DNA Virus Infection Research Articles

Patients with Central Nervous System Lymphoma Undergoing Thiotepa, Busulfan, and Cyclophosphamide-Conditioned Autologous Stem Cell Transplantation Are at a Higher Risk for DNA Virus Infections Than Patients with Systemic Non-Hodgkin Lymphoma Receiving Traditional Conditioning

Background: Consolidative high-dose therapy and autologous stem cell transplantation (ASCT) with thiotepa, busulfan, and cyclophosphamide (TBC)-conditioning results in highly favorable outcomes in patients with central nervous system lymphoma (CNSL), but it is met with regimen-related toxicity. In a recent analysis, we noted a higher than expected incidence of DNA virus reactivations and several cases of serious viral organ disease (Scordo et al., BBMT 2017). We aimed to compare the incidence of DNA virus infections between patients with CNSL undergoing TBC-conditioned ASCT and those with systemic non-Hodgkin lymphoma (NHL) undergoing carmustine, etoposide, cytarabine, and melphalan (BEAM)-conditioned ASCT. We hypothesized that patients receiving TBC are at a higher risk for viral infections, and may require unique post-ASCT surveillance and follow-up.Methods: We retrospectively evaluated adults with chemosensitive CNSL undergoing TBC-conditioned ASCT and those with systemic, chemosensitive diffuse large B-cell lymphoma undergoing BEAM-conditioned ASCT between 2013 and 2016. We recorded all positive DNA virus reactivations infections by serum polymerase chain reaction (PCR) from the start of conditioning until 6 months post-ASCT, and then assessed for evidence of clinically relevant viral infection. We used a combined viral infection endpoint that included: cytomegalovirus (CMV), adenovirus (ADV), Epstein-Barr virus (EBV), and human herpesvirus-6 (HHV-6). The cumulative incidences (CI) of combined viral PCR reactivation and clinically relevant viral infection were compared by the log rank test. Cox proportional hazard analysis was used to compare the risk of viral infection between both groups. Variables with p-values of < 0.2 in the univariate analysis were included in the multivariate analysis.Results: We evaluated 67 patients that underwent BEAM-conditioned and 54 patients that underwent TBC-conditioned ASCT. Baseline patient characteristics including age, gender, disease status, pre-ASCT absolute lymphocyte count (ALC), day +30 ALC, and steroid use during the first 30 days post-ASCT (prednisone 40 mg equivalent or higher) were similar between groups, and are shown in Table 1. There were 6 viral reactivations (5 HHV-6 and 1 CMV) among the BEAM patients (CI 9.1%), and 19 (1 ADV, 5 CMV, 13 HHV-6) among TBC patients (CI 35.2%), p=0.0003, as shown in Figure 1. No BEAM patients had a clinically significant viral infection, while there were 7 clinically significant viral infections (2 CMV, 1 ADV, 4 HHV-6) among TBC patients, p=0.0003, as shown in Figure 2. Among all patients in the univariate analysis, receiving TBC conditioning was the only characteristic that was associated with a higher risk of viral reactivation/infection, hazard-ratio (HR) 4.78 (1.91-12.0), p<0.001. In the multivariate analysis, receiving TBC conditioning was associated with an increased risk of viral reactivation [HR 5.43 (2.1-13.8), p<0.001], and advanced age [HR 0.97, (0.94-0.99), p=0.03] was associated with a slightly reduced risk of viral reactivation as shown in Table 2.Conclusions: Patients with CNSL undergoing TBC-conditioned ASCT are at an increased risk for DNA virus reactivation and clinically relevant DNA virus infections when compared to patients receiving BEAM. This may reflect the higher myeloablative intensity of TBC compared to BEAM, and possibly inherent differences in immune function in patients with CNSL compared to systemic NHL. These data highlight the need to implement early post-ASCT viral serum PCR monitoring for patients undergoing TBC-conditioned ASCT, with the goal of pre-emptive treatment of clinically relevant infections. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Low-Density Lipoprotein Receptor Suppresses the Endogenous Cholesterol Synthesis Pathway To Oppose Gammaherpesvirus Replication in Primary Macrophages.

