory DNA-induced activation of the IFN signaling pathway compared with the UL41-null mutant virus (R2621), and ectopic expression of UL41 decreased cGAS/STINGmediated IFN-␤ promoter activation and IFN-␤ production. Further study indicated that UL41 reduced the accumulation of cGAS to abrogate host recognition of viral DNA. In addition, stable knockdown of cGAS facilitated the replication of R2621 but not WT HSV-1. For the first time, HSV-1 UL41 was demonstrated to evade the cGAS/ STING-mediated DNA-sensing pathway by degrading cGAS via its RNase activity.IMPORTANCE HSV-1 is well known for its ability to evade host antiviral responses and establish a lifelong latent infection while triggering reactivation and lytic infection under stress. Currently, whether HSV-1 evades the cytosolic DNA sensing and signaling is still poorly understood. In the present study, we found that tegument protein UL41 targeted the cGAS/STING-mediated cellular DNA-sensing pathway by selectively degrading cGAS mRNA. Knockdown of endogenous cGAS could facilitate the replication of R2621 but not WT HSV-1. Furthermore, UL41 was shown for the first time to act directly on cGAS. Findings in this study could provide new insights into the host-virus interaction and help develop new approaches against HSV-1.KEYWORDS HSV-1, vhs/UL41, cGAS, DNA sensing T he innate immune system is the first line of defense against invading pathogens and is crucial for the subsequent activation of the adaptive immune response. The first step in innate immunity is to detect the invading pathogen through various pathogen recognition receptors (PRRs) which recognize pathogen-associated molecular patterns and trigger the production of type I interferon (IFN) and other antiviral factors (1, 2). Besides Toll-like receptors in the cellular membrane or endosome, Nod-like receptors and the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) in the cytoplasm, there are also several recently discovered cytosolic DNA sensors, such as cyclic GMP-AMP (cGAMP) synthase (cGAS), gamma interferon-inducible protein 16