DDX4 enhances antiviral activity of type I interferon by disrupting interaction of USP7/SOCS1 and promoting degradation of SOCS1.

DEAD-box helicase (DDX) family members play differential roles in regulating innate antiviral immune response. However, the physiological roles played by DDX4 in antiviral innate immunity remain unclear. In this study, we unveiled that DDX4 acts as a positive regulatory molecule of Type-I interferon (IFN-I)-mediated antiviral activity. Our findings demonstrate that IFN-I upregulates DDX4 protein levels, and subsequently, overexpression of DDX4 enhances the IFN-I-mediated signaling pathway. This creates a positive feedback loop that amplifies the antiviral response. DDX4 was found to bind with deubiquitinase ubiquitin-specific protease 7 (USP7), leading to the disruption of the interaction between USP7 and suppressor of cytokine signaling 1 (SOCS1) and the subsequent degradation of SOCS1. This process enhances the antiviral function of IFN-I. Our findings provide new insights into the regulatory role of DDX4 in the IFN-I response.IMPORTANCEDDX4, identified as a putative RNA helicase that modulates RNA secondary structure through RNA binding, is primarily acknowledged for its role in regulating mRNA translation within the germline. Nevertheless, the extent of DDX4's involvement in the antiviral innate immune response remains largely unexplored. This study presents evidence of a previously unrecognized positive feedback loop between DDX4 and the antiviral response, suggesting that disruption of this loop may serve as a novel mechanism for viral evasion. Furthermore, our findings elucidate a positive regulatory mechanism by which the DDX4/USP7/SOCS1 axis mediates the antiviral activity of Type-I interferon, which provides new insight into strategies for improving the efficacy of IFN-based antiviral therapy.

Mn-doped carbon-Al2SiO5 fibers enable catalytic ozonation for wastewater treatment: Interface modulation and mass transfer enhancement.

Heterogeneous catalytic ozonation is an efficient approach to remove hazardous and refractory organic contaminants in wastewater. It is crucial to design an ozone catalyst with high catalytic activity, high mass transfer and facile separation properties. Herein, easily separable aluminosilicate (Al2SiO5) fibers were developed as carriers and after interface modulation, Mn-doped carbon-Al2SiO5 (Mn-CAS) fibrous catalysts were proposed for catalytic ozonation. The growth of carbon shells on Al2SiO5 fiber surface and the introduction of metal Mn provided abundant Lewis acid sites to catalyze ozone. The Mn-CAS fiber/O3 system exhibited superior reactivity to degrade oxalic acid with a rate constant of 0.034 min-1, which was about 19 times as high as Al2SiO5/O3. For coal gasification wastewater treatment, Mn-CAS fibers also demonstrated high catalytic activity and stability and the COD removal was over 56%. Computational fluid dynamic simulations proved the high mass transfer properties of fibrous catalysts. Hydroxyl radicals (•OH) were identified as the predominant active species for organic degradation. Particularly, the catalytic pathways of O3 to •OH on Mn-O4 sites were revealed by theoretical calculations. This work provides a novel fibrous catalyst with high reactivity and mass transfer as well as easy separation characteristics for catalytic ozonation and wastewater purification.

Enhanced Anaerobic Wastewater Treatment by a Binary Electroactive Material: Pseudocapacitance/Conductance-Mediated Microbial Interspecies Electron Transfer.