Gammaherpesviruses are ubiquitous pathogens that establish lifelong infections in >95% of adults worldwide and are associated with several cancers. We have shown that endogenous cholesterol synthesis supports gammaherpesvirus replication. However, the role of exogenous cholesterol exchange and signaling during infection remains poorly understood. Extracellular cholesterol is carried in the serum by several lipoproteins, including low-density lipoproteins (LDL). The LDL receptor (LDL-R) mediates the endocytosis of these cholesterol-rich LDL particles into the cell, thereby supplying the cell with cholesterol. We found that LDL-R expression attenuates gammaherpesvirus replication during the early stages of the replication cycle, as evident by increased viral gene expression in LDL-R-/- primary macrophages. This was not observed in primary fibroblasts, indicating that the antiviral effects of LDL-R are cell type specific. Increased viral gene expression in LDL-R-/- primary macrophages was due to increased activity of the endogenous cholesterol synthesis pathway. Intriguingly, despite type I interferon-driven increase in LDL-R mRNA levels in infected macrophages, protein levels of LDL-R continually decreased over the single cycle of viral replication. Thus, our study has uncovered an intriguing tug of war between the LDL-R-driven antiviral effect on cholesterol metabolism and the viral targeting of the LDL-R protein. IMPORTANCE LDL-R is a cell surface receptor that mediates the endocytosis of cholesterol-rich low-density lipoproteins, allowing cells to acquire cholesterol exogenously. Several RNA viruses usurp LDL-R function to facilitate replication; however, the role of LDL-R in DNA virus infection remains unknown. Gammaherpesviruses are double-stranded DNA viruses that are associated with several cancers. Here, we show that LDL-R attenuates gammaherpesvirus replication in primary macrophages by decreasing endogenous cholesterol synthesis activity, a pathway known to support gammaherpesvirus replication. In response, LDL-R protein levels are decreased in infected cells to mitigate the antiviral effects, revealing an intriguing tug of war between the virus and the host.

Inducible ATP1B1 Upregulates Antiviral Innate Immune Responses by the Ubiquitination of TRAF3 and TRAF6.

The antiviral innate immune responses are crucial steps during host defense and must be strictly regulated, but the molecular mechanisms of control remain unclear. In this study, we report increased expression of human ATPase Na+/K+ transporting subunit β 1(ATP1B1) after DNA and RNA virus infections. We found that the expression of ATP1B1 can inhibit viral replication and increase the levels of IFNs, IFN-stimulated genes, and inflammatory cytokines. Knockdown of ATP1B1 by specific short hairpin RNA had the opposite effects. Upon viral infection, ATP1B1 was induced, interacted with TRAF3 and TRAF6, and potentiated the ubiquitination of these proteins, leading to increased phosphorylation of downstream molecules, including TGF-β-activated kinase 1 (TAK1) and TANK-binding kinase 1 (TBK1). These results reveal a previously unrecognized role of ATP1B1 in antiviral innate immunity and suggest a novel mechanism for the induction of IFNs and proinflammatory cytokines during viral infection.

Clinical impact of multiple DNA virus infections in nondepleted haploidentical and unrelated allogeneic hematopoietic stem cell transplantation.

Few studies have compared the clinical impact of multiple DNA-virus infections in haploidentical hematopoietic stem cell transplantation (haplo-HSCT) with posttransplant cyclophosphamide (PTCy) and unrelated donor allogeneic hematopoietic stem cell transplantation (UD-HSCT) with thymoglobulin, so we retrospectively analyzed viral infections in the first 6mo posttransplant in these scenarios. Fifty-nine patients underwent to haplo-HSCT, and 68 to UD-HSCT. The most frequent infection was cytomegalovirus (CMV) (76.3% in haplo-HSCT and 69.1% in UD-HSCT) (P=.878) and in the group of patients with CMV reactivation, maximal CMV viral load over 2500UI/ml correlated with worse overall survival-hazard ratio (HR) 1.93 (95% confidence interval [CI] 1.04-3.59) P=.03. The cumulative incidence of multiple DNA virus within 180d of posttransplant was 78.7% for one virus and 28.4% for two or more viruses with no difference regarding the type of transplant. Viral infections, age, and acute graft versus host disease (GVHD) grades II-IV were risk factors for worse overall survival in multivariate analyses: one virus HR 2.53 (95% CI 1.03-6.17) P=.04, two or more viruses HR 3.51 (95% CI 1.37-9) P<.01, age HR 1.03 (95% CI 1.02-1.05) P<.01 and acute GVHD II-IV HR 1.97 (95% CI 1.13-3.43) P=.01. Also, age over 50y HR 4.25 (95% CI 2.01-8.97) P<.001, second CMV reactivation or having both CMV and BK polyomavirus (BKV) HR 2.65 (95% CI 1.26-5.56) P=.01 and acute GVHD grades II-IV HR 2.23 (95% CI 1.12-4.43) P=.022 were risk factors for nonrelapse mortality in the multivariate analyses. In conclusion, multiple DNA-virus infections are frequent in both haplo-HSCT and UD-HSCT and a risk factor for worse overall survival.

DNA-PK senses DNA virus infection in human cells

Abstract The type I interferon (IFN-I) response to virus infection is initiated by the detection of nucleic acids by intracellular pattern recognition receptors (PRRs). The sensing of DNA viruses by PRRs is carried out by a number of DNA-binding PRRs that signal via the adaptor protein stimulator of interferon genes (STING) to drive IFN-I transcription. We previously described the role of DNA-dependent protein kinase (DNA-PK) as a viral DNA sensor in murine fibroblasts. In this study we show that DNA-PK is essential for the host response to DNA and DNA viruses in human fibroblasts. In the absensce of the catalytic subunit of the DNA-PK heterotrimer, DNA-PKcs, fibroblasts are deficient in their ability to activate a IFN-I response to DNA. DNA-PKcs is activated rapidly following exogenous DNA transfection or DNA virus infection and is required for signalling via STING and the kinase TBK-1 to the transcription factor interferon regulator factor 3 (IRF-3). Most wild-type DNA viruses combat intracellular DNA PRRs using immunomodulatory proteins encoded in their genomes and are effective at blocking IFN-I responses in infected cells. Here we make use of attenutated vaccina and herpes simplex 1 viruses that are lacking the immunomodulators that target DNA sesining mechanisms. We show that DNA-PKcs can sense these viruses and is required for triggering the IFN-I response in infected cells. These data cement the role of DNA-PK in the sensing of DNA virus infections in human cells.

The leaked mitochondrial C1QBP inhibits activation of the DNA sensor cGAS

Abstract Cytosolic DNA released from microbial pathogens triggers the activation of DNA sensor cyclic GMP-AMP synthase (cGAS) which catalyzes the synthesis of the cyclic GMP-AMP (cGAMP), a second messenger that triggers a signaling cascade leading to type I interferon (IFN) production. The cGAS cannot discriminate the origin and sequence of dsDNA; thus, it is also activated by self-DNA leaked from the nucleus or the mitochondria. Recent studies have shown that DNA virus infection triggers mitochondrial stress, leading to the release of mtDNA to the cytosol and activation of cGAS; however, the regulatory mechanism of the mtDNA-mediated cGAS activation is not well elucidated. To seek potential regulators for cGAS, we used proteomics to map the protein interactome of cGAS in macrophages and found C1QBP as a novel binding partner of cGAS. C1QBP is predominantly localized in the mitochondria matrix and leaked to the cytosol upon DNA virus infection. C1QBP binds to the NTase domain of cGAS and inhibits the cGAS activity in cells and in vitro. Overexpression of the cytosolic form of C1QBP inhibited the cytosolic DNA-induced immune response and facilitated HSV-1 infection. By contrast, deficiency of C1QBP leads to elevated innate immune responses and impaired HSV-1 infection. Taken together, our study suggests that C1QBP is a cGAS inhibitor hidden in the mitochondria.

UNC93B1 curbs cytosolic DNA signaling by promoting STING degradation.