Anaerobic digestion (AD) is a promising method to treat organic matter. However, AD performance was limited by the inefficient electron transfer and metabolism imbalance between acid-producing bacteria and methanogens. In this study, a novel binary electroactive material (Fe3O4@biochar) with pseudocapacitance (1.4 F/g) and conductance (10.2 µS/cm) was exploited to store-release electrons as well as enhance the direct electron transfer between acid-producing bacteria and methanogens during the AD process. The mechanism of pseudocapacitance/conductance on mediating interspecies electron transfer was deeply studied at each stage of AD. In the hydrolysis acidification stage, the pseudocapacitance of Fe3O4@biochar acting as electron acceptors proceeded NADH/NAD+ transformation of bacteria to promote ATP synthesis by 21% which supported energy for organics decomposition. In the methanogenesis stage, the conductance of Fe3O4@biochar helped the microbes establish direct interspecies electron transfer (DIET) to increase the coenzyme F420 content by 66% and then improve methane production by 13%. In the complete AD experiment, electrons generated from acid-producing bacteria were rapidly transported to methanogens via conductors. Excess electrons were buffered by the pseudocapacitor and then gradually released to methanogens which alleviated the drastic drop in pH. These findings provided a strategy to enhance the electron transfer in anaerobic treatment as well as guided the design of electroactive materials.

Revisit the Role of Salinity in Heterogeneous Catalytic Ozonation: The Trade-Off between Reaction Inhibition and Mass Transfer Enhancement.

Heterogeneous catalytic ozonation (HCO) is an effective technology for advanced wastewater treatment, while the influence of coexisting salts remains unclear and controversial. Here, we systematically explored the influence of NaCl salinity on the reaction and mass transfer of HCO through lab experiments, kinetic simulation, and computational fluid dynamics modeling, and proposed that the trade-off between reaction inhibition and mass transfer enhancement would affect the pollutants degradation pattern under varying salinity. The increase of NaCl salinity decreased ozone solubility and accelerated the futile consumption of ozone and hydroxyl radicals (•OH), and the maximum •OH concentration under 50 g/L salinity was only 23% of that without salinity. However, the increase of NaCl salinity also significantly reduced the ozone bubble size and enhanced the interphase and intraliquid mass transfer, with the volumetric mass transfer coefficient being 130% higher than that without salinity. The trade-off between reaction inhibition and mass transfer enhancement shifted under different pH values and aerator pore sizes, and the oxalate degradation pattern would change correspondingly. Besides, the trade-off was also identified for Na2SO4 salinity. These results emphasized the dual influence of salinity and offered a new theoretical perspective on the role of salinity in the HCO process.

A spatiotemporally controlled recombinant cccDNA mouse model for studying HBV and developing drugs against the virus.

Covalently closed circular (ccc) DNA is the template for hepatitis B virus (HBV) replication. The lack of small animal models for characterizing chronic HBV infection has hampered research progress in HBV pathogenesis and drug development. Here, we generated a spatiotemporally controlled recombinant cccDNA (rcccDNA) mouse model by combining Cre/loxP-mediated DNA recombination with the liver-specific "Tet-on/Cre" system. The mouse model harbors three transgenes: a single copy of the HBV genome (integrated at the Rosa26 locus, RHBV), H11-albumin-rtTA (spatiotemporal conditional module), and (tetO)7-Cre (tetracycline response element), and is named as RHTC mouse. By supplying the RHTC mice with doxycycline (DOX)-containing drinking water for two days, the animals generate rcccDNA in hepatocytes, and the rcccDNA supports active HBV gene expression and can maintain HBV viremia persistence for over 60 weeks. Persistent HBV gene expression induces intrahepatic inflammation, fibrosis, and dysplastic pathology, which closely mirrors the disease progression in clinical patients. Bepirovirsen, an antisense oligonucleotide (ASO) targeting all HBV RNA species, showed dose-dependent antiviral effects in the RHTC mouse model. The spatiotemporally controlled rcccDNA mouse is convenient and reliable, providing versatile small animal model for studying cccDNA-centric HBV biology as well as evaluating antiviral therapeutics.

Effect of interventional embolization based on absolute ethanol for peripheral arteriovenous malformations.