UNC93B1 is a trafficking chaperone of endosomal Toll-like receptors (TLRs) and plays an essential role in the TLR-mediated innate signaling. However, whether it is also involved in other innate immune sensing or cellular pathways remains largely unexplored. Here we investigated the role of UNC93B1 in cytosolic DNA-triggered cGAS-STING signaling in mouse and human cell lines. We showed that while UNC93B1 deficiency blunts the signal transduction by TLR3, it augments innate immune responses to cytosolic DNA stimulation and DNA virus infection. Mechanistic study reveals a distinct action of UNC93B1 upon STING, but not other parts along the cGAS-STING-TBK1 axis, through regulating the protein level of STING at both resting and cytosolic DNA-stimulated conditions. UNC93B1 can directly interact and traffic along with STING, and the disruption of this interaction causes accumulation of STING that subsequently leads to augmented signaling responses upon its activation. These findings reveal a new function of UNC93B1 in negatively regulating STING-mediated signaling responses.

Loss of Mitochondrial Protease CLPP Activates Type I IFN Responses through the Mitochondrial DNA-cGAS-STING Signaling Axis.

Caseinolytic mitochondrial matrix peptidase proteolytic subunit (CLPP) is a serine protease that degrades damaged or misfolded mitochondrial proteins. CLPP-null mice exhibit growth retardation, deafness, and sterility, resembling human Perrault syndrome, but also display immune system alterations. However, the molecular mechanisms and signaling pathways underlying immunological changes in CLPP-null mice remain unclear. In this study, we report the steady-state activation of type I IFN signaling and antiviral gene expression in CLPP-deficient cells and tissues, resulting in marked resistance to RNA and DNA virus infection. Depletion of the cyclic GMP-AMP (cGAS)-stimulator of IFN genes (STING) DNA sensing pathway reduces steady-state IFN-I signaling and abrogates the broad antiviral phenotype of CLPP-null cells. Moreover, we report that CLPP deficiency leads to mitochondrial DNA (mtDNA) instability and packaging alterations. Pharmacological and genetic approaches to deplete mtDNA or inhibit cytosolic release markedly reduce antiviral gene expression, implicating mtDNA stress as the driver of IFN-I signaling in CLPP-null mice. Our work places the cGAS-STING-IFN-I innate immune pathway downstream of CLPP and may have implications for understanding Perrault syndrome and other human diseases involving CLPP dysregulation.

Quantitative conversion of biomass in giant DNA virus infection

Bioconversion of organic materials is the foundation of many applications in chemical engineering, microbiology and biochemistry. Herein, we introduce a new methodology to quantitatively determine conversion of biomass in viral infections while simultaneously imaging morphological changes of the host cell. As proof of concept, the viral replication of an unidentified giant DNA virus and the cellular response of an amoebal host are studied using soft X-ray microscopy, titration dilution measurements and thermal gravimetric analysis. We find that virions produced inside the cell are visible from 18 h post infection and their numbers increase gradually to a burst size of 280–660 virions. Due to the large size of the virion and its strong X-ray absorption contrast, we estimate that the burst size corresponds to a conversion of 6–12% of carbonaceous biomass from amoebal host to virus. The occurrence of virion production correlates with the appearance of a possible viral factory and morphological changes in the phagosomes and contractile vacuole complex of the amoeba, whereas the nucleus and nucleolus appear unaffected throughout most of the replication cycle.

Inhibition of the DNA-Sensing pathway by pseudorabies virus UL24 protein via degradation of interferon regulatory factor 7

The cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway plays an important role in the innate immune response by the production of type I interferon (IFN) against DNA virus infection. However, viruses have evolved a variety of strategies to antagonize the host antiviral response to facilitate infection and replication. Pseudorabies virus (PRV), a DNA virus that causes great economic losses to the swine industry, encodes approximate 70 proteins, including some that are involved in evasion of host immunity. However, the mechanism employed by PRV to regulate type I IFN remains unclear. The results of the present study showed that the transcription levels of type I IFN were significantly upregulated by a UL24-deleted PRV strain. Furthermore, IFN-β activation induced by poly(dA:dT) or stimulated by cGAS-STING was inhibited by UL24 overexpression in PK15 cells. Co-immunoprecipitation analysis demonstrated that UL24 interacts with and can degrade interferon regulatory factor 7 (IRF7) through the proteasome pathway in a dose-dependent manner. Together, these results showed that PRV UL24 interacted with IRF7 via the proteasome pathway and antagonized cGAS-STING-mediated activation of IFN-β.

Tripartite Motif 22 (TRIM22) protein restricts herpes simplex virus 1 by epigenetic silencing of viral immediate-early genes.

Intrinsic resistance is a crucial line of defense against virus infections, and members of the Tripartite Ring Interaction Motif (TRIM) family of proteins are major players in this system, such as cytoplasmic TRIM5α or nuclear promyelocytic leukemia (PML/TRIM19) protein. Previous reports on the antiviral function of another TRIM protein, TRIM22, emphasized its innate immune role as a Type I and Type II interferon-stimulated gene against RNA viruses. This study shows that TRIM22 has an additional intrinsic role against DNA viruses. Here, we report that TRIM22 is a novel restriction factor of HSV-1 and limits ICP0-null virus replication by increasing histone occupancy and heterochromatin, thereby reducing immediate-early viral gene expression. The corresponding wild-type equivalent of the virus evades the TRIM22-specific restriction by a mechanism independent of ICP0-mediated degradation. We also demonstrate that TRIM22 inhibits other DNA viruses, including representative members of the β- and γ- herpesviruses. Allelic variants in TRIM22 showed different degrees of anti-herpesviral activity; thus, TRIM22 genetic variability may contribute to the varying susceptibility to HSV-1 infection in humans. Collectively, these results argue that TRIM22 is a novel restriction factor and expand the list of restriction factors functioning in the infected cell nucleus to counter DNA virus infection.

Chicken cGAS Senses Fowlpox Virus Infection and Regulates Macrophage Effector Functions.

The anti-viral immune response is dependent on the ability of infected cells to sense foreign nucleic acids. In multiple species, the pattern recognition receptor (PRR) cyclic GMP-AMP synthase (cGAS) senses viral DNA as an essential component of the innate response. cGAS initiates a range of signaling outputs that are dependent on generation of the second messenger cGAMP that binds to the adaptor protein stimulator of interferon genes (STING). Here we show that in chicken macrophages, the cGAS/STING pathway is essential not only for the production of type-I interferons in response to intracellular DNA stimulation, but also for regulation of macrophage effector functions including the expression of MHC-II and co-stimulatory molecules. In the context of fowlpox, an avian DNA virus infection, the cGAS/STING pathway was found to be responsible for type-I interferon production and MHC-II transcription. The sensing of fowlpox virus DNA is therefore essential for mounting an anti-viral response in chicken cells and for regulation of a specific set of macrophage effector functions.

91 - Scheduled Donor-Derived Viral Specific T-Cells for Prophylaxis Against Double Stranded DNA Viral Infection after Pediatric Allogeneic Hematopoietic Stem Cell Transplantation

91 - Scheduled Donor-Derived Viral Specific T-Cells for Prophylaxis Against Double Stranded DNA Viral Infection after Pediatric Allogeneic Hematopoietic Stem Cell Transplantation

In vitro complex formation of human PYRIN domain-only protein 3 prevented by self-oligomerization of ASC PYD domain.