BACKGROUND: Interventional embolization schedules based on absolute ethanol are usually used for peripheral arteriovenous malformations (PAVMs), and clinicians often choose the scheme according to the classification. AIM: To evaluate different interventional embolization schedules based on absolute ethanol for PAVMs. METHODS: A retrospective study was performed of 165 patients with PAVMs treated with interventional embolization based on absolute ethanol in Henan Provincial People's Hospital from January 2018 to May 2021. PAVMs were classified as type II (n = 67), type III (n = 81) and type IV (n = 17) according to the Yakes classification system, including 123 maxillofacial, 13 trunk and 29 limbs. Effectiveness of embolization was based on PAVM devascularization on angiography: 100% (total), 90%~99% (near-total), 70%~90% (substantial), 30%~70% (partial) and 0%~30% (failure). RESULTS: PAVMs were classified as type II (n = 67), type III (n = 81) and type IV (n = 17) according to the Yakes classification system, including 123 maxillofacial (74.55%), 13 trunk (7.88%) and 29 limbs (17.58%). There are statistical differences in the angiographic outcomes among different Yakes classification and between different methods (P < 0.05), and there was a statistical difference in the failure rates among different Yakes classification (P < 0.05). CONCLUSIONS: PAVMs occur maxillofacial usually, and Type II can achieve better effect by spring coil and absolute ethanol, while Type III and Type IV have no ideal effect by Pingyangmycin + iodized oil + PVA + absolute ethanol and spring coil + absolute ethanol, respectively. Both the two happen to be complications, and wound accounts the highest.

Vitamin C promotes ACE2 degradation and protects against SARS-CoV-2 infection.

ACE2 is a major receptor for cellular entry of SARS-CoV-2. Despite advances in targeting ACE2 to inhibit SARS-CoV-2 binding, strategies to flexibly and sufficiently reduce ACE2 levels for the prevention of SARS-CoV-2 infection have not been explored. Here, we reveal vitamin C (VitC) administration as a potent strategy to prevent SARS-CoV-2 infection. VitC reduces ACE2 protein levels in a dose-dependent manner, while even a partial reduction in ACE2 levels can greatly inhibit SARS-CoV-2 infection. Further studies reveal that USP50 is a crucial regulator of ACE2 levels. VitC blocks the USP50-ACE2 interaction, thus promoting K48-linked polyubiquitination of ACE2 at Lys788 and subsequent degradation of ACE2 without affecting its transcriptional expression. Importantly, VitC administration reduces host ACE2 levels and greatly blocks SARS-CoV-2 infection in mice. This study reveals that ACE2 protein levels are down-regulated by an essential nutrient, VitC, thereby enhancing protection against infection of SARS-CoV-2 and its variants.

Single-Atom Fe-N4 Sites for Catalytic Ozonation to Selectively Induce a Nonradical Pathway toward Wastewater Purification.

Nonradical oxidation has been determined to be a promising pathway for the degradation of organic pollutants in heterogeneous catalytic ozonation (HCO). However, the bottlenecks are the rational design of catalysts to selectively induce nonradicals and the interpretation of detailed nonradical generation mechanisms. Herein, we propose a new HCO process based on single-atom iron catalysts, in which Fe-N4 sites anchored on the carbon skeleton exhibited outstanding catalytic ozonation activity and stability for the degradation of oxalic acid (OA) and p-hydroxybenzoic acid (pHBA) as well as the advanced treatment of a landfill leachate secondary effluent. Unlike traditional radical oxidation, nonradical pathways based on surface-adsorbed atomic oxygen (*Oad) and singlet oxygen (1O2) were identified. A substrate-dependent behavior was also observed. OA was adsorbed on the catalyst surface and mainly degraded by *Oad, while pHBA was mostly removed by O3 and 1O2 in the bulk solution. Density functional theory calculations and molecular dynamics simulations revealed that one terminal oxygen atom of ozone preferred bonding with the central iron atom of Fe-N4, subsequently inducing the cleavage of the O-O bond near the catalyst surface to produce *Oad and 1O2. These findings highlight the structural design of an ozone catalyst and an atomic-level understanding of the nonradical HCO process.

Efficient catalytic ozonation via Mn-loaded C-SiO2 Framework for advanced wastewater treatment: Reactive oxygen species evolution and catalytic mechanism.