The formation of inflammasome complexes contributes inactivation of inflammatory caspases viz caspase 1, which is generally considered essential for the innate response. Three proteins constituted this inflammasome complex, such as Nod-like receptors (NLRP or AIM2), ASC possessing caspase-recruiting domain, and caspase-1. The ASC proteins comprise two domains, the N-terminal PYD domain responsible for the interaction of various proteins, including PYD only protein 3 (POP3), and the CARD domain for association with other proteins. The PYRIN Domain-Only Protein POP3 negatively regulates responses to DNA virus infection by preventing the ALR inflammasome formation. POP3 directly interacts with ASC, therefore inhibiting ASC recruitment to AIM2-like receptors (ALRs). In the current study, we designed various constructs of the PYRIN Domain-Only Protein 3 (POP3) and ASC PYD domain to find the best-overexpressed construct for biochemical characterization as well as our complex studies. We cloned, purified, and characterized the PYD domain of pyrin only protein 3 and ASC PYD domain under physiological conditions. Our in vitro study clearly shows that the ASC PYD domain of corresponding amino acid 1–96 aa with ease self-oligomerization in physiological buffer conditions, and complex formation of POP3 PYD (1–83 aa) was inhibited by ASC PYD domain. Besides, we purified the PYD of POP3 protein in low and high salt conditions and different pH values for their biochemical characterization. Our results showed that POP3 formed a dimer under normal physiological conditions and was stable under normal buffer conditions; however, the purification in extremely low pH (pH5.0) conditions shows unstable behavior, the high salt conditions (500 mM NaCl) influence the protein aggregation. SDS PAGE arbitrated the homogeneity of the PYD domain of pyrin only protein 3 and ASC PYD domain of corresponding amino acids 1–83 and 1–96, respectively. Furthermore, our native PAGE shows the PYD domain of pyrin; only protein 3 did not form a complex with ASC PYD domain because of oligomerization mediated by the PYD domain.

Agent-based modeling reveals benefits of heterogeneous and stochastic cell populations during cGAS-mediated IFNβ production.

The cGAS pathway is a component of the innate immune system responsible for the detection of pathogenic DNA and upregulation of interferon beta (IFNβ). Experimental evidence shows that IFNβ signaling occurs in highly heterogeneous cells and is stochastic in nature; however, the benefits of these attributes remain unclear. To investigate how stochasticity and heterogeneity affect IFNβ production, an agent-based model is developed to simulate both DNA transfection and viral infection. We show that heterogeneity can enhance IFNβ responses during infection. Furthermore, by varying the degree of IFNβ stochasticity, we find that only a percentage of cells (20-30%) need to respond during infection. Going beyond this range provides no additional protection against cell death or reduction of viral load. Overall, these simulations suggest that heterogeneity and stochasticity are important for moderating immune potency while minimizing cell death during infection. Model repository is available at: https://github.com/ImmuSystems-Lab/AgentBasedModel-cGASPathway. Supplementary data are available at Bioinformatics online.

Immune response to cytosolic DNA via intercellular receptor modulation in oral keratinocytes and fibroblasts.

Double-strand (ds) DNA-enveloped viruses can cause oral infection. Our aim is to investigate whether oral mucosal cells participate in immune response against cytosolic dsDNA invasion. We examined the response to transfected herpes simplex virus (HSV) dsDNA via intracellular receptors in oral keratinocytes (RT7) and fibroblasts (GT1), and the effect of TNF-α on those responses. Transfected dsDNA increased CXCL10 expression via NF-κB activation in both cell types, while those responses were inhibited by knockdown of RIG-I, an RNA sensor. Although IFI16, a DNA sensor, was expressed in the nuclei of both types, its knockdown decreased transfected dsDNA-induced CXCL10 expression in GT1 but not RT7 cells. IFI16 in GT1 cells was translocated into cytoplasm from nuclei, which was attributed to immune response to cytosolic dsDNA. TNF-α enhanced transfected dsDNA-induced CXCL10, and knockdown of IFI16 decreased TNF-α and dsDNA-driven CXCL10 expression in both RT7 and GT1 cells. Finally, the combination of TNF-α and transfected dsDNA resulted in translocation of IFI16 from nuclei to cytoplasm in RT7 cells. RIG-I and IFI16 in oral mucosal cells may play important roles in host immune response against DNA viral infection, while TNF-α contributes to development of an antiviral system via those intracellular receptors.

A Critical Role for STING Signaling in Limiting Pathogenesis of Chikungunya Virus.