Heterogeneous catalytic ozonation (HCO) is attractive for water decontamination and catalyst is a core element. However, it is difficult to maintain high efficiency and stability of catalysts under stern conditions. In this study, we proposed Mn-loaded C-SiO2-Framework (Mn-CSF) which contained stable silica core and robust carbon shell for efficient catalytic ozonation. The pseudo-first-order kinetic rate constant for oxalic acid removal of Mn-CSF catalytic ozonation was 160 % and 875 % higher than those of Mn-SiO2 and pristine CSF, respectively. Mn-CSF was also proven effective in gasification wastewater treatment, where the COD was decreased to 46 mg·L-1, 37 % lower than that of Mn-SiO2. These results indicated that the graphitization carbon layer and Mn significantly enhanced the activity of the catalyst. Furthermore, a fulvic-like component and a protein-like component were recognized through 3D-EEM in coal gasification wastewater. It was proven that Mn-CSF catalytic ozonation exhibited higher fulvic-like component and protein-like component removal compared with ozonation. Moreover, O2- and 1O2 were identified to be responsible for organic degradation in this research. Sufficient external specific surface area and porous structure were important for complex wastewater treatment. Specifically, external specific surface area could enhance the degradation of macromolecular organics while porous structures were vital for smaller molecular pollutant removal. The results highlighted that Mn-CSF was a promising HCO catalyst for advanced wastewater treatment, and this study provided evidence of relationship between structure of catalysts and HCO efficiency.

Nonproductive Hepatitis B Virus Covalently Closed Circular DNA Generates HBx-Related Transcripts from the HBx/Enhancer I Region and Acquires Reactivation by Superinfection in Single Cells.

Hepatitis B virus (HBV) infection remains a public health problem worldwide. Persistent HBV infection relies on active transcription of the covalently closed circular DNA (cccDNA) in hepatocytes, which is less understood at the single-cell level. In this study, we isolated primary human hepatocytes from liver-humanized FRG mice infected with HBV and examined cccDNA transcripts in single cells based on 5' end sequencing. Our 5' transcriptome sequencing (RNA-seq) analysis unambiguously assigns different viral transcripts with overlapping 3' sequences and quantitatively measures viral transcripts for structural genes (3.5 kb, 2.4 kb, and 2.1 kb) and the nonstructural X gene (0.7 kb and related) in single cells. We found that an infected cell either can generate all viral transcripts, signifying active transcription, or presents only transcripts from the X gene and its associated enhancer I domain and no structural gene transcripts. Results from cell infection assays with recombinant HBV show that nonproductive transcription of cccDNA can be activated by incoming virus through superinfection. Moreover, upon HBV infection, cccDNA apparently can be transcribed in the absence of HBx and produces HBx, needed for productive transcription of other viral genes. These results shed new light on cccDNA transcription at the single-cell level and provide insights useful for improving the treatment strategy against chronic HBV infection. IMPORTANCE Hepatitis B virus (HBV) infection can be effectively suppressed but rarely cured by available drugs. Chronic HBV infection is based on persistence of covalently closed circular DNA (cccDNA) and continuous infection and reinfection with HBV in the liver. Understanding transcriptional regulation of cccDNA will help to achieve permanent transcriptional silencing, i.e., functional cure of HBV. In our study, we found that an infected cell either can generate all viral transcripts, signifying active transcription, or presents only transcripts from the X gene and its associated enhancer I domain and no structural gene transcripts. The nonproductive transcription of cccDNA can be activated by incoming virus through superinfection. Upon an infection, cccDNA apparently can be transcribed in the absence of HBx to produce HBx, necessary for subsequent transcription of other HBV genes. Our studies shed new light on the mechanism of HBV infection and may have implications for a functional cure regimen for HBV.

Menthone inhibits type-I interferon signaling by promoting Tyk2 ubiquitination to relieve local inflammation of rheumatoid arthritis.