The stimulator of interferon gene (STING) pathway controls both DNA and RNA virus infection. STING is essential for induction of innate immune responses during DNA virus infection, while its mechanism against RNA virus remains largely elusive. We show that STING signaling is crucial for restricting chikungunya virus infection and arthritis pathogenesis. Sting-deficient mice (Stinggt/gt) had elevated viremia throughout the viremic stage and viral burden in feet transiently, with a normal type I IFN response. Stinggt/gt mice presented much greater foot swelling, joint damage, and immune cell infiltration than wild-type mice. Intriguingly, expression of interferon-γ and Cxcl10 was continuously upregulated by approximately 7 to 10-fold and further elevated in Stinggt/gt mice synchronously with arthritis progression. However, expression of chemoattractants for and activators of neutrophils, Cxcl5, Cxcl7, and Cxcr2 was suppressed in Stinggt/gt joints. These results demonstrate that STING deficiency leads to an aberrant chemokine response that promotes pathogenesis of CHIKV arthritis.

RNF115 plays dual roles in innate antiviral responses by catalyzing distinct ubiquitination of MAVS and MITA

MAVS and MITA are essential adaptor proteins mediating innate antiviral immune responses against RNA and DNA viruses, respectively. Here we show that RNF115 plays dual roles in response to RNA or DNA virus infections by catalyzing distinct types of ubiquitination of MAVS and MITA at different phases of viral infection. RNF115 constitutively interacts with and induces K48-linked ubiquitination and proteasomal degradation of homeostatic MAVS in uninfected cells, whereas associates with and catalyzes K63-linked ubiquitination of MITA after HSV-1 infection. Consistently, the protein levels of MAVS are substantially increased in Rnf115−/− organs or cells without viral infection, and HSV-1-induced aggregation of MITA is impaired in Rnf115−/− cells compared to the wild-type counterparts. Consequently, the Rnf115−/− mice exhibit hypo- and hyper-sensitivity to EMCV and HSV-1 infection, respectively. These findings highlight dual regulation of cellular antiviral responses by RNF115-mediated ubiquitination of MAVS and MITA and contribute to our understanding of innate immune signaling.

MYSM1 Represses Innate Immunity and Autoimmunity through Suppressing the cGAS-STING Pathway

The immune system is not only required for preventing threats exerted by pathogens but also essential for developing immune tolerance to avoid tissue damage. This study identifies a distinct mechanism by which MYSM1 suppresses innate immunity and autoimmunity. The expression of MYSM1 is induced upon DNA virus infection and by intracellular DNA stimulation. MYSM1 subsequently interacts with STING and cleaves STING K63-linked ubiquitination to suppress cGAS-STING signaling. Notably, Mysm1-deficient mice exhibit a hyper-inflammatory response, acute tissue damage, and high mortality upon virus infection. Moreover, in the PBMCs of patients with systemic lupus erythematosus (SLE), MYSM1 production decreases, while type I interferons and pro-inflammatory cytokine expressions increase. Importantly, MYSM1 treatment represses the production of IFNs and pro-inflammatory cytokines in the PBMCs of SLE patients. Thus, MYSM1 is a critical repressor of innate immunity and autoimmunity and is thus a potential therapeutic agent for infectious, inflammatory, and autoimmune diseases.

KAT5 acetylates cGAS to promote innate immune response to DNA virus

The DNA sensor cGMP-AMP synthase (cGAS) senses cytosolic microbial or self DNA to initiate a MITA/STING-dependent innate immune response. cGAS is regulated by various posttranslational modifications at its C-terminal catalytic domain. Whether and how its N-terminal unstructured domain is regulated by posttranslational modifications remain unknown. We identified the acetyltransferase KAT5 as a positive regulator of cGAS-mediated innate immune signaling. Overexpression of KAT5 potentiated viral-DNA-triggered transcription of downstream antiviral genes, whereas a KAT5 deficiency had the opposite effects. Mice with inactivated Kat5 exhibited lower levels of serum cytokines in response to DNA virus infection, higher viral titers in the brains, and more susceptibility to DNA-virus-induced death. Mechanistically, KAT5 catalyzed acetylation of cGAS at multiple lysine residues in its N-terminal domain, which promoted its DNA-binding ability. Our findings suggest that KAT5-mediated cGAS acetylation at its N terminus is important for efficient innate immune response to DNA virus.