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease. RA development is mediated by the abnormal activation of multiple signaling pathways. Recent studies have revealed that type-I interferon (IFN-I) signaling plays an essential role in the occurrence and development of RA. However, how to target IFN-I signaling to develop anti-rheumatoid arthritis drugs remains largely unexplored. Here, our study showed that IFN-I signaling was over-activated in articular synovial cells from collagen II-induced arthritis (CIA) mice. Interestingly, we found that a small molecule compound, menthone, strongly inhibited the activation of the IFN-I signaling pathway. Further studies revealed that menthone promoted K48-linked polyubiquitination of Tyk2, thus lowering the protein level and stability of Tyk2. Importantly, menthone administration in the local articulus of CIA mice significantly attenuated the local inflammation in CIA mice. This study could promote our understanding of rheumatoid arthritis, and also suggests a potential strategy to develop anti-RA drugs.

E3 ubiquitin ligase MID1 ubiquitinates and degrades type-I interferon receptor 2.

Type I interferon (IFN-I) is a common biological molecule used for the treatment of viral diseases. However, the clinical antiviral efficacy of IFN-I needs to be greatly improved. In this study, IFN-I receptor 2 (IFNAR2) was revealed to undergo degradation at the protein level in cells treated with IFN-I for long periods of time. Further studies found a physical interaction between the E3 ubiquitin ligase midline-1 (MID1) and IFNAR2. As a consequence, MID1 induced both K48- and K63-linked polyubiquitination of IFNAR2, which promoted IFNAR2 protein degradation in a lysosome-dependent manner. Conversely, knockdown of MID1 largely restricted IFN-I-induced degradation of IFNAR2. Importantly, MID1 regulated the strength of IFN-I signalling and IFN-I-induced antiviral activity. These findings reveal a regulatory mechanism of IFNAR2 ubiquitination and protein stability in IFN-I signalling, which could provide a potential target for improving the antiviral efficacy of IFN-I.

Depression compromises antiviral innate immunity via the AVP-AHI1-Tyk2 axis.

Depression is a serious public-health issue. Recent reports have suggested higher susceptibility to viral infections in depressive patients. However, how depression affects antiviral innate immune signaling remains unknown. Here, we revealed a reduction in expression of Abelson helper integration site 1 (AHI1) in the peripheral blood mononuclear cells (PBMCs) and macrophages from the patients with major depressive disorder (MDD), which leads to attenuated antiviral immune response. We found that depression-related arginine vasopressin (AVP) induces reduction of AHI1 in macrophages. Further studies demonstrated that AHI1 is a critical stabilizer of basal type-I-interferon (IFN-I) signaling. Mechanistically, AHI1 recruits OTUD1 to deubiquitinate and stabilize Tyk2, while AHI1 reduction downregulates Tyk2 and IFN-I signaling activity in macrophages from both MDD patients and depression model mice. Interestingly, we identified a clinical analgesic meptazinol that effectively stimulates AHI1 expression, thus enhancing IFN-I antiviral defense in depression model mice. Our study promotes the understanding of the signaling mechanisms of depression-mediated antiviral immune dysfunction, and reveals meptazinol as an enhancer of antiviral innate immunity in depressive patients.

Hydrogen peroxide and peroxymonosulfate intensifying Fe-doped NiC-Al2O3-framework-based catalytic ozonation for advanced treatment of landfill leachate: Performance and mechanisms.

The biotreated effluent of landfill leachate still contains numerous refractory organic contaminants, which poses potential threats to human health and ecosystems. Influenced by landfill ages and other factors, the concentration of organic matter varies. Heterogeneous catalytic ozonation (HCO) is a promising technology for advanced wastewater treatment. Aiming to achieve the up-to-standard discharge of low-concentration landfill leachate (COD ≈ 108 mg·L-1) and improve the biodegradability of high-concentration landfill leachate (COD ≈ 1720 mg·L-1), the active component Fe was incorporated into a firm Ni-induced C-Al2O3-framework (NiCAF) composite support to synthesize a Fe-NiCAF catalyst for efficient catalytic ozonation. When the Fe-NiCAF dosage was 4 g·L-1, the gas flow rate was 0.5 L·min-1, and the ozone concentration was 20.0 mg·L-1, the COD of low-concentration landfill leachate effluent decreased to 43 mg·L-1, and the COD removal rate constant of low-concentration landfill leachate was 154% higher than that of pure ozone. For high-concentration landfill leachate with the BOD5/COD of 0.058, the COD removal efficiency in Fe-NiCAF/O3 increased from 39% to 57% compared with ozonation, and the effluent BOD5/COD increased to 0.282. Furthermore, the addition of hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) can further enhance the treatment performance of Fe-NiCAF/O3 process and different strengthening mechanisms were revealed. The results indicated that surface hydroxyls on the Fe-NiCAF catalyst surface were the main catalytic sites for ozone, and hydroxyl radical (•OH) and singlet oxygen (1O2) were identified as the main reactive oxygen species for the removal of organics in landfill leachate. Adding H2O2 can promote the generation of •OH for nonselective degradation of various organics, while PMS mainly enhanced the production of 1O2 to decompose macromolecular humus. This work highlighted an efficient Fe-NiCAF ozone catalyst and an innovative peroxide intensified HCO strategy for the advanced treatment of landfill leachate.

Control the greenhouse gas emission via mediating the dissimilatory iron reduction: Fulvic acid inhibit secondary mineralization of ferrihydrite.

Reducing methane emission is of great importance to control the global greenhouse effect. Dissimilatory iron reduction (DIR) coupling of organic matter decomposition may suppress methane production via reducing primary electron donors available for methanogenesis. However, during DIR, the amorphous iron oxides (e.g., ferrihydrite) are easy to transform into more stable crystalline iron minerals, which slowdowns the rate of DIR. Humic substance (HS) with redox activity has been extensively reported to facilitate DIR via "electron shuttles" mechanism, yet little known about the effect of HS on mediating the mineralization of iron oxides and the subsequent influences on DIR and methanogenesis. To clarify this, ferrihydrite and fulvic acid (FA) (as the model substance of HS) were supplied to anaerobic methanogenesis systems. Results showed that FA could significantly decrease the formation of crystalline iron oxides, enhance DIR rate by 13.72% and suppress methanogenesis by 25.13% compared to ferrihydrite supplemented only. By X-ray absorption spectra analysis, it was found that FA could complex with ferrihydrite via forming a Fe-C/O structure on the second shell of Fe atom. Quantum chemical calculation further confirmed that FA reduced the adsorption energy between Fe(II) and ferrihydrite. Our study suggested that rational use of HS to mediate mineralization pathway of iron oxides could efficiently improve the availability of iron oxides to drive DIR and control the conversion of organics into CH4 in natural or engineered systems.

LATS1 is a central signal transmitter for achieving full type-I interferon activity.

Interferons (IFNs) have broad-spectrum antiviral activity to resist virus epidemic. However, IFN antiviral efficacy needs to be greatly improved. Here, we reveal that LATS1 is a vital signal transmitter governing full type-I IFN (IFN-I) signaling activity. LATS1 constitutively binds with the IFN-I receptor IFNAR2 and is rapidly tyro-phosphorylated by Tyk2 upon IFN-I engagement. Tyro-phosphorylation of LATS1 promotes LATS1 activation and YAP degradation, thereby promoting IFN-mediated antiproliferation activity. Moreover, activated LATS1 translocates into the nucleus and induces CDK8-Ser62 phosphorylation, which in turn phosphorylates STAT1 at Ser727 and induces full IFN-I antiviral activity. LATS1 deficiency restricts in vivo IFN-I signaling and attenuates host antiviral immune response. Our study identifies IFN-I as a previously unidentified extracellular diffusible ligand signal for activation of the Hippo core LATS1 pathway and reveals Tyk2-LATS1-CDK8 as a complete signaling cascade controlling full IFN-I activity.

A Natural Plant Ingredient, Menthone, Regulates T Cell Subtypes and Lowers Pro-inflammatory Cytokines of Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is an autoimmune disease with nearly 1.6 billion patients worldwide and an incidence of 0.5-1%. In recent years, basic and clinical studies have revealed that immune cell responses and corresponding secretion of inflammatory factors are important in the control of RA development. Our study found that a natural plant ingredient, menthone, could be used as a potential antirheumatism compound. In vivo observations demonstrated that menthone alleviates collagen II-induced arthritis (CIA) in mice. Furthermore, we found that menthone regulates the number of Th1 and Th17 cells in CIA mice. Importantly, menthone significantly inhibits the release of pro-inflammatory cytokines, including TNF-α, IL-1ß, and IL-6, in CIA mice. Our study suggests a potential component for the development of drugs to treat rheumatoid arthritis.

High salt activates p97 to reduce host antiviral immunity by restricting Viperin induction.

High-salt diets have recently been implicated in hypertension, cardiovascular disease, and autoimmune disease. However, whether and how dietary salt affects host antiviral response remain elusive. Here, we report that high salt induces an instant reduction in host antiviral immunity, although this effect is compromised during a long-term high-salt diet. Further studies reveal that high salt stimulates the acetylation at Lys663 of p97, which promotes the recruitment of ubiquitinated proteins for proteasome-dependent degradation. p97-mediated degradation of the deubiquitinase USP33 results in a deficiency of Viperin protein expression during viral infection, which substantially attenuates host antiviral ability. Importantly, switching to a low-salt diet during viral infection significantly enhances Viperin expression and improves host antiviral ability. These findings uncover dietary salt-induced regulation of ubiquitinated cellular proteins and host antiviral immunity, and could offer insight into the daily consumption of salt-containing diets during virus epidemics.

Ubiquitin E3 ligase MID1 inhibits the innate immune response by ubiquitinating IRF3.

Interferon regulatory factor 3 (IRF3) is a critical transcription factor for inducing production of type I interferons (IFN-I) and regulating host antiviral response. Although IRF3 activation during viral infection has been extensively studied, the inhibitory regulation of IRF3 remains largely unexplored. Here, we revealed that Midline-1 (MID1) is a ubiquitin E3 ligase of IRF3 that plays essential roles in regulating the production of IFN-I. We found that MID1 physically interacts with IRF3 and downregulates IRF3 protein levels. Next, we demonstrated that MID1 can induce K48-linked polyubiquitination of IRF3, thus lowing the protein stability of IRF3. Our further studies identified Lys313 as a major ubiquitin acceptor lysine of IRF3 induced by MID1. Finally, MID1-mediated ubiquitination and degradation of IRF3 restrict IFN-I production and cellular antiviral response. This study uncovers a role of MID1 in regulating innate antiviral immunity and may provide a potential target for enhancing host antiviral activity.

Ubiquitin E3 Ligase c-Cbl Is a Host Negative Regulator of Nef Protein of HIV-1.

Nef is an accessory protein encoded by human immunodeficiency virus type-1 (HIV-1) and plays important roles in regulating HIV-1 infection and viral replication. Interestingly, HIV-1 Nef can promote degradation of numerous host proteins to disrupt cellular antiviral immune response. However, how HIV-1 Nef is degraded by host factors remains largely unexplored. Here, we identified c-Cbl as a host ubiquitin E3 ligase of HIV-1 Nef. We found that c-Cbl interacts with Nef and reduces protein levels of HIV-1 Nef. Further studies demonstrated that c-Cbl promoted Lys48-linked polyubiquitination of HIV-1 Nef, thus attenuating protein stability of HIV-1 Nef. Importantly, cellular c-Cbl ubiquitinated and degraded Nef proteins produced by HIV-1 NL4-3 virions, and ultimately attenuated HIV-1 virulence for infection of THP1 cells. This study reveals a ubiquitination and proteasome-dependent degradation mechanism of HIV-1 Nef protein, and could provide potential strategies for fighting against HIV-1.